CA2165173A1 - Active electromagnetic shielding - Google Patents

Abstract

A cancellation circuit provides active electromag-netic shielding for canceling inductive noise in electri-cal circuits caused by electromagnetic flux. The can cellation circuit includes amplitude-adjustment and phase-adjustment circuits for adjusting amplitude and phase of electrical signals, and a means for combining electrical signals such that the effects of electromagnetic induction cancel. An electromagnetic pickup is provided with a can-cellation circuit for canceling its response to electromag-netic flux. An electromagnetic drive coil is provided with a cancellation circuit for canceling electromagnetic flux in a predetermined region of space, and a compensation cir-cuit is disclosed for compensation for frequency-dependent phase and amplitude variations in electrical pickup signals and transmitted electromagnetic flux. The cancellation and compensation circuits may be combined to provide a de-vice that can simultaneously transmit and receive electro-magnetic radiation.

Description

1 7 ~

.

Oh~AG~ETIC SHrELDI~G

~,4CKG~OU~D OF l~ IN17EN'rION

This application is re~ted to application Ser. Nr. 08-0~7272, Filed ~uly ~3, 1993.
~he pre~ent invent;~n rel~tes to electromagne'dc ship~ ng for shiplding electrorn~netic pickups, o~er types of elec~onic e~lipment, and spe~ c ~e~iol~s of çp~ce from electro~ etic ~dia~on, and more particularly to ~cti~ el~tromagne~c shielding f~r

2~ providing an elec~ical cancell~tion si~l ~r canc~ing ele~tro~rlagnetic r~3~t;~n or canceling ~e response of ~n elec~onic de ~ice ~ elec~omagnetic ~rli~ion, It has IOI1~ been kr ~wn that volta~es are induc~d in all conduc~ors e~poscd to f h~n~;n~ magn~tic fields regardless of the cl~nfigurati~ n of s~ch conducturs.
Elecb~orn~elir ra~ inn will induc electrical ~i~nals in electronic de~riccs accord~ng to 30 ~e laws of magn~t;C in.~1~ctJo~. Thus it has been desirable in som~ applir~tinnc of eiec~rol~c ms~um~ht;nn to reduce ~e induct~ve noise c~used by elec:romagnetic radiat~on.
A cornmon method for pro~iding elec~omagnetic ~hi~klin~ 701ves the ~se of p~si~e electrama~,netic chiP~ n~ A shield .onsistir~g of lay~s of hi~h and lou 35 perm~bility mat~ial may be used to at~ tp elec~o~agnet:ic radiatic~n p_SSLrlgthrough i'L Huwe~er, his passi~e electrom~netic shi~ n ad~s su~stan~ial bukk and w;eight to the system whlch it shields.
Anot~er method for providing elec~o~nagnetic shielding Is to u~ e cancel~tion coils ~nr generating a cance~ orl electr~ gr.Ptir rad~a~on m ~pposilion to i~l~dent 40 rad;.ation produced by ex~emal sources ~n o~der to callcel the e~ects of ~e incident radiation. In U.S. Pat N~. 5,0~6,891, Harrold presellts a n~agnetic field senC;n~ and canceling circuIt for use with a c~thode ray tu~e (CRT). Magne~c flu~ ~ate ~ellsors prwid~ out~ut signal~ 'd~t are func~ions ~f detected fields. These sigr~s are th~n used to contr~l the cu}rent in the can~PII~finrl coils whic-h produce a c~nc~llat:i~n magne~c field.
Harold cxpl~ins ~21t it is of great importance that ~e C~T in a co~or monitor be ., protected from ~e ef~ects of e~ternal ma~ne~ic fields, and, in p~rticular, tirne-varying magne~c fields. However, ~ me~od pro~ides no compellsa~ion tc t~e ~equency-dependent amplihlde and phase responses of the sens~r ~at picks up incident elcc~omagnetic ~i~tio-~ and the d~vic~ which generates the cancella~on ~diation.

AMENDED SHEET

WO 95/03686 Z 1 fi 517 3 PCT/US94/08247 Likewise, in U.S. Pat. No. 5,132,618, Sugimoto shows a magnPhr resonance imsging system that includes active shield gradient coils for msgnr~hrAlly rAnrPlin~
leakage fields that would otherwise produce eddy ~;U~ in the heat shield tube.
A common method for providing shiPl~ling to an electromagnphr pickup is to utilize i-lPnbrAl pickup coils connPrt~-l in series or in parallel so as to cancel the effects of UlLirUIm electromagnPh~ radiation. P~;al~llo shows such a system in U.S. Pat. No.
5,045,784 for reducing inductive noise in a tachometer coil. An electric t_chometer is a t coil of wire that may be At~s~hP 1 to a moving part of a motor that passes through a s~s-tionsry ms~nPhr field. The motion of the wire through the msgnPhc field induces a voltage that is in-lirs,bve of the motor's speed. However, if the motor is powered by - ;Ly~ changes in the ~u lenL powering the motor will cause a ma~nPt r flux, which will also produce a voltage in the coil. Pi~;cdlello shows a stationa~y pickup coil ~hat is JUllSive to magnPhr flux, and a means for subtracting the pickup voltage from the n.. .P~r voltage.
Likewise, in U.S. Pat. No. 4,901,015, POa~u;q_l.il shows a cAnrPllshon circuit for l;..g the lt:~pu..se of a m~sgnPhr pickup generators to ambient ele_L~....AgnPhrfields. Pickups used in integrated drive ge~ldlula are n~ol~ive to ambient ele_h-----agnPffr fields produced by the generator. A first msgnPhc pickup ~ JUn~iV~ to the ambient mA~nPffr field and a mo~ lstPrl flux field ~ro.luced by a rotating shaft is 20 combined with a second msgnPhr pickup le~yG~SiV~ to the ambient ele~;hv---agnPti~
fields in order to cancel the indu~:live effects of the ambient el~lr~,...A~nPhr field. Such pickup AcsPmblies are also used with electric guitars and are known as "hum-bucking"
pirl~r5 This l~ l~ ue is not e~f~Lve for providing a high degree of cAn~PllAhon bec~use slight dirrè,e,~ces between the ~i,kuys, even pickups that are subs~Ant-~lly 25 i~l~ntirAl~ cause the frequency~ependent amplitude and phase ~e:.yu"se of the yichuys to differ $ignifirantly from each other. Thus the pickup signals will not be exactly out of phase and equal in allL~lilude when they are combined.
A prior-art method for providing chiPl~lin~ to an electroma~nr~hr pichup from anel~_h~...AgnPhr source that produces a non-ul~irc,l~, field is to "7lnhAlAnrP~' either the 30 pickup device or the ele_L~ù...agnPhr source. Such a method is described by Hoover in U.S. Pat No. 4,941,388. Hoover uses a.~.ylilude-adjtl~hnent techniques to comyel~sale for amplihude variahions between the ~:ayullses of se~ ale pickups to electromAgnPhr radiation generated by an elechromagnPtir s..~ device for driving the vibrations of a string on an ele_h;c guitar. However, Hoover does not comy~ - - for .lirre~l~ces 35 in the pickup coils which cause the al.lyLlud~variahion of the n:s~on;es of the pickups to be frequency-depPn~lPnt, thus rec~llting in poor rAnrPll~tion over a broad range of Le~luel~y. FlulLellllore, Hoover does not co..ly~nsate for ~hase variations that occur between dir~el~ent pickup coils. The rPc~llffng rAnrPll~ff~)n from the -nhAlAnring method is poor.
Hoover describes the operation of ,legdhve feedback in a system where a mAgnPhr pickup provides an Pl~ch~rAl signal to a magnPhr driver which generates a mA~nPtir field to which the pickup responds. Hoover mentions that the syst~n tends to drift from the ne~;.,Lve feedback condition at higher freq~lPnriPc~ and id~ntifi~c the cause of this drift as distortions in the phase~ yonse of the system reclllbng from the pickup, driver and amplifier in the system. Hoover does not yle:~ellt an e~e Live method for controlling the phase .e ~yol~se of the system, nor he does not yre~ent the mathPmatiral relationships between phase and frequency resulting from the driver and pickup coils. Rather, Hoover yroyoses the use of a low-pass filter to reduce the gain of ffle system at which the negative feedback condition breaks down.

~ =
~ WO ~5/03686 216 517 3 PCT/US94/OQ47 Methods of active phase-compensation are described by Rose in U.S. Pat No.
4,907,483, U.S. Pat. No. 5,123,324, and U.S. Pat No. 5,233,123. Rose uses active ~ ui6 for d~ the rl~u~l~r or Lr~u~n.:y range of an Pl~h i~Al signAI from an ele_l.o."agnetic pickup. Active phase-a.lj..~l...rnt is applied to the pickup signal, which 5 is used t~ power an electromagnPhc driver that generates an ele_l,v...agnetic driving force on a vibratory ferromAgnPhc Pl....~..t of a musical i~ ent The pullJose of the ~llase a~ aL.~..t of the pickup signal is to provide a dlivil~g force to the vibratory element that is sul~ --I;ally in-phase with its natural motion. BP~ e the yu~yose of Rose's in~ention is to improve the ~rr; ;--~ r of the electromagn~h~ drive force on the 0 element, it is a~ar.:l~t that a passive phase~o...~ atinn circuit would be ~,~f~able to Rose's active phase~oulyt:. ,c~ l;on circuit. However, Rose does not realize themathPmatical relationships between phase and Lc~ut ~y which provide the basis for ccJl~ u~ gaya~- v~ phase~u.~ I;nn network. Fu~ ore~Rose'sillv~hu does notprovide simllll~...~o.lJ phase-co~.y~ --tion to more than one hArrnoni~
Another mPthn~l for providing ele~;ho.. agnPti.~ shipl~ling is to orient the angle of a pickup coil to incident electromagnPh~ radiation such that ff~e ~ - ;. al Cullellt in~ eti in the coil by the ele_hU~A~T~Ph~ radiation will ~lhstAnhAlly cancel. One a?plication of t~is method is shown by Burke in the Handbook of Ma~nPhr P'lenomena, published in 1986. Burke uses a L~ ...iu;~ coil that produces 20 ~ o.;~nPbr radiation and a receive coil which senses radiation. The two coils can be col~rig u~d in such a way that no energy is Lal~ ,~l between the 1~ C~.IiU;-~; and iVil~g eoils. Burke shows the receivil~g coil oripntptl with the axis of its turns at right angles to 1he direction of the ma~nPhr field p~ùduced by the L~ .iU;.~ coil. Burke explains ~tat the i.. '~ ..~us gel~c~al~.l voltage of the l~ive coil is ~lPt~rminP~l by 25 the i"~l~"~ 5 rate of change of the ma~nPhc flux ~7- C ~; through the coil. If 1he flux is ~lu~ d at right angles to the coil's axis, none of it is i~ r~ cl by the coil, and the i..~ .Pous rate of change through the coil is æro. This mPt~otl of ro-nrPllot ~n was used in an el~_hu..~a~nPhr S~Q~--in device for PlPc~r gui'car_ mAr~ by T Tâuri Research of Wilmette Illinois in November, 1988, and ~al, ~l~ by Tumura, ~ul~eall Patent Application No. 92307423.1 filed on August 13, 1992, and U.S. Pa~ No. 5,292,999.
The actual err~:liv~-ess of this l~lu~iq~le is limitPd by several f~~ tor.c, such as the ~ilo~l-.ity of the pickup coil's winrling,c~ the L~nirù~ iLy of the electroma~nPhr radiation r~ear the pickup, inl~rere~.ce due to other nearby condu~ g mAtP~lc, and the ~liffirnllty of precisely positioning a pickup coil in a field whose i.~ ci~y varies as the inverse square of the ~ e from its source.
Ano~er method for providing active electromagnPtir shiPl~ing is the dirr~r~lliall~al~fO~ er âlsO shown by Burke. The dilr~.~enlial lral~u~ er co~ .ses a drive coil for g~n~àli~ a ma~nPhr flux, and two pickup coils ~la~ed around a ferroma~nPhr core that inrl~ Pc a moveable ArmAhlre that, when moved, varies the rell~r~nre of the mAgnPhr path ~ccoriAtP~l with each pickup coil. If the two pickup coils are identical, and if the two magnetic paths about which they are wound are i~lPnbrAl, the voltages induced in each pickup coil will be the same. However, Burke explains that the two pickup coils nor the two mA~nehr paths can be made exactly the same, IL~ vle a dirrer~ ~tial llal~ro~ er will always have some outputvoltage under zero stimulus.
Coils of wire whose ~:Ull~ U~J~JO~l mAgnPhr fields in space function as Ant~nn~c ratli~tin~ ele~L~ ---AgnPhr energy. There are several cAnrPIlAtinn methn~lc used with AntPnnAc that act as elechromAgnPtir shi~l~ling. One of these mPtl~n-lc is the basis of operahon for a sidelobe canceller which uses an auxiliary antpnna in addition to a main antPnna Combining the ou4uls from the two antPnn~c result~s in rAnrPllAtion of the AntPnnA beam p~rn in the direction of a noise source so that the ~Lrecli~ gain of the , _ _ _ _ _ WO 95l03C86 2 ¦ 6 ~ PCT/US94/08247 An~nr.~ in that direction is very small. Likewise, the multiple sidelobe r~nrell~r add.~sses ~e ~.o~ , of multiple noise sùlll~es.
Delay line ~An~ rs are used in ~y ~ s where multiple radar pulses are trAncmitt~, and are used to detect moving objects. In a single~lPment delay line5 cAn~eller, a f~eiv~d pulse is delayed and added to a~ pulse received later so that the pulses r~fl~r~ by stationary objects are out of phase and thus cancel, whereas the pulses reflec~ by moving objects do not cancel.
Several methods are used to allow an Ant~nn~ to sim~ ..~usly l~ a...il and receive electrnmA~ radiation. For example, in a cc,llhl.uous w~ n~,ll, radar sysbem, a single An~nn~ may be employed since the ~ecs~, y isolation between trA--~ and l~c~iv~:d signals is a~lu~:v~d via s~,-llalion in rr~u: I~;y as a result of the Doppler effect. The leceiv,t:d signal enters t~e radar via the AntPnnA and is L~lt .udy~ed in a mixer with a ~Ul liu~ of the tr~ncmitl~-l signal to ~roduce a Doppler beat frequency.
An ;~tF~ t~frequency l~ivel may use separate An~lllAC for trAncmiCcinn and reception. A portion of the h~ signal is mixed with an i,,l_. "~f~ AtJ?
L~u~ y~ then a narrow-band filter selects one of the ci~ n~1.s as the refelence signal which is mixed with the signal from the l~eiv~ l A~
It is one ob)ect of &e ~Ica~ nt invention to provide active ele~ nPffr ~h~ ing for c~ g the effects of el~-hlv~agn~hr induction in ~ h ir~ ;u Lb. It isa related object of &e ~.cse~.t illvcllliull to reduce i~,l_. r~ e between L ~ ..~.. . ill~. a and ece~iv~l . of ele~hv...Agn~h~ radiation that o~i.lle sim~ .oously. It is anot&er object of &e ~resent invention to provide a ~Anl~llAb~n circuit that allows a single ~ IA
~l~mPnt to $im~ u~lsly transmit and receive el~hv...Agn~hr radiation. It is still 25 another object of the ~lcaent invention to co,l.~--.C~t~ for ~L~uer,~;y-dependent a~ de and phase lea~onses of ele_L~-...agn~h~ iVel;~ and L
SUMMARY OF THE INVENTION
In accordance with the ~i cacl~l invention, a r~nr~ ffnn circuit is provided forc~ g the inducffve effects of ele~llo-~AgnPffr radia'don. The cAn~-Pllahon circuit COl~l~l ;ses a means for acquiring or generating an rl~r~ l . ;.'Al lc~ ce signal that is similar in shape to the in~lllrhve PlPChirAl signal produced by the ele~Lu...A~nPhr radiation~ an a~ Llllde-A lj.~ .l ..Pnt circuit that adjusts the a~.~Llude of either or both 35 the l~reicl ce signal and an Pl~ l pickup signal co..l~;..;..g an inrl~lrtive noise CO~Ol~el~t~ a phase-adjllchnPnt arcuit that adjusts the relative phase between the lcr~rel~ce signal and the pickup signal such that when these signals are combined, the inductive noise co.l,~ol~ent will be ~ "- ~ , and a combining circuit that comhinP5 the rer~i~nce and pickup signals to l~rodu~e a pickup signal that is s~lbstAnti~lly free fTom 40 inductive noise.
In one aspect of the ~J~C5el~t invention, the leÇ~ e signal is obL~ ed from an ele~L. ..,agnPtir pickup that is res~ol aive to P~tPrnAl ma~nPtir flux. In another aspect of the present invention, the ~erence signal is ol>l~,h~ed from part of the PlPCtrirAl signal that is used to generate the ext~rnAl mA~nPti~ flux. In still another aspect of the ~l~s~llL
45 invenhion, the i~r~ ce signal is generated by a signal generator.
The present invention provides sllhstAnb~l electromAgnPhr chiPl~lin~ capabilities co~ aled to prior-art chi~kling devices. Because the p.ea~:lll invention actively shields from electromAgnPffr flux, it is non-il.h..~ive compared to ~as_:ve chiPl~iin~
technologies which r~~ e complete ~n~lns~ in order to provide optimum chiPl~ing 50 and use m~tPriAlc that are heavy and buLky. Thus the pl~ael~t invention may be used in WO 95/03686 216 517 ~ PCT/USg4/08247 order to reduce or Pliminate the need for yz5_:v~ ele_llo~ agnPhc shielding in certain applicationa. F.lrll,è.Jl.ore, in addition to being superior for shiPl~in~ elect~oma~nP~i~
~ iabon compared to prior-art active elc~ho. agnPh~ chiPlrling technologies, the y~eae~lt invention may be adapted to prior-art s~liP1~1ing devices to improve their 5 ye ~, .zn.P
The ran~Pllahon effect of the ~es~:nt invention allows electromagnPffr pickups to operate in ~Vilv .. .Pn~: co ~Ini~i g high levels of ele_l.v a~gnPh~ noise. For example, the ~ael~t invention may be integrated into a c .~ g device for a ~h-~lged musical i~ah ull~ent as lDs~ihe~ by Rose and Hoover, and provide a very small sustain device 10 that both picks up and drives the vibrations of a string on the musical illaL ~unent. This sn~ain device would be much cmallPr than the devices shown by either Rose or Hoover ~ ce the i~ d shiPl~ing capability of the ~.esellt invention allows for the ele_Lo.. a~nPh~ )s, which pick up string vibrations, and the driver, which generates an ele~hv .~agn~h~ flux to drive &ose vibrations to be placed very doâe to 15 each other, or even share the same sl~ ;hlle without the effects of el~-L~ agnphr fè~ cê. Other appli~^Ation~ of the ~.~s~.l invention inrhlrlP Pl~h ~ tA~ hometPrs that operate near devices that generate large amounts of magnPhc flux, and otherelectromagnPff~ a such as radars that operate near so~ces of ele_ho.~.qgnPtir radiation~ This aspect of the y~escllt invention allows an elechromAgnPhr qntPnnq to 20 sim.llhn~ously operate as a L..~...;UPI and l~:ceivc~ by de ù.l~Llg the le~ci~
e~yol~se to the h~ lP l signal. The ~le__~lt invenhon may also be used to cancel the ~p.,...qe of a radar to ground clutter.
An.other aspect of the present invention further includes a cou~ypl~cabon cira~it for adjusting the pickup signal's a.l~lilude and or phase in order to cc,~ q~q for 25 L~cqucl- y~PppnflL-qnt amplihude and phase lcayol se of the pickup. The comyf~ A I ;nn circuit may also co...~-e.~ for Læqucl..y~qpen~l~qnt amrlib~le and or phase variations of electromagnqhr flux ~;el.c~aled by an elc~;hu...agnPhr flux ~,clleldtur, such as a drive coil. The ~SelLt invenffon may be i,~lcg,,.le~ into a prior-art acffve mAgnrqffr shielding circuit that gel~clales a ~ -g magnPh~ flux for -A--- ~li"f~ exhqrnAl 30 mAgnrhr flux. The y~csèllt invenffon would provide a more ac~lual~ lcsyul se to PxtPrnAl magnqhr flux, and IL_lcby improve the rAnrrll~ffon effect of the circuit Such a circuit may be used to provide acffve el~h~ A~gnPhr shi~ 1ing to il~h- ...Pnh that are sel~.hve to magnPhr or ele_Lo..~gnPt.c fields, and have applicaffons as ~hiPlfling devices for atomic clocks, magnr-ffr resonance im~ging apparatus, tacffcal 35 il~h~ ;o.-, cathode ray tubes, sAtPllitpc~ and spacecraft.
~ a~nother embo l;... .~t of the ~selll il~vel~hOn, the clc~h~....agnrffc flux generated by the drive coil provides a mAgnPffr force upon a moving ferromagnPhrPlPmP~t The phase of the ele_hv...agnf~hr flux generated by the system may be adjuJlèd to provide ele_ho...~gnPhr damping to the ferromAgnPhc element, and thus 40 act as a stabilizer for that PlPmPnt The elechromAgnPtic flux may be a~lj.tsle~l in phase to drive the csrillAhonc of the ferromA~nehr Pl.. ~.,t, as .licc.. ~s~.1 by Rose, except that a broad range of d1;vil~g Le ~ ;P.c may be co~ c~lefl~ ~hus allowing for the driving of the harnnonics as well as the fundamental r~llellcy of the PlPmPnt These and other aspects of the ~ enl invention will become a~l,a1enl to those skilled in the art upon consideration of the following let~ilP~i des~ Lons of the p~f~èd embo-limPntc.
BRIEF DESCRI~IION OF THE DRAWINGS
so FIG. 1 is a s~hPmA~bc view of a prior-art cAnrPllAhon circuit.

WO 95/03686 2 i ~ ~17 3 PCT/US94/08247 FIG. 2 is a srhPmA1ir view of a canr~llAffon circuit of the ~esellt invention.
FIG. 3A is a srh~mAffr view of a phasc . Ijustment circuit that may be used in ~e llAtion circuit of the ~eséllt invention.
FIG. 3B is a srhPmAtir view of anollle~ phase-A. lj .~!~..ent circl~it that may be used in the cAnrPllAffon circuit of the y~esent invention.
FIG. 3C is a srhPmAffr view of a circuit of a.,o11æl embo~limPnt of the p.est:l~L
invention.
FIG. 4A is a srhpmAbr view of a canrpllAffon circuit of the ~.es~l t inven~on l~at illuslralea anollæl method of phase-A~ m~nt that may be llffli7P.l 0 l~IG. 4B is a s~hPmAffr view of another phase-A~ nt circuit that may be used in ~e canr~llAhon circuit of the ~.ese.~t il~v~l~hon.
FIG. 4C is a srhPmAffr view of a~ hase ^ ~ ctmpnt circuit that may be used in ~he cAnrPllAhoIl circuit of the ~.~aent il~v~lio~.
FIG. 5 is a plot of cAnrPllAhon relative to signal L~u~y for three di(r..~llt 5 rAnrPllAffon circuits.
FIG. 6 is a s~hPmAhr view of a cAnrPllAhon circuit of the ~.est nl invention that generabes an ele~h.. agnPtir flux in l~a~u.~se to a pickup signal, and inrl~ c a co~p~ caffon circuit for compPn~Qffng for L~uel~cy-dependent phase and or a~,t,lilude variations in PlPChi~Al signals used to gel~t~dl~ the electromagnPhr flux.
FIG. 7 is a s~hPmqffr view of a rAnrPllAffr~n circuit of the ~.es~l~t invention that inrlllrlcs a cc..~ ffon circuit, and is used to provide an electron~Agnehc drive force to a ferromA~Ph~ PlPmPnt FIG. 8A is a srhPmAhr view of a cv~ ffon circuit of the ~.~sent invention.
FIG. 8B is a srhPmAffr view of another CO~.~l saLvn circuit of the ~.esel,t 25 il~v~l~hol~.
FIG. 8C is a s~hPmAffr view of al,vtll ~ cul.,p~ 5,1;0n circuit of the ~.csel.t invention.
FIG. 9 is a srhPmAffr view of al,ollær rAnr~qllAffon circuit of the y~s~ t invention wherein rAnrPllqhnn of inri~lPnt ele.llv...AgnPffr flux is aclu~v~d by generating an out-30 of-phase ele_hvAgnPhr flux.
FIG. 10 is a s~hPmAht view of a rAnrPllAffon circuit of the ~l~se~t invention wherein a pickup coil and the drive coil are ~_y~ed around the same core.
FIG. 11 is a srhPmatic view of a cAnrPllAtion circuit of the p.esel t invention wherein the pickup and drive coils are ~IApped around the same core.
lFIG. 12 is a srhPmAffr view of a rAnrPllqffon circuit of the ~ sel.l invention wherein the rært:.~nce signal is obtained from a signal generator used to provide a drive signal that ~,~l,c~ates the electromA~nPffr flux.
FIG. 13 is a srhPmAffr view of a rAnrPllqff~.n circuit of the ~rese.LL inventionwherein the r~r~r~.lce signal is Gl~tail,ed from splitting the drive signal used to ~ .al~
an el~ a~neh~ flux.
FIG. 14A is a S~ hPmAff~' view of a cAnrPllAbon circuit of the ~.ese..t invention for a single-PlPment hA...~ il/receive system that includes a harmonic compensation circuit for ranrpling the non-linear ~ se of nearby p~lmPAhle matPri~
FIG. 14B is a srhPmahr for a harmonic compensation circuit of the present 45 invention.
FIG. 14C is a srllPmAtir for another harmonic compPncahon circuit of the ~res~t invention.
FIG. 14D is a srhPmah~ for another harmonic compensation circuit of the p.esel.linvention.

~Wo 95/03686 216 ~ 17 ~ PCT/US94/08247 FIG. 15 is a s~hPmatif view of another cAn~PllAht~n circuit of the ~.~S~.It invention for a single~lPmPnt transmit/receive system.
FIC~. 16 is a sfhPmAbf view of a cAn~PllAhon circuit of the yresellt invention used in a device that compensates for magnetic fields.
FIG. 17 is a srh~mAhc view of another fAnfPllAtion circuit of the ~s~.,t invention used in a device that compPnCAtPc for mA~nPffr fields.
FIG. 18 is a s~ hPmatic view of a rAnrPllAt on circuit of the ~l~se.,t invention for another singlc el~."ent trAncmit/receive system.
DETAILED DESCRIPTION OF PREFFRR~r~ EMBODIMENTS
A prior art bAl~nrin~ device for a pair of ele l,~ ...a~n~fff pickups is shown in FIG. 1 as in~ h~flin~ a two coil assemblies, 10 and 12, two amplifiers, 14 and 16, and a combining means 18. The first pickup coil 10 has values of rfJCi~lAnre and indllrtAn~ P of 15 Rl and L~, le~e~liv~ly. The second pickup coil has values of r~;~ e and inflllrtAnre of R2 and L2, le~liv~:ly. The pickup coil 10 is fO~ J~ to the input of the amplifier 14 and the pickup coil 12 is co....~læf~ to the input of the other amplifier 16. The inputs to the amplifiers 14 and 16 each have a rApArit~r Cl and C2, ~ liv~ly, co....P~ l to PlPC~irAl ground as is commonly done to filter out high-frequency and white noise 20 from the pickup cignAlc. The o~ ls of the al,lplili~. ,14 and 16 are comhinp~l by a comhining circuit 18, which may be a voltage divider, a s~mmin~ amplifier, or a dilræl~"lial amplifier.
The pickup coils 10 and 12 are l~o.L~ive to the time-rate-of change of the flux of mA~nPtir induction, also r~f~led to as "ele~Lu~lotive force," and herein~ for ~implifity~
25 referred to as "maf~nPh~ flux." A ma~nPhc flux is l~r~ d to as an "Px~DrnAl" mA~nPhr flux if it is produced by a source P~-. ..Al to the pickup coils 10 and 12. F.~tPrnAl ms)~,n--l;r flux in~lucec a first PlPrtnrAl pickup signal in pickup coil 10 and a second el~ at pickup signal in pickup coil 12. Due to coil-pocihoninf~ with le~e~;L to the t .J.al mAgnphr flux, coil ~r~t:lLes, and ~r~lLes of mAtDriAlc (notshown) which 30 the coils 10 and 12 may s~luu~,d, the amplitude of the first~ 1 pickup signal will most likely differ from the amplitude of the second PlPChi~Al pickup signal. Thus amplifiers 14 and 16 may be used to change the amplitude of either or both of the first and second el o~ ~ . ;r~l pickup ci~nAlq If the pickup signals are out of phase, the comhining circuit 18 is a voltage divider or a s~ i..g amplifier. If the signals are in 35 phase, then the combining circuit 18 is a dilr~ r.lial amplifier. However, the relative phase between the first and second rl~ l signals will tend to be sllhstAnbAlly diLf~.e.,t ~an 0 or 180 degrees, thus providing poor rAnrPllAtion of the signals at the output of tlhe combining circuit 18.
The impedance Z1 of the first pickup coil 10 is related to the coil's 10 n~ .. e40 R~ and in~ rtAnrP Ll: Z1 = Rl + ia)Ll. Likewise, the impedance Z2 of the second pickup coil 12 has the value: Z2 = R2 + ia~L2, where ~ e.l6 the fl~ cy of the pickup signals mulltiplied by 2 Pi. The voltage Vljl, at the input of the first amplifier 14 is V~, = Vl [(1 - a)2CILl) - i~3ClRl]/[(l~D2ClLl)2 + o)2Cl2Rl2], where Vl is &e voltage induced in the coil 10 by ~xtPrnAl magnPti~ flux. The voltage 45 V2,l, of the second pickup signal is 2in V2 [(1 - ~1) C2L2) - ia)C2R2]/l(lff)2C2L~2 + ~2C 2R 2]
where V2 is the voltage induced in the coil 12 by ~ al magnPbr flux. Incidentally, V
and V2 are l~.u~o.lional to the magnit~ of ~xtPrn~l m~gnPhr flux at the locus of each WO 95/03C86 PCT/US94/08247 ~

pickup coil 10 and 12. The gain imparted to one or both pickup signal voltages Vl and V2 by the amplifiers 14 and 16 will correct for dir~lel~es in the a~l~lilude betweenVl and V2 but will not correct for phase dil~le~ s between those si~nalc. The phase of the first pickup signal voltage Vl~, has the value 01 - -ArcTan (~ClRJ(1~2ClLl)), and the phase of the second pickup signal voltage V2il, has the value 02 ~ -ArcTan (~C2R2/(1ff)2C2L~)).
It is typical for the values of Ll and Rl to differ subst~ntiolly from the values of L2 and R2, ,c5~e~liv~1y, even for pickup coils having itlPnti~al nurnbers of win~lingc For 10 example, two coils of 34 gauge copper wire, each wound 330 times around irlPnff~ ~1 cores yielded values of ~ e of 16.5 and 16.7 ohms, and values of ind~rtAn~P of 205 uH and 194 uH, r~s~e~ liv~ly. Thus when only the amplitudes of the two signals are adjui.l~d so that they are equivalent, ~e relative phase between the signals ~evt l,b optimal ran~F~llation of the si~nolc The ex~le~sions shown for the pickup voltages V1i~, and V2~, are very accurate, but not exact le~r~ L~hnns for illu~ g the dif~ nces in the phase variatiorLs between ~he pickup coils 10 and 12. The exact impe~lonrP rpl-o-tio~c for the pickup coils 10 and 12 should also include co-porihve effects. Other factors that may contribute to phase variations between the signals ~ro.luced by the pickup coils 10 and 12 in~20 ground os~ ffons, complexities rPsnlffn~ from the fact that each of the pickup coils 10 and 12 acts as a source for the rl~ pickup si~ possible PlPC1TirAl lo~in~
between the two pickup coils 10 and 12, and variations in how the voltage leads the ~ul~ent in the coils 10 and 12 res~l1hng from in~ < 1~ and cApArit~n~e in each of ~e coils 10 and 12. Although the ~x~.essions shown for the pickup voltages V3;" and V2lr, 25 do not provide exact ~e~s~ ; I ;nl~5 for the di~.cl,ces in the phase between the pickup coils 10 and 12, these eA~lessions are accurate to a great degree, and le~.es~lt the basis from which e~hcl~.ely e~c live rAnrPllAhon circuits can be ~lpsignp~l Itwill be a~u~l~iated that even more precise rc~ ffons of the PlPch i~l signals induced in mAgnPh~ u~s will enable the design of cAn~Pll~ffon circuits that are even more 30 ~r~Liv~.
An embo~limPnt for a cAn~Pll~ffon circuit of the ~le~e~t invention is shown in FIG. 2 as inrl~ ing a pair of pickup coils 20 and 22, a pair of am~lilude-adjustment uib 24 and 26, a phas~adjl~ctment circuit 25, and a combining circuit 28. The pickup coil 20 is co....P~ to a phase-A~ ctmP~t circuit 25, and the output of the phase-35 adjnctment circuit 25 is co.~ .l to the input of an amplitude-adj!-~l ...Pnt circuit 24.
The pickup coil 22 is co....P~IP~l to the input of an amplih~ jn~tment circuit 26. The oulp.lb of both amplitud~a~ .rnt circuit_, 24 and 26, are co.~P~ l to a combining circuit 28. The output of the combining circuit 28 provides an Pl~trirAl signal that is s~hst~nff~lly free from the effects of PlP~I. ;. Al noise caused by t~e le:.~G.~se of &e 40 pickup coils 20 and 22 to PxtPrnAl m~nPh~ flux.
The pickup coils 20 and 22 are le:~ul~ive to external m~gnPh. flux, which illduces a first signal voltage Vl at the output of the first pickup coil 20, and a second signal voltage V2 at the output of the second pickup coil 22. The phase of signal voltage Vl will be 01 and the phase of signal voltage V2 will be 02. Because bo~ 01 and 02 are 45 functions of signal Leque..cy o~, we will write 01(~3) and 02(~)) The pickup coil 20 is cù~".~1~.1 to the input of a phase-adjl.ctmentcircuit25 which provides a ~hase shift F(a)) = (02(~) ~ 01(a~)) to Vl in order to compensate for the phase-difference between signals vl and v2. The nature of the t)l~s~ adjllctrnent circuit 25 is ~l t~ by the _ _ _ _ _ _ _ _ _ _ _ _ ~WO 95/03686 216 5 17 3 PCT/USs4/08247 frequency-range of signal~AnrPllAtion leq~d. The output of the phase-adj~ c~ nt circuit 25 is conn~cte.l to the input of an amplitude-adjustment circuit 24. The pickup coil 22 is conn~t~l to an amplitude-adillctm~nt circuit 26. Both amplitude-adj~lctmPnt ciLcuib, 24 and 26, may provide amplitude-adplctm~nt to the pickup signals Vl and V2, 5 ~ea~e~;lively~ or only one of the amplitude-adjustment circuits 24 or 26 may provide a L.~lilude adjustment while the other circuit 24 or 26 acts only as a buffer. Because phase-adjuaLL~cnt cil.;uib, such as phase-adj..~l ...~nt circuit 25, typically change signal-amplitude as well as phase, it is preferable that the amplitude-adjllctm~nt ~ Ui6~ 24 and 26, have little effect on signal-phase. Thus the amplitudc ~ ent ~ uib~ 24 0 and 26, may cc.mp.lse non~ LL~, all.pliri~s. The oulyub of the alL~ylLIude-adj~ n~nt ~iL~_Ui6, 24 and 26, are combined in the combining circuit 28 in order to cancel the effects of ~ al m~ hr flUX picked up by coils 20 and 22. Depending onwhether the output signals of the alLI~Llude-~ ...2nt ~ uib, 24 and 26, are in-phase or out of phase, the combining circuit 28 may comprise a voltage divider, a a~ n.... i-~g 15 amplifier, or a diffe.ellLal amplifier. It will be a~l~iated that the coils 20 and 22 may be ~la~ped around a core ~not shown) such as a core com~.;Jil~; a ferromS.gn~ffrmaterial. It will also be a~ple~;at~d that one or more additional yllasc adju;~ cnt Cil~ ~lila may be inrl~ in series with coil 20 and or coil 2æ Ful ll.~l~.ore, it will be ay~.~ iated that amplitude-adj~chnPnt circuits such as amplitude-A~ hmpnt circuit 24 20 may precede phase-adj. ~! ...Pnt ....uils, such as yl~zse a~ nt circuit 25.
Se~eral p' --e adj~ ntcircuits are shown in FIG. 3 which may be used in ~e circuit shown in FIG. 2. The circuit in FIG. 3A is commonly referred to as an "all-pass filter," and provides a yhase shift of 0 = 180 - 2 ArcTan (a) R6 C3) while producing little amplitude-variation with l~ay~l to signal L~.en ;y. The circuit shown in FIG. 3B
25 is also an all-pass filter, and produces a phase-shift of 0 = 2 ArcTan (~ R8 C4). The all-pass filter~; in FIG. 3A and 3B may be preceded by a buffer a~ lifl~l (not shown).
It is so~.eli~ desirable to have s~lhstAnhAl noise-rAnrPllAhon over orlly a narrow La~ - y-range. This is called "notch-rAnrPl1Ahon" and may be used in a single-L~q uel~.y or band-1imitP~l system. One app1irAhon for notch-r~nrPllAt;on is 30 when an external mA~nPh~ flux co~ ins a weak signal having a si~-ir;~ 1y dirrele,ll L~uency than the noise that accompanies it, then a cAnrPllAtion circuit which cancels a narrow L~.lel.cy range inr11-~1ing the noise, but not the desired signal would be ~f~ble. FerromagnPhr matPriA1c used for pickup cores have the ~rO~e~ly of non-linear ~e_r~o~ el~ess to mAgnPhr flux, which can be ol,s_~ ~/ed in the pickup signal of a 35 coil as exh~bihng a higher harmonic of the L~uel. y of the magnpffr flux. In order to ol~t l ~e the extent of the core mapriA1's non-1inPArity-, it is preferable to cancel only the primary pickup signal, which has the same L~uel~y (D as the a~Led mAgnPh~ flux.
Typically, the higher harmonic ~ignAtllres caused by a core's non-1;.~P~ is atleast several orders of magnih~le less than the ;~ oc;ly of the prima~y signal in~l11re~l in the 40 coil. Thus the method of notch~AnrP11Abon provides an advantage over conventional PlP,~ 1 fi1tPring techniques in both simplicity and p~ nrP
FIG. 3C shows another embo~1iment for a rAnrPllAhon circuit of the ~l es~..t invenhion. Two pickup coils 30 and 32 are each co..n~ l~.l to a phase-adjustment circuit 35 and 37, le~eLlively. The phase-adjllctm~nt cil~;uib 35 and 37 are each co..~ .1 to 45 the input of an amplitude-adj--<-l .n~nt circuit 34 and 36, ~spe~ liv~ly. The olllpu6 of the amplitude-adjustment cin;uib 34 and 36 are combined by a combining circuit 38. ~he output of the comhining circuit 38 is provided that is s11hstAnbA11y free from inductive noise. The phase-A..~ -..ent .;in ui6 shown in FIG. 3A and 3B may be used as the~hase adj--~l.nt~nt ci~ li6 35 and 37 shown in FIG. 3C. Fu l~ ore, the phase-50 adjusl-l.ont c.r ui6 shown in FIG. 3A and 3B include a means for adjusting the WO 95/03C86 PCTIUS94108247 ~
216~173 al..ylilude of elech~l signals through adjnchn~nt of the re~ialo~ ~ Rs and E~7 in FIG. 3A, and r~si~l-,rs Rg and Rlo in FIG. 3B.
For the case of notch~An~PllAhon in which the relahve phase between the pickup signals from the first and second pickup coils 30 and 32 is very small, such as when the 5 coils 30 and 32 are very close to being j~lPnhrAl or when a ~has~ adjllctment circuit (not shown) has already created this col,diLo." then it is preferable to select types of phase-adjl~ctmPnt ~ir~;uib 35 and 37 that will cause a very narrow L~l~ncy-range in which the rAn~Pll~hon is subs~AntiAl. If the pickup signals from the two pickup coils 30 and 32 are in phase, this may be acc.,~,pLshed by 5fl~l;..g the all-pass filter shown in FIG 3A
10 as one yhase A~jnctmPnt circuit 35 and sPlPchn~ the all-pass filter shown in FIG 3B as the other phase-A~ ctment circuit 37. This sPlPction is suEj~;e~l~d ~eca~se as the signal-Lluen~y aD chal.~;es, the phase of the pickup signal of one of the phase-a~ljusL.llent uil~ 35 will increase while the phase of the pickup signal of the other phase-adj~ctmPnt circuit 37 will de l.as~, thus c~ g a rapid change in the relative phase 15 with r~s~e~;l to L~uen~y a~. To maximize the change in the relative phase near the "notch rr~llellcy~ where the rAn~PllA~;orl is most s1lhstAntiAl, one could select values of R6 and C3 in FIG. 3A and values of R8 and C4 in FIG. 3B such that ~nR6C3 and ~nR8C4 are nearly equal to 1 for the notch frequency aDn. To further narrow the ~An~PllAtion notch about the notch rr~uen~:y n~ ~he phasc . ~ ;.t circuits 35 and 37 may each inr P
20 multiple all-pass filters as shown in FIG. 3A and FIG. 3B.
For the case in which rAn~ ffoI~ is desired over a broad Lequ~.i-r range, such as when the ~ ups 30 and 32 ar_ part of a feedback circuit that is prone to osrill~, n~Al~in~ it ..PcP~sa. y to cancel ffle higher harmonic terms thatwill Arcompany &e primary signal, then phase-adjl~chnPnt circuits 35 and 37 may be sFlF~ to 25 broaden the rAnr~ hon notch about the notch L~uell~y 6Dn. For e~a.l-~lc, the choice of ~>hase a.lj~ t .il~uib 35 and 37 for two pickup signals that are in phase may both be of the type of all-pass filters shown in FIG. 3A or FIG. 3B where the values of ..re R6 or R8 and cAp^~tAnre C3 or C4 arP chosen to --i--;---i,~ the relative phase and amplitude variaffons with l~e l to L~u~ y between the two pickup si~nAlc.
30FIG. 4A shows how two phase circuits may be i~ gldl~d into a circuit comprising two pickup coils 40 and 4æ Coil 40 is co....P L~.l to series element 45 which may inrlll~P l~isl~la and or in~ rtors (not shown) co~t~P~ in series with the coil 40.
Likewise, coil 42 is co.~..~ Ie~l to series el...._..t 47 which may include l~islor~ and or in~ rtors (not shown) connpct~l in series with the coil 42. Series PlPmPnt45 is 35 co.~.~P. 1.,.l to ~he input A of an a~ ilude~ c~nr-nt circuit 44 and series elPment 47 is c~ "~ ~ to the input B of an al,.p~iludc .~ .l ."pnt circuit 46. Input A inr~ c a r R3 co---~IP~1 to PlPctrirAl ground, and input B in~ irc a læsi~ R,~ co...~r~
to PlPc~ir~l ground. Tog~ ., the series ~ e..t 45 and lesisl..r R3 form one phase-adj--chn~nt circuit, and the series ~l~rnPnt 47 and the .e~i~.~r R4 form another phase-40 adj..ctm~nt circuit The ou~ul~ of the amplitude-adjnchl~Pnt circuits 44 and 46 are co...~PclPfl to the input of a combining circuit48 which combines the output signals of the amplitude-adjnchnpnt circuits such that the nolse signal caused by external mA~nPffr flUX sllhstAnff~lly t':-n~PlC, The er[~Lv~ impedance of the coil 40 at the input A of the amplitude-adjustment 4s circuit 44 inr~ Pc the actual impe~lAnre of the coil 40 added to the impedance of the series PlPmPnt 45~ and is l~ Pc~ .l by Zl = Rl + icDLl. The t:rr~Liv~ impedance of the coil 42 at the input B of the amplitude-~ c~nent circuit 46 inrlll-lr-c the actual impe-l~nre of the coil 42 added to the impedance of the series Pl~ nt 47, and is 21651~13 rep~esented by 22 = R2 t- ifDL~. The voltage of ~e pickup Siglla~ uced iIl lh~ coil 40 by extemal llla~netic flux }~in~ ~requenc~ ? llleasured at the input A is y,~ 3 Vl / (Rl ~ R3 ~ i~L ~ i~Ll), where Vl is che voltage-m~gnit~lde of ~he si~n~l induced in ~e pickup coil 40 by the 5 extemal ~agl~etic n~ Thc si~Ilal ~olta~c induc~d in ~lle coi~ 40 ~y e};tern~l magnetic flux h~-~ing fre~uenc~,? ~, me~sured at ~he input B is V2~ (R~ ~ R,, + iwL~, where V2 is tilP ~oltage-m~gnitllde of the ~ig~ duced ~n the pickup coil ~2 ~y the extem~l mA~netjc flux. l'he pbase of the voltage of ~e pich~p si~n~l ~t the inp~lt A is 01 = ArcTan(~Ll~3+Rl)~, and the phase of ~e ~o]tag2 of the pickup signal ~t t~e input A is 0; =~4rcTan(~L~/(R4+R2)) In order that 01 = 0~, for a broad range of signal-fre~uerlcies, a), it is Iiecessa~y at the series e~elnen~ 45 ~nd or series elemenl 47 be ad~usted such that Lli~R~+Rl) -L~i(R~ + R,). This may ~lso be accompL;shed by c.djustin~ resistors R3 and or R~. However if we look at the equations for sig~lal voltage at the inputs A arld B of the irnplitude-adiustmen~ circui~s ~4 and ~? respec~vely? we not2 ~at equIvalence of ~e r~tios just discussed does not, by itself, provide ~he c~nrii~ion whereby ~e magnitude of the ~oltage differe~ce V~ 2~ rem~s substantialIy co~h~t as ~ chan~es. Thus in order to assur~
20 optirnal cancellation ~ver a broad range of si~n~l fre~uencies, it is necessary ~at ~e series elements 4~ and 47 be adju~ i such ~at ~le effect~ve r~istanc~ and ~ are e~uivalent and the effec'dve induc~nces Ll and L~ are equrvalent. It is also necess~ry that resistanc~ R~ equal res~stance ~,~. It is possib~e to replace ~ u~ and R~ Wi~L
cAFI;7~itors (l)Ot ShOWrl) for filtering ~ut hIghfr~lue~ nois~, H~wwer, for ~p~irnal 25 cancella~on ~e~ a broad range of sign~ equencies, it is ne~essary that both of ~hese c~r~;fnrs (not shown) h~ve subsl~n~ally e~ual values.
It will ~e i~l e~idLed ~m the equations represen~in the voltages YiA and V2B at~e ~mrlifi~r iIlpslts A and B, respectively, that the series elemeclts 45 alld 47 m~y each include a lar~Ee vahle of series res;~, nGe so as to ~crease ~e effec~r~e ~ic~7ces ~1 and 30 R2 of ~le pickup co;ls 40 and 42, r~sp~c~vely. This will r~du~e ~e ~re~uEncy-dependent pIi~lde ant phase vana~ons of the pickup signa)s VIA and V~. However, it is pre~e~able that the increase ul the effective resistances Rl and R2 of the pick~p coils 40 arld 4~, l cs~.,e~L~ e~, ~ot be ~e or~ means ~f phase-~djLIstmen~ user~ in the ~ircuit ~.~
other ~hase e~feots that are ~lated to the signal-volhge e~ua~ons for Vlh a~d V2B tend 35 to ~ccur.
Consider ~e c~rcuit shown in F~s. 4A in tbe ~se in which it is not opt ed for c~nCplin~ the effe~ts of ~ l m~netic flux. The phase~shif~ between vol~ges Vl~ and V~ reqyired to match ~eir phases is F(a)) = ~rcTan~-~Ll/(R3~RL)~ - Arc~ R,~
4Q A ph~se-a~nent circuit tha~. pro ~ides the required ph~se-s~ ay ~liclude a ~uher~cl input and ~e~ede ei~er or bo~ amp~ e-adjus~anent c~rc~its 44 and 46, or may ~ollow ~ither or bo~ arnI~Iihl~e-adjus~lent circuits 44 an~ 46. The compt~nOElts ~f this phase-ad3ustment ci~cuit are shown in FIG. 4B and FTG. 4~
The phase-adjustmen~ circuit shown in FIG. ~B is a passi~e Iead r~et~oris. An 4!~ input v~ltage Vin is applied across termnlals C alld ~. The oulpul: v~ e VOUt of this circuit ~s m~asured across termin~Is D and G. The ou~llt Yol~a~e is Y~.t = Vin R12 (i¢~CloRll + 111(E~I~(i~cl~Rll + 1~ + ~

AMENDED SHEET

~f R~ Rl2, therl the phase-shi~ 0 = .~r~Tan (~R~1C~Q).
The phas~-ad3us~nent circuit shown ~n FIG. 4C is a pa~s~ve lag network. An inpt~t.
voltage Vm is applied a~oss t~nrn~lc E and C. The out~ut o~ ge Vout of ~e c~rc~
measured a~ross t~ninals F aIItl G The output voltage is Vout--~in R14 / ((Rl; + R~3) ~ R~
If ~4 ~ :~ Rl3t ~en ~e phase-shift 0 = -ArcTan (~R14Cls).
The circuit~ Ll FIG. 4B ~nd FIG. ~C pmvide ~e ba~is for COllstlll~::tillg F(~); On~
can use ~e passrJe lead network shou n in F'IG. 43 in se~es wi :h the pa~ e lea~nel;work shown ~n F~G. 4(::, utili~ing ~ppropriale ~uffering between the lead and lag 0 networ~ such as a bu~fere~ arnplifier (not ShOWIl~t and selectin~ 4 and C~; such ~at Rl~Cls = Ll~(R3 + R13 and selectiIlg Rll and ~ such that RllClo = L2,'(R4 + ~.
A~other c~ncf~ f;on circuJt is shown in~ . 4D. ~nd includes a fiIst pick1lp coil50 wrapped arou~d a first core 51 in 2 predet~llined directil~n, ~ ~ond pickup coil !~2 ~appcd in th~ opposite dkectio~ around a ~econd core 53 ~nd connected in series with the fil St pichlp coil 50r ~ld a posifioning device ~5 for adjust~ng ~e posLt~n or orienl:ation of the second core 53. The first pickup coil 50 has resistance ~1 ~nd ~d~lctance Ll. The ~cond pickup coil 52 7~S r~sistance R2 and induc~nc~ L2. The ~pedance Zc of ~e pickup coils 5Q and 5~ at the out~tlt of the second pickup coil 52 is ~C = Rl + Rz ~ im (L~ + L~. The volta~e indLIced ill each pickup coil, 50 and 5~, by 20 m~gnelic flux will tend ~o b~ su~st~ y 18n degre~s o7~t of phase as the pickup coils 50 an~ 52 ~r~ conne~ed in senes, which allows opposite signals to be induced in ~e combined picl~up device w~ subst~7ltially identica~ frequeng7-dependeIlt ~pli~ude and phase relatir~nchirs- Arnplitud~-ad~us~ent is provided by ~he posit;nIl;n~ d~ic.e ~5 which tr~nclatPs ar d nr rotates ~e seconll core 53 relative to e4uipot~ial lines of 26 magnetic fllLx (not s~}own) which induce electric21 pickup ~ignals m the sec~ d pic}sup coil 5~. Th~ posilioniI~ device 55 may move the second core 53 clcser to or f~rther aw~y ~o~n the so~ce of m~ tic Qux ~ not shown ~. Lik~e ~e positinning rle~ice 55 may tilt the second core 53 so as to adiust the ~rr Flitude of ~e elec~ l signal induced in the pi~hlp coil 52. Similarly, ~e positioning de~ice .~5 may adillst t~le position of the 30 second core 53 ~ ue ~o the second pich~p coil 5~ so as to adjust the m~nihlde of ma~netic flux inside ~ pickup c~il 5~, whic}l adjusts ~e a~plitude of the ~lechical signal induced in ~le pick~p coil 5Z. It will also be appfe~ted th~t the p~si~n~l~ dwic~
55 may be used to moYe the sou~e of m~netic flu~ ~not shown) for adju~ng ampl~ude of the elecSncal picl;up sign~ uced ill ~e firs~ ~nd secc)nd pick~p c~
35 50 ant 52. Thus it is a~arelll ~at th~re are se~eral u~ay~ to provide arr pli~de-adjus~rlent by ad~ius ;~ tbe relati~e posi~;onc between a p~ p core and a source of ma~nletic flu~L However, due to the invers~-squa~e relation of ~e intensity of ~na.~netic fl~ ~x with ~spect to dist~ce ~om ~e source of magnetic flu~, it is necessaIy to provide precise degree ~f position-~d~rlt in order to obtain a s~nific~nt de~ree of 40 c~nc~ of the ~lduced pickl~p signals. ~or ~is reason, th~s mcthod of amplitude-adj~ctm~nt is n~t as prefe~ble as the me~ds which u~ e electri~al Yai~l or attPnl ~ti for amplihlde cont~oL
It should be apyu~ci~t~d that the ph2 e~ c~ment c~cui~s sh~ in FI&. 3 alld FIC:. 4 ~re only a few of ~e many ph2se-~dJtlctrn~t circuits that can be t~sed in a ~5 ~ n cPll~tioll eircuit for subs~antially Plimin~tin~ e~ectrical noise in ~ pickup si~nal caused by P~rt~ m~netic flux. The phase-~djus~ent circuils shown, as wel~ ther phase-adJustment circuits may be used in combina~on for ei~r broadening or narrowing ~e ~equency r~nge where a hih de~ree o~signal can~lation occurs.
Ph~se adjl~s~nent circuits may also be used for ~dju~ng amplitudes.of electrical AMENDED SHEET

-~WO 95/03686 216 51 7 3 PCT/USs4/08247 signqlc~ alnd thus may be employed as combined phase and amplitude-adjustment circuits. -A graphical analysis of dirr~ nt types of rAnrqll-q~on is shown in FIG. 5. This graph plots cq-nr~ qffrJn in decibels and l~ c æl.t~ the combined output of two pickups 5 at the ou~put of a combining circuit, such as the voltage-n~-q-gnib~ q Vout of combining circuit4~ shown in FIG. 4A, divided by the voltage-m~nihl~l~ of the pickup signal at one of the inputs to the combining circuit 48. In this graph, rqnrf llqffon is plotted qgpin~t signal Lequen~;y (Hz).
Plot 1 of FIG. 5 lc~ 6 r-q-nrqllqffon obl~il.ed by a circuit that does not 0 c~ ensate hr phase~lirrt lences beL~cn two pickup cignAl4, such as the prior art circuit shown in FIG. 1. Plot 2 of FIG. 5 le~lest:r.6 "notch-cAnr~llnborl" as explained above with ~ .ence ~o the cAnr.~llAffon circuit shown in FIG. 3C The L~ ,cy at which the notch occurs can be rhqng~ by adjl,slillg the ~hacc adjustntent ~ uils 35 and 37. Plot 3 of FIG. 5 l~.esellb cAnrqllAff~ln ol,l~ined by a ~Anrf~llAffon circuit, such 15 as the cAnr~llAffon circuit shown in FIG. 4A, fftat provides subs~AnffAl cAnrr-llAffon of A1 mAgr~f~ffr flux over a relatively broad range of L~1U~1~LY. This curve illllsll..~s a very broad notch centered at a notch L~uell~y a~n. At L~- .P~r;~ C below and above the notch L~ue~l~;y ~Dn the degree of rAnrPllAffon begins to deteriorate. In the case where one uses a cAnrrll~fff ~ circuit such as the one shown in FIG. 4A, it is possible to 20 improve the rAnrPllAtion at r.~. .e.~ c below the notch ~ lell.y a~n by A~lj- .c! ;. .~, the l~;ctAnre in either or both series elements 45 and 47 so that Rl better ay~rox;---A~q the value of R2. Thus Zl better ap~ro~ ;~ A~S Z2 at low Le~ c. It is also possible to improve the rAnrrllAffon at r~..P.~. ;Pc above the notch L~ y ~n by adjusting the ind--~ I~..re in either or both series PlPmPntc 45 and 47 so that Ll better a~.ox;..~Atr~C the 25 value of L2. Thus Zl better a~rv~ ;---AtPc Z2 at high rl~P-~ s Fu~ - ---ore, t~e overall le~el of rAn~Pll~ n over the entire Le~lell~ range may be im~,o~èd by adju~ , the values of ~ L .l;~ R3 and R~ such that the values of these l~ s bet~r a~p~oxill.ate each other. It will be a~eciated that additional phase ~ir uils may be used to provide com~ Affng ~ha~:e shifts at low and or high Le~ - ;-3;, in order to 30 broaden the notch ~el~le~ll at the notch frequency a)n.
FIG. 6 shows a cAnrPll~ffon circuit of the ~lesellt invention which comprises two pickup coils 60 and 62, ~' --e adiuaL~ t circuits 65 and 67, a~ lilude-adj~ lent ~ir~;ui6 64 and 66, a combining circuit 68, a prea~ lifler 74, a power a~ ie~ 76, and a drive coil 70. The pickup coils 60 and 62 and or the drive coil 70 may also inrl~ P one 35 or more ferromagnPhr cores ~not shown).
Pickup signals are induced in the pickup coils 60 and 62 by PYtPrn:~l m~Phr flux. In this case, the l?AI~ 1 ms~gnPtir flux is generated by the drive coil 70. The pickup signal from the first pickup 60 is adjusted in phase by the phase-adju .l.l.ent circuit 65 and the pickup signal from the second pickup 62 is ~ l in phase by the 40 phase-adj~sl~-cnt circuit 67 such that the phases of the two pickup signals are substantially in phase (0 degrees) or out of phase (180 degrees) for a broad range of signal L~~ c. The amplitude of ~e firstpickup signal is adju31ed by the al.-l,lil~d~adj ~ ..ent circuit 64 and the amplitude of the second pickup signal may be adjusl~d by the amplitude-adjustment circuit 66. However, the au~lilude-adjllctmpnt 45 circuit 66 may act only as a buffer and provide no amplitude-adjl.~l...?nt to the second pickup signal. It will be appreciated that ~e all.ylilude-adjustment ci~ ib 64 and 66 may provide either gain or at~n~ on to the pickup .ci~n~l~ It will also be appreciated that the amplitude-adjl -~...Pnt ~ uib 64 and 66 may be replaced by a means for adjusting l~e pocibl.n and or oriPn~;nn of the pickup coils in order to provide r... ~ J~

2~6~17~

adjustment to the ~ pl~ Or lhe pickup signals ~duced hl ~ithe~ or bot:h pich~p coil~
60 and 62. The outputs of both Amrlilude ~djus~ent ~i~cuits 64 and 66 ar~ received by a col~buli~g circuit 68 th~t combines the pick~ signal~ such that the pickup ~ als ~nduced by the exten~al magnetic flux generated by the dr~ver 70 substantially cancel.
The output uf th~ c~rnhinin circuit 68 is amplified by a prearnp~ifier 74. The output of the pre~m~lifie~ 74 i~ amp~ified into a drIve si~nal by a pnwer amplifiler 76 The ~2ive sig~ ows through a d~ive coil 70 ~hich ~enerates a magnetic flux in response to an eYtPrn~i m~netic ~ C frorn a source oLh~r ~ e drive coil 70, or a mag~etic flux caused ~y th~ motion of a ferrornagnetic Plem~nt (not ~ho~) in a m3gnetic field.o For the circuit sho~7n in FIG. 6, it ~s necessary that a ~ligh de~ree of cancellal:ion be obtained f~r a broad r~2~e of frequencies else the c~rcuit will unde~o oscillation due to direct magne~c feedback. In general a circuit will oscillate at a frequ~ncy at which ~e feedback ~in is po~ ~ve, th~t is, when the circuit gain exceeds the circuit losses. I~ e circuit in FIG. 6 achieves a canceLa~on profile similar to plot 3 in FlC; 5, l~n the circuit rllay be lilu~ly to oscillate at a relatively high ~e~uency where the c~ncellation i~ not hS
effective. However, 3 lov~-p~ss ~lter may be inc]uded in ~e f~edback circuit t~ reduce ~e feedb~ck ga~n of the circu~ For ~ample, pre~nplifiPr 74 Ir~y co~pnse ~1 acli~e low-pass filter. l~kewise, one ~r mor~ hi~h-pass or ~ndr~cs filters may be used to elimir~t~
c~i~ osciL~l;ion. It is ~so possible ~lat ~e phase-adjushnent ci~cui~i 65 and 67 and or amplitude-adjustment circl~it~ 64 and G6 ~f the cancPll~tinn cIr~it may be designed specifically to filter certa~ h equ~n~ie~.
The phase-adjushnent CirCllitS G5 and ~7 are designed specificall~ for compenC~hng for frequency-dependen~ phase~ idLions between the pickup sigl~als o~
pickup~ 60 ~nd 62. Howev~, the phase-ad,justrnent cir~uits 65 and ~7 may pro~ide a specific o~e~ll phase-~hift tD ~e comhined pickt~p signal at the output of ~e comb~ning circuit 68. This o~er~ll pha~e-shift may compensate for the phase-shift in~oduced to ~e driv~ Ilal as a ~sult oI the fr~4uency r~s-ponse~ o~ e pickups 60 ~ld 6~ and the dri~er 70 The phase-adjus~nent cira~ 65 and ~7 may also be used to co.llFe,~sate for phase-shifts in the circuit due to other c9rcuit elemen~s that m~y precede the d~e coil 70.
The phase-adjuslment arcui~c 65 and 67, most prefer~b1y are preceded by a ~uff~r (llOt show~, and m2y plecedP or follow ~e ~mplihlde-~us~nent cirQ~its 64 and 6B.
~n ernbodiment for a c~nc~ tion circl~it of the present invention is shown in FI~. J. T~e circuit i~ Fl~. 7 includes a Illan~tic elem~t 81, a ferroma~ne.tic core 8~, two pickup coils 80 and 82 wrapped ~round ~e core 83, a phase-adjustment circuit 85, the inp~t to the phase-ad3ncln~Pnt circuit being cl nnee~d t~ elec~ical grou~ld by a 1 esisl~ R3. ~le output of the phase-adjustment ~ircuit is conne~ted to the input of an ;~lnp~ de-adjus~nent circuit 84. The pickup coil ~ i5 CUIUleCted tU the ulput of an Amplil~de ~dju~ent c~rc ~it 86, t~is Input also includes 2 re~slor ~ conne~t~ft to elecbieal ~round. The Qutputs of each amplitude-adjusknent circuit 84 and 86 ~s co~nected to a combining circuit 8B~ The output ~ f~hc comh~nin~ circuit 88 is connected to a cl~n~rçn~at;Qn circuit 89. Tll~ compensation ci~cuit ~9 is coslnected l~
ampl;fier ~6 which amplifics an input signal in~o a dr~ve signal whi~ s through a dr~e coil ~O wrapped around a f~omagnetic cor~ 9~
The pic~up coils 80 and 82 are shown ~ Yi~ t~ly equidisb~t to ~e dr~e coil 90, which g~ne~t~ an external magnetic flux F. The pickup coils 80 and 82 receive ~pprox~mate~y equal intensities of the e~ernal ma~neti~ flt1x F gene~ted by the drive co;l 90. Ampli~de-adj-lctm~nt of the piclmp signa~c induced ill ~e pidsup coils 8~ and 8~ by ~e drive coil's 90 generated extemal m~ne~;r fu~ F colllp~te for differences tllat may occur between ~e pich~p ~ lAlC, such as differences in ~e int~hcifiec of ~e AMENDED SH~

WO 95/03686 216 ~17 3 PCT/US94/08247 drive coil's 90 generated magnPhr flux F at the location of each pickup coil 80 and 82, distortions in the drive coil's 90 generated magnPhr flux F rpc~ ng from neall,ycc "d~ g or magnPff~ Ally pPrmP~hle m~tPni~lc such as ferromagnPhr Pl~mPnt 95, and dir~,ellces in the amplitude re~ol~se between the pickup coils 80 and 82 to m~gnPhc s flux inrll~ling Leq~ dependent a~ LIude l~s~ul~se. ~kewise, the pickup signalsinduced in the pickup coils 80 and 82 by wu~u,," PxtP~n ~l magnPh~ flux and m~gnPhr flux generated by other m;~gnPffr suul~e~> (not shown) ~licpose~l in the plane that is the pe~pPn~lirnl~ b;se_lur of the height ~limPn~ of the drive coil 90 will also be s-lhs~nff~lly equal in amplitude. Thus after yhase shifflng by the ~hase ^~ .,t 0 circuit 85 and combining by the combining circuit 88, the signals in~lllrPtl in the pickup coils 80 and 82 by ~.il~ ~rnAl m~ hr flux, the magnPffr flux F generated by ~e drive coilL 90, and m~gnPffr flux generated by any other m~gnPhr sources (not shown) dis~osed in the plane that is the y~ r l);~e~;lor of the height ~limpncion of the drive coil 90 will cancel.
The e~nrPllAbr,n of the effecb of the drive coil's 90 ~;el~ .l magnetic flux F on the combined pickup slgnal is altered if either a permeable or coJ~ g obiect enters the space shared by the field p~t~rnc F of the drive coil 90 and the pickup coils80 and 82. If the intruding object is pprmp~ble~ the field y~ . .. F su,.o.-..~inE the pickup coils 80 and 82is.1islu. l~d, and energy passes dil~Llly from the drive coil 90 to the pickup coils80 and 82 through the dialu~ k~d field. Thus if the ferromaEnPhr ~lPmPnt 95vibrates, the L~uell~y of its motion is ,~").1~ in the combined pichlp signal.
e of the c~nrPll~hQn of ~xt~n-l m~znPhr flux, the output of the combining circuit 88 will comprise only the pickup signals intll-rP-l by the motion of theferrom~gllP~ir PlPmPnt95.
The com~ saLo.~ circuit 89 provides a phas~ shift to the output signal of &e combining circuit 88. The output signal of the ph- - e ar~ ment circuit 88is amplified by the amplifier 96 into a drive signal which flows through the drive coil 90 and generates the m~gnPh~ flux F. This mAgnF~hr flux F may be used to either drive or damp the motion of the ferrnm~gnPhr ~l~mPnt 95 ~lppen~ling on the phase of the dnve signal. It is p.~rel~.ble to provide drive forces to the ferrom~gnPh~ Plement 95 such that the phase~relahonship of the drive force to the motion of &e ferrnm~EnPhr elPmPnt 95 is not changed by the ~l~uen~;y of the element's 95 mohion. This is ~a~ ularly O~Idnt if the motion of the ferrom~gnPhc ~1. ..~..1 95 comprises a plurality of ~lirr~.. l,tfi~..~... ;PC.
For the circuit shown in FIG. 7, the signals from the pickup coils 80 and 82, after being combined, may have a total phase-shift of 0p ~ ArcTan( ~L2/(R4+R2) )-The ~has~ shift of the drive signal at the drive coil 90 is 0d '= ArcTan(~3Ld/Rd ), where Rd and Ld are the ~' ~ . e and in~lnrt~nr~P, leape~liv~ly~ of the drive coil 90.
Ignoring any ~has~ shifts caused by other elements in the circuit, the total phase-shift between the magnPbr flux F generated by the drive coil 90 and the rt-s~ol se of the u~s 80 and 82 to the magnPffr flux F generated by the drive coil 90 is 0t = 0p + 0d.
By adjusting the values of resistances R2, R4 and Rd, and or the values of ind~lrt~nrPc L2 and Lp, or combinaffons Illeleor, it is possible to cause the ratios L2/(R4+R2) and Ld/Rd be subst~nliAlly equal, and thus the value of 0t will be s~lhst~nh~lly æro for a broad range of signal r~ r~P~
The ~i~uib shown in FIG. 8A and FIG. 8B may be used in a cAnrPll~t;on circuit as phase-adjustment ci~uib~ such as phase-adjusllllent circuit 85, for providing phase-~ ~5~ 73 16 shifts to pickup signals before they are combined, or may be used in the feedback loop of FIG. 7 as a phase~c,.~ sation circuit, such as phase-c~ ens~Alion circuit 89. The circuit shown in FIG. 8A is a common l1.V~1 lin~ amplifier. A buffer amplifier 94 may precede the first impe-l n~e ~l~m~nt Z11. The second impedance ~l~ment Z12 provides 5 feedback between the output and illv~ , input of amplifier 98. The gain rrstllffn~
from this i1~V~1 li..g al..yLri~l is Gl = Z12 / Z11- Thus the ratio Z12 / Z11 may be a~l; ~~
to com~l.sal~ for phase-shifts. The circuit shown in FIG. 8B is a common non-il.v~.lillg a~ liriel com~ .mg an amplifier 99 and gain~ontrol impedance values Z13 and Z1~.The gain of the non-ir,~ ~ lin~, al..yliLe. is G1 = 1 + Z1~ / Z13- ~L~ewise, the ratio Z1~. /
10 Z13 may be fl.lj~ to compPnc~ for phase-shifts.
The ~ .;Uit~ shown in FIG. 8 also pro-vide a means for co...p~ tin~ for frequency-dependent amplitude variations in the f~~ signal caused by the L~u~ y le:a~vi~se of the pickup coils 80 and 82, the drive coil 90, and any other circuit ~l~m~ntc in the fee.lh~ k loop. For example, the circlAit shown in FIG. 7 will produce a 15 pickup signal voltage Vp = VB R / (R2 + R~ + iaDI~) at the input of a~.~l;Ler 86, where V8 is the voltage in~ll-re~l in the pickup coil 82 by PYtPrnAl maf~nPbr flux B. The voltage VB is ~l~o~o.lional to the mA~nih~le of the ma~nPhr flux B. The ma~nih~ of m~nPhr flux B is ~ro~ol lional to the al..pLI~de of drive ~u~lellt Id in the drive coil 90, where It =
Vd / (Rd + i~Ld) and VD is &e drive voltage. Thus the pickup signal voltage Vp is 20 ~o~o.lional to VB R / (R2 + R4 + ia)L2) (Rd + iC3Ld). One can observe from the equation for Vp that as ~ 6S~, the pickup signal voltage Vp will de loase.
An example of a circuit design &at can com~el~ e for &e L~uel~y-dependent a~.~Ll.lde variation of the pickup signal voltage Vp is two il~Vel ling amplifiers as shown in FIG. 8A c.. ~k ~ in series. The impe~l~nre DlPment Z12 of the first amplifier 25 98A co~.~L;aes a ~ ' ~ r Rl2 (not shown) and in~lllrt~r Ll2 (not shown) co.~. .~ Ie.l in series. The value of the leai~ R12 is ( R2 + R~ ) and the value of the inductor Ll2 is L2.
The value of &e imre~lAnre ~lPmPnt Zl1 of the first amplifier 98A is R4, where a is a scalar cOl~lal~L The impe~Anre ~lPmf~nt Z12 of the second a.,.~ . 98B comprises a resi~lo~ R22 (not shown) and inductor L22 (not shown) co....~~ in series. The value of 30 the ~e~ )r R22 is Rt and the value of the i~ . lur L22 is Ld. The value of the impedance PlPm~nt Z21 of the second amplifier is aR4. The gain Gl of the first amplifier is (R2 + R4 + i~DL2) / aR4. The gain G2 f the second amplifier is (Rd + ioLd) / aR4. The total gain of this circuit is Gt - GIG2, and Gt multiplies the pickup voltage Vp so that the Læ~lu~...y-dependent nature of the pickup voltage a~ ,liLude is CO~ .cak.~ It should be nobed 35 that the values of R2, R4, and Rd may be i~ eased to reduce the Lequell~;y-d~e~dent effects on the pickup signal voltage Vp, l-o.. il~weasil~g the value of Rd s~lhstAnb~lly reduces the magnihl~le o magnPhr flux generated by the drive coil 90.
l~e ~equel,~y-dependent phase-shifts and amplitude variations that typically occur between a pickup coil and drive coil may be ~llhstAntially compensated over a 40 broad range of signal fl~ c, a), through the sPlPch- n yiocess of the values for PlPctriral com~ullell~ in the co~ cation circuits that adjust both amplitude andphase-l~2s~0l~se. Typically, for a feedback system such as shown in l~IG. 7, where the motion of a ferrom~gnphr ~lPmPnt is driven by the P~t~ m~gnPhr flux generated bythe drive coil 90, the frequency-depPn.l~nre of the phase of the drive signal is of more 45 illkle~l than the frequency-dep~n-lPnre of the amplitude of the drive signal. However, for a feedback system in which a drive coil generates a specific magnetic flux in -~Wo 95/03C86 PCT~Ss4/08247 2 1 6 ~ 1 7 3 ul~se to an PxtPrn~l ma~nPtic flux, such as for the ~Ul~ose of ~,.nr~l;..g an ~xt rn~l m~gn~tir flux in a sperifir region space, controlling both ff~e phase and amplitude of the drive signal is impol Lal~t.
Another embo~imPnt for a r~nrPll~t on circuit of the ~l~sent invention is shown 5 in FIG. St. The circuit in FIG 9 inrl~ Pc a pickup coil 104 wrapped around a pickup core 105. The pickup core 105 may be made of a ferrom~gnptir ma1~ri~l and may be m~gn.~ l The pickup coil 104 is co~ r~l to a compensation circuit 106, which con.,e~ to a splitting circuit 108. The spLlli,lg circuit 108 has a first output co....P~I~
to a first pl~ase arljnctmPnt circuit 109 and a second output ~o~ to a second phase adjl.~L~ent circuit 110. The first ~>hase adinc~npnt circl~it 109 is co.~ to the input of a first a~ 111 and the second ~has~ adjustment circuit 110 is co~ to the input of ~ second a~ 112. The output of the first amplifier 111 is c~ .1 to a first drive coil 100, and the output of the second amplifier 112 is co...~ A to a second drive coil 102. Both the first and second drive coils 100 and 102, ~ ;L~r~ly, are 5 ~la~ed around a drive core 101, and generate a magn~hr flux F. The drive core 101 may be made of a ferromagn~hr mA~ri~l~ and may be mA2~ l. In this case, &e drive core 101 is shaped so that both of its endpoles are in close proxill~ity to a ferroma~nPhr PlPmPnt 115. The ferroma~nPhr elPmPnt 115 induces a c~nl in the pickup coil 104 when its motion di~ s the dishibution of ma~nPt r flux F that passes 20 through the pickup coil 104.. The shape of the drive core 101 conc~nhd~. the ma~nPhr flux lines F generated by ~ .l in the drive coils 100 and 102 so as to provide a more PfflriPnt ma~nffir drive force to the ferroma~nphr PlPmPnt 115.
An P1~ l signal VD1 is induced in the pickup coil 104 by m~nPh~ flux generated by the first drive coil 100, and 102, and another pickup signal VD2 is induced 25 in the pickup coil 104 by m~nPhr flux gene~l..t~d by the second drive coil 102. An Pl~rhi~al pickup signal Vp,~",4, is in~l-re-l in the pickup coil 104 by magnPffr flux produced by other su.u.~s such as the ferroma~nPhr PlPm~nt 115 moving thrûugh a static mA~nPhr field. The ele_hi...l signals .ll.luceli in the pickup coil 104 pass l~lou~l, the comluel)saLon circuit 106 to the splitting circuit 108 which splits the pickup signal 30 into two drive 5i~lc One of the drive signals passes through the first phase-adjnctmPnt circuit 109 and is amplified by the first amplifier 111. The other drive signal passes through the second phase-adj~L~..Pnt circuit 110 and is amplified by the second amplifier 112. The first drive coil 100 has an err~;liv~ cicl~re of RD1 and an eL~;liv~
in~lllr~nre LD1 which results in a total im~nre of Zl = RD1 + io~LDl, where (i) is the 35 r~ n y of the drive signal. The second drive coil 102 has an ~rr~;liv~ lesisl~l.L;~ of RD2 and an ~rr~liv~ indl~rt~nce LD2 which results in a total imre l~nre of Z2 = RD2 +
iaDLD2. B~a~ ~e 1~e impe~lAnrPs Zl and Z2 of drive coils 100 and 102, 1~ e~Lv~ly, will tend to dif~er from each other, a drive signal flowing through the first drive coil 100 having the same ~ n.~ ~ as a drive signal flowing through the second drive coil 40 102 will tend to differ in phase and amplitude from the second drive signal.
The phase-adjustment circuits 109 and 110 compensate for Leq.lency-dependent phase dirf~r~nces between the first and second drive S;gnA1C~ and the amplifiers 111 and 112 may provide amplitude-adjustment to either or both of the drive signals in order to compensabe for amplitude diffelel.ces between the signAlc The phase and amplitude-4s A~lj.. l...~nt is ~ lful,l.ed such that the signals VD1 and VD2 in~ rPrl in the pickup coil104 by the rirst and second drive coils 100 and 102, ~ ~Lvl:ly, are s~lbst~nhAlly equal in mAgnitll~le and 180 degrees out of phase so that they cancel. It will be ay~r~iated that the splitting circuit 108 may be used to adjust the relative m~gnit l~les of the drive signals in the drive coils 100 and 102. It will also be appreciated that the phase-216~1~3 adj~Ls~nent circuits 109 ~nd 1 lû may ~e posi~oned so ~at they each follc~w ~e ampl~iers 1l l ~nd 112, respectiveLy. Becau~e I~hase-~jus~ent and arn~litude-adjustlnent need on~y ~e applied to one ~f ~e two drr~e signals, this ~llows ~o~ ~le removal of one of ~e phase-adju~nent circuils 109 or 110.
Anot}ler method of amplitude and phase-adjus~nent involves changing ~e effec~ive resist~ nd ~2 and or ~e effect.ive ~lductance LD1 and Lp~, of either or ~o~ lri~e coiLs 1~)0 and lO~. Ther~fore, the phase-adjus~nent circuits 10~ a~d llO
follow ~e amp~ifiers 111 and 112, respec~ely. The phase-~djus~nelll circuits 109 ~nd 11~ wuuld comp~ tol~ (not ~hown) and or ~nduct~r~ (not shown~ connected in o series wi~ me ~rrve coils 100 ~ld 102 s~ ~s ~ a~ t their ef~c~e resistance K~1 and R~z and or ~ffec~:iv2 inducbnce LD1 and LD2. In order for ~ relative phase between ~e ~ d~netic flux ~enerated ~y each dri~e co~l 10~ and 10~) to be substantially 180 degreec, the relation~hip. ArcTan~ ,D~ = ArCTan(~DLD2/~D~ ) must hold for a wide ran~e offr~quellcies ~ us ~Dl~RD~ - LD2/RD~. Ho~ever, Ln order for d~ relative ~mpl~ les bel:ween ~e m~gnetic flux ~ene~ated by e~ch drive coil 100 and ~ n2 to be subst;Lnffally equal for a broad range ~f si~lal freqllencies ~, it is preferal~1e ~at the e~ctive resistances RD1 = RD, a~d thc effective induct~ce. Lnl ~ l~2- It will beappreciated that because the eff~ctive~ resistance R~,l ~ d RD2 and ~ ffec~e indUCtanCe LD1 aIld LL~ ~n he ~djusted tv control b~th ~e phase and arnpli~ude of the dri~ ignals ~n the drive coils 10~ and 102, ~en only ~ s~ngle arnplifi~r (no~ shown) ~or amplifying a pickup ~i~nal int.o a dri~e sig~al is neeess~y. Ar~ alLernativ~ c~ncella~on circuil would D~clud~ a single amplifier c~rcuit (not shown) placed between the eompensation circuit 106 and l~le splitting c~rcuit 10~ d the ampllfiers 111 and 112 may ~ mo~ed. The phase-ad~ nent circui~s 10~ and 110 could p~wide bo~
amplitude arld phase-a~ st:ment to l~le drive signals going to each dr~c c~il 100 and lû~ as described a~ e.
An emb~diment for a canc~D~ n circuit of th~ present invention i~ shown in FIG. 10. The circuit in FIG. 10 ~ncludes a fr~t ~ickup coil 120 w~apped around a pickup core 121, ~ second pi~kup c~il 1~ wr~ped around a second core 1~l, and a dr~ve c~il 130 wrapped around the second e~re l31. The first pickup coil 120 is conrl~cted to the inp~lt of arl a~plitud~-adJustment circuit 1~Z4. Thc output Gf the amplitude-adjustment circu~.t 1~4 is co~n~t~ to ~e i~put of a phase-adjustment circui~ 125. The second pic~tlp coil 1~!? is c~nnected to the input of an a~ )l;lude-adjustment circuit 126. The OUtpllt of the ~mr~ ude-ad~us~n~nt circuit 126 is c ~nnect~d to a phase-adju~ ent circuit 127. The outputs of ~he phase-adjus~nent circuits 125 and 127 are connected to 3 combinin ci~cuit 1?8. The output of the com~ning c3icuit 1~ is connected to a compen~atio~ circuit 129. The co~ aE:ion urt,~it 1~9 is conne~ted to ~n amplifier 136 Wh~ m~ e~ the np~lt signal into a dr~ve signal which ~ows l~ou~h ~e dri~e coil 130~ ~i genen~f~s a rnagn~
Thc pichlp coils 1'~0 and 1~2 are responsive to ~he ~gnefic fl~Lc g~ner~ted by the drive coil 130. ffo~ er due tQ the pru,~ y of the second pichlp coil 12~ to the driv~
coil 130, the econd pickllp coil 1~2 recei~es a gre~te~ ~m~ itllde of l~agne~c flux generated by the dr~ve ~o~1130 th~n does ~e first piclmp coil 12Q. Tt w~ll ~e a~precia~ed that the second pickup coil 12~ may bP localed inside of ~h~ dri~e coil 130, or ~at ~e pich~p coils 1~ and 1~ m~y be positioned, ~hiet~lGd or ~lerwise designed ~uch th~t ~e second pickup coil 1~2 receives greater m~gnptic ~lux generated by ~e dr~?e coil 130 than does ~e filrst pich.1p coil l20. The ~llplitudes ~f ~e pi~p responses of the first and second pickup coils 120 and 1Z2 iI~du~ed by ~he magnetic flux generated ~y the drIve coil l 30 are made equi ~a~ent by either or bo~ of the amplitude-~djustr~lent AMENDED SHEET
. . _ _ _ _ _ .

~16517~ ,9 CilCllits ~ d 1~6. The phas~s ~f ~e pi~lsup respo~ses of the first and second pickup co~ 120 and 122 induced hy the magnetic ~LX generated by ~e drive coil 1~0 are compensated by either or bo~ of the pha~e-adjustment circuit~ 125 and i~7 so ~t when ~e pichlp Si~ S ~e c~ bined in the cnmhinin~ clrcuit 128, th~y ~
substantially canccl. ~owever, the response of ~e pickup coils l~Q and 12~ to uniforrn ex~mal m~netic flux ~ result ~1 a ~on-zero con~ibu~on to ~e eo~bmed signal at the QUtpUt of the c~mbining circuit 128. The compensa~ion ci~cuit 129 m~y ~mpnseeith~r or bo~ phase-adjus~nent ~d ~r~rlih~de-~djus~:ment c~rcults (not sho~) foradjllsting ~e phase and or alnplit:ude response of ~e dr~ve ~ign21. The dr3:ve sigIla~ ~S
throu~h ~e drr~Je c~ 0 and g~n~rates ~ unifo~n r~netic flux ~nside the dnve coil13û tllat subst~ntially cancel~ th2 uniform ~nagnetic llux inslde ~e dr~ve ~oil 130 gerlerated by o~er s~urces ~not shown).
Tlle core 121 may be ~ fer~magnetic core, howeve~, ~en om~gnetic maten~ls tend to have a non-line~rr~ onse to magne~c flux, res~ ng in pickup ~ignals compns~nghigher~ rnonic si~ The ~ore 131 }s preferably co~npnse~ of a non-ferromane~c nalerial havu~g a hollow center. If the core 1~1 is made of a ferro~ netic material, then it ~ prefen~ble ~at ~e core 131 be made of a sin~ilar ~errom~gnetic materi~l so ~t ~e noIl-linea~ responses ~ ~e cores 121 and 131 of ~he piclcups 12~ al~d 12~ su~stan~ally cancel.
Because ~e dr~ve coil 130 generates a very ~niform magnetic flux along its a~s iL
i5 preferable ~at ~e region uf ~pac~ l~ic-ll cancelL~ n of magnetic flux is desired be surrounded by ~he d~e coil 130, howeverJ it will be appreciated that the region of space i~ which c<~ncell~t30n i5 desired may be extemal to the dr~ve coil 130. It ~ill also be appreciated that the secoild pi~h~p coil 1'~ could be wrapped around the core 1~1 2:: witllout bein~ inten~ oven with ~ e coil 130 as shown. It will also be appreaated th~t the~e me~hor~s ~or canceling magne~ic ~u~ may be used alnng w,th ~ de~ice ~at genera~es a static magnetic field ror e~nc~lln ext~mal 5tatic magnetic fie~ds.
Another ~n~ho nent f~r a c~n~ nnn circuit of th~ preseIlt invelltioll is shown in FIG. 11. The c~ra~t in FIC 11 mr~ a first pich~p coil 1~0 wra~ped around a core ~o 1 4l, a second pich~p coil 142 wrapped around ~le core 1~1, an~ a dn ~e c~ 0 wrapped around ~e core 141. The first pic~p coil 1~0 is cann~cted tD th~ lIlpUt 0~ a p~l~se-adj~chn~lt c~cuit 145. The out~ut of ~e phase-ad~us~nent circuit 145 is connected to the input ~f an amplitude-adJus~nent c~rcuit 144. The second pickup c~il 14~ is connected to t~e input of an ~Tnrli~l~e-adjus~ent circuit 146. It will beappreciated ~at ei~er alnplitude-ad3ustrn~nt circ~it ~44 or 146 may act only ~s a buffer, ~s ~nnrlihlde-ad~us~nent of only one of ~e pidmp coil 140 and 14~ outputs is nece~sa~y.
The ou~ut o~ t he ~plih~le-adjus~mellt ~rcuits 144 and 146 are conn~cted to a com~lg circuit 148. l'~e ou~ut of ~he cclrnbinin~ circuit 14~ is conn~cl~d ~o a compel~atin~ circuit 14~. The co~ sation cira~it 148 is connected to An ~nplifier 15fi. The Amplifier 156 arnplifies its input sig~lal inlo a driYe si~n~l which flow~ thrnllgh the drrYe coil 150, ar~d ~ener~tes ~ m~gnetic flux.
The pickup coils 140 ~nd 1~ are respon~n~e to the PlftPrn~l rnagIleli~
generated by the d~e coil 150. The pich~p coiIs 140 and 142 may be posif;onerl relative to the ~ive coil 150 a~ sho iIl FIG. 11 such ~lat one of the pickup coils, such as pickup coil 140, receives a ~reater n~lgni~-~æ of the magnet~c flux ~enerated ~y ~e dr~v coil 150 than does ~e se~ond pickup coil 14:~. Thus wheIl the ~mr~litudes and phases ~f the pickup sign~s from each of ~e picl~p coi~s 140 and 142 are adjusted so that ~le col~kib,l~ons of m~gnetic flux generated by the driYe coil 150 cancel when ~ese pickup signals are comhinPd at ~e c~mhir-ing circuit 14~, the combined response of the pichlp coils 140 and 142 to unifo~n exten~al rn~gnphc flux urill be substanti.a]ly .

AMENDED SHEET

WO 95/03686 PCT/USg4/08247 ~
1 7 ~

non-zero. It will be appreciated that other methods may be used to adjust the ic~o"ses of the pickup coils 140 and 142 to PxtP-nAl mA~nPffr flux such as llbli7ing di~rèl~:nt numbers of coil win~lingC in the ~.chl~,s 140 and 142, or rhAn~ing the size, shape or matPriAl of the core 141 which the pickup coils 140 and 142 are ~la~ed around.
The co~ sation circuit 149 may comprise either or both p' --e adju~ cnt cil~.~i6 (not shown) and amplitude-A.~ c~mPnt circuits (not shown) for adjusLil.g ffie phase and or amplitude r~ol,se of the drive signal so that the drive signal has a sperific amplitude and phase relationship to the P~tlPrrlAl mA~nPhr flux ,~.pingil~g on the pickup coils 140 and 142. The drive signal flows through the drive coil 150 and gel~e~alès a u~ o~ mAgnPhr flux inside the drive coil 150 that cancels the PxtPrn mA~nPffr flux inside the drive coil 150.
It will be appreciated that the circuit shown in FIG. 11 may be used to drive ordamp the motion of a ferromAgnPbr rl~ t ~not shown) that generates a ma~nPhr flux by moving through a mAgnPffr field. In ~his case, the core 141 may be made of a ferromagnPhr mAtP~Al, and it may be shaped so that both endpoles of the core 141 are in close proxi,~.ily to the ferromA~nPffr PlPmPnt (not shown) for providing a more powerful and concentrated driving or da~ u.g force to the ferromAgnPh~ PlPmPnt To produce a driving force, the drive coil 150 would preferably gelle~ a mA~nPhr flux that is in-phase with the moffon of the ferromAgnPhr PlPmpnt~ in~ as~ L~ as the speed of the ferromA~nPhr PlPmPnt toward the core ili~ LSeS. To ~-oduce a damping force, the drive coil 150 would preferably generate a magnPhr flux that is out of phase, hence op~G:.ing the motion of the ferron A~nPffr ~l...., .~
An ernboAiment for a ~ AnrPllsffon circuit of the ~lQent i"v~:,.Lon is shown in FIG. 12. The circuit in FIG. 12 inrln~lPc a pickup coil 160 ~la~ed around a pickup core 25 161, a signal generator 162, and a drive coil 170 ~v~aylJed around a second core 171. The pickup coil 160 is co.n.~l~ to the input of an amplitude-A.~ t circuit 164. The signal generator 162 provides a signal to an amplifier 176 which a~ lifles the signal for producing a drive signal. The drive signal flows tl~rvu2;l. the drive coil 170 and generates a mA~nPhr flux. The signal generator 162 is co....~ 1~1 bo the input of a phase-âdj . 1~ nt circuit167.Theoutputofthe~ e ~ chnPntcircuit167isco.. P~l~ to an amplitude-A~ -..rnt circuit 166. The oul~ub of the amplitude-A~ljnchnent circuits 164 and 166 are connPctp~l to a combiring circuit 168. The output of the combining circuit 168 provides a pickup signal that is 5~ s~Anb~lly free from the ~ o.~se of the pickup coil 160 to the magn~hr flux generated by the drive coil 170.
3s The rAn~rll~hon circuit shown in FIG. 12 demonstrates that in order to provide a pickup with a rAnr~llAffon signal, it is not .~rr~csa. ~ to have a second pickup device. In fact, any ~l~h-ir~ C~ ;on of a drive signal that has the proper phase and amplihude cL~alr- l~ may be used to cancel the i~s~ se of the pickup to f~xtPrnal mAgn~hr flux generated by that drive signal. In this case, the waveform of the drive signal is generated by a signal gel~e~ ,. 162. The output of the signal generator 162 is adjusted by a phase-adj--~ -rnt circuit 167 and an a~,~lilude-adjusL,l.cnt circuit 166 before it is combined with the output of ~e pickup coil 160. An amplitud~adju:.L...ent circuit 164 is shown co....~l~l to the output of the pickup coil 160 witlh a lc~ai~lu~ R
co~ to ~l~chirAl ground. It will be a~l~;ated that either amplitude-a.lj..~ nt circuit 164 or 166 may act only as a buffer, as amplitude-A~ .c~nent of one of the signals from either the pickup coil 160 or the signal g,e,~fdh~r 162 is ..~Pcs~ly. Itwill also be a~ ~;iated that the output signal Vo~,t of the combining circuit 168 may be supplied to an input of the signal generator 162 for generating or controlling the frequency and amplitude of the generated signal output to the amplifier 176 L~ A~

WO 95/03C86 ~ 1 6 5 1 7 ~ : PCT/USg4/08247 The magnPh- flux generated by the drive coil 170 induces a voltage VB in the pickup coil 160 which is ~ru~orlional to magnihl~le of the m~gnPh- flux. The mAgnihlAe of the magnetic flux generated by the drive coil 170 is plOpu~ Lonal to the drive current ID in the drive coil 170. The drive current ID = VD/(RD + ia~LD), where RD
5 and LD are the err~liv. rP!.iC~ e and in.l~ ~Lvely, of the drive coil 170, and VD is the drive voltage. The drive voltage VD = G VO, where G is the gain of the amplifier 176 and VO is the signal voltage produced by the signal ~ el~tor 162. The voltage Vp of the pickup coil 160 at the input of the amplitude-adj~ ent circuit 164 is VP - VB R / (R + RP + i~DLp) =B Vo R / (R + RP + i~LP)(RD + i~LD) 10 where Rp and LP are the eLr~Lv~ læ~;~.lA...~e and ind~ e Liv~ly, of the pickup coil 160, and Bis a proportionality consl~nl that l~ s_rlb the contribution of gains and losses in the circuit. The signal voltage at the input of the combining circuit 168 which is ~ o....P.I~ to the output of the amplitude-adj~lchnf~nt circuit 164 is Vcp = A Vp = A B Vo R / (R + RP + i~LP)(RD + i(DLD), 5 where A is the gain of the amplitude-adj~cl Pnt circuit 164. In the case where the combining circuit 168 is a dirræ~æl~Ual amplifier circuit, it is desirable that the input signal, V~O~ from the output of the a~ de-adjnctment circuit 166 be substAnhAlly nbrAl lto Vcp in order for cAnrpllAhon to occur.
One possible design for a circuit that may be used as the phase-adjllc-hnent andamplitud~Aj~ n~nt ~ih;ui6 167 and 166, l~s~livæly, is two illV~l lil g amplifierui6 c~.. ~ It'A in series as shown in FIG. 8C. The impedamce ~lement Zll of the first ~V~:l Ling amplifier circuit would comprise a ~ l (not shown) having the value (R +
Rp) and an inductor (not shown) having the value Lp, the reai~lor and inductor being co..r-P~ in seAes. The jm~eAAnre olf ...~/~t Z1l of the second inver'dng amplifier circuit 2s would comprise a leai:~lur (not shown) having the value RD and an i,~ r (not shown) having the value L~, the reDiDIul and u.lu~lur being co....P.~ in series. The impeAAnre el~ t Z12 of the first illvel lill~, a~ lilièr 98A, and the impedance PlPmPnt of the second i~lvel Lil.g amplifier 98B would have values such that their product equals the value; A B R. Any buffer amplifiers such as amplifier 94 would provide unity gain.
30 Thus the input signal VCO into the combir~ing circuit 168 will be subctAntiAlly ~clPntiral to the other input signal Vcp~ and thus will cancel. It will be ay~l~iated that the example shown illustrates only one of many APcignc for combined phase and amplitud~A-ljn~nPnt ~;-l.uil~ that may be used as am~Ltude and phase-adju~Lu.cntwl~uil~ 166 and 167, l~_~;1ively. Fu~ ,ore, it will also be a~l~;iated that either or 3s both phase and amplitude-A.lj.--l ..ent may be ~ .,ed on the signal from the pickup coil 160, such as pickup signal Vp, in addition to, or incteA~1 of the phase-adj~lchnPnt and amplitude-adjll~Lu,ent ~e~Ç~ u.ed on the signal VO ~e~ aled by the signal generator 162. For example, the amplitude-a~ Pnt 164 circuit may be preceded or followed by, or comprise a phase-adj.lchnPnt circuit (not shown) that adjusts the phase 40 of the signal from the pickup coil 160.
Another embodiment for a cAnrPllAtion circuit of the p.ese~.t invention is shownin FIG. 13. The L~Ceive and trancmit PlPmPrltc in FIG. 13 inr~ e a pickup coil 180 wrapped around a pickup core 181, and a drive coil 190 wrapped around a second core 191. The pickup coil 180 is coll..P.~ to the input of an amplitude-a-lju~L~.ent circuit 4s 184 at TPrrnin~l A. An amplifier 196 generates a drive signal at TprminAl B which flows through the drive coil 190 and generates a mA~nPhr flux. The ouhput of the amplifier 196 is colu~e~;le~i~ ~utE~of~ la~a~s~e-adju~Lu.cnt circuit 187. Preferably, there is some 2165~7~

sort of bu~ not shown) ~s part of ~e ~hase-~djushnEnt circuit 187~ such as a lar~e value of resistance that ~orms a volhge divider with the drive coil 190 for 2tt~t1~tin~ the input signal to th~ ph~adjustrnent c~cuit 187. The output af the phas~-adjushnent circuit 187 i~ ~onnected to ~n ~rnplihlde-adjustrnent ~rcuit 186. The outputs of the arnplib~de-adjus~ment circuits 184 and 186 are connected to a ~amb~g circuit lg8.
The output of the ~omhinin~ c~rcuit 188 provides a pic~up si~n31 at ~he input of ~e arnp~ifier 196 (~e~ninal C~ that is iubslAl IL;~ Y free ~r~m the res~ODse of the pi~kup coil 180 l:o the m~nelic flux ~ener~ed by ~e drhe coil 1~0.
The c~n~ tion circuit shown in F'JG. 13 d~nonstrates that in order to pro~?ide apickup wi~ a c~ncell~tion sign~, it ~s nolt necessar~ to ha~Je a secoIld pic~up ~3evice.
Rather, part of ~he d~iv~ signal used to gene~ate an external ~nagnetic flux may be combined with 2 pickup si~nal t~ cancel ~e response ~f lhe pick1~ de~ice to tllat exterl~al ma~ne~ic flu~ The signal VA at Terrnmal A represents a pickup signal ~V~3 induced ~y ~e ma~ne'dc flux g~nerated by the drive e~il 1 gO, where Vu ~s the volt~ge of th~ driYe signal flowing through the dri~)e coil 190 and 13 is a sCalill5~ factor that represer~ts losses between the m~ e of ~e dnve signal YO ill ~e drive c~il 190 and ~e rn~gn;hlde ~f ~e pi~kup coil's 180 respol~e to t~at ~ve signal VD a~er being amplified by the ~mr~ ad~ nen~ circ-~it 184 The signal YA at T~ninal 1~ o includes an a~ditional pickup signalV~jc~,", induced by ma~ne~ fluxr~cltl~ing from ~er sources o~ ~an ~he dr~ve coil 1gO. Thus ~--~3VD ~ ~;Ch~P The signal a~ Te~inal Bis VB--VD + VUP~ where ~nxc~ is the signal that the dr*e coil 1~0 pick~ up due lo PYtPrn~l sourc~s of m~gnet~c ~ux. Hvwe~er, if ~D i5 much ~reater th~n VDP;~,D WC C~n omit V~s;~p ~ thus we c~n write: YB - V~. The signal Y~ is a~tenuated by a f~ctor of ~3 and il~ ph~se is ad~usted ~n ~e fe~h~rk loop er~mpri~m~ de an~ ph~se-adjustsrlent CirCl~it5 186 and 1~7, respec~ely, SUdl ~at wh&n it is combined at ~e combir~ng circuit 18~ wi~ ~e pickup signal VA = ~D T ~Pi~hll- from Te~al A, ~e resl7l~ outp~t of ~e combining circuit 1~ ern~inal c) is ~c = YPjC~,;D. Thus fee~7haclc thAt would r~ om ~e pich~p coil's l 80 rPsponse to ~e ma~ne~c flux ~enerated by ~e d~ e CQil l90 ~s sl~hst~nti~l~ eliminated.

3~ A c~~ Affrn c~cl~it of ~e presf:nt invention is shoum in FlC. 14A A signal gener~tor ~0~ genesates an elechical signal ~lat is a~plified ~y an ~nplifler 203 to - prod~ce a drive si~nal a~ TermL-~al ~ The drive si~nal flows through a dnve c~il 200 and generat.es a magnetic n~. The drit~e coil 200 .~ay be wrapped around a core such ~s ~orc ~1. Te-Tnin~ A is connected to an ~mpli~lde-ad.iu.s~rnent circuit 204, which - ~5 ~r~f~ bly draws only a ~mall por~on of ~le dnve signal. Thus the input of ~e Amplitude-~djus~n~nt circuit 2Q4 may i~clude a buffer ~not shown) such as a high-v~lue re~istor. The Ol~tpUt of ~le amplitude-adjus~nerlt circuit 204 ~s connected to ~e input of a phase-ad)us~nent circuit 205. The sigr~l ge~lerator 20~ has ~ second UUtp~lt (Terrninal B) w:hich produces ~ s~nal tha~ is simj~ to the signal input to the ~mplifier 203, but may di~er in phase and or aInplitude. The second outpul of the signal generator 202, T~ml~nal B, may sinlply be an output ~at is spljt from th~ input of th~ fi~r 203 by a sp3itti~ cuit (not shou~). ~Prm~n~l B ls connected to the input o~ a h~nonic cornl~nsation circuit ~1~. The ou~put of the harmonic colllpens~tion circuit 210 is connected to Te2nninal C, which is conneçted to an arnplit~de-adjusknent circuit 20~. 'r

4 5 The output of t~}e ~mr~lih d~-adjus~nent c~rcuit 206 is cnnnected to the input of a phase-adjus~ t circuit 2~7. Thc outputs of b~th p~ase-adjust~ent circuif5 205 and 207 ~re cnr~necl:ed ~ separate inpu~s of a comh;nin circui~ ~08. The colnhining c~rcuit 208 AMENDED SHEET

WO 95/03686; ~16 517 3 PCT/US94/08247 produces an output signal VOI~t that results from cAn~qllotiQn of the drive signals generated by the signal g~..e~dtor 202.
l'he drive coil 200 is r~yo~iv~ to ~ rnAl mAgnPhr flux, even while a drive signal ii5 flowing through the coil 200 If the drive coil 200 is not in close ~oxill,ity to

5 mAtPriAIc that have a non-linear r~i~yonse to e~t~rnol magn~hr flux, then higher harmonic effects in the drive and or pickup signal of the drive coil 200 will besl hstontiolly n~gligible. Collse lu~nlly, the harmonic com~e..szlion circuit210 may be replaced by a short co ~ , Termin-o-l B to Tr-rminol C The signal voltage at T~ormin~l A is VA = VD + VP~,h,P ~ where VD is the voltage of the drive signal and VpiCb,p is 0 the voltage of the induced pickup signal in the drive coil 200 due to ~xtPrnql mAgnP~;r flux The signal voltage at Tr~rmin-q-l B is: VB = Q VD~ where Q is a pl C ~Ol Lonality con~-qn1 Because the drive coil 200 has a complex impedance ZD = RD + ia)LD, and other circuit Pl~m~ntc (not shown) qCSoriabqrl with the drive coil 200 may also contribute fr~tu~n~ dependent terms to the er~e~liv~ impe-lAnre of the coil 200, it is ~e-- ~ y that phalse-A~ nent be l,elr~ ,Lod to co."~,sate for phase-variations between the dAve comp.,.lel.6 VD of the signal voltages VA and VB at T~r ninqlc A and B, f~spe~;lively. After phase and amplitude-adplctm~nt has been ~ lru~ ed on either or both of the signals V~ and Vv &ese signals are combined in the combining circuit 208 such that &e signal colll~un~nls related to the drive voltage VD cancel, leaving only a signal that is related to &e pickup signal Vp~, This method of cAnrP~ tion allows a single unit, such as the drive coil 200 shown in FIG 14A, to cim~ usly lla~
and ~c~ve el~ . agn~hr cignAlc It will be a~ iated that the output signal Vo"t may inr1~ 1e an ir~t~rfare (not shown) to the signal gel.~lalul 202 to conhol lhe amplihudle, frequency and phase of the signal ~ al~d by the signal 2;enel~t~)r 202.
It will be furlll~ a~.~iated that if the core 201 is made of a ferromAgn.~hr n-q~ri~l, a voltage VH 1 ~llhn~ from the non-linear lèSlJO~ of that mA~rri~l to the n~s~nPffr flux t;e~ at~:d by the dnve coil 200 will be inrlndP~l in the signal voltage V,~
at T~rminAl A: VA ~ VD + VP~ + V{~. Such nnnl;.-~. ;Iy creates even harmonics VH in the flm~ mental dl;villg Lequel..;y VD that are not reducible to zero by prior-art 30 ~nrPll~ffon ~rhniques Thus it may be ~P~CS~ ~ to PliminAbo the signal voltage VH
r~c~lting from the non-linear l~s~ol~ce of the core 201 mAt~riql by providing the circuit with a filber means (not shown) for fil~ring out these higher harmonic effects, or a harmonic co ~l ~ caht.n circuit, such as h~rmcTIi~ co~ c~hon circuit 210 FIG 14B shows a design for a circuit that may be used as the harmonic 35 com~Pnc~lffon circuit 210 The circuit in FIG 14B inrl~ s a coil 212 wrapped arourld a core 211 tlhat has a s~hstAnffAlly idenffcal non-linear ~o.~ce to magn-off-~ flux as does the core 201. The coil 212 may be ~ ..t~l with re~ l to magn~tir flux generated by the coil 200 such that the ~l.c" l - ;- Al signals induced in the coil 212 by the ma~nPhr flux will subst~nti~lly cancel The coil 212 ~nay be provided with active n~a~nPffr .chi~lfling 40 such as a cAncPllAbon circuit (not shown), or magnPhr shi~l~lin~ m~tPriAlc (not shown) for substAnffAlly ledu~ing the re~o.,se of the coil 212 to magnPffr flux generated by Px~rnAl magnPtir sources (not shown) The material of the core 211 responds to the magnPffc flux generated by ~e signal outputVB of the signal generator 202 at ~rminAl B and sllhstAnhAlly reproduces the non-linear effect in the signal V8 that will be used to 45 cancel the signal VA-FIG 14C shows a design for a circuit that may be used as the harmoniccompensalion circuit 210 The circuit in FIG 14C includes a splitting circuit 213 for splitting the input signal from Terminal B into two signals at out~lb TPrminAlc B1 and .

6 PCT/US94/08247 B2. The output tPrminAl~ TPrminAl B2, is csi...~.1 to an input tPrminAl~ T~rminAl C2, of a combining circuit 223. TP~ninAl B1 is cc,....s~. lt .~ to a harmonic generator circuit 214 which ~llhst~nffAlly ~ oduces the shape of the harmonic signal VH in the signal voltage VA at TPrminAl A. The harmonic gt ,~elalor circuit 214 may in~ one or more 5 ha~nonic-generator circuits (not shown) known to ~ O.~S skilled in the art as "frequency-doublers" or "L~ut ncy-triplers." The output of the harmonic-generabor circuit 214 is CQ~ to a phasc . ~jllctm~nt circuit 218. The ~l ase adj~ nPnt circuit 218 is conn~i to an input of an amplitude~ ...ent circuit 219. The output of theamplitude-A.lj-J~ nt circuit 219 is ~O~ ~ ~l to an input, TprminAl Cl, of the 10 combining circuit 223. A signal that is ~IO~cl Lonal to the drive signal VD is input to the combining circuit '~?~ at TPr nin~l Q A signal that is ~/fu~Ju~ Iional to the harmonic signal VH is adju~ in phase and or al.lplilude by the phase-fltlillc~n~nt circuit 218 and the amplitude-adjl,~L,ent circuit 219 before being input tû ~e combining circuit 223 at TerminAl C1. The signal voltage Vc at the output of the comhinin~ circuit '~ 7-~, 15 T~rminol C, has amplitude and phase relqffc~--cl.;~,s between signals VD and VH such that when that signal Vc is combined with the a.,.lJLL.ldc ~ t~ ,hasE adju~L~ d signal V~ at the combining circuit 218, the contributions of the hArmorlif te~ms VH and the drive signal terms VD will sllhstAnffAlly cancel.
FIG. 14D shows a design for a circuit that may be used as the harmonic 20 compensation circuit 210. The circuit in FIG. 14D inf ll~lPs a a~ g circuit 213 for splitting the input signal from Tf nninAl B into three signals at oulp..b T~qrminqlc B1, B2, and B3. T~qrminAl B3 is co~ P. l~?fl to an input ~o~ninAI, TPrminAl C3, of ffle combining circuit ~7~. T~ nAl B2, is CO~...f~ to the input of an a~ Llude-adj~ -.t nt circuit 216. TprminAl B1 is ~.C~ f'~ ~ to a coil 212 that is ~l~ped around a core 211. The core 211 is made of a mA~riql that has a s~lhs~Anholly i~lPnffrAl non-linear ~a~uf~ie to magn~ff~- flux as does the mA~riol of the core 201. Thus the output of the coil 212 comprises a signal voltage that has a com~u~lent that is ~o~u~ lional to the drive signal VD and a CO~ u.~llt that is ~.u~lional to the harmonic signal VH. The coil 212 is CO.~I~f~ l~ to the input of a ~11a5~ A~f~ .-.. t circuit 221. The output of the 30 ~has~ adju~l".entcircuit221is ~u~ f~~ totheinputofana~ LIude-a~ .-ent circuit 215. The o~ ub of the a~ lilude-adjustment circuits 215 and 216 are cc,..~
to a combining circuit 217, which combines the GU4.1b such that &e contril~uLo.~ that are ~ G. Iional to the drive signal voltage VD sl~hstAntl-o-lly cancel, leaving only a signal that is ~.o~u. l ional to the horm~ ir signal VH. The output of the combining 35 circuit 217 is co~...~ IP.~ to a phase adj.~ t circuit 218. The output of the phase-adj.9cl --~nt circuit 218 is co...-P l~.l to the input of an amplitudc --ij..~! --~nt circuit 219.
The ou~put of the amplitude-adjustment circuit 219 is co~ to the input T~rminol C1 of the combining circuit 223. The combining circuit 223 combines the hormnnicsignal VH and the drive signal VD such that their relative ~yul liûn and phase are 40 substAnb~lly j~lenb-~l to the relative ~iO~Jul Lon and phase of the harmonic signal VH
and drive signal VD in the signal VA.
It will be appreciated that the splitting circuit 213 and the combining circuits 217 and ~ shown in FIG. 14C and FIG 14D may control relative amplitudes between the split and combined s~l~lr;. ~1 ci~ es~e~liv~ly, and thus ~limin~te the need for 45 a~ lilude-adj~ Pnt circuits 215, 216, and 219. In FIG. 14C and FIG. 14D t~e output of the amplitude-adjustment circuit 219 is shown CO~ to an input t ~rmin~l of ~he combining circuit 223, however it will be a~.e. iated that the output of the a~ lilude-adjllc~ nt circuit 219 may be co....~l~ to the output Vo"t of the combining circuit 208.

WO 95/03686 ~16 517 3 PCT/USs4/08247 T~e circuit shown in FIG. 15 shows an embodiment of a rAnr~llAbon circuit of the ~esent invention as it would be used in a simnlt-n~ous trAncmit/l~ceiv~ system.
An ele_l. ;cdl signal VB at T~rminAl B is au.~ ied into a drive signal VD at the output (Tr minAl A) of an amplifier 233. T~rminAl A is cc,....~l~l to a drive coil 230 that may 5 be w~ ed around a core 231. T~rminAl A is also cc,....~ 1*.~ to an amplitude-adj ~ nt circuit 234, which typically will provide at~nl~-ff~A~n so that the output of the amplitude-adjustment circuit 234 is substAnffAlly lower in amplitude than the drive signal VD. The output of the amplitude-A~lj.lctment circuit 234 is co~ r~ lt~i to the input of a yhasc . ~justment circuit 235. TPrminAl B is co....~ ~1 to the input of an amylilu;le-0 adjustment circuit 236. The output of the a~ lilude-adj!.cl...~nt circuit 236 and the output of the phase-adj~lctTn~nt circuit 235 are co....P~ .l to a combining circuit 238. The output of the combining circuit 238 is co .. .~ l.~.1 to a ~.~a~ lifier 232. The output of the .ea~ Jlifier 232 is co...~ k~ 1 to T~rminAl B.
Th~e signal-voltage VA at T~rminAl A comprises a drive voltage VD~ which flows 15 through the drive coil 230 to generate a magn~hr flux, and a pickup voltage Vp,~p ~at is in-lllre~ in the drive coil 230 by other solu~es (not shown) of ma~nPffr flux. In this case, it is t,ie~e.dble that ~e mat~riAl comprising the core 231 has a sllhstAnbAlly linear ~s~o~se to the m~gn~h~ flux so as to m;--;-..;~ the additive harmonic cignAl~lre VH that is caused by non-linear les~ es of the core 231 mat~riAl to magnPhr flux and would 20 otherwise be jnrll~lefl in the signal voltage VA. The signal-voltage VB at Tr-rminAl B
n~ e~.b the drive signal VD before it is amplified by the amplifier 233. The phase-r-lj,-~1 ..~nt circuit 235 and the amplitudc ^-lj.. I..,j-nt ~ Ui6 234 and 236 adjust the relative phase and amplitude of the signals VA and VB SO that the com~o.~ ..b in thê
signals VA and V8 that are related to the drive signal VD can be made to substAnhAlly 25 cancel when they are combined at the combining circuit 238.
The total gain of a feedback loop is cAlrlll~t~l by AC$~ , the gains and losses of each co~ ,ne..l in the feedback loop. For ~x~ , the gain of the first fee~lhflrl~ loop in FIG. 15 is ~Ccpcse~ slal Li~lg at TrrminAl B, moving through the amplitude-adj~ nt circuit 236 to the combining circuit 238, then through the ~eam~Lfier 232 back to 30 TPrminAl B. The amplitude-adj~-~lrnt circuit 236, and the preamplifier 232 may provide gain or AttPnl~Affon to the elPctricAl signAlc. The combining circuit 238 provides an efr~live AttPnl~tion to the elF 1. ;- ~l signals by virtue of it A~ g the r-l~?rh~rAl signals le~ s~ g the drive signal VD. Thus if the total gain of this first feedback loop is less than one, then this part of the circuit will not cause osrill~hr,n.
The gain of the second fee lh--k loop in the circuit shown in FIG. 15 is ~'~;r ~S~
sl~ ling at TPrminAl A, going through the all,plilude-arljl.chnent circuit 234 and the ~llase adj~ .cnt circuit 235 through the comhining circuit 238 to the preamplifier 232, and finally, through the a~ liflel 233 l~l--- ..;..~ to TPl-millA1 A. The amplitude-adj~la~ ent circuit 234 includes a means for fltt~nnAting the signal VA at TrrminAl A.
The preamLplifier 232 and the amplifier 233 will typically provide substAnhAl gain to the elech ical signal while the phase-adju~Lu.ent circuit 235 will usually have little effect on the amplitude of the elechical signal. The combining circuit 238 will provide a sllhstAnhAl er~ ve A~nllAtion to the Plechiral signal flowing through it by virtue of it rAnrPling the signal-voltage that is related to the drive signal VD. If this rAn~PllAbon is large enough, it will cause the total gain of the second feedback loop to be less than one, ILe~efore the circuit will not os~ tP
The pickup signal Vpf~ p that is induced in the drive coil 230 is amplified and rehlrnP~l to the drive coil 230 to generate a mAgnPhr~ flux, while the feedback effects of _ _ _ _ _ _ _ _ _ _ _ _ WO 95/03686 PCT/US94/08247 ~
2~173 the drive signal VD in the circuit are r~n~Pl~ to y.~:v~llt osr;ll~hon. This allows the drive coil 230 to transmit and receive an electromA~nPh~ signal sim~ ..Pously. It will be a~u~ iated that if the core 231 is made of a mAtPriAI that has a non-linear l~yo~se to magnPhr flux, the c~n~PllAhon circuit may utilize a design to cancel the PlP~ t~Al 5 signals rPslllt n~ from the non-linear lc:,~ol~e of the core 231 ma~riAl, such as is shown in FIG. 14B through FIG. 14D. It will also be a~,~;iated that either or both of the signals VA and V8 from Tprm-inAlc A and B, resyeLliv~ly~ may have amplitude and or phase-a~ ...F~t applied to them such that the signal col,.yu~lenb related to the drive signal VD will cancel at the comhinin~ circuit 238. Fu~ ....ore, it will be a~.~iated 10 that a comrPn~tion circuit (not shown) may be inrlll~1P~l in the feedback loop or y~æc~ , ~e drive coil 230 in order to provide a specific phase and or amplitude rrlsh~ nchir between the piclcup signal Vp~p and the drive signal VD.
The circuit shown in FIG. 16 is an emborlimPnt of a rAnrPllAffon circuit of the p~es~ t invention that cancels both stahc ma~nPtir fields and ma~nPh~ flux in a specific region of space. The circuit in FIG. 16 inrlll~c two ma~nPhr field sel,so,;. 240 and 242, each of which generates an Pl~ l signal thatis ~.o~ullional to the scalar ma~nih~le of the maf~n~hr field ~ in a specific direction at the locahon of each sensor 240 and 242. The Sen50.~ 240 and 242 may be flux gate S~ nS(S~;., or the like. The signal from the first sensor 240 is a.ljus!~ in phase by a yhase a.lj~ .Pr~t circuit 241, and 20 amplitude by an amplitude-A~ ctnlent circuit 244. The signal from the second sensor 242 is a~ cb~ l in phase by a ~hase ^ lj..~l...,."t circuit 243, and a.rl~Ll.lde by an amplitude-A~ t circuit 246. The oul,u.lb of the all.~Llude-adjustment ~ ;ui6 244 and 246 are cc,....P. l.?.l to a combining circuit 247. The output of the combining circuit 247 is cor ~ .1 to a com~u~llsaliol~ circuit 248, which is .~o....~ l~.~ to the input of an 25 amplifier 249. The amplifier 249 amplifies an input signal into a drive signal VD that Iqows through the drive coil 250 and produces a mAgnPhl field 1hat is !FllhstAnt~lly parallel, though o~osil~ to the mAgnPh~ field ænsed by the SèllSO~ 240 and 24æ
The first sensor 240 is po~iLolled in dose proximity to the coil 250, or inside the coil 250 in order to sense both the mAgnpti~ field ~;el~ ted by the coil 250 and the 30 magnPff.- field generated by extPrnAI souhæs (not shown). The second sensor 242 is positioned in such a mAnnPr so that it is s~ ivæ to the mAgn~h~ fields generated by P~ l soulces (not shown), but not as se~ iv~: to the mAgn~tir field ge~elal~d by the coil 250 as is the first sensor 240. Each of the SC 1~ 240 and 242 has a specific ra~o of le~ul,se between the mAgnPti~ field g~llelated by the coil 250 and the magnPh~ field 3s generated by the P~rnAI magnPh~ sou~es (not shown). It will be a~u~leciated that there are many ways to change the ratio of l~a~onse of one of the sel SOli~ 240 or 242, fl,1j. .~ g the position being only one of the ways, howevcr the im~o. l~l~t point is to provide one of the senso.~ 240 or 242 with a di~rele.lt ratio of ~ayollse than l~e other sensor 242 or 240. The amplitude and or phase of the signals produced by the sel~sol;~
40 240 and 242 are adiual~d by amplitude-adju;,lll,el.t circuits 244 and 246"eaye liv~ly, and phase-adjllctm~?nt ~ uila 241 and 243, lea~ecliv~ly~ such that the com~onel,b of those signals that are related to the drive signal VD will subst~nh~lly cancel when they are combined at the comhining circuit 247. However, the output of the combining circuit will comprise a voltage VEXt that is ~JlO~JUl lional to the m~gn~hc field i..~ y 45 generated by the external sources (not shown).
The amplitude of the signals ~l~duced by the Sèl~SO.;. 240 and 242 will typically need to be adjusl~d in order to cancel the dc signal r~c~lting from the n~agn~hc field generated by the drive coil 250. However, as the magnitl~le of the drive signal VD
changes in Lé~yo~lse to a l-h~nging external m~gn~h~ field, there may be some response ~ - -216~1i3~, an~malies between the two sensors Z40 and ~2 rel~t;ed to ~e rate-of-change (llux) of t~le ~ e signal VD. Thus it may be necessa~y to compensate for flLuc-dependent amplitude alld rate-of-response ~phase) diL~ereIlces be~ween the two seIl~or~ 2~0 and ~42.
1`he dn~e coil ?50 generates a highly Imirorm magnetic lleld within the region of ~pace that it ~l~loses. Thus it is preferable to ut~i~e the interior of ~e coil 250 as the space in which ~m~fn~ magnetic fields will be ~an~eled HoweJer, ~lue to the induc~ve ~U~ ies of the c~il 2;~ and the possib}e flux-dependent ampli~ude and phase charact~risti&s ~f the ~ensors ~40 and 242, it is necessary to provide ph2se and or a~plit:ude-compensat~on using a comppnsatio~ circuit, such a~ co.~1pen~atinn circuit 248, ~n order ~o pro~ride substantial cance~lation of magnetic ~ux.
The circuit shown in FIG 17 is ~o~e~ embod~ment of a c~lceIlation c~cuit of the present invention that canceLs both sta~ic m~gnefic fields and m~gnet.ic fl~Lx in a specific regiuII of space. rhe circuit in FIG. 17 includes a m~n~t;C ~leld senso~ 262 which gene{~ ec~ic,~l sign~l th~t is proportional to the sc~lar magnitude uf In~ e~ic rleld jtrength in a speciflc direction a~ ~e location ~f ~e sensor 262. It will be apprec~ted that ~e sensor ~6~ may be a flllx g~te ser~sor, or ~e lilc~ The signal produc~d by the sensor 202 ~s sen~ to an automatic control unit 264. The automatic controI u~t 2~4 con~o~s the gain of an an~plifier 266 conne~d to a dc~ l gene~t~r ~65. T~2e OtltpUt of ~e amplifier 266 iS an ~mrlified or attprlu~ted dc~ el drrve signal VG
that is passed through a compensation c~rcuit 267 t~ a d~i~e coil 260, which geneTates a netic fielcL
The magnetic field sensur 262 preferably is rlr~Cit inned inside the reei~n of spac~
where cancellation of magne~c fields is desired. The magrl~tic ~leld sensor 262 produces a signal that is proportional to the an~pl~ude of t~le m~netic field Lt senses, which co~rnC~ the magnetic field gene~ted ~y the drive coil 2B0 and magnetic fields ger~el ated by ot~er so~ (nol showl~)~ The a~LLol~latic control unit 264 determines if a m~gnetic field is present at ~e senst)r 26~ and coI~ s the amplifier 2G6 so ~t the e si~n~LI V~ in ~e dr~ve coil 26û produces a rn~npti~ fi~d ~ha~ cancels the magne~c field at the sensor 262. Because i~e dri.~e c~ 60 bas inducti~e properties, there will be an inducL-~e lag ~n the dri~e si~nal VD ~OWin~ ~hrOUgh ~le drive co~ 2~0 wh~ ~e ~mplitude of that signal changes. Likewise, the effec~e nnpedance ~ = RD + icoLL, of ~e coil ~60 changes ~nth ~nal ~equency a:, thus a si~al flux will result in a vanation ~f ~e ~nplitude of ~e m~neffc neld generated by ~le drive coil 260. The CU11LIJer1SatiOn c~rCuit 267 prwides phase and amplitude-ad~tlchl-Pnt tQ l~e drive signal V~ so t~at ~he drhe coil ~61~ is a~le to provide subsl~n~ial canc~llatinn of ~oth static ~nd dynam~c magne~c field~
It will he ~r~ciated that ~e C~ c7linIn circu~t 267 may also provide compPne~tinn for any flw~-dep~ndent ~mrlihlde and phase varia'dons in ~le ~esponse of the sens~ 2~2. It will also b~ ap~l~c~ t the Al~toln~tic control unit may ~ncIude a means ~r prQuidin~ a~ U ~liLude and phas~-c~ ti~l~ t~ the ~ve signal VD. The c~ cuits shown D FIG. l 6 ~nd FIG. 17 show metllods of c~ncelin~ magnecic fields along a single ~x~s, howe~er, a superposition of three such circu~ts, each alang an url~ugonal axisr will provide comple~e callcellatiol1 of m~ tjC fields ~n ~hree fl;m~ncirmc~ -Bacause coi~s of wire whose cun ents ~u~ c~ l InA~netic fields in space filnct;on as ~nt~n~s ra~;ai;n el~kol~a~ne~c energy, it as obvious ~hat ~e c~nce~ ;on and or comp~nC~tioIl cira~i~ shown above may be used ~n rad~r systems for providing noi~e-c~ncPII~tion and gimult~neous ~nsmi~receive r~<r~ki~

AMENDED SHEET

WO 95/03C86 ~ S ~ 3 PCT/USg4/08247 The circuit shown in FIG. 18 is a ~c~clled embo~lim~nt of a c.qnrPll~qhon circuit of 1he p~sent invention. A signal gel~alul 276 gcllc~atcs an PlPch~rAl generator signal VG that is amplified by a power amplifier 274 and passed ~rough a jlln~ffnl 272 to an ant~nn~ element 270, which both emits and reccivc . ele_~o...AgnPff~ radiation. The 5 antPnn~ element 270 is ~e .~Ol~:vc to other SoUI~es (not shown) of el~llu...Agn~hr radiation, and produces an elech i Al pickup signal Vp. I~e junction 272 is co...~ .l to an input of a comhining circuit 275, which receives the pickup signal Vp along with a leakage signal VL from the power amplifier 274, which is a portion of the ~ ICl~LUr signal VG. The signal generator 276 also ~ru~uces a ~cfelcl,~e signal VR that is sirnilar in 10 shape to the gcl~.dtur signal VG . The refclcl~ce signal VR passes through an amplitude-adjl~ctmPnt circuit 271 and a phase-adjllctm~nt circuit 273 to an input of the combining circuit 275. The output of the combining circuit 275 is amplified by an amplifier 278.
The junction 272, which the generatûr signal VG passes through on its way to theant~nn~ f~lPmpnt 270 may be a circulator (not shown) which directs most of ffle power from the power amplifier 274 to the Ant~nn~ PlPmPnt 270. However, I,ec.. use the PffiriPncy of a circulator is frequency-.lepPn~l~nt on the ek~ch irAl signals ~
through it, the ~.~....~nrP of the circulator (not shown) will be degraded by the use of large signal-bandwidths or multiple r~q--~ s as well as other operational limitAtions. The~rore some of the energy from the power a~ lil;c~ 274 will leak into 20 the combirling circuit 275. The amplitude-adj-.~l...rnt circuit 271 will provide L~u~l.cy-~epen~l~snt amplitudc ~ L to the ~ ence signal VR such that its a~ lilude is s ~hs~-snbs11y i~lPnhrA1 to the amplitude of the leakage signal VL leakesd from the power amplifier 274 into the combining circuit 275. It will be a~ Liated ffiat the amplitude-A~ -"rnt circuit 271 may be a circulator that is similar to the circulator 25 used as the j11nrhon 272. The output of the amplitude-adj~ nt circuit 271 would then be s~h^~snhs11y ~rOpUl Lonal to the ~.-.plilude of the leakage signal VL. The phase-adj..-l...~nt circuit 273 adjusts the phase of the ~Çt l~:nce signal VR such fflat it will cancel the l~sAl~Age signal VL at the combining circuit 275. Preferably, the phase-nt circuit 273 will produce a s~hstAnbA11y c~" c~ phase ~lwecn the leakage 30 signal VL and the ~ e signal VR over the desired frequency range of generated signals VG. Thus the output of the combining circuit 275 will comprise a pickup signal Vp that is sllhstAnhAlly free from the effects of lPAl~Age signal VL Pm~nAffn~ from the power amplifier 274.
It will be a~ Liated that many possible tl~ ignc exist for can~P11Ahon Lil~ lib to 35 cancel the effects of signal in~. r~,el,~e between the trAncmifflng and ~ect:iving PlPmPnh of a ra~iAting system, the circuit shown in FIG. 19 being only one of these ~le.ci~nc, lilude and or ~hase ~ jllctr~lpnt circuits (not shown) may be il.le,posed in thecircuit between the junc'don 272 and the combining circuit 275. Fu~ ....ore~ in the case where amplitude-mo~1~1A~I and or Llu~ y-mo~1~1Ate-l signals are generated and 40 ~ceiv~l, the circuit may include filters (not shown) for h1tPring out the carrier r~ èl~cy before the rAn~PllAtion circuit removes the trAncmi*P~ signal from the received signal.
The phase-adj~1c1ment circuit 273 may include a delay a~al ~IU5 (not shown), such as delay lines, for delaying part of the rert:le~lce signal VR such that some of the 45 trAncmitkP-l radiation ~mAn~hn~ from the AntPnnA element 270 that .~le~ Is back from nearby objects, such as ground clutter, may be cAn~e1P~l from ffle pickup signal Vp. The reference signal VR may also include ~1PchicA1 signals ~at are similar in shape to signals induced by other noise source~ (not shown) in the An~nnA elPment 270, and ~n~.A~ 7~

_ 216Sl73 29 separa~e amplihlde and phase-adjusbnent may be 2pplied for canceli~ ~e r~sponse of the ~ntPnn~ element 2~0 to ~ese other nois~ sources ~not shown). Furtherrnore, ~e ante~lna elemen~ 27G may be responsive to inc~dent radi~tion for pr~du~n~ a dri~e signal 5 tha~ allows an antenna, such as ~e ~ntenna elelnent ~70, ~ h~nsmit elec~romagIlel:ic r~Ai~tio~ tbat cancels the re~ection of ~e incident radia~on off ~f the an~a element 270 or ~ome other object (llOt sho~. Thus the re~ected radiation may be canceled 2t a d;.st2~nt receiver ~not sho~n).
~lagnetic pic~up~ compn~cing picl;up coil~ a,re shown in thc circ~itç of FIÇ. 2 through FIG. 15, however ~ny type of rn~ne~ic pichlp m~y be used witl:L these ~pes of c~nc~ n circslits. Lil~ew~se, a ~ompPnl~a~inr~ circuit may be used to cQ~ sate ~or ampLitude and ph~se ano~r~lie~ ~nsing from any pickup de~ice ~hat pr~duces an elec~ical picL~up signal, a~ld a r~nc~ tiorl circuit may be used to cancel tlle elec~
sigIlals ~nsing ~om the respon~ of the pi~sup device to noise. ~or ex~nplP~ a ~cella~ion circuit may be us~d for calnceling the signals generated by an optical sensor's elec~ic21 response to ba~rollnd eleckomagnetic radiation. In many of ~le figures, a drnJe coil is illus~ated ~ ~e element that g~nerates an electro~agnet:ic field, howeY~r, con~y~nsatio~ circuit~ may be used to compensate for ~ response 20 characteristics P~hibit~d by any s~uctures which gener~te elec~orna~ne~c fields.
The ~ ~Lred methods of amplitud~-adjushnent were shown to be ~lect~ical gain and attenuation con~ols. Howe~er, it w~ll be appreciated that oth~r me~ods of amp1itude-adjustment Ina~ be used, such as positior-adjustInent of the pichlp coils, ffie dn~e coils, ~e cores for ~e picXup c~>ils and drn~e coDs, or near~y penneable and or cond~ n~ ate~ials. It will also be appr~aa~d that ~e induc~lce of a coil may be changed by chang~ng ~he reluctanc~ of ~e pa~h seen by ~at co;l's magnetic field The m~gnih~de of electriu~ current in ~e pickup coils wa5 co~ci-l~red to be V21ysmaL~ thus ~e ~nulatio~ of the equa~ons repr~cen~ing ~e ~le~t~ical pichlp siI~1s induced in the pickup co~s ~y m~ etic fl~L~ have not ~cluded the induc~ve effects 3~ ~Lh~ the pickup cuils ~ y have on e~ch o~er. Howe~er, the scope and spint of ~e p~esent ~nven'don would not be ~h~llenged by co~cid~ ~e inductive effects between pickup coils ~hen ~i~ci~n~n~ the cancell~t-or c~ui~ thermore, consideration of the more su~t~e elect~oma~r~etic aIects~ such as ho~ c~paci~nce ill th2 pickup coil5 a~fects 'che induction of elec~ical signals ~ the pich~p coils and the cancellation and 35 co~ s~tion cira~ at Inay be desi,~ed accordingly, has been clearly ~nlicirAted by is invcntion.
Al~ugh ~e Invention has been de~;cnb~d in ~etail wi~h refe ence to ~e ated p~ ed embodilnent.~, var~aliolls ar~d m~diss~ onc exist wi~hin ~e scope and sp~rit of the ~ tion as described alld as defined in ~ ~oDowi~s cl~ims.
4~

i A~ENDED SHEET
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Claims (13)

1. A cancellation circuit for canceling inductive noise in electrical circuits resulting from magnetic flux, the cancellation circuit comprising a first magnetic pickup means responsive to external magnetic flux for producinga first pickup signal, a second magnetic pickup means responsive to external magnetic flux for producing a second pickup signal, an amplitude-adjustment means for adjusting the amplitude of either or both saidfirst and second pickup signals for substantially equalizing the amplitudes of inductive noise in said first and second pickup signals, a phase-adjustment means for adjusting the relative phase between said first andsecond pickup signals to a predetermined phase-relationship such that when said first and second pickup signals are combined, said inductive noise substantially cancels, and a combining means to combine said first and second pickup signals for producing combined pickup signal that is substantially free from inductive noise.

2. The cancellation circuit of claim 1 wherein said predetermined phase-relationship is 0 degrees or 180 degrees.

3. The cancellation circuit of claim 1 wherein said phase-adjustment means and said amplitude-adjustment provide substantial cancellation of inductive noise over a broad range of signal-frequency.

4. The cancellation circuit of claim 1 wherein said phase-adjustment means and said amplitude-adjustment provide substantial cancellation of inductive noise over a narrow range of signal-frequency.

5. The cancellation circuit of claim 1 wherein said phase-adjustment provides a predetermined phase-shift to said first and second pickup signals for providing said combined pickup signal with a predetermined phase-shift.

6. The cancellation circuit of claim 1 further comprising an amplifier means for amplifying said combined pickup signal into a drive signal, and a magnetic drive means for receiving said drive signal and generating a magneticflux.

7. The cancellation circuit of claim 1 further comprising a compensation means for providing a specific frequency-dependent amplitude and or phase to said combined pickup signal.

8. The cancellation circuit of claim 6 further comprising a compensation means for providing a specific frequency-dependent amplitude and or phase to said combined pickup signal.

9. The cancellation circuit of claim 1 wherein said first magnetic pickup means comprises a first pickup coil wrapped around a core, and said second pickup means comprises a second pickup coil wrapped around said core.

10. The cancellation circuit of claim 6 wherein said magnetic drive means comprises a first drive coil wrapped around a core, and a second drive coil wrapped around said core.

11. The cancellation circuit of claim 10 wherein said core is curved or otherwise shaped such that the magnetic field generated by said magnetic drive means is substantially concentrated and confined to a predetermined region of space.

12. The cancellation circuit of claim 6 wherein said first magnetic pickup meanscomprises a first pickup coil wrapped around a core, and said magnetic drive means comprises a drive coil wrapped around said core.

13. The cancellation circuit of claim 12 wherein said second magnetic pickup means comprises a second pickup coil wrapped around said core.