CA1200886A - Ultrasonic transmitter - Google Patents

Abstract

PHN.10.264 15 5.11.82 ABSTRACT
"Ultrasonic transmitter"
The transmitter comprises an array of electro-acoustic transducers (1), each of which is connected to an oscillator circuit (9) which has a start input (11).
The start inputs (11) successively receive start signals from a start signal generator (13) which comprises a number of comparators (15), each of which comprises a first input (17) and a second input (19). The first inputs (17) are together connected to an output of a sawtooth generator (21), the second input (19) of each comparator (15) being connected to a direct voltage source (23). A direct voltage source (23) is provided for each start signal to be successively generated at least some of the direct voltage sources being controllable in common.

Description

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PIIN.10.264 l ~.11.82 "Ultrasonic transmi-t-ter"

The invention relates to an ultrasonic transmitter for the examination of an object, comprising an array of elec-tro-acoustic transducers and means for activating the transducers in different phases, said means comprising a number of oscillator circuits which each have a start input, and also comprising a start signal generator which serves to supply start signals successively to the start inputs o~ the various oscillator circuits.
A transmitter of this kind is known from German Patent Specification 1,698,149. The start pulse generator of the known transmitter comprises a number of monostable multivibrators, each of which is associated with one of the oscillator circuits. The trigger inputs o~ all multivibrators are together connected to a pulse generator and the duration of the pulse generated by each multivibrator can be individually controlled by means o~ an adjustable voltage divider. A detector which is connected to the output of the multivibrator detects the trailin~ edge of the pulse and in response thereto it generates a start pulse which is applied to the start input of the relevant oscillator circ~it.
Because the trailing edges of different multivibrator pulses occur at different instants, the oscillator -circuits are also activated at different instants, so that the transducers are activated in different phases. The direction of a beam of ultrasonic energy emitted by the transducer array is determined by the phase differences. Once the voltage dividers associated with the various multivibrators ha~e been adjusted, the beam direction can be varied by variation of a control ~,`

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P11l~1O.~64 1 2 5.l1.82 voltage applied -to them. The ra-tios between -the voltages applied to the various multivibrators, and hence also the ratios be-tween the dura-tions of the pulses generated, however, are fixed by -the setting of the vol-tage dividers.
It is an object of the invention to provide a transmitter of -the kind set forth in which the delay times of the activation voltages applied to the various transducers can be varied in more than one way by variation of one or more control voltages.
To this end, the transmitter in accordance with the invention is characterized in that the start signal generator comprises a number of comparators, each of which has a first input and a second input, all first inputs being together connected to an output of a sawtooth generator, the second input o* each comparator being connected to a direct voltage source, a direct voltage source being provided for each start signal to be successively generated, at least some of the direct voltage sources being controllable in common.
A comparator in the transmitter in accordance with the invention sup~plies a start signal to the associated oscilla-tor circuit when the sawtooth voltage equals the direct voltage generated by -the associated direct voltage source. The various delay times can be varied by variation of the sawtooth voltage and by control of the direct voltage sources. The sawtooth voltage may be or may not be linearly time dependent.
An embodiment of the inven-tion in which the controllability in common of the or some of the voltage sources is achieved in a reliable and inexpensive manner is characterized in that each direct voltage source comprises an amplifier circuit whose gain for a voltage applied to a first input thereo* is adjusted to a predetermined value~ the *irst inputs of the amplifier circui-ts of the direct voltage sources which can be = = . . . . ~ .. . . . ..

Pll\.l0.~64 ~ 3 5~11,82 controllecl in comrnon being together connected -~o a first controllable voltage generator.
~ further embodiment in which no-t only the beam direction can be controlled but also -the bearn focus is characterized in that a-t least sorne of the amplifier circuits are constructed as adder circuits, for which purpose they have a second input, the gain for the voltage applied to the second input also being adjusted to a predetermined value~ the second inputs being connected to a second con-trollable voltage generator.
The invention will be described in detail hereinafter with reference to the drawings. Therein:
Figure 1 is a schematic diagram of a first, simple ultrasonic transmi-tter in accordance with the invention.
Figure 2 is a diagram illustrating the variation in time of a number of voltages in the transmitter shown in Figure 1.
Figure 3 diagrammatically shows the operation of the transmitter shown in Figure 1.
Figure 4 is a schematic diagram of a signal generator for a second ultrasonic transmitter in accordance with the invention.
Figure 5 diagrammatically illustrates a detail of the opera-tion of the transmitter shown in Figure 4, and Figure 6 is a further diagrammatic illustration of the operation of the transmitter shown in Figure 4.
Figure 1 is a schematic diagram of an ultra-sonic transmitter for the examination of an object, for example a part of -the human body. The transmit-ter comprises an array of electro-acoustic transducers 1, each of which consists of a plate 3 of piezo-electric material with a first electrode 5 and a second electrode 7. This very simple embodiment comprises five transducers 1 which are arranged in a row at the same distance from .. . . ... . . . _ _ ..

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Pll~'.l0.26LI ~ ~l 5.11.82 one another. The number oP transclucers will generally be substantially larger in prac-tice. All firs-t electrodes 5 are grounded and -the second electrode 7 of each -transducer 1 is connected to a known oscillator circuit 9 which is associated with the relevant transducer and which has a start input 11.
The start inputs 11 of the oscillator circuits 9 are connected -to outputs of a s-tart signal generator 13 which serves to apply start signals successively to the start inputs of the various oscillator circui-ts. The start signals are generated by comparators 15, one of which is associated with each oscillator circuit 9 in the present embodiment. Each comparator 15 has a first input 17 and a second input 19. All first inputs are together connected to the output of a sawtooth generator 21. The second input 19 of each comparator 15 is connected to a respective direct voltage source 23 which comprises an amplifier circuit which consists of an operational amplifier 25 whose positive input 17 is grounded whilst its negative input 29 is connected to the output 33 via a first resistor 31 and, via a second resistor 35, to the input 37 of the ampli~ier circuit.
All inputs 37 are together connected to the ou-tput of a controllable direct voltage generator 39.
The diagram o~ Figure 2 serves to illustrate the operation o~ the start signal generator 13 described.
The diagram shows the variation of a number of voltages V during one period of the sawtooth generator 21, the time t being plotted along the horizontal a~is. The voltage generated by the sawtooth generator 21 is denoted by Vs. In the present embodiment the sawtooth generator 2l serves to generate a linear sawtooth voltage. This means -that the rising part o~ Vs varies according to a straight line~ Other sawtooth voltages where the rising part of Vs varies according to a curved line are also feasible 7 i~ desired.

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.10.261~ , 5 5.11.82 The vol-tages generated by the ~`ive clirect vol-tage sources 23 are indicated as Val -to Va5, Va1 being generated by the lowermost direct voltage source in ~igure 1, V 2 by the second source from the bottom etc.
The value of each of the direct voltages depends on the one hand an the voltage supplied by the direct voltage generator 39 and on the other hand on the ratio between the resistors 31 and 35. In the embodiment sh~wn, for example, the resistor 31 may have the same value R for all direct voltage sources 23, whilst the resistors 35 successively have the values 5R, 4R, 3R, 2R and R, pro-ceeding upwards from the bottom~
At the instant at which the sawtooth voltage s equals the direct voltage Vai of one of the direct voltage sources 23, the output voltage Vci of the associated comparator 15 becomes high. This output voltage is applied to the start input 11 of the associated oscillator circuit 9 as a start signal, so that the associated transducer 1 is activated. When the sawtooth voltage Vs is linear and the difference between two successive direct voltages Vai and Vai ~ 1 is always the same, like in the present embodiment, the period o~ time expiring between two successive start signals is always also the same. This period is denoted as ~
in ~igure 2. If the ~awtooth voltage V starts to rise at the instant t = O, the first start signal Vcl appears at t = ~ , the second start signal Vc2 at -t = 2 ~ I etc.
The kno-rn consequence of such actlvation of the transducers with different delays is tha-t an array of transducers 1rhich constitutes a straight line emits a beam of ultrasonic energy whose direction is at an angle other than 9O to this line. This is diagrammatically shown again in Figure 3. The five transducers are denoted therein by the references T1 to T5. They are situated on a straight line ~1 at equal distances from one another.
lvhen a transducer Ti is activated at the instant t = i r .. . . . . . .

~ ."6~ 5,11.82 t~e resuLt is -the same as i~ a transducer T'l whicll is situated at a clistance i r c be~hind the transdllcer Ti ~ere activa-ted at the instant t = O. c is tt-Le velocity of sound in the medium in which the transducers are situa-ted, so -that i~c is the distance travelled by an ul-trasonic wave during the period i, . The successively activated -transducers T1, T2 ... T5 on the ]ine 41 -thus act as simul-taneously activated virtual transducers T 1~ T ~ -- T'5 1~hich are situated on a line 43 which is at an angle ~ to the line 41. The direction o~ the beam o~ ultrasonic energy which is emitted by these transducers and which is indicated by an arrow 45, there~ore is at an angle ~ to -the normal 47 to the lS line 41. Variation of the voltage generated by the direct voltage generator 39 causes a proportional variation of all direc-t voltages Vai, so that the delay times are also varied; however, their ratios remain the same.
The angle ~ which determines the direction of the emi-tted beam can thus be controlled. The same effect is obtained by variation of the slope o~ the sawtooth voltage V . The ratios be-tween the various delay times can be varied by ma~ing the sawtooth generator 2~ generate a non-linear sawtooth voltage Vs instead o~ a linear sawtooth voltage.
I-t is possible to construct the direct vol-tage amplifier circuits as adder circuits so that they can be connected to two or more controllable direct vol-tage generators, so that the possibilities for control of the delay times ~ are substantially increased. The signal generator may also be adapted so that the cen-tral transducer of the array is always activated at -the instant t = O, wllils-t -the transducers wllich are situated to one side o~ the centre are activated sooner and the transducers which are si-tuated to the other side of the centre are activated later. ~n e~ample of a signal generator incorpo-rating both -these possibilities is shown in ~igure 4 in I'IIN.IO.~ 7 5.l1.o2 the l`o:rm o~ a schemat:ic diagram. The parts s~hic}l correspond to -those of the s:ignal generator 13 are denoted by re:ference numerals whic:h correspond -to Fig~lre 1. The signal generator which is shown in Figure 4 rnay replace the signal generator 13 o~ Figure 1, its outputs being connected -to the corresponding inputs 11 of the oscillator circui-ts 9. These outputs are successively deno-ted by E n~ E 1, Eo, E1, ... E ~rom the bo-ttom upwards in Figure 4. The associa-ted transducers,which are no-t shown in Figure 4, are regularly distributed on a straight or curved line, the central output E controlling the oscillator circuit of the central transducer, the outputs E 1, E 2' -- controlling the oscillator circuits o~ the transducers which are successively situated to one side of the centre of the line, whilst the outputs E1, E2, ... control those o~ the transducers successively situated to the other side o~ the centre.
Each of the amplifier circuits 23, ~ith -the e~ception of the circuits which are connected to the central output E and the two e.Ytreme outpu-ts E alld En~
is construc-ted as an adder circuit; ~or -this purpose it has two inputsO The first of these inputs is the input 37 ~hich has already been de~cribed with re~erence to Figure 1 and l~hich is connected to the direct voltage generator 39. The second inpu-t 49 is connected to a second controllable direct voltage generator 51. Bet~een the second input 49 and the negative inpu-t o~ the operational amplifier 25 there is connected a third resistor 53. The two e~treme ampli~ier circuits 23 do not have a second input 49. The central amplifier circuit 23 ef~ectively has only the second input 49; this actually means that i-t has a first input 37 which is no-t connected to a voltage source (floating input ). In this embodimen-t the sawtooth genera-tor 21 serves to generate a linear sa~tooth voltage wllose mean value equals appro~imately zero. This means that tilis vol-tage .

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P~IN.IO.''6~i 1 8 5.l1.82 starts 1~ritll a negLtive value, equals zero a~pprox:imately halt'~ay -t~1rough the period ancl subsequently assumes a posi-tive value, Ignoring the second inputs 49 for the time being, it ~ill be seen -tha-t -the amplifier circui-ts 23 which are connected to the ou-tputs E 1 to E n are connected to the firs~ direct voltage generator 39 in -the same way as the amplifier circuits of -the start signal 10 generator 13 of Figure 1. The amplifier circuit 23 which is connected to the output Eo has a floating negative input, so that its ou~put voltage equals ~ero. The first inputs 37 of the amplifier circuits 23 which are connected to -the outputs E1 to E are connected to the first direct vol-tage generator 39 via an inverting circuit 55.
The inverting circuit 55 is formed by an opera-tional amplifier 57 whose positive input is grounded whilst its nega-tive input is connected to the output via a resistor 59 and to the first direct voltage generator 39 20 via a resistor 61, The values of the resistors 59 and 61 are equal.
~he vaiue of the firs-~ r-;istors 31 of the amplifier circuits 23 is the same for all these circuits.
The value of the second resistors 35 increases as the 25 amplifier circuits are associated with an input Ei whose absolute value of the sequence number i is higher.
Consequently, start signals successively appear on the oUtpUts En, En-1~ ~ Eo~ - E_n~1~ E_n- ~ en the voltages of the sawtooth generator 21 and the direct 30 voltage generator 39, and the values of the resistors 31 and 35 are chosen so that the time interval between two successive start signals always equals ~, the start signals successively appear at the instants -n`~_, -(n-1) ~, , ..., O, ..., (n-1) L, n Z . The phase shif-t 35 of the activation signals for the transducers is, there-fore, symmetrical with respect to the central transducer.
In comparison with the situation shown in Figure 3) this ~ o.~6~l ~ 9 5.1l.~2 m~ans that the line L~3 on which the virtual transducers are arranged intersects the centre of -the :Line 1~1 on WhiCIl -the actual -transducers are arranged. This offers -the advantage -tha-t when ~ is varied (and ~lence ~ is also varied), the line ~3 is no-t ro-tated about one of its ends but about i-ts centre, so tha-t the cen-tre of -the emit-ted beam always origina-tes from -the same poin-t.
Eor the sake of simplicity, -the effect of -the voltage applied to -the second inputs L~g of the direct voltage amplifier circuits 23 will be first described witllout taking into account the described effect of the voltage applied to the first inputs 29. To this end it may be assumed that all first inpu-ts 29 are floating, so that all start signals would appear at -the same instant t = O.
The ampli~ication of the voltage which is applied to the second inputs and which originates from the second direct voltage generator 51 is determined bv the ra-tio of the value of the first resistor 31 to that of the third resistor 53. Because all first resistors 31 are equal as assumed before, the amplifica-tions are inversely proportional -to the values of the third resis-tors 53. The amplified voltage is again compared in the comparator 15 ~ith the value o~ the sawtooth voltage from the sawtooth generator 21; when both voltages are equal, a start signal is produced. If the values of the third resistors 53 are chosen to be highest for the amplifier circuit 23 associa-ted with the central output E , and to decrease as the absolute value of the sequence number i of the output Ei is higher, a start signal will appear on the e~treme outputs E and E n ~whose amplifier circuits do not have a second inpu-t ~9) at the instant t = O and s-tart signals will appear on the outputs which are situated furtller inwards at successive, later instants, the last start signal appearing on the central OUtp-lt E . I~hen -the -transducers ~Q(~
~T~.10.264 ' 10 5.11.82 are arranged in a s-t:raigllt :Line, a focussed beflm of ultrasonic energy is then ernit-ted i.ns-teacl ol a paral.lel beam.
Figure 5 diagrammatically illustra-tes how such focussing is achieved. This Figure shows three transducers To, T1~ T2 of an array of transducers~ To be:ing the central transducer of the array, T1 beirlg an intermediate transducer ~hilst T2 is the last transducer. The trans-ducers are situated on a straight line 63. The centraltransducer T is activated last, so that i-t acts as a virtual transducer T' l~hich is situated at a distance D'o behind the ~ransducer To. The transducer T1, being activated sooner, acts as a virtual transducer T'1 which is sit.uated at a distance d'1 behind T1, and the last transducer T~ is activated l~ithout delay. The magnitude of the distances d' and d'1 depends on the voltages of the second direct voltage generator 51 and -the sa~tooth ge.nerator 21 and also on the values of the third resistors 53. These resis-tors may be chosen so that the virtual transducers T' and T'1 are situated on a first arc of circle 65 whose centre is denoted by -the reference F1.
The ultrasonic l~aves emit-ted by -these virtual transducers are then in phase at the point F1 and the emitted beam of ultrasonic energy is focussed at this point.
l~hen the output voltage of the second direct voltage generator 51 is increased, all delay tirnes increase proportionally and hence also all distances d'o, d'1. The central transducer To -then acts as a virtual transducer T"o at a distance d"o behind To and the transducer T1 acts as a virtual transducer T"1 at a distance d"l behind T1. .For the sake of clarity, the distances d" and d"1 are not sho~;n in Figure 5. The last transducer T~ is still activa-ted without delay. The transducers T"o, T"1, T"2 are situated on a second arc of circle 67 havirlg a centre F2, -tile emit-ted bearn being focussed at F~.

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. '10. .~64 1 1 5 . 1 1 . 82 The l~igure s~hows tha-t the vir-tual transducers T'1 and L`"1 whiclL correspond -to the inter111ediclte trans-ducer T l are situatecl exactly on the Qrcs of circle 65 and 67, respectively, only if they are shifted not only straigh-t backwards over a given distance with respec-t to -the transducer Tl, but also to -the right over a smaller distance. Obviously, the virtual transclucer in reali-ty is always situated straight behind the ac-tual transducer, so that the vir-tual transducer has undergone a small lateral shi~t with respect to the ideal posi-tion shown in Figure 5. However, if the radii rl and r2 of the arcs of circle 67 and 65, respectively, are large enough, the error then arising will be negligibly small. It has been found in practice that focussing is very satisfac-tory when the radius is chosen to be larger than appro~imately five times the distance between the central and the last -transducer.
1~hen the transducers are situa-ted on a curved line, if desired the third resistors 53 may also be chosen so that the ultrasonic energy emi-tted by the transducers together forms a flat wave front. Focussing introduced by the configuration of the transducers can thus be elimina-ted.
As has already been noted, the amplifier circuits ~3 shown in Figure 4 are constructed as adder circuits, This means that the vol-tages applied to their inputs 37 and 49 are summed a~ter an amplification which is determined by the ratio of the resistors 35 and 53 on the one hand to the resistor 31 on the other hand. It has been e~plained that the voltage applied to the ~irst inputs 37 determines the beam direction, whils-t the voltage applied to the second input 49 de-term nes -the focussing. Because these two voltages are summed, the start signal generator shown in ~igure 4 en~bles independent control of the beam direction as well as of the focal distance to be obtained. The result of the ~2~
l'll~.1O.'64 1 12 5.11.82 combinatlon of -these two possibLli-tles :Ls clLagrammatlcally shown in Figure 6 for an array of five transducers T 2~
r 1, rO, T1, T2 which are situa-ted on a s-traight line 69, The voLtage applied to the firs-t inpu-ts 37 results in virtual transducers which are situated on a straight line 71 which is at an angle to the ~ne 69. The voltage applied to the second inputs 49 shifts the posi-tions of the virtual transducers 80 -that they are situated on an arc of circle 73. The ultimate positions of the virtual transducers are again denoted by indices in the manner used in Figures 3 and 5. The virtual transducer correspon-ding to T1 happens to coincide with T1. This means that ~he ~-o ~oi~age3 ap~l-ed to ~he ~l~O inpu~s 3~ 49 of the relevant adder circuit 23 cancel one another a~ter amplification and addition. The ultrasonic beam emitted by these virtual transducers is at an angle ~ to the normal 75 to the line 69 (denoted by the arrow j7) and is focussed at a point F.
There are many alternatives to the described embodiments. For example, the direct voltage generators 39, 51 may be replaced, if desired, by alternating voltage generators. The amplifier circui-ts 23 need not be direct voltage amplifier circuits in tllat case. However, it ~rill then be necessary to connect a rectifier to the output 33 of each of these amplifier circ~lits.
It is alternatively possible to derive the negative voltage for the ampli~ier circuits 23 which are connec-ted to the outputs E1 to E of the start signal generator shown in Figure 4 from a third, negative direct voltage generator. The inverting circuit 55 which is connected to the first direct voltage generator 39 can then be dispensed with.

Claims (8)

PHN. 10.264 13 THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PRO-PERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An ultrasonic transmitter comprising:
a plurality of oscillator circuits, each oscillator circuit having a start input and an output;
a like plurality of electro-acoustic transducers, each transducer being connected to the output of a cor-responding oscillator for activation thereby;
a like plurality of comparators, each comparator having a first input, a second input, and an output; the output of each comparator being connected to the start input of a corresponding oscillator;
generator means for producing a sawtooth voltage at an output which is connected to the first inputs of all of the comparators; and voltage source means which supply controllable DC volt-ages to the second input of each of the comparators, the DC voltages supplied to each of one or more groups of at least two of the comparators being con-trollable by a common control.

2. A transmitter as claimed in Claim 1, wherein the voltage source means comprise a plurality of voltage ampli-fiers, each amplifier having a predetermined gain and having an output connected to the second input of a corresponding comparator; and one or more first controllable voltage generators, connected to first inputs of corresponding ampli-fiers, at least one first controllable voltage generator having an output connected to parallel first inputs of a group of amplifiers whose output voltages are subject to common control.

3. A transmitter as claimed in Claim 2, wherein one or more of the amplifiers comprise adder means which sum input voltages so that the output voltage of the amplifier is a function of the sum of a first input voltage and a second input voltage and further comprising a second con-PHN. 10.264 14 trollable voltage generator connected to supply second in-put voltages to the adder means.

4. A transmitter as claimed in Claim 3, wherein the controllable voltage generators generate DC voltage and the amplifiers comprise DC voltage amplifiers.

5. A transducer as claimed in Claim 2, wherein the controllable voltage generators generate DC voltage and the amplifiers comprise DC voltage amplifiers.

6. A transmitter as claimed in Claim 1, wherein the transducers are disposed along a line;
the generator means produces a linear sawtooth voltage having a mean value approximately equal to zero;
and the voltage source means function to supply a positive DC voltage to comparators which are associated with transducers on a first side of the center of the line and function to supply a negative DC voltage to the comparators which are associated with trans-ducers on the opposite side of the center of the line.

7. The transmitter of Claim 6 wherein the trans-ducers are disposed along a straight line.

8. The transmitter of Claim 6 wherein the trans-ducers are disposed along a curved line.