US2478223A - Electrostrictive translator - Google Patents

Description

Aug. 9, 1949. G. A. ARGABRITE ELECTROSTRICTIVE TRANSLATOR Filed March 1, 1946 INVENTOR.

' ATTORNEY.

Patented Aug. 9, 1949 ELECTRO STRICTIV E TRAN SLATOR George A. Argabrite, North Hollywood, Calif., as-

signor to Clarkstan Corporation, Los Angeles, Calif., a corporation of California Application March 1, 1946, Serial No. 651,269

3 Claims. 1

This invention relates generally to mechanicoelectrical translators wherein static, dynamic, or oscillatory mechanical variations are translated into corresponding electric potential variations, and to electrico-mechanical translators wherein static, dynamic, or oscillatory electric potential variations are translated into corresponding mechanical variations.

More specifically, it relates to mechanico-electrical translators which operate by electrostriction, wherein varying mechanical forces or pressures are applied to electrostrictive means with resulting variations in mechanical strain and variations in electrical potentials, and also to electrico-mechanical translators which operate by electrostriction wherein varying electric potentials are, applied to electrostrictive means whereby variations in mechanical strain and mechanical pressure or force are obtained. The mechanico-electrical and electrico-mechanical translators hereinabove mentioned are of the type wherein the normal ratio of the mechanical movement to the electrical potential is mechanically amplified. However, this invention also contemplates and includes mechanico-electrical and electrico-mechanical translators wherein no such mechanical amplification takes place.

More particularly, this invention contemplates the use of mechanico-electrical translators and electrico-mechanical translators as hereinabove set forth wherein are utilized electrostrictive materials such as, for example, quartz crystals, Rochelle salts crystals, and numerous other electrostrictive crystals well known in the art.

Throughout this application the term electrostriction" shall include :both the direct piezoelectric effect, wherein a separation of electrical charges occurs as a result of mechanical strain and the inverse piezo-electric effect wherein mechanical strain occurs as a result of applied electric potentials. The term electrostrictive shall include any materials subject to electrostriction as above defined, without excluding other properties of such materials.

In the past there 'have been numerous mechanico-electrical and electrico-mechanical translators using quartz crystals, Rochelle salts crystals, or any of the other well known electrostrictive crystals and which have obtained a substantial amplification of the normal ratioof mechanical movement to electrical potential. One type of such mechanico-electrlcal and electrico-mechanical translator well known in the art consists of two rectangular, parallelepiped, electrostrictive crystal plates, the adjacent surfaces of which are joined together, one end ofsaid joined crystals being fixedly supported or mounted, the rest of said joined crystals being mounted for free movement. Electrodes are then placed in contact with the two outermost surfaces of the joined crystal plates and an additional electrode is placed in contact with the adjacent, joined surfaces of said crystal plates. Electrical potentials of the proper polarity are then applied to said crystal plates in a manner which causes one of said crystal plates to expand in a longitudinal direction and the other crystal plate to contract in the same direction. This causes a force couple which results in the bending of the joined crystal plates and asubstantial deflection of the unsupported end of said joined plates. The deflection of the unsupported ends of the joined crystal plates will be much greater than the longitudinal movement of either of the said crystal plates. Thus a mechanical amplification has taken place.

Conversely, the same type of unit has been used where a transverse mechanical force has been applied to the outer, unsupported, joined edges of the two crystal plates. This movement has resulted in a compression of one of the crystal plates and an elongation of the other, thus creating electric potentials on the surfaces of said crystal plates.

In the examples just set forth, both of the crystal plates were so cut from the original crystals with respect to the electric axes and the clastic constants of the crystals that the electrostrictive deformation of said crystals, while opposite in direction, is parallel. This type of element is known as a bending element. If a twisting element is desired, where one end is fixed and the application of electric potentials causes the other, unsupported end to deflect torsionally, two crystal plates are again joined together, as before mentioned. However, in this case, the two crystal plates are so oriented with'respect to each other and their electric axes and elastic constants as to cause one plate to deform oppositely and at an angle to the deformation of the other plate which is joined thereto. The force couple thus resulting causes a torsional deflection or twisting of the free, unsupported end of the two, joined, crystal plates. Conversely, torsion applied to the outer, unsupported, free end of the joined crystal plates will result in electric potentials on the surfaces of said crystal plates. This type of element is known as a twisting element.

The above-mentioned examples are given for illustrative purposes only, and there are numerous posssible combinations of crystals for aeraaaa various purposes in which the electric axes and the elastic constants of the crystals are variously oriented with respect to each other, or, in other words, crystals of different cuts are joined together, thus making it possible to achieve almost any desired movement.

However, all of the above mechanico-electrical and electrico-mechanical translators wherein mechanical amplification takes place have had numerous disadvantages. For one thing, if for example, the bending element mentioned above were being used as a voltmeter and electric potential were being applied to said crystal element and the deflection of the outer, free, unsupported end of said two joined crystal elements were taken as a measure of the applied electric potential, the instrument would have what is known as zero drift, that is, the outer, free, unsupported, joined ends would not return exactly to zero position after the' applied electric potential was removed. This is a fatal defect in an electrical measuring instrument. The instrument must, in every case, return exactly to zero after the applied potential is removed. The same is true if the twisting element above-mentioned were used as a voltmeter. In other words, an inherent defect of the abovementioned type of element is the fact that it has a substantial tendency toward zero drift.

Another of the numerous disadvantages inherent in the types of elements hereinabove mentioned was the fact that the joining together of two crystals necessitates a considerable mass and no way of altering the ratio of the mass of the element to the resonant frequency thereof has been known other than by changing the shape and physical dimensions of the element. The stiffness of such an element could not be changed without changing the mass of the element to a substantial degree at the same time.

In the prior art, a type of mechanico-electrical and electrico-mechanical translator wherein the before-mentioned mechanical amplification is not used is an oscillating crystal, such as is used in crystal wave filters, etc. and such as is used when it is desired to stabilize the frequency of electrical oscillations in an electrical circuit, Such devices operate in a manner well known in the art. Such devices have had no means of varying the ratio of the mass of the crystal to the resonant frequency thereof other than to change the physical size and conformation thereof, and such devices have had no means for readily adjusting the stiffness thereof without changing the size and physical dimensions thereof.

With the above points in mind, it is an object of this invention to provide an improved mechanico-electrical and electrico-mechanical translator which is capable of bending, and which may comprise a single electrostrictive crystal plate and a restraining means joined thereto, such as, for example, a fiat plate of metal or any other suitable non-electrostrictive material joined to one surface of the electrostrictive crystal plate. The electrostrictive crystal plate and the join (1 restraining means which restrains one surfac of said crystal plate causes a force couple in the same plane as the longitudinal axis of the element, thus causing a transverse bending of the element. If the element is supported at one end, the outer, free, unsupported end will then.

trostrictive element.

Another object of the invention is to provide a mechanico-electrical and electrico-mechanical translator of the torsional or twister type in which a plate of electrostrictive crystal material is joined to a restraining means, such as a plate (of metal or any other suitable non-electrostrictive material) in such a manner that an electrical potential applied to the electrostrictive crystal ma-.

terial causes a deformation of the crystal at an angle to the longitudinal axis of the restraining means or metal plate. A force couple thusstrictive crystal element.

Another object of the invention is to provide a mechanicoelectrical and electrico-mechanical translator of either the bending or twisting type wherein the crystal element is joined to a restraining or backing member, which, for example, might be a plate of metal or any other suitable non-electrostrictive material, so as to substantially eliminate zero drift because of the resilient mechanical support given to said crystal element by said backing member.

Another object of the invention is to provide a mechanico-electrical and electrico-mechanical translator wherein the ratio of mass to resonant frequency, the resonant frequency, and the stiffness of the element may be readily adjusted by applying varying non-electrostrictive restraining means or backing to one side or more of the electrostrictive crystal element. Said backing means may be of varying thicknesses and may cover varying portions of the surface or surfaces of the crystal. Said backing means may be placed at various angles to the longitudinal .axis of the crystal plate and may be of various materials of difierent modulus of elasticity, thus making it possible to readilyadjust and vary the massresonance ratio, the resonant frequency, and the stiffness of the element.

Another object of the invention is to provide an element of the character described wherein dielectric contact change caused by temperature change is inhibited because of the non-electrostrictive, restraining, backing member which acts to inhibit dimensional changes in the crystal resulting from temperature changes.

Another object of the invention is to provide a mechanico-electrical and electrico-mechanical translator which may be used in a much higher frequency range because of the low mass resonance ratio which may be obtained by joining together the crystal plate and a non-electrostrictive, restraining, backing member of suitable stiffness.

In the mechanico-electrical and electrico-mechanical translator of the type where no mechanical amplification occurs, such as the type used in crystal wave filters and wherever it is desired to stabilize an alternating current frequency, it is an object of this invention to provide such an element wherein the mass resonance ratio and the stiffness is readily adjustable by means of a non-electrostrictive, backing, restraining member of varying thickness and varying modulus of elasticity.

Referring to the drawings,

Fig. 1 is a perspective view of a bending type element embodying my invention.

Fig. 2 is a perspective view of a twister type of element embodying my invention.

Fig. 3 is a perspective representation of another embodiment of a twister type element embodying my invention. -f

Fig. 4 is a side view of a frequenc stabilizing type of device embodying my invention.

Fig. 5 is a side view of a second embodiment of my invention in a frequency stabilizing type of device.

Generally speaking, the embodiment of my invention shown in Figs. 1 and 2 comprises an electrostrictive crystal, the bottom surface of which is joined to the top surface of a restraining member, the left end of the two-joined members being fixedly mounted. In these figures, the left end is shown mounted between non-conductive blocks which might, for example, be of rubber and which are fixed to a primary support. However, any other suitable method of mounting might be used. An electrical contact is connected to the lower surface of the crystal and an electrical contact is connected to the upper surface of the crystal.

More specifically, in Fig. 1 the crystal plate I (which, for example, might be a zero or Y cut, rectangular, parallelepiped, and which may be cut, as is well known in the art, at an angle to the optical axis so as to obtain an even longitudinal deformation of said crystal when the electric potential is applied to the surfaces thereof by means of the electrodes) is joined to a backing, restraining plate 2 which might, for example, be made of metal or any other suitable non-electrostrictive material such as plastic, impregnated and pressed cloth, etc. The plate 2 might be placed on the surface of the crystal plate I by vapor deposition or it might be cemented on the surface of the crystal plate I or joined to the surface of the crystal plate I by any other suitable means. In this case, the backing, restraining plate 2, being electrically conductive, constitutes one of the electrodes in contact with the crystal plate I. The upper electrode 3 might be a very thin aluminum film deposited by vapor deposition in a manner well known in the art. The backing, restraining plate and electrode 2 and the upper electrode 3 are connected to wires 4 and 5. The left end of the whole assembly, comprising the crystal plate I, the backing, restraining plate and electrode 2, and the upper electrode 3, is then clamped between two rubber blocks 6 which are fixed to a support I.

If an electrical potential of the proper polarity is applied to the upper and lower surfaces of the crystal plate I by means of wires 5, upper electrode 3, wires 4, and lower electrode and backing, restraining plate 2, the crystal plate I elongates. The backing, restraining member 2 restrains the bottom of the crystal plate I from elongating, thus creating a force couple which causes the right hand end of the crystal plate I and the backing, restraining plate 2 to deflect downwardly and in a clockwise direction a substantial distance (as schematicall indicated by dash lines). Conversely, if force is applied in an upwardly vertical direction to the right hand end of the crystal plate I and the backing, restraining plate 2, a substantial measure of compression occurs in the crystal plate I, thus causing electric potentials to be created on the upper and lower surfaces of the crystal plate I which are picked up by the electrodes 2 and 3 and fed to wires 4 and 5. It is to be understood, of course, that if the electric potentials or mechanical movements are reversed, the foregoing action is also reversed.

In the first embodiment of a twisting element shown in Fig. 2, a rectangular, parallelepiped crystal member 8 is joined in any suitable manner to a non-electrostrictive, restraining member 9, the upper surface of said'crystal member 8 having an electrode I0 thereon. Said electrode I0 may be a thin, aluminum film deposited by vapor deposition in a manner well known in the art. A wire II connects with said electrode I9. In this use, the restraining, backing member 9, being electrically conductive, constitutes one of the electrodes in contact with the crystal member 8. The restraining, backing member 9 connects with a wire I2. The right end of the whole assembly, comprising the crystal member 8, the restraining, backing member and bottom electrode 9, and the upper electrode I0, is fixed to a primary support I4. The crysta1 member 8 is so cut from the crystal that electrostrictive deformation thereof is at an angle to the longitudinal axis of the whole element. Thus when an electric potential is applied to the electrostrictive element 8 by means of wires I I, electrode III, wire I2, and electrode and backing member 9, a force couple results which causes a torsional movement or twisting of the left, unsupported, free end of the element. Conversely, torsional movement applied to the left end of the element will produce electric potentials on the surfaces of the electrostrictive crystal 8 and pick up said potentials through electrode III, wire II, restraining, backing member and electrode 9, and Wires I2.

A second embodiment of a twister type element, as shown in Fig. 3, comprises a rectangular, parallelepiped, electrostrictive element I5 and a. non-electrostrictive, restraining, backing member I6 joined to one surface of said crystal member I5 by any suitable means. Said backing member I6 does not cover a full surface of the crystal member I5 but onl a portion thereof and the axis of said backing member I6 is at an angle with respect to the axis of the crystal member l5. Electrodes I1 and I8 are placed on opposite surfaces of said crystal member I5. Said electrodes I! and I8 may be thin aluminum films in contact with the surfaces of said crystal member I 5. The electrodes I7 and I8 are connected to wires I9 and 20. The left end of the Whole assembly, comprising the crystal I5, the backing element I6, and the electrodes I1 and I8, is attached as by means 2I to a primary support 22. In this case, the crystal element I5 is so cut with respect to its electric axes and elastic constants that an applied electric potential will cause either a longitudinal, electrostrictive deformation which is at an angle to the aXis of the backing member or so cut as to cause an electrostrictive deformation parallel to the axis of the backing member I6. In either case. a force couple results which causes a torsional deflection of the right, unsupported end of the element. Conversely, a twisting movement or torsional deflection of the right, unsupported end of the element will cause electrical potentials to appear on the surfaces of the crystal member I5 and be fed through the electrodes I! and I 8 and wires I9 and 20.

In Figs. 4 and 5 I illustrate a typical example of my invention applied to an electrostrictive crystal of the type used in stabilizing alternating current wave frequencies and also used in crystal wave filters and the like, etc. It comprises a crystal plate 23 which may be cut in any of the many ways well known in the art, the bottom any suitable means such as surface fusion. vapor deposition, cementing, etc. to a non-electrostrictive, restraining, backing member 24 which may be of any suitable material. An electrode 25 is placed in contact with the upper surface of the crystal plate 23. The electrode 25 may be a thin aluminum film and be connected to a wire 26. In the case where the restraining, backing member 24 is electrically conductive, it comprises the bottom electrode and is electrically connected to a wire 21. If such restraining, backing member 24 is not electrically conductive, a bottom electrode similar to the top electrode may be inserted between the restraining, backing member 24 and the crystal 23 and connected to the wire This is also true of any of the other embodiments of my invention.

Fig. shows an apparatus similar to Fig. 4 with the addition of a second restraining, backing element 28 on the upper surface of the crystal plate '23. Otherwise, the device shown in Fig. 5 is the same as the device shown in Fig. 4.

In the devices shown in both Figs. 4 and 5,

- the restraining elements 24 and/or 28 act to change the stiffness of the crystal element 23 without substantially changing the mass of the entire unit. Thus the mass resonance ratio of the units may be varied within wide limits by applying either one or two non-electrostrictive, restraining, backing members to either the whole area of the crystal element 23 or parts thereof and by varying the thickness of said backing, restraining members, and by varying the modulus of elasticity of the material of which said backing, restraining members are composed. This makes it possible to vary the resonant frequency and/or the mass resonance ratio of the unit within wide ranges without substantially changing the size of the element. For example, an element such as is shown in Fig. 5 might have backing members 24 and 28 composed of a material with an extremely high modulus of elasticity, such as beryllium. This would result in an extremely high resonant frequency and an extremely low mass resonance ratio in the element. Or, if so desired, in an element such as is shown in Fig. 5,-the restraining, backing members 24 and 28 might be composed of some ma terial of great mass and very low modulus of elasticity, thus resulting in a low resonant frequency and a high mass resonance ratio in the element.

Thus it can readily be seen that I have provided an improved element of the type described which is extremely versatile and can be designed within an extremely broad range of characteristics for optimum performance for any given use.

Without attemptingto enumerate all possible uses of the devices described hereinabove (or to limit the uses and adaptations of the devices) those skilled in the art will appreciate that they may be employed in acousto-electric and electrico-acoustic transducers such as, for example, pick-ups, microphones, speakers, recorders, reproducers, and the like, etc., and as a frequency stabilizer in oscillatory circuitssuch as, for example, radio transmitters, etc. They may also be employed as an equivalent capacitance or inductance with an extremely high reactance to resistance ratio such as, for example, in a crystal wave filter, etc. Obviously the leads connected to the terminals may be connected to measuring devices of various types or to sources of electrical energy, as circumstances dictate. The movable end of the device may be operably connected to a mirror, indicator lever system, scribe, or the like. depending upon the use to which it is being put. 1x

It is to be clearly and distinctly understood that the examples given herein are for illustrative purposes only and should not be construed as the full scope of my invention. There are multitudinous combinations of electrostrictive means and restraining, non-electrostrictive means and my invention properly includes all such combinations and is to be considered limited only by the scope of the claims appended hereto.

I claim:

1. A crystaloscillator device for use in wave filters, control oscillators and the like, said device comprising a body of electrostrictive material and a non-electrostrictive means of a high elasticity and low mass attached to a portion of the surface of the body, the non-electrostrictive means effectively altering the mass-resonance ratio of the device to render the frequency response of the body, to non-steady state input, more uniform in a desired frequency range.

2. A method of producing an oscillating crystal of desired mass-resonance ratio and desired frequency from crystals of different sizes which comprises: applying a non-electrostrictive layer of material to a portion of the surface of a crystal, and varying the mass and elasticity of the layer thus applied in accordance with the mass-resonance ratio of the combined crystal and layer to produce a desired resonant frequency characteristic therein.

3. A mechanico-electrical translator of the twisting type comprising: an electrostrictive crystal member provided with electrodes on opposite surfaces, and a non-electrostrictive means attached to a portion of one surface of the crystal, the axis of the non-electrostrictive means being at an angle to the axis of the crystal member, whereby torsional deflection of the device is obtained by the application of potential to the electrodes.

. GEORGE A. ARGABRITE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 20,213" Sawyer Dec. 22, 1936 1,802,782 Sawyer Apr. 28, 1931 1,803,274 Sawyer Apr. 28, 1931 2,343,059 Hight Feb. 29, 1944 OTHER REFERENCES Walter G. Cady, Piezoelectricity, pages 198- 199, McGraw-Hill, New York.

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