US2671178A - Piezoelectric transducer - Google Patents

Description

March 2, 1954 J, TOMCIK 2,671,178

PIEZOEILECTRIC TRANSDUCER Filed May 16, 1950 IN V EN TOR.

Z .W) W

Patented Mar. 2, 1954 Daniel J. Tomcik,

South Bend, 1nd,, assignor 'to Electro Voice, 1110., Buchanan, Mich, a corporation of Indiana Application May 16, 1950, Serial No,,162,293

2 Claims.

This invention relates to improvements in piezoelectric transducer for converting mechanical vibrations into electrical energy and vice versa, Transducers of this character are commonly used on phonograph pick-ups and microphones and this invention is well suited for use on both of these applications, and also for use as a phonograph record cutter. The primary object of the invention is to provide a novel, simple and inexpensive device operable to actuate asingle slap or late type of piezoelectric device for the purpose of generating an electrical potential.

A further object is to provide a device of this characterwherein apiezoelectric member or plate of the expander bar type, which is adapted to generate a voltage when expanded or contracted in its plane, has attached thereto a novel, simple and highly efficient harness construction for effecting expansion and contraction of the piezoelectric element.

A further object is to provide a device of this character wherein a piezoelectric member is mounted in a harness characterized by a central member which straddlesthe iezoelectric element and has clearance therewith, said member being anchored in fixed position upon a support at one end and which harness also includes diagonally extending parts connected torthc opposite ends cfthe harness in such a manner as to apply to the piezoelectric element forces which tend to twist the central structure in such a manner as to expand and contract the piezoelectric member.

A further object is to provide a device of this character having a 'be'ingadaptcd-to be twisted incident to mechanical vibration and having arms extending at an angle therefrom and secured to opposite ends of the piezoelectric member; said construction, so

mounting the piezoelectric member that said member is adapted to swing coincident with the twisting of the harness in certain conditions, and in so doing to assist in the transmission of forces tending to contract and expand said piezoelectric member.

Other objects will "be apparent from the following specification, considered-with the accompanying drawing in which Fig. 1 is a perspective view of the device;

Fig. 2 is a perspective trating the manner in which the device operates;

Fig. 3 is a schematic view illustrating the forces acting upon the iezoelectric element through the harness .to contract the piezoelectric member;

Fig. 4 is a view similar to .Fig. 3 illustrating harness including a portion diagrammatic view illusthe manner in which the forces transmitted by the harness act to expand the piezoelectric member;

Fig. 5 is a schematic view illustrating the manner in which the bodily movement of the piezoelectric member with the harness applies .contracting forces to the piezoelectric member;

Fig. .6 is a view similar to Fig; 5 illustrating the manner in which the movement of the piezoelectric member acts to assist in expansion there- Of;

Fig. 7 is a schematic view illustrating the action of the forces generated "by the action tending "to contract the piezoelectric member, as illustrated in Figs. 3 and 5;

Fig. 8 is a view illustrating the action of the forces generated by the action tending to expand the piezoelectric member, as illustrated in Figs. 4 and 6';

Fig. 9 is aperspective view of aharness employing the same principle but positioning the crystal in a different orientation relative to :its support.

Referring to the drawings, and particularly Figs. 1 to 8 which illustrate the preferred embodiment of the invention, the numeral l0 designates a piezoelectric element of the single slab or single plate type. The element will preferably be a Rochelle salt crystal which is of the 45 X-cut type. The characteristic of such a single sla-h 45 X -cut Rochelle salt crystali-s that it will generate a voltage or electrical potential when either lengthened or shortened in its plans. The piezoelectric element will include electrodes and will have leads 1'2 projecting therefrom.

The piezoelectric unit is mounted upon a base or support, hereillustrated as plate M. This sup port has fixedly carried-thereby-in lateral or perpendicular relation to one face thereof a hridge structure including spaced substantially coplanar leg portions l6 substantially parallel to one another and spaced apart a distance greater than the thickness of the piezoelectric element 10. The upper end portions of the legs 56 are fixedly secured together at 13. The piezoelectric element is positioned to extend through the bridge structure so as to have clearance with each of the parts 14, It and I 8.

A member is is fixedly securedto the upper transverse part It connecting the legs It. The member 20, in the case of a phono raph pick-up, may comprise a tube which serves to mount a needle or stylus (not shown). .In the case of a microphone it may comprise a link .or member for attachment to a microphone diaphragm (not shown)- The member z-flpreferabily extends perpendicularly to the part l8 and also at a substantial angle to the legs l6. The member is adapted to be connected to the actuator therefor in a manner to be oscillated laterally at its free end in a plane substantially parallel to the base [4 and transversely of the piezoelectric element In. Specifically, the oscillation of the member 20 is adapted to be such as to produce the action of the bridge structure l6l 8 which is illustrated in Fig. 2. This construction essentially constitutes rotation or oscillation of the cross member l6 connecting the legs I6 about the axis 22 so that the leg portions are tilted between the nor mal position thereof shown in full lines and the actuated positions illustrated in dotted lines.

Each of the legs l6 has fixedly secured thereto at its upper end at or adjacent the transverse member l8 one of the elongated arms 24, 26. These arms 24, 26 extend in planes substantially parallel to the plane of H) which is positioned therebetween but tend to converge inwardly toward said piezoelectric element so as to contact the same at or adjacent their ends. As seen in Fig. 1, the arms extend somewhat diagonally with respect to the piezoelectric element and, at their outer ends, engage and are secured to the outer ends of said piezoelectric element H1 at the center thereof, being cemented thereto in any manner found suitable and well understood in the art. Each of the legs l6 has one of the elongated arms 28, projecting therefrom in a plane substantially parallel to the plane of the piezoelectric element Ill. The arms 28, 30 project from the fixed or anchored ends of the legs I6, that is, from said legs at a point adjacent their connection with the mounting plate l4. The arms 28,,30 extend in directions opposite the directions in which the arms 24, 26 carried by the same leg extend, so that each of the legs l6 cooperating with the two arms at its inner and outer ends projecting therefrom define substantially a Z-shaped member. Stated differently, as viewed in Fig. 1, the arm 24 which is connected to the left-hand leg l6 at its free end extends to the left, as seen in Fig. 1, whereas the arm 30 carried by the same left leg 16 extends to the right in Fig. 1; while the arm 26 connected .to the right leg l6 extends to the right, and the arm 30 connected to the same right leg l6 extends to the left.

The points of connection of the arms 24, 26 with the left end of the piezoelectric element are substantially the same, that is, both arms are connected at the center of the end portion of the piezoelectric element, and the same situation pertains relative to the arms 26 and 30 shown at the right.

The harness units [6, I8, 24, 26, 28, 3i] are each substantially rigid although, as illustrated in Fig. 2, the legs l6 are sufiiciently flexible so as to provide the swinging oscillating movement of the cross member l6. Similarly, the connections of each of the arms 24--30 with the mounting legs are somewhat flexible and tend to act as hinges. In this connection the arms projecting from each of the legs will preferably be formed integrally therewith, as by being bent therefrom. As here illustrated, the arms 24, 26 are preferably bent from the inner edges of the legs l6, and the arms 28, 30 are preferably bent from the outer edges of the legs 16, but such construction is intended to be illustrative and not limiting.

In the operation of this piezoelectric device,

the piezoelectric element the manner of operation at low frequency differs from that which occurs at high frequencies.

The operation at high frequencies, that is, at frequencies high enough so that the mass or weight of the crystal retards or prevents its rotation about the axis 22 with the harness, only the arms 24 and 26 are active. In other words, as best illustrated in Figs. 3 and 4, the twisting movement of the bridge cross member l8 acts upon the arms 24 and 26 and through them upon the piezoelectric element 10. In Fig. 3, where it is assumed that a clockwise rotation of the cross member l8 has occurred with reference to center position illustrated in dotted lines, it will be observed that this clockwise movement has pulled upon each of the arms 24 and 26, thereby pulling inwardly upon the opposite end of the piezoelectric element with forces, here designated Fe and Fe. The opposite phase of the oscillatory movement, that is. swinging of the bridge cross member l8 in counterclockwise direction, as illustrated in Fig. 4, results in an action of that part pushing outwardly upon the arms 24 and 26 and tending to expand or elongate the piezoelectric element. The outward forces tending to elongate the piezoelectric member H! are illustrated in Fig. 4 and are designated by Fb and Fe. Inasmuch as the piezoelectric element is of the type which generates an electrical potential incident to elongation and contraction, the lengthening or shortening, or stretching and compression thereof in its plane, it will be apparent that the alternate actions illustrated in Figs. 3 and 4 will produce an electrical potential thus energizing the device, the same being the result of the application to the device of the forces which produce the movement of the bridge l8, as illustrated in Fig. 2. During this time the arms 28 and 30 act only to supplement the effect of the weight of the piezoelectric element H) in holding that element stationary.

When the actuator member 20 of th device is operated at low frequencies, the bridge structure I6 is oscillated in the manner illustrated in Fig. 2. Assuming, however, that the frequency of movement is low enough so that the mass of the piezoelectric element will not retard its oscillation. then that member will oscillate about the axis 22 swinging from side to side, as illustrated in Figs. 5 and 6. The clockwise rotation of the piezoelectric element illustrated in Fig. 5, which occurs in conjunction with the action illustrated in Fig. 3. is such that the ends of the element l0 pull upon the fixedly anchored arms 28 and 30 and thereby apply contracting forces upon the element'in its plane. These forces are designated in Fig. 5 as Fe and Fe, and it will be seen that they supplement the forces Fe, Fe through th arms 24, 26, as illustrated in Fig. 3. Consequently, the action at low frequencies is, as illustrated diagrammatically in Fig. '7, the total forces acting upon the piezoelectric element at this time being Fb plus Fa at one end and Fe plus Fe at the other end. In other words, the additive forces ar created in the arms tending-to contract or expand the crystal along the longitudinal axis 32 thereof. It will be borne in mind in considering this action and the schematic Figs. 3 to 6, inclusive, that the bends in the harness or the points of connection of the arms with the legs, act as hinges to accommodate the operation illustrated in said figures. The action of the device at low frequencies during that part of the movement which entails a counterclockwise swinging of the cross member I 8 and the piezolectric element is as illustrated in Figs. 4, 6 and 8, the action being such that the forces acting on arms 26 and 30 are added to pull upon one end of the crystal, and the forces acting upon the arms 24 and 28 are added to pull against the other end of the crystal, so that the resultant forces are as shown in Fig. 8, being Fb plus Fa and Fe plus Fe.

Another embodiment of the invention is illustrated in Fig. 9 and is characterized by the location adjacent to the longitudinal center line of the opposite faces of the crystal of the point of mounting thereof and of stress application rather than positioning thereof at the edges as in the Fig. l embodiment. This embodiment of the invention also permits the mounting of th piezoelectric element substantially parallel to the base plate rather than perpendicular or at an angle thereto as in the Fig. l embodiment.

The Fig. 9 embodiment comprises a base or support 40, such as a plate, to which is fixedly anchored at an intermediate portion of the harness a foot member or base 42 from which extend perpendicularly the substantially longitudinal central lower harness portion 44, the same being positioned clear of but adjacent to the longitudinal center line of the lower face of a piezoelectric element, illustrated in dotted lines as 46. From the opposite ends of the lower central harness portions 44 extend oppositely diagonally extending portions 48 and 50 in substantially parallel relation with their planes offset slightly. At their opposite ends the arms 48, Q downturned flanges 52 and 54 formed at the ends of cross plates 56 and 58 which are positioned substantially parallel to the plate 46 and have the opposite ends of the piezoelectric member 4% bearing thereon and fixedly anchored thereto. turned flanges 6t and 62 of the cross members 56, 52, '54, the same being at greater than the thickness of the piezoelectric element. From the upper ends of the flanges 66, 62 extend diagonal arm 64, 66, the same passing clear of the upper surface of the piezoelectric element and extending diagonally inwardly toward the center of the upper face of that element where they are joined together by a central upper portion 68 which lies in substantially the same plane as the lower part 44 and which is adapted to mount the member for connection with a stylus in the case of a phonograph pickup, or with a microphone diaphragm in the case of the microphone. for applying mechanical forces to the unit.

This construction applies to the piezoelectric element, upon the oscillation of the member 10 are formed at the ends 58 opposite the flanges a height substantially in the direction illustrated by the arrows, forces which tend alternately to pull upon the arms 64 and B6 or to push outwardly thereon.

These forces tend to swing the piezoelectric element in its plane, yet this tendency is resisted and counteracted :by the lower arms 48, 56. The action is such that the forces exerted by the arms 48 and 64 are added to act upon one end of the piezoelectric element 46, while the forces of the arms 50 and 66 are additively applied to act upon the opposite end of the piezoelectric element. It will be observed that, as in the preferred embodiment, the arms atone side or face of the piezomerge with the electric element extend along one diagonal, while the arms along th other face of the piezoelectric element extend along the opposite diagonal. The same advantages of the preferred construction are, therefore, substantially achieved by this alternate construction.

While the preferred embodiments of the invention have been illustrated and described herein, it will be understood that changes in the construction may be made within the scope of the appended claims without departing from the spirit of the invention.

I claim:

1. A piezoelectric device comprising a member adapted to generate an electric potential when subjected to stress in its plane, a support, a harness structure carried by said support and mounting said member at opposite ends of said member, said harness including two pairs of arms, the arms or each pair being located at opposite sides of and having a common point of connection with said member and extending angularly relative to each other, one arm of each pair being connected with said support substanstantially midlength of said member, said member being positioned between the connection of the first arms with said support and the connection of said other arms with said actuator, said harness including a bridge straddling the mid portion of said member with clearance and fixed at one end to said support, said arms and actuator being connected to said bridge.

2. A piezoelectric device comprising a member adapted to generate an electric potential when subjected to stress in its plane, a support, a harwith said support substantially midlength of said member, and an actuator connected to the other DANIEL J. TOMCIK.

References Cited in the file of this patent UNITED STATES PATENTS OTHER. REFERENCES Modern Crystal Phono Pickups,

Radio Electromcs, October 1948, page 29.

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