US2155035A

US2155035A - Piezoelectric crystal apparatus

Info

Publication number: US2155035A
Application number: US57187A
Authority: US
Inventors: Carl A Bieling
Original assignee: Bell Telephone Laboratories Inc
Current assignee: AT&T Corp
Priority date: 1936-01-02
Filing date: 1936-01-02
Publication date: 1939-04-18
Anticipated expiration: 1956-04-18

Description

P 1939- c. A. BlELlN 2,155,035

PIEZOELECTRIC CRYSTAL APPARATUS Filed Jan. 2, 1936 5 Sheets-Sheet l OUTPUT INPUT F/G./

84 78 77 v 76' a4 a6 7:

67 ao1- so g} 6/- lNVEN TOR C. A B/E L ING ATTORNEY April 18, 1939. c. A. BIELING 2,155,035

PIEZOELECTRIC CRYSTAL APPARATUS Filed Jan. 2, 1936 3 Sheets-She'et 2 FIG. 6 FIG. 8

l 1 1 1 1 40 94 42 T if, I06 /07 "25 I 9/ TE I 1 ?F ,50 so /02 /N V5 N 7' OR CAB/EL/NG A T TORNE) p l 1939- c. A. BIELING 2,155,035

PIEZOELECTRIC CRYSTAL APPARATUS v Filed Jan. 2, 1936 5 Sheets-Sheet 3 III II? 4 INPUT -1 INVENTOR C. A B/E L ING ATTORNEY Patented Apr. 18, 1939 UNITED STATES PATENT OFFICE 1 PIEZOELECTRIC CRYSTAL APPARATUS Carl A. Bieling, Westfield, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York This invention relates to piezoelectric apparatus and particularly piezoelectric crystal holders suitable for electric Wave filter systems, oscillation systems or electromechanical vibrating systems generally.

One of the objects of this invention is to permit unrestricted and independent simultaneous vibration of a plurality of piezoelectric crystal elements.

Another object of this invention is to improve the constancy of frequency of vibrating piezoelectric crystal elements.

Another object of this invention is to mount in the same holder piezoelectric bodies of various shapes, sizes and modes of motion.

Another object of this invention is to clamp a piezoelectric crystal element under uniform contact pressure.

A further object of this invention is to clamp a piezoelectric crystal element in such a manner that its position will be maintained.

Still another object of the invention is to reduce wear of the electrodes integral with the faces of a piezoelectric crystal element.

In accordance with this invention, a plurality of piezoelectric crystals may be supported from a single or common mechanical supporting structure in such manner that each crystal although, mechanically interconnected with other crystals is free to vibrate at its own frequency with minimum losses and a minimum amount of mechanical vibratory coupling between the plurality of vibrating crystals. The crystals may have the same or different frequencies andyet vibrate independently at their respective frequencies although supported from a. single or common mechanical structure. The supporting structure may be such as to support a plurality of crystals having divided or split electrodes with a resulting saving in the number of crystals employed.

The crystal supporting structure is such as to result in .a lowered cost, economy of space, simplification of electrical connections, reduction of and minimum unbalance in distributed capacities, and balanced capacity between the interconnected elements. The plurality of crystals may be clamped under substantially equal pressures. A plurality of resiliently supported metallic clamping projections may nodally clamp the crystals and also serve as electrical contacts with metallic electrodes which may be integral with or otherwise closely associated with the crystal surfaces.

Resilient means in the form of cantilever springs suitably supported at one end only thereof may support the crystal clamping projections disposed at the free ends thereof. The cantilever springs may be separately pivotally mounted at one end only thereof to revolve about suitably spaced centers to electrically connect one or more sections of crystal electrodes and to support or accommodate in the same holder one or more crystals of various shapes, sizes and modes of vibration. To secure uniform contact pressure with the crystal and to reduce Wear of the crystal electrodes, the clamping areas of each of the clamping projections may have rounded corners and may be composed 15 of or heavily coated with non-corrosive metal or metals relatively softer or less hard than the metal of the, crystal electrode in contact therewith. To nodally locate or center the crystal with respect to any of the clamping areas, a small projection may extend from the center of the clamping area of the clamping projection to cooperate with a small hole or depression in the surface of the crystal at a nodal point thereof.

While the crystal or crystals herein referred to may be any suitable piezoelectric body of any suitable cut or orientation, the invention is described particularly with reference to mounting quartz piezoelectric crystal plates or bars of the so-called Curie or perpendicular cut, that is, one so cut that its major or electrode surfaces are parallel to the optic axis and perpendicular to an electric axis. The electrode faces of the crystal plate may be coated wholly or partly with a layer or layers of suitable conductive material such as for example aluminum, platinum, or chromium'on top of platinum which may be applied in vaporized form in a. vacuum, for example, to closely unite the material with the surfaces of the plate to form electrodes integral with the crystal element.

The apparatus hereinafter described is suitable for mounting crystals which cover a very large range of frequencies. The lengths of the crystal plates may range for example from over five inches to less than half an inch for vibration in a longitudinal mode of vibration.

For a clearer understanding of the nature of this invention and the additional features and objects thereof, reference is made to the following description taken in connection with the accompanying drawings, in which like reference 6 characters indicate like or similar parts and in which:

Fig. 1 is a perspective View of one embodiment of the invention;

Fig. 2 is a perspective view of part of the device shown in Fig. 1;

Fig. 3 is a view taken on the line 33 of Fig. 2.

Fig. 4 is an enlarged sectional view of a crystal clamping arrangement.

Fig. 5 is a perspective view of the device shown in Fig. 1 adapted to mount a piezoelectric crystal vibrating in the longitudinal mode of motion at the second harmonic frequency;

Fig. 6 is a view taken on the line 6--6 of Fig. 5.

Fig. 7 is a perspective view of the mounting of Fig. 1 adapted to support a piezoelectric crystal vibrating in the fiexural mode of motion;

Fig. 8 is a view taken on the line 88 of Fig. 7.

Figs. 9 to 11 are views of the mounting of Fig. 1 adapted to support a tuning fork type of piezoelectric crystal; Fig. 10 being a view taken on the line l0l9 of Fig. 9, and Fig. 11 being a side view of part of the device shown in Fig. 9.

Figs. 12 and 13 are respectively front and side views of another embodiment of the invention;

Fig. 1a is a perspective view of still another embodiment of the invention; and

Fig. 15 is an enlarged sectional view of a crystal clamping arrangement suitable for the holder shown in Fig. 14.

Referring to the drawings, Figs. 1 to 11 illustrate a piezoelectric crystal holder adapted to mount and drive one or more piezoelectric crystals vibrating in various modes of motion such as longitudinally, in shear, or flexurally, for example and having one or more well defined nodal areas.

In Fig. 1, two piezoelectric quartz crystals l0 and each having four equal area metallic electrodes 32 to 31 disposed lengthwise thereof and integral therewith are nodally clamped and held in position by eight cantilever leaf springs 46 to 41 each having a metallic clamping projection 56 secured to its free end for nodally clamping and making individual electrical con nection with the several electrodes to 31 of the piezoelectric crystals Ill and 20. Three

insulating spacers

58, 61 and 62 composed of a phenol product as Bakelite or of Isolantite or other suitable high resistance dielectric, separate the leaf springs to 41 a suitable distance apart. A bolt 6 extends through openings in the insulating spacers 85, GI and 62 and also extends through openings in the springs 40, 4|, 44 and 45 and is suitably insulated therefrom by two insulating collars 55. and 66 surrounding the bolt 64. A nut unit 61 engages the threaded bolt 64 to clamp together the springs 40, 4i, 44 and 45 and the

spacers

60, 6! and 52. Another bolt 10 engaging the nut 61 similarly clamps together the

springs

42, 43, 46 and 41 and the

spacers

60, 61 and G2. The

bolts

64 and 10 and the nut unit 51 are suitably insulated from the springs 40 to 41.

The clamping forces exerted by the clamping projections on the piezoelectric crystals Ill and 20 may be controlled by varying the thicknesses of the

spacers

60 and 62 disposed between the springs 40 to 41. The values of spring tension for the springs 40 to 41 may be computed by the formula where W is the force, (1 is the deflection of the spring, E is Youngs modulus of the spring material, b is the width of the spring, It is the thickness of the spring and Z is the distance from the support of the spring to the center of the clamping contact 50.

The springs 48 to 41 may be constructed of any suitable resilient material such as steel, phosphor bronze or phenol fibre, for example. Where the springs 40 to 41 or the clamping projections 50 are composed of an insulating material, they may be coated wholly or partly with metallic or conductive material such as tin to form suitable individual electrical connections between the crystal electrodes 35 to 31 and the corresponding terminal lugs 12 to 19 of the springs 40 to 41. Such metallic coating may be applied to the surfaces of the springs 40 to 41 and the projections 50 by any suitable method such as for example by spraying molten metal thereon by means of a Schoop metal spray gun for example.

The eight springs 49 to 41 may extend through or have connections extending through suitable insulated openings in a copper cover 80 of a copper can or container 82 which houses the assembly comprising the piezoelectric crystals l0 and 20, the springs 40 to 41 and the common supporting means therefor which includes the spacers 60 to 62 and the

bolts

64 and 10. The assembly may be supported from the cover 80 of the can 82 by four bolts 84 and a suitable insulating member 86.

The eight terminal lugs 12 to 19 connected with the eight metallic springs 40 to 41 may be utilized to connect the eight divided or split platings 30 to 31 of the piezoelectric crystals l0 and 20 of suitable frequencies in any desired circuit such as for example in a lattice type filter circuit as illustrated in Fig. 1 wherein the terminal lug 12 connected with the terminal lug 11 interconnects the electrode 30 of crystal IO and the electrode 36 of the crystal 20, the terminal lug 13 connected with the terminal lug 14 interconnects the crystal electrodes 3! and 34, the terminal lug 15 connected with the terminal lug 18 interconnects the

crystal electrodes

33 and 35, and the terminal lug 16 connected with the terminal lug 19 interconnects the

crystal electrodes

32 and 31. The terminals 14 and 16 may be the input terminals and the terminals 12 and 18 may be the output terminals of such filters as shown in Fig. 1.

The clamping projections 50 may be constructed of any suitable metal or metals such as gold or silver for example, or as shown in Fig. 4, the clamping projections 50 may have an internal core 5| of metal such as for example soft brass or alternatively of insulating material such as for example a phenol product as Bakelite. The tips or clamping areas of the clamping projections 50 as the clamping areas of Fig. 4 are flat and also coplanar where used in contact with any single surface of a crystal and may be of circular, square, rectangular or other suitable configuration to best suit the nodal area of the vibrating crystal such as the crystal l0 clamped therebetween.

As shown in Fig. 4, the flat areas 52 of the cores 51 of the clamping projections 50 may be disposed in parallel relation with respect to the

fiat electrodes

30 and 31 of the crystal l0 and may have rounded corners or edges 53. The cores 51 and particularly the flat areas 52 and the rounded corners 53 thereof may be covered with a heavy layer 54 of tin or other suitable metal 7 or metals of similar roperties relatively softer than the metal coatings 30 to 31 of the piezoelectric crystals I0 and 20.

The layer of tin 54 may have a thickness of about .004" for example and may be applied to the projections 50 electrolytically or by metal spray for example. The contact portions of the clamping areas 55 of the tin deposit 54 are flat to conform to the corresponding fiat surfaces of the metallic coatings 30 to 31 of the piezoelectric crystals l0 and 20 and may have rounded outer edges or corners 56 to prevent concentration of stresses at such corners of the clamped areas 55 to thereby prevent wear of the platings 3|] to 31 which may result in lowering the so-called Q or ratio of reactance to resistance of the piezoelectric crystals II] and 20.

If desired, the outer'surfaces of the projections 50 may be gold or silver plated and such plating or the tin deposit 54 or both may serve to make good electrical contact at all times and being relatively pliant under pressure exerted by the springs 4|) to 41, the continuity of contact with the metallic films 30 to 31 on the surfaces of the piezoelectric crystals I0 and 20 is not interrupted and wear of the crystal electrodes 30 to 31 is reduced.

A small projection 51 may extend from the center of the clamping area 55 into a larger depression 58 in the crystal electrode 3| at a nodal point of the crystal I0 to nodally locate and center the crystal H] with respect to the clamping projections 50. It will be understood that by reversal of parts, the projections may extend from the crystal electrode 3| at the nodal point of the crystal l9 into an opening or depression in the clamping area 55 of the clamping projections As shown in Figs. 1 to 3, the crystals H) or 20 of Fig. 1 may be mounted for longitudinal vibration at the fundamental frequency thereof. In this instance, the nodal-area 0f the crystal l0 or 20 is located on a line passing essentially through the Width of the crystal midway between the small ends. The clamping areas of the clamping pro- J'ections 50 nodally clamp the crystals l0 and 20 along such nodal lines as shown in Figs. 1 to 3 and are sufficiently small in area to prevent excessive damping of vibrations. The clamping areas of the projections 50 may be square, circular, rectangular or any suitable shape. Every corresponding set or pair of clamping projections 50 is disposed in coaxial alignment. For example, the clamping projections 50 of the springs 40 and 4| are coaxially aligned with each other and the clamping projections 50 of the

springs

42 and 43 are in coaxial alignment with each other. The coaxial alignment position of the corresponding pairs of clamping projections 50 may be obtained for example by suitably locating them on the free ends of the springs 40 to 41 and by rotating the pivotally mounted springs 4|) to 41 about the clamping

bolts

64 and 10. The springs 40 to 41 exert sufficient pressure to clamp and rigidly hold the crystals Ill and 20 therebetween.

As a modified arrangement, it will be understood that in place of mechanically separate springs, the springs 4| and 44 for example may be placed back-to-back to mechanically form a single spring having two projections 50 contacting with the crystal electrodes 3| and 34 in the same manner as shown in Fig. l. The electrical connections may be separated if desired by insulating material disposed between the springs. Similarly the

springs

43 and 46 for example may be mechanically combined but electrically separated. In such mechanical arrangement, the coaxial pro- J'ections 50 exert substantially equal pressures on both crystals I0 and 20.

The metal container comprising the copper can 82 and its cover 80, as shown in Fig. 1, may be hermetically sealed if desired. To avoid the condensation of moisture on the crystals I0 and 20 or on other elements housed within the enclosing

container

80, 82, dry air may be blown through the container through small openings therein immediately preceding the final sealing of the container, or the container may be evacuated before final sealing thereof. While a particular form of container 88, 82 has been illustrated in Fig. 1, it will be understood that any suitable form may be utilized to house any of the various crystal holders illustrated herein.

Figs. 5 and 6 show the crystal clamping means of Figs. 1 to 3 pivotally adjusted about the

bolts

64 and 10 to mount and drive one or more piezoelectric crystals, such' as the'crystal III, at a longitudinal harmonic mode of vibration along the length 1. While in Figs. 5 and 6 the second harmonic mode of vibration of the crystal I0 is illustrated, it will be understood that the holder is also suitable for mounting and connecting crystals vibrating in other modes of harmonic vibration. In the case of the second harmonic longitudinal mode of motion, as illustrated in Figs. 5 and 6, the crystal I0 may have two pairs of electrodes comprising four separate equal-area metallic coatings to 93 integral therewith. The platings 9|! to 93 are divided or separated at 94 midway between the small ends of the crystal Ill. The distance of separation at 94 may be any suitable distance. The side edges and the small end edges of the crystal ID are, in the example shown, free of metallic coating.

The nodal points or areas of the crystal Hi, When driven as shown in Figs. 5 and 6 at its second harmonic mode of longitudinal motion, are located on lines passing through the width of the crystal In between the sides and 0.25 the length I of the crystal from its small ends as shown in Fig. 6. The projections 59 of the springs 4!] to 43 nodally clamp the crystal l0 at such nodal points or areas. The clamping areas may be sufiiciently small to prevent excessive damping of the vibrations of the crystal Ill and may be circular, square, rectangular or of other suitable shape. Where the clamping areas of the projections 50 are rectangular in shape, the axis of greatest length thereof may extend in the direction of the nodal lines of the crystal In. The projections 50 of the cooperating springs 40 and. 4| as well as of every other pair of corresponding springs are disposed in coaxial alignment. All springs such as the springs 40 and 4| or 42 and 43 may exert suflicient pressure to rigidly clamp and hold the crystal therebetween. The spacing between the projections 50 of the pivotally mounted springs for example may be varied to any desired amount by rotation of the springs about the bolts 54 and H1.

Figs. 7 and 8 show the crystal clamping means of Figs. 1 to 3 pivotally adjusted about the

bolts

64 and 10 to nodally mount one or more piezoe electric crystals such as the quartz crystal In for flexural vibration. The nodal points or areas of the crystal In when driven in the fiexural mode of motion are located on a line I05 passing through the length l of the crystal I] midway between the side edges and 0.224 times the length l of the crystal from its small ends. The projections 50 of the springs 40 to 43 nodally clamp the crystal I at such nodal points formed by the intersections of lines I05, I06 and I0! shown in Figs. '7 and 8. The clamping areas of the projections 50 may be sufficiently small to prevent excessive damping of the vibrations of the crystal I0. A circular clamping area is preferred for mounting crystals of this type vibrating in flexure as shown in Figs. '7 and 8.

To drive the crystal I0 in the fiexural mode of vibration as shown in Figs. 7 and 8, the crystal I0 may have electrodes divided at I04 into four separate metallic coatings I00 to I03 integral with the two major surfaces of the crystal I0. The coaxial projections 50 of the springs 40 and H make contact with the equal area metallic platings I00 and IOI. The coaxial projections 50 of the

springs

42 and 43 make contact with the equal area metallic platings I02 and I03.

As an alternative method of dividing the metallic platings of the crystal [0 to provide two separate electrical circuits in a single crystal I0, the division I04 between the platings instead of being disposed as shown in Figs. 7 and 8 at a small angle with respect to the line I passing through the length of the crystal midway between the side edges of the crystal, may be disposed along such midway line I05. The coaxial projections 50 of the springs 43 and H being then disposed on the line I06 slightly above such midway line I05 to make contact with the two oppositely disposed upper plates and the coaxial projections 50 of the

springs

42 and 43 being disposed on the line I01 slightly below such midway line I05 to make contact with the two oppositely disposed lower plates.

Figs. 9, 10 and 11 show the crystal clamping means of Figs. 1 to 3 adapted to nodally mount and drive one or more tuning fork piezoelectric crystals such as the U-shaped quartz crystal IIO having four sets or pairs of metallic electrodes III to H0 integral therewith and connected by metallic connection plates I to I23 also integrally adhering to the U-shaped quartz crystal The connection plating I20 interconnects the electrodes I I I and I H which are equal in areas and also oppositely disposed with respect to the electrodes II2 and H3 interconnected by connection plating IZI. Similarly, electrodes I I3 and i I5 interconnected by connection plating I22 are equal in area and oppositely disposed with respect to the electrodes I I4 and I I6 interconnected by connection plating I23. The nodal points of the crystal IIO are located on a line I25 passing through the yoke of the crystal IIO midway between the two forks thereof. The coaxial projections 50 of the cantilever springs and 4| nodally clamp the piezoelectric crystal I I0 at such nodal points and make contact with the connection plates I20 and I2I respectively at such nodal points. Similarly, the coaxial projections of the cantilever springs 42 and 43 nodally clamp the crystal H0 and make contact with the connection plates I22 and I23 respectively. The clamping areas of the projections 50 may be of such form as hereinbefore described as to prevent excessive damping of vibrations of the crystal I i0 and to provide uniform contact pressure. Electrical connections with the connection platings I20 and E2! are established by the projections 50 and the springs 40 and M. Electrical connections with the connection platings I22 and I23 are established by the projections 50 and the

springs

42 and 43.

It will be understood that the arrangement disclosed in Figs. 1 to 11 may be utilized as an allpurpose holder to support one or more piezoelectric bodies of various sizes and shapes vibrating in various modes of motion and with uniform contact pressures exerted thereon by the plurality of cantilever springs 40 to 41 which may adjustably pivot or revolve about the

bolts

64 and 61 to accommodate crystals of various sizes and which also may serve as metallic connectors to connect or interconnect one or several sections tallic coaxial clamping projections 50 secured to the free ends of five cantilever springs I50 to I54. Each of the springs I50 to I54 is pivotally supported at one end only thereof by a bolt I extending through coaxial openings in the springs I50 to I54, and engaging a nut I6I. insulating collar I52 may surround the bolt I60 to insulate the bolt I60 from the springs I50 to I54 when the springs I50 to I54 are metal or metal coated. Similarly, insulating washers I63 An :n

and I64 may insulate the bolt I60 and nut I6I :,.3

from the springs 1'50 and I54 respectively. Insulating spacers I06 may separate the springs I50 to I54 9. suitable distance apart to allow for the thicknesses of the piezoelectric elements I4I to I44 and to provide a suitable pressure on the clamping projections 50 to nodally and resiliently clamp the piezoelectric crystals I4I to I44. The springs I50 to I54 may be constructed of insulating material as phenol fibre, or of steel, phosphor bronze or other suitable resilient material. Where the springs I50 to I54 are made of phenol fibre or other insulating material, they may be metallically coated in whole or in part to provide electrical connections between the metallic contacts 50 and the corresponding terminals I10 to I14. The crystals I4I to I44 may be of suitable piezoelectric material such as quartz having metallic electrodes I46 integral with each of the oppositely disposed major surfaces thereof. be formed of suitable conductive material such as for example thin equal-area coatings of platinum alone or chromium on top of platinum deposited on both major surfaces of each of the crystals I4I to I44. I4I to I44 as shown in Figs. 12 and 13 are adapted to vibrate in the longitudinal mode along the length l but it will be understood that other piezoelectric elements may be utilized to vibrate in any desired mode of motion. clamping projections 50 may be silver rods or wires secured to the springs I50 to I54 or as hereinbefore described in connection with Fig. 4, may have metal cores or phenol fibre cores coated with suitable metal or metals to secure electrical The crystal electrodes I46 may 7 The piezoelectric crystals The coaxial 1:"

tive material which is relatively soft with respect to the metal coatings I46 of the crystals I M to I 44 as hereinbefore described.

The piezoelectric crystals MI and I43 may be of equal frequency to form the lattice arms of an electric wave filter structure. To form the series arms of such filter structure, the piezoelectric crystals I42 and I44 may be of equal frequency with respect to each other but of different frequency with respect to the crystals MI and I43. The mechanical structure is of sucn vibration absorption characteristics as to prevent mechanical coupling between the piezoelec tric crystals I M to I44 vibrating at the same or different frequencies. To form the connections for the lattice structure, the crystals I4I to I44 are connected in series circuit relation in the form of a Wheatstone bridge by means of a circuit including the metallic electrodes I46 of the crystals I4I to I44, the metallic clamping projections 50, the metallic springs I50 and I54, and a connection I15 between the terminals I10 and I14. Connections a and d connected with the terminal lugs HI and I13 respectively may form the input terminals for the lattice structure. Terminals b and connected respectively with the terminal lug I12 and the connection I15 may form the output terminals thereof.

While in Figs. 12 and 13 the piezoelectric crystals I4I to I44 have been illustrated as being connected to form an electric wave filter structure of the lattice type, it will be understood that some or all of the crystals I4I to I44 may be connected in any desired circuit, such as for example in a network of the ladder or T type. It will be understood that the two supporting projections 50 associated with any of the springs II to I53 may, if desired, be electrically separated as by insulating material disposed therebetween to establish any connections with the crystals that may be desired.

Fig. 14 shows another form of multiple crystal holder nodally clamping a plurality of piezoelectric crystals I4I to I44. The crystals I4I to I44 may be of the same type and have the same filter circuit connections as those of like reference characters disclosed in connection with Figs. 12 and 13. In Fig. 14, four metallic bent cantilever springs 200 to 203 are each rigidly supported at one end only thereof by

brass brackets

205 and 206 secured by screws 201 to opposite ends of a phenol fibre or other suitable insulating block 208. The block 208 extends through a central opening in another phenol fibre insulating block 209 and may be secured thereto by a bolt 2I0. Four similar metallic clamping projections 220 to 223 may be secured to each end of the phenol fibre block 209 for nodally clamping the crystals I M to I 44 with respect to the coaxial free ends of the corresponding springs 200 to 203. The clamping projections 220 and 22I and also the

projections

222 and 223 may consist of two separate metallic members as shown extending through two separate openings in the phenol fibre block 209 where electrical connection therebetween is desired as for example to form a filter structure of the type shown in Fig. 12. Where no connection between the metallic projections 220 and 22I or between the

projections

222 and 223 is desired, they may be separated and insulated from each other. The crystal clamping areas of the springs 200 to 203 are coaxially disposed with respect to the corresponding clamping areas of the projections 220 to 223 to nodally clamp the crystals I4I to I44 therebetween. It

will be understood that the clamping areas of g the springs 200 to 203 and those of the projections 220 to 223 may be constructed as to shape, extent of areas, metallic coating, rounding of corners and in all other respects like those of the projections 50 hereinbefore described.

If desired, small depressions 58 may be made at the nodal points of the crystals I4I to I44 to cooperate with small projections 51 disposed at the centers of the clamping areas 55 of the clamping projections 220 to 223 and of the springs 200 to 203 as shown in Fig. 15 and as described in connection with Fig. 4, to more readily locate the nodal points of the crystals and retain the crystals in clamped position.

It will be understood that any of the various embodiments of the invention disclosed herein may nodally and resiliently clamp a plurality of piezoelectric crystals for independent simultaneous vibration, that the crystals clamped in any of the holders disclosed may be quartz or other suitable material of any suitable cut and orientation, may have the same or difiering frequencies, may vibrate in various modes of motion as in the fundamental or harmonic mode of motion, and may have electrodes of divided or split plating as illustrated in Figs. 1 to 11 or of the nondivided plating as illustrated in Figs. 12 to 15, that any of the springs may be pivotally mounted at an extreme end or intermediate the ends thereof, that any of the contact clamping areas of the clamping projections 50, 200 to 203, or 220 to 223 may have rounded corners and may be composed of suitable metal such as silver or may be coated with metal relatively softer than that of the crystal electrodes in contact therewith to establish good electrical connections, to exert uniform pressures, to reduce wear on the crystal electrodes and to maintain the crystal at a high value of ratio of reactance to resistance, that any of the clamping projections may have a small additional projection extending from the clamping area thereof insertable in a small depression formed in the crystal and crystal electrode at a nodal point of the crystal to center and position the crystal, that the clamping or contact areas of the clamping projections may be rectangular, round or other shape to suit the nodal points or areas of the particular crystal clamped therebetween and sufficiently small in areas to prevent excessive damping of vibrations of the crystal, that, as pressure changes tend to change the response frequency of the crystal, the springs may be adjusted to equalize or otherwise control the degree of pressure of the clamping areas on the frequency of the crystal, that any of the various features herein disclosed may be applied to any or all of the various embodiments of the invention illustrated in the figures and disclosed in the specification.

While this invention contemplates other forms to resiliently and nodally clamp a plurality of piezoelectric elements without coupling therebetween, it will be noted that the cantilever form of springs, such as the springs 40 to 41, I50 to I54 or 200 to 203 is a very useful form for this purpose, particularly where such crystals are used in an electric wave filter structure as shown in Figs. 1, 12 or 14 for example, and while particular arrangements of the springs 40 to 41, I50 to I54 and 200 to 203 have been illustrated in Figs. 1, 2 and 14 respectively, it will be understood that these or similar cantilever springs may be suitably supported at or adjacent one end thereof from any suitable form shape or size of insulating block or supporting means and mayextend from the supporting points in any desired direction to clamp any suitable crystal or crystals by means of the clamping projections disposed at or near the free ends thereof. Thus, while in Figs. 1 and 2, the corresponding pairs of the springs 40 to- 41 extend from the supporting points 64 and 1'0 in substantially parallel directions and while in Figs. 5 and '7 they extend in non-parallel directions, it will be understood that they may extend in any desired directions by suitable spacing or disposition of the supporting points 64 and it with respect to the insulating supporting means utilized or by suitable spacing or disposition of the clamping projections 50 with respect to the crystals and crystal electrodes utilized. For example, the four pairs of the springs 40 to ll of Fig. 1 may be rotated outwardly about their supporting points 64 and ill from the parallel position shown in Figs. 1 and 2, beyond the acute angular positions as shown in Figs. 5 and 7 up to the degree position, for example as illustrated by springs 20| and 202 or 280 and 203 in Fig. 14, in which 180 degree angular position the pairs of springs 40 to 47 of Fig. 1 may conveniently accommodate four filter crystals connected in closed series circuit relation as illustrated in Fig. 14.

Or, instead of being rotated outwardly about the supporting points 64 and '10 to the 180 degree relative positions as last-mentioned, the corresponding parallel pairs of springs 40 to 41 of Fig. 1 may be rotated about the clamping projections 50 to the 180 degree positions so that the parallel pairs of springs 40 to 4! of Fig. 1 are supported by suitable insulating blocks (not shown) disposed at the sides of the crystals 19 and 20 rather than from the

blocks

60, 6| and 62 disposed at the top as shown in Fig. 1. It will be understood that single springs of the type shown in Fig. 14 may be utilized in place of the cooperating pairs of the springs 40 to 41 of Fig. 1 to clamp the crystals ID and 20 of Fig. 1.

While in Fig. 1, the pairs of springs 40 to 41 as for example the pair of

springs

40 and 41 have a common axis supporting point 64, as an alternative arrangement, the supporting points for the pair of springs 40 and M for example may be spaced apart along the surface of the insulating block 60 to form a V-shaped arrangement of springs with the coaxial clamping projections 50 of

such springs

40 and 41 forming the apex of the V arrangement.

The pressure exerted on the crystal by any of the springs illustrated herein may be adjusted to any suitable value by any suitable means such as by adjusting screws disposed intermediate the supporting point and free end of any of the springs; as for example, between the supporting point 201 and the free end 51 of the spring 201 of Fig. 14, a screw (not shown) may engage the spring Elli and the insulating block 209 to adjust the pressure exerted on the crystal I42 by the spring 201.

It will be understood that the crystals such as the crystals ill and 20 of Fig. 1, and the crystals Mi to I44 of Figs. 12 and 14 may have suitable frequencies and interconnections as illustrated in Figs. 1, 12 and 14, for example to constitute an electric wave filter structure adapted to pass a selected band of frequencies and attenuate all other frequencies.

It will be noted that in Figs. 12 and 14, the four crystals [41 to I44 are connected in closed series circuit relation to constitute an electric wave filter system having input and output circults as illustrated in Fig. 12. In Fig. 14, the input circuit terminals may be terminals 2M and 215 corresponding respectively to the terminals Ill and I13 of Fig. 12, and the output circuit terminals of Fig. 1 may be terminals M2 and H3 corresponding respectively to the terminals I15 and H2 of Fig. 12.

In order to adjust the anti-resonance oi such crystals within desired limits, auxiliary adjustable air condensers suitable for use at radio frequencies may be connected in parallel circuit relation with each crystal. Such condensers may consist of short lengths of brass tubing having adjustable concentric brass pins or crews mow able longitudinally within the tube to adjust the capacity thereof as illustrated for example in True United States Patent 1,676,417 of July 10, 1928, and may be inserted in suitable holes or cavities in the supporting insulating block, as the block 209 of Fig. 14, adjacent the corresp ing crystals to form a compact unit particuaiiy useful at high frequencies.

Although this invention has been described and illustrated in relation to specific arrangements, it is to be understood that it is capable of application in other organizations and is therefore not to be limited to the particular embodiments disclosed, but only by the scope of the appended claims and the state of the prior art.

What is claimed is:

1. An electric wave filter system including electromechanical vibratory apparatus comprising a plurality of piezoelectric bodies, common supporting structure therefor, and means carried by said structure and including springs having free ends, and a clamping projection secured to the free end of each of said springs for nodally individually clamping and electrically interconnecting said plurality of bodies for independent simultaneous vibration to obtain said wave filter.

2. An electricwave filter system including electromechanical vibratory apparatus comprising a plurality of piezoelectric bodies each having electrodes formed integral therewith, common supporting structure, and means carried by said i structure and engaging said electrodes for clamping said plurality of bodies to hold said bodies against bodily movement out of a predetermined position and for independent simultaneous vibration, and means including said clamping means and said electrodes for establishing such electrical connections with said plurality of bodies as to obtain said wave filter.

3. An electric wave filter system including electromechanical vibratory apparatus comprising a plurality of piezoelectric bodies each having electrodes formed integral therewith, common supporting structure, and resilient means including springs each having one end carried by said structure and an opposite free end, conductive clamping projections secured directly to the free ends of said springs and conductively engaging said electrodes for clamping and electrically connecting said plurality of bodies for independent simultaneous vibration at difierent frequencies to obtain said wave filter.

4. Electromechanical vibratory apparatus comprising a plurality of piezoelectric bodies each having electrodes fonned integral therewith, and means including a plurality of cantilever springs each having free ends and supported at one end only for nodally clamping said plurality of bodies from said free ends of said springs.

5. An electromechanical vibrator comprising an electrically deformable body having electrodes posed clamping members between which the crystal is clamped and held within a nodal region at opposite points on each of said pairs of electrodes, and means including springs having free ends secured to at least some of said members for pressing said members against said crystal.

'7. An electromechanical vibrator comprising a vibratory body having plated electrodes formed integral and closely united therewith, a support, and means carried by the support for rigidly nodally clamping the body and engaging said electrodes to hold the body against bodily movement out of a predetermined position, said clamping means including a leaf spring having a free end and a conductive clamping member secured to and supported by said free end and disposed in electrical contact with one of said electrodes.

8. An electromechanical vibrator comprising a iezoelectric body, a pair of coaxial clamping projeotions, and means including a spring having a free end secured to and supporting one of said projections for rigidly nodally clamping said body between said projections to hold the body against bodily movement out of a predetermined position.

9. An electromechanical vibrator comprising a piezoelectric body having opposite electrodes formed integral therewith, a pair of conductive coaxial clamping projections oppositely disposed in contact with said electrodes, and means including a spring having a free end secured to one of said projections for rigidly clamping said body within a nodal region to hold the body against bodily movement out of a predetermined position between said projections.

10. An electromechanical vibrator comprising a piezoelectric body having electrodes formed integral therewith, a pair of conductive coaxial clamping members disposed in contact with said electrodes, and means including a spring having a free end secured to and supporting one of said members for clamping said body at oppositely disposed points of relatively small area within a nodal region to hold said body nodally against bodily movement out of a predetermined position between said members, said members having metal tips relatively softer than said electrodes in contact therewith.

11. An electromechanical vibrator comprising a piezoelectric body having electrodes formed integral therewith, a pair of conductive coaxial clamping members disposed in contact with said electrodes, and means including a spring having a free end secured to and supporting one of said clamping members for clamping said body at oppositely disposed points of relatively small area within a nodal region to hold said body nodally against bodily movement out of a predetermined position between said clamping members, said clamping members having metal tips disposed in contact with said electrodes, said metal tips having rounded corners adjacent said electrodes and being relatively softer than said electrodes in contact therewith.

12. An electromechanical vibrator comprising a piezoelectric body havlng electrodesformed integral therewith, a pair of conductive coaxial clamping members disposed in contact with said electrodes, and means including a spring pivotally supported at one end only and having a free end secured to and supporting one of said clamping members for clamping said body at oppositely disposed points of relatively small area within a nodal region to hold said body nodally against bodily movement out of a predetermined position between said clamping members, said clamping members having metal tips disposed in contact with electrodes, said metal tips having rounded corners adjacent said electrodes and being relatively softer than said electrodes in contact therewith.

13. An electromechanical vibrator comprising piezoelectric body having electrodes formed integral and closely united with opposite surfaces thereof and having a depression therein within a nodal region, a pair of conductive coaxial clamping members oppositely disposed in contact with said electrodes, and means including a spring pivotally supported at one end only and having a free end secured to and supporting one of said clamping members for clamping said body at oppositely disposed. points of relatively small area within said nodal region to hold said body nodally against bodily movement out of a predetermined position between said clamping members, said clamping members having metal tips disposed in contact with said electrodes, said metal tips having rounded corners andbeing relatively softer than said electrodes in contact therewith, at least one of said metal tips having a projection insertable in said depression to nodally position said body with respect to said projection.

14. Electromechanical vibratory apparatus comprising a piezoelectric body, a pair of opposit-ely disposed clamping members between which said body is clam ed. and means including a pair of springs each pivotally supported at one end and having o posite free ends attached to and individually supporting said clamping members, for clamping said body at oppositely disposed points of relatively small area to hold said body against bodily movement out of a predetermined position between said clamping members.

15. Electromechanical vibratory apparatus comprising a piezoelectric body having oppositely disposed electrodes formed integral therewith, a pair of opposite conductive clamping members disposed in contact with said electrodes, and means including a pair of springs each pivotally supported at one end and having opposite free ends attached to and individually supporting said clamping members, for clamping said body at oppositely disposed points of relatively small area to hold said body against bodily movement out of a predetermined position between said clamping members.

16. Apparatus for mounting a piezoelectric body having electrodes formed integral therewith comprising means including clamping members for clamping said body therebetween, at least one of said clamping members having a projection insertable in a depression in one of said electrodes in the surface of said body adjacent thereto to position said body with respect to said clamping members.

1'7. Apparatus for mounting a plurality of piezoelectric bodies for independent simultaneous vibration comprising common supporting structure, and means carried by said structure for nodally individually clamping said plurality of bodies at oppositely disposed points of relatively small area to hold each of said bodies against bodily movement out of a predetermined position.

18. Apparatus for mounting a plurality of piezoelectric bodies each having opposite electrodes formed integral therewith comprising a plurality of pairs of oppositely disposed conductive clamping projections engaged in electrical contact with said electrodes of said plurality of bodies at oppositely disposed points of relatively small area, a common support, means carried by said common support for resiliently and individually clamping said plurality of bodies between said plurality of pairs of projections to hold each of said bodies against bodily movement out of a predetermined position.

19. Mounting apparatus for a piezoelectric crystal comprising a plurality of pairs of oppositely disposed clamping projections for clamping the crystal therebetween, means for supporting the projections on one side of the crystal, and means including separate springs having free ends secured to and independently supporting the projections on the opposite side of the crystal.

20. Mounting apparatus for a piezoelectric crystal having two pairs of opposite electrodes formed integral therewith comprising two pairs of conductive clamping projections for nodally clamping the crystal therebetween and establishing individual electrical contacts with the two pairs of electrodes thereof, means for supporting one pair of said projections, and means including springs individually secured to the other pair of said projections for independently supporting said other pair of projections.

21. Apparatus for mounting a piezoelectiic body having a plurality of pairs of electrodes formed integral with opposite surfaces thereof comprising a plurality of pairs of oppositely disposed con ductive clamping projections between which said body is held in contact with said corresponding electrodes, and means including a plurality of cantilever springs having free ends secured individually to said corresponding projections for clamping said body therebetween at oppositely disposed points of relatively small area to hold said body against bodily movement out of a pre determined position.

CARL A. BIELING.