Art of mounting piezoelectric crystals

June 8, 1943. _s. a. bokovqy 2,321,358

ART OF MOUNTING PIEZOELECTRIC CRYSTALS

Filed June 30, 1941

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Patented June 8, 1943

2,321,358

UNITEp STATES PATENT OFFICE

2421,358

ART OF MOUNTING PIEZOELECTRIC CRYSTALS

Samuel A. Bokovoy, Audubon, N. J., assignor to Radio Corporation of America, a corporation of Delaware

Application June 30,1941, Serial No. 400,451

Claims. (Cl. 171—327)

This invention relates, to the art of mounting Figure 3 is a side elevation and Figure 4 an piezoelectric crystals and, though hot limited thereto, has special reference to the mounting of so-called “thickness-mode” quartz crystals.

It has heretofore been proposed to make the 5 necessary two electrodes for “thickness-mode” and “contour-mode” piezoelectric crystals in the form of adherent metallic coatings or films applied directly to the surface of the crystal. Heretofore, such “metalized crystals” have been 10 mounted either by the application of a clamping force applied at opposite points along a nodal axis of the crystal or by a pair of clamps which engage both major surfaces of the crystal adjacent the opposite ends thereof. In the former 15 case, the crystal may move as on a pivot and the resulting friction may wear away the thin metal films, whereas in the latter case the application of a clamping force to the major or electrode surfaces over a substantial area ad- 20 jacent the ends thereof may inhibit maximum oscillatory movement of the crystal.

Accordingly, the principal object of the present invention is to obviate tide foregoing and other less apparent objections to prior art mountings 25 for metalized crystals.

Another and important object of the present invention is to provide a simplified, inexpensive and trouble-free pressure-type mount for metalized piezoelectric crystals, and one requlr- 30 ing the minimum of skill in the assembly and adjustment of its parts.

The foregoing and other objects are achieved in accordance with the present invention by extending the usual metal electrode coatings be- 35 yond the electrode or “major” surfaces of the crystal so that they at least partially cover certain of the minor surfaces thereof, and by applying the clamping force to the said metalized minor surfaces, or to the metalized right angled 40 or beveled edges defining the boundaries of the said major and minor crystal faces, rather than to the major surfaces, per se. The clamping force is preferably supplied, in accordance with the invention, by a pair of expansible spring 45 metal rings or clips mounted intermediate the ends of the crystal and which are bent or otherwise fashioned to contact only the metalized minor surfaces or edges of the crystal.

In the accompanying drawing: 50

Figure I is a plan view, with the cover removed, of a crystal holder embodying the invention,

Figure 2 is an end elevation of the crystal and the support therefor of Fig. 1, 55 end elevation of another crystal holder embodying the invention,

Figure 5 is a top plan view, and Figure 6 a side elevation of a “duplex” crystal holder incorporating the invention.

In Fig. 1, C designates an oblong crystal element or plate or bar possessing piezoelectric properties and which may be constituted of quartz, tourmaline or Rochelle salts. This crystal is provided with a pair of electrodes I and 2 which, as shown, preferably comprise adherent foil-like or integral film-like coatings or silver or other suitable metal. These electrodes partially cover the two major faces of the crystal and extend over the edges of the crystal at its end zones ία, 2α and cover the minor side and- end faces of the element within these zones. Since each coated minor side-face of the crystal is electrically connected to a metalized major face the metal on the minor end-faces lb and 2b of the crystal may be omitted or erased, if desired.

The crystal C is supported in accordance with the invention, preferably intermediate its ends by a pair of clamping elements 3 and 4 (later described) which exert their clamping force upon the metallized minor faces la, 2a of the crystal (as shown more clearly in Fig. 2) or upon the edges of the crystal which define the boundary between its major faces and its minor side faces, (as shown in Figs. 4 and 5). In this later case the said edges of the crystal may be beveled as indicated at c, Fig. 4.

The supporting clamps 3 and 4 (Figs. 1-4) are constructed and positioned, in accordance with the invention, to permit of accurate and rapid mounting and replacement of a crystal by an unskilled operator, and to this end comprises expansible rings (Figs. 1-4) or jaws (Figs. 5 and 6) constituted of spring metal. Thus, as shown in Figs.. 1 to 4, inclusive, each clamp may comprise a spring metal strip which is secured at one end to the insulating base 5 of the holder as by means of a metal stud or screw 6 and a somewhat narrower free end / which is bent around the crystal C and extends through an elongated slot g struck out from the strip adjacent its fixed end h. The slotted portion, of the strip extends a sufficient distance above (or at a right angle to) the base 5 to provide a clearance space between the surface of the base and the bottom of the loop. Thus, the clamp may be expanded to permit the crystal C to be entered therein simply by pressing the free end ' , / 3.S f downwardly or inwardly in the direction of the base. ⁷

In accordance with the principle of the invention the clamping force is confined to the minor side faces of the crystal or to the side edges thereof and is not applied to its major surfaces. Accordingly, referring particularly to Fig. 2, when the mounting force is to be applied to the minor side-faces of the crystal the spring metal loops or clamps may be flattened at the area indicated at j, where it contacts the said faces of the crystal and is bowed outwardly, as indicated at p, away from the major faces of the crystal.

Where, as shown in Fig. 4, the clamping force is to be applied to the edges of the crystal, the loop may be bowed outwardly away from both the major faces and the minor side faces Of the crystal so that its clamping force is confined to the said edges. As previously set forth, and as shown at c. Fig. 4, the edges of the crystal C to which the clamping force is applied may be beveled, if desired.

The “duplex” holder shown in Figs. 5 and 6 is designed to support two metalized oblong plano-convex crystals Cl, C2, respectively, on opposite sides of an insulating upright 7 which is provided for the purpose on a socket base 5. The clamping members, which are here designated 8, 9, 10 and II, respectively, instead of being in the form of loops or rings are of U-shape construction and are secured at the base of the U to the upright support 7 by means of screws 10. The legs of these U-shape members extend outwardly at an obtuse angle with respect to the base, and then inwardly toward each other, preferably at a right angle, as indicated at r, Fig. 5. The clamping force is applied to the crystals along their metalized edges by the angularly disposed legs of these flexible clamps. In order to prevent longitudinal movement of the crystals in either direction a tongue t may be struck out from the edge of each clamp 8—11 and bent outwardly across the plane of that minor end-surface of the crystal which is adjacent thereto.

Other embodiments and modifications of the invention will.suggest themselves to those skilled in the art. It is to be understood therefore that the foregoing is to be interpreted,, as illustrative and not in a limiting sense except as required by the prior art and by the spirit of the appended claims.

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