US2315392A - Art of mounting piezoelectric crystals - Google Patents

Description

March'30, 1943. s. A. BOKOVOY 2,315,392

ART-OF MOUNTING PIEZOELECTRIC CRYSTALS Filed July 5, 1941 3nventor attorney Patented Mar. 30, 1943 ART OF MOUNTIN CRYS o rmzonmc'rmc TALS Samuel A. Bokovoy, Audubon, N. 1., assignor to Radio Corporation Delaware of America, a corporation of Application July 5, .1941, 'Serial No. 401,102

Claims.

This invention relates to the art of mounting piezoelectric crystals and particularly to improvements in so-called shock proof mountings for such vibra'tile elements.

In mounting a piezoelectric crystal for use in aircraft 'and other installationsofthe type normally subjected to shocks and tremors -of appreciable magnitude, the usual practice has been to apply a compression force to the crystal as by means of a pair of clamps arranged to grip the crystal usually at those selected surface: points or areas which are known to give rise to the least possible vibration-damping effect. In such cases some damping is to be expected and can be tolerated within limits provided the clamping force is constant and not variable, since in the latter case suddenrjumps or gradual shifts in the operating frequency of the crystal may take place.

As a practical matter, it is difficult to prevent changes in frequency in crystal installations of the general character described. This.

is so because, usually, the surfaces of the crystal are as flat and smooth as it is possible to make other hermetic closure since in this event neither the mount nor the crystal is accessible for purposes of inspectionand repair.

The foregoing and other less apparent objections to prior art methods of mounting Diem-- electric crystals are substantially overcome, in accordance with the present invention, by subjecting the crystal in a novel manner to tension or to a stretching force, instead of to the usual vertically applied compression or clamping force. Certain details of construction together with other objects and advantages will be apparent and the invention itself will be best understood by. reference to the following specification and to the accompanying drawing, wherein:

Figure l is a side elevational view of a metalized crystal having a dished electrode face and mounted under tension, inaccordance with the principle of the invention;

Figure 2 is a fragmentary side elevational view force of the springs S and S,

' mounting elements or jaws J and J and Fig. 3 a fragmentary sectional view of a crystal support showing alternative means for subjecting a dished crystal to tension;

Figure 4 is a sectional view showing one means of applying the invention to a crystal having flat'and parallel electrode faces; and I Figure 5 is a front elevational view of a piezoelectric crystal mounted in accordance with the invention and contained in a hermetically sealed casing. v

In Fig. 1," P designates generally a quartz piezoelectric crystal having a substantial flat "bottom major face and a top" major face which is dished outwardly from its center to provide a rim r, r along opposite of its end zones or surfaces. The particular crystal illustrated comprises a so-called V-cut crystal; its length thus lies along a Z+0 axis, its width along a Y+0 axis and its thickness dimension along an X+0 axis. The invention, however, is not limited in its useful application to crystals of the above described orientation. The two necessary electrodes are in the form of adherent metal coatings or films e and 2' each of which partially covers both major faces of the crystal.

In accordance with the invention the crystal P is subjected to tension or to a stretching force (instead of to the usual vertically applied compression or clamping force) as by means of 1 two springs S, S, respectively, which are anchored at one end to suitable immovable supports A, A", and are secured at their opposite ends to inflexible jaws J, J which engage the "flat bottom face and the upturned edges or rims r, 1'', respectively, on the metalized major top face of the crystal. The laws J and J which engage the rims r, r of the crystal are preferably constituted of an inflexible metal and, since they are urged outwardly by the biasing they subject the crystal to substantially constant tension without danger of their being .pulled outwardly over the upturned edges r, 1''. These separate c-shape may extend across the crystal and are applied to the thinnest or dished parts thereof and then moved outwardly to contact the rims 1", r'. In the alternative form of mounting element shown in Fig. 2 the tensioning force is applied to the crystal P through one or more metal screws 0 which are shown threaded in one of the arms of the support J and contact the metalized rim rof the crystal in a direction substantially normal to the inner face of the said rim. As in the previous described embodiment of the invention the substantially c-shape mounting elements J may exopposite arm of the C is provided with a bend b so that it contacts the metalized flat bottomface of the crystal along a narrow line.

Referring particularly to Fig. 3: In some cases, as where the installation may be subjected to shocks tending to cause lateral movement of the crystal P in its holders J, one or more retaining members may be provided to prevent such displacement. The retaining members or member may be in the form of a pin n mounted in or ,on the tensioning element C and extending into a hole or recess 72., provided for the pu p se, preferably in the rim r of the crystal.

Fig. 4 shows one method .of applying a tensional supporting force to a crystal P having duplicate flat, parallel electrode faces. In this case the crystal is provided with'one or more holes or recesses adjacent the opposite end zones of the crystal and which preferably extend into the crystal in a direction normal to its major faces. comprise theelectrodes, for the crystal cover the inner surface or walls of the recesses o and 0 thus make contact with the tensioning springs S and S which, as shown, extend into or through the said recesses or holes.

Where, as shown in Fig. 5, the crystal and its support are mounted in a hermetically sealed envelope E, the springs S and S which supply the tensioning force for the crystal P may be anchored either to the walls or the envelope or to auxiliary conductive supports A, A adjacent the opposite ends of the envelope and which are connected as by leads m to prongs g, on its base. To prevent twisting or turning of the crystal two tensioning springs B may be provided preferably adjacent one of its end-zones.

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.

The metal coatings e and e which I of said crystal.

What is claimed is:

1. Method of mounting a piezoelectric crystal which comprises subjecting said crystal to tension applied at spaced points adjacent the surface thereof.

2. Method of mounting a piezoelectric crystal which comprises subjecting said crystal to tension applied adjacent opposite end zones of said crystal.

3. Method of mounting a piezoelectric crystal which comprises subjecting said crystal to tension applied to the electrode faces of said crystal.

4. Method of mounting a piezoelectric crystal which comprises subjecting said crystal to tension applied at spaced subsurface areas in the body of said crystal.

'5. Method of mounting a piezoelectric crystal which comprises subjectinl said crystal to tension applied to said crystal at the minimum number of points required to define the plane 6. In combination, a piezoelectric crystal, and means for applying a tensional supporting force to said crystal at spaced points adjacent the surface thereof.

7. In combination a piezoelectric crystal having a raised portion on an electrode face adjacent opposite ends thereof, and means for apply ing a tensional supporting force to said raised portions of said crystal.

82 In combination, a piezoelectric crystal having a; recess adjacent opposite ends thereof, and means within said recesses for applying a tensional supporting force to said crystal.

9. A holder for a piezoelectric crystal comprising, a support, and spring means on said support for applying a tensional supporting force to said crystal.

10. A holder for a piezoelectric crystal comprising means for applying a tensional supporting force to said crystal at the minimum number of points required to deflne' the plane of said

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