GB255463A - Improvements in piezo-electric devices - Google Patents

Abstract

255,463. British Thomson-Houston Co., Ltd., (Assignees of Ellis, A. L.). July 14, 1925, [Convention date]. Piezo-electric crystal units. - Piezo-electric crystal oscillators are arranged in such a way as to prevent air-friction or the effect of temperaturevariations upon the mountings from affecting the constancy of their free vibration period. In Fig. 1, " twinned " crystals 1 - - 4, arranged side by side and in one plane as shown in Fig. 4 are mounted upon an electrode 5 connected to the lead 7 through a screw 8, the upper electrode 9 being supported by a spaced conducting wall 10 connected through a screw 12 to the lead 11. The change in form of adjacent crystals under electrostatic influence is as shown in Fig. 5, producing a minimum overall change in the length and width of the slab as a whole, and thus reducing the frictional effects both on the mounting and on the surrounding air. Alternatively the supporting electrode 5 and the spacing member 10 may be composed of materials, such as " invar " and copper, designed to have such a combined coefficient of thermal expansion that the spacing between the crystal and its surroundings is maintained constant irrespective of temperature charges. Or the upper electrode 9 may be supported from the lower electrode 5 by bimetallic strips similar to those used in thermostats. Again the upper electrode may have slots formed in the surface adjacent to the crystal for the purpose of minimizing air-friction effects. Fig. 9 shows a construction in which the crystal oscillator 31 is mounted between curved supports 32, 33 pressed together by a spring 37, the whole being contained in an evacuated vessel 34.