GB535507A - Piezo-electric devices - Google Patents

Abstract

535,507. Piezo-electric crystals telephone instruments. ELECTRICAL RESEARCH PRODUCTS, Inc. March 28, 1940, No. 5556. Convention date, April 5, 1939. [Classes 40 (iii)] and 40 (v)] [Also in Groups XXXVI and XXXIX] A piezo-electric device comprises two or more superposed plates of piezo-electric material, each provided with electrodes and clamped together so as to vibrate as a unit, one or more of the plates consisting of a material having a different Curie point from the other plate or plates. The arrangement is designed to give efficient working over a considerable temperature range and three substances for use in combination are sodium potassium tartrate, sodium potassium tartrate crystallised from heavy water this having a higher Curie point, and sodium rubidium tartrate having a lower Curie point. The plates may be mounted so as to produce longitudinal vibration or to produce warping. Fig. 6 shows an electromechanical wave filter in which circuits 10, 11 are coupled to a longitudinally vibrating bar 12 by means of piezo-electric units 13, 14 each comprising six plates arranged to expand or -contract simultaneously, and consisting of materials having different Curie points. Fig. 7 shows a stack of plates arranged to produce bending and provided with a mirror 19 which, in conjunction with a light source, serves as a light valve or oscillograph. Fig. 9 shows a telephone receiver in which a square piezo-electric element 25 is clamped across one diagonal by a bar 24, the bending of the other diagonal serving to operate a diaphragm 22 through blocks 26, 27. The diaphragm is held between the two halves of a moulded casing by a metal ring 23.