GB590688A - Improvements in or relating to piezoelectric devices - Google Patents

Abstract

590,688. Piezo electric crystals. BRUSH DEVELOPMENT CO. June 2, 1944, No. 10689. Convention date, Jan. 18, 1943. [Class 40 (v)] A piezo-etectric unit comprises a flexible plate of piezo-electric matter and a, flexible restraining plate disposed face to face, but spaced apart for the major part of their length and. connected together at their ends. In Fig. 1, a compound bender element is formed by removing the centre of a crystal slab 1 so as to constitute the plates joined by integral end parts 5. Electrodes 3 are applied to both surfaces of both plates. When the inner electrodes are connected to one pole of a source of potential and the outer electrodes are connected to the other pole, one plate extends while the other contracts, thus producing bending. The plate described is of Rochelle salt, cut in a plane perpendicular to the X-axis and with the length at 45 degrees to the Y- and Z-axes. Other materials may be used such as beryllium sulphate and oxide, primary ammonium phosphate and the alkali phosphates and arsenates, tourmaline, &c. Fig. 2 shows a modification comprising two plates 7 cemented together at thickened end parts 9. In Fig. 4, a bender element comprises two simple plates 11 cemented into grooves in a member 13 and to a spacer 15. One or more spacers 17 prevent buckling of the plates. If end 15 is clamped, end 13 executes a transverse movement. Fig. 6 shows a bender comprising a simple plate 21 cemented into end ridges 9 of a plate 7. Various slight modifications designed to reduce the shear stress on the cement are described (Figs. 7-10, not shown). Fig. 11 shows a compound twister element in which the plates are cut with edges parallel to the Y- and Z-axes, the upper plate 27 being cemented at the raised corners 25 only of the lower plate 23. A number of modifications are described of plates which are formed for inter-locking engagement at the corners to make twister elements (Figs. 14-20, not shown). The restraining plate may comprise a sheet of non- piezo-electric material, for example berylliumcopper. Specifications 318,934, [Class 40 (v)], 454,595 and U.S.A. Specifications 1,438,974 and Re-issue 20,213 are referred to.