GB634775A - Improvement in piezoelectric crystal means and method of using same - Google Patents

Abstract

634,775. Piezo-electric crystals. BRUSH DEVELOPMENT CO. Oct. 16, 1945, No. 27112. Convention date. June 8, 1944. [Class 40 (v)] [Also in Group XL (b)] A piezo-electric body is composed, apart from impurities, of primary ammonium phosphate, and has a pair of parallel electrodable surfaces perpendicular to the Z axis of the crystal. Fig. 2 shows a mother crystal 15 from which plates 17 and 27 may be cut. If electrodes are applied to the major surfaces of plate 17 a surface shear plate is produced in which expansion and contraction takes place along the diagonals as shown by arrows in Fig. 4. From this plate may be cut an expander plate 25 having its major dimensions parallel to the diagonals of plate 17. When electrodes are applied to the minor end faces of plate 27, Fig. 2, the mode of vibration is a pure shear controlled by the smallest dimension of the plate. If the Z dimension of the plate is reduced the capacity is increased without substantially altering the frequency. Two expander plates 25 may be joined together face to face with an interposed electrode to form a bender unit for driving a loud-speaker (Fig. 10, not shown). A Z-cut shear plate 17 may be used as in Fig. 11 to drive a loudspeaker diaphragm 91, the lower edge of the shear plate being fixed to a base 90. Two shear plates may be joined face to face to form a twister element 51, Fig. 13. One edge and the centre line are held clamped between rubber pads 52, 53. The free end then executes a pure twist, and may be coupled by rod 54 to the stylus of a gramophone pick-up or record cutter as described in Specification 521,435. Specifications 318,934, [Class 40 (v)], 569,285 and 600,853 also are referred to. The Specification as open to inspection under Sect. 91 also includes the following matter. Fig. 8 (Cancelled) shows plates 37, 38 cut at angles of 45 degrees to the faces of a block 36 which is cut with its faces at 45 degrees to the major faces of the mother crystal. Plates 37, 38 are stated to be thickness expander plates. Reference is made to mixed crystals formed by the addition of the phosphates and arsenates of rubidium, caesium and thallium. Arrangements for light modulation and colour television are also described (see Group XL (b)). This subject-matter does not appear in the Specification as accepted. Reference has been directed by the Comptroller to Specification 641,469, [Group XL (b)].