GB239175A - Improvements in piezo-electric frequency control devices - Google Patents

Abstract

239,175. Western Electric Co., Ltd., (Assignees of Marrison, W. A.). Aug. 26, 1924, [Convention date]. Piezo-electric crystal units.-A piezo-electric crystal for use as a frequency control element is designed so as to vibrate at lower frequencies than usual, for example, frequencies within the voice range, whilst still remaining of small dimensions. According to one method, the natural frequency of the crystal for longitudinal vibrations is brought within the audible range by increasing the ratio of mass to restoring force by forming the crystal of dumb-bell shape 11, Fig. 3. The crystal is preferably cut with its longer axis 1 perpendicular to one of the natural faces of the original crystal. According to a second method, low-frequency vibrations are produced by causing the crystal to vibrate transversely. This is effected in a parallelepipedshaped crystal by placing the metallic plates 13 supplying the exciting voltage along one edge of the crystal as shown in Fig. 5. In the arrangement shown in Fig. 8, both halves of the crystal mav be used bv connections as ;hown, or an E.M.F. of natural frequency approximating to that of the crystal mav be applied to plates 13 and a resultant E.M.F. of frecueney determined solely by the crystal may be taken off at plates 13<1>. Specifications 245.810 and 258,707, [Class 40 (iv), Telephones &c.], are referred to. The Specification as open to inspection under Sect. 91 (3) (a) comprises also arrangements for obtaining transverse vibrations by arranging one electrode 17 centrally. This may be effected by drilling a central hole 16, Fig. 9, or by saw-cuts, Fig. 12. In another arrangement, the central electrode may comprise one or more light spiral springs, Fig. 11, which give a larger electrode area. This subject-matter does not appear in the Specification as accepted.