GB464894A - Improvements in or relating to piezo-electric crystals - Google Patents

Abstract

464,894. Piezo - electric crystals. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Sept. 9, 1936, No. 24610. Convention date, Sept. 30, 1935. [Class 40 (v)] A quartz piezoelectric crystal is cut so that its principal surface is inclined at an oblique angle of 37‹ to 40‹ to the optic axis and parallel to an electric axis, and its length and width are proportioned so as to render the crystal capable of oscillating at one frequency only in its electric axis mode of vibration. If the desired frequency is f and x is the dimension in the electric axis, fx=k where k is a constant determined from the curves A of Figs. 7, 8, 9, according as the low, normal, or upper mode of vibration is to be utilized. The ranges of the constant k so taken are further limited by consideration of curves B, relating k to the frequency variation with temperature. Thus, a valve of k is selected corresponding to a zero frequency variation with temperature, e.g. for curve A, Fig. 8, k will be 242.1. The abscissa corresponding to this is 0À463 and is the ratio of the width to the length. The thickness d is determined by the equation d = f<1>k, where f<1> is the frequency of oscillation in the thickness dimension and k = 67. The curves of Figs. 7, 8, 9, correspond to an angle of 38À6‹ between the optic axis and the face of the crystal. The Specification indicates how the curves are modified for other angles between 37‹ and 40‹.