GB457342A - Improvements in or relating to piezo-electric crystals - Google Patents

Abstract

457,342. Piezo - electric crystals. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Bokovoy, S. A.; 705B, Woodlynne Avenue, West Collingswood, and Baldwin, C. F.; 100, Manheim Avenue, Oaklyn, both in New Jersey, U.S.A.) May 31, 1935, No. 15929. [A Specification was laid open to inspection under Sect. 91 of the Acts, Jan. 3, 1936.] [Class 40 (v)] Relates to methods of cutting piezoelectric oscillators from a mother crystal, so as to operate with zero temperature coefficient or with a desired positive or negative coefficient. The method covers the cutting of crystals intended to vibrate at a frequency which is a function of their thickness dimension, or of their contour, i.e. their length or breadth. As shown in Figs. 1, 2 and 3 the crystal element 4 or 5 is cut from a block 3 forming part of the section 2 cut at right-angles to the optical axis Z. The top and bottom surfaces of the element 4 or 5 are parallel to an X axis, but are inclined at specified angles both to the Z axis and to the plane of a major face M or a minor face N of the mother crystal. A formula is given which relates the thickness of the crystal element to the required frequency, the length or breadth in this case being immaterial. The element can be selected to give a definite positive or negative temperature coefficient by varying the angle of cut. Alternatively, as shown in Fig. 12, cutting of the crystal element 4 or 5 is orientated with respect to W-axes (which cut the X axes at certain specified angles) and is tilted about a Y axis to secure the desired temperature coefficient. Fig. 9 shows how the characteristics of a " cut varies as it is rotated through 360‹ about the optical or Z axis. The method is also applied to the cutting of " contour " crystals which vibrate either along their length or breadth, irrespective of their thickness.