GB822536A - Improved mechanical filter having mechanical resonators coupled by means employing poisson's effect - Google Patents

Abstract

822,536. Electromechanical filters. STANDARD TELEPHONES & CABLES Ltd. Dec. 6, 1957 [Dec. 6, 1956], No. 38026/57. Class 40 (8). An electromechanical filter comprises a series, 3-8, of longitudinal mode resonators which are loosely coupled by elements 9-13 which utilize Poisson's effect. The resonators and elements are stamped from a single sheet of metal such as nickel and the input and output are provided by coils 2 and 14 on resonators 3 and 8 respectively, utilizing the magnetostrictive effect. Each resonator is half a wavelength long and a quarter of a wavelength wide at the mean operating frequency. The transverse oscillations owing to Poisson's effect at the centre of oscillator 3 are coupled to element 9, which is a quarter of a wavelength long, and cause longitudinal oscillations therein. By a repetition of this process longitudinal vibrations are produced in resonator 8 and are picked up by coil 14. In the embodiment of Figs. 2 and 3 (not shown) the width dimension of alternate resonators is perpendicular to that of the remaining ones. The device of Fig. 4 (not shown), has an odd number of coupling elements each of a quarter of a wavelength long, between two resonators, with alternate elements having a greater width than the remaining ones. Fig. 5 (not shown) has a coupling element an even number, at least four, of quarter wavelengths long which is clamped in the centre. In other modifications the length of the resonators is a multiple of a half wavelength ; the width being a quarter wavelength or an odd multiple of a quarter wavelength in order to prevent direct coupling between the coupling elements.