GB1034591A - Electromechanical filters - Google Patents

Abstract

1,034,591. Electromechanical filters. STANDARD TELEPHONES & CABLES Ltd. Jan. 6, 1964, No.557/64. Heading H3U. An electromechanical filter of the kind comprising one or more resonator units of circular cross-section arranged coaxially between input and output transducers and coupled thereto by coaxially arranged rods of circular cross-section comprises at least one further resonator unit disposed coaxially with respect to the other units but beyond the input and output transducers so as not to lie directly in the transmission path coupling them. The resonator units may be of cylindrical shape; alternatively they may be of dumb-bell shape as shown in Fig. 6. The dumb-bell units, Fig. 7 (not shown), are provided with a hole at each end into which the coupling rods or "necks," which may be of a different material, are a push fit. The resonator units are tuned to vibrate in the torsional mode at the operating frequency of the filter; input and output units 28 and 29 are coupled magnetostrictively to coils 34 and 35. The units 36, 37 may be tuned to resonate over the pass-band of units 25, 26, 27 in which case attenuation takes place over this band instead. Alternatively, they may resonate on the same or opposite sides of the pass-band, thus providing attenuation to one or both sides of the pass-band. More than one additional unit may be arranged at either end of the filter.