GB865093A - Electro-mechanical filters - Google Patents

Abstract

865,093. Electromechanical filters. TOYO TSUSHINKI KABUSHIKI KAISHA. April 18, 1957 [April 23, 1956 (3); Feb., 26, 1957], No. 12759/57. Class 40(8) An electromechanical filter has piezo-electric quartz crystal transducers and mechanical resonators also made of quartz crystal. In the filters of Figs. 1(a) and 1(b) the transducers 1, resonators 2 and coupling members 3 are formed from a single block of quartz. The filter is supported by leads 5 soldered to the electrodes of the transducers. These filters are stated to be of the constant-K type and their electrical analogues are discussed in the Specification. It is stated that the transducers may vibrate in a bending torsional, thickness or lateral mode. The transducers in the embodiment of Fig. 3b vibrate in a longitudinal extensional mode as indicated by the arrows. The transducers are joined by a main coupling rod 10 of length equal to four half-wavelengths, this rod being coupled at intervals of one half-wavelength to three-elongated resonant elements 9. The elements 9 are excited at points displaced from their centre points in such a manner that they are antiresonant at two spaced frequencies. The filter so formed is of the in-derived type being the equivalent of the electrical filter shown in Fig. 3c. Similar antiresonant effects are obtained in the filter of Fig. 4a by asymmetric coupling of the longitudinal-mode transducers and resonators 11, 13. The equivalent electrical network Fig. (4b, not shown) is again of the in-derived type. The construction of Fig. 5a is similar to that of Fig. 3b except that it also includes resonant elements 16 which modify the equivalent circuit of Fig. 3c by the addition of series-resonant elements to the series branches of the circuit.