GB788159A - Improvements in and relating to frequency sensitive electro-mechanical apparatus - Google Patents

Abstract

788,159. Electro-mechanical filters &c. PHILCO CORPORATION. May 28, 1954 [May 29, 1953], No. 15850/54. Class 40 (8). [Also in Groups XXXVI and XL (c)J An electro-mechanical device, e.g. a frequency filter, comprises an electrostrictive element, of e.g. Rochelle salt or polarized barium titanate, secured to a vibratory reed. The reed 10, Fig. 2, which may be made of metal or of glass, is secured to the electrostrictive element 14 by means of a thermosetting bonding material. The element is provided with platinum input or output electrodes on its upper and lower surfaces and is polarized along an axis joining these two surfaces. It is secured to a massive base 20 and overhangs this base by a substantial amount in order to allow flexural vibration of the assembly in a vertical plane. The neutral axis of the longitudinal compressive and tensile stresses associated with this vibration is arranged to coincide with the upper face of the element. An input signal may be applied by means of an electromagnet 22 and the output detected by means of a detector 26. Alternatively, the input may be applied by means of a second electrostrictive element secured to the reed 10 opposite the first element 14 (Fig. 4, not shown). Two such assemblies comprising reeds 60, 62, Fig. 5, and elements 66, 68, 70, 72 may be mechanically coupled by a block 74 and mounted on a common base 76. The mechanical coupling 74 causes the reeds 60, 62 to vibrate 180 degrees out of phase, thus minimizing the coupling to the base 76. The pairs of elements 68, 70 and 66, 72 are polarized so that like charges appear on their exposed surfaces, the input and output connections being made as shown. Alternatively, the polarization and connections may be arranged so that one adjacent pair, e.g. 66, 68, of elements serves as the input and the other, e.g. 70, 72, as output. The mechanical coupling block 74 may be secured directly to or formed integrally with the reeds 60, 62 in which case the inner elements 68, 70 may be positioned above the block. One pair of elements, e.g. 66, 68 may be omitted to produce an asymmetric system. Several such pairs of reeds tuned to the same or to slightly different resonant frequencies and having, if desired, different bandwidths may be combined in a single assembly (Fig. 6, not shown). Such a system may be connected up to provide frequency characteristics, e.g. of the band-pass type, Fig. 7A, or of the type shown in Fig. 7B.