GB1073964A - Improvements in or relating to electromechanical oscillators - Google Patents

Abstract

1,073,964. Electromechanical oscillators and filters. SIEMENS A.G. May 20, 1964, No. 31573/66. Divided out of 1,073,962. Heading H3U. A mechanical resonator oscillating in the bending mode carries two piezoelectrio crystals having their planes perpendicular to the longitudinal axis of the resonator, being located predominantly in a region bounded by two adjacent nodes of oscillation, one crystal on each side of the neutral axis of the oscillator, and being mutually oppositely polarized, the crystals being arranged to divide the resonator into two distinct parts. In Fig. 1, steel bars 1, 2 are united by two crystals 3, 4 which are soldered to the bars via layers of silver used for applying the polarizing voltages. A gap S prevents parasitic oscillations and permits the directions of polarization to be opposite. Further resonators can be attached at the nodes 7, 8 to provide a multistage filter. A quadripole element can be obtained by including a second pair of crystals in a further gap in the bar (Fig. 3, not shown). This pair may or may not be of the same thickness as the first pair. The phase of the output then depends on the relative directions of polarization of the two pairs of crystals. Alternatively, the crystals can be divided by a conducting layer in a plane at right angles to the axis of the bar (Fig. 4, not shown). In another form of construction (Fig. 8, not shown) pairs of crystals are included in one or both arms of a tuning fork. These crystals may be divided by a conducting, layer as in Fig. 4. The resonating member may be of quartz instead of steel and may be of circular instead of rectangular cross-section. Harmonic suppression using the arrangement of the invention is described in Specification 1,073,962.