GB1073962A - Improvements in or relating to electromechanical oscillators - Google Patents

Abstract

1,073,962. Electromechanical oscillators and filters. SIEMENS A.G. May 20, 1964 [May 21, 1963], No. 20712/64. Heading H3U. A mechanical resonator of electrostrictively inactive material carries one or more piezo - electric crystals in a slot therein which does not extend beyond the neutral axis of the resonator and lies predominantly in a region bounded by two adjacent nodes of oscillation. In Fig. 1 a steel bar 105 carries in a slot a piezo crystal (e.g. lead zirconate) 106 bounded by silver electrodes 108, 109 and an insulating material 110, e.g. quartz glass, both being on one side of the neutral axis 13. A polarizing voltage is applied to the silver electrodes by leads 116, 117, the latter being at an oscillation node 8. The resonator is mounted by connections 11, 12 at the nodes, which also serve for coupling to further resonators in a multi-stage filter. The crystal and plate 110 can be attached to the bar by coating with metal and then soldering, or by shrink-fitting as the bar cools down. In a modification (Fig. 3, not shown), the glass plate is replaced by a second piezo crystal polarized in a direction opposite to the first so that the alternating stress imparted to the bar by the two crystals act to reinforce one another. Such a pair of crystals may be incorporated in a tuning fork in one or both of the arms, between the prongs (Fig. 6, not shown) or in a slot at the base (Fig. 7, not shown). In the last-named case the system may be operated as a quadripole by including an insulating material such as quartz glass between the crystals (Fig. 8, not shown). Depending on the mutual polarization directions of the crystals the input and output signals are either in phase or antiphase. More than two crystals may be incorporated in the slot (Fig. 9, not shown). In another form (Fig. 10, not shown) the polarizing voltage is applied at right angles to the axis of the resonator to use the transverse piezo-electric effect, and this may be applied to the tuning-fork type as well. The resonator may be of steel or quartz glass and may be of rectangular or circular cross-section. There may be two separate slots carrying crystals, on the same side of the resonator, or opposite one another, or staggered (Fig. 4, not shown).