| 摘要 |
1,073,963. Electromechanical oscillators. SIEMENS A.G. May 20, 1964 [May 21, 1963], No. 20713/64. Heading H3U. An electromechanical resonator is divided into sections by two or more piezo-electric elements so located as to excite one or more even harmonics and suppress the fundamental and odd harmonics, or to excite the funda. mental and one or more odd harmonics and suppress the even harmonics; the piezoelectric elements are each composed of two plates, one on each side of the neutral axis of the resonator and have their planes perpendicular to the longitudinal axis of the resonator so as to excite bending oscillations therein; the piezo-electric elements are located at stress nodes of the harmonics to be suppressed, or are arranged so that the stresses cancel out at harmonics to be suppressed. The construction of the resonator and the attachment of the piezo-electric elements thereto is the same as in Specification 1,073,964. In Fig. 7 two pairs of piezo-electric crystals 15, 17 are located equi-distant from the centre and are oppositely polarized, so that stresses at the even harmonic frequencies cancel out. If the crystals are at nodes of the third harmonic this also will be supprossed, leaving only the fundamental, fifth and higher odd harmonics. By changing the direction of polarization in one 'pair of elements (Fig. 8, not shown) the fundamental, and odd harmonics will be suppressed, and by locating the elements at the nodes of the fourth harmonic only the second, sixth and higher even harmonics will be excited. By adding two further pairs of crystals to the arrangement of Fig. 7 (Fig. 13, not shown) the fifth harmonic will also be suppressed. Modifications of Fig. 7 which produce the same result are (a) one pair of crystals at the centre and one pair at the node of the third harmonic, the two pairs being mutually oppositely polarized (Fig. 12, not shown), and (b) each crystal being replaced by a pair of oppositely polarized crystals with a conductive layer between them (Fig. 10, not shown). |
