分割電極屈曲圧電振動子のスプリアスレスポンスの抑圧

抄録

It is well known that in piezoelectric vibrators higher modes can be excited and that these higher modes act as unwanted spurious responses for those vibrators utilizing only the first mode. In most piezoelectric vibrators, the suppression of unwanted spurious responses is of paramount importance. The author has previously reported on the suppression of spurious responses for a piezoelectric bimorph vibrator, it seems, however, that as to a flexural piezoelectric vibrator, the suppression method of its spurious responses over a wide frequency range has not been found except for the suppression methods of partial spurious modes. This paper deals with the suppression method of unwanted spurious responses for a flexural piezoelectric vibrator with a split-electrode and the experimental results. The method for suppressing the spurious response is essentially the same as that described in a previous paper. In the first place, a method is described to suppress the spurious modes of two piezoelectric vibrators with electrodes of different shapes. The split-electrode of a vibrator is formed functionally for the vibrator to vibrate only in the first mode (Fig. 1 (a), (b)). Secondly, the equivalent circuit constants and the capacitance ratios of piezoelectric vibrators of two kinds (Type A, Type B) are shown. The equivalent circuit constants can be adjusted by changing electrode width, but the effect of spurious mode suppression is kept constant. The equivalent capacitances of type A and type B vibrators becomes equal when electrode width ratio t_1/t_2≒0. 707 for both vibrators and when t_1/t_2=0 for type A and t_1/t_2=1. 0 for type B; the same can be said for the equivalent inductances of two vibrators (Fig. 3). The capacitance ratio is minimal when t_1/t_2≒0. 173 for type A and t_1/t_2=1. 0 for type B. The capacitance ratios are compared with those of vibrators with a non-function-shaped electrode (Fig. 5, Fig. 6). Finally, the frequency responses of rectangular flexural piezoelectric vibrators with electrodes of different shapes are shown (Fig. 8, Fig. 9). These results show that a function-shaped electrode is useful for the suppression of unwanted spurious responses when the width-to-length ratio of a vibrator is small.