At frequencies above 60 MHz , tuning-free surface acoustic wave (SAW) resonators with many reflectors using Rayleigh SAW are generally used. However, Rayleigh SAW resonators for use in the 60–150 MHz range have some disadvantages such as cost. We have already developed a BGS wave resonator, which is being used commercially in the 30–60 MHz range. When we improved the characteristics of BGS wave resonators by using small-particle , poreless ceramic substrates developed for high-frequency BGS waves, we obtained good resonance characteristics up to 160 MHz. We also obtained good characteristics when we tested the resonator in a DECT demodulator circuit.

Experimental and theoretical studies on the applied voltage-displacement characteristics of a piezoelectric series type bimorph were performed. The displacement increased with an increase in the applied voltage until dielectric breakdown. An electric field higher than its coercive field (E c) can be applied to the bimorph, because its poling direction is opposite to the field, owing to an electric charge balance between its two layers. On the other hand, the displacement of a parallel-type bimorph fell to zero when the applied voltage per unit length equalled E c. The series-type bimorph displayed larger displacement and higher reliability than the parallel-type bimorph.

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