Analysis of piezoelectric ceramic length‐expansion‐mode resonators using interdigital electrodes for both poling treatment and ac excitation

Abstract

AbstractWhen interdigital electrodes set on the surface of a rectangular piezoelectric plate are used for poling and ac excitation, a length‐expansion‐mode resonance in the Lamé‐mode system alone is emphasized. However, this does not occur easily in conventional length‐expansion‐mode resonators having a uniform poling across the thickness and electrodes on the entire surface. The proposed method offers a resonator with very little spurious oscillation in this mode. To obtain a guideline for designing interdigital electrodes, the relationships between the width of electrodes, the period of electrodes and the capacitance ratios were analyzed theoretically in detail by using conformal mapping. The strength and direction of the dc electric field of this type of resonator at a poling state vary with positions, since the poling treatment is also carried out with interdigital electrodes, i.e., its dielectric constant, piezoelectric constant, and elastic constant vary significantly with positions. In this analysis, the distributions of these constants in various positions were considered by using the dependence of the poling electric field obtained experimentally, and they are not averaged. The results of the analysis agree well with the experimental values. The characteristics of two configurations were compared: a piezoelectric longitudinal coupling with electrodes set rectangularly to the direction of vibrations; and piezoelectric transverse coupling with electrodes set in parallel to it.