The key factor to the miniaturization of piezoelectric devices is power density, which is limited by the heat generation or loss mechanisms. There are three loss components in general in piezoelectric vibrators/resonators, i.e., dielectric, elastic and piezoelectric losses. The mechanical quality factor, determined by these three factors, is the Figure Of Merit (FOM) in the sense of loss or heat generation. In this paper, we introduce a new loss phenomenology and innovative measuring methods based on the theory. First, quality factors at resonance and antiresonance for the k31, k33, kt and k15 vibration modes are derived theoretically, and the methodology for determining loss factors in various orientations (i.e., loss anisotropy) is provided. For simplicity, we focus on materials with ∞ mm (equivalent to 6 mm) crystal symmetry for deriving the loss factors of a polycrystalline ceramic, and 14 different loss factors among 20 in total can be obtained from the measurements. Second, we propose the experimental methods for measuring both mechanical quality factors QA and QB at the resonance and antiresonance modes: a continuous admittance/impedance spectrum measuring method (traditional with temperature rise) and a burst mode (to circumvent the temperature effect).

We developed a new high power piezoelectric characterization system, and report its application for characterizing the resonance and antiresonance vibration performance in this paper. Although the traditional constant voltage measurement was improved by using a constant current measurement method, the conventional technique was still limited to the vicinity of the resonance. In order to identify a full set of high power electromechanical coupling parameters and the loss factors of a piezoelectric, both resonance and antiresonance vibration performance should be precisely measured simultaneously. However, the high power characterization across antiresonance has not been addressed previously in the literature. Our new high power characterization system reported here is capable of measuring the impedance/admittance curves by keeping the following various conditions: (1) constant voltage, (2) constant current, (3) constant vibration velocity of a piezoelectric sample, and (4) constant input power. In addition, the system is equipped with an infrared image sensor to monitor the heat generation distributed in the test sample. We demonstrated the usefulness of the new system in a rectangular piezoelectric plate in the whole frequency range including the resonance and antiresonance frequencies. The results clearly concluded that compared to the resonance mode, the antiresonance mode exhibits a higher mechanical quality factor Q M and the same vibration amplitude/velocity under a smaller input electrical power and lower heat generation. This may suggest a superiority of the antiresonance mode usage to the resonance mode from the high power application viewpoint (i.e., ultrasonic motors, transformers).

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