Abstract：The Langevin sandwich structure is widely used in the stator design of ultrasonic motors, in which the piezoelectric vibrator works in the thickness vibration mode. Because the existing equivalent circuit model does not fully consider the inherent loss characteristics of the piezoelectric vibrator, it is unable to evaluate the mechanical quality factor. In this paper, the decoupling electromechanical equivalent circuit model of a piezoelectric vibrator with three types of losses is firstly established to study the influence of three types of inherent losses of piezoelectric ceramics on the mechanical quality factor. Then, the electromechanical equivalent circuit model of the Langevin sandwich structure is established, and the influence of material and structural parameters on resonance frequency, anti-resonance frequency and electromechanical coupling coefficient is discussed. Finally, a Langevin structural prototype is fabricated, and its impedance-frequency characteristics and vibration characteristics are tested. The accuracy of the theoretical model is verified. This paper provides theoretical support for designing a vibrator structure with a high mechanical quality factor and further develops a high-performance ultrasonic motor by revealing the differential influence of the inherent loss of piezoelectric vibrators on its output characteristics.
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