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Heat generation by internal loss factors of piezoelectrics is one of the critical issues for high power density piezoelectric applications, such as ultrasonic motors, piezoelectric actuators and transducers. There are three types of internal losses in piezoelectric materials, namely dielectric, elastic and piezoelectric losses. In this paper, a decoupled equivalent circuit is proposed to emulate a piezoelectric disk in radial vibration mode considering all three types of internal losses. First, the decoupled equivalent circuit is derived according to the conventional electromechanical equivalent circuit model. Then, a piezoelectric disk configuration in radial vibration mode is explored and simulated. The resonance and antiresonance frequencies and their corresponding mechanical quality factors are achieved by the proposed circuit. In order to verify the accuracy of the simulation results, the piezoelectric disk is fabricated and tested. Simulation results with the new circuit exhibit a good agreement with experimental results. Finally, the equivalent circuit with only dielectric and elastic losses are simulated and compared which further validates the accuracy improvement of the new equivalent circuit considering all three losses.

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The focus of this paper is to propose a contact model of a radial standing wave ultrasonic motor in order to evaluate the motor performance accurately. The contact behavior between the stator and rotor is characterized by test and a continuous contact on the contact interface is confirmed. A contact model describing the continuous contact is then developed with analytical method. The stator vibration, the force transmission between the stator and rotor, and the output of the motor are analyzed. The impacts of different vibration amplitudes and structural parameters on the performances of the motor are evaluated based on the proposed model. Finally, a test platform for measuring the performance of the motor is built and torque-speed curves of the motor under different voltages are measured. The accuracy of the contact model is verified by comparison between measurement and calculation results. The proposed model not only can be used for design and optimization of the radial standing wave ultrasonic motor but also offers insight into the contact mechanics of standing wave ultrasonic motors.