A Piezoelectric Micromotor Using Build in Feedback Elelctrode for Vibration Monitoring

Ultrasonic micromotor based on piezoelectric material offers great force with advantages of quick response, low consumption, and electromagnetic radiation free. Its performance depends on the ouput displacement which could be reached its maximum if the driven signal frequency is near the resonant frequency of micromotor. But the resonant frequency is an environment sensitive value. In this paper, a build-in feedback electrode design was used in a ring-shaped piezoelectric micromotor fabricated by lead zirconate titanate film to monitor the resonant frequency shift. Isolated electrodes between top driven electrodes were made as feedback electrode, and the piezoelectric voltage between feedback electrode and common bottom electrode was measured to value displacement variation. Two type feedback electrodes with different shape were determined by simulation, and their voltage-frequency output relationship was valued when micromotor driven by signals with different frequency and amplitude. Two micromotor has resonant frequency of 98.4kHz and 99.8kHz, and the maximum output voltage frequency of feedback electrodes are 98.6kHz and 99.5kHz. When driven voltage increase from 0.5V to 2V, the feedback electrodes output reflected the linear-nonlinear behavior of resonator with the maximum output frequency increased 0.8kHz and 0.9kHz. Those results ensure the ability for feedback electrode to monitor the resonant frequency shift. This design offered an optional method to accomplish closed-loop self-calibration function of micromotor.