A Study on Oscillation Circuits for a Piezoelectric Self-powered Ultrasonic Sensor

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  • 圧電素子を用いた自己給電型超音波センサの発振回路の検討

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<p>This study concerns an oscillation circuit for a piezoelectric self-powered active sensor which has a functionality of vibration energy harvesting to power itself and ultrasonic excitation of the host structure. The proposed oscillation circuit in this study consists of a piezoelectric element attached to the structure, a negative resistance element called lambda diode, a lowpass filter, a bias coil, and a capacitor as a power source which is charged by the energy harvesting circuit. In this paper, the nonlinear voltage-current curve of the lambda diode was approximated by a piecewise linear function, and its nonlinear behavior was investigated by using the describing function method. The limit cycle frequency and amplitude were obtained by drawing the loci of the describing function of the lambda diode and the admittance of the remaining circuit including the piezoelectric element on the complex plane. The resultant limit cycle frequency agreed with the experimental result with high accuracy. The limit cycle amplitude had 20% error which may be caused by the approximate calculation of the describing function.</p>

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