Research On Driving And Parameter Measurement System Of Piezoelectric Device

Piezoelectric ultrasonic transducer is a kind of piezoelectric device, which energyis provided by the ultrasonic signal generator. The basic requirement for driving thetransducer is that with a fast and stable output-response ultrasonic signal generator.According to admittance circle, this paper is analyzed the relationship betweenfrequency and the equivalent circuit parameters of transducer in the vicinity of theresonance frequency. And it also determined the current in the transducer almost reachesthe maximum and the phase difference between the voltage and current nearly zero,when transducer occurs resonance. Hence, dynamic resonance method was adopted tomeasure the parameters in this paper. The current and phase difference are chose as thefeedback quantity for the control system. The central control part is AVR SCM andFPGA in system which signal is generated by the DDS integrated chip and amplitudecontroller is composed by the DAC and analog multiplier. The microcontroller program,FPGA program and host computer program were also completed.Single current feedback cannot quickly determine the gradient of frequency, whilethe resonant frequency and anti-resonant frequency of the transducer corresponding tothe phase difference both are zero. Suppose that only used the phase difference as thefeedback quantity, it may be tracked to the anti-resonant frequency in mistake. Thecurrent and phase difference were all chosen as the feedback quantity in this paper, and Ialso designed the frequency tracking algorithm. Taking the non-linear relationshipbetween the phase difference and frequency into account, we let different phasedifference to get different proportional gain, in order to obtain the appropriate stepfrequency and accelerate the tracking speed.Finally, we have done some device test using the system referred above and get agood result. The setting time of output current waveform probed by oscilloscope is2-3ms.