Ultrasonic Impedance Measurement System Development Based On Chaotic Duffing Oscillator

Applications for the piezoelectric devices tested, an ultrasonic impedance measuring system of piezoelectric devices is developed, which has taken a ARM Cortex-M3 to control the core, the theory of zero-cross detection to measure the phase difference, and the switching algorithm to obtain accurate parameters.Its bandwidth ranges from 1kHz to 900 kHz, with its stepping accuracy 0.1 Hz.Based on the equivalent circuit model of piezoelectric devices, using the theory of admittance circle diagram to measure the transducer impedance parameter and the theory of zero-cross detection to measure the phase difference, an impedance measuring system of piezoelectric devices performance parameters is developed. In the established system, a sine wave with fixed amplitude and variable frequency is generated by a Microcontroller, After being amplified by power amplifier, the piezoelectric devices is driven to vibrate by the generated sine wave at high frequency. Then, the microcontroller collects the voltage, current and phase difference during the working process of piezoelectric devices. The collected signals are transmitted to PC by the serial port RS232 and the impedance characteristics parameters and graphics of piezoelectric devices can be displayed. Therefore, we can obtain relevant performance parameters of the piezoelectric devices.When it comes to the hardware, the system consists of six major components, which was composed by the sweep signal generation module (DDS), power amplifier module, resistance switching module, a signal processing module, True RMS voltage and current signals acquisition module, the control module etc. In addition, it has also made a detailed elaboration to the optical isolators, serial communications and so on.When it comes to the Software, the control system of the C software under lower computer has been developed to control the effective operation of each module in Keil uVision5. Based on the man-machine interactive interface of Labview, the PC of impedance measuring system can achieve five kinds of characteristic curves, which contains frequency-Logarithmic impedance, frequency-phase, frequency-admittance real part\ imaginary part, frequency-impedance real part\imaginary part of piezoelectric device,and can also calculate impedance parameters of piezoelectric device. Finally, results of the established impedance test system are compared under impedance analyzer PV70 domestic and international standards Agilent4294A. The experimental results demonstrate the feasibility of the sets of equipment hardware and software systems, the developed system is capable of measuring the main parameters of piezoelectric devices and of displaying the dynamic characteristic impedance curves, the developed impedance measurement system can also be used for the parameters testing and performance evaluation of piezoelectric devices. Meanwhile, for the system deficiencies, methods of the chaotic Duffing vibrator to detect weak signals are introduced, which can detect weak signals of strong noise and estimate its amplitude value. This method can give us a new idea and make further signal processing as long as the estimate accuracy is high enough, it is convenient for the test system to do further optimization and improvement.