Evaluation of the Electrical Parameters of a Piezoelectric Transducer Using a Low-Cost Set-Up and FFT Analysis

Ultrasonic piezoelectric technology is under study in fields like biomedical applications, data transmission, or non-destructive analysis. The behavior of the ultrasonic transducer is commonly described by using the Butterworth-Van Dyke model, and the determination of the lumped equivalent electrical parameters of the model is important in applications of ultrasonic devices. The model parameters are assessed by exploiting the values of the transducer admittance at different supply frequencies. In this paper the admittance was derived in the following way. A low-cost set-up designed to apply a periodic square-wave signal to the piezoelectric device under test was developed, the corresponding periodic voltage and current signals of the piezoelectric transducer were acquired by an oscilloscope and, after applying the FFT analysis, the first harmonic of each signal was taken and the admittance was calculated. In order to verify the method, two pairs of piezoelectric devices of two different manufactures were considered. The relevant measurements were carried out by both an LCR meter and by the proposed low-cost method. The determination of the Butterworth-Van Dyke model parameters was performed starting from a preliminary estimation based on analytical relationships, and then by using a MATLAB® numerical identification. The electrical parameters derived from the data sets obtained by the developed prototype system resulted in very good agreement with those obtained by the LCR meter, demonstrating the effectiveness of the low-cost method presented in this paper.