Influence of Transducer and Signal Processing on the Measurement of Ultrasonic Nonlinear Parameter

Abstract

indicating that LiNbO3 transducers are advantageous for the measurement of the pure ultrasonic nonlinearity of materials.; The ultrasonic nonlinear parameter is generally measured from the magnitudes of the fundamental frequency component and the second-order harmonic frequency component. To measure the magnitudes of the fundamental frequency component and the second-order harmonic frequency component, spectral analysis of the received signals based on the fast Fourier transform is generally performed. In this study, the effects of ultrasonic transducer and signal processing in accordance with the window function were experimentally researched for the measurement of nonlinear parameters. To analyze the effect of the window function, the Hanning window and Tukey window were compared. The two window functions showed similar performance with sufficient reliablity for the measurement of nonlinear parameter. To confirm the effects of the transducer, lithium-niobate (LiNbO3) piezoelectric transducers (disk type, 36° Y-cut, 5 MHz: thickness 0.67 mm, 10 MHz: thickness 0.33 mm) of 0.95 cm in diameter and lead-zirconate titanate piezoelectric transducers (PZT, commercial type) of 0.63 cm in diameter were compared. For the experiment, Al 6061-T6 specimens were prepared with eight heat-treatment times. The change in the nonlinear parameters according to the heat treatment time was compared for the different transducers. The change in the nonlinear parameters was similarly measured regardless of the transducer type. However, the inherent transducer nonlinearity was lower in the LiNbO3 transducers than the PZT transducers