Demodulation technique to identify nonlinear characteristics of vibro-acoustic NDT measurements

Abstract

A novel approach for nonlinear ultrasonics is presented which uses the demodulated response of a nonlinear vibro-acoustic signal. The demodulation process is similar to the quadrature demodulation process used in telecommunications. It is shown that the demodulation method provides an alternative approach for the analysis of nonlinear behavior compared to the analysis of frequency spectra or other techniques. The proposed method suggests that a representative reconstruction of the time-domain nonlinearity behavior of the system can be obtained. The paper provides a theoretical background to the technique as well as experimental validation. The proposed method is demonstrated for the analysis of four different types of contact acoustic nonlinear interfaces. It is shown that the demodulated waveforms are consistent with the expected mechanical behavior of the different interfaces. The results suggest that this method can provide more insight into the nonlinear behavior of a system compared to conventional spectral amplitude analysis techniques.