Detection of Local Defect Resonance Frequencies for Defect Imaging: A Nonlinear Ultrasound-Based Approach

Abstract

The diagnosing of complicated defects in any structures can be performed effectively with high accuracy using nonlinear wave spectroscopy (NWS). The flaws present in any material can be detected using NWS technique based on local defect resonance (LDR) phenomenon. The present work discusses a technique of detecting the LDR frequency of a flat-bottom hole (FBH) damage by an advanced signal processing tool called bicoherence estimation. The analytical solution of the LDR is used to estimate a frequency sweep range of the input chirp signal. Signal processing using fast Fourier transform and bicoherence estimation is carried out on the output signal for obtaining the damage frequency and its second-order harmonics, respectively. Subsequently, steady-state analysis is performed in order to validate the results obtained from bicoherence estimation. The technique of bicoherence estimation is found to be very efficient in detection of LDR frequencies of plate with FBH.