Mechanical Strain Monitoring in Plates Using Wavelet Coherence Based Filter of Wideband Ultrasonic Guided Waves

Time reversal or cross-correlation technique can be applied to monitoring the strain in metallic plates by observing the decrease on the time reversal signal's peak. In order to analyze the sensitivity to mechanical strain, the wavelet coherence is applied to wide band guided waves signals. A new time reversed reference signal is obtained by applying a filter based on the continuous wavelet transform. This filter removes the stationary modes, synthesizing a highly sensitive signal which is used as a reference for cross-correlations of the received signals at different strain levels. Experiments revealed that this filter led to a tenfold increase in the sensitivity to longitudinal strain.