WAVLET-BASED ACTIVE SENSING FOR HEALTH MONITORING OF PLATE STRUCTURES USING BASELINE FREE ULTRASONIC GUIDED WAVE SIGNALS

摘要

A wavelet-based active sensing technique for health monitoring of isotropic thin plate-likestructures using baseline-free ultrasonic guided Lamb wave signals is presented. In this technique, abuilt in clock-like piezoelectric (PZT) wafer array of small footprint comprising of a single transmitterand multi-receivers (STMR) is considered. The recorded signals in absence of defects are comparedwith a theoretical model first, and the velocity and amplitude dispersion of guided waves are studied inan effort to tune an appropriate guided wave mode. A five cycle Hanning pulse is transmitted, and thepulse-echo data recorded at the receivers is processed using two novel algorithms, namely damageindex 1 (DI1) and damage index 2 (DI2), based on wavelet transformation to identify defects in theform of cracks and loose rivet holes, which are located both near and far away from the array. In bothcases, damage index (DI) maps are generated for identification of defects in a particular coverage areaon demand by considering the reflected fundamental guided wave modes. Simulation studies are also carried out to demonstrate the effectiveness of the proposed sensing technique. The DI maps clearlyshow higher values of DI at defect locations enabling identification of multiple defects. The DI2 isfound to produce better angular resolution of the defect location than the DI1.