Extraction of patch-induced Lamb waves using a wavelet transform

Abstract

An attempt is made herein to locate the fundamental anti-symmetric Lamb wave in leadzirconium titanate (PZT) integrated beams using a wavelet transform. The Lamb wave wasgenerated by feeding to a surface-mounted PZT patch a voltage in the form of sine bursts.The actuating burst consists of a small number of cycles ranging from 2.5 to 4.5 cycles.The wave propagation was monitored by two miniature accelerometers. A typeof continuous wavelet transform employing the Gabor wavelet was applied toextract the dominant wave group from the measured acceleration signals. On thebasis of the frequency and speed of the extracted wave, the flexural modulus wasdetermined. Wave speed measurement was performed on an aluminum beam and a brassbeam. The moduli thus characterized were compared with the reference values, asobtained by the resonant beam method. Such a comparison provides a means toassess the effectiveness of the wave extraction process. It was found that thepatch-induced Lamb wave exhibited a frequency higher than that of the actuatingsine bursts. Hence, the correct frequency value should be employed in order toachieve an accurate characterization of the flexural moduli. Moreover, a successfulwave extraction process requires an appropriate frequency term in the Gaborwavelet. With the above considerations, the characterized moduli harbor a range oferror from 1.3% to 5.1%, thus signifying the effectiveness of the wave extractionprocess.