Extraction of patch-induced Lamb waves using a wavelet transform

An attempt is made herein to locate the fundamental anti-symmetric Lamb wave in lead zirconium titanate (PZT) integrated beams using a wavelet transform. The Lamb wave was generated 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 type of continuous wavelet transform employing the Gabor wavelet was applied to extract the dominant wave group from the measured acceleration signals. On the basis of the frequency and speed of the extracted wave, the flexural modulus was determined. Wave speed measurement was performed on an aluminum beam and a brass beam. The moduli thus characterized were compared with the reference values, as obtained by the resonant beam method. Such a comparison provides a means to assess the effectiveness of the wave extraction process. It was found that the patch-induced Lamb wave exhibited a frequency higher than that of the actuating sine bursts. Hence, the correct frequency value should be employed in order to achieve an accurate characterization of the flexural moduli. Moreover, a successful wave extraction process requires an appropriate frequency term in the Gabor wavelet. With the above considerations, the characterized moduli harbor a range of error from 1.3% to 5.1%, thus signifying the effectiveness of the wave extraction process.