FRF-based lamb wave phased array

Abstract

In the former work, a SHM system was proposed by Kudela et al based on the concept of Lamb wave focusing by the piezoelectric array. According to the pre- and post-compensations, the Lamb wave is focused on the interested point. This allows the system to scan the structure point by point, and then get the damage localization results with high-resolution compared with the beamforming method. However, the efficiency of the method is limited by the ways of signal processing and scanning: 1) the amount of measurement should be equal to the number of inspection points; 2) and the compensation calculations must be done for every measurement. The situation is further compounded by the average step for inspection points. 3) the central frequency of excitation is fixed in the whole processing, to optimize the input waveform means redoing the scan. To address these problems, a novel mode of signal processing for the piezoelectric phased array is proposed based on the Frequency Response Function (FRF). In the present method, the point-by-point scan is replaced by a single measurement for FRF with the “Single Input, Multiple Output” (SIMO) mode, which ensures the scan work can be established in N times excitations (N is the number of piezoelectric wafer, much smaller than the amount of inspection points). Furthermore, the present method is based on FRF, which means the excitation waveform can be virtually selected and changed after recording. It provides a more flexible path for the piezoelectric array concept in SHM. Experiments shows that the developed method is effective for one-dimensional and two-dimensional arrays. The work enriches the intension and implementation of piezoelectric phased array.