Chapter 11 - Wave Tuning with Piezoelectric Wafer Active Sensors

Abstract

This chapter deals with a basic aspect of the interaction between PWAS and structure during the active SHM process, i.e., the tuning between the PWAS and the Lamb waves traveling in the structure. Under electric excitation, the PWAS undergo oscillatory contractions and expansions, which are transferred to the structure through the bonding layer to excite Lamb waves into the structure. In this process, several factors influence the behavior of the excited waves: PWAS length, excitation frequency, wavelength of the guided wave, etc. The interaction of PWAS with the ultrasonic waves generated into the structure is modeled analytically and a solution is developed using space-domain Fourier transform for linear PWAS in interaction with straight-crested Lamb waves and Hankel transform for circular PWAS in interaction with circular-crested Lamb waves. The physical-domain solution is obtained through the residue theorem. Tuning opportunities are shown to exist through matching between the characteristic direction of PWAS expansion and contraction, on the one hand, and the half wavelength of the elastic wave, on the other. The tuning is especially beneficial when dealing with multimode waves because it allows one to select a certain Lamb wave mode as needed by the SHM process. Also studied are the directivity patterns associated with tuning of rectangular PWAS. The theoretical predictions are confirmed by carefully conducted experiments.