Piezoelectric Wafer Active Sensor Embedded Ultrasonics in Beams and Plates

In this paper we present the results of a systematic theoretical and experimental investigation of the fundamental aspects of using piezoelectric wafer active sensors (PWASs) to achieve embedded ultrasonics in thin-gage beam and plate structures. This investigation opens the path for systematic application of PWASs for in situ health monitoring. After a comprehensive review of the literature, we present the principles of embedded PWASs and their interaction with the host structure. We give a brief review of the Lamb wave principles with emphasis on the understanding the particle motion wave speed/group velocity dispersion. Finite element modeling and experiments on thin-gage beam and plate specimens are presented and analyzed. The axial (S0) and flexural (A0) wave propagation patterns are simulated and experimentally measured. The group-velocity dispersion curves are validated. The use of the pulse-echo ultrasonic technique with embedded PWASs is illustrated using both finite element simulation and experiments. The importance of using highfrequency waves optimally tuned to the sensor–structure interaction is demonstrated. In conclusion, we discuss the extension of these results to in situ structural health monitoring using embedded ultrasonics. KEY WORDS—Piezoelectric wafers, piezoelectric sensors, active sensors, in situ diagnostics, structural health monitoring, piezoelectrics, ultrasonics, elastic waves, P-waves, Swaves, shear waves, axial waves, flexural waves, Rayleigh waves, Lamb waves, plate waves, surface waves, wave speed, dispersion, group velocity, pulse-echo, acoustoultrasonics