Measurement of Surface and Lamb Waves with Application on Acoustic Sensing and Non-Destructive Evaluation

This paper summarizes the design and fabrication of several novel ultrasound transducers for measuring surface and Lamb waves. The experimental setup and measurement method for each developed transducer are also addressed. According to piezoelectric materials being used, two types of ultrasound transducers are discussed which are PVDF focusing transducers and micro-machined PZT transducers. For the PVDF transducers, a defocusing measurement along with a V(f,z) waveform processing technique are developed which allow accurately determination of dispersion curves of either surface waves of a layered medium or Lamb waves of a thin plate. Elastic properties of coating layers and thin plates are therefore non-destructive determined. For the micro-machined PZT transducers, a differential type wave velocity measurement is developed which is extremely sensitive to small wave velocity variation. Hence, the mechanical and dielectric loading effects of a fluid to the Lamb waves of a piezoelectric plate are experimentally and theoretically characterized, which can be used for acoustic sensing of fluids.