Propagation Characteristics of Leaky Lamb Waves in Layered Substrate and Operation Performance of Interdigital Transducer

摘要

Propagation characteristics of seven lowest modes of leaky Lamb waves in a layered substrate composed of a piezoelectric ceramic plate and an acrylic plate, under the condition of a liquid-solid boundary at the acrylic plate side, are described relative to operation performances of an interdigital transducer (IDT) for underwater ultrasound. The IDT operates effectively for radiating or detecting via a mode conversion from the leaky Lamb wave to a longitudinal wave in a liquid. The incorporation of a layered substrate is useful for multiple-mode operations with higher transducer efficiencies, while retaining sufficient mechanical strength. It is noticeable that the cross points of the velocity curves of the leaky Lamb wave modes and the longitudinal wave modes in two kinds of thin plates for the layered substrate are unique for the transducer operations. The transducer operations are examined in the construction of a liquid delay line. The transducers designed for operating on the cross points of three modes are well explained in comparison between the calculated and experimental results.