Propagation characteristics of leaky Lamb waves in a liquid-loaded double-layered substrate consisting of a thin piezoelectric ceramic plate and a thin glass plate

Abstract

Operational performance of a leaky wave interdigital transducer on a double-layered substrate composed of two thin plates, a piezoelectric ceramic plate and a glass plate, is described for the purpose of two kinds of transducer functions—one for the effective radiation of underwater ultrasound and the other for liquid sensing. Two parameters, electromechanical coupling coefficient (k2) and mode conversion ratio (C), are evaluated on a two-dimensional p-fd plane as the fundamental factors for the leaky wave transducer, where p is the thickness ratio of the ceramic part and the double-layered substrate, and fd is the product of the frequency (f ) and the total thickness of the substrate (d). For an effective transducer for underwater ultrasound, both k2 and C should be large at a certain operation point of p and fd. The maximum transducer efficiency from the product of k2 and C in the second mode operation in the case of p=0.37 is three times as large as that in the case of a single-layered piezoelectric ceramic plate. For constructing a concise liquid sensing device, on the other hand, a combination of large k2 and small C is required. A condition satisfying the above requirement is recognized in the third mode operation in the case of p=0.55 and fd=3.4 MHz⋅mm. The combination of a piezoelectric ceramic plate and a glass plate is promising for realizing highly functional ultrasound transducers for underwater ultrasound and for liquid sensing.