Reflection of ultrasonic Lamb waves produced by thin conductingstrips

摘要

The reflection of ultrasonic Lamb waves produced by a periodicnarray of thin conducting strips deposited on a piezoelectric plate wasninvestigated both theoretically and experimentally. A repetitivelynmismatched transmission line model was used to analyze the performancenof the reflector. The reflection coefficient of a single strip is givennby R≈Δv/v, where Δv/v is the fractional change innvelocity produced by electrical shorting of the propagation surface. Annattractive property of Lamb waves is that they can provide a much highernvalue of Δv/v than is possible with surface acoustic waves.nTherefore, efficient Lamb wave reflectors can be realized withnrelatively few strips in the reflector. For example, reflectionncoefficient very close to unity, R≈0.98, has been obtained in a Lambnwave reflector consisting of just 12 strips on a Y-X lithium niobatenplate. The reflector has been used to realize a unidirectionalntransducer (UDT). A Lamb wave delay line consisting of two UDTs showsninsertion loss of less than 3 dB with fractional bandwidth greater thann7%