Reflection of ultrasonic Lamb waves propagating in thin piezoelectric plates

This paper presents the first report on the reflection of ultrasonic Lamb waves produced by a periodic array of thin conducting strips deposited on a piezoelectric plate. A repetitively mismatched transmission line model was used to analyze the performance of the reflector. The reflection coefficient of a single strip is given by r approximate to Delta v/v, where Delta v/v is the fractional change in velocity produced by electrical shorting of the surface. An attractive property of Lamb waves is that they can provide a much higher value of Delta v/v than is possible with surface acoustic waves. Efficient Lamb wave reflectors can therefore be realized with relatively few strips in the reflector. Experimental results obtained with a number of Lamb wave reflectors confirm this hypothesis. For example, reflection coefficient very close to unity, R approximate to 0.98, has been obtained in a SH wave reflector consisting of just 12 strips. To obtain comparable reflection with SAWs, one would need to use more than 70 strips. Details of the theoretical analysis used and experimental results obtained will be presented.