Efficient reflectors for ultrasonic Lamb waves.

The reflection of ultrasonic Lamb waves produced by a periodic array of thin conducting or mass loading strips is investigated both theoretically as well as experimentally. A repetitively mismatched transmission Line model is used to analyze the performance of the reflector. It is found that Lamb waves propagating in thin elastic plates can be reflected much more efficiently than surface acoustic waves (SAWs). Efficient reflectors can therefore be realized with relatively few strips in the array. The characteristics of a number of reflectors fabricated on thin plates of lithium niobate have been evaluated and found to be in good agreement with theory. The reflectors have been used to realize various useful devices such as unidirectional transducers, low loss, wide bandwidth delay lines, and Lamb wave resonators.