Reflecting Love waves by 90 degrees

In conventional touch panels using Rayleigh waves, the waves make two right-angle turns on their way from transmitter to receiver. These turns are produced by arrays of mirror-like strips of deposited material tilted 45 degrees. To render these panels insensitive to water, Love waves may be used in place of Rayleigh waves. When two Rayleigh waves intersect under a 90° angle, they share the same up and down motion, so that addition of a point mass produces coupling between the two waves. But, when two Love waves intersect at 90°, their particle motions are orthogonal. We will show that useful Love-wave coupling is best achieved by perturbing the stiffness of the wave-carrying layer, not by adding mass. We have studied reflections of Love waves using two reflector-array test patterns: One, six strips of heavy and soft material deposited on a Love wave substrate, and the second, six grooves etched into the glass top layer of a similar substrate. Amplitude and angular distribution measurements demonstrate that such etched grooves are preferred for Love-wave touchscreen design.