Ultrasonic attenuation in acoustic touch panels

This paper presents a quantitative investigation of the sensitivity of Rayleigh waves (RW) and Love waves (LW) to water and finger touches as well as oil. Both theoretical and experimental results are presented. In the theoretical analysis, the influence of water on RW is analyzed using the leaky wave model. Damping of LW by water is modeled by a perturbation calculation of power transfer to a viscous fluid. Experimental measurements of attenuation for both RW and LW are based on the observation of amplitude changes when material is placed on the acoustic path between a pair of wedge transducers. Results confirm that LW touch panels are indeed much more immune to water contamination than RW touch panels. The non-zero viscosity of water leads to a small amount of LW damping by water. Data suggests that with appropriate thresholds, LW touch panels may respond to finger touches while rejecting signals due to water and even light oils, A direction for future research is the theoretical calculation of a finger touch sensitivity of LW using a visco-elastic model of the human finger.