Confinement of Vibrotactile Stimuli in Narrow Plates: Principle and Effect of Finger Loading

On a touch surface, providing a local vibrotactile feedback enables multiuser and multitouch interactions. While the vibration propagation usually impedes this localization, we show in this article that narrow strip-shaped plates constitute waveguides in which bending waves below a cut-off frequency do not propagate. We provide a theoretical explanation of the phenomenon and experimental validations. We thus show that vibrations up to a few kHz are well confined on top of the actuated area with vibration amplitude over 1 micrometer. The principle was validated with piezoelectric actuators of various shapes and a linear resonant actuator (LRA). Investigation of the effect of a fingertip load on the system through theory and experimentation was conducted and revealed that almost no attenuation was brought by the fingertip when using low frequency evanescent waves. Finally, a perceptual validation was conducted and showed dynamic stimuli with a large frequency spectrum could be felt and distinguished.