Local friction modulation using non-radiating ultrasonic vibrations

Ultrasonic friction modulation can elicit texture sensations on a smooth surface but is currently limited to single touch exploration. This paper introduces a technique that locally modulates tactile friction on a surface to allow for a multitouch exploration. Using this technique, the friction modulation effect is co-located with the actuator through the use of specific non-radiating frequencies. Because waves do not propagate in the surface at these specific frequencies, the vibration amplitude is controlled locally with a simple harmonic excitation of the actuators. The existence of such frequencies is explained through a semi-analytical model of piezoelectric actuation. The ability to locally control the vibration field and to modulate the friction independently for each actuator is demonstrated experimentally on a thin glass plate.