Ultrasonic emission tactile sensing

This article describes an ongoing study for a new type of tactile sensing device which is based on instantaneous localization of acoustic emissions caused by touch and/or contact movement. The authors assume a sensor structure which consists of a flexible, spherical, fingertip-like body and a quadruple polyvinylidene fluoride (PVDF, a kind of piezoelectric polymer) sound-sensing matrix embedded at the center of the body. Any points on the spherical surface work as emission sources when touched, and the body transmits the waves inward. The PVDF matrix works as a wideband acoustic emission (AE) transducer which is capable of detecting arrival directions of the waves, packet by packet. This means it can independently resolve and localize a series of ultrasonic emissions caused by a touch and slip. In order to realize this type of tactile sensor, the authors consider two important questions: 1) What kind of ultrasonic emissions appear by touch, and are they detectable? 2) How can the multiple wave packets be resolved and localized instantaneously? For the first question, the authors develop a theory of wave generation at collision, and examine detectability by several experiments. For the second question, the authors show how their sound localization algorithm for an auditory sensor is applied. By assuming the use of this algorithm, and from several experiments under various contact and slip conditions, the authors confirm that the following features and tactile information are obtainable: 1) quick localization of touch and separation; 2) sensation of surface roughness under movements; and 3) quick detection of precursor of slip