Measuring surface wave propagation during vibrotactile stimulation

The objective of the present set of experiments was to characterize the properties of travelling waves induced by vibrotactile stimulation of the skin and to determine whether these varied significantly at three different locations on the body: the palm of the hand, the forearm and the thigh. These locations are often considered for use in tactile displays used for spatial cuing. A custom designed flexible printed circuit board containing an array of accelerometers was fabricated for this purpose. The results indicated that there was a marked decrease in the frequency of vibration when measured on a compliant surface such as the skin as compared to a rigid fixture and that the magnitude of this decrease varied significantly among the sites tested. The surface wave elicited by the vibrating motor on the skin was markedly attenuated by 8 mm on all the sites tested but was still measurable at 24 mm, suggesting that for the type of motor tested the spacing between motors in a display should exceed 24 mm if precise spatial localization is required. There were differences between the glabrous and hairy skin in terms of the frequency and amplitude measured for the same mechanical input. These findings suggest that it is important to take into consideration the mechanical properties of the skin when designing tactile displays as these will affect the responses of cutaneous mechanoreceptors.