A hybrid natural/artificial electrostatic actuator for tactile stimulation

Two modes of tactile communication have been previously explored-electrocutaneous and electrostatic. The electrostatic mode has the significant advantage of not passing electrical current into tissue to effect stimulation of afferent touch nerves. In previous research, we microfabricated electrostatic tactile displays on a 4-inch wafer using standard clean room processing. Tactile perception studies performed on those showed that subjects could discriminate simple spatial geometric patterns. The focus of the current work is to develop a better understanding of the basic mechanism of perception (activation of receptors) during electrostatic stimulation at the skin-display interface. Three displays were constructed with polyimide (PI) dielectric layers of varying thickness. Studies were performed on human subjects to determine the dependence of threshold of sensation on the PI thickness using both the method of limits and two-alternate forced-choice techniques. The theoretical model for the behavior of the interface (a parallel-plate capacitor) suggests a linear relationship between voltage and dielectric thickness. However, our results indicate that the thickness has little or no effect on the threshold. The results are promising in that they may provide an indirect estimate of the depth of the subcutaneous conductive layer of the skin, and a better understanding of the interface.