Tactile Perception of Electroadhesion: Effect of DC versus AC Stimulation and Finger Moisture

Abstract: Electroadhesion has emerged as a viable technique for displaying tactile feedback on touch surfaces, particularly capacitive touchscreens found in smartphones and tablets. This involves applying a voltage signal to the conductive layer of the touchscreen to generate tactile sensations on the fingerpads of users. In our investigation, we explore the tactile perception of electroadhesion under DC and AC stimulations. Our tactile perception experiments with 10 participants demonstrate a significantly lower voltage detection threshold for AC signals compared to their DC counterparts. This discrepancy is elucidated by the underlying electro-mechanical interactions between the finger and the voltage-induced touchscreen and considering the response of mechanoreceptors in the fingerpad to electrostatic forces generated by electroadhesion. Additionally, our study highlights the impact of moisture on electroadhesive tactile perception. Participants with moist fingers exhibited markedly higher threshold levels. Our electrical impedance measurements show a substantial reduction in impedance magnitude when sweat is present at the finger-touchscreen interface, indicating increased conductivity. These findings not only contribute to our understanding of tactile perception under electroadhesion but also shed light on the underlying physics. In this regard, the results of this study extend beyond mobile devices to encompass other applications of this technology, including robotics, automation, space missions, and textiles.