The application of tactile, audible, and ultrasonic forces to human fingertips using broadband electroadhesion

We report an approach to controlling friction forces on sliding human fingertips in order to produce simultaneous vibrations across an exceedingly broad range of tactile, audible, and ultrasonic frequencies. Vibrations in the skin can be felt directly by the fingertip, and vibrations in the air can be heard emanating from the proximity of the finger. We introduce and detail an experimental apparatus capable of recording friction forces up to a frequency of 6 kHz, and describe a custom designed electroadhesive amplifier and system with a flat current to force magnitude response throughout this entire measurement range. Recordings with a MEMS microphone confirm the existence of ultrasonic forces applied to the finger and further reveal the ultra wideband capability of broadband electroadhesion. Implications for the design of surface haptic and general audio-haptic displays are discussed.