Flexible Electrostatic Transducers for Wearable Haptic Communication*

We describe a wearable thin-film flexible electrostatic transducer (FET) design capable of delivering haptic stimulation directly to the skin over a broad frequency range. The FET vibrates a curved electrode on a thin film against the skin to generate perceivable displacement. Performance was characterized and studies were carried out to benchmark the comfort and perceptibility on human subjects. Specifically, we conducted a psychophysical experiment to estimate detection thresholds at low (26Hz) and high (260Hz) frequencies and estimated the maximum level at which the stimuli remained comfortable. The displacement response of the FET was highly nonlinear, actuating close to either zero or maximum displacement after a threshold driving amplitude. The 260Hz vibrations were detected at lower displacements than the 26Hz vibrations. In user studies, the detection thresholds indicated that the current FET design achieved a 10dB perceivable stimulation range at both frequencies. No significant difference was found for gender or forearm location. Participants found all low amplitude signals to be comfortable, while at maximum amplitude the low frequency (26Hz) signal was preferred. The present study provides a methodology to quantitatively characterize actuator performance in terms of human perception.