The present paper describes a thin and flexible electrotactile display having an array of microneedle electrodes that present tactile sensation on the forearm in a two-dimensional manner at low voltages. Tactile displays elicit tactile sensation by artificially stimulating tactile receptors. Electrotactile displays stimulate tactile receptors electrically and can be designed to be thin, light, and flexible, and therefore wearable. We developed an electrotactile display having microneedle electrodes that penetrate the high-impedance stratum corneum, thereby decreasing the threshold voltage to provide tactile sensation. Stimulation at a point and in a line was successfully demonstrated in our prior work. In this paper, we demonstrate an electrotactile display that can present tactile sensation in a plane with two-dimensionally distributed microneedle electrodes. The display is expected to increase the variety of tactile sensation and the amount of available information. We conducted experiments to determine the optimal gap between the microneedles to efficiently present a plane-like sensation. When the gap is too large, the subjects do not perceive a plane-like tactile sensation but only point-like stimulations at the electrodes, whereas the small gap leads to difficulties in manufacturing. A gap of 3 mm was experimentally found to be optimal. Using the manufactured electrotactile display, smooth/rough sensation in a plane was successfully presented on the forearm.
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