Robust capacitive touch sensor using liquid metal droplets with large dynamic range

In this paper, we introduce an interesting design for a capacitive touch sensing mechanism using liquid metal (LM) droplets to maintain the advantage of the floating electrode (robustness) and simultaneously improve the dynamic range of the device. LM has electric conductivity, thus it can be used as a floating electrode, and it simultaneously has the deformability of liquid, which does not suffer from fatigue. Therefore, the robustness of the device can be improved. The sensor uses changes in capacitance caused by the overlap area between the LM droplet and a pair of flat-bottom electrodes to improve its dynamic range. To verify the performance of the sensor, a total of 36 sensing elements with a spatial resolution of 2 mm and arranged in a 6 × 6 array were successfully fabricated using micromachining techniques. The performance of the fabricated device was analysed by one-cell and multi-touch tests. The device has a large dynamic range (∼40 pF). In addition, using the merits of the device, we applied our concept to an end-effector.