Coil-Tac: Coiled Capacitor Mechanism With Liquid Metal for Tactile Sensing

Exploiting the high conductivity and fluidity of liquid metal, Coil-Tac is a soft transduction mechanism based on measuring change in capacitance as a flowable liquid metal core moves within a conductive helical coil. Using finite difference methods, a model is derived that estimates the response of Coil-Tac with various coil pitches to within 0.0502 pF of our experimental results in the range of 0–2.5 pF, corresponding to a lateral liquid metal movement of up to 35 mm. The Coil-Tac mechanism is demonstrated to be capable of oscillatory tactile sensing at 5 Hz and touch location estimation when coupled to a soft interface. The mechanism coupled with the interface is sensitive enough to locate the centre of the contact to within 0.23 mm, and estimate the incident angle between the axis of the dome and a flat surface to within 0.53$^{\circ }$.