Soft-matter sensor for proximity, tactile and pressure detection

Efforts in soft-matter sensing with liquid metal (LM) have largely focused on pressure, strain, and bend sensing by measuring changes in capacitance or resistance of LM circuits embedded in a soft elastomer. Here, we show that LM electronics can be used to combine pressure sensing with proximity detection and remote finger tracking - sensing modalities not previously demonstrated in a soft electronic skin (E-Skin). This is accomplished with a novel architecture composed of 9 capacitive sensors arranged in two layers and placed below a spiral-shaped pressure transducer. The E-skin is composed of eutectic gallium-indium (EGaIn) LM alloy and Pt-cured EcoFlex 0030 elastomer. The multi-modal sensor is able to detect the proximity and motion of a finger as it moves above the sensor and is able to detect touch and pressure once the finger comes into contact. Proximity sensing and contact pressure are distinguish by comparing changes in capacitance and resistance of the embedded LM circuitry. Measurements on a cm-scale prototype suggest proximity sensing with a range of 8.7 cm and maximum contact pressure of 110 kPa.