A piezoresistive normal and shear force sensor using liquid metal alloy as gauge material

We present a novel normal and shear force sensor by using liquid metal alloy (Ga-In-Sn) as piezoresistive gauge material encapsulated in a polydimethylsiloxane (PDMS) substrate. By using liquid metal alloy as gauge material, it can detect large forces without breaking the sensor wires. Since the liquid-metal piezoresistors deform with the elastomeric substrate, shear and normal forces can be detected with resistance changes of the piezoresistors. Each force sensor comprises a pair of symmetric piezoresistors, which is screen-printed on the cavity of PDMS substrate with tilt angle around 30° to be sensitive to both normal and shear forces. Normal force will compress both piezoresistors as common mode while shear force will shorten one piezoresistor but elongate the other as differential mode. The testing results demonstrate the sensitivity of the force sensor in both normal and shear directions. The hysteresis of the force sensor was also measured.