A non-differential elastomer curvature sensor for softer-than-skin electronics

We extend soft lithography microfabrication and design methods to introduce curvature sensors that are elastically soft (modulus 0.1-1 MPa) and stretchable (100-1000% strain). In contrast to existing curvature sensors that measure differential strain, sensors in this new class measure curvature directly and allow for arbitrary gauge factor and film thickness. Moreover, each sensor is composed entirely of a soft elastomer (PDMS (polydimethylsiloxane) or Ecoflex (R)) and conductive liquid (eutectic gallium indium, eGaIn) and thus remains functional even when stretched to several times its natural length. The electrical resistance in the embedded eGaIn microchannel is measured as a function of the bending curvature for a variety of sensor designs. In all cases, the experimental measurements are in reasonable agreement with closed-form algebraic approximations derived from elastic plate theory and Ohm's law.