The researchers at the Electronics Laboratory of the ETH Zurich have demonstrated the fabrication of an inertial sensor integrated in an on-skin patch. Their proof of concept design uses a eutectic gallium-indium alloy circuit imbedded in a flexible and elastic silicone elastomer. Eutectic gallium-indium (eGaIn) alloys, in which their melting temperature can be tailored around room temperatures, have been used previously in microfluidic channels to create electrodes and electrical circuits [1-3]. This work presents several technical innovations in creating a wearable radio frequency enabled remote read-out of an inertial-sensor.
The skin-patch is fabricated using an Elastosil membrane as a substrate and the eGain RF circuit being sprayed on through the use of a stencil and then encapsulated with a final silicone layer. The inertial sensor is formed by the creation of a silicone blister partially filled with glycerol and an eGain droplet. The movement of this eGain droplet within the blister causes a change in resonant frequency of the inductive coil, which can be read by a remote radio receiver.
The researchers were able to demonstrate read-outs of movement on a human arm on a proof of concept demonstration. They also showed an interesting way to fabricate flexible, stretchable and conformal electronic circuits using spray-on techniques and a liquid metal circuit that provides more flexibility than some previous on-skin electronic circuits .