Active on Skin Sensing Using Stretchable Substrates and Liquid Interconnects
As microprocessors, MEMs devices, and discreet sensors become smaller and more power-efficient, the platforms for interconnecting these components into a complete system have remained largely unchanged over the last 30 years. Conventional rigid and flexible circuit board materials based on copper-clad laminations are mechanically incomparable to the pliability of human skin as they are unable to stretch and conform to the range of natural human motions. This fundamental limitation of conventional printed circuit board (PCB) technology provides a unique challenge for the designers of wearable medical devices. Both data integrity and patient compliance depend upon the ability of sensors to remain comfortable while in intimate contact with the skin. Contact electrode systems like EKG, EEG, and EMG sensors require continuous skin contact to collect reliable data. Here we present a novel construction of an actively amplified EMG sensor system fabricated using a thermosetting stretchable film substrate, carbon-doped silicone conformal dry electrodes, and a eutectic gallium indium gel conductor to form the interconnect and via system. The assembly is entirely pliable and can be held comfortably against the skin using a conventional compression wrap while data is continuously collected. This novel, pliable, electronic system is compared with an identical rigid circuit built with traditional electrical assembly methods and indicates improved performance without discomfort associated with rigid PCB EMG systems.