Broadband Mechanoresponsive Liquid Metal Sensors

Stretchable electronics have the fundamental advantage of matching the complex geometries of<br/>the human body, providing novel opportunities for real-time biomechanical sensing. We report a<br/>new method for high frequency AC-enhanced resistive mechanical sensing that leverages the<br/>deformability of liquid metals to enhance low-power detection of mechanical stimuli in wearable<br/>electronics. The fundamental mechanism for this enhancement is the geometrical modulation of<br/>the AC skin effect, which induces current crowding at the surface of a liquid metal trace. We<br/>apply 1-50 MHz excitation in combination with DC sensing to quantitatively pinpoint<br/>mechanical modes of deformation such as stretching in-plane and compression out-of-plane that<br/>are otherwise impossible to distinguish by traditional methods. This novel sensing method,<br/>which we explore by FEA simulations, is experimentally employed in a glove to simultaneously<br/>detect various hand gestures and tactile forces as well as a respiratory sensor band to monitor<br/>breathing rate. In addition to this multifunctionality, we show how this AC sensing modality can<br/>enable high SNR readout at 100X lower power consumption compared with DC, enabling a new<br/>generation of efficient wearable radio-frequency (RF) systems for haptics and biomedical<br/>sensing.