Hetero phase nanocomposite based posture sensor with stretchable connector-sensor interface

Abstract

During recent years, stretchable and flexible sensors for wearable application have gained a lot of interest, but one of the grand challenges that yet to be addressed is the interface between the soft and stretchable sensor and the hard and rigid circuits. The mechanical mismatch between soft sensors and hard connectors to external circuits makes the interface prone to quick failure under mechanical strain and deformation.Here, we report a soft piezoresistive posture sensor made of a hetero-phase nanocomposite with the stretchable connector-sensor interface for the robust sensing of the posture. The hetero-phase nanocomposite is made of Gallium-indium (GaIn) in the liquid phase, carbon nano tube (CNT) and polydimethylsiloxane (PDMS) in the solid phase. The sensor with the Young’s modulus of 158 kPa shows comparable mechanical softness to the skin, which is essential for accurate sensing. Further, we developed liquid metal (LM) based stretchable connections between the soft sensor and the connectors to the external circuit to enable the stable operation of the sensor under deformation. The developed posture sensor has a gauge factor (GF) of 0.815 under 20 % and 0.32 between 20 % and 60 % of applied tensile strain. The sensor was successfully used for sensing of the posture with the sensitivity of 1 % change in its electrical resistance per 10 degrees of neck tilting and strain sensitivity of 2 % of applied strain. The fabrication of the CNT-LM-PDMS posture sensor employed a scalable and cost-effective process. The presented stretchable connection is a solution that can be applied to many soft and stretchable wearable sensors and circuit interfaces with various physiological sensing applications.