Ultrasensitive and highly stretchable sensors for human motion monitoring made of graphene reinforced polydimethylsiloxane: Electromechanical and complex impedance sensing performance

Abstract

Highly stretchable sensors based on graphene nanoplatelet (GNP) reinforced polydimethylsiloxane (PDMS) are manufactured for human motion monitoring purposes. The strain sensing analysis shows ultra-high gauge factor (GF) values from 40 to 300 at low strain levels up to 106 at high deformations at tensile conditions, and a decreasing sensitivity as GNP content increases. The compressive behavior shows an initial decrease of the electrical resistance, due to the prevalence of in-plane mechanisms, followed by a stable increase, due to the prevalence of out-of-plane mechanisms. In this regard, the Electrical Impedance Spectroscopy (EIS) analysis shows an increase of the complex impedance with increasing compressive strain. The equivalent RC-LRC circuit allows to explain the electrical mechanisms governing the compressive behavior, where the LRC element denotes the contact and intrinsic resistance and the RC element the tunnelling effect. Finally, a proof of concept of human motion monitoring proves the capability of the scalable and easy-manufactured sensors to detect frowning, raising eyebrows, blinking, breathing, blowing and, even, vocal cord motion, where each phoneme follows a unique pattern, with a robust electrical response.