A Systematic Study of Wearable Multi-Modal Capacitive Textile Patches

Abstract

We present a study on wearable capacitive patches with engineered dielectrics to be used as a strain sensor and a piezoelectric sensor with multi-modal sensing capabilities. The patches consist of a parallel plate capacitive structure with highly (100%) stretchable textile electrodes and silicone or PDMS elastomers. The gauge factor of the capacitive strain sensor is enhanced two-fold with the inclusion of high- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}$ </tex-math></inline-formula> Barium Titanate (BTO) nanoparticles dispersed in the silicone dielectric layer without sacrificing their excellent linearity or superb durability easily exceeding 2000 cycles. In addition to enhanced dielectric response, inclusion of BTO as well as other additives, namely PZT and PVDF-TrFE, in PDMS also induces piezoelectricity in the sensors at different weight ratios systematically studied by bending and vibrational tests. Corona poling of the piezo dielectrics improves their voltage output by at least two folds. Besides the piezoelectricity, tests on unpoled samples also uncovered evidence for triboelectricity in the nanocomposites. The proposed textile patches can simultaneously detect multiple stimuli such as strain, pressure, temperature, bending, vibration, and acoustic feedback. Deployed in appropriate locations and geometries, the patches can capture critical information on the type, strength, and duration between episodic movements and environmental factors, as demonstrated via a shoe-insert, elbow tracker, respiratory and heart-rate monitors. Accordingly, capacitive textile patches offer unique capabilities for multi-modal sensing in biomedical and robotic applications as well as overall system integration that are advantageous for sensor fusion and machine learning.