Capacitive\nSensors with Hybrid Dielectric Structures\nand High Sensitivity over a Wide Pressure Range for Monitoring Biosignals

Abstract

Various\ndielectrics with porous structures or high dielectric constants\nhave been designed to improve the sensitivity of capacitive pressure\nsensors (CPSs), but this strategy has only been effective for the\nlow-pressure range. Here, a hierarchical gradient hybrid dielectric,\ncomposed of low-permittivity (low-<i>k</i>) polydimethylsiloxane\n(PDMS) foam with low Young’s modulus (low-<i>E</i>) and high-permittivity (high-<i>k</i>) MWCNT/PDMS foam\nwith high Young’s modulus (high-<i>E</i>), is designed\nto develop a CPS for monitoring biosignals over a wide force range.\nThe foam-like structure with hybrid permittivity (low-<i>k</i> + high-<i>k</i>) is facilitated to improve the sensitivity,\nwhile the hierarchical structure with gradient Young’s modulus\n(low-<i>E</i> + high-<i>E</i>) contributes to\nbroadening the pressure sensing range. With the hierarchical gradient\nhybrid structure, the flexible pressure sensor achieves an enhanced\nsensitivity of 2.155 kPa^–1, a wide pressure range\n(up to 500 kPa), a minimum detection limit (50 Pa), and an excellent\ndurability (>2500 cycles). As a demonstration, a venous thrombosis\nsimulation and smart insole system are established to monitor venous\nblood clots and plantar pressures, respectively, which reveal potential\napplications in wearable medicine, sports health prediction, athlete\ntraining, and sports equipment design.