Toward Flexible Wireless Pressure-Sensing Device via Ionic Hydrogel Microsphere for Continuously Mapping Human-Skin Signals

Flexible pressure-sensing systems have attracted more attention recently. Here, a novel kind of flexible wireless pressure-sensing device is reported based on a chip-type ionic alginate hydrogel (IAH) microsphere, which is sandwiched by a folded polyethylene terephthalate film with a continuous silver pattern as both antenna and electrode through a stack of double-sided tape as bonding frame. The whole device can be seen as an inductance (L)/capacitance (C)/resistance (R) (LCR) oscillation circuit and the main sensing mechanism is based on the variation of contact electric double-layer capacitance (C-EDL) at the IAH microsphere/electrode interface. Through theoretical analysis, the performance of the wireless pressure sensor is optimized step by step. Under the defined parameters, the final sensitivity of device is up to 9.32% kPa(-1) (to working frequency) with a detectable unit as low as 25 Pa, showing with great repeatability and durability. In addition, the efficiency of this wireless devices is further verified through continuously mapping human-skin signals (muscle motion at human hand, pulse signals at human wrist), exhibiting excellent sensing performance.