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.