Polyimide-derived laser-induced porous graphene-incorporated microwave resonator for high-performance humidity sensing

Bulk absorption-based microwave humidity sensing characteristics of a laser-induced graphene (LIG) is investigated for the first time. An LIG flake with a 3D network of high-porosity patterned on a polyimide substrate using CO₂ microlaser is integrated into the capacitive sensing region of a 1.985 GHz microwave resonator. The performance evaluation reveals that the developed microwave-LIG sensor linearly detects the wide range of relative humidity (10%-95% RH) with a high sensitivity, short response and recovery times (< 6 s), and small hysteresis (up to 0.375% RH); thus validating the high-performance intrinsic humidity sensing characteristics of LIG at microwave regime.