High-Sensitivity FBG Humidity Sensors Enabled by Electrohydrodynamically Printed Carbon-Nanofiber Functionalized Gratings

Fiber Bragg grating (FBG) humidity sensors face manufacturing challenges in depositing sensitizing films, which are typically complex and costly. Herein, we propose a near-field electrohydrodynamic direct-write printing (NEHDP) strategy to fabricate flexible FBG humidity sensors functionalized with carbon nanofiber@multi-walled carbon nanotube (CNF@MWCNT) nanocomposites. This approach enables rapid, low-cost, and precision patterning of sensing films while maintaining high performance. The optimized sensor exhibits ultrahigh sensitivity (2.0 pm/%RH) with near-perfect linearity (R² = 0.997) in the 11-54% RH range, alongside rapid response/recovery times (1.3 s/2.0 s) at 20 ℃. Although signal saturation occurs at high humidity (75-95% RH), the sensor demonstrates exceptional reversibility (>98% signal retention) and stability (