An Ultra‐Miniaturized Fiber Humidity Sensor Based on Near‐Parallel Ion Pathways Induced Efficient Water−Electricity Conversion

Abstract Humidity sensors are vital for ambient monitoring, but existing sensors focus on moisture absorption, overlooking the indispensable role of ion channels in the water‐electricity conversion process. Here, an ultra‐miniaturized fiber humidity (MFH) sensor based on near‐parallel ion pathways is presented. The well‐designed nanochannels significantly facilitate ion transport due to the stable charge distribution and the confined ions migration within near‐parallel nanostructure, which improves the water‐electricity conversion efficiency of moisture‐sensitive fibers. Optimized nanochannels enable the MFH sensor to improve the response/recovery speed by ≈5 times compared to the disordered nanochannels. Additionally, the MFH sensor can be woven for ultra‐miniaturization (0.50 mm²), which is much smaller than current sensors. Therefore, the integrated MFH sensor array demonstrated exceptionally high spatial resolution (sensor density of 1 mm⁻¹), highlighting its potential in flexible wearables. This work provides new optimization strategies and assembly means for designing the high‐performance humidity sensors of the next generation.