Freestanding crosslinked PVA-MSP sensor for wireless humidity sensing applications

A novel two-layer freestanding wireless humidity sensor made of crosslinked water-sensitive polymer, polyvinyl alcohol (PVA), coated on a magnetostrictive particle (MSP) sensor platform was developed. Fundamental research was carried out to optimize the ratio of GA and PVA to obtain a crosslinked PVA with high water absorption capability. The optimized weight ratio of GA:PVA is 1:100. It was found that the sensor signal, i.e., the delta resonant frequency of the crosslinked PVA-MSP sensor, was linearly dependent on the relative humidity (RH) in the testing range. The sensor signal was also linearly dependent on the thickness of the PVA coating layer. Moreover, good stability was observed during a cyclic test of more than 20 days. Besides, temperature dependence tests of the MSP sensors were studied. The newly developed humidity sensor has many advantages, such as low-cost, small-size, and wireless (i.e., remote) detection feature, which is promising to be used as a freestanding wireless humidity sensor in many applications.