A Textile Humidity Sensor for Wearable Applications in the 4.0 Era

This work addresses the development, fabrication and experimental characterization of a fully-textile, wearable chipless for humidity sensing purposes in the 4.0 Era perspective. The proposed device is a 50 Ω microstrip line loaded by two chipless resonators. For guaranteeing full integration with clothes, the device was fabricated using a jeans substrate, which also enables the humidity sensing capability of the device. The basic idea is to exploit the variation of the dielectric properties of the jeans substrate as a results of the variation of humidity: this, in turn, leads to a shift of the resonance frequency of the two resonators. Through measurements of the magnitude of the transmission scattering parameter of the microstrip line, it is possible to relate the value of the relative humidity to the value of the resonance frequency of each of the two resonators. Experimental results carried out in controlled environmental conditions (in a range of humidity between in the range 30%–90%) demonstrated the feasibility and the potential of the proposed solution to be used for wearable monitoring purposes.