SilicaGel-Integrated Chipless RF Tag for Humidity Sensing

In this paper, a new microwave sensor is presented for contactless monitoring of humidity in dry air stream. The platform is based on a pair of passive ring resonators, which are magnetically coupled. The chip-less sensing tag is implemented on a flexible RF substrate and is coupled to the reader resonator, as a result, contactless and highly sensitive sensing has been enabled. The tag integrated within commercial silica gel adsorbent holders to monitor the humidity. The microwave sensor operates at 3.47 GHz including the coupled tag. The noncontact nature of the proposed structure enables humidity monitoring in harsh industrial environment.