Microwave Characterization of Chitosan Hydrogel and Its Use as a Wireless pH Sensor in Smart Packaging Applications

pH is an important parameter in cold chain applications, identified as a key food freshness indicator, especially in perishables. In view of this, in recent years the traction of low-cost RFID tags has increased, especially in the domain of physical parameter sensing. In this paper, we present the electromagnetic characterization of the chitosan-based hydrogel in ultra-wideband (UWB) frequencies, and its use as a pH sensor with chipless radio frequency identification (RFID) resonators. This paper also shows the complete preparation process of hydrogel, and how chitosan hydrogel changes its physical responses to different pH levels. Moreover, we show the changing hydrogel's physical properties and its correlation with changes in frequency response, enabling low-cost pH sensing in UWB. Chipless RFID sensors are relatively low-cost, but they offer enormous design flexibility in diversified applications such as cold chain, smart packaging, and digital agriculture.