Wireless Ice Detection and Monitoring Using Flexible UHF RFID Tags

Owing to its low relative permittivity, very few microwave sensors have been developed for monitoring ice deposition. This paper presents the first use of UHF RFID tags for wireless RF ice sensing applications. Despite its low permittivity, the existence of ice as a superstrate on a planar ultra-thin dipole antenna can lower the resonance frequency of the antenna significantly. The RFID tags, having a measured unloaded range of 9.4 m, were evaluated for remotely detecting the formation of ice in various scenarios up to 10 m from the reader, as well as monitoring the ice thawing, based on the Relative Signal Strength (RSS) in a phase-free approach. In most RSS-based sensing approaches, the tag's read-range is reduced as the RSS decreases in response to the stimulant. However, the proposed sensing mechanism does not reduce the tag's range; the ice superstrate improves the impedance matching of the tags and increases their radar cross section (RCS), resulting in a 10 m loaded read-range with over 12 dB ice-sensitivity, in an echoic multi-path environment. The proposed sensing mechanism achieves an accuracy of 86% for tags positioned between 0.5 and 10.5 m with various obstructions. When subjected to line-of-sight metallic obstruction, the sensor still maintains 80% accuracy. The long range and high sensitivity of the proposed sensing mechanics show that UHF RFID is a promising method for detecting the formation of ice in future smart cities.