Miniaturization of UHF RFID Tag Antenna Sensors for Corrosion Characterization

Three ultra-high frequency (UHF) radio-frequency identification (RFID) tag antenna-based sensor designs for steel corrosion sensing with miniaturization are proposed in this paper. To characterize corrosion, a new antenna adopts the structure of patch antenna with a meanderline feed based on microstrip line theory. The impedance change of the meanderline feed results in detuning in the tag antenna so that this change can be captured with threshold power of the tag. Folded antenna with 3-D structure has been redesigned for miniaturization from the non-folded antenna to reduce the antenna size for spatial resolution enhancement, but the gain is reduced as well as sensitivity. A T-shape antenna is proposed to increase the gain of the miniaturized antenna and the sensitivity. Experimental studies with ThingMagic development kit on dedicated corrosion samples have been undertaken to validate the antenna designs. Resonant frequency features of the developed antenna are studied for corrosion characterization, but the bandwidth of UHF RFID limits the measurement range. Principal component analysis method is applied to evaluate different corrosion stages and reduce environmental interference.