Remote Identification of Liquids Using Absorbent Materials: A Passive UHF RFID-Based Method

Remote characterization of liquids can be beneficial in various industry sectors such as food and oil industries, medical diagnostics, agriculture or waste management. However, current wireless solutions are often expensive and labor intensive. Antenna-based sensors (ABSs) can potentially decrease the complexity and cost of current solutions. Ultra-high frequency (UHF) radiofrequency identification (RFID) sensors for liquid characterization have the potential to provide remote monitoring while fulfilling the previous requirements. This work demonstrates the combined effects of the dielectric properties on the operation of RFID-based sensors and it presents an innovative approach for estimating the dielectric properties of a liquid under test (LUT) from the read range peak frequency and magnitude variations of a UHF RFID tag. The tag antenna consists of a patch-like antenna with an absorbent embedded into its substrate. Filling the absorbent with different LUTs modifies the dielectric properties of the substrate which has a measurable effect on the tag read range. Measurements show that the proposed method together with the specific sensor design enables the dielectric characterization of liquids using an energyefficient and low-cost solution achieving an accuracy over 93.5% and 84% in the estimation of the LUT relative permittivity and the loss tangent, respectively, compared to the transmission line method.