Passive Wireless UHF RFID Antenna Label for Sensing Dielectric Properties of Aqueous and Organic Liquids

The in situ wireless sensing of dielectric properties for organic aqueous solutions with a wide range of relative permittivities is presented. The use of a UHF passive label antenna design attached to either clear borosilicate glass bottle or petri plate is proposed and which allows for the unobtrusive, safe monitoring of the liquid solutions. The meandered dipole antenna (with a parasitic loop matching component) frequency is highly reliant on the chosen container as well as on the liquid present within, and adjusts with shifting dielectric properties. Tested solutions of high relative permittivity (such as water) along with low permittivity, lossy liquids (such as xylene) presented distinctive frequency characteristics with read distances of up to 7 meters for each type of container tested. The sensor was also able to detect ‘unknown’ solutions and determine the dielectric properties by utilizing standard curve analysis with an accuracy of ± 0.834 relative permittivity and ± 0.050 S·m-1 conductivity (compared to a standard dielectric measurement system available on the market). With the accuracy known, tuning the design to fit any necessary frequency is possible as a means to detect specific changes in any one liquid system. This sensor is a possible candidate for discreet real-time monitoring of liquid storage containers and an alternative for low-cost bulk liquid dielectric property identification which could be implemented in areas requiring, constant, or remote monitoring as needed.