Experimental Analysis of UHF RFID Tags Mounted on PET Liquid Containers Subjected to External Forces

This paper presents the design of a battery-free UHF RFID tag for fluid-based sensing applications. The proposed system utilizes a polyethylene terephthalate (PET) container as the antenna substrate, which is filled with a mixture of three fluids: air, water and oil. A vibration detection RFID sensor is implemented by exploiting changes in the tag antenna's input impedance caused by variations in the state of the fluids within the PET container. These variations are captured using a self-tuning integrated circuit (IC). The method is initially validated through experiments involving a microstrip transmission line (TL) and an RFID tag. In the experiment, the fluid container is shaken to mix the fluids, inducing changes in the dielectric properties of the substrate. These changes are analyzed using S-parameter measurements for the TL and sensor code readings for the self-tuning RFID IC. The experimental results demonstrate the sensor's ability to continuously monitor fluid state changes during the relaxation process following an initial disturbance. This study highlights the potential of the proposed approach for real-time fluid state monitoring in sensing applications.