A Reusable Battery-Free RFID Temperature Sensor

A new passive radio frequency identification (RFID) temperature sensor is presented for monitoring the temperature of the surrounding environment of perishable goods, such as foods and medicines, in the cold supply chain. Specifically, this sensor self-tunes between 902 and 928 MHz, operating in the RFID UHF band, as the temperature rises or falls beyond a certain threshold. The novelty of this passive sensor is its ability to operate through multiple high-/low-temperature cycles. The design consists of a planar dipole antenna with a customized integrated T-match network (ITMN) that is actuated above a ground plane. The actuation shifts the operating frequency and is controlled by liquid crystal elastomers (LCEs), which are programmable and reversible temperature-dependent polymers. As a result, our design can be reconfigured to operate at various temperature ranges for which the LCE is designed to operate. The analysis is performed to examine the performance of the proposed sensor near practical items and when it is in close-proximity to an additional sensor with varying orientation. Finally, the sensor's performance was validated through full-wave simulations using ANSYS HFSS and measurements. Both the simulation and measurements agreed well with theory.