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An autonomous and continuously operating Radio Frequency Identification (RFID) temperature sensor is designed, manufactured, and tested. This sensor is battery-free and can detect temperature threshold crossings for multiple (room-to-cold and cold-to-room) temperature cycles, respectively. The proposed sensor conveys temperature threshold crossings through the controlled switching of its operating frequency within the 902-928 MHz Ultra High Frequency (UHF) RFID band. For the first time, shape morphing cold-temperature reactive Liquid Crystal Elastomers (LCEs), which provide reversible actuation, are utilized. The proposed sensor design consists of a patch antenna with a customized slot. A passive mechanical switch is connected across this slot and provides the frequency switching as it is activated and deactivated. The integration of this switch with the antenna is achieved using a co-simulation method. Furthermore, the cold-temperature reactive LCE triggers the switch when a temperature violation has occurred, thereby switching the operating frequency of the sensor based on temperature changes. Additionally, a high-dielectric constant substrate and a single matching network that operates at two discrete frequencies are used to design our compact frequency-domain temperature sensor. Moreover, based on the RFID platform, this sensor operates effectively in close-proximity to other sensors. Also, is provides identification and temperature information through an autonomous, continuous, and cost-effective design. Therefore, the proposed sensor has the potential for operation in the Internet of Things (IoTs) applications, where large amounts of data is collected from numerous sensors to extract valuable information for the benefit of users, manufacturers, and delivery companies in the virtual domain of the internet. Finally, ANSYS HFSS and Circuit Designer are used for the simulation modeling. The performance of our sensor is validated using measurements and simulations that agree very well.

The antenna design presented here supports a new generation of battery-free RFID sensing technology in which the antenna element dynamically conforms to the changing environment in a controlled manner. Specifically, we propose a sensing antenna that reversibly and repeatedly switches operating frequencies from 905MHz to 923.5 MHz based on a temperature threshold crossing. The developed antenna is a patch antenna matched to an RFID IC and integrated with a customized slot. The antenna shifts its operating frequency by using a novel thermal responsive polymer or Liquid Crystal Elastomer (LCE) which is programmable and operates reversibly. Furthermore, 4D printed LCE structures are to be coupled with an Ultra Subminiature Mechanical Switch (USMS) which shorts the slot when the LCE is activated. Finally, as the thermal excitation is removed, the switch returns to the open state. The short and open states of the switch will enable the frequency shift of the antenna structure. In this paper, the methodology of the frequency shift in the patch antenna and the novel LCE switch mechanism are described through simulation and measurements.

A novel passive RFID temperature sensor is proposed in this paper. The sensor utilizes an integrated T -match network (TMN) for matching the antenna to the RFID IC. Furthermore., the sensor detects changes in temperature by shifting its operating frequency. The frequency shifts are accomplished by a 3D printed liquid crystal elastomer (LCE) array that can reversibly actuate depending on the temperature to move the antenna and change its distance from the ground plane.

A passive RFID temperature sensor is presented. This sensor design utilizes a patch antenna integrated with a customized slot. Using a novel Liquid Crystal Elastomer (LCE) switch, the slot is shorted when the temperature reaches a specified threshold. When the temperature decreases below this threshold, the switch retracts to the original position. As a result, the antenna operates at one of two states corresponding to a controlled shift in frequency within the RFID band. Additionally, a single impedance matching network is designed to accommodate a favorable match between the two antenna states and the RFID IC.