A Patch Antenna with Liquid Crystal Elastomer Switching for Passive RFID Temperature Sensing

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.