Enhancing the Remote Distance of LC Passive Wireless Sensors by Parity-Time Symmetry Breaking

Inductor-capacitor (LC) passive wireless sensors are implemented by loose coupling between an external read-out coil and an inductor that receives power through this inductive coupling. They allow for continuous real-time detection in harsh or sealed environments where physical access is difficult. Changes in the sensors are wirelessly and remotely detected by the read-out coil. For implanted medical devices or sealed package applications, however, geometrical constraints such as small and noninvasive coils reduce the inductive coupling, turning the remote distance into a fundamental challenge. Here we propose theoretically and demonstrate experimentally that a parity-time (PT) symmetry breaking regime can be utilized to extend the remote distance of the LC passive wireless sensors. In our prototypes, a capacitive humidity sensor is fabricated with graphene oxide (GO) as a sensing material. The variable capacitance in the external read-out coil is cyclic scanned so as to keep the PT-symmetric configuration. Our results show that the read-out distance of the sensors with the PT-symmetric configuration is approximately 4 times as long as that with conventional methods while keeping the same for their sensitivity. The use of PT-symmetry-breaking regimes for the LC passive wireless sensors should enable the interrogation of applications in the implanted or sealed fields.