Robust Wireless Temperature Sensing With High Resolutions Based on LC Fano Resonance

Abstract

LC passive wireless sensors are excelling in wearable devices with the advantages of wireless sensing and compatibility with multiple fabrication processes. Classical LC sensing systems face the challenges of misdiagnosing at different interrogation distances since the frequency detection of the Lorentzian resonance is affected by mutual coupling. Here, we propose the asymmetric LC Fano resonance to improve robust wireless interrogation by detecting the peak and valley frequencies simultaneously, making the frequency calibration insensitive to the coupling coefficient. To form the asymmetric Fano resonance in an LC wireless sensing system, we introduce a negative impedance compensation (NIC) to the classical LC temperature sensor embedded in a wearable bandage. A sharp resonant peak is generated and able to be detected by coupling to a continuum resonance provided by an external readout. Moreover, high-temperature resolutions are observed by monitoring the peak and valley frequencies of Fano resonance. We test the wearable temperature sensing bandages from $36~^{\circ }$ C to $42~^{\circ }$ C to imitate the healing and inflammation process. Compared to the traditional LC sensors with Lorentz resonance, the Fano-resonant sensor features coupling-independent interrogation and possesses temperature resolutions as high as $0.07~^{\circ }$ C. The proposed Fano-resonant LC wireless sensing system provides a potential approach for robust wearable sensing systems with high resolutions.