Ultrahigh-Resolution Wireless Capacitance Readout Based on a Single Real Mode in a Perturbed PT -Symmetric Electronic Trimer Sandwich

High-performance interrogation of an inductor-capacitor microsensor has been a long-standing challenge due to the limited size of the sensor. Parity-time ($PT$) symmetry, an intriguing concept originated from quantum physics, has been utilized to improve the spectral resolution and sensitivity of the conventional readout circuit, while the $PT$-symmetry condition has to be satisfied. In this work, a sandwich-type wireless capacitance readout mechanism based on perturbed $PT$-symmetric electronic trimer without manual tuning of the reader circuit is proposed. Theoretical eigenvalue analysis by solving the system equations shows that the system exhibits single real mode in weak coupling regime whose eigenfrequency changes in response to the capacitance of the neutral resonator. Furthermore, the proposed readout system exhibits wider readout capacitance range compared to the standard $PT$-symmetry-based system while retaining higher $Q$ factor compared to the conventional readout method, which has been validated with the experimental prototype based on printed circuit board. Our work not only enriches the underlying theory of non-Hermitian physics, but also shows potential applications in scenarios where longer interrogation distance is required, such as implanted medical devices, parameter detection in harsh environment, etc.