Inductive Displacement Sensing Based on Voltage Amplitude Ratio of PT-Symmetric <i>LC</i> Resonators

Inductive coupling can be used to detect variations in displacement or distance of an object when it is shielded by non-metallic obstacles. We propose a wireless displacement sensing system that employs triple sequentially and inductively coupled LC resonators and satisfies the parity-time symmetry. In the proposed system, the voltage amplitude ratio of the two resonators within the reader is detected to sense the displacement change between the sensor and the reader, based on the mode-localized phenomenon of coupled resonators. The coupling coefficient between the two resonators within the reader is taken as a design parameter to optimize the sensitivity for applications with different sensing distance. The system is analyzed analytically using the coupled mode theory. The experimental results show that the sensitivity of the proposed amplitude ratio detection features an order of magnitude higher than that of the traditional frequency shift detection.