An exceptional-point wireless sensor featuring non-reciprocal and electronic-tunable coupling

Abstract

Traditional exceptional-point (EP)-based wireless sensors using inductively coupled inductor–capacitor resonators require mechanical EP tuning, which is cumbersome and limits practical applications. In this Letter, we propose an electronic EP tuning strategy by adding an inductive coupling branch to the original gain–loss pair. This branch replicates and scales the original energy mode to create a unidirectional, electrically tunable coupling. The non-reciprocal coupling breaks the parity-time symmetry yet retains the EP. EP tracking is achieved by monitoring the single zero-crossing of the imaginary part of the input impedance using a vector network analyzer. Eigenfrequency retrieval from the same zero-crossing avoids the linewidth broadening inherent in conventional readout methods. Simulations and experiments validate the flexible electronic tuning and a 1/2-power-law sensitivity enhancement for a tiny loss perturbation. This work markedly enhances the practicality of fully passive EP-based sensors and is readily extendable to other non-Hermitian platforms, such as photonics and acoustics.