Multimodal Wearable Sensing Systems based on Higher-Order Parity-Time Symmetry

Parity-time (PT) symmetry, a salient landmark in the realm of non-Hermitian physics, reveals that non-conservative Hamiltonians upholding both parity (P) and time-reversal (T) operators may present entirely real eigenspectra [1]–[3]. The advent of PT symmetry has facilitated a plethora of applications, ranging from wireless sensor telemetry and power transmission to dynamic wave manipulation and cloaking [1], [2]. In particular, PT-symmetric systems have exhibited formidable efficacy in ultra-sensitive wireless sensing [3]. It has been observed that the eigen frequencies of such a system bifurcate at an exceptional point (EP), where they demonstrate remarkable sensitivity to minuscule perturbations. This phenomenon culminates in superlative sensitivity, considerably outstripping that of traditional $LC$ resonator-based sensors. Nonetheless, despite these appreciable benefits, current $PT -$symmetric systems are limited to the detection of singular resistive or capacitive parameters. These systems fall short in identifying and discerning each parameter when resistive and capacitive variations coexist. This constraint curtails the applicability of $PT -$symmetric systems in certain real-world scenarios. For instance, in wearable biomedical monitoring situations, multiple biomarkers may vary simultaneously, thereby necessitating more multiplexed detection systems.