Dual-Coupling Induced Singularities and Ultra-Sensitivity in Non-Hermitian Electromagnetic Systems

We herein introduce a new type of non-Hermitian sensing system respecting the parity-time (PT) symmetry, which is established by a dual-coupling (i.e., inductive and capacitive coupling at the same time) scheme. We demonstrate that this dual-coupled structure can not only exhibit the spectral degeneracy-exceptional point (EP)-but also an additional divergent point (DP). Further, the occurrence of this DP can be engineered as will by manipulating the strength of two types of coupling, which may even make the DP coalesce with the EP. Beyond the EP, we show that the existence of DP may greatly enhance the eigenfrequencies bifurcation, rendering an unprecedented sensitivity. We also provide experimental validations by practical measurements of temperature and relative humidity, which agree well with our theoretical analysis. Our work may open new paradigms for investigating PT-symmetric electronic sensors.