Abstract
We propose and experimentally demonstrate a parity-time-symmetric electronic system exhibiting the self-dual emitter-absorber property with a remarkable modulation depth in the radio-frequency (rf) region. The dramatically different rf responses between the emitter and absorber modes may allow detection of ultrasmall conductive or reactive perturbations. Our measurement results show that even a perturbation on the order of 10(-2) can greatly change the system's output intensity by more than 30 dB, consistent with the theoretical prediction. The measured sensitivity is far beyond the sensitivity of traditional sensors based on a Fabry-Perot resonator, and may lead to monotonic rf sensors with high sensitivity and resolvability.