General Impedance Matching via Doped Epsilon-Near-Zero Media

The emerging technique of photonic doping endows epsilon-near-zero (ENZ) media with a broadly tunable effective magnetic permeability. Here, we theoretically and experimentally demonstrate that a finite-size doped ENZ region counterintuitively behaves as a lumped circuit element, modeled as a controllable series reactance. Based on this concept, a general matching network is constructed to match a load with arbitrary complex impedance, while, interestingly, its operating bandwidth can also be modified by fine-tuning the dopants' properties. To demonstrate the universality of the concept, different kinds of loads are matched, including microwave circuits, antennas, and absorbing particles. Since this general impedance matching technique is not limited to a specific type of load, nor a specific geometry, and can be readily transplanted from microwave to optical regimes, the proposed methodology facilitates impedance matching for maximum usage of power in quite general scenarios, and thus, exhibits promising potential for broad applications.