Realization of significant magnetic-field enhancement in a photonic-doped epsilon-near-zero medium

Photonic doping can tailor the effective permeability of an epsilon-near-zero (ENZ) medium to realize an epsilon-and-mu-near-zero (EMNZ) state, thus enabling strong magnetic-field localization within the dielectric dopant. Here, we demonstrate magnetic-field enhancement in a photonic-doped ENZ medium through theoretical analysis, full-wave simulations, and experimental validation. Numerical results reveal the dependence of magnetic-field enhancement on the dopant's permittivity, size, number, and arrangement. Experimentally, a metallic waveguide cavity operating near the cutoff frequency is employed to emulate an ENZ medium, with a dielectric rod serving as the dopant. Internal magnetic-field distributions are measured using a low-perturbation coplanar-waveguide (CPW) magnetic probe through distributed tiny apertures. At the EMNZ frequency, the measured field enhancement factor reaches 59.5 at the rod center, closely matching the simulated probe-based value of 64.6. These results demonstrate robust magnetic-field concentration within the dopant, offering potential applications in directive antennas, electromagnetic (EM) sensing, and laser ignition.