Electromagnetic Tokamak Field Effect Induced by Toroidal Dipole Metamaterials

Tokamak-like electromagnetic field confinement, characterized by closed-loop poloidal current distributions and quasi-homogeneous localized energy circulation, provides a unique topology for constrained field manipulation, typically relying on massive, high-power coil systems. In this work, the electromagnetic tokamak field effect is generated by proposing a passive subwavelength toroidal metamaterial element for exciting the dominant toroidal dipolar mode. The proposed metamaterial element consists of eight split-ring resonators arranged in a toroidal geometry, the toroidal dipolar contribution of which is investigated by multipole expansion. The induced tokamak field effect features confined simulated quasi-homogeneous field distribution and spatially consistent resonant field enhancement up to 13.6-fold under the plane-wave illumination. A 3 × 3 metamaterial array prototype was fabricated and experimentally validated, exhibiting a consistent quasi-homogeneous field distribution with fluctuations below 0.81 dB. The proposed toroidal dipole metamaterial and the induced electromagnetic tokamak field effect provide a potential strategy for generating quasi-homogeneous localized field distribution for the upcoming applications in electromagnetic shielding, three-dimensional sensing, and ultra-resolution imaging.