Enhanced Magnetic Field Shielding with Metamaterial Hourglass Lens

This paper presents a novel design for a metamaterial (MM) hourglass lens which can achieve a significant improvement in magnetic field shielding when compared to a MM slab of equal dimensions. The shape of the structure and the material properties of near-zero permeability MM(s) are used to attain this enhancement. The improvement in the magnetic shielding is demonstrated by theoretical studies involving magnetic flux models and 3D full-wave electromagnetic simulations. The operating frequency for this study is chosen to be 13.56 MHz in the ISM band, and the relative permeability of the mu-near-zero MM is considered to have a real component of 0.02 and a loss tangent of 0.01. The MM hourglass lens is constructed using a staircase approximation of planar MM slabs. The mutual inductance of a two-coil system with coils of 5 cm radius at different separation distances and with the MM lens or slab is used to compare the shielding efficiency between the MM structures. The proposed lens design constructed using 15 slabs provides about 12% reduction in mutual inductance at a thickness of 30 mm and about 45% reduction at a thickness of 70 mm when compared to the MM slab for a coil separation distance of 25 cm.