Isotropic negative permeability metamaterials and left-handed metamaterials based on miniature structure

We propose an isotropic structure based on double split-ring resonator. We investigate experimentally and numerically the electromagnetic resonant properties of the proposed structure. The result shows that when the electromagnetic wave transmits in the directions parallel and perpendicular to the plane of the split ring resonator, respectively, the resonant bands having the negative permeability both arise at the same frequencies. However, when the electromagnetic wave transmits with oblique angle, the resonant characteristic is still unchanged. That is to say, resonant characteristic of the proposed structure is independent of incidence angle. This result indicates that the proposed structure is an isotropic medium. Combining the proposed double split-ring resonator structure with the wires, the left-handed metamaterial with negative refractive index can be obtained. In addition, the proposed structure has the merit of the miniaturization due to adding the metallic via-hole, which can increase the electric length of the structure. As a result, the resonant frequency of the structure shifts toward lower frequency greatly without increasing the dimension of the structure, and then the structure is still compact in the low frequency case. The introduction of the metallic via-hole can reduce the dimension of the structure by 50%. Therefore, the proposed structure will be a good candidate in the microwave applications such as antennas, filter, among others.