what is typical coupling coefficient for a toroid

A different configuration proposed by the same group achieves Fano resonance observed in electromagnetically induced transparency system in addition to the toroidal response. used asymmetric mirrored double split-ring structure and a combination of the split ring with dogbone metalization to generate toroidal dipole resonances in planar media. One such 3D configuration is the split loop structures immersed in a dielectric medium. In conventional artificial media, a careful design procedure must be followed to suppress the excitation of electric and magnetic dipoles and to enhance toroidal dipole response. They can also be used for creating a negative refractive index medium. Artificial media exhibiting strong toroidal excitation are used for the creation of electromagnetically induced resonant transparency. Recently, there has been an immense interest in the development of toroidal metamaterials for electromagnetic wave manipulations. The far-field scattering pattern of a toroidal dipole is indistinguishable from that of an electric dipole. Their excitation in the nuclear system was first reported by Zel’dovich. Toroidal dipoles are exempted from classical multipole expansion theory and are caused due to the surface current circulating on a metallic torus along its meridians. The simultaneous excitation of electric and magnetic dipoles is used to tailor both magnitude and phase of transmission/reflection coefficients from a metamaterial composite. An electric dipole is created by the separation of positive and negative charges, whereas a magnetic dipole is generated by virtue of circulating currents on a composite. The classical electromagnetic theory accounts only the scattering from electric and magnetic dipoles in the multipole scattering formalism. Recent research interest has been focused on the scattering studies of a special type of excitation known as toroidal dipoles in composite metamaterial structures.

What is typical coupling coefficient for a toroid