Calculation and measurement of bianisotropy in a split ring resonator metamaterial

A medium that exhibits artificial magnetism can be formed by assembling an array of split ring resonators SRRs —planar conducting elements that exhibit a resonant response to electromagnetic radiation. The SRR exhibits a large magnetic dipole moment when excited by a magnetic field directed along its axis. However, the SRR also exhibits an electric response that can be quite large depending on the symmetry of the SRR and the orientation of the SRR with respect to the electric component of the field. So, while the SRR medium can be considered as having a predominantly magnetic response for certain orientations with respect to the incident wave, it is generally the case that the SRR exhibits magnetoelectric coupling, and hence a medium of SRRs arranged so as to break mirror symmetry about one of the axes will exhibit bianisotropy. We present here a method of directly calculating the magnetoelectric coupling terms using averages over the fields computed from full-wave finite-element based numerical simulations. We confirm the predicted bianisotropy of a fabricated SRR medium by measuring the cross polarization of a microwave beam transmitted through the sample. We also demonstrate that the magnetoelectric coupling that gives rise to the bianisotropic response is suppressed by symmetrizing the SRR composite structure and provide measurements comparing the cross polarization of the symmetric and asymmetric structures. © 2006 American Institute of Physics. DOI: 10.1063/1.2218033