Toroidal Metasurface for High Efficiency Sensing

Revisiting Toroidal Dipolar Moment in Planar Metamaterial

“…However, it should be noted that the lateral incidence is not the only arrangement to excite the toroidal dipolar moment. Recently, the normal incidence of plane EM waves on a PCB has also been studied to generate the toroidal moment by a few groups [1], [13],…”

“…Despite these efforts, the understanding of the operation of the flatland metasurface upon normal incidence leading to the occurrence of toroidal moments is not complete. For example, the circulating magnetic field in the plane of metasurface PCB obtained by the eigenmode analysis gives the impression of the toroidal moment along the normal direction [1]. However, the circulating magnetic field patterns emerging from the eigenmode analysis can also be the result of superimposed degenerate modes.…”

“…However, the circulating magnetic field patterns emerging from the eigenmode analysis can also be the result of superimposed degenerate modes. To explain which mechanism is responsible for the effects observed in [1], a more detailed study is needed. In this work, we revisit the theory of toroidal dipole momenta in planar metasurfaces under normal illumination.…”

“…In this work, we revisit the theory of toroidal dipole momenta in planar metasurfaces under normal illumination. To this end, we carefully examine the results obtained in [1] using multipole expansion of the EM field. We also compute the scattering power of various dipole moments to identify the mechanism producing a circulating magnetic field.…”

“…ETAMATERIAL structures that generate toroidal dipole moments have recently been gaining significant interest due to their unusual property that may help design innovative devices for sensing [1]- [3], electromagnetic energy confinement [4], lasing [5], imaging [6] and modulation [7]. The first theoretical discovery of toroidal excitation was made during the study of Dirac particles under weak interaction by Y. Zel'dovich, who coined the term 'anapole' in 1957 [8].…”