Magnetoelectric‐Field Electrodynamics: Search for Magnetoelectric Point Scatterers

Abstract

Resonant scattering of electromagnetic (EM) waves by small particles is considered as one of the basic problems in metamaterial science. At present, special subwavelength resonators are considered as structural elements in chiral and bianisotropic metamaterials. There is a general consensus that these small scatterers behave like "artificial atoms" with strong electrical and magnetic responses and an interconnection between these responses. However, the observed effect of magnetoelectric (ME) coupling in these meta-atoms is not associated with the near-field manipulation properties caused by intrinsic magnetoelectricity. This arises the question whether ME point scatterers of EM radiation really exist. In this paper, we show that there are mesoscopic structures with electric and magnetic dipole-carrying excitations that behave like point scatterers with their inherent magnetoelectricity. In such subwavelength resonators, coherent oscillations of the electric polarization and magnetization can be considered as quasistatic oscillations described by electrostatic (ES) and magnetostatic (MS) scalar wave functions. The ME resonance effect arises from the coupling of two, ES and MS, oscillations. The near fields of these resonators, called the ME near fields, are characterized by simultaneous violation of time reversal and inversion symmetry. In study of ME fields and EM problems associated with these fields, we put forward the concept of ME-field electrodynamics.

Magnetoelectric Energy in Electrodynamics: Magnetoelectricity, Bi(an)isotropy, and Magnetoelectric Meta‐Atoms

“…This effect of mesoscopic-scale quantization is described based on the quasi-magnetostatic and quasi-electrostatic scalar wave functions. [43,[64][65][66][67] Such quantized states are well observed in the cavity ME effect. This effect demonstrates the relationship between the ME meta-atom and the ME photon.…”

“…The energy eigenstate problem can be correctly formulated as the quasistatic resonance problem in a subwavelength domain. [29,43,64,65] This distinguishes our concept from the concept of ME energy density proposed in ref. [76].…”

“…They constitute the imaginary ("chiral") part of the ME energy. [29,43,64] This analysis can clarify the physical meaning of the energy density terms in Equation (31).…”

“…[4] When the basic concepts of bianisotropy are analyzed from the EM far-field characteristics (without noting about any mechanism of the energy of local coupling between the electric and magnetic dipoles), we just have only "far-field illusion of the intrinsic magnetoelectricity". [43] It becomes obvious that when studying ME energy, it is necessary to use the near-field technique which is based on the effects of violation of both spatial inversion symmetry and time reversal symmetry. There is a common consensus [44][45][46] that, in the dipole approximation, local ME characteristics of bianisotropic meta-atoms can be retrieval from parameters of a small dipole antenna illuminated by a time-harmonic plane wave.…”