19 Magnetoelectric Near Fields
525
frequency range. Due to strong coupling of EM waves with dipole-carrying excitations and temporal dispersion of the material, polaritons display enhanced field
localization to surfaces and edges. Properties of vacuum near-fields originated from
a small non-ME (dielectric or magnetic) sample become evident when this sample
has sizes significantly smaller than the EM wavelength in all three spatial dimensions. The matter of fact is that near such a scatter we can only measure the electric
E
or the magnetic field
H with accuracy. As volumes smaller than the wavelength are
probed, measurements of EM energy become uncertain, highlighting the difficulty
with performing measurements in this regime. There is Heisenberg’s uncertainty
principle binding
E and
H fields of the EM wave [13, 24].
Taking all this into account, let us consider now a subwavelength ME sample. The
near-field structure of such a point scatterer is dominated by two types of the fields:
the electric and magnetic fields, which are mutually coupled due to the intrinsic
properties of a ME material. This fact gives us much greater uncertainty in probing
of the fields. In total, such fields can be represented as the structures of cross
E ×
H
or dot
E ·
H products in a subwavelength region. Due to PT symmetry of ME
structure, the ME near fields of a subwavelength sample should be characterized
by a certain pseudoscar parameter. Moreover, supposing that in a subwavelength
region both structures of cross
E ×
H and dot
E ·
H products exist, one should
assume the presence of helicity properties of the fields. It is evident that such a nearfield structure—the ME-field structure—is beyond the frames of the Maxwell theory
description [1].
When we are talking on ME dynamics, we have to refer also to an analysis of
artificial structures—bianisotropic metamaterials. The notion “bianisotropic media”
had been introduced to generalize different effects of coupling between magnetic
and electric properties [25]. The local bianisotropic media is supposed as the media
composed by structural subwavelength elements with “glued” pairs of electric and
magnetic dipoles. The consideration of high-order quadrupole and multipole transitions is actually an account of spatial dispersion [26, 27]. It is assumed that
bianisotropy (chirality) in metamaterials arises from a “local ME effect” [28–31].
Such a “first-principle”, “microscopic-scale” ME effect of a structure composed by
“glued” pairs of electric and magnetic dipoles raises a basic question on the ways
of probing the dynamic parameters, since the near field structure of such a probe
should violate both the spatial and temporal inversion symmetries. However, in metamaterial bianisotropic (chiral) structures, the known experimental retrieval of the
cross-polarization parameters is via far-field measurement of the scattering-matrix
characteristics [32–34]. Far-field retrieved permittivity and permeability frequently
retain non-physical values, especially in the regions of the metamaterial resonances
where most interesting features are expected. Far-field retrieved cross-polarization
parameters of “bianisotropic particles” retain much greater non-physical value. The
observed far-field phenomena of bianisotropy (chirality) can be very weakly related
to the near-field manipulation effects. We can say that the cross-polarization properties of small “glued-pair” bianisotropic particles are incompatible with the effects
of Rayleigh scattering.
525
frequency range. Due to strong coupling of EM waves with dipole-carrying excitations and temporal dispersion of the material, polaritons display enhanced field
localization to surfaces and edges. Properties of vacuum near-fields originated from
a small non-ME (dielectric or magnetic) sample become evident when this sample
has sizes significantly smaller than the EM wavelength in all three spatial dimensions. The matter of fact is that near such a scatter we can only measure the electric
E
or the magnetic field
H with accuracy. As volumes smaller than the wavelength are
probed, measurements of EM energy become uncertain, highlighting the difficulty
with performing measurements in this regime. There is Heisenberg’s uncertainty
principle binding
E and
H fields of the EM wave [13, 24].
Taking all this into account, let us consider now a subwavelength ME sample. The
near-field structure of such a point scatterer is dominated by two types of the fields:
the electric and magnetic fields, which are mutually coupled due to the intrinsic
properties of a ME material. This fact gives us much greater uncertainty in probing
of the fields. In total, such fields can be represented as the structures of cross
E ×
H
or dot
E ·
H products in a subwavelength region. Due to PT symmetry of ME
structure, the ME near fields of a subwavelength sample should be characterized
by a certain pseudoscar parameter. Moreover, supposing that in a subwavelength
region both structures of cross
E ×
H and dot
E ·
H products exist, one should
assume the presence of helicity properties of the fields. It is evident that such a nearfield structure—the ME-field structure—is beyond the frames of the Maxwell theory
description [1].
When we are talking on ME dynamics, we have to refer also to an analysis of
artificial structures—bianisotropic metamaterials. The notion “bianisotropic media”
had been introduced to generalize different effects of coupling between magnetic
and electric properties [25]. The local bianisotropic media is supposed as the media
composed by structural subwavelength elements with “glued” pairs of electric and
magnetic dipoles. The consideration of high-order quadrupole and multipole transitions is actually an account of spatial dispersion [26, 27]. It is assumed that
bianisotropy (chirality) in metamaterials arises from a “local ME effect” [28–31].
Such a “first-principle”, “microscopic-scale” ME effect of a structure composed by
“glued” pairs of electric and magnetic dipoles raises a basic question on the ways
of probing the dynamic parameters, since the near field structure of such a probe
should violate both the spatial and temporal inversion symmetries. However, in metamaterial bianisotropic (chiral) structures, the known experimental retrieval of the
cross-polarization parameters is via far-field measurement of the scattering-matrix
characteristics [32–34]. Far-field retrieved permittivity and permeability frequently
retain non-physical values, especially in the regions of the metamaterial resonances
where most interesting features are expected. Far-field retrieved cross-polarization
parameters of “bianisotropic particles” retain much greater non-physical value. The
observed far-field phenomena of bianisotropy (chirality) can be very weakly related
to the near-field manipulation effects. We can say that the cross-polarization properties of small “glued-pair” bianisotropic particles are incompatible with the effects
of Rayleigh scattering.