151 research outputs found
Electromagnetic Boundary Conditions Defined in Terms of Normal Field Components
A set of four scalar conditions involving normal components of the fields D
and B and their normal derivatives at a planar surface is introduced, among
which different pairs can be chosen to represent possible boundary conditions
for the electromagnetic fields. Four such pairs turn out to yield meaningful
boundary conditions and their responses for an incident plane wave at a planar
boundary are studied. The theory is subsequently generalized to more general
boundary surfaces defined by a coordinate function. It is found that two of the
pairs correspond to the PEC and PMC conditions while the other two correspond
to a mixture of PEC and PMC conditions for fields polarized TE or TM with
respect to the coordinate defining the surface
Electromagnetic boundary and its realization with anisotropic metamaterial
A set of boundary conditions requiring vanishing of the normal components of the D and B vectors at theboundary surface is introduced and labeled as that of DB boundary. Basic properties of the DB boundary arestudied in this paper. Reflection of an arbitrary plane wave, incident with a complex propagation vector, isanalyzed for the planar DB boundary. It is shown that waves polarized transverse electric TE and transversemagnetic TM with respect to the normal of the boundary are reflected as from respective perfect electricconductor and perfect magnetic conductor planes. The basic problem of current source above the planar DBboundary is solved by applying TE and TM decomposition for the source. Realization of the DB boundary interms of an interface of uniaxially anisotropic metamaterial half-space with zero axial medium parameters isconsidered. It is also shown that such a medium with small axial parameters acts as a spatial filter for wavesincident at the interface which could be used for narrowing the beam of a directive antenna. Application of DBboundary as an isotropic soft surface with low interaction between antenna apertures also appears possible.Peer reviewe
Towards a systematic design of isotropic bulk magnetic metamaterials using the cubic point groups of symmetry
In this paper a systematic approach to the design of bulk isotropic magnetic
metamaterials is presented. The role of the symmetries of both the constitutive
element and the lattice are analyzed. For this purpose it is assumed that the
metamaterial is composed by cubic SRR resonators, arranged in a cubic lattice.
The minimum symmetries needed to ensure an isotropic behavior are analyzed, and
some particular configurations are proposed. Besides, an equivalent circuit
model is proposed for the considered cubic SRR resonators. Experiments are
carried out in order to validate the proposed theory. We hope that this
analysis will pave the way to the design of bulk metamaterials with strong
isotropic magnetic response, including negative permeability and left-handed
metamaterials.Comment: Submitted to Physical Review B, 23 page
Realization of a spherical boundary by a layer of wave-guiding medium
In this paper the concept of wave-guiding medium, previously introduced for
planar structures, is defined for the spherically symmetric case. It is shown
that a quarter-wavelength layer of such a medium serves as a transformer of
boundary conditions between two spherical interfaces. As an application, the
D'B'-boundary condition, requiring vanishing of normal derivatives of the
normal components of D and B field vectors, is realized by transforming the
DB-boundary conditions. To test the theory, scattering from a spherical DB
object covered by a layer of wave-guiding material is compared to the
corresponding scattering from an ideal D'B' sphere, for varying medium
parameters of the layer
Plasmonic Cloaking of Cylinders: Finite Length, Oblique Illumination and Cross-Polarization Coupling
Metamaterial cloaking has been proposed and studied in recent years following
several interesting approaches. One of them, the scattering-cancellation
technique, or plasmonic cloaking, exploits the plasmonic effects of suitably
designed thin homogeneous metamaterial covers to drastically suppress the
scattering of moderately sized objects within specific frequency ranges of
interest. Besides its inherent simplicity, this technique also holds the
promise of isotropic response and weak polarization dependence. Its theory has
been applied extensively to symmetrical geometries and canonical 3D shapes, but
its application to elongated objects has not been explored with the same level
of detail. We derive here closed-form theoretical formulas for infinite
cylinders under arbitrary wave incidence, and validate their performance with
full-wave numerical simulations, also considering the effects of finite lengths
and truncation effects in cylindrical objects. In particular, we find that a
single isotropic (idealized) cloaking layer may successfully suppress the
dominant scattering coefficients of moderately thin elongated objects, even for
finite lengths comparable with the incident wavelength, providing a weak
dependence on the incidence angle. These results may pave the way for
application of plasmonic cloaking in a variety of practical scenarios of
interest.Comment: 17 pages, 11 figures, 2 table
Isotopic insights into the early Medieval (600-1100 CE) diet in the Luistari cemetery at Eura, Finland
In this article, we present the results of an isotopic study of diet for the early medieval (Merovingian, Viking, Early Christian) humans buried in the unique Luistari cemetery at Eura (ca. 600-1400 CE), southwestern Finland, the largest cemetery of the region. Isotope analysis was conducted on 37 humans for dentine and bone collagen (delta C-13, delta N-15, and delta S-34), and five of them were also studied using compound-specific nitrogen isotope analysis. Dental enamel and/or bone carbonate delta C-13 values were studied from altogether 65 humans, five cattle, and five sheep/goats. The bone and dentine collagen and carbonate data show that throughout the centuries, freshwater fish was a stable part of the diet for the population. Our results do not show systematic dietary differences between estimated males and females, but differences can be large on the individual level. We also discovered a possible temporal change in the enamel carbonate delta C-13 values that could be related to the increasing role of carbohydrates (e.g., crops) in the diet. Luistari burials are well comparable to contemporary Swedish Viking trading communities like Birka in their higher protein intake. But contrary to the wider Viking network, they do not show the same marine signal.Peer reviewe
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