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Register a new userManipulating the Loss in Electromagnetic Cloaks for Perfect Wave Absorption
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Christos Argyropoulos Mr
Publication date
2009
fields
Physics
and research's language is
English
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We examine several ways to manipulate the loss in electromagnetic cloaks, based on transformation electromagnetics. It is found that, by utilizing inherent electric and magnetic losses of metamaterials, perfect wave absorption can be achieved based on several popular designs of electromagnetic cloaks. A practical implementation of the absorber, consisting of ten discrete layers of metamaterials, is proposed. The new devices demonstrate super-absorptivity over a moderate wideband range, suitable for both microwave and optical applications. It is corroborated that the device is functional with a subwavelength thickness and, hence, advantageous compared to the conventional absorbers.
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A radial-dependent dispersive finite-difference time-domain (FDTD) method is proposed to simulate electromagnetic cloaking devices. The Drude dispersion model is applied to model the electromagnetic characteristics of the cloaking medium. Both lossless and lossy cloaking materials are examined and their operating bandwidth is also investigated. It is demonstrated that the perfect invisibility from electromagnetic cloaks is only available for lossless metamaterials and within an extremely narrow frequency band.
We report experimental and theoretical investigations of coherent perfect channeling (CPC), a process that two incoming coherent waves in waveguides are completely channeled into one or two other waveguides with little energy dissipation via strong coherent interaction between the two waves mediated by a deep subwavelength dimension scatterer at the common junction of the waveguides. Two such scatterers for acoustic waves are discovered, one confirmed by experiments and the other predicted by theory, and their scattering matrices are formulated. Scatterers with other CPC scattering matrices are explored, and preliminary investigations of their properties are conducted. The scattering matrix formulism makes it possible to extend the applicable domain of CPC to other scalar waves, such as electromagnetic waves and quantum wavefunctions.
We consider single-layer arrays of electrically small lossy bi-anisotropic particles that completely absorb electromagnetic waves at normal incidence. Required conditions for electromagnetic properties of bi-anisotropic particles have been identified in the most general case of uniaxial reciprocal and nonreciprocal particles. We consider the design possibilities offered by the particles of all four fundamental classes of bianisotropic inclusions: reciprocal chiral and omega particles and nonreciprocal Tellegen and moving particles. We also study the reflection/transmission properties of asymmetric structures with different properties when illuminated from the opposite sides of the sheet. It has been found that it is possible to realize single-layer grids which exhibit the total absorption property when illuminated from one side but are totally transparent when illuminated from the other side (an ultimately thin isolator). Other possible properties are co-polarized or twist polarized reflection from the side opposite to the absorbing one. Finally, we discuss possible approaches to practical realization of particles with the properties required for single-layer perfect absorbers and other proposed devices.
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Robert N. C. Pfeifer
, Timo A. Nieminen
, Norman R. Heckenberg andn Halina Rubinsztein-Dunlop
2009
Almost a hundred years ago, two different expressions were proposed for the energy--momentum tensor of an electromagnetic wave in a dielectric. Minkowskis tensor predicted an increase in the linear momentum of the wave on entering a dielectric medium, whereas Abrahams tensor predicted its decrease. Theoretical arguments were advanced in favour of both sides, and experiments proved incapable of distinguishing between the two. Yet more forms were proposed, each with their advocates who considered the form that they were proposing to be the one true tensor. This paper reviews the debate and its eventual conclusion: that no electromagnetic wave energy--momentum tensor is complete on its own. When the appropriate accompanying energy--momentum tensor for the material medium is also considered, experimental predictions of all the various proposed tensors will always be the same, and the preferred form is therefore effectively a matter of personal choice.
It is shown that nonlinear elastic pre-stress of neo-Hookean hyperelastic materials can be used as a mechanism to generate finite cloaks and thus render objects near-invisible to incoming antiplane elastic waves. This approach appears to negate the requirement for special cloaking metamaterials with inhomogeneous and anisotropic material properties in this case. These properties are induced naturally by virtue of the pre-stress. This appears to provide a mechanism for broadband cloaking since dispersive effects due to metamaterial microstructure will not arise.
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