Cloaking through cancellation of diffusive wave scattering.

A new cloaking mechanism, which makes enclosed objects invisible to diffusive photon density waves, is proposed. First, diffusive scattering from a basic core-shell geometry, which represents the cloaked structure, is studied. The conditions of scattering cancellation in a quasi-static scattering regime are derived.

Molding acoustic, electromagnetic and water waves with a single cloak.

We describe two experiments demonstrating that a cylindrical cloak formerly introduced for linear surface liquid waves works equally well for sound and electromagnetic waves. This structured cloak behaves like an acoustic cloak with an effective anisotropic density and an electromagnetic cloak with an effective anisotropic permittivity, respectively. Measured forward scattering for pressure and magnetic fields are in good agreement and provide first evidence of broadband cloaking.

Thermal invisibility based on scattering cancellation and mantle cloaking.

We theoretically and numerically analyze thermal invisibility based on the concept of scattering cancellation and mantle cloaking. We show that a small object can be made completely invisible to heat diffusion waves, by tailoring the heat conductivity of the spherical shell enclosing the object. This means that the thermal scattering from the object is suppressed, and the heat flow outside the object and the cloak made of these spherical shells behaves as if the object is not present.

Phase properties of high-reflectance two-material periodic mirrors: application to oblique-incidence tunable filters.

Mathematical expressions are developed for the phase-shift derivative with respect to the wavelength, in the case of nonquarter-wave, two-material, high-reflectance, periodic mirrors. These expressions are applied to the case of oblique incidence, and a condition relating the layer indices, which provides identical phase dispersion curves for both the P and S polarizations, is derived. The use of such mirrors in Fabry-Perot filters results in a common peak wavelength for both polarizations when the filter is used at oblique incidence, instead of the two separate spectral peaks usually observed.

Anisotropic conductivity rotates heat fluxes in transient regimes.

We present a finite element analysis of a diffusion problem involving a coated cylinder enabling the rotation of heat fluxes. The coating consists of a heterogeneous anisotropic conductivity deduced from a geometric transformation in the time dependent heat equation. In contrast to thermal cloak and concentrator, specific heat and density are not affected by the transformation in the rotator.

Transformation thermodynamics: cloaking and concentrating heat flux.

We adapt tools of transformation optics, governed by a (elliptic) wave equation, to thermodynamics, governed by the (parabolic) heat equation. We apply this new concept to an invibility cloak in order to thermally protect a region (a dead core) and to a concentrator to focus heat flux in a small region. We finally propose a multilayered cloak consisting of 20 homogeneous concentric layers with a piecewise constant isotropic diffusivity working over a finite time interval (homogenization approach).

Focussing light through a stack of toroidal channels in PMMA.

We propose a transformational design of an axi-symmetric gradient lens for electromagnetic waves. We show that a metamaterial consisting of toroidal air channels of diameters ranging from 23 nm to 190 nm in a matrix of Polymethylmethacrylate (PMMA) allows for a focussing effect of light over a large bandwidth i.e.

Plasmonic space folding: focusing surface plasmons via negative refraction in complementary media.

We extend designs of perfect lenses to the focusing of surface plasmon polaritons (SPPs) propagating at the interface between two anisotropic media of opposite permittivity sign. We identify the role played by the components of anisotropic and heterogeneous tensors of permittivity and permeability, deduced from a coordinate transformation, in the dispersion relation governing propagation of SPPs. We illustrate our theory with three-dimensional finite element computations for focusing of SPPs by perfect flat and cylindrical lenses.

Study of the sticking of a hydrogen atom on a graphite surface using a mixed classical-quantum dynamics method.

The sticking of one hydrogen atom chemisorbed on the (0001) graphite surface is investigated using a mixed classical-quantum method. The phonon modes of the system in the collinear scattering approach are included in the dynamics calculations. The vibrational degrees of freedom of the surface (phonons) are treated classically, while the H-surface motion is treated using a one-dimensional quantum wave packet propagation method.

Transformational plasmonics: cloak, concentrator and rotator for SPPs.

We adapt tools of transformation optics to surface plasmon polaritons (SPPs) propagating at the interface between two anisotropic media of opposite permittivity sign. We identify the role played by entries of anisotropic heterogeneous tensors of permittivity and permeability--deduced from a coordinate transformation--in the dispersion relation governing propagation of SPPs. We apply this concept to an invisibility cloak, a concentrator and a rotator for SPPs.

Negative refraction, surface modes, and superlensing effect via homogenization near resonances for a finite array of split-ring resonators.

We present a theoretical and numerical analysis of liquid surface waves (LSWs) localized at the boundary of a phononic crystal consisting of split-ring resonators (SRRs). We first derive the homogenized parameters of the fluid-filled structure using a three-scale asymptotic expansion in the linearized Navier-Stokes equations. In the limit when the wavelength of the LSW is much larger than the typical heterogeneity size of the phononic crystal, we show that it behaves as an artificial fluid with an anisotropic effective shear modulus and a dispersive effective-mass density.

Ultrabroadband elastic cloaking in thin plates.

Control of waves with metamaterials is of great topical interest, and is fueled by rapid progress in broadband acoustic and electromagnetic cloaks. We propose a design for a cloak to control bending waves propagating in isotropic heterogeneous thin plates. This is achieved through homogenization of a multilayered concentric coating filled with piecewise constant isotropic elastic material.

Broadband cylindrical acoustic cloak for linear surface waves in a fluid.

We describe the first practical realization of a cylindrical cloak for linear surface liquid waves. This structured metamaterial bends surface waves radiated by a closely located acoustic source over a finite interval of Hertz frequencies. We demonstrate theoretically its unique mechanism using homogenization theory: the cloak behaves as an effective anisotropic fluid characterized by a diagonal stress tensor in a cylindrical basis.

Quantum dynamic of sticking of a H atom on a graphite surface.

A quantum study of the sticking of a hydrogen atom chemisorbed onto graphite (0001) surface was carried out also including the phonon modes of the system in the collinear scattering approximation. A new model was developed to extract the substrate vibrational modes from density functional theory (DFT) calculation and include them in the total system dynamics. The resulting coupled-channel equations are numerically developed along time using the wave packet methods.

Adsorption, diffusion, and recombination of hydrogen on pure and boron-doped graphite surfaces.

Boron inserted as impurity by substitution of carbon atoms in graphite is known to modify the reactivity of the surface in interaction with hydrogen. Boron induces a better H retention capability in graphite while it makes easier the recombination into molecular hydrogen under heating in thermal-desorption experimental conditions. It has already been calculated that boron modifies the electronic structure of the surface, which results in an increase of the adsorption energy for H.