Grazing-angle scattering of electromagnetic waves in gratings with varying mean parameters: grating eigenmodes

A highly unusual pattern of strong multiple resonances for bulk electromagnetic waves is predicted and analysed numerically in thick periodic holographic gratings in a slab with the mean permittivity that is larger than that of the surrounding media. This pattern is shown to exist in the geometry of grazing-angle scattering (GAS), that is when the scattered wave (+1 diffracted order) in the slab propagates almost parallel to the slab (grating) boundaries. The predicted resonances are demonstrated to be unrelated to resonant generation of the conventional guided modes of the slab. Their physical explanation is associated with resonant generation of a completely new type of eigenmodes in a thick slab with a periodic grating. These new slab eigenmodes are generically related to the grating; they do not exist if the grating amplitude is zero. The field structure of these eigenmodes and their dependence on structural and wave parameters is analysed. The results are extended to the case of GAS of guided modes in a slab with a periodic groove array of small corrugation amplitude and small variations in the mean thickness of the slab at the array boundaries.Comment: 16 pages, 6 figure

Acoustic response of a rigid frame porous medium slab with a periodic set of inclusions

The acoustic response of a rigid frame porous slab with a periodic set of inclusions is calculated by use of a multipole method. The acoustic properties, in particular the absorption, of such a structure are then derived and studied. Numerical results together with a modal analysis show that the addition of a periodic set of high-contrast inclusions leads to quasi-modes excitation of both the slab and the gratings, and to a large increase of the acoustic absorption of the initial slab, this being partly due to the quasi-modes excitation.Comment: submitted to Journal of Sound and Vibratio

Modeling of primary dendrite arm spacing variations in thin-slab casting of low carbon and low alloy steels

Solidification structure of a High Strength Low Alloy (HSLA) steel, in terms of dendrite arm spacing distribution across the shell thickness, is studied in a breakout shell from a thin-slab caster at Tata Steel in IJmuiden. Columnar dendrites were found to be the predominant morphology throughout the shell with size variations across the shell thickness. Primary Dendrite Arm Spacing (PDAS) increases by increasing the distance from meniscus or slab surface. Subsequently, a model is proposed to describe the variation of the PDAS with the shell thickness (the distance from slab surface) under solidifiction conditions experienced in the primary cooling zone of thin-slab casting. The proposed relationship related the PDAS to the shell thickness and, hence, can be used as a tool for predicting solidifcation structure and optimizing the thin-slab casting of low alloy steels

An ultra-thin waveguide twist constructed using fish-scale metallic wires

This study theoretically and experimentally investigates the transmission properties of a metamaterial slab comprised of two layers of metallic fish-scale structure arrays and a sandwiched dielectric layer. Calculations show that the asymmetric transmission can be tuned by varying the slab thickness, due to evanescent interlayer coupling. The spatial evolution of the local field inside the structure indicates that the slab functions as a perfect polarization transformer at certain frequencies in the manner of a waveguide twist. Measured transmission spectra are in good agreement with calculated results when material dissipation is considered

Electromagnetic Field Enhancement in Bloch Surface Waves

We present a systematic comparison between guided modes supported by slab waveguides and Bloch Surface Waves (BSWs) propagating at the surface of truncated periodic multilayers. We show that, contrary to common belief, the best surface field enhancement achievable for guided modes in a slab waveguide is comparable to that observed for BSWs. At the same time, we demonstrate that, if one is interested in maximizing the electromagnetic energy density at a generic point of a dielectric planar structure, BSWs are often preferable to modes in which light is confined uniquely by total internal reflection. Since these results are wavelength independent and have been obtained by considering a very wide range of refractive indices of the structure constituent materials, we believe they can prove helpful in the design of future structures for the control and the enhancement of the light-matter interaction.Comment: 8 pages, 6 figure