Thin Lossy Research Articles

Plasmon-polariton waves guided by thin lossy metal films of finite width: Bound modes of symmetric structures

Plasmon-polariton waves guided by thin lossy metal films of finite width: Bound modes of symmetric structures

Scattering of electromagnetic waves by a perfectly conducting cylinder with a thin lossy magnetic coating

We study the scattering interaction of electromagnetic (EM) waves with an infinite cylinder coated with a lossy dielectric material with frequency-dependent material properties. These properties are hypothetical, yet representative of a wide class of available materials. The monostatic and bistatic scattered widths (SW) are evaluated for the TM or TE polarization cases. These calculations require the use of algorithms to evaluate Bessel-Hankel functions of complex arguments. These algorithms are based on a continued fraction approach, which ensures stability of the recursion relations. The bistatic plots of the TM and TE scattering widths for the coated body are displayed in a convenient color-graded scale. The reductions in the scattering widths produced by this type of coating are determined in selected frequency bands and angular sectors, in both polarization cases. It is quantitatively shown how curvature and polarization shift the effectiveness band of the coating. The determined regions in which the SW are minimally affected are the most suitable for target identification purposes.

Complex source radiation in a cylindrical radome of metal-dielectric grating

The radiation fields of a line source enclosed in a circular dielectric radome with grating consisting of an array of thin lossy metal strips are analyzed. The variations of the directivity of the source beam with respect to the beam direction are studied. The possibility of damping these variations by an appropriate design of the radome is demonstrated.

Modification of the finite difference scheme for efficient analysis of thin lossy metallayers in optical devices

A method is proposed for the analysis of optical devices with lossy metal layer by including an analytical formulation into the finite difference expressions. Losses of TM0 mode in an electro-optic switch for wavelength 1523 nm, exhibiting a sharp maximum of 37 dB are computed by this method. The results show very good agreement with the data obtained by the Mode Matching Method and Finite Difference Beam Propagation Method.

Energy Efficient Transfer of Microwave Power to Thin Lossy Dielectrics

Microwaves beamed on a dielectric are partly reflected on, and partly transmitted to the dielectric. If the dielectric has a finite thickness the microwaves propagating through the dielectric consists of forward as well as backward moving waves. The reflected wave on the dielectric means loss of energy, the backward components of the wave in the thin dielectric are causing strong oscillatory behavior of absorption in the dielectric which can lead to hot spots. For thin dielectrics, in general, the power penetration depth cannot be used to calculate the power absorption in the dielectric. In this paper it will be shown that with oblique incidence, in a special case, all power irradiated to a thin dielectric can be absorbed and that for this situation the power penetration depth can be used to calculate the power absorption because backwards waves are not present in the dielectric. It will be shown that this occurs also if a suitable medium is situated around the dielectric to be heated. Also in this case all power is absorbed by the dielectric and the power absorption can be described by the power penetration depth. Both possibilities mean a very efficient energy transfer to the dielectric. For thick dielectrics all energy beamed to the dielectric is absorbed.

Kapitza conduction by thin lossy surface layers

The authors consider the Kapitza conductance due to absorption and emission of phonons by a lossy surface layer which has complex elastic constants and/or complex mass density. They find a series connection of two heat resistances, one between the layer and the solid, and another one between the layer and the helium. A propagator matrix formalism is used to calculate the phonon absorption coefficients, and hence the Kapitza conductance, as a function of angle, frequency and layer thickness in the limit of continuum acoustics with anisotropy. The resulting conductance is large enough to account for the Kapitza anomaly.

Scattering by thin lossy dielectric plates‐a finite‐difference time‐domain approach

AbstractThis Letter discusses the computation of scattering by thin lossy nondispersive dielectrics using the finite‐difference time‐domain (FD‐TD) method. The time‐domain relationship between the electric fields normal to a lossy material boundary is used in a “smart cell” approach which allows the thickness of the dielectric to be less than the spatial grid size. These results are compared to the “brute force” FD‐TD approach. © 1993 John Wiley & sons, Inc.

Lossy dielectric and thin lossy film models for 3-D steady state TLM

The 3-D steady state TLM technique (SS-TLM) is extended to provide TLM models for lossy materials and thin lossy films in the frequency domain. The models are evaluated by comparing with time domain TLM (TD-TLM) and analytic solutions.

An analysis of scattering and emission from sea ice

Abstract Scattering and emission models for multilayered inhomogeneous media are developed based on the matrix doubling method. They are made applicable to media closely packed with scatterers by using the complete scattered field expression in the derivation of the scattering phase function. These models are applied to sets of multifrequency, multiangle, multipolarization, active and passive measurements from simulated sea ice prepared under laboratory conditions and from field experiments on sea ice where ground truths were gathered. It is found that identical surface and ice parameters in agreement with ground truth information may be used to predict both emission and scattering. Such a combined approach can give an indication as to the consistency between active and passive data levels and angular trends. Furthermore, it is found that for thin lossy ice above a water surface, scattering and emission from water could be significant.

Electromagnetic scattering from arbitrarily shaped conducting bodies coated with a thin layer off lossy magnetic material

An efficient moment solution is given for the problem of electromagnetic scattering from an arbitrarily shaped, three-dimensional conducting body coated with a thin layer of lossy magnetic material. The surface equivalence principle is used to replace the conductor with a surface electric current, and the volume equivalence principle is used to replace the coating with a magnetic volume current. The behaviour of the field in the thin coating justifies approximating the volume current by a surface magnetic current residing next to the surface electric current. The boundary condition on the tangential component of the total magnetic field is used to express the magnetic surface current in terms of the electric surface current. The boundary condition on the tangential component of the electric field is then used to obtain an integral equation for the surface current. The method of moments is used to solve this equation approximately. The computed numerical results are in excellent agreement with the exact data for the case of a spherical scatterer.

Field feedback computation of scattering by 2-D penetrable objects

The field feedback formulation is applied to the solution of time-harmonic plane wave scattering by 2-D penetrable objects of arbitrary shape and composition. A conformal mesh, finite element algorithm is employed in the forward operator construction while a near-field Green's function integration is used in forming the feedback operator. Scattering validations for midresonance sized objects include a circular cylinder, a two-region bisected cylinder, a half-circular cylinder, a semiconductor shell and a thin lossy planar strip.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A Hallen-type integral equation for symmetric scattering from lossy circular disks

A rigorous technique is presented for calculating the current induced on a thin lossy disk by rotationally symmetric sources, and the resulting scattered field. A Hallen-type integral equation is developed for the current using the magnetic vector potential, and it is solved by the method of moments. It is shown that the diffraction lobes usually associated with radiation above a finite circular ground plane can be reduced dramatically by the addition of loss. Application to a quarter-wave monopole radiating above a finite circular perfectly conducting ground plane shows good agreement with experiment. >

An efficient formulation to determine the scattering characteristics of a conducting body with thin magnetic coatings

Two new and efficient surface integral equations, derived from corresponding volume integral equations, are developed to calculate the scattering of electromagnetic (EM) waveform from an arbitrarily shaped conducting body coated with thin lossy magnetic film. Their numerical solutions by the method of moments (MM) for two-dimensional structures with full or partial coatings are presented. It is shown that the radar cross-section of a conducting body can be significantly reduced by coating it with a lossy magnetic film. To verify the validity and accuracy of the proposed formulation, another method based on the expansion of cylindrical harmonic functions with real arguments is also developed to calculate the scattering of a plane EM wave from an electrically large coated circular cylinder. The same problem was also solved by the proposed formulation, and excellent agreement between the two approaches was achieved. In addition, numerical results of the scattering from a rectangular coated cylinder is shown to be consistent with that obtained by a modified finite-difference-time-domain (FDTD) method.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Theoretical and numerical study of gratings consisting of periodic arrays of thin and lossy strips

We start with the study of gratings consisting of periodic arrays of thin lossy strips with arbitrary cross sections. Then we investigate the behavior of such gratings if they are sandwiched between multilayered structures. Taking advantage of theoretical considerations recently published, we propose an approximate method and stress the numerical aspect. The resulting computer code seems interesting mainly for the study of gratings in the far-infrared and microwave ranges.

A Time-Domain, Finite-Volume Treatment for the Maxwell Equations

ABSTRACT For computation of electromagnetic scattering from layered objects, the differential form of the time-domain Maxwell's equations are first cast in a conservation form and then solved using a finite-volume discretization procedure derived from proven Computational Fluid Dynamics (CFD) methods 1 . The formulation accounts for any variations in the material properties (time, space, and frequency dependent), and can handle thin resistive sheets and lossy coatings by positioning them at finite-volume cell boundaries. The time-domain approach handles both continuous wave (single frequency) and pulse (broadband frequency) incident excitation. Arbitrarily shaped objects are modeled by using a body-fitted coordinate transformation. For treatment of complex internal/external structures with many material layers, a multizone framework with ability to handle any type of zonal boundary conditions (perfectly conducting, flux through, zero flux, periodic, nonreflecting outer boundary, resistive card, and lossy ...

A three-dimensional Maxwell's equation solver for computation of scattering from layered media

The differential time-domain Maxwell's equations are cast in a conservative form and then solved using a finite-volume discretization procedure derived from computational fluid dynamics methods applied to linear/nonlinear gasdynamics equations. The formulation accounts for any variations in the material properties (time, space, and frequency dependence) and can handle thin resistive sheets and lossy coatings by positioning them at finite-volume cell boundaries. The time-domain approach handles both continuous-wave (single-frequency) and pulsed (broadband-frequency) incident excitation. Arbitrarily shaped objects are modeled using a body-fitted coordinate transformation. For treatment of complex internal/external structures with many material layers, a multizone framework with ability to handle any type of zonal boundary conditions (perfectly conducting, flux through, zero flux, periodic, nonreflecting outer boundary, resistive card, lossy coatings, etc.) is implemented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

UTD solution for electromagnetic scattering by a circular cylinder with thin lossy coatings

A uniform geometrical theory of diffraction (UTD) solution is obtained for the field exterior to a two-dimensional circular cylinder with a thin lossy dielectric coating. The solution is convenient for engineering applications due to its simple ray format. In the lit region, the geometrical optics (GO) solution consists of the direct incident ray and the reflected ray. In the shadow region, the geometrical theory of diffraction (GTD) uses the creeping-wave format to calculate the diffracted field. In the transition regions adjacent to the shadow boundaries, where the pure ray optical solution fails, a 'universal' transition integral is used for the UTD solution to calculate the field. Numerical values for the essential transition integral are deduced, by a heuristic approach, from alternative representations of the Green's function for a circular cylinder with coating. Numerical results obtained from the UTD solution show excellent agreement with the eigenfunction results for cylinders with thin dielectric coatings. >

Electromagnetic transmission through mesh covered apertures and arrays of apertures in a conducting screen

The problem of electromagnetic transmission through wire mesh covered arbitrarily shaped aperture or arrays of apertures (possibly covered by a thin lossy dielectric sheet) in a perfectly conducting ground plane is considered. The equivalence principle and image theory are used to derive an integral equation for the equivalent magnetic currents. The method of moments is utilized to solve the integral equation, with the aperture modeled by triangular patches. Numerical results are presented for transmission coefficients and transmission cross-section patterns for electrically small apertures.

Transmission Modes in a Braided Coaxial Cable and Coupling to a Tunnel Environment

Radio frequency transmission in a semicircular tunnel containing a braided coaxial cable is considered. The general formulation accounts for both the ohmic losses in the tunnel wall and a thin lossy film layer on the outer surface of the dielectric jacket of the cable. Using a quasi-static approximation, it is found that the propagation constants of the low-frequency transmission line modes are obtained through the solution of a cubic equation. However, for the special case when the conductivity thickness product of the Iossy film layer vanishes, this cubic equation reduces to a quadratic. The spatially dispersive form of the braid transfer impedance is also accounted for. It is shown that the quasistatic theory is well justified for frequencies as high as 100 MHz for typical tunnel geometries. Finally, special characteristic impedances are derived for the various modes of the equivalent multiconductor transmission line.

Integral equation method for scattering and absorption of electromagnetic radiation by thin lossy dielectric discs

An integral equation for the current induced in a dielectric body by incident electromagnetic radiation is solved for the case of a thin flat circular disc of homogeneous lossy dielectric material. The equation is reduced by using the method of moments to a linear algebraic matrix equation for the coefficients in an expansion of the current density as a linear combination of basis functions. The matrix elements consist of integrals involving the basis functions. The novel computational aspects of this work lie in the choice of basis functions and in the techniques which this choice enabled to handle singularities in the integrands when evaluating the matrix elements, to reduce the matrix size and to rigorously preserve symmetries in the matrix. Expressions are given for the scattering and absorption cross sections in terms of the expansion coefficients. The results are most suitable in the resonance range of wavelengths when the disc radius and free-space wavelength are of the same order of magnitude.