Dielectric Obstacles Research Articles

High resolution spherical microwave holography

A practical technique is developed to determine the electric and/or magnetic field on objects and sources inside a spherical measurement surface. The technique, known as spherical microwave holography (SMH), provides a nondestructive, nonintrusive method of point-by-point evaluation of antennas and radomes over their spatial extent. The resolution capability of SMH is developed and demonstrated by measurements. Resolution in SMH is only limited by the measurement system's capabilities. Dielectric and metallic obstacles on the surface of a radome are located and identified. Resolution as small as 0.33/spl lambda//sub 0/ is demonstrated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

A boundary element method for electromagnetic transmission problems

Time-harmonic electromagnetic waves are scattered by a homogeneous dielectric obstacle. We transform Maxwell's equations via an ansatz into a system of second kind integral equations on the interface. Uniqueness and Fredholm properties of the boundary integral operator are proven. A Garding inequality is satisfied and ensures the stability of the corresponding Galerkin scheme.

Electromagnetic scattering from dielectric-coated axisymmetric objects using the generalized point-matching technique (GPMT)

This paper describes the use of the generalized point-matching technique (GPMT) in analyzing plane electromagnetic (EM) scattering from 3-D bounded objects consisting of (or modeled by) an arbitrarily shaped axisymmetric perfect electrically conducting (PEC) or dielectric obstacle embedded in an arbitrarily shaped dielectric body of revolution and arbitrarily disposed with respect to the propagation direction of an arbitrarily polarized incident electric field vector. The treatment may be validly applied to scatterers whose boundary surfaces must have no sharp corners or edges which will introduce a discontinuity in the direction of the unit vector normal to the core and/or outer coat surfaces. It should be pointed out, however, that when applicable, the method is remarkably robust and capable of providing highly accurate numerical modelling predictions for the full-vector EM wave interactions with a large variety of arbitrarily shaped two-layered structures. Numerical results for a variety of scatterer configurations are provided and compared to exact or otherwise available results to demonstrate the potency and versatility of the suggested GPMT formulation. >

Scattering by an E plane dielectric sheet in rectangular waveguide

A method for the computation of S-parameters associated with a rectangular waveguide with a rectangular dielectric obstacle is presented. The method uses the Method of Lines and discretization of the dielectric permittivity to treat the dielectric discontinuity along the discretization direction. In this way, the Method of Lines can be applied to analyze waveguide discontinuity with dielectric inhomogenousity along the discretization direction. The numerical results have been verified by both theoretical and experimental results.

Field strength prediction behind lossy dielectric obstacles by using the UTD

A comparison is made between the measured and theoretically predicted field strength in the shadow region of a lossy dielectric obstacle. The field is measured along a cylindrical arc behind the obstacle at a frequency of 50 GHz. The theoretical model uses the uniform theory of diffraction including corner, edge-to-edge, and edge-to-corner diffraction, heuristically extended to include effects of nonperfect conductivity. The agreement between the measured and theoretically derived results is excellent for both orthogonal polarisations considered. The field behind a lossy block-shaped obstacle proves to be less polarisation dependent than behind a perfectly conducting one.

Scattering by a dielectric obstacle in a rectangular waveguide

A method for the computation of S-parameters associated with a rectangular waveguide with a rectangular or cylindrical obstacle of arbitrary complex scalar permittivity is presented. The method uses modal analysis and integral relationships to connect appropriate components of the field. In this way, convergence is achieved faster than by point-matching techniques. Our method is well adapted to resonance problems, as illustrated by comparison with both theoretical and experimental results.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Boundary integral equations for the scattering of electromagnetic waves by a homogeneous dielectric obstacle

SynopsisTime-harmonic electromagnetic waves are scattered by a homogeneous dielectric obstacle. The corresponding electromagnetic transmission problem is reduced to a single integral equation over S for a single unknown tangential vector field, where S is the interface between the obstacle and the surrounding medium. In fact, several different integral equations are derived and analysed, including two previously-known equations due to E. Marx and J. R. Mautz, and two new singular integral equations. Mautz's equation is shown to be uniquely solvable at all frequencies. A new uniquely solvable singular integral equation is also found. The paper also includes a review of methods using pairs of coupled integral equations over S. It is these methods that are usually used in practice, although single integral equations seem to offer some computational advantages.

TE Wave Excitation and Scattering by Obstacles in Guiding and Surround Regions of Asymmetric Planar Dielectric Waveguide

Scattering of bound surface waves by dielectric obstacles along planar dielectric waveguide is studied. An asymmetric planar dielectric waveguide is formed by the tri-layered substrate/film/cover environment, typical of integrated circuits for millimeter and optical wavelengths. An electric Green's function (believed new) is constructed for the TE field maintained in either the film or cover layers by currents immersed in those regions. Using a direct complex analysis approach, the Green's function is expanded in the discrete and continuous propagation spectrum components for the asymmetric planar waveguide. This electric Green's function is exploited to study scattering of TE surface waves by uniform dielectric discontinuity placed arbitrarily along the asymmetric waveguide. A polarization EFIE description of the discontinuity region is developed. Scattering coefficients are subsequently calculated in terms of the induced field. Method of moment (MOM) numerical solutions are implemented for slice discont...

Three-dimensional finite-element solution of dielectric scattering obstacles in a rectangular waveguide

A numerical approach is described for the analysis of scattering from dielectric obstacles in a rectangular waveguide. The approach is a combination of the finite-element method and the analytical solution. In order to save computer memory, the substructure method is introduced in the finite-element method. To combine the uniform waveguide region with the finite-element-method region, evanescent modes and propagating modes are considered in the analytical solution. Spurious fields like the spurious solutions generated in the finite-element analysis of three-dimensional eigenvalue problems can appear in the three-dimensional discontinuity problems when the variational expression in terms of three components of the magnetic field is used. To suppress and eliminate the spurious fields, the penalty function method is also introduced. To confirm the validity and usefulness of the approach, numerical examples are shown for a rectangular dielectric scattering obstacle in a waveguide.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Improving the characteristics of rectangular waveguide branchings by cylindrical obstacles

The scattering matrix of a transition between one or two parallel rectangular waveguides and a larger rectangular waveguide which contains two metallic or dielectric cylinders is investigated by means of the orthogonal expansion method. Mathematical programming is applied in order to improve the characteristics of the branchings. Reflection at a rectangular step discontinuity can be reduced by 30 dB using metallic or dielectric obstacles. Using Teflon cylinders, coupling of a transition can be reduced by 40 dB without debasing reflection. Physical interpretations are given with the help of field patterns.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Variational bound analysis of a discontinuity in nonradiative dielectric waveguide

The application of the variational bound method to nonradiative dielectric waveguide is described for the analysis of scattering by a dielectric obstacle, in this case a rectangular, air-filled discontinuity (hole) in the dielectric center strip. A variational bound is obtained on the phase shift, which measures the amount by which the asymptotic solution for the fields in the guide in the presence of the discontinuity is displaced relative to the guide without a discontinuity. A major advantage of the procedure is that a closed-form expression for the equivalent network is obtained that can be used directly in the design of networks using reactive components, such as filters. Measured data agree well with the theoretical calculations. >

Finite element analysis of H-plane rectangular waveguide problems

The equivalent circuit parameters of rectangular waveguide H-plane junctions, bends and obstacles may be found by a two-dimensional finite element method. Results are presented for perfectly conducting and dielectric obstacles, and for a waveguide bend. Good agreement is obtained with previously published results.

MASS TRANSFER ENHANCEMENT BY SMALL FLOW OBSTACLES IN ELECTROCHEMICAL CELLS

Mass transfer enhancement by small obstacles attached to the cathode in electrolytic flow cells of 5x5 mm cross-section and 500 mm length was investigated. Double beam laser interferometry was used to observe the local mass transfer boundary layer thicknesses preceding and following rod-shaped dielectric obstacles placed normal to the direction of electrolyte flow. Flow patterns have been visualized by use of suspensions of small inert particles and dark field photography. For the evaluation of the effectiveness of mass transport enhancement, pressure drops, and limiting currents for the reduction of ferricyanide have been measured in the range of Reynolds Number 80 to 3200. The degree of enhancement increases with decreasing obstacle spacing until an optimal spacing of approximately 15 times the obstacle size is reached. A three to five-fold increase in the average mass transfer coefficient is achieved by the use of obstacles with a small fraction of the pumping power required to obtain the same limiting...

Numerical computations on one-dimensional inverse scattering problems

In this note we present an approximate method to detemine the index of refraction of a dielectric obstacle. For simplicity we treat one-dimensional models of electromagnetic scattering. The governing equations yield a second-order boundary value problem, in which the index of refraction appears as a functional parameter. The availability of reflection coefficients yields an additional initial condition. We approximate the index of refraction by a kth-order spline which can be written as a linear combination of B-splines. For N/2 distinct reflection coefficients, the resulting N/2 initial value problems yield a system of N nonlinear equations in N unknowns which are the coefficients of the B-splines.

Experimental investigation of the interaction between the plasma of an electrically exploded wire and a plane obstacle

The results of an investigation of the physical processes that occur when pulses of dense low-temperature plasma, generated by electrical explosion of a wire, flow over a plane dielectric obstacle are presented.

Scattering of sharply focused beams by arbitrarily shaped dielectric particles: an exact solution

By expanding the incident focused beam field in terms of its plane wave spectrum and by using the technique we developed earlier to treat the problem of the scattering of plane waves by arbitrarily shaped dielectric obstacles, we have been successful in solving the problem of the scattering of sharply focused beams by arbitrarily shaped dielectric particles. It was found that the presence of the curvature of the incident wave front and the nonuniformity of the incident wave intensity affect greatly the scattering characteristics.

Crosspolarisation in scattering at low frequencies

Formulas for the amplitudes in forward and backward scattering are derived for the scattering of electromagnetic waves by dielectric obstacles which are small compared with the wavelength. Both zero- and first-order scattering are considered. It is also shown that in the zero order it is always possible to arrange that a particle of real permittivity produces no crosspolarisation.

Scattering from axisymmetric obstacles embedded in axisymmetric dielectrics: The method of moments solution

The electromagnetic scattering from axisymmetric conducting or nonconducting (dielectric) obstacles, embedded in an axisymmetric dielectric body is treated. A surface integral equation formulation, consisting of coupled Fredholm equations of the first kind for the electric and magnetic fields, is solved by the method of moments. The outer surfaces of the internal obstacles and the embedding dielectrics can be nonconcentric, depart significantly from a spherical shape, but must be rotationally symmetric about a common axis. The embedding dielectric can be multilayered. Computer implementable expressions are given for the scattering cross sections for any desired polarization and for both backscatter (monostatic) and bistatic illumination. Comparisons are made with the extended boundary condition method for homogeneous dielectric bodies and the Mie theory extended for dielectrically clad conducting spheres. The generality of the present formulation is demonstrated for several other cladded scatterer configurations.

Another method of extending the boundary condition for the problem of scattering by dielectric cylinders

Another method of extending the boundary condition resembling the extended boundary condition first developed by Waterman for the problem of scattering by homogeneous isotropic dielectric obstacles is presented. Differences between both methods are discussed from theoretical and numerical viewpoints.

Analysis of a Three-Dimensional Arbitrarily Shaped Dielectric or Biological Body Inside a Rectangular Waveguide

This paper presents a method for the analysis of three-dimensional arbitrarily shaped dielectric obstacles inside a rectangutar waveguide. The numerical computation involves a dyadic Green's function containing a double infinite series, which is evaluated by a partial summation technique.