Lossy Structure Research Articles

Homogenization of Maxwell's Equations in Lossy Biperiodic Metamaterials

A novel homogenization technique is proposed for computing the quasi-static effective parameters of the lossy bi-periodic artificial structure materials. This technique is based on the Floquet's Theorem which allows reducing the studied domain to the elementary cell with pseudo-periodic conditions on the lateral sides. The studied domain is extended by adding a vacuum layer in order to impose correctly the Silver-Müler absorbing boundary condition. This homogenization technique is a numerical method using the Finite Element Method and based on the evaluation of the macroscopic fields by averaging the local fields on the elementary cell. The effective constitutive parameters are obtained from the macroscopic fields and inductions. The numerical validation of this approach is presented in 2D and 3D by computing the effective conductivities for square cylinders and cubes suspended in a host isotropic medium. The obtained results are compared to our previous approach based on Unfolding Method and Finite Element Method (UFEM). On the one hand this technique can be applied to homogenize any bi-periodic metamaterial with elementary cells having inclusions of arbitrary geometry and on the other hand it takes into account the effect of the inclusions shape on the effective parameters.

Fast measurement of antenna pattern overlap matrix in reverberation chamber

Presented is a fast way for the measurement of the pattern overlap matrix in an arbitrary multi-port antenna system by a reverberation chamber. This parameter is central for calculation of the spatial correlation between different elements with arbitrary terminations. To the authors' knowledge, this is the fastest method for the measurement of the pattern overlap matrix in a lossy structure.

Lateral shifts of a Gaussian beam reflected from lossy layered structure

We study the electromagnetic surface waves, the so-called Tamm states, and Gaussian beam reflection from a semi-infinite one-dimensional photonic crystal made of right-handed materials. We show that such layered structures can demonstrate a giant lateral Goos–Hänchen shift of the scattered beam accompanied by a splitting of the reflected and transmitted beams due to the resonant excitation of surface waves at the interfaces between the left-handed metamaterial and photonic crystal. The beam shift can be either positive or negative, depending on the type of the surface waves (forward or backward) excited by the incoming beam. Also, to make our predictions more realistic, we study the effect of losses on the lateral Goos–Hänchen shift.

Dielectric Properties in Fresh Trabecular Bone Tissue from 1MHz to 1000MHz: A Fast and Non Destructive Quality Evaluation Technique

The increasing research on development of novel bio-materials has resulted in several studies on non-destructive evaluation methods for characterizing these materials and the biological materials receiving them. A broad range of techniques are available. As an alternative tool, electrical impedance spectroscopy, has become a widely used, non destructive and low cost technique in material quality evaluation. Particularly in bones, it has also been demonstrated that mechanical characteristics are strongly correlated to dielectric properties. In this work, non destructive estimation (the same samples can be tested using other techniques) of the dielectric properties of fresh trabecular bones (layered lossy structure) using coaxial probes is analyzed from 1MHz to 10MHz (in frequency domain) and from 80MHz to 1GHz (in both, frequency and time domain). Frequency domain system identification is used to build the estimation in the low frequency range and an orthonormal based identification approach, for the high frequency data. Comments on conductive samples, non Debye dielectrics and polarization effects are added. The methodology was applied to a particular human sample population of aged adult femur heads and results are presented here. A comparison with destructive test, in which the samples were machined into cylinders of 7mm diameter, is also performed.

Multimodal Solution for a Waveguide Radiating Into Multilayered Structures—Dielectric Property and Thickness Evaluation

Open-ended rectangular waveguides are widely used for microwave and millimeter-wave nondestructive testing (NDT) applications, such as detecting disbond and delamination in multilayered composite structures, thickness evaluation of dielectric sheets and coatings on metal substrates, etc. When inspecting a complex multilayered composite structure that is made of generally lossy dielectric layers with arbitrary thicknesses and backing, the dielectric properties of a particular layer may be of particular interest (e.g., radome inspection). The same is also true when one is interested in the thickness, or, more importantly, thickness variation, of a particular layer within such complex structures. An essential tool for closely estimating the complex permittivity and/or thickness is an accurate forward electromagnetic model for simulating the reflection coefficient at the aperture of the probing open-ended waveguide. To this end, this paper provides a full-wave accurate forward model for calculating the reflection coefficient from a generally lossy multilayered composite structure possessing an arbitrary number of layers and respective thicknesses while accounting for the influence of higher order modes. This model is subsequently validated through comparisons with a commercial numerical tool and actual measurements. Furthermore, a measurement model is provided, which results in an iterative inverse technique for estimating the complex permittivity and thickness of a dielectric layer. Subsequently, this technique is applied to the measured reflection coefficients of several structures. To evaluate the accuracy of this technique, an analysis on its sensitivity to various sources of errors, and, most importantly, the effect of a finite flange size, is also demonstrated by using the simulated data. Finally, the potential of this model to accurately estimate the thickness of an individual layer, which represents a thin disbond, in a multilayered composite structure is presented.

Noninvasive measurement of dielectric properties in layered structure: A system identification approach

In this paper, estimation of the dielectric properties of layered lossy structure using open-ended coaxial probes is analyzed. Theoretical and empirical exponential approximations of the relaxation process are generalized for two, three and four-layers structures. As measurements are taken in the 10MHz to 1GHz frequency range, a wide frequency spectrum measurement procedure is proposed, providing a fast method to approximate parameters (thickness and dielectric properties) of each layer. Application of the methodology depends on some prior knowledge of the properties of the dielectric layers (i.e. number of layers and approximate values of their thicknesses and permittivities). A linear System Identification method is proposed using time domain measurements to find the corresponding frequency responses. Although these approaches and techniques have been already considered individually, they are combined here, resulting in a novel methodology to process time domain reflectometry data that is robust and numerically well-behaved. Simulations and experimental results in phantom and a biological tissue are provided. Dielectric relaxation is assumed to follow a Debye model, but comments on other parameterizations are also summarized. Experimental frequency validation data are reliable up to 700MHz.

Linear source in a circular tunnel

We study models for propagation in circular tunnels. The excitation is a fundamental electric current source. We produce expressions for the fields in terms of a Fourier transform over the axial variable. We perform an asymptotic analysis of the complex wavenumbers for use as initial estimates in a complex root finder. We then produce the modes in the lossy structure by contour integration techniques. We include numerical results for the field intensity as a function of axial distance for several frequencies and constitutive parameters of interest.We comment in particular concerning the modal content and the specific form of the field both near to and far from the antenna source.

RECIPROCITY IN SIMULATIONS OF BOLOMETRIC DETECTORS IN TRANSMITTING MODE

Bolometric detectors used in radio-astronomical instruments such as the ESA Planck Surveyor, operate as incoherent receivers of electromagnetic radiation. Meanwhile, the optical (quasi-optical) parts of the instruments (feed horns, telescope mirrors) are conventionally designed in transmitting mode when a coherent source of radiation (supposedly, equivalent to the bolometric detector) replaces the detector and radiates the electromagnetic waves through the optical system to the sky. The rules of reciprocity in such a replacement of a detector by an “equivalent transmitter” located in a lossy (open) structure (a bolometric cavity coupled via the feed horn with the outer space) are not obvious and usually ignored. A conventional simplistic approach used in this problem may cause errors in the design of such systems. By considering simple, analytically solvable models that simulate bolometric detectors surrounded by some structures, we find the rules of reciprocity providing the necessary equivalence in replacing the receiver by an appropriate transmitter as needed for the rigorous simulations of infrared and submillimetre-wave bolometric systems.

Wireless propagation in circular tunnels

We study models for propagation in circular tunnels. The excitation is either a circular magnetic or circular electric current loop. We produce expressions for the fields in terms of a Fourier transform over the axial variable. We then produce the modes in the lossy structure by contour integration techniques. We include numerical results for the field intensity both as a function of axial distance and as a function of radial distance for several frequencies, radii, and constitutive parameters of interest. We comment in particular concerning the specific form of the field both near to and far from the antenna source.

Data streaming algorithms for efficient and accurate estimation of flow size distribution

Knowing the distribution of the sizes of traffic flows passing through a network link helps a network operator to characterize network resource usage, infer traffic demands, detect traffic anomalies, and accommodate new traffic demands through better traffic engineering. Previous work on estimating the flow size distribution has been focused on making inferences from sampled network traffic. Its accuracy is limited by the (typically) low sampling rate required to make the sampling operation affordable. In this paper we present a novel data streaming algorithm to provide much more accurate estimates of flow distribution, using a "lossy data structure" which consists of an array of counters fitted well into SRAM. For each incoming packet, our algorithm only needs to increment one underlying counter, making the algorithm fast enough even for 40 Gbps (OC-768) links. The data structure is lossy in the sense that sizes of multiple flows may collide into the same counter. Our algorithm uses Bayesian statistical methods such as Expectation Maximization to infer the most likely flow size distribution that results in the observed counter values after collision. Evaluations of this algorithm on large Internet traces obtained from several sources (including a tier-1 ISP) demonstrate that it has very high measurement accuracy (within 2%). Our algorithm not only dramatically improves the accuracy of flow distribution measurement, but also contributes to the field of data streaming by formalizing an existing methodology and applying it to the context of estimating the flow-distribution.

Full-wave 2D and 3D spectral domain analysis of HTS multistrip multilayer lossy structure

The 2D and 3D CAD tools for modeling planar microwave devices are developed. The full-wave 2D analysis based on Method of Moments (MoM) is used for calculation of propagation characteristics of slot- and stripmulticonductor lossy lines embedded in multilayer lossy media. The 3D analysis based on MoM allows considering an arbitrary conductor structure embedded in a multilayered anisotropic media. Two examples of simulation are given. The modeling of the structure consisting of four coupled slots in HTS film based on a bilayered substrate with a tunable upper ferroelectric layer was performed by 2D-analysis. The results of simulation are analyzed for estimation of the insertion loss for each propagation mode. The simulation by 3D-analysis of the HTS microstrip resonator based on ferrite-MgO substrate has been done. The comparison of the HTS microstrip line current distribution simulated by 2D and 3D approaches is implemented and a high accuracy of used models is demonstrated.

Full‐wave analysis of microstrip lines on a highly lossy substrate

AbstractThe finite‐element method has been used for analyzing open microstrip line structures on highly lossy substrates. The geometry descritization has been carried out by using quadrilateral elements, and the spurious solutions are avoided by employing tangential vector formulation. The difficulties associated with finding the propagation constant of a highly lossy structure by solving a generalized eigenvalue problem are discussed. A methodology is presented for a fast and efficient computation of the attenuation and propagation constants of the lossy transmission lines. Numerical results are presented to illustrate the application of the proposed approach for the case of an open microstrip line. © 2003 Wiley Periodicals, Inc. Microwave Opt Technol Lett 37: 325–329, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10908

Multimode Network Analysis of Absorption Characteristics of Lossy Dielectric Periodic Structures

In this paper, the absorption characteristics of lossy periodic structure are investigated using a method which combines the multimode network theory with the rigorous mode-matching method. The dependence of the absorption characteristics on the incident wave and structure parameters is quantitatively analyzed; the guidelines to the design and optimization of absorbers in anechoic chamber and other applications are thus given.

The effect of mode guiding in edge emitting electroluminescent GaInAsP/InP diodes

The calculation of spontaneous electroluminescence from an GaInAsP active layer and the spectral modification of the emitted radiation due to the propagation to the edge of a GaInAsP/InP heterostructure diode is presented. By using the exact solution of a lossy dielectric waveguiding structure, the gain/absorption coefficients calculated for relevant layers of the heterostructure have been transformed into effective absorption coefficients assigned to guided modes. The relevant modes that could propagate through the heterostructure diode have been calculated numerically and the complex effective index of refraction has been evaluated for all existing guided modes. The observed double peak spectra of edge emitted electroluminescence are interpreted in terms of fundamental and higher-order guided modes.

Propagation modeling of periodic laminated composite structures

A new model based on filament-current and thin-current assumptions is proposed to analyze the propagation problem associated with the lossy periodic multilayer structure of conducting fibers situated in a dielectric matrix. To discuss the combined effect of fibers and dielectric matrix, reflection and transmission matrices at the air-matrix, and grating interfaces together with suitable phase correction are incorporated in the model in which the fiber grating is regarded as a thin Floquet layer. To reduce the central processing unit (CPU) time, an extended filament-current model for the same multilayer structure is also examined. In this study, numerical results for the graphite/epoxy (G/E) fiber-reinforced planar laminated composite materials are presented and discussed. In particular, the parameters that influence their shielding and reflection characteristics are investigated in detail. The new model is useful in characterizing the G/E fiber-reinforced laminated composites even up to the frequency of 100 GHz.

Guided modes in spontaneous edge electroluminescence from GaInAsP/InP heterostructure diodes

The calculation of spontaneous electroluminescence from GaInAsP active layer and the spectral modification of emitted radiation, due to the propagation towards the edge of GaInAsP/InP heterostructure diode is presented. By using the exact solution of lossy dielectric waveguiding structure, the gain/absorption coefficients calculated for relevant layers of the heterostructure have been transformed into effective absorption coefficients assigned to guided modes. The observed double-peak spectra are interpreted in terms of fundamental and higher-order guided modes.

Reflection and transmission characteristics of lossy periodic composite structures

A periodic surface integral formulation is proposed to analyze the reflection and transmission properties of a lossy periodic composite structure which has circular conducting fibers embedded in a dielectric matrix. This formulation is based on the equivalence principle which represents the unknown electric and magnetic currents over the material discontinuity interfaces, and uses the structure periodicity and Poisson summation formula to reduce the problem to a periodic cell. These surface integral equations are then solved numerically, using the method of moments with pulse bases and point matching. Only the transverse magnetic (TM) case is analyzed and the numerical results such as reflected, transmitted, and dissipated powers for a single-layer fiber-reinforced composite structure are presented, in detail, to discuss the effects of frequency, incident angle, fiber radius, fiber conductivity, embedding dielectric, etc. A convergence study and a comparison with the previous published results are also included to confirm the accuracy of the new formulation.

Shielding and reflection properties of periodic fiber-matrix composite structures

The plane-wave shielding and reflection properties of a single-layer composite material are analyzed, based on a filament-current phase-correction model that treats the composite material as a lossy periodic structure of fibers situated in a dielectric matrix. The scattering effect of the fibers is dealt with by calculating the scattered fields from the fiber currents, which are assumed to be concentrated along the centers of the fibers. To include the effect of the dielectric matrix, multiple reflection and transmission at the air-matrix interfaces, as well as the phase correction across the fiber grating, are incorporated in the analysis. In this study, only numerical results for the TM case are presented for graphite/epoxy composite materials. In particular, the parameters that influence the shielding and reflection characteristics, such as the angle of incidence and the frequency of the incident wave, the conductivity and radius of the fibers, and the dielectric constant of the matrix, are investigated in detail. Also included are results to illustrate the frequency-selective phenomena associated with composite structures.

Electromagnetic field calculations used for exposure experiments on small animals in TEM-cells

Three-dimensional electromagnetic calculations for loaded transverse electromagnetic (TEM) transmission cells are presented. Based on those calculations a prediction of the perturbation of the standard uniform field in the TEM-cell, due to the scattering by inhomogeneous structures placed inside the cell cavity, is given. The influence of the dimensions of a lossy structure and its position in the TEM-cell on its absorption of the electromagnetic fields is presented. Knowing the perturbation of the uniform field is important for good interpretation of the biological experimental results.

Phase Constraints for Lossy Symmetric Structures

The bounds on the phase difference between the waves reflected and transmitted by lossy structures having up-down symmetry are derived. The phase bounds are demonstrated to be sufficient to ensure physical energy properties when the lossy structure is a component of a more general optical system. The corresponding bounds which apply to lossy systems incorporating gratings or grids used in a Littrow mounting, and possessing left-right symmetry are given.