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A five-slot hexagonal shape chipless RFID tag is designed, simulated, and manufactured on FR4 substrate. The designed tag's copper geometry was replicated on a wide range of dielectric substrate to quantify the impact on resonance quality factor (RQF) and resonating frequencies. The tag's performance was assessed in three configurations. First, a hexagonal shape tag's radar cross section (RCS) was studied over different dielectric substrates. The various dielectric substrate effects were investigated over the maximum read range, resonant frequencies and RQF. In the second evaluation, the physical geometry of the tag was adjusted to achieve the spectral signatures in 2–7 GHz frequency band with high RQF. In step three, the optimized tag geometry was manufactured on FR4, Roger Duroid 5880, and polyethylene naphthalate (PEN) substrates. Denford milling machine for PCB engraving and inkjet printing for silver nanoparticles deposition were used for tags manufacturing. During tag manufacturing, copper and silver were used as conducting materials for RCS backscattering. The tag RCS response was measured by vector network analyzer with bi-static antenna setup. The analysis of different dielectric substrate provides a pathway of designing a novel substrate by using various nanomaterials. [ABSTRACT FROM AUTHOR]

Syntactic materials (spheroplastics), having a low density due to their structural features, depending on the material of the microsphere walls, may have a rather high strength and low thermal conductivity, which makes them promising as heat-insulation materials. By selecting the material of the microsphere walls and the concentration of the components of the spheroplastics, one can change significantly their dielectric characteristics. In this work, the task of modeling the effective dielectric characteristics of a syntactic material with a polymer binder and filler in the form of hollow glass microspheres is considered taking into account the presence of technological impurities in the material. A model for calculating the effective permittivity of a sample of a syntactic material is proposed based on the model of a matrix composite with several types of inhomogeneous or homogeneous inclusions. A generalized effective-field approximation for a heterogeneous medium with coated inclusions is used for the calculation. Model calculations are carried out for syntactic foam with a polydimethylsiloxane organosilicon binder and hollow microspheres with an E-glass shell, in the presence of some moisture in the material. The frequency dielectric characteristics of this material are obtained in the range of 102–1010 Hz. It is shown that an increase in the volume fraction of hollow microspheres leads to a decrease in the dielectric permittivity and dielectric-loss tangent. It is also shown that the calculated values are in satisfactory agreement with the experimental data obtained at an electromagnetic-field frequency of 9.8 GHz. [ABSTRACT FROM AUTHOR]

To evaluate the average dielectric property, the effective permittivity (EP) of multi-component media in low frequency region is the first issue. The most classical formula is the Maxwell–Garnett (MG) model. However, it needs guidelines to restrict the applicability of MG model. Later on, the strong fluctuation theory (SF model) and QCA-CP model (quasi-crystalline approximation with coherent potential) have been studied. Similarities and difference between these models need to be clarified. In this paper, all these models are derived in a consistent way. Numerical examples show the difference between the EPs of these models. It is found that when the dielectric perturbation is not large (dielectric particle is not quite different from background) and especially, the fractional volume of inclusions is not large (e.g. less than 0.15), all these models are good enough to evaluate EP. But, if these pre-conditions are not well met, the MG model becomes unsuitable. Thus the SF and QCA-CP models are better than MG in either cases of strongly or weakly fluctuating cases. If the discrete spherical particles are well defined, e.g. size, complex dielectric constant, the QCA-CP would be a rigorous model for the calculation of EP and extinction coefficient. [ABSTRACT FROM AUTHOR]

A simple and accurate approach for computing the effective permittivity of metasurfaces embedded within arbitrary stratified media is presented. The proposed model provides accurate estimation of the effective permittivity for stackups with several dielectric layers with arbitrary thickness and permittivity. The effect due to the unit cell geometry is also taken into account. The accuracy of the model is rigorously verified by comparing the effective permittivity estimated by the approximate model with the one extracted by using full-wave method of moments (MoM) simulations as a function of the substrate thickness. [ABSTRACT FROM AUTHOR]

With the rapid development of industrial production and aerospace, how to measure the plasma density has also developed rapidly. So a radio-frequency plasma transducer based on a three-layer dielectric substrate antenna with a high dielectric constant is introduced. The top and bottom layers are dielectric plates, which protect the internal antenna structure and improve the equivalent permittivity of the antenna. The middle layer is the structure layer of the designed antenna. And the antenna size is 3.8 × 2 × 1.8 mm3. When the plasma frequency changes from 0.3 GHz to 7 GHz, the corresponding dielectric substrate antenna resonant frequency (RF) changes from 4.076 to 5.213 GHz. The minimum unit is 0.1 GHz, and all the measurement accuracy is more than 90%. The method based on the effective dielectric constant of plasma will change under different plasma frequencies, so the RF of the antenna is different. In this paper, the radio-frequency plasma transducer is studied theoretically and analyzed numerically. [ABSTRACT FROM AUTHOR]

This paper presents a slow-wave artificial dielectric substrate for planar microstrip device miniaturization. The proposed substrate supports the improvement of the permittivity of a given substrate, and in turn offers guided wavelength reduction, leading to obtaining size reduction using low cost printed circuit board (PCB) process. In this structure, two rows of metal vias are located on either side of a microstrip line (ML), which are connected to the ground plane of the substrate. In addition, a row of metal mushroom-shaped vias is placed and connected at the center of the line, which is inserted inside the dielectric media. This would lessen the effective distance between the microstrip line and the ground, and so, the capacitance per unit length is increased leading to obtaining a slow-wave substrate. The proposed structure is numerically investigated using full wave software for specified parameters and the microstrip line characteristics are compared with those of the conventional line. A prototype of the introduced line is implemented and its measured propagation features, including phase constant and effective permittivity, are reported. Results show a perfect agreement with those of simulation, which confirms that a 50.6% longitudinal size reduction is feasible. [ABSTRACT FROM AUTHOR]

A great number of numerical and theoretical models have been proposed, by several authors to estimate the effective permittivity of heterogeneous multiphase structures. The physical effective properties of both composite and nanocomposite materials are known for its depending on the composition and the arrangement of its components. Until now the existing literature is not able to take into account the effect of the geometry except the effect introduced via the depolarization factor presented by some models, which depends on the inclusion geometry and which is known only for a limited number of inclusions, with classical shapes like the disc or some regular equilateral polygons. This issue presents a limitation to study many systems with non-regular geometries. In this paper, a new model, based on the association of capacitors is presented, gives us two new bounds of the effective permittivity. The new results are compared with the existing models and the results obtained by applying the finite element method (FEM). The results of the present model are shown in good agreement with the existing data. Moreover, the new model improves considerably the calculation time compared with the finite element method. [ABSTRACT FROM AUTHOR]

Reliable and efficient analysis of electromagnetic scattering by cylindrical components of vegetation is important for microwave remote sensing of vegetated terrain. It allows for the characterization of anistropicity of the effective permittivity for vegetation or tree canopy, where averaging operation over distribution of cylinder orientation is needed in general. In this paper, we propose a T-matrix formulation based on our virtual partition method (VPM) for the whole cylindric component of either homogeneous or inhomogeneous nature. Numerical simulations demonstrate that the proposed T-matrix preserves all the desirable features of the VPM method, including high fidelity prediction of the scattering amplitude function and fulfillment of energy conservation as well as the reciprocity theorem. More importantly, in the evaluation of averaging over orientation distribution, the proposed method is usually faster than the VPM by two orders of magnitude. The predicted effective permittivity for an exemplary orientation distribution shows appreciable difference from that of the infinite cylinder approximation. With its qualitatively characterized region of validity, the proposed method is expected to be helpful in multiband coherent scattering models of vegetated terrain. [ABSTRACT FROM PUBLISHER]

After reviewing some theoretical facts and early theories, this work presents a study of the dielectric properties of carbon black (Raven 7000) dispersions in an insulating epoxy matrix (diglycidylic ether of bisphe-nol F) in the frequency range 1kHz to 15MHz. In an earlier study,[1]it was shown that different mixture laws (Maxwell Garnett, Bruggeman, Lichtenecker, and Rother) correctly account for the experimental values of the effective complex permittivity at low particle concentrations. However, they fail to represent the data at the larger concentrations studied. Here, the two-exponent phenomenological percolation equation is used to characterize the permittivity of these composites. It is discussed whether or not this phenomenological equation is capable of representing the effective permittivity versus carbon black volume fraction. [ABSTRACT FROM PUBLISHER]

Abstract: In this work, two-dimensional simulations of the microwave dielectric properties of models with ellipses and realistic models of trabecular bone tissue are performed. In these simulations, finite difference time domain methodology has been applied to simulate two-phase structures containing inclusions. The results presented here show that the micro-structure is an important factor in the effective dielectric properties of trabecular bone. We consider the feasibility of using the dielectric behaviour of bone tissue to be an indicator of bone health. The frequency used was 950MHz. It was found that the dielectric properties can be used as an estimate of the degree of anisotropy of the micro-structure of the trabecular tissue. Conductivity appears to be the most sensitive parameter in this respect. Models with ellipse shaped-inclusions are also tested to study their application to modelling bone tissue. Models with ellipses that had an aspect ratio of a/b =1.5 showed relatively good agreement when compared with realistic models of bone tissue. According to the results presented here, the anisotropy of trabecular bone must be accounted for when measuring its dielectric properties using microwave imaging. [Copyright &y& Elsevier]

Abstract: The effective properties of composite materials are closely related to the composition and arrangement of its constituents. Many studies and articles are actively studying the dielectric properties of heterogeneous structures with random and periodic arrangement. In the quasistatic limit, we use the finite element method as a numerical tool to evaluate the effective permittivity of two and three component composites. Two heterostructures are investigated; the first is formed by crossed dielectric cylinders in permanent contact and arranged in three layers. The cylinders are immersed in a dielectric host medium. The second structure is similar to the first except that the tubes are covered by an interphase layer. The numerical tool used to extract the exact value of the effective permittivity takes into account all internal multipolar interactions which contribute to the polarization of the material medium. The impacts of the relative permittivity and volume fraction of cylinders, the thickness of interphase and its dielectric constant are reported. The Maxwell–Garnett theory fails to predict the effective permittivity of the studied structures for high volume fraction and permittivity contrast. To overcome this problem, an amendment was made to the McLachlan equation McQ also termed the Two Exponent Single Percolation Equation TESPE. The first exponent t is held equal to 1 and the other exponent s is depending on the volume fraction. s is calculated so that the whole values of the effective permittivity obtained by the McQ rule are exactly the same values obtained by the simulations. Finally, we obtained a chart and a model to find the values of s, a fast way that is very useful for practitioners and design engineers of composite materials. [Copyright &y& Elsevier]

The finite element method is used for study of the 2–component heteregoneous samples. The effective permittivity of the grainy 2–component sample can be described by the linear rational functions. The random texture of irregular clusters is better described by the mixing formulas of the Lichtenecker or logarithmic type. [ABSTRACT FROM PUBLISHER]

A coplanar waveguide type microwave phase shifter using ferroelectric liquid crystal is constructed and its fundamental characteristics are measured. An analysis procedure of the effective permittivity of the phase shifter is explained. The decrease of the width of the center conductor in the phase shifter leads the increase of the dielectric permittivity change, consequently increasing the phase shift. The distance between the center conductor and ground plane needs the same as the width of the center conductor. Furthermore, it is confirmed that the arrangement of the dielectric substrate instead of the liquid crystal layer is useful technique. [ABSTRACT FROM AUTHOR]

The impetus of this work was to investigate the electromagnetic and tensile properties of several commercially available plastoferrites (PFs) at ambient conditions. The approach involved selection of a set of PFs, and measuring their complex effective permittivity ε = -jε" under uniaxial stress at microwave frequencies in the range 0.1-4.5 GHz at room temperature. The E' spectra have been analyzed for intensively strained PFs up to 3%. Comparing the experimental e values against several dielectric relaxational behaviours, we find that the main physics cannot be understood with a single relaxation mechanism. More importantly we show that the ε measurements under stress can be explained in terms of a Gaussian molecular network model in the limit of low stress. The present results have important applications in magnetoactive smart composite materials, e.g. flexible circuit technology in the electronics industry (sensors, actuators and micromechanical systems), functionalized artificial skin and muscles for robotic applications. [ABSTRACT FROM AUTHOR]

In many materials, strong electrical fields can cause highly conductive pathways to occur due to dielectric breakdown, which can cause the material to “jump” to a higher permittivity state. This effect is often undesirable and can lead to electrically-induced failure of a device, for example due to overheating. The overall goal of this work is to estimate the volume fraction and properties of the particulate additives needed to reduce the electrical load carried by a bulk material, in order to avoid dielectric breakdown. [ABSTRACT FROM AUTHOR]

Bounds on the effective permittivity circumscribe 2D area in the complex plane representing possible values of permittivity. It is shown that the corresponding possible values of reflectivity occur within the interval determined by the lowest and the highest reflectivity value, which represent minimum and maximum values of reflectivity found at the permittivity bounds. [ABSTRACT FROM AUTHOR]

An understanding of the polarization characteristics is vital to the rational design of future dielectric nanostructures. In this work, a finite-element methodology has been applied to simulate 2-D two-phase heterostructures containing a dielectric inclusion with arbitrary shape. The development does not impose any restriction on the shape of the inclusion. Given the paucity of experimental and numerical data, we set out to investigate systematically the trends that shape and permittivity contrast between the inclusion and the host matrix have on the depolarization factor (DF). The effect of the first- versus second-order concentration virial coefficient on the value of the DF is considered for a variety of inclusion shapes and a large set of material properties. Our findings suggest that the DF for a 2-D inclusion is highly tunable depending on the choice of these parameters. These results can provide a useful insight for the design of artificial two-phase heterostructures with specific polarization properties. [ABSTRACT FROM AUTHOR]

The rigorous second-order accurate finite-difference time-domain method equations at dielectric interfaces are straightforwardly derived though the discretization of the integral forms of Maxwell's curl equations on the nonuniform Yee's lattice and Taylor series extending of continuous field components over finite volumes including the interfaces. It is shown that to obtain second-order accuracy, we not only require to construct proper effective permittivities in the grids containing the dielectric interfaces, but also to choose nonuniform Yee's grids available in the vicinity of the interface. The attempts in the past are not appropriate for this purpose based on the uniform Yee's lattice. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 3007–3011, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22912 [ABSTRACT FROM AUTHOR]

In this article, a design of Lüneberg lens with slices made from low loss dielectric material with hemispherical air-holes drilled appropriately on the top and bottom surface of each of them is presented. A formula to estimate the values of radial dependent effective dielectric constant of air-holes dielectric composite material is suggested. The estimated values are compared with the ones calculated from finite difference time domain method electromagnetic simulations of a periodic lattice of spherical and cylindrical air-holes embedded in a dielectric slab using Nicolson–Ross method. Calculation of S-parameters and near field of lens with hemispherical air-holes under an incident plane wave, using estimated effective constants by the suggested formula are compared with ones using precise theoretical values of dielectric constants. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2332–2337, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22751 [ABSTRACT FROM AUTHOR]

We present an inverse scattering approach for the bulk electromagnetic characterization of composite materials, based on a prior proof that artificial metallo-dielectric photonic crystals can be described by effective highly resonant response functions in a wide frequency range, including several passbands/bandgaps. The method becomes complete and unambiguous at high frequencies by employing the analytic continuation of the optical path length and a consistency criterion to ascertain the physical meaning of the extracted effective parameters. It may also be used as a fast simulator or as a measurement-based predictor of the performance of multilayered structures using the scattering matrix (simulated or measured) of a single monolayer of that material. The approach is applied for the characterization of metamorphic materials, which are recently introduced artificial structures that exhibit distinct macroscopic states of behavior as far as the reflected electromagnetic field is concerned. According to interconnect topologies of their scatterers, they appear, at a single frequency, as electric conductors, absorbers, amplifiers, and passive or active magnetic conductors. Detailed evaluations are given of the complex dispersive wave impedance, refractive index, and permittivity and permeability functions for each metamorphic state of a specific three-state metamorphic material. It is found that, as a rule, the electric and magnetic wall states are related to resonant permittivity and permeability values, respectively. Furthermore, the analysis reveals broad regions with negative values of permittivity or permeability. Both resonant and negative values of εeff, μeff occur within bandgaps or at band-edges. Finally, the approach is applied to the negative refractive index metamaterial composed of a cylinder and two split-ring resonators, which reveals the existence of a high-frequency band with negative group velocity. [ABSTRACT FROM AUTHOR]

We have derived a general formula for the prediction of the effective pyroelectric coefficient of composites. In this relation, the pyroelectric coefficient of the composite is written as a function of the pyroelectric coefficients and dielectric constants of the constituents and the effective dielectric constant of the composite material. In contrast to other formulas in the field, shape and spatial arrangement of the components and the volume ratio are not directly involved in our relation. The influence of these is completely included in the effective dielectric constant of the composite. Therefore, the new relation gives a correct description for all kinds of connectivities and provides an easy tool for the optimization of pyroelectric composites. [ABSTRACT FROM AUTHOR]

In steel fiber reinforced concrete, steel fibers are randomly oriented in the concrete host. This article presents a full-wave homogenization technique for the computation of the effective permittivity of perfectly conducting wires embedded in a dielectric host. The technique is illustrated with numerical examples and is compared with predictions from a classical mixing formula. [ABSTRACT FROM AUTHOR]

This paper introduces a treatment of electromagnetic wave scattering by many particles based on the method of analysis (DUR method) proposed by one of the authors and compares it with conventional methods. It is explained that electromagnetic wave scattering can be treated systematically by the DUR method for the cases ranging from a periodic distribution of particles to a random distribution, and that the condition can be given when the particle distributions are random from a coherent field point of view. Next, two application examples of the DUR method are presented. One is the calculation of the effective permittivity of a random medium consisting of many dielectric spheres. In contrast to the calculation by conventional three multiple scattering analysis methods, the present calculation results can be applied to particles with higher permittivity and hence the method is the best one at this time. The other example involves microwave active sensing of the moisture content of soil. It is shown that the polarization ratio of the incoherent scattered power is useful for estimation of moisture content in the cases where the moisture content is more than 5% in the surface layer and where the surface is dry in the deep layer. Finally, it is pointed out that accurate analysis of electromagnetic wave scattering in random media is becoming increasingly important in the development of new materials and new technologies for high-speed, high-reliability communications and high-precision sensing. © 2005 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 88(10): 10–18, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.20183 [ABSTRACT FROM AUTHOR]

In this paper, we propose a periodic Green's function-based method for computing the static effective permittivity of metallic crystals. The method is valid for arbitrary lattice structures and inclusion shapes. We show that the homogenization problem can be reduced to an integral equation over the boundary of a generic metallic inclusion. The kernel of the integral equation is a periodic Green's function. This Green's function corresponds to the static potential from a three-dimensional array of point charges plus a uniform density of charge. Different representations of the Green's function are presented and discussed. We apply the developed formalism to characterize the effective permittivity of a three-dimensional array of thin metallic wires. [ABSTRACT FROM AUTHOR]

Employing the strong fluctuation theory for random media, this article presents numerical results for the effective permittivity and conductivity transition for composite material of dense, nonspherical particles. It shows the functional dependence of anisotropic properties of composite material upon the particle shape and fraction. [ABSTRACT FROM AUTHOR]

A new expression has been developed far calculating the effective permittivity of rectangular microstrip antenna elements with various thicknesses of substrates. This technique is original, simple, and easily adaptable to a wide variety of dielectric materials, scalable over wide frequency ranges, and included in a CAD system. The results obtained from this technique confirm those calculated from formulas reported elsewhere. [ABSTRACT FROM AUTHOR]

• The interplay between the material composition and deformation-induced effective permittivity in dielectric elastomer (DE) composites is studied. • DE composites with periodic microstructures of (a) circular and (b) elliptical inclusions, (c) pair of inclusions, and (d) randomly distributed inclusions with varying number of the particles in the unit cell, and periodic porous composites are analyzed. • An explicit relation between the effective permittivity and stretch is derived. • The permittivity tunability in DE periodic porous composites structures experiencing elastic instabilities is realized numerically. We study the interplay between the material composition and deformation in dielectric elastomer (DE) composites with periodically and randomly distributed particles embedded in a soft matrix. We focus on the deformation-induced tunability of the effective permittivity in DE composites. We examine the effects of microstructural periodicity and its transition towards random distribution. In particular, we analyze the DE composites with periodic microstructures of (a) circular and (b) elliptical inclusions, (c) pair of inclusions, and (d) randomly distributed inclusions with different numbers of the particles in the unit cell. The finitely deformed DE composites with ideal dielectric elastomer constituents are analyzed numerically. In addition, for the periodic DE composites with circular inclusions, we derive an explicit relation between the effective permittivity and stretch. The effective permittivity of DE composites with periodic microstructures changes with deformation, whereas in DE composites with randomly distributed inclusions, the permittivity is barely affected by deformation. For the latter case, the effective permittivity attains a certain value as the number of particles in the periodic cell increases. To provide the insights on the composite behavior, a two-particle periodic system is examined. The permittivity is found to be sensitive to the orientation of the pairs with respect to the applied electric field, and the distance between the particles. The geometrical effects amplify significantly as the inter-particle distance becomes less than their two diameters. Finally, we illustrate the permittivity tunability in DE periodic porous composites structures experiencing elastic instabilities. [ABSTRACT FROM AUTHOR]