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As the demand increases in the field of wireless communication system, the interest of researchers increases to develop and analyzes the antenna for these applications. This article present metasurface (MS) frequency reconfigurable antenna (FRA) which is optimized using neural network (NN) approach. The designed structure is a multilayer consists of three-layer patch antenna placed under the MS structure. The resonating patch is a rectangular shaped and substrate is a circular shaped show as to reduce the geometry of the antenna. The proposed structure is fabricated on FR-4 substrate of thickness 1.6 mm. The MS structure consists of split ring rectangular (SRR) strips made up of copper. The antenna reconfigured the operating frequency from 4.85 to 7 GHz having overall bandwidth of 2.15 GHz with wide range of tuning. The central frequency of rectangular patch antenna is 6.15 GHz. The MS is analyzed by using effective parameters i.e., effective permittivity (εr) & effective permeability (μr) and it is observed that the MS is behaving as a metamaterial in the desired range of frequency. The reconfigured operating frequency (ROF) is found at the anticlockwise rotation angles of 0°, 30°, 600 and 90°. The realized gain and radiation efficiency are calculated at each ROF. The validation of proposed MS based FRA is carried out first by simulating using Ansys HFSS and then measured inside the anechoic chamber. The proposed antenna is optimizes using NN model which shows minimum error during analysis and synthesis process. [ABSTRACT FROM AUTHOR]

Optics of negative index material is known for its unconventional results. In the perspective of nonlinear optics, it has a revolutionary impact. We, thus, investigate the effect of Kerr nonlinearity on the characteristics of a representative isotropic, frequency independent negative index material by defining an intensity-dependent effective permittivity and compare it to that in positive index material. Using the intensity-dependent permittivity, responses of essential characteristic features like phase and group velocities are studied and found to exhibit unconventional behavior with incident field intensity in the negative index material. At a threshold intensity, i.e., at an intensity at which effective permittivity vanishes, the material shows features of epsilon near zero and/or near zero index materials i.e., a diverging phase velocity with zero group velocity. The study shows the prospect of altering or tailoring characteristic features of a negative index material by tuning the field intensity of the propagating wave or pulse in the material. [ABSTRACT FROM AUTHOR]

This paper introduces compact Printed Ridge Gap Waveguide (PRGW) phase shifters tailored for millimeter-wave applications, with a focus on achieving wide operating bandwidth, and improved matching and phase balance compared to single-layer technology. This study proposes a unique approach to achieve the required phase shift in PRGW technology, which has not been previously explored. This study also introduces a novel analytical approach to calculate the cutoff frequency and propagation constant of the PRGW structure, a method not previously addressed. Furthermore, the utilization of multi-layer PRGW technology enables the realization of multi-layer beamforming networks without crossing, thereby supporting wideband operation in a compact size. The proposed design procedure enables the realization of various phase shift values ranging from 0 ∘ to 135 ∘ over a broad frequency bandwidth centered at 30 GHz. A 45-degree phase shifter is fabricated and tested, demonstrating a 10 GHz bandwidth (approximately 33% fractional bandwidth) from 25 GHz to 35 GHz. Throughout the operating bandwidth, the phase balance remains within 45 ± 5 ∘ , with a deep matching level of −20 dB. The proposed phase shifter exhibits desirable characteristics, such as compactness, low loss, and low dispersion, making it a suitable choice for millimeter-wave applications, including beyond 5G (B5G) and 6G wireless communications. [ABSTRACT FROM AUTHOR]

An approach is proposed for calculating effective physical characteristics of a inhomogeneous medium with several levels of nesting of its microstructure—the generalized effective-field approximation. With the help of this approach, an expression is obtained for an effective permittivity tensor of an inhomogeneous medium with ellipsoidal inclusions in a multilayered shell, the boundaries of all layers of which are ellipsoids. The proposed approach allows to take into account probabilistic distributions of orientations and forms of inclusions, as well as the presence of several types of inclusions. Two cases of matrix composites are considered: (1) with spherical isotropic inclusions with a multilayered shell; (2) with ellipsoidal anisotropic inclusions with a multilayered shell. For an inhomogeneous medium with homogeneous inclusions, this approximation is shown to produce the same result as the generalized singular approximation. [ABSTRACT FROM AUTHOR]

In this paper, the effective permittivity of inhomogeneous anisotropic dye-coated nanoparticles is calculated and compared using the internal homogenization method and the electric field-weighted averaging method. The relative errors of the two effective medium methods are analyzed by comparing the calculated absorption factors with those calculated by the original model. The filling factor, core size, material, and anisotropy degree of the dye molecular layer are considered, and the results showed good agreement for larger filling factor, smaller core radius, and radial dielectric constant of the shell. The highest reliability of the effective permittivity predicted by the two methods is achieved when the filling factor, core radius, and radial dielectric constant are 0.8, 15 nm, and 4, respectively. In general, the accuracy of the homogenization method within the studied wave band is higher than that of the electric field-weighted averaging method, but the electric field-weighted averaging method can be applied to anisotropic medium with arbitrary morphology, which provides a new idea for calculating the dielectric properties of inhomogeneous anisotropic medium. [ABSTRACT FROM AUTHOR]

This paper introduces compact Printed Ridge Gap Waveguide (PRGW) phase shifters tailored for millimeter-wave applications, with a focus on achieving wide operating bandwidth, and improved matching and phase balance compared to single-layer technology. This study proposes a unique approach to achieve the required phase shift in PRGW technology, which has not been previously explored. This study also introduces a novel analytical approach to calculate the cutoff frequency and propagation constant of the PRGW structure, a method not previously addressed. Furthermore, the utilization of multi-layer PRGW technology enables the realization of multi-layer beamforming networks without crossing, thereby supporting wideband operation in a compact size. The proposed design procedure enables the realization of various phase shift values ranging from 0∘ to 135∘ over a broad frequency bandwidth centered at 30 GHz. A 45-degree phase shifter is fabricated and tested, demonstrating a 10 GHz bandwidth (approximately 33% fractional bandwidth) from 25 GHz to 35 GHz. Throughout the operating bandwidth, the phase balance remains within 45 ± 5∘, with a deep matching level of −20 dB. The proposed phase shifter exhibits desirable characteristics, such as compactness, low loss, and low dispersion, making it a suitable choice for millimeter-wave applications, including beyond 5G (B5G) and 6G wireless communications.

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]

• This is the first sensor based on a band stop FSS sensing the effective permittivity of 3D printed hollow structures. • High Q factor. • Wide angle and polarization insensitivity. In this paper, a metamaterial sensor is proposed based on a band stop frequency-selective surface (FSS) with high Q factor of 421.9 at 8.032 GHz. The sensor consists of a square loop FSS and a F4B dielectric substrate. This is the first sensor based on a band stop FSS sensing the effective permittivity of 3D printed hollow structures. The equivalent circuit method is used to analyze the characteristics of the sensor, and the results agree well. Two materials under test and four different hole radii of 3D printed hollow structures are used to verify the sensing function. At the same time, the effective permittivity of the 3D printed hollow structure is analyzed, and the correctness of the effectiveness is verified by simulation inversion and Maxwell-Garnett formula. The sensor has the advantages of high Q factor, wide incidence angle and polarization angle insensitivity, which can provide some guidance in metamaterials sensing. [ABSTRACT FROM AUTHOR]

We investigate using a reconfigurable metamaterial structure based on high permittivity dielectric elements in a flexible origami framework to control the electromagnetic response of a suspended patch antenna. Origami-inspired dielectric structures are fabricated by additive manufacturing of origami elements using an ABS-30 vol% BaTiO3 filament (permittivity ${\sim }11$ ). The printed millimeter-scale elements are then assembled into an origami structure using flexible polymer hinges. Alternatively, dielectric origami structures are also achieved using a flexible, polymer-only origami lattice pre-fabricated by stereolithography into which shaped high dielectric elements (permittivity ${\sim }18$ ) of ABS-60 vol% CaTiO3, manufactured by field assisted sintering, are inserted. The various dielectric origami designs are inserted into the air gap between a suspended patch antenna and a ground plane, designed to operate at a resonant frequency of 1 GHz. The presence of the dielectric origami modifies the antenna resonant frequency and tunablity is then achieved through different configurations of the dielectric origami, actuated by hand or mechanically. Tunability arises because varying the configuration, and overall density, of the dielectric origami varies its effective permittivity and thus the patch resonant frequency. The dielectric origami structures provide a tunable range up to ${\sim }14\%$ , in good agreement with numerical simulations. Simulations are also used to show how broader tunability could be achieved easily, for example, by optimizing the size of the dielectric elements. Overall, the results using these preliminary dielectric origami structures, enabled by combining advanced manufacturing techniques, suggest that the approach offers a wide design space with the potential to realise novel antenna functionality and flexibility.

This work presents a vertical hyperbolic metamaterial (vHMM) consisting of a vertically stacked metal-dielectric multilayer that operates in the visible spectrum. The vHMM is designed by exploiting the relation between negative refraction and effective permittivity along the perpendicular direction of the layers (ε ⊥). When a vHMM has a high loss tangent defined by tan δ ⊥ ≡ Im(ε ⊥)/Re(ε ⊥), even a vHMM composed of relatively thick layers can generate negative refraction. A fabricable vHMM composed of gold and copolymer resist (EL8) which exhibits negative refraction at the wavelengths between 450 and 550 nm is designed using critical layer thickness analysis. The largest negative refraction is observed at the wavelength of 500 nm, where the angle of refraction reaches −1.03°. The corresponding loss tangent and equivalent refractive index are 1.08 and −0.47, respectively. However, negative refraction is not observed at the wavelengths longer than 550 nm due to low tan δ ⊥. We uncover that the tan δ ⊥ of a vHMM is the dominant condition for generating negative refraction rather than the ratio of layer thickness to wavelength.

A method of measuring the impedance of a microstrip transmission line using a vector network analyzer is proposed. The problem of determining the frequency dependence of the impedance of a microstrip line is very important in order to create circuit models of the electronic components and touchstone-files in the virtual strip channel with a reference impedance of 50 Ω. Circuit models of the components and files are used in computer-aided design systems of integrated microwave devices. It is proposed to solve the problem of measurement by a vector network analyzer in the entire frequency range of operation, by the LTR method. From the measurement results, for a network analyzer in the coaxial channel, of the S-parameters and coefficients of reflection of two segments, short and electrically long microstrip transmission lines, the phase velocity and a damping factor of an electromagnetic wave propagating in the strip line transmission were determined, as well as the converted S-parameters of two distorting adapters modeling contact fields of the coaxial and strip lines. Over the range 0.02–2.00 GHz, the impedance was found from the coefficients of reflection from the coaxial ports of the distorting adapters at two fixed frequency points, at which the reactive capacitive component of the complex impedance is compensated by the inductance of the contact fields of the coaxial and strip lines. The frequency dependence of the real part of the impedance, passing through these frequency points, is determined over the range of frequencies of operation of the network analyzer, by means of the circuit model of the microstrip Beatty standard in the NI AWR Design Environment computer-aided design system. The model of this standard of a line with an air section between two segments of strip lines with an insulation foundation was derived by means of an MLIN circuit analog, suitable for the physical prototype of the line. The importance of the measurement of impedance of the microstrip line is shown by a vector network analyzer on the example of identifying the characteristic parameters of the chip resistors. [ABSTRACT FROM AUTHOR]

The dielectric properties of polymer nanocomposites (PNCs) are crucial in designing electronic packaging, energy storage capacitors, electromagnetic shielding, and biomedical sensors and actuators. The conventional mixing rules-based methods such as the Kerner model, Maxwell–Garnett (MG) model, Maxwell–Wagner-Sillars (MWS) model, Bruggeman model solely rely on the volume fraction (vol%), which is often inadequate to predict the frequency dependency of the effective permittivity of the PNCs, they also do not account for the sizes of the inclusions. A computational model was developed to estimate the dielectric permittivity and the dielectric loss of PNCs using COMSOL multi-physics. Experimental data from previously published references confirmed the validity of the finite element analysis (FEA) based model. Next, the COMSOL model was utilized to quantitatively analyze the complex dielectric constant as a function of the applied frequency, the dielectric properties of the inclusion and the polymer matrix, and the volume fraction of the inclusion. The study was conducted with a polymer matrix of polymethylmethacrylate (PMMA) and five nanoparticles including semiconductor material silicon (Si), inorganic zinc-sulfide (ZnS), metal gold (Au), metal-oxide titanium oxide (TiO2), and dielectric fillers BaTiO3 (BT). The results show that the frequency-dependent dielectric relaxation behavior, the MWS interfacial polarization, significantly influences the dielectric properties. A 10 vol% inclusion of Si, ZnS, and BT resulted in MWS frequency of 103, 1584, 105 Hz. The charge barrier is most substantial in low frequency as it restricts electric field propagation around the inclusion. However, at a significantly high frequency, the charge barrier breaks, lowering the dielectric constant of the composite. In addition to that, a unique behavior was observed in high conductive fillers PNCs (e.g., Au) as the permittivity showed a fillers size dependence even with the same volume fraction. At frequency nearing 105 Hz, the Au-PMMA composite showed a higher permittivity with smaller nanoparticles inclusion. This is a significant finding contrary to the existing understandings based on the conventional mixing rules (e.g., MWS, MG, Bruggeman, Kerner model), which does not account for the size of inclusions. The present study has important implications for device engineers and materials manufacturers to choose appropriate materials with desired properties for optoelectronic packaging applications. [ABSTRACT FROM AUTHOR]

The use of a low-cost split-ring resonator (SRR) passive sensor for the real-time permittivity characterization of hydrocarbon fluids is proposed in this paper. The characterization of the sensor is performed through both full-wave simulation and measurements. Thanks to the analysis of several crude samples, the possibility of discrimination between different types of crude and the estimation of several of their properties are demonstrated. Between them, the estimation of sulfur, aromatic hydrocarbons, and salt-water concentrations either in normal ambient conditions or in a high-pressure and high-temperature environment can be mentioned. Experiments were run both at normal ambient conditions and pressures up to 970 bar and temperatures up to 200 °C. [ABSTRACT FROM AUTHOR]

A ring resonator used to study the effective permittivity and the loss of substrate integrated suspended line (SISL) is presented in this article. The effective permittivity is obtained by calculating resonant frequency and the relative value of loss is calculated by comparing unloaded quality factor (Q factor). For the four cases of uniform ring resonators, their S‐parameter, effective permittivity, unloaded Q factors are simulated, measured and investigated. The effect caused by the height of air cavity, the material of dielectric substrate, dielectric loss tangent is also investigated. Finally, the calculated results indicate that the effective permittivity of SISL structure at operating frequency is very closed to 1, which manifests that within a certain substrate‐material range the relative permittivity of substrate has little influence on SISL platform that is instructive for SISL circuits design. And the use of metalized via‐hole connection with dielectric removal can reduce the circuit loss dramatically. [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]

Purpose. To develop a two-dimensional numerical-field model for determining the effective permittivity of a multicomponent material represented by a system of homogeneous volumes with known physical characteristics. Methodology. The model is based on the solution by the finite element method of an electrostatic problem with the subsequent determination of the energy contained in the volume under consideration. Than we have compared this result with the energy of a flat capacitor with a rectangular cross-section of the plates and determined the effective permittivity of test material. We also have used Rayleigh, Odelevsky and Lichtenecker models and the model with a perpendicular arrangement of layers relative to the main electric flux. Results. Based on the developed field model, the effective permittivities for dry, wet and transformer oil-soaked insulating papers of various grades, including taking into account ash, are determined. We have proved that a macroscopically homogeneous multicomponent material is well approximated by uniformly spaced cylindrical volumes with a substance of different nature in a matrix of another substance. We have showed a significant error of the layer model and the Rayleigh model relative to the proposed model. We have showed the equivalence of models with the location of inclusions in the nodes of a rectangular and parallelogram mesh. Originality. For the first time we have proposed wet paper models with an asymmetric arrangement of a cylindrical volume of water with a circular and segment cross-section in a cylindrical pore. For the first time we have proposed models of insulating paper with evenly spaced cylindrical inclusions of different volumes. Practical value. The proposed model allows to calculate the effective permittivity of an inhomogeneous material with a given accuracy without restricting the shape of the components. Based on the proposed field model, it is possible to determine the Lichtenecker index, which allows to calculate the effective permittivity for any ratio of the volumes of the components of a heterogeneous material.

This paper presents the design and synthesis of a low-loss substrate with low effective permittivity (εeff ) for microwave and mm-Wave applications. The proposed design is based on the two-phase Maxwell Garnet mixing theory, where the εeff of the RF substrate can be synthesized depending on the geometry and the permittivity of mixing particles and the permittivity of the host material. A comprehensive review and error analysis of the most common mixing techniques are conducted to guarantee an accurate design for high-performance RF substrates. Several analyses based on the geometries of various particles are carried out to identify the most accurate mixing model used in the design of the proposed substrate. The effects of the direction of excitation as well as the polarization of the incident field on the εeff of the anisotropic particle are analyzed and discussed. The proposed method enables the use of existing high-performance materials that do not necessarily provide a low dielectric constant and low loss tangent. For mm-Wave antenna applications, materials with a dielectric constant of 2-4, and loss tangent of less than 0.002 are desirable to maximize gain and radiation efficiency. Commercial RF substrates can satisfy those requirements, however limited thermal expansion coefficient and lamination difficulties increase the cost significantly. The proposed method enables the use of inexpensive materials that provide excellent thermal properties and great compatibility with a multi-layer fabrication process with desirable εeff and loss tangent. For validation of the analysis, samples are fabricated and tested in the microwave frequency (S-band) at 3.5 GHz as well as in the mm-Wave frequency (W-band) at 77 GHz. Measured results show a reduction of 45% in the εeff and 38% in the loss tangent values in the S-band, and 32% and 72% reduction in εeff and tanδ, respectively, in the mm-Wave frequency band. The measured results are in excellent agreement with the simulation and calculated results.

A new novel structure is proposed for cellular composite radar absorbing materials, and an equivalent method of electromagnetic scattering for the new material is also proposed for the first time. By covering the target surface with non-uniform medium cellular cell elements horizontally, the scattering characteristics of the coated target show strong surface anisotropy, leaving an imaginary space for optimizing the electromagnetic stealth performance of the coated target. In this paper, the equivalent dielectric tensor of horizontal directional composite honeycomb cell element has been calculated by using the equivalent method of electromagnetic scattering based on strong fluctuation theory (SFT) of anisotropic medium. Under the condition of plane wave irradiation with a frequency of 3 GHz, we use FEKO software to estimate the backscatter field of several typical models coated with this new structure. It has been proved that the strong fluctuation theory applied to the honeycomb composite absorbing material of the structure are effective for calculating the equivalent scattering. Based on the validity of the equivalent results, we further estimate the scattering characteristics of complex targets coated with the novel cellular medium.

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]

A generalization of the Maxwell Garnett approximation for a textured matrix composite consisting of ellipsoidal inclusions with a shell is proposed; using it, an expression for an effective permittivity tensor of a given medium is obtained. It is shown that, in the case of a matrix composite with spherical inclusions in the shell, this expression coincides with the formula obtained in the generalized effective-field approximation, if the matrix is taken as the comparison medium. [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]

Usually, in situ electrical polarization measurements (in geophysical prospection referred to as induced polarization or spectral induced polarization (SIP)) are carried out at frequencies below 1 kHz. These techniques have mainly been used for mining exploration, followed by a larger panel of environmental applications. However, in this ultra low and extremely low-frequency domain, the duration of each individual measurement is long, i.e., typically several tens of minutes for a single full SIP spectrum down to the mHz range. This restriction makes it unrealistic to implement high-density measurement mapping campaigns over large areas, which would otherwise be possible at higher frequencies. In the intermediate frequency range [3 kHz–3 MHz], laboratory studies of soil and rock samples have shown that they can be strongly polarized notably in the presence of clays, and this property has been confirmed by several in situ mapping experiments using electromagnetic induction in the time and frequency domains (FDEM and TDEM), as well as by an electrostatic method (often named capacitive-coupled resistivity or CCR). The present paper recalls these results in an effort to promote polarization measurements at intermediate frequencies and to emphasize the importance of measuring this phenomenon. [ABSTRACT FROM AUTHOR]

The use of a low-cost split-ring resonator (SRR) passive sensor for the real-time permittivity characterization of hydrocarbon fluids is proposed in this paper. The characterization of the sensor is performed through both full-wave simulation and measurements. Thanks to the analysis of several crude samples, the possibility of discrimination between different types of crude and the estimation of several of their properties are demonstrated. Between them, the estimation of sulfur, aromatic hydrocarbons, and salt-water concentrations either in normal ambient conditions or in a high-pressure and high-temperature environment can be mentioned. Experiments were run both at normal ambient conditions and pressures up to 970 bar and temperatures up to 200 °C.

This paper proposes a new approach to relate the effective thermal conductivity of open-cell solid foams to their porosity. It is based on a recently published approach for estimating the dielectric permittivity of isotropic porous media. A comprehensive assessment was performed comparing the proposed mixing relation with published experimental data for thermal conductivity and with numerical data from state-of-the-art relations. The mixing relation for the estimation of thermal conductivities based on dodecahedrons as building blocks shows good agreement with experimental data over a wide range of porosity.

In order to calculate the effective permittivity of a mixture with multilayer ellipsoids, this paper presents a self-consistent approximation (SCA) on the basis of the Bruggeman’s analytical model. The effective permittivity of a mixture with aligned multilayer ellipsoids is derived directly from the linear system of equations, which are built using the boundary condition of the electric field on the confocal ellipsoidal interface in the ellipsoidal coordinate system. Furthermore, for a mixture with multilayer ellipsoids oriented randomly, an effective ellipsoid is introduced to substitute the original multilayer ellipsoid, and the permittivity of the effective ellipsoid is derived by jointly solving the two linear systems of equations for the situation of the original multilayer ellipsoid and that of the effective ellipsoid, then the effective permittivity of the mixture can be calculated by the existing Maxwell-Garnett formula. After comparisons, it is revealed that there is a good agreement between this SCA method and existing theories.

Open-cell solid foams are rigid skeletons that are permeable to fluids, and they are used as direct heaters or thermal dissipaters in many industrial applications. Using susceptors, such as dielectric materials, for the skeleton and exposing them to microwaves is an efficient way of heating them. The heating performance depends on the permittivity of the skeleton. However, generating a rigorous description of the effective permittivity is challenging and requires an appropriate consideration of the complex skeletal foam morphology. In this study, we propose that Platonic solids act as building elements of the open-cell skeletal structures, which explains their effective permittivity. The new, simplistic geometrical relation thus derived is used along with electromagnetic wave propagation calculations of models that represent real foams to obtain a geometrical, parameter-free relation, which is based only on foam porosity and the material’s permittivity. The derived relation facilitates an efficient and reliable estimation of the effective permittivity of open-cell foams over a large range of porosity.

Porous plastics are used in various fields of industry, including radio- and electrotechnical fields. They are characterized by good heat- and sound proofing, dielectric and mechanical properties, and resistance to various external factors during operation. The problem of predicting the effective permittivity of foam-polymer materials with a large volume fraction of pores, in particular, polyepoxide foam materials, are considered. Two methods for solving it, both based on the matrix composite model are proposed. In the first method, the matrix is considered as a polyepoxide binder, and cavities filled with gas are taken as inclusions. In the second method, polyepoxide walls separating cavities are taken as inclusions, and gas filling cavities are considered as a matrix. To obtain the calculation formulas, the generalized singular approximation of the random field theory is used in both cases. Based on the derived expressions, model calculations of the effective permittivity are performed for macroscopically isotropic foam plastic with polymer binder based on ED-20 and cavities filled with freon, depending on the apparent material density. The calculations in the generalized singular approximations are performed for the case where the matrix is considered as the reference medium and using the self-consistent method. In the calculations using the second approach, two shapes of material cells are considered, i.e., weakly leaked and heavily leaked polyhedron. The dependences calculated by all methods show qualitative agreement with the experimental data. [ABSTRACT FROM AUTHOR]

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In the first part, the scattering characteristics of an isolated dielectric coated conducting rod have been investigated. The types of considered coatings for the scattering analysis are realistic materials including barium strontium titanate, magnetodielectric, gallium arsenide, and silicon carbide. It is found that the gallium arsenide coating can be used to significantly reduce the scattering from a thin perfectly electric conducting cylindrical rod at specific observation angles. In the second part, the effective permittivity and permeability of metamaterials composed of two dimensional periodic arrangements of these dielectric coated conducting cylindrical rods have been studied. An increase in the double negative (DNG) bandwidth of a metamaterial composed of barium strontium titanate coated conducting rods has been observed in contrast to the corresponding bandwidth of a metamaterial composed of only barium strontium titanate material rods. Also an additional plasmonic epsilon negative (ENG) bandwidth has been found in case of a metamaterial composed of barium strontium titanate coated conducting rods. It is further studied that the widest ENG, mu negative, and DNG bandwidths exist for a metamaterial composed of gallium arsenide rods. [ABSTRACT FROM AUTHOR]

An enhanced finite‐difference time‐domain (FDTD) algorithm is built to solve the transverse electric two‐dimensional Maxwell's equations with inhomogeneous dielectric media where the electric fields are discontinuous across the dielectric interface. The new algorithm is derived based upon the integral version of the Maxwell's equations as well as the relationship between the electric fields across the interface. To resolve the instability issue of Yee's scheme (staircasing) caused by discontinuous permittivity across the interface, our algorithm revises the permittivities and makes some corrections to the scheme for the cells around the interface. It is also an improvement over the contour‐path effective permittivity algorithm by including some extra terms in the formulas. The scheme is validated in solving the scattering of a dielectric cylinder with exact solution from Mie theory and is then compared with the above contour‐path method, the usual staircasing and the volume‐average method. The numerical results demonstrate that the new algorithm has achieved significant improvement in accuracy over other methods. Furthermore, the algorithm has a simple structure and can be merged into current FDTD software packages easily. The C++ source code for this paper is provided as supporting information for public access. [ABSTRACT FROM AUTHOR]

Unique properties of carbon nanotubes (CNTs) such as high anisotropy could be utilised in liquid crystal (LC) medium and it may improve the physical properties of the host medium. In this regard, enhancement of permittivity and flexoelectric coefficients of the medium is calculated through doping an LC planer cell with single-walled carbon nanotubes (SWCNTs), here. These calculations consider the effect of the applied electric field. A splay type curvature orientation is induced in the medium as a result of the converse flexoelectric effect. It is reported experimentally by Petrov et al. that the presence of SWCNTs enhances the curvature orientation and its polarisation. We discussed the case theoretically and calculated the variations of the mentioned physical properties through doping with SWCNTs. A generalised Maxwell-Garnett mixing rule is considered to calculate the effective permittivity of the medium and extend it to estimate the modified flexoelectric coefficients of the medium. In low concentrations of SWCNTs, the model calculates the increase of the dielectric anisotropy and flexoelectric coefficient up to twofold and fivefold, respectively, which is in good agreement with reported data by other researches. [ABSTRACT FROM AUTHOR]

Layered dielectric materials are currently in use for electric field stress control, but are limited by charge accumulation at the dielectric–dielectric interfaces. The current work uses micrometric particles to modify the effective permittivity of epoxy resin samples. Two broad kinds of samples are considered: discrete layered material (DLM) samples and functionally graded material (FGM) samples. DLM samples are obtained by bonding layers of epoxy resin with different filler loadings such that abrupt variation in permittivity might occur along the sample thickness. FGM specimens are prepared by hot pressing a comparatively large number of very thin layers of micro‐filled epoxy resin with very small differences in permittivity one over the other, thus creating a gradual spatial permittivity gradation. Dielectric properties of FGM and DLM specimens are compared in this study. Space charge accumulation is studied using the pulsed electroacoustic method; the accumulated charge density is seen to be lower in FGM. The uniformity of electric field distribution under applied electric stress is computed, and the field utilisation factor in FGM is seen to have a higher value. Also, the dissipation factor is lower and the short‐term breakdown strength is higher in FGM than in DLM samples, providing reason to prefer FGM for insulation to control electric stress. [ABSTRACT FROM AUTHOR]

A microwave microfluidic sensor for detecting binary liquid mixtures with a dielectric method at RF/microwave frequencies is presented in this article. The sensor is based on a split-ring resonator (SRR) that is implemented in a microstrip transmission line, with interdigitated electrodes (IDEs) being integrated into the ring for liquid detection. Based on the equivalent circuit of the IDE-SRR device and with a series of finite element simulations, the detection theory is developed, and the device design optimization is investigated. The validation measurements on water–isopropanol liquid mixtures with various concentrations show that the proposed IDE-SRR sensor has higher sensitivity than the previous standard SRR sensor. The IDE-SRR sensor is then used to detect two binary liquids, i.e., water–methanol mixtures and water–tetrahydrofuran mixtures. The measured effective permittivity results of the binary mixtures at RF/microwave frequency range are compared with the existing mixing models for binary dielectric mixtures at zero frequency. [ABSTRACT FROM AUTHOR]

In this article, the Babinet principle is applied for complementary periodic sub wavelength metallic elements $A^{e}$ and $A^{c}$ at the interface between different substrates. For the problem, the restriction of the Babinet principle is mainly resulted from the inhomogeneity of the different substrates or the anisotropy of the metallic elements. In order to break the restriction, a virtual substrate with an effective permittivity is inserted into the interface to cover $A^{e}$ and $A^{c}$ as an updated physical boundary condition. As the thickness of such a virtual effective substrate layer approaches zero, the updated model will not only remain the same as the original one for $A^{e}$ and $A^{c}$ but also can be solved by the existing Babinet principle with a feasible mathematical method. Finally, according to the network transmission theory and Babinet principle, the proposed theory gives the specific mathematical relationship between the tangential transmission matrices of $A^{e}$ and $A^{c}$. Two examples are simulated to verify the theory, regardless of the substrate, metallic elements, and incidence angle. This method not only greatly simplifies the solutions of complementary metasurfaces but also shows higher precision than the previous work. [ABSTRACT FROM AUTHOR]

A new analytical model is proposed for the nanocomposite permittivity εeff in mean‐field approach using integrated coefficients for the inclusion clustering and matrix reaction effects. Predictions for εeff are in a satisfactory agreement with the Lichtenecker and Bruggeman mixing rules, depending on whether the reaction field is ignored or incorporated into the theory. The observed differences between the Maxwell–Garnett, Lichtenecker, and Bruggeman results are interpreted in terms of the fraction of the stored dipolar energy they take into account. A novel analytical expression for the average dipolar field ⟨E⃗μ⟩ in the film shows a U‐shaped dependence on the filler packing fraction η, with an absolute maximum at ηm = 1/e. New analytical expressions derived for the average dipolar energy umμ and dipole–dipole interaction energy umμμ in the nanocomposite depend on the cluster orientation parameter γ, and take into account the film boundary effects. It is found that the enhancement of εeff at higher γ is associated with an increase in the inclusion dipole moment μp in the oriented clusters resulting from dipole–dipole correlations, which inflate the energy up stored inside the inclusions. [ABSTRACT FROM AUTHOR]

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Through this theoretical study, nanoparticles-based Terahertz (THz) emission is explored out by considering the graphite nanoparticles (NPs) of two different shapes, i.e., spherical (SNPs) and cylindrical (CNPs), oriented in two normal directions, i.e., one having their basal plane perpendicular to the electric field of the laser and second with their basal plane parallel to the electric field of the laser. The nonlinear ponderomotive force is exerted on the electronic cloud of NPs by the field of two incident super-Gaussian lasers of frequencies ω1 and ω2, which on excitation gives rise to the nonlinear macroscopic current density at beating frequency ω = ω1 − ω2. It is observed that efficient THz emission takes place when the beat frequency matches with the effective plasmon frequency of the NPs. Most importantly, THz generation strongly depends on the shape of the NPs as CNPs contribute more efficiently towards THz generation but orientation of NPs with respect to the electric field feebly affects the THz generation. [ABSTRACT FROM AUTHOR]

• Analytical model of capacitive nature of lymphocyte suspension. • Dielectric anisotropy in the cell and nuclear membranes has been considered. • Variation of electrical parameters with cell count has been observed. • Low frequency phenomenon has been observed. • The study is focused on the rapid count of lymphocytes in a suspension. Biological constituents have unique dielectric properties by virtue of which these can be analyzed both quantitatively and qualitatively by employing bio-dielectric measurement techniques and electrical impedance spectroscopy exhibits immense potential in this context. In this study, an analytical impedimetric model has been developed to describe bio-dielectric behavior of the lymphocyte suspensions with different cell counts. Emphasis has been given to incorporate the effect of dielectric anisotropy which is apparent between the cell and nuclear membranes and measured in the low frequency range. The relatively low frequency range is chosen to probe the strong dependence of complex membrane behavior provided by the cells. Such dielectric anisotropy originates from the flow dynamics of ions through the hydrophobic interior of polar lipid-bilayer membrane. Successive models have been developed and compared with the relevant experimental data for formulating the system capacitance in a most generalized approach. The capacitance values have been observed to decrease with both the increase of measuring frequency and cell count, however, its impedance decreases with frequency and increases with cell count. Such nature is attributed to the localization of polar response in the membrane-base solution interfaces. The work demonstrates a rapid and deterministic approach to estimate lymphocyte count which will augment the existing prediction techniques for relevant physiological disorders. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering (17264073) is the property of Republic of Iraq Ministry of Higher Education & Scientific Research (MOHESR) and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The main purpose of this work was to extract valuable metals from EAF dust with the addition of biochar, using microwaves to control and optimize the carbothermical reduction process. To achieve better microwave penetration and the most homogeneous electromagnetic heat source distribution possible in a sample, the content of EAF dust and biochar in centimeter-size spherical particles prepared by the pelletization process was considered to be radially heterogeneous. The content of EAF dust was determined experimentally and the effective permittivity, permeability, and thermal conductivity of the EAF dust as well as biochar–EAF powder mixture were determined using effective medium approximation. The microwave heating of a multilayered pellet of biochar-containing EAF dust was simulated and investigated. The influence of the distribution of the components within the pellet on the effectiveness of the microwave heating was investigated, as was the influence of the biochar conductivity. The interaction of the pellet with both plane waves in free space and with H10 mode waves in a single-mode waveguide was considered. The most optimal distribution of EAF dust and biochar within the pellet for the reduction process was determined.