Lossy Dielectric Material Research Articles

Characterizing Lossy Dielectric Materials in Shock Physics by Millimeter-Wave Interferometry Using One-Dimensional Convolutional Neural Networks and Nonlinear Optimization

When a dielectric material undergoes mechanical impact, it generates a shock wave, causing changes in its refractive index. Recent demonstrations have proven that the modified refractive index can be determined remotely using a millimeter-wave interferometer. However, these demonstrations are based on the resolution of an inverse electromagnetic problem, which assumes that the losses in the material are negligible. This restrictive assumption is overcome in this article, in which a new approach is proposed to solve the inverse electromagnetic problem in lossy and shocked dielectric materials. Our methodology combines a one-dimensional convolutional neural network architecture, namely Inverse problem of Lossless or Lossy Shocked Wavefront Network (ILSW-Net), with a nonlinear optimization technique based on the Nelder–Mead algorithm to estimate losses within dielectric materials under a mechanical impact. Experimental results for both simulated and real signals show that our method can successfully predict the velocities and the refractive index while accurately estimating the shock wavefront.

Two split rings resonator-based perfect metamaterial absorbers with the incident and polarization angle independent for sensing applications

The perfect metamaterial absorber (PMA) optimized for high-performance absorbers to find the multiple sensing application. The structural composition of the PMA consists of two split ring resonators with six split gaps configured in an exhibit symmetry of rotation. The fundamental component of the design has three distinct layers: (1) the top and bottom layers, composed of a metallic substance with copper dielectric substrate with a thickness of 0.035 mm that exhibits lossy metal; (2) the middle layer, made of a lossy dielectric material referred to as Rogers RT5870 dielectric substrate with a thickness of 1.575 mm. The findings reveal that the absorber achieves a broad absorption spectrum, with simulated results from the CST Microwave Studio simulator indicating absorption peaks at 5.88, 9.20, and 15.88 GHz. whereas the strong absorbance is 99.91, 99.99, and 99.97 % with a good quality factor (Q) 29.40, 9.20, 13.23, respectively. The structural dimensions (7 × 7 mm2) are designed to deliver remarkable performance. The tri-band PMA exhibits polarization independent at various angles, including 0, 45, 90, 135, and 180° for both transverse magnetic (TM) and transverse electric (TE) modes. It has excellent absorption capabilities across multiple angles of incidence from 0 to 80°, including the whole operational spectrum. A comparative investigation of the circuit indicates the enhanced performance of the PMA, demonstrating its potential for exceptional functionality inside the advanced design system (ADS) software. Furthermore, the structures under consideration, which were simulated using the High-Frequency Structure Simulator (HFSS), demonstrate a strong agreement with the highest level of absorption seen at each resonance peak in the CST simulation outcomes. This paper introduces an alternative protocol, expressed in terms of the TE and TM modes, for use with the restricted symmetric structure to find multiple sensing application. The proposed study highlights the exceptional properties of PMA provides several practical advantages, including its high absorption capacity, in multiple sensing application, insensitivity to incident and polarization angles, satellite technology, raw satellite feeds, and radars owing to these performance features.

Topological Singularity Pair in Nonreciprocal Non-Hermitian Lossy-dielectric Gyromagnetic Metasurface

The transmission properties of a nonreciprocal non-Hermitian metasurface composed of lossy dielectric and gyromagnetic materials are studied with closed-form analytical solutions. It is found that a pair of opposite topological singularities of isolation ratio exist in a two-dimensional (2D) parameter space, and their evolution with parameter adjustment is preliminarily studied. These results provide clues for the design of optical devices. Further study of the mechanism of this singular behavior may reveal the complex systematic effect of non-Hermiticity and non-reciprocity on optical performance.

Design of a novel dual-polarized microwave sensor for human bone fracture detection using reactive impedance surfaces

This paper presents a novel miniaturized dual-polarized transceiver sensor system for detecting fractures in human bone tissues. The system features a patch antenna and a Reactive Impedance Surface (RIS) layer that reduces its size by 30% compared to conventional designs, resulting in enhanced fracture detection accuracy. Additionally, the system includes a dielectric plano-concave lens that adapts to the human body and improves impedance matching for optimal performance. The lens contains via holes filled with a lossy dielectric material similar to human fat tissue, which concentrates electromagnetic (EM) power and increases penetration depth for more effective crack detection. To detect fractures, two identical sensors are placed opposite each other on the tissue and moved simultaneously. The amount of EM power collected by the receiver sensor is measured using S-parameters; the transmission coefficient (S21) phases and contrast between the crack and surrounding tissue are used to construct images of fractured bones. Full-wave simulations and experimental measurements on a semi-solid human arm mimicking phantom demonstrate the proposed dual-polarized sensor's ability to detect the location and orientation of narrow cracks in the millimeter range. The system exhibits reliable performance across different human bodies.

A Novel Ultra-Wideband Electromagnetic-Wave-Absorbing Metastructure Inspired by Bionic Gyroid Structures.

Traditional honeycomb-like structural electromagnetic (EM)-wave-absorbing materials have been widely used in various equipment as multifunctional materials. However, current EM-wave-absorbing materials are limited by narrow absorption bandwidths and incidence angles because of their anisotropic structural morphology. The work presented here proposes a novel EM-wave-absorbing metastructure with an isotropic morphology inspired by the gyroid microstructures seen in Parides sesostris butterfly wings. A matching redesign methodology between the material and subwavelength scale properties of the gyroid microstructure is proposed, inspired by the interaction mechanism between the microstructure and the material properties on the EM-wave-absorption performance of the prepared metastructure. The bioinspired metastructure is fabricated by additive manufacturing (AM) and subsequent coating through dipping processes, filled with dielectric lossy materials. Based on simulations and experiments, the metastructure designed in this work exhibits an ultrawide absorption bandwidth covering the frequency range of 2-40GHz with a fractional bandwidth of 180% at normal incidence. Moreover, the metastructure has a stable frequency response when the incident angle is 60° under transverse electric (TE) and transverse magnetic (TM) polarization. Finally, the synergistic mechanism between the microstructure and the material is elucidated, which provides a new paradigm for the design of novel ultra-broadband EM-absorbing materials.

Hybrid Absorber With Dual-Band Performance and High Absorption Rate

Low-profile absorbers are of interest for compact shielded enclosures for making antenna measurements. Furthermore, the cost should be minimized for practical systems since massive production is required. In this work, a novel dual-band hybrid absorber based on structured resonators and lossy dielectric material is proposed to meet these requirements. The lossy material enables improvement in the absorption rate and operating bandwidth. The proposed absorber operates at 2.4- and 5.0-GHz Wi-Fi spectra and covers the low-frequency bands with a reflection coefficient lower than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 25 dB and a large part of the high-frequency ones with reflection lower than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 20 dB. Moreover, some of the Wi-Fi bands are covered with a reflection coefficient better than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 30 dB. In order to validate the proposed concept, the dual-band absorber is manufactured and tested, and the agreement between the simulation and measurement results is good. The presented structure is cost-effective since it only uses conventional printed circuit board (PCB) technology for manufacturing and commercial lossy dielectric material.

Can the container-dielectrics control heating patterns for microwave assisted material processing? A finite element based introspection

This work investigates the effect of acrylic and glass containers on microwave heating of a representative low lossy dielectric material enclosed in the container and exposed to uniform plane microwaves from one side. Microwave heating characteristics are determined via detailed mathematical models for the electric field and temperature distributions within the semi-infinite sample–container assembly. An in-house FORTRAN based algorithm involving Galerkin finite element method is developed to solve the governing equations and determine the heating characteristics (power and temperature distributions) for various sample dimensions as a function of container thickness. It has been found that the acrylic container can be safely used without any significant alteration of the heating characteristics of the dielectric samples. On the other hand, the glass container can lead to a significant alteration of the heating characteristics as a function of container thickness. The power absorption, heating pattern (location of the heating fronts) and spatial heating uniformity within dielectric samples are found to vary significantly with the thickness of the glass container. The results indicate that the glass container can play the critical role to alter the heating characteristics based on the processing requirement (uniform heating or targeted heating at varying locations). These results are expected to play important roles for material processing and the role of the glass containers towards optimal microwave processing applications is revealed for the first time. These results are also important for further investigations on the containers (materials, shapes etc.) and their potential applications for the enhanced, controlled or targeted microwave processing of materials.

The Dielectric Properties of Worker Bee Homogenate in a High Frequency Electric Field

Biological tissues, including insect tissues, are among lossy dielectric materials. The permittivity properties of these materials are described by loss factor ε″ and loss tangent tgδ. The dielectric properties of the worker honeybee body homogenate are tested in the range of high frequencies from 1 MHz to 6 GHz. The homogenate is produced by mixing whole worker honeybees and tested with an epsilometer from Compass Technology and a Copper Mountain Technologies vector circuit analyser VNA. Due to their consistency, the homogenate samples are placed inside polyurethane sachets. The measured permittivity relates to two components of a sample: homogenate and polyurethane. For five samples, two extremes were specified for the permittivity, loss factor ε″, and the loss tangent tgδ, for the frequency range 20 ÷ 80 MHz and 3 GHz. Four techniques of testing permittivity in biological tissues were used to determine the dielectric properties of the homogenate. A calculation model was developed featuring a minimum measurement error of the loss factor ε″ and the loss tangent tgδ. The power absorbed per unit volume is described for the whole frequency range.

Characteristic Mode Formulations of Composite PEC and Lossy Dielectric Objects

Lossy dielectric substrate affects the performance of a nearby perfect electric conductor (PEC) antenna. This letter presents a set of formulae for characteristic mode analysis (CMA) of composite PEC and lossy dielectric objects. It is based on the volume-surface integral equation and substructure treatment that separates the radiation and dissipation powers of the composite structure. A narrow PEC plate (that represents a dipole antenna) is placed in proximity of a thick, lossy dielectric material, and CMA of this structure is presented as an example. The separation gap between the PEC and dielectric objects affects the resonance and radiation efficiency of the antenna, and it is shown that CMA accurately captures those effects. The influence of dielectric loss on the modal orthogonality is discussed. Since the PEC item dominates over the coupling one in the substructure operator, the computed modes maintain good orthogonality with low-loss dielectrics. Owing to the physical insights of CMA, it has many potential applications associated with lossy materials.

An epsilon-near-zero-based Dallenbach absorber

We report a theoretical analysis of total absorption conditions in a structure consisting of a lossy coating layer on top of a metal substrate, which is known as a Dallenbach absorber. All possible combinations of complex refractive indices of the coating material and thicknesses of the coating layer providing complete absorption are described for the case of normal incidence of a plane wave. The resulting solution space allows Dallenbach absorbers to be designed both with the use of conventional lossy dielectric or semiconductor materials having a refractive index greater than unity and with the use of epsilon-near-zero (ENZ) materials. Simple analytical relations are obtained for the total absorption conditions in ENZ materials. For coatings with different values of the refractive index, we present a comparative analysis of the angular dependences of the absorption coefficient and the profiles of the electromagnetic field distribution. The design of an indium-tin oxide (ITO) coating on an aluminum substrate is presented by the example of an ENZ-based Dallenbach absorber. It is shown that by varying the concentration of free carriers in ITO in the range 1019 − 1021 cm−3, the total absorption can be achieved at any wavelength in the range of approximately 1–10 μm.

Role of shapes (smooth surface and edges) for uniform and targeted heating objectives of a model dielectric material incident with microwave irradiation

Role of shapes involving smooth surface (circle) and edges (square and triangular-types 1 and 2) for dielectric materials with identical cross section has been investigated for objectives of uniform heating or targeted heating of a representative low lossy dielectric material. The material is incident with microwaves from one side (lateral irradiation) and symmetrically at outer surface (radial irradiation) while the material is exposed to microwaves in free space. Governing equations for microwaves and thermal transport are solved using Galerkin finite element method. Radiation boundary condition (RBC) based on scattering effect has been implemented for microwave propagation. Finite element analysis has been carried out for discretization and detailed implementation on integral form of RBC has been elucidated using finite element method. Average power absorption data for various cross sections have been considered for detailed analysis of uniform volumetric heating or targeted heating effect for various length scales: small samples (Regimes 1 and 2) and large samples (Regimes 3 and 4). Length scales of Regime 2 involving circle-square are optimal for uniform volumetric heating or targeted central heating in the presence of radial irradiation. Triangular materials are very effective for targeted multiple high heating zones at the surface for Regimes 3 and 4 in the presence of lateral irradiation. In general, lateral irradiation provides larger heating effects compared to radial irradiation involving larger length scales (Regimes 3 and 4).

A novel microstrip antenna using circular ring defected ground structure for X band applications

In this manuscript, a novel Circular Ring Resonator (CRR) defected ground structure has been proposed for X-band applications. The proposed structure uses inset feed modified square ring as the radiating layer, two concentric circular conductive copper rings as Defected Ground Structure (DGS) over a lossy Flame Retardant-4 substrate dielectric material. This DGS is an emerging technique which is used for enhancing the various parameters of patch antennas. The dimensions of the radiating element are 0.3λ × 0.3λ × 0.04λ at first resonating frequency and exhibits impedance bandwidth for S11 < −10 dB at 9.7 and 11.4 GHz which is useful for military radar and satellite terrestrial communications. Finite element technique based HFSS 19 has been used for simulation.

Suppression of Spurious Cavity Modes Using Lossy Dielectric Material in X-Band Tunable Coaxial Pulse Magnetron

This article presents the electromagnetic and particle-in-cell (PIC) simulation results of an X-band coaxial magnetron obtained using commercially available 3-D simulation tools CST particle studio. The operating frequency of the magnetron is 9.5 GHz with the tuning range of 8.5-9.5 GHz and the output power of 200 kW. It is observed by simulation that stable operation is not possible without eliminating the spurious cavity modes. For this purpose, the inner wall of the anode block has been loaded with the lossy dielectric material in the form of an annular cylinder having dielectric permittivity 23 and loss tangent 0.24. When the anode wall is loaded with lossy dielectric material, eight space charge spokes are observed during the stable operation of the magnetron which correspond to π-mode of operation in a coaxial magnetron having 16 vanes. A clear oscillation spectrum with a single peak is observed at 9.350 GHz with no other noticeable peaks. The radiated output power obtained in simulations is about 235 kW, with an anode voltage of 23 kV and an anode current of 30 A. The applied external magnetic field is 0.36 T and the corresponding efficiency of the magnetron operation is ~34%. The frequency tunability of the magnetron and the effect of frequency variation on the output power of the magnetron have also been studied by varying the length of the outer coaxial cavity. The frequency has been varied from 8.65 to 9.577 GHz and the corresponding variation in the output power is about 16%.

Propagation of Surface Plasmon Waves along Multi Wall Carbon Nanotube with Gold Core

We have studied the propagation of surface plasmon waves along multiwalled carbon nanotube with gold core. We have modeled the shells of multiwalled carbon nanotube as impedance sheets with axially directed surface conductivity incorporating inter shell coupling in an integral equation approach. We have found that in low frequency regime optical interband transitions did not occur and guided waves propagated with low attenuation in an multiwalled carbon nanotube which has metallic shells. In the same frequency range the axial polarizability of a finite length multiwalled carbon nanotube has a resonant behavior due the antenna length matching effect. The shells with surface conductivity due to interband transitions suppressed guided wave propagation. Surface Plasmon wave propagation in a multiwalled carbon nanotube with gold core showed that in the near infrared and visible regime the shells behaved as lossy dielectric materials and suppressed surface wave propagation along the gold core. The electromagnetic characteristics of carbon nanotube based antennas have been examined in different frequency regime ranging from the microwave to the visible regime. Carbon nanotube has been demonstrated to play a crucial role connected electrically to planner periodic structures of single wall carbon nanotubes, carbon nanotube bundles and carbon nanotube arrays. The inter shells interaction leaded to inter shell electron tunneling or hopping. Fermi momentum of two incommensurable shells do not coincide within the first Brillouin zone and the inter shell tunneling vanished. In the presence of localized defects inter shell conduction increased and defectfree shells were managed by neglecting intershell conduction. We have used microscopic model for multiwalled carbon nanotube and radiation characteristics were determined by its waveguiding properties, the dispersion equation for guided wave propagation on an infinitely long multiwall carbon nanotube. We have found that the guided wave has strong retardation and high attenuation so that the frequency of a geometric resonance is not connected to the free space wave length but to a shorter effective wavelength that depends on the material properties. The obtained results were compared with the previously obtained results and were found in good agreement.

Three-Dimensional Printing of Honeycomb Microwave Absorbers: Feasibility and Innovative Multiscale Topologies

In this article, we propose to apply 3-D printing technology to the design and realization of honeycomb microwave absorbers. First, printability of simple honeycomb structures, made of a lossy dielectric material, was evaluated and validated by measurement in the 2-18 GHz frequency band. Effective dielectric properties of honeycomb structures with different dimensions are also discussed. Then, the interest of 3-D printing technology was highlighted by the design, fabrication, and measurement of a multiscale honeycomb absorber that can significantly increase the relative bandwidth. The 3-D printed honeycomb absorbers are compared with others technologies. The potential of this technology was also illustrated by the fabrication and measurement of a pyramidal honeycomb absorber that demonstrates an absorption level of more than 22.9 dB over the 2-18 GHz frequency band.

Design of ternary-component X-band microwave absorber based on FeCo/Sr hexaferrite/PANI nanocomposite in silicon resin matrix

This work reports on the design and investigation of a new microwave absorber prepared from the combination of Sr-hexaferrite as a hard magnetic material, FeCo nanoparticles as a soft magnetic material, and polyaniline PANI as a dielectric-loss material. The prepared microwave absorber was characterized structurally and morphologically by X-ray diffractometry and scanning electron microscopy. The magnetic properties of the absorber were studied by vibrating sample magnetometer. Vector network analysis was used to perform the electromagnetic characterization of the absorber, which shows an excellent microwave absorption performance in the X-band. The minimum reflection loss was −22.1 dB at a matching frequency of 8.5 GHz, and the bandwidth under −10 dB was 2.6 GHz at a low loading percentage of 30 wt% and a thickness of 2 mm. The good microwave absorption characteristics were linked to the synergistic effect of combining magnetic and dielectric lossy materials. The effect of the chemical nature of silicon resin matrix on the microwave absorption performance was investigated. The presence of polar Si-O groups in silicon resin enhanced the minimum reflection loss and decreased the matching frequency.

On the representation of thin wires inside lossy dielectric materials for FDTD‐based LEMP simulations

The finite‐difference time‐domain method is one of the most widely used numerical electromagnetic computation techniques, and it has become an effective tool for analyzing electromagnetic transient phenomena in three‐dimensional structures and grounding systems. However, the available approaches for representing thin wires apply only to bare conductors such as overhead power lines and earth electrodes. In this work, we demonstrate the applicability of thin‐wire representation techniques to wires surrounded by both lossy and lossless media, such as reinforcing bars inside lossy concrete. The validated technique is then illustrated through the study of a reinforced‐concrete building struck by lightning to evaluate the effect of concrete on the penetration of lightning electromagnetic pulses inside the building. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley &amp; Sons, Inc.

Analysis on the Effects of the Human Body on the Performance of Electro-Textile Antennas for Wearable Monitoring and Tracking Application.

Previous works have shown that wearable antennas can operate ideally in free space; however, degradation in performance, specifically in terms of frequency shifts and efficiency was observed when an antenna structure was in close proximity to the human body. These issues have been highlighted many times yet, systematic and numerical analysis on how the dielectric characteristics may affect the technical behavior of the antenna has not been discussed in detail. In this paper, a wearable antenna, developed from a new electro-textile material has been designed, and the step-by-step manufacturing process is presented. Through analysis of the frequency detuning effect, the on-body behavior of the antenna is evaluated by focusing on quantifying the changes of its input impedance and near-field distribution caused by the presence of lossy dielectric material. When the antenna is attached to the top of the body fat phantom, there is an increase of 17% in impedance, followed by 19% for the muscle phantom and 20% for the blood phantom. These phenomena correlate with the electric field intensities (V/m) observed closely at the antenna through various layers of mediums (z-axis) and along antenna edges (y-axis), which have shown significant increments of 29.7% in fat, 35.3% in muscle and 36.1% in blood as compared to free space. This scenario has consequently shown that a significant amount of energy is absorbed in the phantoms instead of radiated to the air which has caused a substantial drop in efficiency and gain. Performance verification is also demonstrated by using a fabricated human muscle phantom, with a dielectric constant of 48, loss tangent of 0.29 and conductivity of 1.22 S/m.

Ear-to-Ear Propagation Model Based on Geometrical Theory of Diffraction

An ear-to-ear (E2E) propagation model based on geometrical theory of diffraction (GTD) is presented. The model uses the creeping wave loss along the geodesic paths that connect the ears. It is the first model to investigate which geodesic paths that link the ears. The model uses GTD expressions for a lossy dielectric material, which is a much better approximation of the human body than the perfect electric conductor approximation often used. The model is validated for the industrial, scientific, and medical band at 2.45 GHz. The model is valid at any frequency range as long as the propagation loss through the head is significantly higher than the propagation loss around the head. Similarly, the model could be used for other areas of the body. The comparison with simulations shows strong correlation. The antenna orientation and frequency sweeps were performed to further investigate the model. The sweeps change the radiation pattern of the antenna to utilize different paths around the head, but the model still correlates with the simulation. This validates the model's division of the E2E propagation into different geodesic paths around the head.

Constructing excellent electromagnetic wave absorber with dielectric-dielectric media based on 3D reduced graphene and Ag(I)-Schiff base coordination compounds

The dielectric-dielectric composite (SRGA) for electromagnetic absorber was fabricated via integrating Ag(I)-Schiff base coordination compounds (SSBCC) with three-dimensional reduced graphene aerogel (3D-rGA) powders. SRGA showed excellent electromagnetic wave absorption properties in terms of reflection loss, absorption band width and absorber thickness. Specially, when the mass ratio of SSBC to 3D-rGA powders was 1:3 (SRGA-25), the maximum value of reflection loss at 2 mm was up to −63.82 dB and the effective frequency bandwidth of 6.28 GHz (10.16–16.44 GHz) at 2.5 mm can be obtained. The mechanism investigation of electromagnetic wave absorption for SRGA showed that the enhanced electromagnetic wave absorption was ascribed to enhanced polarization loss derived from good 3D-conductive-network units of 3D-rGA, abundant interfaces caused by the media heterostructure due to the introduction of SSBCC and the good impedance matching condition. And 3D-rGA based materials might be put into practical application only in powder state due to the very low strength of the buck state. Therefore, the investigation on SRGA in our contribution is considered to be an actual performance evaluation of the materials based on three-dimensional graphene for microwave attenuation. This work also provided a method for fabricating excellent graphene-based electromagnetic wave absorbers by simply mixing a suitable dielectric lossy material, e.g. SSBCC.