Electromagnetic Properties Of Composites Research Articles

Electromagnetic composites: From effective medium theories to metamaterials

Electromagnetic (EM) composites have stimulated tremendous fundamental and practical interests owing to their flexible electromagnetic properties and extensive potential engineering applications. Hence, it is necessary to systematically understand the physical mechanisms and design principles controlling EM composites. In this Tutorial, we first provide an overview of the basic theory of electromagnetism about electromagnetic constitutive parameters that can represent the electromagnetic properties of materials. We show how this corpus allows a consistent construction of effective medium theories and allows for numerical simulation of EM composites to deal with structure–property relationships. We then discuss the influence of spatial dispersion of shaped inclusions in the material medium on the EM properties of composites, which has not been systematically illustrated in the context of this interdisciplinary topic. Next, artificial composites or metamaterials with peculiar properties not readily available in nature are highlighted with particular emphasis on the control of the EM interaction with composites. We conclude by discussing appropriate methods of electromagnetic measurement and practical aspects for implementing composites for specific applications are described. Overall, this Tutorial will serve the purpose of introducing the basics and applications of electromagnetic composites to newcomers in this field. It is also anticipated that researchers from different backgrounds including materials science, optics, and electrical engineering can communicate to each other with the same language when dealing with this interdisciplinary subject and further push forward this advancement from fundamental science to technological applications.

Engineering Magnetic Type Radio-Absorbers Based on Composites with a Dual-Phase Polymer Matrix

This work is focused on the optimization of electromagnetic and mechanical properties of magnetic polymer composites for EMI applications as radio absorbers (RAs). Polymer composites with a dual-phase polymer matrix, vinyl-terminated polydimethylsiloxane (PDMS) in epoxy (ER), were investigated for fabricating highlyfilled manganese zinc ferrite (MnZn) and carbonyl iron (CI) composites with respect to radio-absorption and mechanical properties. The dielectric and magnetic properties of the composites were determined by the type, concentration as well as the polymer matrix composition. Increase of the filler and the PDMS concentration leads to an increase in magnetic losses due to a decrease in the demagnetizing field. The electromagnetic properties of the composites were evaluated in the RF band using the impedance method (1 MHz–3 GHz). Based on the complex permittivity (ε*) and the complex permeability (μ*), the reflection loss RL (dB) of single-layer metal-backed RAs were calculated. The RAs with a MnZn ferrite demonstrated a larger bandwidth to thickness ratio in comparison with the CI-based RAs due to a proper ratio between ε* and μ* which leads to the better impedance matching conditions. According to the mechanical analyses (DMA, Charpy impact strength) the significant increase of stiffness up to 125% and the impact strength up to 150% was achieved due to the optimal composition of the polymer matrix and the filler.Graphical Abstract

Comparative study of polymer-based nanocomposites microwave absorption performance in X–band

The present work focused on electromagnetic (EM) absorption performance comparison of different polymer nanocomposite structures. Synthesis and fabrication of polymer nanocomposite composed of graphene, polyurethane (PU), epoxy was done using in situ polymerization and resin transfer moulding respectively. The effect of polymer on EM properties of composite was carried out using waveguide measurement technique in X-band. Reflection Loss (RL) and shielding effectiveness (SE) were measured for various nanocomposites using EM wave theory. From the results it is observed that 2.5 wt% of PU/epoxy graphene nanocomposite has shown RL value −35 dB at 12.1 GHz and SE value of −45 dB.

Preparation and Characterization of High Magnetic Loss Microwave Absorber for Splitter Load

Microwave absorbing material was prepared using epoxy resin as matrix and spherical carbonyl iron powder (s-CIP), flaky carbonyl iron powder (f-CIP) as absorbing agent. Microwave absorbing, mechanical properties and structure of the composites containing different kinds of carbonyl iron powder (CIP) were investigated. The results show that the microwave absorber with flaky CIP have better electromagnetic properties than composites with spherical CIP. With concentration of spherical CIP increasing the electromagnetic properties of composites becomes better, except for the mechanical performance. The flaky CIP/epoxy resins composites with a loading of 79 wt% plate-like CIP has attenuation constant of 25.443 dB/cm in 3 GHz. The absorber prepared using flaky CIP has homogenous, dense structure and has excellent mechanical properties.

Electro-magnetic properties of composites with aligned Fe-Co hollow fibers

A novel Fe-Co binary hollow fiber was synthesized by electroless plating using hydrolyzed polyester fiber and its anisotropy characteristic was investigated for electromagnetic wave absorbing materials. The hollow fibers in parallel with magnetic field show higher saturated magnetization of 202 emu/g at the applied magnetic field of 10 kOe and lower coercivity (27.658 Oe), compared with the random and vertical oriented hollow fibers. From complex permittivity measurement, the Fe-Co hollow fiber composites clearly display a single dielectric resonance, located at ∼14 GHz. The Fe-Co hollow fibers not only provide excellent EM properties in GHz frequency ranges, resulting mainly from the strong resonance, but also adjust the soft magnetic properties through fiber alignments. The cavitary structure of the Fe-Co hollow fibers, not only giving rise to a dielectric loss resonance and also adjusting its peak frequency, may be a pathway to useful EM wave absorptive devices in GHz frequency ranges.

Electromagnetic and microwave absorbing properties of carbonyl iron/BaTiO3 composite absorber for matched load of isolator

Composite absorbers made from carbonyl iron powder and BaTiO3 were prepared by blending technique with the matrix of epoxy resin. The structure and microtopography of the carbonyl iron and BaTiO3 particles were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The microstructure and electromagnetic properties of the as-prepared composites were investigated by SEM and vector network analyzer (VNA). The effect of the mass ratio of BaTiO3/carbonyl iron on the electromagnetic properties of the composites is investigated. The bandwidth with an absorption loss exceeding 30dB is obtained in the whole measured frequency range for all composites, and an optimal reflection loss drop below 1.5dB with 24wt% BaTiO3. It is found that the carbonyl iron/BaTiO3 composite absorber can be a promising candidate as a matched load for the isolator.

Microwave permittivity and permeability of magnetic wire composites

This paper provides a comprehensive review on electromagnetic properties of composites with magnetic microwires. The analysis is made in terms of the effective parameters: permittivity and permeability. The use of magnetic components in wire media makes it possible to realize controllable or tunable materials. A variable magnetoimpedance controls the dispersion region resulting in broadband transmission modulation. The conditions of strong tuning including directional changes in the static magnetization, magnetoimpedance, stress impedance, and optimal skin effect are discussed. Diluted composites with magnetic wires having specific circumferential or helical anisotropy may also have large values of the effective permeability at high frequencies up to few GHz. This is important to design materials possessing the both effective parameters in the same frequency band. Considering the variation in the impedance due to internal stress/temperature distribution, the magnetic wire composites can be regarded as materials with distributed sensors. A range of potential applications for structural health monitoring is discussed.

Electromagnetic properties of composites containing graphite nanoplatelets at radio frequency

The effect of three different carbon-based nano and microfillers on the electromagnetic (EM) performance of polymeric composites was examined through the measurement of the effective complex permittivity in the frequency range from 8.2 to 18 GHz. Results show that polymeric composites based on graphene nanoplatelets are much more easily processable than composites filled with carbon nanotubes, while still retaining much of the EM performance over the investigated frequency band, as well as being light weight.

Effect of transition layers on the electromagnetic properties of composites containing conducting fibres

The approach to calculating the effective dielectric and magnetic response in bounded composite materials is developed. The method is essentially based on the renormalisation of the dielectric matrix parameters to account for the surface polarisation and the displacement currents at the interfaces. This makes it possible the use of the effective medium theory developed for unbounded materials, where the spatially-dependent local dielectric constant and magnetic permeability are introduced. A detailed mathematical analysis is given for a dielectric layer having conducting fibres with in-plane positions. The surface effects are most essential at microwave frequencies in correspondence to the resonance excitation of fibres. In thin layers (having a thickness of the transition layer), the effective dielectric constant has a dispersion region at much higher frequencies compared to those for unbounded materials, exhibiting a strong dependence on the layer thickness. For the geometry considered, the effective magnetic permeability differs slightly from unity and corresponds to the renormalised matrix parameter. The magnetic effect is due entirely to the existence of the surface displacement currents.

Electromagnetic properties of composites containing elongated conducting inclusions

We present a detailed theoretical study of the dielectric and magnetic response of composites containing elongated conducting inclusions---sticks. These composites are widely used as engineering materials. They can be also considered as a model to describe many processes occurring in nature, e.g., dielectric enhancement in grain-saturated porous rocks. An approach is proposed that is based on the idea of a scale-dependent local dielectric constant. We develop an effective-medium approximation and derive an equation to calculate an effective dielectric constant of the composites in the quasistatic case and for the high frequency when there is a strong skin effect in the conducting sticks. Our theory predicts very large values of the effective dielectric constant in a wide range of the stick concentration. We find that the dielectric constant can exhibit various dispersive behaviors. It can have relaxation behavior, power-law scaling behavior, or resonance dependence on the frequency. The resonance dependence occurs when the skin effect is strong and wavelength is comparable to the stick length. Then the real part of the dielectric constant has negative values in some frequency ranges. The possibility of a wave localization is discussed in that case. We consider effective magnetic properties of the conducting stick composites. We propose that the composites with nonmagnetic components will have a giant paramagnetic response as a result of a collective interaction of the sticks with an external magnetic field. \textcopyright{} 1996 The American Physical Society.