Broadband Electromagnetic Absorption Research Articles

Lightweight, ultra-broadband SiOC-based triply periodic minimal surface meta-structures for electromagnetic absorption

Lightweight, wide-band ceramic-based electromagnetic (EM) absorbers have great application demand in the field of high-temperature EM wave absorption. However, it is difficult for traditional ceramic-based structural EM absorbing materials (EMAMs) to balance the contradiction between broadband absorption and good impedance matching due to resonance effect. Herein, three novel non-resonant SiOC-based triply periodic minimal surface (TPMS) meta-structures named Schoen G (SG), Schwarz D (SD) and Schwarz P (SP) with a density of 0.556 g/cm3 were successfully synthesized by digital light processing (DLP) 3D printing and polymer-derived ceramics (PDCs) method. Through the structural design of multilayer arrays and holes, three metamaterials achieve good impedance matching and broadband EM absorption. The effective absorption bandwidth (EAB) of all three meta-structures reaches 9.80 GHz (8.2–18.0 GHz) in a wide matching thickness range, covering the entire X-Ku band. In addition, the minimum reflection loss (RLmin) of −55.68 dB is obtained at a matching thickness of 3.02 mm for SD meta-structure in X-band. Besides, the SG meta-structure tested by the arch method has an ultra-wide EAB of 11.88 GHz (6.12–18.0 GHz), exhibiting ultra-broadband EM absorption properties. It is significant that the intrinsic relationships between TPMS meta-structures and EM responses are explored by CST simulation. This work provides a new perspective for the design of lightweight, broadband ceramic-based EM metamaterial absorbers under high-temperature, harsh environments.

Design of broadband gradient resistive film metamaterial absorber based on genetic algorithm

In recent years, electromagnetic (EM) wave absorbing devices based on metamaterials have attracted widespread attention, due to their advantages such as broadband, easy preparation, and flexibility to tailor EM waves. Nevertheless, a review of the existing research reveals that the inherent sub-wavelength characteristics of metamaterials and metasurfaces impose certain constraints on their applications in low-frequency ranges. In order to achieve low detectability that takes into account both low-frequency and broadband absorbing performance, this work, presents a metamaterial absorber based on 5-layer gradient resistance film and dielectric composite structure, as shown in <xref ref-type="fig" rid="FigureAbstract">Fig. (a)</xref>. To begin with, we introduce the structural design of the initial element, and based on this, the transmission line theory and impedance matching principle are used to analyze the strong wave absorption conditions of the absorber element. In terms of the element structure optimization, the genetic algorithm is adopted to globally search for the optimal solution in the multi-variable domain, resulting in the rapid determination of metamaterial elements’ configurations and resistance parameters that meet the design goals. In the simulation, the wave absorption performance and mechanism of the designed absorbing element are also investigated in an in-depth manner. Simulation results show that the designed metamaterial absorber can achieve more than 90% EM wave absorption in a frequency range of 1.62–19.16 GHz (with a relative bandwidth of 168.8%) under normal incidence of linearly polarized plane waves, which effectively expands the absorption bandwidth to the L band and K band. In addition, the simulations for oblique incidence at different polarizations provide strong evidence for the device’s insensitivity to both polarization and angle. The radar cross section (RCS) curves obtained by the time domain (TD) simulation illustrate that the novel structure can achieve more than 10 dB RCS reduction in a frequency range of 1.7–20 GHz. In the device's performance verification process, a metamaterial absorber with 20 × 20 elements and dimensions of 1.566<inline-formula><tex-math id="M1">\begin{document}$ {\lambda }_{l} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="7-20231781_M1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="7-20231781_M1.png"/></alternatives></inline-formula>×1.566<inline-formula><tex-math id="M2">\begin{document}$ {\lambda }_{l} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="7-20231781_M2.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="7-20231781_M2.png"/></alternatives></inline-formula>× 0.113<inline-formula><tex-math id="M3">\begin{document}$ {\lambda }_{l} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="7-20231781_M3.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="7-20231781_M3.png"/></alternatives></inline-formula> is fabricated and tested by using the bow method reflectivity test system. The absorptivity curves under 5° oblique incidence of different polarizations, show that the proposed metamaterial absorber can realize more than 80% EM absorption in an entire frequency range from 2 to 18 GHz, the test results of different polarizations are basically consistent. The test results at oblique incidence (<i>θ</i> ≥ 30°) show that although the measured and simulated curves exhibit discrepancies in certain frequency bands due to human error or material dispersion characteristics, the overall experimental results are consistent with our expectations, which fully proves that the designed metamaterial absorber has potential application value in the field of low-frequency and broadband EM absorption.

Graphene-based polarization insensitive ultrathin broadband terahertz absorber for material sensing applications

In this paper, a tunable broadband electromagnetic absorber for sensing applications at terahertz frequencies is proposed. The proposed design consists of a graphene based multiple slot loaded rectangular resonator, dielectric material and gold based metallic ground plane. The dimensions of proposed absorber’s unit cell are 10 μm × 10 μm. The proposed absorber has more than 90% absorption over a frequency spectrum of 4.86–18.33 THz (% fractional bandwidth > 116.22%). The proposed absorber is symmetric which makes the structure polarization insensitive. It has stable characteristics for incidence angle (θ) ≥ 40∘ for both Transverse-Electric (TE) and Transverse-Magnetic (TM) waves. The effects of different substrate materials, different analyte materials, variations in the graphene parameters and water level on the proposed absorber’s performance are also analyzed. This absorber can be used to detect different materials including water and thickness of water layer present on its top surface. The proposed graphene-based absorber dominates previously reported wideband THz absorbers in terms of relative bandwidth, more than 90% absorption peak values, oblique stability and overall volume.

Synthesis of nitrogen-doped graphene-based binary composite aerogels for ultralightweight and broadband electromagnetic absorption

The development of ultralightweight and broadband electromagnetic wave (EMW) absorbing materials remains a big challenge. In this work, porous magnesium ferrite microspheres decorated nitrogen-doped reduced graphene oxide (NRGO/MgFe2O4) composite aerogels were prepared by a two-step route of solvothermal synthesis and hydrothermal self-assembly. Results of microscopic morphology characterization showed that NRGO/MgFe2O4 composite aerogels had a unique hierarchical porous structure. Moreover, the influence of additive amounts of graphene oxide on the electromagnetic parameters and EMW absorption properties of NRGO/MgFe2O4 composite aerogels was explored. Remarkably, the attained binary composite aerogel with the content of NRGO of 70.21 wt% exhibited the best EMW absorption performance. The minimum reflection loss reached up to −55.7 dB, and the corresponding effective absorption bandwidth was as large as 5.36 GHz at a thin matching thickness of 1.98 mm. Furthermore, when the matching thickness was slightly increased to 2.29 mm, the widest effective absorption bandwidth was enlarged to 7.1 GHz, covering the entire Ku-band. The magnetodielectric synergy and unique hierarchical porous structure in NRGO/MgFe2O4 composite aerogels not only improved the impedance matching, but also greatly enhanced the EMW absorption capacity. It was believed that the results of this work could be helpful for the preparation of graphene-based magnetic composites as broadband and efficient EMW absorbers.

3D printed carbon based all-dielectric honeycomb metastructure for thin and broadband electromagnetic absorption

Excellent electromagnetic absorbers with comprehensive performances of thin thickness, lightweight, broadband and strong absorption have become a significant requirement for electromagnetic interference and stealth technologies. In this study, a honeycomb metamaterial absorber with the conductive coating is designed and proposed, with 3D printed honeycomb skeleton coated by the conductive coating composed of carbon fibers, carbon nanotubes and resin. The optimized metamaterial absorber realized > 90% absorption in 5.65 ∼ 40 GHz with a total thickness of 6 mm, indicating a relative bandwidth of 152.9% with a relative thickness of 0.107. The excellent performances of the proposed absorber were contributed by the synergy effect of the electric parameters of the fabricated composites as well as the geometry parameters of the honeycomb meta-structure, which induced multiple loss modes. The synergy design on the 3D printed honeycomb skeleton and conductive coating would give a new insight into designing lightweight ultra-broadband microwave metamaterial absorbers.

Design and fabrication of multi-material broadband electromagnetic absorbers for use in cavity-backed antennas

We investigated the feasibility of designing and fabricating novel broadband radiofrequency (RF) absorbers for use in cavity-backed antennas. Fabricating the absorber involved a multi-material additive manufacturing (AM) approach that combined two polymer filaments: a low-loss dielectric filament and a lossy carbon-loaded filament. An iterative optimization algorithm was developed to deploy these filaments and create gradient distributions of material properties that minimize reflectance over a desired frequency band and a range of incident angles to achieve wideband electromagnetic absorption. The chosen material profiles were effectively realized using a spatially varying subwavelength lattice structure printed via fused filament fabrication. Experimentally, validation results demonstrated low reflectance over a wide frequency band, 10 to 40 GHz, and a range of incident angles, 0°–50°. Finally, this printed multi-material absorber was integrated within a cavity-backed spiral antenna and used to suppress backlobe radiation while maintaining an acceptable radiation pattern in the forward direction. While this study investigated cavity-backed antennas, these computational and experimental methods are potentially useful for a wide range of other applications.

Hierarchical graphene@MXene composite foam modified with flower-shaped FeS for efficient and broadband electromagnetic absorption

• Ultralight magnetic composite foam with hierarchical structure is fabricated. • Loading of MXene/FeS on rGO promotes the formation of hierarchical impedance in foam. • Hierarchical impedance structure facilitates the entrance and dissipation of EMW. • Optimization of impedance structure improves absorption capacity and bandwidth. Developing high-performance broadband microwave absorption material becomes an urgent concern in the field of electromagnetic protection. In this work, an ultralight magnetic composite foam was constructed by electrostatic self-assembly of MXene on the surface of graphene skeletons, and subsequent hydrothermal anchoring of flower-shaped FeS clusters. Under the synergistic effect of MXene coating increasing conductive loss and FeS clusters improving magnetic loss, the rational construction of hierarchical impedance structure in foam can effectively promote the entrance and consumption of more incident electromagnetic waves. The minimum reflection loss (RL min ) reaches –47.17 dB at a thickness of 4.78 mm, and the corresponding effective absorption bandwidth (EAB) is up to 6.15 GHz. More importantly, the microwave absorption performance of composite foam can be further optimized by controlling the loading of MXene and thermal treatment at a low temperature. The maximum of EAB for GMF-300 can be extended to an unprecedented value of 11.20 GHz (covering 6.10–17.30 GHz).

Porous carbon sphere decorated with Co/Ni nanoparticles for strong and broadband electromagnetic dissipation

In order to eliminate the hazards induced by electromagnetic pollution, the preparation of microwave absorbing composite incorporating biomass-derived porous carbon with efficient magnetic component has been recognized as a valid route. Herein, a serious of Co/Ni NPs decorated porous carbon sphere were successfully prepared via a combined method of activation, hydrothermal and annealing process. By controlling the addition amount of activator and the concentration of precursor, the appropriate morphology and impedance matching can be obtained in the as-prepared hybrid. Thus, the super-wide EAB of S4 can reach 7.30 GHz for only 2.3 mm thickness, and its maximum RL is −76.54 dB at 12.23 GHz with a thickness of 2.5 mm. This outstanding microwave absorption properties could be attributed to the synergistic effect of magnetic and dielectric loss under decent impedance matching condition, which includes the primary nature and exchange resonance, destructive interference, together with multiple reflection and scattering effect, and the subordinate effect of dipole and interface polarization loss. This work offers a novel route to prepare biomass-derived porous carbon loaded with magnetic NPs for strong and broadband electromagnetic absorption.

Design of metamaterial- and graphene-based tunable broadband electromagnetic absorber at the terahertz region

A metamaterial- and graphene-based broadband terahertz (THz) electromagnetic wave absorber that is composed of a stack of patterned gold film layer, patterned graphene layer, polyimide layer, and silicon layers was studied in detail. Our study is based on numerical simulations and electromagnetic absorption level higher than 90% over 2.09 THz band was demonstrated. The absorption frequency band significantly depends on the thickness of the polyimide layer and red shifts in parallel with its thickness. The major role of the added patterned graphene layer is to introduce frequency tunability property to the almost perfect absorption. As the Fermi level of graphene changed from 0 to 0.6 eV, the center frequency of the absorption band blueshifts from 6.19 to 8.15 THz. We also investigated incoming beam angle of incidence dependence and polarization sensitivity of the absorption. Metamaterial-based tunable absorbers prospected to be utilized in high-performance THz devices as a performance boosting critical element.

Green Nanocomposite-Based Metamaterial Electromagnetic Absorbers: Potential, Current Developments and Future Perspectives

The use of the natural materials instead of conventional materials as electromagnetic absorbers promotes environmental sustainability, cost-effectiveness, and ease of accessibility. Furthermore, these materials may also be designed as absorbers and as reinforcements in building materials in a lightweight form. The absorbing ability of composite materials can be customized based on the chosen fillers. Specifically, magnetic and dielectric fillers can be incorporated to improve the absorption of a composite material compared to traditional materials. This work aims to review recent developments of electromagnetic absorbers enabled by nanocomposites, metamaterial and metasurface-based, as well as green composite alternatives. First, the background concepts of electromagnetic wave absorption and reflection will be presented, followed by the assessment techniques in determining electromagnetic properties of absorbing materials. Next, the state-of-the-art absorbers utilizing different materials will be presented and their performances are compared. This review concludes with a special focus on the future perspective of the potential of metamaterial based nanocellulose composites as ultrathin and broadband electromagnetic absorbers.

Heat treatment of commercial Polydimethylsiloxane PDMS precursors: Part I. Towards conversion of patternable soft gels into hard ceramics

The commercially available polydimethylsiloxane (Sylgard®184) is a commonly known material in microelectronic and microfluidic industries as flexible substrates, device packing elements, lab-on-a-chip, or stamps. Recently, PDMS derived materials have attracted much interest in the development of broadband electromagnetic absorbers in the terahertz and microwave regions. When exposed to high temperature (T > 900 °C) PDMS undergoes profound transformations leading to derived solid nanocomposites made of graphitic phase embedded into silicon oxycarbide structure.In this work, we discuss the PDMS thermal changes that have been evaluated using different analytical techniques (thermogravimetry-coupled mass spectrometry, and Raman spectroscopy). The pyrolysis of cross-linked gels in an inert atmosphere gave 50.94 wt% of solid residue at 1500 °C. It was observed that the presence of Si–H bonds in the curing agent promotes cross-linking between the siloxane backbones containing vinyl groups (Si–C2H3) through hydrosilylation reaction. However, excessive addition of curing agent impedes ceramic yield down to 20%. Above 1000 °C, Raman spectra show the formation of disordered sp2 carbon that subsequently organizes with the heat-treatment temperature. These carbon-rich silicon oxycarbide materials are remarkably resistance to oxidation even at 1500 °C.

Moore's curve structuring of ferromagnetic composite PE-NiFe absorbers

A ferromagnetic material involving nickel-iron particles embedded in a polyethylene matrix is synthesized and electrically characterized between 1 and 12 GHz. These measurements show the combination of electric and magnetic activity along with significant loss terms. We take benefit of these properties for the design of broadband electromagnetic absorbers. To this aim, we use a fractal structuring based on Moore curves. The advantage of etching patterns over metallic ones is clearly evidenced, and several pattern absorbers identified by their Moore's order iteration are designed and analyzed under oblique incidence.

From nanoscale to macroscale: Engineering biomass derivatives with nitrogen doping for tailoring dielectric properties and electromagnetic absorption

Since achievement in electromagnetic (EM) technology dramatically promotes the critical requirement in developing advanced EM response materials, which are required to hold various advantageous features in light weight, small thickness, strong reflection loss and broadband absorption, the most important requirements, i.e. strong reflection loss and broadband absorption, are still highly pursued because of the intrinsic shortage in conventional EM absorbers. For addressing such critical problems, a unique three-dimensional nitrogen doped carbon monolith was demonstrated to understand the effects of the nitrogen doping on the dielectric and microwave absorption performance. The chemical components of the nitrogen doped carbon monoliths have been quantitatively determined for fully understanding the effects of nanoscale structures on the macroscopic composites. A modified Cole-Cole plot is plotted for guiding the chemical doping and material process, aiming to realizing the best matching conditions. The results have promised a universal route for achieving advanced materials with strong and broadband EM absorption.

Design of a broadband electromagnetic absorbers based on TiO2/Al2O3 ceramic coatings with metamaterial surfaces

This paper presents a design method of wide-band radar absorber (RA) based on TiO2/Al2O3 ceramic coatings with metamaterial surfaces. The metamaterial surfaces are made up of periodic array of metallic patches consisting of circular and square aluminum film. The effects of design parameters on the reflectivity of RA were discussed, including the size, the period of metamaterial surfaces, and the thickness of ceramic coating. In addition, the effects of incidence angles for transverse electromagnetic (TE) and transverse magnetic (TM) polarization on the microwave absorption properties of RA were also investigated. Simulated results indicated that the microwave absorbing properties can be improved and adjusted by selecting the suitable unit dimensions of metamaterial surfaces, the RL is generally insensitive to incident angle from 0° to 30°. Finally, the design parameters of RA were optimized by Genetic Algorithms (GA) approach under normal incidence. Both the simulated results and measured results indicated that a bandwidth of reflection loss (RL) of single TiO2/Al2O3 ceramic coating below −10 dB is 0 GHz in the frequency range of X-band and Ku-band. By combination of metamaterial surfaces to ceramic coatings, a bandwidth with the reflectivity of RA below −10 dB can be obtained in the frequency range of 8.2–18 GHz for the thickness of the TiO2/Al2O3 coating of only 1.7 mm. The minimum value of reflection loss is −29 dB at about 10.6 GHz.

Broadband Absorbing Exciton-Plasmon Metafluids with Narrow Transparency Windows.

Optical metafluids that consist of colloidal solutions of plasmonic and/or excitonic nanomaterials may play important roles as functional working fluids or as means for producing solid metamaterial coatings. The concept of a metafluid employed here is based on the picture that a single ballistic photon, propagating through the metafluid, interacts with a large collection of specifically designed optically active nanocrystals. We demonstrate water-based metafluids that act as broadband electromagnetic absorbers in a spectral range of 200-3300 nm and feature a tunable narrow (∼100 nm) transparency window in the visible-to-near-infrared region. To define this transparency window, we employ plasmonic gold nanorods. We utilize excitonic boron-doped silicon nanocrystals as opaque optical absorbers ("optical wall") in the UV and blue-green range of the spectrum. Water itself acts as an opaque "wall" in the near-infrared to infrared. We explore the limits of the concept of a "simple" metafluid by computationally testing and validating the effective medium approach based on the Beer-Lambert law. According to our simulations and experiments, particle aggregation and the associated decay of the window effect are one example of the failure of the simple metafluid concept due to strong interparticle interactions.

Using γ-Fe2O3 to tune the electromagnetic properties of three-dimensional (3D) polypyrrole (PPy) and its broadband electromagnetic absorber

Electromagnetism such as gravity can be considered an omnipresent force, which plays an important role in the functional activities of organisms.

Negative impedance shunted electromagnetic absorber for broadband absorbing: experimental investigation

The traditional tuned mass absorber is widely employed to control the vibration of a primary structure by transferring the vibrating energy to the absorber. However, the working band of the absorber is very narrow, which limits the application of broadband vibration control. This study presents a novel broadband electromagnetic absorber by first introducing two negative impedance shunts to improve broadband damping of the absorber. The electromagnetic absorber is modeled, and the corresponding electromagnetic coupling coefficient is tested. A cantilever beam is employed to verify the broadband vibration absorption of the negative resistance (NR) shunted electromagnetic absorber (NR absorber) and the negative inductance NR shunted electromagnetic absorber (NINR absorber). The governing equations of the beam with two absorbers are derived, and the experiments are set up. The results point out that the NR and NINR absorbers can attenuate the broadband vibration. The proposed absorbers do not need the feedback system and the real-time controller compared to the active absorber; hence, they have great application potential in aerospace and in submarine applications, as well as in civil and mechanical engineering.

Broadband Mid-IR superabsorption with aperiodic polaritonic photonic crystals

We propose an approach for broadband near-perfect absorption with aperiodic-polaritonic photonic crystals (PCs) operating in the phononpolariton gap of the constituent material. In this frequency regime the bulk polaritonic materials are highly reflective due to the extreme permittivity values, and so their absorption capabilities are limited. However, we are able to achieve absorptance of more than 90% almost across the entire phonon-polariton gap of SiC with a SiC-air aperiodic one-dimensional(1D)-PC with angular bandwidth that covers the range of realistic diffraction-limited sources. We explore two types of aperiodic PC schemes, one in which the thickness of the SiC layer increases linearly, and one in which the filling ratio increases linearly throughout the structure. We find that the former scheme performs better in terms of exhibiting smoother spectra and employing less SiC material. On the other hand, the second scheme performs better in terms of the required total structure size. We analyze the principles underpinning the broadband absorption merit of our proposed designs, and determine that the key protagonists are the properties of the entry building block and the adiabaticity of the aperiodic sequencing scheme. Further investigation with derivative lamellar sequences,–resulting by interchanging or random positioning of the original building blocks–, underline the crucial importance of the building block arrangement in an increasing order of thickness. If we relax the requirement of near-perfect absorption, we show that an averaged absorption enhancement across the SiC phonon-polariton gap of ~10 can be achieved with much shorter designs of the order of two free-space wavelengths. Our findings suggest that our aperiodic polaritonic PC route can be promising to design broadband electromagnetic absorbers across the spectrum.

Thin and broadband electromagnetic absorber design using resistors and capacitors loaded frequency selective surface

A new method using resistors and capacitors loaded frequency selective surface (FSS) to design thin and broadband electromagnetic absorber is proposed. The effect of the loaded lumped elements on the absorptivity of the absorber is investigated through transmission-line equivalent circuit model. The simulations show that this multiple components loaded FSS (CLFSS) absorber has double changeable abilities of adjusting the real and imaginary parts of its input impedance, which leads to improvement of the absorber’s impedance matching condition and enhancing of the absorber’s absorptivity. Based on the above analysis, two types of CLFSS absorbers were fabricated to confirm the superiority of the multiple components loaded method. One was singly loaded with resistors and the other alternately loaded with resistors and capacitors. Our further measurements show that the alternately loaded FSS absorber has a better absorptivity than only resistors loaded FSS absorber. The alternately loaded FSS absorber with a total thickness of 3.7 mm exhibits a broadband reflectivity response with 98.7% bandwidth over the frequency range from 5.9 to 17.4 GHz below −8 dB.

Optimal Design Of Electromagnetic Absorbers Using Visualization Method For Wideband Potential Applications

This paper presents a design of broadband electromagnetic absorbers using a square loop shaped frequency selective surface (FSS) loaded with resistors printed on a dielectric substrate. A straightforward visual graphic representation analysis which extends the microwave impedance matching theory into wideband electromagnetic absorbing structure modifying design is carried out on the parametric analysis of the absorbers. Samples of the absorbers with different layers are fabricated. Measured results are in good agreement with the predicted ones, and both show that the novel absorber can reduce reflectivity greatly over a wide frequency range. The study shows that visual graphic representation analysis is simple and practicable to introduce the working principles of the wideband electromagnetic absorbing structure and to derive the best-suited element for wideband absorption.