Dielectric Absorber Research Articles

Analysis of Shielding Performance in Double-Layered Enclosures with Integrated Absorbers

Generally, various technologies, including waveguide below cutoff (WBC), gasket sealing, and bonding, are employed in metallic enclosures to achieve the high electromagnetic shielding performance required for EMP protection and EMC countermeasures in shielding structures or facilities. While the shielding structure or facility is properly constructed and maintained according to design specifications, its electromagnetic shielding performance can remain at the required level, effectively protecting internal electrical and electronic equipment from external electromagnetic interference. However, unintended apertures often occur during the construction or maintenance of shielding facilities, compromising their shielding performance. Therefore, it is crucial to develop technologies that prevent shielding effectiveness degradation caused by both intentional and unintentional apertures. This paper proposes a structure incorporating a composite absorber (made of dielectric and magnetic absorber) within a double metal panel of enclosure featuring an aperture, aimed at maintaining and improving the facility’s shielding performance. The effectiveness of the proposed structure was validated through numerical simulation.

Dielectric Properties and Microwave Absorbing Properties of Silicon Carbide Nanoparticles and Silicon Carbide Nanowhiskers

Silicon carbide (SiC) is well known for their outstanding microwave absorbing properties. SiC nanomaterials (SiCNMs) are expected to have better microwave absorption performance due to their high specific surface area. To date, no study was reported to compare the dielectric properties and microwave absorbing properties of different type of SiCNMs. Therefore, the objective of this paper is to compare the dielectric properties and microwave absorption properties of different types of SiCNMs. In this paper, SiC nanoparticles (SiCNPs) and SiC nanowhiskers (SiCNWs) were characterised using SEM and XRD. In addition, their dielectric properties and microwave absorbing properties were measured using network analyser and transmission line theory. It was found that SiCNWs achieved higher dielectric constant and loss factor which are and εr’ =17.94 and εr″ = 2.64 compared to SiCNPs that only achieved εr’ = 2.83 and εr″ = 0.71. For microwave absorbing properties, SiCNWs and SiCNPs attained minimum reflection loss of -10.41 dB and -6.83 dB at 5.68 GHz and 17.68 GHz, respectively. The minimum reflection loss of SiCNPs and SiCNWs obtained in this study is much lower than the nanometer-SiC reported previously. These results suggested that SiCNWs can be an ideal candidate of microwave susceptors for various microwave applications.

Synthesis, Structural, Morphology and Magnetic Properties: Effect of La on Multiferroic Nature of BiFeO3 Nanoparticles

Objectives: The present study focuses on developing La-doped BiFeO3 multiferroic materials for dielectric absorber applications. Methods: The samples are characterized by X-ray Diffractometer (XRD). Further, the morphology is examined using field emission electron microscopy (FESEM) and Transmission Electron Microscopy (TEM). The dielectric parameters and ac-electrical parameters are carried out by impedance spectroscopy. The magnetic properties are studied using a vibrating sample magnetometer VSM, P-E loop. Findings: XRD confirms the rhombohedral (trigonal) structure of BLFO nanoparticles. The grain and particle size values are determined by SEM and TEM, respectively. The dielectric and ac-electrical parameters for all the samples are thoroughly discussed at room temperature. The Maxwell-Wagner or interfacial polarization is noticed at low input field frequencies for x=0.2-0.8. The impedance analysis shows the contribution of grain and its boundary in the electrical conduction mechanism. The multiferroic behavior is examined using M-H loops, P-E loops, and μi-f plots. Novelty: The samples are synthesized by the hydrothermal process to prepare La-doped BiFeO3 nanomaterials. Keywords: Nanoparticles, Electron Microscopy, Multiferroic, Magnetization, Polarization, Permeability

A dual-band polarization independent dielectric metasurface-based absorber for sensing application in the visible light regime

We present a dual-band, polarization-independent dielectric terahertz absorber exhibiting near-perfect absorption and minimal reflection at frequencies of f 1 = 419 THz and f 2 = 528 THz. Using electromagnetic theory, we modeled the structure to derive the surface electric admittance and magnetic impedance of the metasurface, elucidating the conditions required for perfect absorption in terms of inverse electric and magnetic polarizabilities. The absorber features a tunable symmetrical design, facilitating precise frequency adjustment by modifying structural parameters and ensuring polarization independence for perpendicularly incident electromagnetic waves. This scalable and versatile absorber, constructed from readily available materials, is optimally suited for applications in resource detection, imaging, sensing, and medical diagnostics, attributed to its simplicity, cost-effectiveness, and high performance.

An ultra-broadband multi-layer dielectric gradient honeycomb microwave absorber enhanced by the double layer metasurface

A novel, 12 mm multilayer dielectric gradient honeycomb absorber (MGHA) was designed, fabricated and analyzed with a double layer metasurface consisting of a resistive film and an artificial magnetic conductor (AMC) checkerboard. Despite its thin profile, the MGHA demonstrates significantly enhanced absorption performance across a wide frequency range due to the impedance of the composite structure. Furthermore, two distinct metasurfaces are integrated into the dielectric gradient multilayer honeycomb absorber to further enhance its low-frequency properties without increasing thickness. This structure exhibits wideband absorption from 2.8 GHz to 18 GHz, featuring three absorption peaks at 3 GHz, 11 GHz and 16 GHz. The relative bandwidth can reach nearly 136.6 % of that achieved by a common honeycomb absorber with the same thickness, while maintaining an absorption peak reflection of about −22dB. The great attenuation of incident waves is attributed to Ohmic loss on the resistive film, electric resonance effect on the checkerboard, and magnetic resonance near 17 GHz on the checkerboard metasurface. The proposed MGHA structure holds significant potential for applications in aerospace and military.

Biological template hydrothermal synthesis of hollow La-doped one-dimensional CaMnO3 fibers and their enhanced microwave absorption performance

The advancement of military technology, 5G communication, and electronic equipment has increased the demand for efficient electromagnetic wave absorption materials. Calcium manganate (CaMnO3) is a commonly used dielectric absorber due to its excellent dielectric polarization effect. However, traditional ceramic materials like CaMnO3 have low conductivity, making it difficult to achieve impedance matching and electromagnetic loss simultaneously. In this work, to address this issue and create ideal wave-absorbing materials, one-dimensional La-doped CaMnO3 materials were synthesized using a simple biological template hydrothermal method. By studying the relationship between doping content and electromagnetic parameters, it was found that the La-doped CaMnO3 material exhibited excellent electromagnetic wave absorption properties, with a minimum reflection loss (RLmin) of −73.62 dB and a maximum effective absorption bandwidth of 3.3 GHz in the X-band. The introduction of La elements, which have different electronegativities from Ca ions, altered the electron cloud distribution in the sample, leading to the formation of electric dipoles that disrupt charge distribution and dissipate electromagnetic waves. The dielectric loss in fibrous La-doped CaMnO3 is mainly due to interfacial polarization. The fibrous structure allows for increased contact area with the air medium, while the porous structure introduces air bubbles that alter the dielectric properties between the sample and the air medium. This not only enhances impedance characteristics to some extent but also triggers interfacial polarization. Both of these factors help improve the material's ability to absorb electromagnetic waves. The successful creation of this one-dimensional absorbing material opens up possibilities for developing new one-dimensional absorbing materials using a straightforward method.

Electromagnetic Interference Shields Based on Highly Crystalline Single-Walled Carbon Nanotubes.

Although the convenience provided by electromagnetic waves used for information exchange is increasing, the energy of unwanted electromagnetic waves unintentionally emitted from devices is increasing as the devices work with higher frequency. In view of this vulnerability, thin films as lightweight electromagnetic wave shields against noise will be necessary for information protection. We propose the fabrication of lightweight electromagnetic wave shields using highly crystalline single-walled carbon nanotubes (HC-SWCNTs), which can be made large and flexible using a method based on a wet process, utilizing the optical and conductive properties of HC-SWCNTs. Electromagnetic wave shields are mainly classified into conductive, dielectric, and magnetic absorbers. We have developed a material synthesis technology for HC-SWCNTs and attempted to form an aqueous composite film using HC-SWCNTs and an organic binder. As a result, we found that the high crystallinity of CNTs suppresses the contact resistance between CNTs and we succeeded in constructing a flexible electromagnetic wave shielding film that can absorb electromagnetic waves in a wide bandwidth equivalent or superior to that of metal foil. This thin film can be applied to curved surfaces as desired because of its wet process, and it is expected to be a lightweight shield that can be used ubiquitously.

A hollow carbonized kapok fiber/nano CoFe2O4 composite for broad bandwidth and enhanced microwave absorber

The development of intelligent and portable electrics necessitates the creation of an enhanced electromagnetic absorption and broad bandwidth microwave absorber. The synthesis of nano cobalt ferrite (CoFe2O4; CFO) combined with hollow carbonized kapok fiber by the Sol-Gel method and annealing process is a promising approach. The microwave absorption of carbonized kapok fiber/CFO was enhanced, and the bandwidth broadened due to the dielectric loss microwave absorber carbonized kapok fiber synergizing with the magnetic loss microwave absorber CFO. The results demonstrated that the minimal reflection loss of carbonized kapok fiber/CFO-6 was −52.2 dB at 8.56 GHz, with a thickness of 3.37 mm, and the broadest effective absorbing bandwidth was 6.2 GHz, with a thickness of 2.31 mm. The simulation results, which were obtained using the CST MWS software, exhibited a high degree of agreement with those obtained from the experimental measurements. The strategy offers a prospective method for the preparation of enhanced absorption and broad bandwidth microwave absorbers.

Surfactant-induced morphology engineering in chitosan-derived carbon aerogels realizing high-efficiency absorption of electromagnetic wave

Despite the significant research advances in dielectric loss-type absorbents, developing high-efficiency electromagnetic wave (EMW) absorbents dominated by the conduction loss are still challenging due to the imbalance between impedance matching and conduction loss. In this study, for the first time, high-efficiency EMW absorption governed by the conduction loss in chitosan-derived carbon aerogels was realized through surfactant-assisted morphology modification. Electrostatic interaction and hydrogen bonding between chitosan and surfactants were ingeniously applied to induce tightly-stacked nanosheets to transform into three-dimensional (3D) interwork structure and loosely-stacked porous nanosheets, respectively, and thus the moderately enhanced conductivity converted the original EMW-transparent carbon to EMW-absorbing carbon. Benefiting from the favorable balance of impedance matching and conduction loss, the carbon aerogels with 3D interwork structure showed a broad effective absorption bandwidth (EAB) of 7.2 GHz (2.8 mm) and minimum reflection loss (RLmin) of −42.6 dB; and moreover, an ultra-wide EAB of 7.84 GHz at 2.9 mm occurred in the samples with loosen and wrinkled nanosheet structure, both outperforming most of reported carbon-based composite aerogels. This work provides a new insight for the morphology regulation and performance optimization of carbonaceous EMW absorbents.

Enhancing the Conductivity and Dielectric Characteristics of Bismuth Oxyiodide via Activated Carbon Doping.

Activated carbon/BiOI nanocomposites were successfully synthesized through a simplistic method. The produced composites were then characterized using XRD, TEM, SEM-EDX, and XPS. The results showed that BiOI with a tetragonal crystal structure had been formed. The interaction between activated carbon and BiOI was confirmed via all the mentioned tools. The obtained nanocomposites' electrical conductivity, dielectric properties, and Ac impedance were studied at 59 KHz-1.29 MHz. AC and dc conductivities were studied at temperatures between 303 and 573 K within the frequency range of 59 KHz-1.29 MHz. The 10% activated carbon/BiOI nanocomposite possessed dc and AC conductivity values of 5.56 × 10-4 and 2.86 × 10-4 Ω-1.cm-1, respectively, which were higher than BiOI and the other nanocomposites. Every sample exhibited increased electrical conductivity values as the temperature and frequency rose, suggesting that all samples had semiconducting behavior. The loss and dielectric constants (ε' and ε″) also dropped as the frequency increased, leading to higher dielectric loss. The Nyquist plot unraveled single semicircle arcs and a decreased bulk resistance, indicating decreased grain boundary resistance. Consequently, the electrical characteristics of BiOI, 1C/BiOI, 5C/BiOI, and 10C/BiOI implied their applicability as dielectric absorbers, charge-stored capacitors, and high-frequency microwave devices.

Dielectric loss and microwave absorbing properties of the prepared MgCu2Nb2O8 composite ceramics

Dielectric loss and microwave absorbing properties of the prepared MgCu2Nb2O8 composite ceramics

Enhanced microwave absorption performance of Fe3Al flakes by optimizing the carbon nanotube coatings.

Fe3Al is a good magnetic loss absorber for microwave absorption. However, due to the relatively high density and poor impedance matching ratio, the potential of Fe3Al cannot be fully released. Herein, a dielectric loss absorber of carbon nanotubes (CNTs) is coupled with Fe3Al to form Fe3Al/CNTs composite absorbers. CNTs are randomly tangled and coated on the surface of the Fe3Al flakes, forming a connecting conductive network. By carefully tuning the content of CNTs, the optimized Fe3Al/CNTs composite absorber with 1.5% of CNTs can combine both magnetic loss and dielectric loss mechanisms, thus achieving an impedance matching ratio close to 1 while keeping strong attenuation for enhanced microwave absorption. As a result, an effective absorption bandwidth (RL ≤ -10 dB) of 4.73 GHz at a thickness of 2 mm is achieved.

Analysis of multilayered shielding panels consisting of conducting and absorbing materials

This paper proposes a multilayered panel consisting of conducting and absorbing layers to improve the shielding performance of conducting panels, which is severely reduced by unintentional openings or gaps in the conducting plates of shielding enclosures or facilities. An analytic solution for a two-dimensional approximated structure with dielectric or magnetic absorbing materials between upper and lower conducting plates with a slit is also presented. The penetrated electric fields are examined in terms of the size of the slits, the thickness of the absorbing layer, and the offset between the two slits. For verification, the results are compared with those obtained through three-dimensional numerical simulation using CST Microwave Studio.

Evolutionary algorithm-based integrated design of material-structural microwave absorption using material extrusion

The development of electromagnetic wave absorbing materials and structures holds significant importance in fields such as aerospace and electronic communications. Traditional absorbing coatings have poor mechanical load-bearing capacity and struggle to meet the requirements of lightweight applications. On the other hand, the research on lossy dielectric absorbers is limited by process constraints, making it difficult to fabricate complex configurations, thereby greatly restricting their broadband absorption performance. In this study, a functional absorbing composite filament was developed using material extrusion technique. A magnetic lossy four-layer gradient honeycomb metastructure was designed, which enables effective absorption in the frequency range of 6.09–37.18 GHz within a thickness of 16 mm. The effective absorption bandwidth covers 81.82 % in the frequency range of 2–40 GHz. This broadband absorbing design achieves the integration of material functionality and structural design by additive manufacturing, enabling effective absorption across a broad frequency range.

Lossy dielectric resonator array absorber made of multiwalled carbon nanotubes/epoxy composite

A cylindrical lossy dielectric resonator array absorber is designed and verified by experiments. The designed cylindrical resonator array is made of a lightweight carbon multiwalled nanotube/epoxy composite material, and the gaps filled with polypropylene are used to fix the cylindrical array. Studies have shown that the lossy dielectric resonator array structure has dual-mode resonance characteristics, and the hybrid array composed of cylinders with different diameters can further generate multi-resonant coupling effects, thereby significantly improving the absorptivity. The total thickness of the designed absorber is 4 mm, and the normal incidence absorptivity is greater than 97% in the frequency range of 8–12 GHz. The measured results are consistent with the simulation, which verifies the reliability of the design concept and preparation method.

Synthesis of porous carbon nanoparticles anchored on MnO nanosheets for enhanced microwave absorption

Dielectric loss materials play a vital role in microwave absorption field due to their excellent permittivity, good chemical stability and lightweight feature. In this work, a high-efficiency dielectric absorber of MnO nanosheets supported nanoporous carbon particles (MnO/NPC) was successfully fabricated by a pyrolysis of MnO2/ZIF-8 precursor. The ZIF-8 derived NPC with an even diameter of ca. 80 nm are firmly attached on both sides of MnO nanosheets. This unique nanostructure could effectively enhance the attenuation ability and optimize the impedance matching. When the pyrolysis temperature is 850 °C, the obtained MnO/NPC exhibit a strong reflection loss (RL) of -52.2 dB and broad effective absorption bandwidth (EAB) of 5.8 GHz at a thin thickness of 1.85 mm. The remarkable microwave absorption performance is apparently superior to the single manganese oxide and NPC. Our work is expected to pave an effective way to improve the microwave absorption performance of dielectric loss type composites.

Tuning N-doping to balance conductivity and polarization relaxation: A strategy for converting SiO2 from an electromagnetic wave-transmitting to absorbing material

Dielectric absorbing materials often need to adjust their conductivity and polarization effects to regulate their response to electromagnetic waves. Thus, the design concept often lies in improving the performance of conductive materials. On the contrary, using insulated wave-transmitting material as a wave-absorbing material and doping single atoms to improve conductivity are novel design mentalities. In this study, the SiO2 hybrid (N-SiO2-x), doped with N atoms and bound by Si-N bonds, was produced utilizing a one-step solvothermal technique without phase transition. Based on SiO2′s imbalanced polarization ability, this research modifies the material's conductivity loss by doping it with N, which successfully balances the polarization and conductivity and turns N-SiO2-x into a wave-absorbing material. The resulting N-SiO2-4 composite has a low matched thickness and a wide absorption band of 5.28 GHz with a minimum reflection loss value of −34.48 dB (2.5 mm). These novel findings offer original suggestions for the creation of SiO2-based wave-absorbing materials.

Tunable Complex Permittivity and Strong Microwave Absorption Properties of Novel Dielectric-Conductive ZnO/C Hybrid Composite Absorbents

Modern electronic information technology has led social life into inevitable electromagnetic pollution, making microwave absorbing materials more and more important. Herein, dielectric-conductive ZnO/C hybrid composite absorbents were prepared by two-step carbonization with ZnO powders and glucose as critical materials. The electrical conductivity, complex permittivity, and reflection loss were analyzed to study the dielectric and microwave absorption properties. Results show that the prepared ZnO/C composite absorbents exist in the form of rod-like ZnO dispersed in the irregular block carbon, and the complex permittivity of the composite absorbents can be adjusted via varying the carbonization temperature. The minimum reflection loss of −25.64 dB is achieved at 1.8 mm thickness for the composite absorbent with 50 wt.% absorbent content as the final carbonization temperature is 750 °C, and the optimum effective absorption bandwidth is 2.21 GHz at 9.64–11.85 GHz. The excellent microwave absorption properties of ZnO/C composite absorbents are attributed to the combination actions of dipole polarization, conductance loss, and interface polarization, which is significant for the purposeful design of superior microwave-absorbing materials with dielectric and conductive absorbents.

Lightweight cementite/Fe anchored in nitrogen-doped carbon with tunable dielectric/magnetic loss and low filler loading achieving high-efficiency microwave absorption

Magnetoelectric composites have promising application in electromagnetic wave absorption for their regulatory structures and interfacial interactions. In this research, a facile one-step pyrolyzing procedure was applied to achieve cementite/Fe nanoparticles anchored on nitrogen-doped carbon nanotubes (Fe3C/Fe/N-CNTs) composites. Fe3C/Fe encapsulated in nitrogen-doped carbon was generated through in-situ Fe-catalyzed carbothermal reactions.The obtained magnetoelectric composites displayed excellent microwave absorption properties with a minimum reflection loss of −54.4 dB at 10.4 GHz, a matching thickness of 2.3 mm, and low filler loading (15%). Moreover, even at a low matching thickness of 1.55 mm, the reflection loss was less than −10 dB in the range of 13.7–18.0 GHz, and an effective absorption bandwidth of 4.3 GHz was achieved. The outstanding microwave absorption performance can be summarized as follows. 1) The CNT network enriches the transmission path, enhancing the dielectric loss capability. 2) The hollow one-diameter CNT structure helps strengthen interfacial polarization, optimizing the impedance matching while promoting multiple reflections and scattering. 3) Magnetic Fe3C/Fe provides a strong magnetic dissipation ability and eddy current losses. 4) The heterogeneous magnetoelectric Fe3C/Fe/N-CNTs possess multiple interfaces, increasing the interfacial polarization and electromagnetic synergistic losses. This study provides a potential strategy for the large-scale synthesis of low filler loading magnetic–dielectric microwave absorbers.

Inorganic–Organic Hybrid Dielectrics for Energy Conversion: Mechanism, Strategy, and Applications

AbstractDielectric materials with higher energy storage and electromagnetic (EM) energy conversion are in high demand to advance electronic devices, military stealth, and mitigate EM wave pollution. Existing dielectric materials for high‐energy‐storage electronics and dielectric loss electromagnetic wave absorbers are studied toward realizing these goals, each aligned with the current global grand challenges. Libraries of dielectric materials with desirable permittivity, dielectric loss, and/or dielectric breakdown strength potentially meeting the device requirements are reviewed here. Regardless, aimed at translating these into energy storage devices, the oft‐encountered shortcomings can be caused by either of two confluences: a) low permittivity, high dielectric loss, and low breakdown strength; b) low permittivity, low dielectric loss, and process complexity. Contextualizing these aspects and the overarching objectives of enabling high‐efficiency energy storage and EM energy conversion, recent advances in by‐design inorganic–organic hybrid materials are reviewed here, with a focus on design approaches, preparation methods, and characterization techniques. In light of their strengths and weaknesses, potential strategies to foster their commercial adoption are critically interrogated.