dB Reflection Loss Research Articles

Exploring Broadband Electromagnetic Absorption Characteristics and Composition Optimization in Novel Synthesized Ni2Fe1+xGe1−x Alloy Powders

This study reports for the first time the successful synthesis of a novel series of Ni2Fe1+xGe1−x (x = 0.25, 0.50, 0.75, 0.90) polycrystalline alloy materials with L21 austenite structure using the mechanical alloying method. Notably, the Ni2Fe1+xGe1−x alloys demonstrate excellent electromagnetic wave absorption performance across the entire 2–18 GHz frequency range, and by adjusting the composition ratio of iron and germanium, it is possible to effectively regulate their complex permittivity () and permeability (), thereby adjusting the reflection loss. All Ni2Fe1+xGe1−x samples show an effective electromagnetic wave absorption effect of more than −10 dB, indicating that 90% of the electromagnetic waves are efficiently absorbed. Among them, the Ni2Fe1.5Ge0.5 sample achieves an outstanding −43.5 dB reflection loss at 3.2 GHz, and the maximum effective absorption bandwidth reaches 5.8 GHz (11.8–17.6 GHz) with just a 1.6 mm thickness, fully covering the Ku band. This excellent absorption ability comes from the strong ability of the material to reduce signal strength and its perfect impedance matching. This study first shows the high potential of Ni2Fe1+xGe1−x ferromagnetic alloys as effective, wide‐range electromagnetic wave absorbers. It suggests the ferromagnetic Ni2Fe1+xGe1−x alloys hold promise as appealing candidates for broadband and high‐efficiency electromagnetic wave absorption.

Electromagnetic wave absorption in polyaniline coated Y3Fe5O12/Carbon-Black hybrid composites

Y3Fe5O12(YIG)1-x/Carbon-Black(CB)x (0.00≤x≤1.00; 0.25 steps) coated with polyaniline (PANI), forming a core-shell structure, were synthesized by in-situ polymerization following sol-gel and solid-state reactions. The crystalline, surface morphology and magnetic properties of YIG1-x/CBx and PANI@YIG1-x/CBx hybrid composites were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM), respectively. Electromagnetic wave (EMW) absorbing properties were investigated by measuring dielectric parameters in the 2–18 GHz frequency range. The reflection loss (RL), impedance matching, and loss tangent were studied in detail. The electromagnetic wave absorbing mechanisms were discussed by considering dielectric and magnetic losses, as well as microstructural properties of the samples. The EMW absorbing performance of the YIG1-x/CBx composites showed a broadband absorption property (7.0 GHz bandwidth at −10 dB reflection loss value) in YIG0.75/CB0.25 composite. When the composites are covered with conductive PANI, the EMW absorbing performance is enhanced in terms of RL (minimum −36.5 dB) and effective absorption bandwidth (EAB) (maximum 10.2 GHz at −10 dB) values due to increasing scattering probability, interfacial polarization and conduction loss of the penetrated EMW. The results showed that a wider absorption frequency range could be obtained by coating PANI on YIG/CB composite.

Synthesis of core-shell NiO/BFO nanocomposites for microwave absorbing applications

Magnetic core-shell nanostructures are often employed in high-performance microwave-absorbing applications due to their strong concurrent magnetic-dielectric losses. However, microwave absorbers designed using a single core-shell nanostructure may not attain the desired bandwidth of absorption. Herein, we introduce core-shell nanocomposites of (100-x)NiO/(x)BiFeO3 (x = 0, 25, 50, 75, & 100), prepared by a facile two-step sol-gel wet-chemical method for high-efficiency absorbing applications. Measurements of microwave absorption performance show that the core-shell 50NiO/50BiFeO3 (x = 50) nanocomposite exhibits a remarkable reflection loss of up to −27.3 dB at a matching thickness of 1.9 mm, and the corresponding −10 dB reflection loss bandwidth extends to 6.8 GHz (in X- and Ku-bands). The study suggests that the fabricated core-shell nanocomposite has the potential to be a promising candidate for lightweight microwave absorbing applications. This is evidenced by its showcased improved efficiency, attributed to the synergistic effects of magnetic-dielectric losses, multiple internal reflections, superior impedance matching, and enhanced interfacial polarization at NiO/BiFeO3 interfaces.

Graphene induced carbon-based fibre composite as microwave absorber for X-band frequency application

Stealth performance for any microwave absorbing material (MAM) is primarily controlled by the intrinsic characteristic properties of the composition of the composite. The inbuilt property of graphene has enrich the interaction of electromagnetic waves (EMWs) when it is impregnated in its compatible components such as naturally occurring organic materials. The present research engraved with a natural fibre composite with graphene as a stuffing in a resin polymer environment. The powdered form of banana-coconut coir fibre dust with 50–50 wt.% of average particle size of 150 µm with graphene has been fabricated as a hybrid composite of Graphene/Banana-coconut (GN/BNN-CCNT). The surface morphology of the fabricated composite is significantly modified with the addition of graphene creating a sustainable and foam-like elastic skeletal structure for compatibility with EMW. The enhanced dielectric values with different microwave properties for stealth performance are computed. At a frequency of 10.63 GHz a significant −15.68 dB reflection loss is found which comprises of power loss of 97.5% showing the effectiveness of the GN/BNN-CCNT/Epoxy hybrid composite as a stealth material for different X band frequency applications.

MOF-derived multicore-shell Fe3O4@Fe@C composite: An ultrastrong electromagnetic wave absorber

Excessive artificial electromagnetic radiation poses significant health risks and disrupts military equipment. To address this, high-performance microwave absorption materials are urgently required. While ferromagnetic materials have excellent absorption but suffer from high density, limited bandwidth, and perishable properties. Carbon materials, especially metal-organic frameworks (MOFs), offer promise due to low density, chemical stability, and high conductivity. In this study, we synthesized a novel multicore-shell Fe3O4@Fe@C composite via solvothermal and in-situ pyrolysis methods. This composite integrated Zn-MOF-derived porous carbon with core-shell Fe3O4@Fe@C, enabling multiple electromagnetic wave routes, strong interfacial polarization, and magnetic-dielectric synergy. It exhibited exceptional electromagnetic wave absorption, with a −59.1 dB reflection loss at 13.36 GHz and a 5.36 GHz effective absorption bandwidth. Our innovative MOF-core-shell approach holds great promise for highly efficient microwave absorbers to mitigate artificial electromagnetic radiation's adverse effects on health and military equipment.

Microwave absorption performance of magnetic-dielectric Fe3O4@C@PPy composites with a core-double-shell structure prepared by a low-temperature self-propagation method

Microwave absorbers have been developed to counter electromagnetic pollution, and enhancing their performance remains an ongoing concern. In this paper, carbon-coated Fe3O4 and polypyrrole (PPy) were combined to construct composites with a core-double-shell structure, and the influences of multiple synergistic effects from ternary components, carbon defects, and microstructure on the electromagnetic properties of Fe3O4@C@PPy composites were investigated. The Fe3O4@C@PPy composites were successfully prepared by the low-temperature self-propagation method and in-situ oxidation polymerization process, achieving a −53.67 dB reflection loss at 12.24 GHz when the sample thickness was 2.13 mm, and the effective absorbing (RL < 10 dB) band covered 4.16 GHz (13.84–18 GHz) with a corresponding thickness of only 1.63 mm. The core-double-shell structure perfectly integrated various advantages of each component as well as provided multiple reflections and scatterings. Meanwhile, the polarization loss was notably enhanced by heterogeneous interfaces, and the dielectric-magnetic loss mechanism cooperatively accelerated the dissipation of electromagnetic wave energy.

Broadband electromagnetic wave absorbing via PANI coated Fe3O4 decorated MoS2 hybrid nanocomposite

High performance electromagnetic wave (EMW) absorbing material systems are required for stealth applications and sensitive electronic devices. Absorbing of an incident EMW in a wide band range still has limitations in terms of materials system and engineering. It is required to extend the bandwidth and minimize the reflection from the material system for the next level stealth technologies. In this work, hybrid nanocomposite structures are developed by semiconductor flower-like MoS2 nanosheets, Fe3O4 magnetic nanoparticles and conductive polyaniline. A systematic study is presented by investigation the structural, magnetic, morphological, thermal, electronic and electromagnetic characteristic of hybrid nanocomposites (Fe3O4:MoS2, PANI@Fe3O4, PANI@MoS2 and PANI@Fe3O4:MoS2). EMW absorption characteristics results showed that Fe3O4:MoS2 and PANI@Fe3O4:MoS2 hybrid nanocomposites exhibit excellent EMW absorption characteristics. While the minimum reflection loss (RL) value was found as − 54.97 dB at 15.99 GHz for the Fe3O4:MoS2 nanocomposite, the broad bandwidth (7.65 GHz) was observed in PANI@Fe3O4:MoS2 hybrid nanocomposite having − 39.96 dB RL. According to the experimental results, a lightweight and high temperature resistance PANI@Fe3O4:MoS2 like-hybrid nanocomposite can absorb almost 90% of incident EMW in a wide bandwidth.

High-Density Nanopore Confined Vortical Dipoles and Magnetic Domains on Hierarchical Macro/Meso/Micro/Nano Porous Ultra-Light Graphited Carbon for Adsorbing Electromagnetic Wave.

Atomic-level structural editing is a promising way for facile synthesis and accurately constructing dielectric/magnetic synergistic attenuated hetero-units in electromagnetic wave absorbers (EWAs), but it is hard to realize. Herein, utilizing the rapid explosive volume expansion of the CoFe-bimetallic energetic metallic triazole framework (CoFe@E-MTF) during the heat treatment, the effective absorption bandwidth and the maximum absorption intensity of a series of atomic CoFe-inserted hierarchical porous carbon (CoFe@HPC) EWAs can be modified under the diverse synthetic temperature. Under the filler loading of 15 wt%, the fully covered X and Ku bands at 3 and 2.5mm for CoFe@HPC800 and the superb minimum reflection loss (RLmin )of -53.15dB and specific reflection loss (SRL) of -101.24dB mg-1 mm-1 for CoFe@HPC1000 areachieved. More importantly, the single-atomic chemical bonding among Co─Fe on the nanopores iscaptured by extended X-ray absorption fine structure, which reveals the formation mechanism of nanopore-confined vortical dipoles and magnetic domains. This work heralds the infinite possibilities of atomic editing EWA in the future.

Design and Manufacturing of a Hexapattern Frequency Selective Surface Absorber for Aerospace Stealth Application.

Integrated frequency selective surface (IFSS) absorbers with larger bandwidth, effective reflection loss, polarization-insensitive characteristics, angular stability with compact/thin design, and ease of fabrication have captivated significant importance in stealth technology. Herein, we report on an IFSS absorber that has been designed, simulated, and implemented for manufacturing to achieve effective stealth properties. Initially, frequency selective surface (FSS) layers have been designed that comprise a closed centroid honeycomb structure surrounded with four annular hexagonal rings, splitted, alternatively, and enveloped with four L-shaped elements. The simulated pattern has been optimized on glass fabric for reflection loss (RC, dB) at a thickness of ∼0.1 mm by choosing sheet resistance of pattern 110 Ω/□. A FSS layer combined with interlayer lossy dielectric laminates (1.8 mm) and a carbon-fabric-reinforced-plastic ground has been simulated as an IFSS absorber. The performance of RC, in normal and angular configuration (0-60°), under transvers an electric/magnetic mode of polarization, including analysis of the displacement current, volume power loss distribution, and complex admittance has been carried on IFSS. Subsequently, the proposed absorber has been fabricated using customized carbon-based resistive ink imprinted on glass fabric by mask lithography compounded with laminates (a carbon black powder/epoxy composite) and ground. Their manufacturing details, including free space and anechoic chamber RC measurements, have been presented. The simulated and experimental RC performances of the absorber are found to be in good agreement, possessing minimal 10 dB reflection loss (90% absorption) with a sample thickness of 1.9 mm (0.05λL, where λL corresponds to a lower operating frequency), covering 76% fractional bandwidth in X and Ku bands. The proposed design architecture of the IFSS is ideally suitable for aerospace stealth platforms.

Highly-malleable microwave absorption foam

Microwave absorption (MA) materials have made great progress in bandwidth optimization and weight reduction; however, it remains a challenge to achieve the malleability of MA materials. The performance of existing dielectric loss-type MA materials critically relies on the dielectric networks, which are fragile due to particle aggregations and junction cracks in practical processing. We here report a foam architecture strategy to attain both malleability and excellent MA properties. The foam consists of micro-balloons bound together by a deformable paste which contains H2O and ions. We observed a linear increase in permittivity with increasing H2O contents. This relationship enables a fine optimization of MA properties. The highly-malleable foam delivers an effective absorption bandwidth of 7.37 GHz at reflection loss (RL) ≤−10 dB and minimum RL of −72.6 dB.

Influence of Exfoliated Boron Nitride for Fabrication of a Lightweight Wideband Microwave Absorbing Material

The study of electromagnetic (EM) wave absorbing materials is a natural response to ever-worsening EM wave pollution in modern days. Several nanomaterials have been explored as wideband, low-thickness, and lightweight microwave absorbing materials (MAMs) for use in both military and civilian realms but require significant improvement. This work presents the synthesis and charcaterization of in situ exfoliated boron nitride coated nickel ferrite (NiFBN) with excellent porous microstructure, using a simple auto-combustion method as well as the fabrication of a NiFBN-multiwalled carbon nanotube (MWCNT)-epoxy-based lightweight, thin nanocomposite for wideband microwave absorption (X-band). With a 2 mm thick sample, the 15-NiFBN-0.75_2mm nanocomposite exhibits effective absorption bandwidth (EAB) of 3.9 GHz and −59.38 dB reflection loss minima (RLmin). Several percentages of boron nitride with nickel ferrite were synthesized using the sol–gel auto-combustion process, and the MWCNT percentage was adjusted for enhanced microwave absorption.

Functionalization of glass fiber woven fabrics by indium tin oxide (ITO) coatings for electromagnetic wave absorption

The effects of surface electrical conductivity and cascading order of ITO surface modified glass fiber woven fabrics (GFWF) on the electromagnetic (EM) behavior of hybrid type multilayered absorber structure were investigated. Additional objective was to create a design guideline for a multilayered absorbing structure according to the needs of specific EM wave absorber applications. For this purpose, indium tin oxide (ITO) sols were deposited on GFWFs by spray pyrolysis technique. The electrical conductivity of these conducting layers was controlled to incorporate EM wave absorbing characteristics to glass fabrics. Surface modified fabrics were then used as reinforcement in a hybrid type multilayered EM wave absorbing structure which is a combination of Jaumann and graded type absorbers effective in 8–12 GHz frequency range (X-band). The highest absorption performance design has been formed by cascading six ITO coated fabrics with gradually increasing electrical conductivity gradient from the front to back layer of the structure. The electromagnetic behavior of the multilayered absorber was tested both with and without metallic backing. The absorber design showed ∼−11 dB reflection loss and ∼−9 dB transmission loss corresponding to ∼80 % average absorption without metallic backing, while its reflection loss and average absorption values were ∼−10.5 dB and ∼93 %, respectively, with metallic backing. The front layer of the multilayered structure with the lowest surface electrical conductivity provided impedance matching between air and receiving surface of the structure minimizing reflection, where the gradual increase in surface conductivity of the layers towards the back provided balanced internal reflection and transmission leading to high overall EM wave absorption. Consequently, by controlling the grading of the surface conductivity of the layers through the thickness, responses of the absorbers can be adjusted to provide tailored characteristics for the required EM wave absorption levels.

Asymmetric magnetic-electric dual-functional composite foams for ultra-efficient electromagnetic interference shielding with unprecedented low reflection

• Magnetic-electric dual-functional network is constructed in TPU by Fe 3 O 4 @rGO and CNT via scCO 2 foaming. • TPU/CNT/Fe 3 O 4 @rGO composite foam exhibits high EM wave absorption property with an RL min of -46.8 dB. • EMI shielding and EM wave absorption are further improved by introducing an Ag reflection layer. • Asymmetric TPU/CNT/Fe 3 O 4 @rGO/Ag composites possess a high EMI SE of 89.2 dB and the lowest reflection of 0.001. Asymmetric composite foams comprised of iron oxide decorated reduced graphene oxide (Fe 3 O 4 @rGO)/carbon nanotube (CNT)/thermoplastic polyurethane (TPU) foams and a silver layer were developed by vacuum-assisted hot-pressing and supercritical carbon dioxide (scCO 2 ) foaming. The magnetic-electric dual-functional network constructed by Fe 3 O 4 @rGO and CNT nanofillers rendered the foam excellent impedance matching and wave attenuation capability, achieving -46.8 dB reflection loss at ∼2 mm sample thickness. With the reflective silver layer, the asymmetric composite foam realized a unique “low reflection-absorption-reflection-reabsorption” EM wave depletion mechanism and reached preeminent total shielding effectiveness (SE T ) of 89.2-103.5 dB with a reflection shielding effectiveness (SE R ) of 0.24-0.83 dB. The optimized composite foam achieved a low reflectivity (R) of 0.05 (Average value) and a minimum value of 0.001, which holds the lowest record among EMI shielding materials with comparable SE. This work provides new insights into the design of high-efficiency shielding materials with ultra-low reflection features for cutting-edge EMI shielding applications.

Tuning layer thickness and layer arrangement in a GdMnO3 and GdMnO3-MoSe2 bi-layer absorber to cover the S, C, and X band frequency range

The bi-layer absorber's microwave absorption performance can be enhanced by adjusting and manipulating the layers' composition, layer thickness, and layer arrangement. Herein, two magnetic and magneto-electric components, GdMnO3 (G) and GdMnO3-50 wt.% MoSe2 (GM), were prepared via a solvothermal method. In particular, the impact of filler loading and layer thickness on microwave absorption characteristics was examined. The findings indicate that a single-layer absorber sample containing G or GM components independently did not have good microwave absorption capability. On the other hand, a bi-layer absorber sample with G as the matching layer (1.5 mm thickness) and GM as the absorber (0.5 mm thickness) possesses exceptional -44 dB reflection loss with 9 GHz of effective absorption bandwidth, which covers S, C, and almost the whole X band frequency range. The optimal 3D network architecture of the G particles' rod-like morphology, which improves the impedance matching property, may be to blame for this phenomenon. Additionally, this special 3D network architecture gives an abundance of interfaces to disperse electromagnetic waves in addition to many channels for microwave reflecting and scattering. More crucially, the composites' microwave absorption mechanism is investigated and studied, which offers a trustworthy guide for making a bi-layer absorber.

Microwave Attenuation Studies of Polypyrrole-SWCNT Nanocomposite Films for Improved EMI Shielding

In the process of finding stable, lightweight, broadband, cost-effective and improved electromagnetic interference (EMI) shielding material, electromagnetic wave attenuation properties of polypyrrole (PPy)—single-walled carbon nanotube (SWCNT) nanocomposite hybrid films were investigated in X-band region (8.2–12.4 GHz) and reported in the present work. The incorporation of SWCNT as a nanofiller in polymer matrix exhibits enhanced EMI shielding performance as compared to pure polymer films. The substantial values of dielectric loss with good impedance matching contribute to improvement in EMI shielding performance. It is found that with an increase of SWCNT loading in polymer matrix from 0 wt% to 5 wt%, nanocomposite films display a gradual increase in AC conductivity and total shielding effectiveness. The maximum total shielding effectiveness of 32.10 dB and minimum reflection loss of −45.54 dB with a wide bandwidth of 3.1 GHz, were obtained for 5 wt% CNT loading. The present results revealed that the prepared nanocomposite films are appropriate materials for lightweight, broadband EMI shields for radar and stealth applications.

Enabling mmWave Wireless Rack Area Networks: Channel Characterization Within a Server Rack

This letter presents 60 GHz radio measurements and channel characterization for wireless rack area network (WRAN) application within a networking enclosure, commonly known as a server rack. The propagation characterization is conducted with wideband and narrowband measurements to characterize the propagation phenomena and investigate the feasibility of a reflected non-line-of-sight (RNLoS) link. The impact of obstruction by networking cables and a human hand is also investigated to extract the fading depth, fading rate, and the time varying shadowing. The implications on WRAN system design are accordingly deduced. It is found that optimal RNLoS channel response is characterized by a clustering effect with a 7.82 dB reflection loss. The obstruction by networking cables introduces significant channel dispersion and contributes to significant fading depth and fading rate values.

A compact TM03 mode penta‐polarization agile MSA for interference mitigation in 5G ultra‐dense point to point environment

Signal interference in the recent 5G ultra-dense environment is becoming severe due to the co-existence of large RF nodes operating in the constrained spectrum. In this article, a polarization agile approach for the designing of an RF system is studied to mitigate interference issues besides the communication and signal processing approach. A compact single-fed single layer penta-polarization agile higher-order microstrip patch is analyzed probably for the first time in the literature. The proposed antenna possesses a very low profile of less than 0.01 λ (λ free-space wavelength). Reconfigurable orthogonal feeding with switches is connected with the horizontal and vertical patch edges. Subsequently, these are excited separately and simultaneously using switchable PIN diodes and appropriate bias networks to realize horizontal, vertical, and 45° slant polarization states. Successively, diagonal patch corners are truncated to initiate right and left-hand circular polarizations. Slots are etched on specific orientation of currents on the patch surface to improve side-lobe levels. A prototype is analyzed, simulated, and fabricated at TM03 mode and operating at 5.8 GHz band with penta-polarization agility. A consistent 11 dBi realized broadside gain is measured covering the 10 dB reflection loss and 3 dB axial ratio bandwidth in both the principal planes.

An X-band meta-structure absorber based on gelated deep eutectic solvent

Herein, a meta-structure absorber (MSA) with gelated deep eutectic solvent (DES) is proposed and investigated at X-band (8.2–12.4 GHz). The ionic property of DES gel assists in enhancing absorption. The unit cell of the MSA is designed using a dumbbell-shaped resonating structure of gelated DES enclosed in a flexible silicone rubber substrate. The embedded dumbbell structure makes the MSA robust by promoting fast recovery after bending. The developed absorber is optimized for wideband absorption. The total thickness of the MSA is &amp;lt;3 mm. The measured results showed −40.02 dB reflection loss at 10.55 GHz with a −10 dB bandwidth of 3.34 GHz (9.06–12.4 GHz). Additionally, the proposed absorber shows polarization and incident angle insensitivity up to an angle of ±50° in both transverse electric and transverse magnetic modes. The mechanism involved in absorption is investigated through field analysis at resonating frequency. Possible application of the designed absorber in antenna isolation is studied for co-sited broadband horn antennas operating at the X-band.

Review on engineering designing of electromagnetic interference shielding materials using additive manufacturing

AbstractRecently 3D printing or additive manufacturing has been one of the most popular techniques for fabricating material. 3D printing or additive manufacturing has taken over the modern material fabrication industry in a revolutionary manner. The present review focuses on designing electromagnetic interference (EMI) shielding materials by 3D printing. The various raw materials such as polylactic acid (PLA), polypropylene, graphene, carbon nanotube (CNT), multiwalled carbon nanotube (MCNT), and so forth, can be successfully used for making effective EMI shielding performances in different frequency ranges. These raw materials have prepared diverse shapes, dimensions, and compositions to attenuate the incident radiations over the shielding material's surface and ultimately protect the electronic devices. When mixed with carbon nanotubes, PLA has been shown 8–15 dB, 30 dB, and 67 dB EMI SE in different frequency ranges, a material with ABS and CNT have −3 to −16 dB reflection loss in X‐band frequency. Also graphene nanofilm/MWCNT composition has shown EMI SE as high as 43–54 dB in X‐band ranges when printed with poly jet printing. These properties gave a cutting‐edge rivalry to the conventional fabrication method and proved that 3D printing is better when designing innovation for EMI shielding materials

An Easily Optimizable Frequency Selective Absorber Design for X-Band

In this paper, a novel frequency selective absorber surface (FSAS) is designed for electromagnetic and radio frequency interference reduction and for to use in stealth technology in X-band (8–12 GHz). At the proposed FSAS, minimum 10 dB reflection loss is achieved for the incidence angles up to 30 degrees. Lumped resistors are inserted into periodic conduction geometries to achieve absorption frequency behavior. Equivalent circuit model of periodic geometries is used in the design and optimization stages. The main advantage of the design is its resonance frequency can easily be optimized by one parameter which controls the equivalent capacitance. In order to achieve this goal, a novel FSAS geometry has been designed in which equivalent capacity is dominant in determining the resonant frequency of the surface.