The defining trick of a high entropy alloy lies in its name. Where a conventional alloy is dominated by a single base metal doped with trace additions, an HEA dissolves five or more elements at concentrations of roughly 5 to 35 atomic percent, typically with atomic radii differing by less than 15 percent. The authors note that the field has converged on a second, thermodynamic definition as well: a genuine HEA must possess a configurational entropy of at least 1.5R, where R is the gas constant, meaning the sheer number of possible atomic arrangements is large enough to stabilise simple solid solution phases instead of brittle intermetallic compounds. The result is a material whose structure and properties can be tuned not by tweaking a trace element but by redesigning the entire elemental recipe.

The review organises the field around four so-called core effects, first outlined by Jien-Wei Yeh and completed by S. Ranganathan in 2003. The high entropy effect favours stable, disordered solid solutions; sluggish diffusion slows the rate at which atoms move and phases transform; severe lattice distortion arises because every atom is surrounded by neighbours of different sizes, straining the crystal; and the cocktail effect captures the surprising composite behaviours that emerge when many elements interact at once. Crucially, each of these effects has a direct electromagnetic consequence. Lattice distortion bends electronic energy bands, splits energy levels and creates localised states between the valence and conduction bands, modulating conductivity and dielectric response in ways conventional alloys cannot easily replicate.

That structural disorder translates into an unusually rich toolbox of electromagnetic loss mechanisms. When a microwave strikes an HEA, energy is dissipated through electronic polarisation, as electron clouds shift against their nuclei in the local electric fields created by chemically distinct atoms; through interfacial polarisation, as charges pile up at grain and phase boundaries; through magnetic loss, as magnetic domains in ferromagnetic alloys containing iron, cobalt, nickel or manganese respond and resonate; and through conductive loss, as free electrons oscillate and convert wave energy into heat via Ohmic heating. The challenge, the authors stress, is balance: too much conductivity turns an absorber into a mirror, and a large mismatch between the material’s impedance and that of free space causes most of the wave to reflect away before it can be absorbed.

Impedance matching is therefore the central design problem, and here HEAs offer unusual flexibility. Because complex permittivity and complex permeability can both be adjusted through composition, HEAs can be engineered to bring the material impedance closer to that of ambient space, minimising the reflection coefficient while maximising the attenuation constant that governs how quickly the wave’s amplitude decays inside the absorber. The quantitative payoff is striking. Reported reflection losses for HEA-based materials span from about minus 10 decibels, the threshold below which 90 percent of incident power is absorbed, down to roughly minus 70 decibels, depending on composition, thickness and frequency. The reviewed literature includes an FeCoNiMnCu0.5 alloy with a reflection loss of minus 71.0 decibels at 6.79 gigahertz from a layer just 2.93 millimetres thick, and boron-doped FeCoNiCr alloys reaching minus 62.5 decibels at 2.11 millimetres.

Getting there, however, takes careful processing. Because pure HEAs tend to be strongly metallic and conductive, the review describes several engineering strategies for taming them. Mechanical alloying, particularly high-energy ball milling, flattens spherical particles into high aspect ratio flakes that promote multiple polarisation events and tune the complex electromagnetic parameters. Annealing then sharpens crystallinity and boosts saturation magnetisation: FeCoNiAlCr0.9 powders improved from minus 26.88 to minus 47.55 decibels after heat treatment, while FeCoNiMn0.5Al0.2 annealed at 500 degrees Celsius delivered minus 44.425 decibels over a 3.825 gigahertz bandwidth. Surface modifications do impressive work too. Phosphating FeCoNiMn flakes produced a protective layer that lifted performance to minus 62.4 decibels at 10.7 gigahertz while adding corrosion and oxidation resistance, and dealloying, which leaches aluminium out of FeCoNiCuAl surfaces, enhanced impedance matching and pushed losses past minus 56 decibels at two separate frequencies.

Doping and compositing broaden the palette further. Adding small amounts of non-metals such as carbon, nitrogen or boron introduces ionic character and dipole oscillations that feed dielectric loss; boron-doped FeCoNiCr alloys achieved a maximum bandwidth of 5.78 gigahertz while retaining mechanical strength and oxidation resistance. Encapsulating HEA nanoparticles in graphitic carbon shells, via routes from arc discharge in methane to metal-organic chemical vapour deposition, simultaneously improves impedance matching and reduces radar cross-section, with one carbon-coated FeCoNiCuMn composite reaching minus 65.8 decibels and an absorption width of 7.68 gigahertz. Pairing HEAs with polymers, oxides or ceramics blends the alloy’s magnetic loss and structural stability with the partner phase’s dielectric loss, as in FeNiCrMn-polylactic acid composites printable by fused deposition modelling, and FeCoNi(Si0.6Al0.2B0.2) powders embedded in paraffin, which the review singles out as among the most versatile performers, combining thin 1.2 to 2.0 millimetre layers with reflection losses down to minus 44.1 decibels in the X and Ku bands.

Measuring all this in a way that matters outside the laboratory is its own discipline, and the review devotes detailed attention to it. Vector network analysers paired with horn antennas measure scattering parameters such as S11 and S21 in free-space fixtures, from which shielding effectiveness and reflection loss are derived; HEA-reinforced carbon fibre composites tested this way achieved total shielding of about 45.9 decibels at 4 gigahertz. Open area test sites, with calibrated ground planes and antennas separated by 3 to 30 metres, serve compliance testing of large enclosures, while indoor anechoic chambers lined with pyramidal absorbers provide reflection-free environments for monostatic and bistatic radar cross-section measurements across controlled angles, polarisations and frequency sweeps. The review reports HEA composite radar cross-section reductions of roughly 10 to 30 decibels in chamber tests, and notes that such measurements bridge laboratory-grade shielding data and real-world electromagnetic detectability.

Obstacles remain before these alloys fly on actual aircraft. The authors highlight the absence of standardised testing protocols across frequency bands and environments, which makes comparing studies difficult; edge effects and sample size limits that hamper scaling VNA results to full components; interfacial stability and oxidation concerns when HEAs are coupled with polymers; and early-stage cost and manufacturability. Even the frequency coverage is lopsided: most HEA research targets the C and X bands central to military radar and communications, leaving S-band and Ku-band coverage comparatively underexplored. The review calls for quantitative assessment of absorption mechanisms, a firmer physical understanding of lattice distortion, scalable synthesis, multi-scale modelling and durability testing under extreme conditions as the priorities that will determine whether laboratory spectacles become fielded technologies.

The most transformative possibility, the authors argue, lies in merging HEA chemistry with additive manufacturing. Because 3D printing can control composition, microstructure and geometry simultaneously, it promises lightweight graded structures whose electromagnetic response is designed in from the melt, capable of surviving high temperatures and corrosive atmospheres while retaining their absorption performance. From stealth platforms and radar-visible UAV signatures to telecommunications, energy storage and even healthcare electronics, the combination of chaotic multielement chemistry and precision manufacturing offers something conventional absorbers cannot: a single material family whose dielectric and magnetic personalities can be tuned almost at will. If the remaining manufacturing and standardisation hurdles fall, the alloys once prized mainly for their strength and heat resistance may quietly become the invisible backbone of an electromagnetically cleaner, harder-to-detect world.

Subject of Research: High entropy alloys as electromagnetic wave absorbing materials for stealth and shielding applications

Article Title: A review on high entropy alloys as an absorber of electromagnetic radiation

Article References: Gowda, N. R., Setupathy, A., Raj, A. A. B., & Thangaraju, S. (2026). A review on high entropy alloys as an absorber of electromagnetic radiation. Journal of Materials Science: Metallurgy, 1(1), Article 5. https://doi.org/10.1007/s44492-026-00006-0

Image Credits: AI Generated

DOI: 10.1007/s44492-026-00006-0

Keywords: high entropy alloys, electromagnetic wave absorption, stealth technology, radar cross section, impedance matching, magnetic loss, dielectric loss, radar absorbing materials, electromagnetic interference shielding, mechanical alloying, additive manufacturing, lattice distortion

The new composite, designated CNGA, is described in the journal Advanced Composites and Hybrid Materials. Rather than packing conductive carbon into a block, the team assembled the material through heterogeneous ice-templated freeze casting, a process in which growing ice crystals sculpt the internal architecture as the suspension solidifies. The result is a hierarchical porous structure in which double-shell hollow microspheres are spatially segmented and joined by controllable bridges of nitrogen-doped carbon nanosheets. Each microsphere and each bridge plays a distinct electromagnetic role, and because the geometry is imposed during assembly rather than left to chance, the balance between attenuation and impedance matching can be tuned deliberately.

The physics behind the approach is subtle but crucial. When an electromagnetic wave strikes a material, two things must happen for effective absorption. First, the wave has to enter rather than reflect away, which requires the material’s impedance to match that of free space. Second, once inside, the wave’s energy has to be dissipated, typically through dielectric polarization, conduction losses, and magnetic losses. Highly conductive fillers are excellent dissipators but terrible reflectors, bouncing incoming waves off the surface. The distributed RLC framework tackles this by separating the two jobs: the carbon nanosheet bridges provide continuous conductive pathways for energy dissipation, while the spatially distributed hollow microspheres introduce a wealth of heterogeneous interfaces that localize electromagnetic loss without overloading the material with conductivity.

The microspheres themselves are engineered for complexity. Each carries a double shell, and their hollow interiors lower the overall density while multiplying the number of internal boundaries at which electromagnetic waves can be reflected, scattered, and attenuated. Nitrogen doping, in the form of pyridinic and pyrrolic nitrogen sites within the carbon lattice, enhances polarization losses by creating defect-rich sites that trap charge under an oscillating electromagnetic field. Meanwhile, nickel-induced graphitization converts regions of amorphous carbon into more ordered graphitic domains, boosting conduction losses. The two mechanisms act in concert, giving the material multiple channels through which microwave energy can be converted into heat.

The measured performance is striking by any standard. The optimized aerogel achieves a reflection loss of –54.86 decibels, meaning that at the absorption peak, only a vanishingly small fraction of the incoming microwave energy is reflected back toward the source. In practical terms, that is deep into the regime prized for radar absorption, where the power of a returned signal is cut by many orders of magnitude. Equally important, the effective absorption bandwidth—the frequency range over which the material reflects at least 90 percent of incident energy—spans 6.56 gigahertz, covering a broad swath of the microwave spectrum rather than a single narrow band.

What makes these numbers especially notable is the filler loading at which they are achieved: only 8 weight percent. In conventional microwave absorbers, achieving comparable performance often requires loading a matrix with 40 to 70 percent functional filler, which drives up weight and can embrittle the composite. A low loading is essential for aerospace platforms, where every gram matters, and for electronics, where thick or heavy shielding layers are unwelcome. The lightweight aerogel also delivers thermal insulation, with a thermal conductivity of just 0.0605 watts per meter-kelvin, comparable to some of the best commercial insulating foams, and an infrared absorptivity exceeding 95 percent.

The thermal behavior is a direct consequence of the architecture. The hollow interiors and hierarchical porosity mean that heat must navigate a tortuous, largely air-filled path through the material, and air is a notoriously poor thermal conductor. Infrared radiation, meanwhile, is absorbed efficiently across the extended surfaces of the carbon components. This combination means the aerogel can simultaneously suppress heat flow and swallow radiant heat, which matters for applications ranging from protecting sensitive electronics from thermal gradients to managing temperature in aircraft structures where hot and cold zones sit close together.

Mechanical robustness, often the weak point of ultralight aerogels, received its own fix. As-synthesized porous carbon architectures tend to be fragile, but the team found that infiltrating the aerogel with resin raised its compressive strength to 45.70 megapascals without degrading electromagnetic performance. The resin fills the load-bearing framework without disrupting the conductive pathways or the interface density that underpins the wave absorption, turning an admittedly delicate laboratory material into something with realistic prospects for structural use. That step matters because a multifunctional material is only useful if it can survive handling, vibration, and compression in service.

The broader significance of the work lies in its structural philosophy. Instead of optimizing one property at a time and accepting compromises elsewhere, the researchers treated the composite as a spatially regulated system in which geometry, composition, and connectivity are co-designed. The segmentation of the microspheres controls where heterogeneous interfaces appear; the controllable connection of the carbon bridges sets the conductivity of the network; and the ice-templating process allows both to be patterned simultaneously. This structure–property strategy offers a template that other teams can apply to different material chemistries, potentially extending the distributed RLC concept to absorbers that operate in other frequency bands or that combine additional functions such as sensing or mechanical damping.

The work was supported by the National Key R&D Program of China, the National Natural Science Foundation of China, and two state key laboratories, reflecting the strategic weight placed on electromagnetic compatibility and thermal management in next-generation technology. As wireless devices proliferate and stealth, radar-cross-section management, and high-frequency electronics demand ever better absorbers, materials that swallow microwaves, block heat, and carry mechanical load in a single lightweight layer will only grow more valuable. The CNGA aerogel is a demonstration that, with the right architecture, the classic trade-off between dissipation and impedance matching can be engineered away rather than merely tolerated.

Subject of Research: Hierarchical hollow microsphere-carbon composite aerogels for electromagnetic wave absorption and thermal regulation

Article Title: Spatial segmentation and controllable connection enabled hollow microsphere-carbon distributed RLC networks for multifunctional EM/thermal regulation

Article References: Spatial segmentation and controllable connection enabled hollow microsphere-carbon distributed RLC networks for multifunctional EM/thermal regulation. (n.d.). https://doi.org/10.1007/s42114-026-02073-2

Image Credits: AI Generated

DOI: 10.1007/s42114-026-02073-2

Keywords: electromagnetic wave absorption, microwave absorbers, hollow microspheres, carbon nanosheets, aerogels, thermal insulation, impedance matching, nitrogen doping, ice-templated assembly, RLC networks, lightweight composites, mechanical reinforcement

Yet conventional EMW absorbers often face a structural trade-off. Carbon-rich systems can reflect waves too efficiently, preventing deep penetration, while metal-based materials can suffer from impedance mismatch, limiting how effectively energy is dissipated. In practical terms, a successful absorber must both “invite” waves in and ensure they are ultimately consumed inside the material.

A research team from Qingdao University addresses this problem with a “heterointerface–defect synergy” strategy. They used solvothermal-electrospinning methods to couple bimetallic sulfides—CoS₂ and NiS₂—with hollow carbon nanofibers (HCNFs), building a composite engineered for a gradient electronic structure that promotes energy loss pathways.

The key mechanism begins at the CoS₂/NiS₂ heterointerface. There, a strong built-in electric field forms, promoting directional charge transfer. This field accelerates conversion of EMW energy into thermal dissipation through polarization and interfacial charge dynamics.

To further intensify losses, the design introduces sulfur vacancies that act as “energy traps.” These defect sites interact with the built-in electric field, strengthening dipole polarization and improving the coupling between structural imperfections and electromagnetic energy.

Meanwhile, the three-dimensional hollow network of HCNFs supports more effective impedance matching and increases the effective propagation length of waves within the absorber. Together, these features enhance multiple reflections and scattering, giving waves more opportunities to be attenuated.

Performance results are striking. At a thickness of 2.6 mm, the effective absorption bandwidth (EAB) spans 8.32–18.4 GHz, covering the full X-band and Ku-band. At 2.4 mm, the minimum reflection loss (RLmin) reaches −48.04 dB, corresponding to absorption of over 99.99% of incident EMW energy.

Compared with single-metal sulfide systems, the EAB increases by 61%. Importantly for real-world deployment, the material maintains excellent absorption even at a low filler loading of 15 wt% under 60° oblique incidence.

The findings were published in Nano Research on 14 May 2026, offering a lightweight, broadband, and highly lossy platform that could support next-generation shielding for civilian electronics and potentially improve stealth-relevant radar mitigation technologies.

Subject of Research: Heterointerface Engineering of Bimetallic Sulfides Enhances Polarization Loss for Superior Electromagnetic Wave Absorption Performance
Article Title: Heterointerface Engineering of Bimetallic Sulfides Enhances Polarization Loss for Superior Electromagnetic Wave Absorption Performance
News Publication Date: 14-May-2026
Web References: http://dx.doi.org/10.26599/NR.2026.94908411
References: Nano Research (14-May-2026); DOI: 10.26599/NR.2026.94908411
Image Credits: Credit: Nano Research, Tsinghua University Press

Keywords

bimetallic sulfides; heterointerface engineering; sulfur vacancies; hollow carbon nanofibers; built-in electric field; polarization loss; electromagnetic wave absorption

As the world embraces the advancements of 5G, the Internet of Things (IoT), and artificial intelligence (AI), the demand for effective solutions to EM wave absorption is more critical than ever. Traditional absorbers have often struggled with various conflicting requirements – achieving a thin profile while ensuring broad absorption bandwidth and strong electromagnetic attenuation. In an inspiring answer to this challenge, the Tongji research team presents their findings in the esteemed journal Nano-Micro Letters, showcasing the potential of Ni-MXene composites to revolutionize how we manage electromagnetic waves.

Electromagnetic wave absorption fundamentally relies on the conversion of EM energy into heat, primarily achieved through either dielectric or magnetic losses. While MXenes, particularly titanium carbide (Ti₃C₂Tₓ), boast impressive metallic conductivity and an expansive surface area, their inherent excessive conductivity can lead to poor impedance matching. This ultimately results in unwelcome reflections of EM waves rather than their absorption. The innovative team addressed this issue with their electron localization strategy, which confines electrons to localized regions to enhance polarization and facilitate effective electromagnetic wave dissipation.

The key to the new electron localization strategy lies within the metal-support interaction (MSI) created by anchoring nickel nanoclusters onto the MXene substrate. This strategic interaction disrupts the symmetrical distribution of electrons across the MXene, confining them into small, localized clusters that act as micro-dipoles. When exposed to alternating EM fields, these confined electrons generate stronger dipole polarization, thereby significantly enhancing average dielectric loss. The presence of these nanoclusters thus transforms the capabilities of MXene from a mere conductive material to a highly effective EM wave absorber.

One of the most distinguishing features of the new Ni-MXene composite is its ability to achieve a remarkable minimum reflection loss (RLₘᵢₙ) of −54 dB, at a thickness of just 2 mm. This performance means that an astonishing 99.999% of incoming EM waves are absorbed by the material—this is a fourfold increase in absorption over pure MXene, which exhibited an RLₘᵢₙ of only −11.9 dB. More impressively, the effective absorption bandwidth (EAB) for the new composite stretches to an impressive 6.8 GHz, ensuring efficient absorption across a considerable range of frequencies critical for modern communication technologies.

The chemical synthesis of these Ni-MXene composites occurs with remarkable precision and scalability. The team begins by preparing MXene through selective etching of the MAX phase Ti₃AlC₂, resulting in Ti₃C₂Tₓ MXene with ample surface vacancies and functional groups—favorable characteristics for anchoring nickel. Following this, they introduce nickel chloride hexahydrate into the MXene matrix and subject the mixture to heat treatment under argon. By meticulously adjusting the nickel precursor concentration, they manage to create various morphologies of nickel anchoring on the MXene that optimally enhance its EM wave absorption properties.

Among the diverse nickel morphologies explored, it was the nickel nanoclusters, roughly between 1 and 2 nm in size, that attained the most significant MSI effect. This ensured that the electron localization and dipole polarization losses were at their optimal levels, substantially increasing EMW dissipation. Conversely, larger nanoparticles yielded excessive electron scattering, diminishing conductivity and polarization impacts, thus underscoring the importance of precise material engineering in the research.

This innovative research not only provides exceptional results in terms of EM wave absorption efficiency but also highlights important dual loss mechanisms. The addition of nickel nanoclusters equips the composite with both dielectric loss—attributed to the MXene—and a magnetic loss component due to the nickel clusters, generating synergistic effects that boost overall absorption capabilities. Advanced characterizations, including X-ray photoelectron spectroscopy and spherical aberration-corrected scanning transmission electron microscopy, validate the strong MSI in the constructs, demonstrating that not only are the nanoclusters uniformly distributed on the MXene, but that the arranged bonds are critical in stabilizing the electron localization and enhancing EM absorption.

When subjected to rigorous evaluations across a frequency spectrum from 2 to 18 GHz—an essential domain for emerging 5G networks and radar technologies—the Ni-MXene composites displayed unparelleled stability and performance. With their remarkable ability to sustain operation over numerous cycles, even when nickel was loaded up to 5 wt%, the samples remained capable of converting significant quantities of EM energy into heat, far surpassing their individual components. The encapsulated design of just 2 mm thickness, in conjunction with the lightweight characteristics mandated by its two-dimensional structure, positions this composite as an ideal candidate for adoption in various flexible and space-limited applications.

In terms of broader implications, this research transcends the realm of EMW absorption, paving possibilities for applications in electromagnetic interference (EMI) shielding. Given that this new composite combines high conductivity and absorption capabilities, it has the potential to substitute conventional heavy metal shielding methods currently employed in the electronics industry. Moreover, the electron localization strategy could revolutionize catalysis and spintronics, enhancing active sites and improving the efficiency of devices that rely on these properties.

Ultimately, the work emanating from the Tongji University research team fundamentally reshapes how one can leverage electron localization to optimize functional materials for addressing real-world challenges like EM pollution. Their use of MSI to manipulate electron dynamics highlights unused potentials within MXenes, offering pathways to greener, more efficient solutions for tackling the environmental concerns that stem from our advanced technological landscape. As global demands for better EM management technologies escalate, the Ni-MXene composites stand poised to become pivotal in developing the next generation of devices, ensuring that innovations in communication and technology can be achieved without compromising our environmental integrity.

Subject of Research: Electron Localization in Metal-Supported MXenes
Article Title: Metal–Support Interaction Induced Electron Localization in Rationally Designed Metal Sites Anchored MXene Enables Boosted Electromagnetic Wave Attenuation
News Publication Date: 23-Jun-2025
Web References: http://dx.doi.org/10.1007/s40820-025-01819-9
References: None available
Image Credits: Xiao Wang, Gaolei Dong, Fei Pan, Cong Lin, Bin Yuan, Yang Yang, Wei Lu.

Keywords

Electromagnetic Waves, MXenes, Nickel Nanoclusters, Absorption Technology, Electron Localization, EMI Shielding, Communication Technology, Nano-Micro Letters.