The physics of radar absorption is deceptively simple to state and notoriously difficult to engineer. When an electromagnetic wave strikes a surface, it can be reflected, transmitted, or absorbed. For a target to disappear from a radar screen, the material must first let the wave enter rather than bounce off—an impedance-matching problem, where the material’s effective permittivity and permeability must be tuned to resemble free space. Once inside, the wave must then be dissipated, typically through dielectric losses such as interfacial polarization, electron hopping, and aggregation-induced charge transfer, or through magnetic losses in ferrite and carbonyl-iron fillers. If either step fails, the wave either reflects away or passes through unattenuated. The review emphasizes that performance metrics such as reflection loss in decibels, absorption bandwidth, matching thickness, and radar cross section reduction must be evaluated together, because optimizing one often degrades the others.

The historical arc traced by the authors begins with the Salisbury screen, a simple resistive sheet placed a quarter-wavelength in front of a conducting backing, patented in 1952. That elegant but narrowband concept dominated for decades, alongside iron-ball paints and ferrite coatings. But modern threats operate across an ever-wider spectrum—from high-frequency over-the-horizon radar in the megahertz range, through the S-, C-, X-, and Ku-bands used by tracking and fire-control systems, up to millimeter-wave, terahertz, infrared, and even laser detection. Single-layer absorbers simply cannot cover this span, which has driven the evolution toward multilayer stacks, graded structures, and resonant architectures that combine broadband and narrowband absorption in one design.

Among the most significant architectural innovations highlighted in the review are frequency-selective surfaces and their absorbing cousins, the so-called rasorbers. These are engineered periodic patterns—printed circuits, resistive meshes, or coated fabrics—that allow certain frequencies to pass through while absorbing others. When integrated into composite laminates, they enable radomes that protect an antenna yet suppress radar returns at other frequencies. The authors describe designs ranging from resistive frequency-selective surfaces embedded in glass/epoxy composites to switchable, dual-polarized absorbers that can flip between absorbing and reflecting states using active elements such as PIN diodes and varactors. Active frequency-selective surfaces take this a step further, allowing both the frequency and the amplitude of absorption to be tuned in real time, a capability demonstrated with graphene-based capacitor structures.

Metamaterials represent another leap in design freedom. By arranging subwavelength resonant elements into carefully patterned arrays, researchers can create perfect absorbers with responses that nature does not offer in bulk materials. The review covers metamaterial absorbers spanning from the optical regime to extremely high frequencies, including polarization-insensitive terahertz absorbers, infrared and laser-compatible stealth structures, and reconfigurable metasurfaces based on phase-change materials such as vanadium dioxide. Shape-memory polymers and kirigami metastructures add mechanical tunability, stretching or deforming to shift absorption bands on demand. The authors note that information metamaterials—programmable surfaces whose electromagnetic behavior is controlled digitally—are pushing the field toward absorbers that can adapt to changing threat environments in real time.

Yet the heart of the review is polymer matrix composites, and for good reason. Aerospace structures are increasingly built from carbon-fiber-reinforced polymers, which are lightweight and strong but electrically conductive in ways that can produce strong radar reflections. The multifunctional solution is to design the structural material itself to absorb. Glass or polyimide fabrics reinforced with carbon black, carbon nanotubes, graphene, or nickel-coated fibers can be tailored layer by layer so that impedance rises gradually from the surface inward, drawing waves deep into the laminate where they are dissipated. Sandwich structures with honeycomb or foam cores add a third dimension: the cellular geometry provides mechanical stiffness while the coated cell walls create multiple internal reflections that extend the effective electrical path length. Graded honeycomb designs, in which the effective permittivity varies across the core, have demonstrated broadband absorption suitable for aircraft inlet applications, one of the most challenging scattering hotspots on a stealth platform.

The filler toolbox described in the review is remarkably diverse. Carbon nanotubes, discovered in 1991, remain a workhorse because their high aspect ratio drives electrical percolation at low loadings, enabling both absorption and mechanical reinforcement. Graphene and its derivatives add two-dimensional conductive networks and enormous interfacial area for polarization loss. MXenes—two-dimensional transition metal carbides first reported for electromagnetic interference shielding in 2016—combine metallic conductivity with low infrared emissivity, making them attractive for radar-infrared compatible stealth. Magnetic fillers such as ferrites, carbonyl iron, and MOF-derived amorphous magnetic powders contribute permeability-based losses that complement dielectric mechanisms, and hybridizing the two is a central strategy for broadband performance. Conducting polymers like polyaniline and polypyrrole, first synthesized in their conductive forms in the 1970s, offer processable, corrosion-resistant alternatives for coatings and textiles.

The review also surveys manufacturing routes, and here the comparison is critical because processing determines whether laboratory performance survives in a real structure. Solution casting and spray coating are simple but struggle with filler dispersion and scale. Electroless plating can metallize fabrics and fibers uniformly, producing nickel- or copper-coated textiles with strong shielding effectiveness. Additive manufacturing emerges as a transformative route: 3D printing enables bio-inspired concentric infill patterns, triply periodic minimal surface meta-structures in polymer-derived ceramics, and seamless meta-sandwich composites that are simultaneously lightweight, load-bearing, and broadband-absorbing—geometries that would be impossible to fabricate by conventional lamination. Nanoimprint lithography is bringing scalable production of multilayer metasurface devices within reach.

Beyond stealth, the authors point to a widening set of applications. Electromagnetic interference shielding is now essential for dense electronics, 5G and 6G hardware, and electric vehicles, and the same materials that absorb radar can suppress unwanted emissions. Flexible and wearable systems—knitted and woven fabrics with stainless steel, silver nanowires, or carbon nanostructures—combine shielding with joule heating, breathability, and durability. Thermal management is becoming a co-design requirement, since absorbed electromagnetic energy converts to heat; recent composites are engineered to absorb waves and dissipate heat simultaneously. Multispectral compatibility is another frontier, with transparent metamaterials and low-emissivity coatings working together to defeat radar, infrared, and laser detection in a single stack.

The review closes with an honest assessment of the challenges ahead. Low-frequency absorption, particularly in the S-band and below, still demands thick or heavy solutions, and achieving it with lightweight structures remains an open problem. Impedance matching across wide bandwidths, environmental durability, scalable manufacturing, and the integration of active components into structural laminates all require further work. The authors point toward high-entropy materials for extreme environments, intelligent electromagnetic materials designed with machine learning, and deeper synergy between material chemistry and structural architecture as the most promising directions. What emerges from their synthesis is a field in transition: radar absorption is no longer a coating problem but a materials-design problem, in which the airframe itself becomes the absorber. If that vision matures, the next generation of stealth platforms may owe their invisibility not to what is painted on them, but to what they are made of.

Subject of Research: Multifunctional radar-absorbing materials integrating structural and electromagnetic performance

Article Title: Review: multifunctional radar-absorbing materials—integration of structural and electromagnetic performance

Article References: Kishor, K., & Sheikh, J. (2026). Review: multifunctional radar-absorbing materials—integration of structural and electromagnetic performance. Journal of Materials Science, 61(43), 33398-33430. https://doi.org/10.1007/s10853-026-13614-x

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13614-x

Keywords: radar-absorbing materials, polymer composites, stealth technology, metamaterials, frequency-selective surfaces, electromagnetic wave absorption, carbon nanotubes, graphene, MXenes, honeycomb structures, additive manufacturing, electromagnetic interference shielding

The biological prototype is Melanophila acuminata, the fire-chaser beetle, whose thoracic pit organs house infrared sensilla capable of detecting the thermal glow of distant burning forests. Using scanning electron microscopy, the team mapped the ultrastructure of these natural photodetectors and found a densely packed array of synaptic-like protrusions separated by gaps, each covered in nanoscale wrinkles and dotted with nanopores. The gaps provide paths for repeated reflection and scattering of incoming radiation, the micrometer-scale protrusions act as resonant structures, the nanoscale wrinkles resonate with far-infrared waves, and the nanopores push the impedance of the sensillum closer to that of air, so that radiation enters rather than bounces off. The sensilla detect infrared rather than microwave radiation, but the researchers recognized that the underlying wave-management principles were transferable.

Crucially, the team emphasizes that the strategy is one of functional translation rather than geometric copying. The beetle’s architecture operates in the infrared regime, whereas the synthetic material targets microwaves in the 2 to 18 GHz band. The designers therefore mapped each biological feature onto a corresponding synthetic element: the cavities and interspaces of the sensillum became a three-dimensional porous carbon framework that lowers the effective permittivity and improves impedance matching with free space; the synaptic protrusions became rough, interconnected carbon struts decorated with cerium dioxide and MXene nanosheets; and the nanoscale wrinkles and pores became abundant heterointerfaces, oxygen vacancies, and surface terminations that act as polarization and loss centers. The result is a hierarchical structure that preserves the beetle’s strategy of multiscale impedance regulation and interfacial energy dissipation while rescaling the characteristic dimensions to microwave physics.

Before fabricating anything, the team validated the concept computationally. They modeled the aerogel as an irregular Voronoi polyhedral framework, a geometry chosen both for its resemblance to the biological template and because structural irregularity favors absorption. Density functional theory calculations on the two chosen nanomaterials, cerium dioxide and Ti3C2Tx MXene, revealed strong electronic coupling at their junction. Differential charge density analysis showed electrons accumulating on the cerium dioxide side and depleting on the MXene side, creating a built-in electric field and prominent interfacial dipoles. Work function calculations quantified the driving force: 6.030 eV for the cerium dioxide surface versus 5.394 eV for Ti3C2OF, the stoichiometry derived from quantitative elemental analysis of the actual synthesized MXene. Electrons therefore flow from MXene to cerium dioxide until the Fermi levels align, strengthening Maxwell-Wagner interfacial polarization, a key dielectric loss mechanism under an alternating electromagnetic field.

The electronic structure calculations added further support. The density of states near the Fermi level is dominated by titanium 3d orbitals, indicating that the heterostructure retains good intrinsic conductivity channeled through the MXene layers, which enables energy dissipation via conduction losses. Significant orbital hybridization among Ce 4f, Ti 3d, O 2p, and F 2p states above the Fermi level creates unoccupied hybridized states into which incident radiation can excite electrons, opening an additional channel for energy dissipation. COMSOL electromagnetic simulations of the materialized unit cell, combined with transmission line theory and the ABCD matrix method, predicted reflection loss below −10 dB, corresponding to more than 90 percent absorption, across nearly the entire 2 to 18 GHz range.

To realize the design experimentally, the researchers used melamine foam as a sacrificial template because its skeletal structure and pore dimensions closely mimic the theoretically optimized Voronoi-like architecture. The foam was impregnated with a dispersion of cerium dioxide and MXene nanosheets, freeze-dried, and then heat-treated under argon at 350 and 800 degrees Celsius, which carbonizes the template and burns it away as a sacrificial scaffold. The resulting aerogels have densities between 0.018 and 0.117 grams per cubic centimeter and shrink only 5.60 to 13.07 percent during formation. X-ray diffraction confirmed cubic cerium dioxide and the characteristic (002) reflection of MXene, Raman spectroscopy identified the component phases and the graphitic carbon framework, and X-ray photoelectron spectroscopy revealed the coexistence of Ce3+ and Ce4+ states, a signature of high oxygen-vacancy concentration in the ceria lattice.

Those oxygen vacancies matter enormously for performance. The presence of Ce3+ introduces additional electronic energy levels and local charge imbalance, generating defect dipoles that relax under an alternating electromagnetic field and convert wave energy into heat. The minor titanium dioxide phase detected in the spectra further enhances interfacial polarization at newly formed heterogeneous boundaries. When the aerogels were vacuum-impregnated with epoxy resin for testing, dielectric measurements showed that increasing nanomaterial loading raised the complex permittivity substantially, while the permeability remained essentially unchanged because the primary components are non-magnetic. Cole-Cole analysis revealed four distinct Debye relaxation processes in the optimal samples, and impedance spectroscopy showed low charge-transfer resistance at high frequencies, consistent with the highly conductive MXene and carbon networks.

The absorption measurements validated every element of the design. The CMX5 sample achieved a minimum reflection loss of −63.10 dB at 3.1 mm thickness and 13.58 GHz, with an effective bandwidth of 6.46 GHz, and reached its maximum bandwidth of 7.82 GHz at 4.0 mm thickness. The CMX3 sample performed even more impressively in bandwidth terms: at 3.9 mm it covered 9.43 GHz, spanning 6.70 to 16.13 GHz, surpassing all previously reported carbon-based absorbers while using an ultralow 3.74 weight percent loading. By simply adjusting thickness, the material can be tuned to cover 100 percent of the X-band and up to 84.5 percent of the Ku-band, or 73 percent of the C-band, because polarization relaxation processes dominate at low and mid frequencies. Radar cross-section simulations confirmed that coated objects would be substantially harder for radar to detect.

The team also demonstrated practical relevance beyond the laboratory bench. When a resin patch of the material was placed over a chip inside a communication device, the measured radiation intensity dropped from 110 volts per meter on the bare chip to roughly 10 to 40 volts per meter, a striking reduction in electromagnetic pollution at the component level. The aerogels additionally proved mechanically resilient, retaining elasticity after compression and supporting a 100-gram load with minimal deformation, thermally insulating, with a cubic centimeter sample keeping its top surface below 50 degrees Celsius on a hot plate at 100 to 200 degrees Celsius, and fire-resistant, with the framework remaining largely intact after direct ablation. Filling the aerogel with epoxy even raised the resin’s thermal conductivity and glass transition temperature, because the continuous carbon network provides pathways for phonon transport and mechanically interlocks with the polymer chains.

The broader significance of the work lies in demonstrating that a biological sensory organ tuned to infrared radiation can be rationally translated into a metamaterial for an entirely different part of the electromagnetic spectrum. Rather than copying the beetle’s geometry, the researchers extracted its design logic, hierarchical impedance grading, radiation trapping through multiple scattering, extended propagation pathways, and interfacial energy conversion, and re-implemented it with cerium dioxide nanoparticles, MXene nanosheets, and a porous carbon scaffold. The synergy between dielectric loss in ceria, conductive and interfacial losses in MXene, and defect dipoles from oxygen vacancies produces complementary attenuation mechanisms that no single component could deliver. With broadband coverage, high absorption efficiency, ultralow density, and minimal filler content combined in one material, the beetle-inspired aerogel points toward next-generation electromagnetic interference shielding, stealth coatings, and protection for the ever-denser wireless electronics of modern life.

Subject of Research: Bio-inspired CeO2/MXene hierarchical aerogels for broadband microwave absorption

Article Title: Modified MXene Aerogel With Broadband Microwave Absorption Inspired by Melanophila Acuminata Beetle

Article References: Liu, Z., Xu, D., Liu, Z., Song, H., Zhang, Q., Zhou, J., & Wen, X. (2026). Modified MXene Aerogel With Broadband Microwave Absorption Inspired by Melanophila Acuminata Beetle. Advanced Science, 13(55), Article e76496. https://doi.org/10.1002/advs.76496

Image Credits: AI Generated

DOI: 10.1002/advs.76496

Keywords: MXene, aerogel, biomimetics, Melanophila acuminata, microwave absorption, electromagnetic interference, CeO2, carbon foam, impedance matching, stealth technology, dielectric loss, DFT calculations

The study, published in the International Journal of Aeronautical and Space Sciences by Seung-Hoon Kang of Sejong University and Younggeun Park and SangJoon Shin of Seoul National University, tackles a problem that has grown steadily worse as stealth analysis has become more demanding. To certify how well a design hides from radar, analysts must compute the monostatic radar cross-section, or RCS, for a sweeping range of illumination angles. Each angle corresponds to a different incident radar wave, and each incident wave requires solving a large system of linear equations derived from a finite-element model of the aircraft or missile. In the language of numerical linear algebra, the analyst faces a system with many right-hand sides, one for every direction the radar might come from.

The finite-element method discretizes the volume of space around and inside the target into millions of small elements, turning Maxwell’s equations of electromagnetism into a gigantic sparse linear system. Solving that system once is already a serious undertaking. Solving it hundreds of times, once per angular sample, multiplies the cost into something that can dominate an entire design cycle. The researchers describe this as the central obstacle in angular monostatic RCS analysis for large-scale finite-element models, and it is precisely the obstacle their new methods are built to remove.

Their starting point is an established technique called the finite element tearing and interconnecting method, or FETI, originally devised in the early 1990s by Charbel Farhat and François-Xavier Roux as a way of tearing a large structural problem into smaller subdomains and then interconnecting the pieces through interface conditions. The dual-primal refinement, FETI-DP, introduced in 2001, added primal constraints at selected interface points that dramatically improved convergence, and the electromagnetic adaptation, FETI-DPEM, extended the approach to wave problems governed by Maxwell’s equations. In FETI-DPEM, the computational domain is partitioned into subdomains, each subdomain problem is solved independently, and an interface problem enforces continuity of the electromagnetic fields across the artificial boundaries between subdomains. The interface problem is solved iteratively with a Krylov-subspace method, a family of algorithms that build up an approximate solution from a sequence of increasingly refined search directions.

The key insight behind the new work is that the many right-hand sides arising from angular sweeps are not independent of one another. When radar illuminates a target from ten degrees and then from eleven degrees, the two incident waves produce scattered-field solutions that are highly correlated. Information generated while solving the first system, in the form of Krylov subspace vectors, is therefore valuable for solving the second. Conventional practice throws that information away after each solve. The researchers’ first proposed variant, which they call recycling FETI-DPEM, or rFETI-DPEM, instead retains and reuses Krylov subspace information from previously solved angles. As each new right-hand side arrives, the method augments the stored subspace with the new search directions using a modified Gram–Schmidt orthogonalization procedure, keeping the recycled vectors orthonormal and computationally cheap to maintain. The result is a sequential solver in which each successive angular solve starts much closer to its answer than a cold start would.

The second variant goes further by attacking the multiple right-hand sides simultaneously. Block FETI-DPEM, or bFETI-DPEM, gathers the incident-wave vectors into a block and first applies a rank-revealing QR decomposition to that block. Rank-revealing QR is a classical matrix factorization technique that identifies which columns of a matrix carry genuinely independent information and which are nearly redundant. In the angular RCS setting, this means the method detects the linear dependency among the incident waves and collapses the block of right-hand sides to a much smaller set of independent representatives. The reduced system is then solved with a block iterative solver, a block version of the BiCGSTAB algorithm that advances all right-hand sides together, sharing search-direction information across the entire set. Because the block dimension has already been pruned, the block solver operates on a far leaner problem than the original sweep would imply.

The numerical experiments reported in the paper show that both variants deliver on their promise. In test cases ranging from canonical scattering objects to large-scale missile geometries, rFETI-DPEM and bFETI-DPEM reproduced the RCS results of the original FETI-DPEM method to the expected accuracy, confirming that the acceleration does not come at the price of fidelity. The speed-ups, however, differed markedly between the two. The block approach proved the more robust of the pair, and in the largest missile analyses it achieved a speed-up factor of up to 19.6 times compared with the baseline method. The researchers attribute this superiority to the block strategy’s ability to exploit the correlation structure among all the right-hand sides at once, rather than only sequentially, and to the dimensionality reduction provided by the rank-revealing QR step, which strips out redundant work before the expensive iterative phase begins.

The significance of such an improvement extends well beyond a single benchmark. Angular RCS analysis sits at the heart of stealth certification, and the cost of that analysis constrains how finely engineers can sample angles, how detailed their finite-element models can be, and how many design iterations they can afford. A nearly twenty-fold acceleration in the large-scale regime effectively multiplies the design exploration budget. It allows analysts to sweep angles more densely, catching narrow specular lobes and grazing-angle signatures that a coarse angular sampling might miss, and it makes it feasible to evaluate radar signatures early in the design process rather than late, when geometric changes are expensive. The work also connects to a broader current in computational electromagnetics, in which domain decomposition, Krylov recycling, and block iterative techniques are being combined to push the frontier of solvable problem sizes.

The methodological lineage of the paper is deep. The recycling idea traces back to foundational work by Parks and colleagues on reusing Krylov subspaces for sequences of linear systems, and recycling BiCGSTAB has found applications from parametric model-order reduction to computational fluid dynamics. Block Krylov methods for multiple right-hand sides have been developed since the early 2000s, including block variants of BiCGSTAB used in lattice quantum chromodynamics. What the Korean team contributes is the careful integration of these ingredients into the electromagnetic FETI-DP framework, together with the observation that angular radar sweeps provide exactly the kind of correlated right-hand-side structure that makes recycling and blocking pay off. The rank-revealing QR reduction, drawn from classical numerical linear algebra, acts as the bridge that makes the block method efficient rather than merely elegant.

For the aerospace community, the message is that the computational wall standing in front of large-scale stealth analysis has just become considerably lower. The authors position the framework as a highly efficient and robust solution for radar stealth analyses of complex aerospace structures, and the reported speed-ups suggest that full-aircraft angular signature studies that once strained computational budgets could become routine. As stealth requirements spread from dedicated attack aircraft to missiles, drones, radomes, and coated components, tools that turn weeks of computation into days, or days into hours, will shape what engineers can design and verify. This study demonstrates that sometimes the most powerful upgrade to a stealth platform is not a new coating or a new shape, but a smarter way of solving the equations that describe it.

Subject of Research: Accelerated domain decomposition methods for angular radar cross-section stealth analysis of aerospace structures

Article Title: Improved Dual-Primal Domain Decomposition Method for the Angular Radar Stealth Analysis

Article References: Kang, S.-H., Park, Y., & Shin, S. (2026). Improved Dual-Primal Domain Decomposition Method for the Angular Radar Stealth Analysis. International Journal of Aeronautical and Space Sciences. https://doi.org/10.1007/s42405-026-01236-1

Image Credits: AI Generated

DOI: 10.1007/s42405-026-01236-1

Keywords: radar cross-section, stealth technology, domain decomposition, FETI-DP, finite element method, Krylov subspace recycling, block iterative solvers, rank-revealing QR, computational electromagnetics, multiple right-hand sides, aerospace engineering, parallel computation

The review’s central claim is unifying. Biomimetic camouflage, multispectral signature management, and adversarial attacks on machine vision have traditionally been studied in separate communities, each with its own vocabulary, journals, and assumptions. By placing them in one framework, the authors reveal a shared evolutionary logic: every advance in perception drives a corresponding advance in concealment, and every new concealment strategy in turn pressures perception to improve. This reciprocal escalation, an arms race in the strict sense, has shaped life on Earth since the first eyes opened, and it now shapes the security of the artificial systems that increasingly see on humanity’s behalf. Understanding the logic, the authors contend, is the key to building the next generation of camouflage, stealth technology, robust sensors, and trustworthy artificial intelligence.

Nature wrote the first chapter. According to the review, roughly seven hundred million years ago cnidarians deployed opsins, light-sensitive proteins that marked the origin of biological vision. The Cambrian ocean then escalated the stakes dramatically. Anomalocaris, one of the era’s dominant predators, hunted with compound eyes containing approximately sixteen thousand lenses, an arrangement that gave it exceptional resolving power for its time. Color vision emerged more than three hundred million years ago, adding an entirely new dimension to both detection and deception. As sensory systems grew sharper, concealment strategies grew more sophisticated in parallel, producing the countermeasures that still define survival in ecosystems today: the disruptive patterns that break up an animal’s outline, the textures that match a background, the behaviors that exploit the blind spots of a predator’s visual system.

What makes the review distinctive is how it traces these biological strategies into human engineering. The lineage is surprisingly direct. Polar bear hollow hairs, which manage light and heat with remarkable efficiency, have inspired low-observable fabrics. The spot patterns of leopards and the stripes of tigers informed the design of digital camouflage. Leaf-mimicking butterflies, ink-squirting octopuses, and death-feigning frogs each map onto human equivalents such as decoys and smoke screens. The historical record of warfare follows the same playbook. In World War I, the British Navy applied dazzle camouflage, not to hide ships but to confuse enemy rangefinders and gunners about a vessel’s heading and speed. In World War II, the Allies assembled an entire phantom army of inflatable tanks and fabricated radio traffic to misdirect German intelligence about invasion plans. Deception, in other words, need not mean invisibility; it can mean corrupting the observer’s interpretation of what is seen.

The technical core of the review addresses what happens when sensing leaves the visible band. Modern imaging spans the electromagnetic spectrum from ultraviolet to microwave, and each band imposes its own physics on the problem of concealment. In the ultraviolet, materials such as avobenzone and zinc oxide nanoparticles absorb or scatter radiation that would otherwise betray a target. Against lidar, which measures reflected laser pulses, micro- and nanostructured surfaces convert mirror-like specular reflection into diffuse reflection, weakening the coherent echoes that make precise detection possible. These are not incremental tweaks; they represent deliberate control over how matter interacts with waves, band by band, using structure and chemistry rather than paint alone.

The thermal infrared band presents its own distinct challenges, and the review identifies three dominant strategies for managing it. The first is replicating the thermal texture of the background, so that a warm object presents the same infrared mosaic as its surroundings. The second is modulating emissivity, the intrinsic tendency of a surface to emit thermal radiation, which can be tuned with engineered coatings. The third is suppressing heat conduction, so that heat generated by an engine or a body does not propagate to the surface where sensors would detect it. Microfluidics, phase-change materials, and aerogels each play roles in these approaches. Aerogel fibers inspired by polar bear hair exemplify the biomimetic thread running through the work, while electro-responsive photonic crystals inspired by chameleons can reversibly shift color from blue to red, offering dynamic rather than static concealment.

In the microwave band, the domain of radar, the toolkit shifts again. Composite absorbing materials soak up incident radar energy rather than reflecting it back to the transmitter. Smoothly curved stealth airframes, of the kind pioneered on modern aircraft, redirect reflections away from the source instead of eliminating them. Reconfigurable metasurfaces, engineered surfaces whose electromagnetic properties can be adjusted on demand, point toward adaptive stealth that can respond to changing threat conditions. Yet the review is candid about the field’s hardest problem: multispectral compatibility. Requirements that help in one band often hurt in another. A surface optimized to absorb radar may glow in the thermal infrared; a coating that suppresses visible reflections may do nothing for ultraviolet sensors. Multifunctional stacking and hybrid integration are the current paths toward full-spectrum signature management, and the authors describe them as bringing genuine cross-band invisibility closer to practical reality.

Then the observer changes entirely. When the beholder is no longer a human eye or even a physical sensor but a neural network, the rules of the contest transform. Machine vision systems built on sensors and deep learning architectures, from convolutional neural networks to models such as DINO and YOLO, now exceed human performance in certain recognition tasks. But capability and vulnerability rise together, because these systems make decisions based on learned decision boundaries in high-dimensional feature space rather than on the physical properties of light. Anti-perception has consequently shifted from manipulating physical signatures to attacking those decision boundaries directly. In the digital domain, the Fast Gradient Sign Method applies perturbations computed from a model’s own gradients, while the one-pixel attack demonstrates that changing a single pixel can flip a model’s classification entirely.

The physical world makes the threat concrete. Adversarial patches, printed patterns that can be held up to a camera, have been shown to reduce pedestrian detection accuracy by more than seventy percent. A famous 3D-printed adversarial turtle is misclassified as a rifle from essentially any viewing angle, demonstrating that such attacks survive real-world geometry and lighting rather than existing only in simulation. The attacks are also spreading across the spectrum. Thermal camouflage patches can cut infrared detection accuracy from 95.7 percent to 45.4 percent, and cross-modal adversarial patches can deceive visible-light and infrared sensors simultaneously, meaning a single physical object can defeat multiple sensing modalities at once. For autonomous vehicles, military platforms, and security systems that rely on machine perception, these results define a new class of vulnerability that no amount of traditional camouflage addresses.

Looking forward, the authors argue that anti-visual perception is moving from isolated exploration toward deep interdisciplinary integration, and they lay out a roadmap along each of their three threads. Biomimetics must progress from mimicking form to mimicking function, which demands cross-scale knowledge graphs that connect biological mechanisms to engineering implementations, together with scalable manufacturing of multiscale structures. Spectral physics must move from passive trade-offs among bands to active design, combining emerging materials such as graphene and phase-change materials with AI for Science inverse-design platforms that can search vast material and structural spaces faster than human intuition allows. Research on artificial intelligence, meanwhile, must bridge the persistent gap between simulated and real-world conditions, forging stronger shields even as sharper spears are built. The review’s deepest message is that the hide-and-seek begun by cnidarians and Anomalocaris has not ended; it has merely changed substrates. Every gain in seeing, whether by a compound eye, a radar array, or a neural network, will be answered by a new way of hiding, and the disciplines that treat this as one continuous story will be the ones that shape what comes next.

Subject of Research: The evolution of anti-visual perception across biomimetics, multispectral signature management, and adversarial attacks on machine vision

Article Title: The eternal hide-and-seek: How anti-visual perception evolved from snow leopards to AI attacks

Article References: The eternal hide-and-seek: How anti-visual perception evolved from snow leopards to AI attacks. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: anti-visual perception, camouflage, biomimetics, stealth technology, adversarial attacks, machine vision, multispectral sensing, thermal infrared, metasurfaces, snow leopard, National Science Review, trustworthy AI

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

Triboelectric nanogenerators harness Maxwell’s expanded displacement current theory, converting low-frequency, chaotic mechanical energy—ubiquitous in soldiers’ movements and machinery vibrations—directly into electrical power via contact electrification and electrostatic induction. Unlike traditional electromagnetic generators that depend on continuous rotation, TENGs leverage mechanically triggered polarization currents, enabling efficient energy harvesting even amidst irregular excitation. Their architecture, grounded in dielectric polymers, offers unparalleled advantages including ultralight weight, radar-wave permeability for electronic stealth, and intrinsic zero-power passive sensing capabilities vital for covert operations.

Among TENG’s diverse operational modes—contact-separation, lateral sliding, single electrode, freestanding layer, and rolling—each presents unique benefits in minimizing friction losses and maximizing electrical output stability. This versatility allows seamless integration across a spectrum of military platforms, from wearable soldier equipment to strategic aero-engines and unmanned underwater vehicles. Notably, fluoroalkylsilane-treated textiles preserve electrical charge in humid settings, while biomimetic materials provide electromagnetic and neutron shielding, demonstrating sophisticated multifunctionality within combat wearables.

On unmanned systems, bioinspired triboelectric whiskers deliver state recognition with over 98% accuracy, crucial for underwater navigation, while owl-wing-inspired anemometers reduce wind speed thresholds for unmanned aerial reconnaissance. Strategic equipment benefits from hybrid triboelectric-variable reluctance generators to wirelessly monitor aero-engine bearings at 600 rpm intervals, and miniature accelerometers maintain linear response under harsh g-force impacts up to 18,000 g—further emphasizing TENGs’ robustness in dynamic environments.

Still, the transition from lab prototypes to battlefield-ready devices confronts three main hurdles: impedance mismatch hindering energy transfer, environmental-induced material degradation, and scalability of manufacturing. The research notes breakthrough solutions including AI-powered power management chips with adaptive impedance matching, military-grade encapsulation complemented by self-healing hydrophobic coatings, and advanced roll-to-roll fabrication aligned with military standards, collectively driving TENGs closer to practical deployment.

Looking ahead, the integration of TENGs with photovoltaic and thermoelectric systems promises hybridized multifunctional energy networks. Moreover, embedding energetic materials could catalyze intelligent ammunition technology while system-level reconfiguration aims at physically encrypted, self-powered tactical meshes. This strategic emphasis transcends energy supply, positioning triboelectric nanogenerator technology as a cornerstone for future electromagnetic stealth and zero-power battlefield cognition.

The comprehensive review not only highlights TENGs’ disruptive potential but also charts pathways to overcome engineering bottlenecks, signifying a leap towards autonomous, resilient, and stealthy military microsystems. As modern warfare demands greater system intelligence with minimal logistical footprints, triboelectric nanogenerators emerge as a seminal advancement, powering the next generation of combat readiness.

Subject of Research: Triboelectric Nanogenerators in Military Applications
Article Title: Triboelectric Nanogenerators in Military: Recent Progress and Critical Challenges
News Publication Date: 4-Jun-2026
Web References: http://dx.doi.org/10.1007/s40820-026-02221-9
Image Credits: Changcheng Bao, Xiaoxia Ma, Min He, Li Yang, Yingting Wang

Keywords

Electromagnetism, Triboelectric Nanogenerators, Military Technology, Energy Harvesting, Self-powered Sensors, Battlefield Stealth