Metamaterials and metasurfaces are a class of artificially constructed materials with microarchitectures specifically designed to exhibit properties not present in naturally occurring substances. These structures demonstrated exceptional behavior that allowed for the manipulation of particles and optical and electromagnetic waves in unprecedented ways. These synthetic materials possess electromagnetic properties that are independent of their chemical constituents; instead, these properties depend on the physical arrangement of the constituent atoms. Consequently, the physical design determines the characteristics of the material. Metamaterials offer greater design flexibility and the potential to achieve novel features, making them a prominent topic in various research fields, including thermodynamics, mechanics, and electromagnetics. They exhibit intriguing features such as negative refraction, cloaking effect, and enhanced absorption. Research on electromagnetic absorbers is rapidly growing due to their promising applications in sensors and stealth. Among these applications, stealth and military uses are particularly noteworthy. From a stealth perspective, grazing stability is a crucial factor. This study provides a brief overview of metamaterials, with a focus on resistive‐based metamaterials for microwave applications. It focuses on advancements in broadband design and grazing angle stability while discussing the applications of resistive electromagnetic metamaterial absorbers. Additionally, it offers forecasts for the future of resistive‐based metamaterials.

Stealth technology is pivotal for military survivability, employing a series of techniques to significantly minimize an asset from being detected by hostile radar. Rather than actual invisibility, contemporary stealth employs passive methods, mostly on geometrical shaping and Radar-Absorbing Materials (RAM) to diffuse and absorb radar signals, making platforms difficult to detect, trace, and engage. But the relentless advancement of multi-frequency radar systems betrays the inherent shortcomings of these static defenses. This has spurred the quest for a revolutionary active countermeasure: “Plasma Stealth.” This science-fictional concept involves surrounding an aircraft with a sheath of ionized gas, or plasma, that can dynamically absorb and steer incoming electromagnetic waves in real time. This review explores the underlying physics of this “magic layer,” from its development as a theoretical curiosity to a technology on the cusp of next-generation stealth mastery. It examines how plasma layers reflect, absorb, and scatter radar waves to achieve electromagnetic attenuation, highlighting recent progress in plasma generation, diagnostics, and modeling, along with growing control over plasma parameters. We also explore its potential to offer tunable, broadband low observability while discussing the critical operational difficulties, such as stability, power efficiency, and system integration, as well as the areas of future research that must be addressed to achieve its full potential.

The utilization of magnetic, dielectric and conducting properties in synergistic manner would be useful for developing novel materials for electromagnetic interference (EMI) shielding applications. Therefore, polypyrrole-CoFe2O4-CaCu3Ti4O12 (PCC) nanocomposites have been synthesized by in-situ chemical oxidative polymerization; where two oxidants ammonium peroxydisulfate i.e., APS ((NH4)(2)S2O8) and iron (III) chloride (FeCl3) are rationally varied. Their effect on the morphological features, microwave dielectric and EMI shielding is investigated comprehensively and analytically. Interestingly, PCC (40 APS) [APS: FeCl3::40:60] nanocomposites show peculiar morphological features as well as highest shielding effectiveness. Morphological analysis establishes the formation of "basket like structure" in the PCC (40 APS) nanocomposites ascribed to the interfacial forces among the cross linking of polymeric chains and the interaction of incorporated ceramic nanoparticles with the functional group of polypyrrole (i.e. -NH). It also exhibits highest shielding effectiveness (SET similar to 31 dB) with absorption dominant contribution (SEA similar to 25 dB) in the X-band. Additionally, PCC (40 APS) nanocomposite has highest dielectric permittivity (epsilon') similar to 80 and dielectric loss similar to 1. These observations are attributed to multiple interfacial polarization relaxation in PCC nanocomposites. These investigations will open the way for tuning shielding effectiveness in the conducting polymer-based nanocomposites by the modification in processing parameters.

Polypyrrole-NiFe2O4-CaCu3Ti4O12 (PNC) nanocomposites are prepared via in-situ chemical oxidative polymerization. In this process, the weight ratio of pyrrole monomer and NiFe2O4 (NFO) is fixed to 1:1 whereas the concentration of CaCu3Ti4O12 (CCTO) is varied from 0 to 1 by weight fraction in the step size of 0.25 to study the influence of dielectric filler incorporation on electromagnetic shielding effectiveness of polymer-based nanocomposites in X-band. XRD and FTIR confirms the successful formation of a multi-phase nanocomposite structure. FESEM imaging reveals increased porosity and surface roughness with increasing CCTO content. Further, microscopic studies confirm the formation of cage-like structures where the nanofillers are attached with the polymeric chain. The nanocomposites exhibit ohmic electrical behaviour with DC conductivity of ∼ 0.2 S cm-1, and ferrimagnetic behaviour with a coercivity ∼ 330 Oe for PNC1. The electromagnetic interference (EMI) shielding observations emphasis on enhanced absorption tendency of the nanocomposites with the inclusion of CCTO. The highest shielding effectiveness (SE) value is achieved for PNC1 (1 wt. % of both nanofillers) ∼ 38 dB with absorption contribution ∼ 32 dB along with absorption efficiency ∼ 99.7%. Microwave dielectric analysis shows a significant increase in relative permittivity (εr) ∼ 65 and attenuation coefficient (α) ∼ 800 Np/m with CCTO loading. Reflection loss (RL) studies further confirm the microwave absorption capability of PNC1, which is approximately −10 dB. The synergistic contribution of dielectric and magnetic losses in PNC nanocomposites corresponds to superior EMI shielding performance, which could be useful in electronic, defence, communication, and aerospace applications.

Biomass-derived activated carbons (BACs) comprising highly porous structures and ultralightweight characteristics are potential microwave-absorbing materials (MAMs). Here, we report diverse BACs from rice stubble (PAAC), bajra husk (BJAC), royal palm leaves (RAC) and amla leaves (ACA) prepared via a two-step process involving carbonisation and KOH activation. The superimposed effect of natural hierarchical structure and activation results in exceptionally large specific surface area i.e., PAAC (1744.6 m2/g), ACA (1704 m2/g), BJAC (1613.5 m2/g) and RAC (1315 m2/g), enabling optimal balance the relatively adverse relationship between dielectric loss and impedance matching to attain effective microwave (MW) absorption. At minimal loading, PAAC10 achieves remarkably strong reflection loss (RLmin) of -69 dB with an effective absorption bandwidth (EABmax) of 4.4 GHz covering 75 % of the Ku band at 1.66 mm thickness. RAC20 exhibits an EABmax of 5 GHz at 1.67 mm, spanning 83.3 % of the Ku band. BJAC15 demonstrates an exceptional EABmax of 6.1 GHz, covering the entire Ku band at 2.2 mm, and 4.16 GHz spanning the whole X-band at 3.1 mm. The activation-induced hierarchical 3D porous conductive network enhances electromagnetic wave (EMW) scattering, interfacial polarization, and conductive losses. Simultaneously, the incorporation of oxygen-containing functional groups induces dipole polarization loss, contributing to a multi-component loss mechanism. Furthermore, by modulating dielectric properties and impedance matching through controlled material loading, BACs exhibit superior MW absorption with strong RL and ultra-broad EAB at minimal thicknesses. These findings provide valuable insights into the potential of BACs as high-performance, lightweight MAMs for advanced EMW absorbing applications.

This study presents the synthesis of neodymium (Nd) doped barium hexaferrite (BHF), with the chemical composition Ba1-xNdxFe12O19 (where x = 0 to 0.20), and its nanocomposites with reduced graphene oxide (rGO) in order to investigate the microwave absorption properties within the X-band of microwave frequency. Pristine and Nd doped BHF nanopowders were synthesized via the sol-gel auto-combustion process, while the nanocomposites were prepared using the sonochemical method. X-ray diffraction (XRD) analysis established the successful formation of the desired BHF phase, as well as the formation of rGO and their nanocomposites. Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy were employed to confirm the structural integrity of the nanocomposites, providing evidence of distinct vibrational bands associated with their formation. The thermal stability of one the synthesized nanocomposites was analyzed using Thermogravimetric analysis (TGA) over the temperature range of 30-800 degrees C. The surface morphology of the synthesized Nd doped BHF/rGO/ epoxy resin nanocomposites was examined using scanning electron microscopy (SEM). The microwave absorption characteristics of the undoped and Nd doped BHF/rGO/epoxy resin nanocomposites were evaluated using a vector network analyzer (VNA) in the X-band of microwave frequency (8.2-12.4 GHz). Among the prepared samples, 3 mm thick Ba0.80Nd0.20Fe12O19/rGO-epoxy nanocomposite resulted a minimum reflection loss of -22.2 dB at 10.5 GHz with an effective bandwidth of 2.5 GHz. The remarkable material properties, along with excellent microwave absorption performance, make the nanocomposites promising candidates for electromagnetic shielding and microwave absorption applications.

We theoretically propose a hybrid terahertz absorber with dual tunability—thermal via vanadium dioxide (VO2) and electrical via graphene. The proposed design features stacked frequency-selective surfaces and demonstrates ultrabroadband absorption from 1.84 to 8.22 THz (absorption >90%). This can happen under the metallic phase of VO2 (σVO2=2×105 S/m) and chemical potential of graphene (μ) of 0 eV. The absorption amplitude can be dynamically tuned from 8% to 90% by varying VO2 conductivity, thereby highlighting excellent thermal responsiveness. While another narrow channel representing the second mode occurs, when only graphene is active (μ=1 eV), the absorber attains an absorption (>90%) band from 1.25 to 3.67 THz (bandwidth: 2.42 THz). Additionally, the structure supports reconfigurable absorption via graphene tuning and remains effective up to 70° and 60° incidence angles. It is also polarization-insensitive, making it suitable for applications in THz imaging, sensing, communication, and filtering.

The electromagnetic wave-absorbing composites, incorporating strontium hexaferrite and molybdenum disulfide (SrFe12O19-MoS2), are synthesized by mixing in different weight ratios. In the present work, strontium hexaferrite (SrFe12O19) is developed through a low-temperature auto-combustion method while two-dimensional molybdenum disulfide (MoS2) is synthesized by a facile hydrothermal process. The materials and their composites undergo analysis using characterization techniques such as X-ray diffraction (XRD), fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM), and vibrating sample magnetometer (VSM) to assess their structural, morphological, and magnetic properties, respectively. The minimal reflection loss (RLmin) of - 47.35 dB is observed at 8.66 GHz for the SrFe12O19-MoS2 (50 %-50 %) composite cast into pellets for microwave absorption analysis in the X-band frequency range. This RLmin is obtained with a sample thickness of 1.7 mm. An adequate bandwidth of 3.1 GHz, representing 77.5 % of the entire X band, is observed for a loss below -10 dB. The synergistic interaction between magnetism and dielectricity makes it an efficient electromagnetic absorber for modern technologies.

In this work, a higher broadband and tunable metasurface absorber based on a novel resonant structure made of $VO_{2}$ is investigated. The excellent broadband performance with over 90% absorption corresponding to 3 to 9.38 THz with an effective bandwidth of 6.38 THz is realized using the proposed structure. Further, our absorber shows perfect polarization-insensitive response along better oblique incidence stability. Furthermore, the absorption of the proposed absorber can be modulated by stimulating the temperature dependent electrical conductivity of $VO_{2}$. The proposed design appears to be quite promising for terahertz imaging, THz detection, and stealth technology, etc.

This chapter gives an overview of functional materials for stealth and camouflage based products to achieve low-observable airborne and ground-based platforms with respect to the sensors deployed by adversary forces. Functional materials based on dielectric/magnetic materials and engineered materials have been described for their applications in the electromagnetic design of microwave absorbers for stealth applications. In addition, various techniques have been discussed for camouflage in various frequency spectra (visual, near infrared, infrared and microwave regions) for ground-based applications. Several examples of camouflage and stealth materials are briefly discussed.

A high-performance stealth platform is one of the crucial requirements in defence technology that could practically be realized by building effective microwave frequency selective surface (FSS) absorbers. Herein, we report the design and manufacturing of an absorber by tuning the rheology of cell architecture. Initially, a fan-shaped cell (10.4 mm2) was designed for its surface and bulk rheology. The FSS overlayer composition was investigated using SEM, EDX, and XRD and tuned for 0.25% carbon: 1.5% silver to achieve the ink resistivity similar to 255 Omega square-1. The bulk rheology was optimized for air (Roha) spacer (thickness similar to 2.8 mm), interlayer dielectrics (0.2 mm each), carbon composition (5%), and cell dimension (10.2 mm). Analyses are presented for absorption loss (RC, dB), bandwidth (GHz), resonance dispersion, and constitutive (epsilon, mu) parameters, compounded with an equivalent circuit model with the settings R = 273.55 Omega, L = 2.25 nH, C = 0.057 pF and the Fabry-Perot reactance mode@10 GHz. The bi-modal response was investigated for induced polarization, electromagnetic fields, volume power distribution, and angular (Theta = 0 degrees-50 degrees) and rotational stability (Phi = 0 degrees-90 degrees) against TE/TM incidences. The FSS pattern was implemented using a screen printing technique to fabricate a prototype absorber and subjected to the free space measurements in an anechoic chamber. The prototype behaviour was found to be commensurate with the simulated performance, thereby achieving a figure of merit of RC similar to-25 dB@10 GHz, accessible bandwidth 4 GHz (in X band) by using the thickness of 0.057 lambda 0. Details are presented in this study. Integrated frequency selective meta surface for efficient microwave absorption.

In this work, a Graphene based terahertz absorber (GTA) with broadband and tunable absorption characteristics is investigated. The advantages and uniqueness of the unit cell are manifested in terms of a higher broadband absorber with an effective bandwidth of 4.93 THz corresponding to 4.07 to 9 THz, providing over 90 % absorption. Moreover, this absorber with substrate thickness of 9.1 mu m also displays the perfect absorber characteristics with highest bandwidth of 2.22 THz for 99 % absorption with compact size which has not been reported earlier, as far as we know. The design of our unit cell is based on coupling multiple resonances to achieve higher bandwidth while maintaining polarization insensitivity and stability against incident angles. It is demonstrated after a detailed investigation that the proposed ultra-wideband absorber possesses a polarization-insensitive response due to its fourfold symmetry of unit cell. It is also observed that the overall absorption level remains above 70 % for the TE polarization illumination with incident angles up to 70 degrees, while for the TM polarization the absorption level is above 70 % up to 65 degrees. Thus, the proposed ultrathin GTA structure exhibits improved absorption bandwidth without compromising on the polarization and overall oblique angle insensitivity. Furthermore, the absorption amplitude spectra of the proposed GTA are modulated from 40 % to over 90 % by stimulating the chemical potential of Graphene from 0.2 eV to 1 eV. To get some physical insight, the power loss density characteristics of the proposed absorber are studied at two frequencies in the operating frequency band. The proposed wideband metasurface absorber appears to be quite promising for next generation devices in the field of imaging, stealth and cloaking, energy harvesting and communication technology.

In this study, we investigate the microwave absorbing properties of epoxy based nanocomposites incorporated with polyaniline-manganese zinc ferrite (PAni-MZF) as hybrid active fillers. Carbonaceous materials due to their high conductivity and weight ratio have emerged as a potential class of electromagnetic interference (EMI) shielding materials while ferrimagnetic materials have unique properties like; magneto crystalline anisotropic and magnetic permeability. Consequently, constructed nanocomposites capable of efficient absorption and shielding to electromagnetic radiation are of paramount importance for electronic and communication applications. Synthesized PAni and MZF nano-fillers have been dispersed with 1.9, 2.4 and 2.9 weight percentages for a series of PAni / MZF-epoxy nano-composites. Synthesized PAni has been characterized for phase and surface morphology using X-ray diffraction (XRD) and Field emission electron microscope (FESEM) respectively. On the other hand, prepared nano-composites were characterized for structural, magnetic and electromagnetic (EM) absorbing properties using FESEM, Vibrating sample magnetometer (VSM) and vector network analyzer (VNA). The combination of magneto-dielectric characteristics has shown the synergetic effect, leading to improved EM absorbing properties for the X Band frequency domains. Constructed nanocomposite’s properties have been demonstrating remarkable reflection loss. Consequently, designed absorbers hold significant application in the EMI shielding, aerospace industries and suppressing of radar signatures.

The requirement in resolving electromagnetic (EM) problems in stealth warhead technologies are excellent absorption ability, lightweight, and thin dimensions. In this direction, this study provides a straightforward hydrothermal one-pot method to synthesize superparamagnetic Mn-based ferrite co-doped with Co and Cu (MCCF), and the article presents its microwave absorption properties. Using cutting-edge techniques, the MCCF nanocomposite phase structure, morphological, superparamagnetic, and microwave absorption properties were measured and analyzed. MCCF-822 ferrite shows superparamagnetic properties simultaneously with a high M-s value 71.4 emu/g. Vector network analysis of MCCF-822 with 70 wt% loading demonstrates an effective absorption bandwidth (EAB) of 5.2 GHz with a maximum reflection loss (RLmax) of -19.2 dB at 2 mm thickness, and it spans almost 92.77 % frequency region (3.3-18 GHz range with RL < -10 dB) by varying thickness 1.7 mm-6 mm. At 60 wt% loading, it covers the whole X & K-u band with a thickness range from 2 to 9 mm with a good EAB of 4.3 GHz at 2.5 mm thickness with RLmax of -16 dB. The dual absorption bands are also present in MCCF-613, which increases the EAB with RLmax -52.99 dB at 9 mm, fulfilling the superparamagnetic properties. Thus, MCCF-822 is proposed as a cost-effective superior ferrite nanocomposite for microwave absorption applications.

This study presents a design for a radar-absorbing structure that has a combo of circular and swastika-shaped surface designs capable of absorbing X and Ku bands. The structure has been created using a specifically developed resistive material with an outer layer resistance of 210 Omega/square, while the substrate material used is Roger RO3003 laminate. A metallic plate (copper) has been used for the bottom layer. The proposed structure has been designed and simulated for its performance. The result showed a minimum of 10 dB reflection loss (90% absorption) over 8 - 20 GHz, covering X, Ku, and a portion of the K band. The structure has a fractionalbandwidth (FBW) of 85.71%, with a 0.102 lambda R (lambda R is the corresponding wavelength to maximum reflection) intermediate layer thickness. The structure has angular stability of up to 50 degrees and polarization insensitivity of up to 90 degrees. The study also examines the performance of power loss and surface current distribution in the structure. It is slim in its architecture and can be fabricated using a customized surface resistive ink, making it an ideal candidate for the aero-stealth application.

The work report on architecture of integrated frequency selective meta-surface (IFSMS) absorbers for aerospace stealth applications. Fabricated IFSMS comprised of a pattern metasurface integrated with dielectric interlayer and conducting ground. Initially, a supercell (2 × 2-unit cell: 24 × 24 mm2) was designed with a fourfold topological symmetry. Supercell produces impedances (R), inductances (L), and capacitances (C) in tune with design on its interaction with microwave. RC performance was tested at variable incident transverse electric/magnetic (TE/TM) modes over, Θ, 0°-60° and at the normal incidence (TE), against a planer, clockwise rotation over, Φ, 0°-90°. The mode stability and rotational invariance was analyzed for displacement current- and power-density distributions. The impedance behavior and phase reversal S11 reflection coefficient studies revealed the emergence of mid-band Fabry-Perot mode distinguishing LC behavior of the circuit. The meta-pattern was manufactured by mask lithography using a customized resistive micro-carbon ink and imprinted onto dielectric/ground tile (dimension: 30 × 30 cm2). Structure-property relationship of the ink material was investigated using SEM, XRD, FTIR, UV-visible spectroscopy to reveled surface properties of imprinted material. The absorber was subjected to the free space measurements over C (4-8), X (8-12), and Ku (12-18 GHz) bands, including pristine interlayer dielectrics. The simulated and experimental RC data was found to be in excellent agreement. The proposed IFSMS design is a potential candidate for the stealth application.

In this work, the laser induced graphene (LIG) based novel metasurface structure for microwave absorber (MWA) applications is proposed. The measured performance of the proposed absorber is outstanding, as it provides 90% absorption bandwidth ranging from 8 GHz to 11.5 GHz covering 87.5% of X -band. The proposed metasurface structure is designed and simulated using the CST Studio, and various structural parameters are optimized to achieve better absorption performance. It is observed that the sheet resistance of LIG is an important property, and hence a detailed analysis is carried out to investigate its effect on the performance of the MWA. The unit cell of the designed structure is especially chosen to make it polarization and incident angle insensitive, thereby making it more attractive from practical perspective. Finally, the prototype based on the optimized design is fabricated and tested for X-band, and a good agreement is observed between the simulated and the measured response. The proposed LIG based absorber working in X-band, appears to be a viable low cost alternative for applications in the stealth technology and satellite communication etc.

The development of lightweight and ultrathin materials is quite important for electromagnetic interference (EMI) shielding of myriads of electrical devices, especially in the telecommunication and the aerospace industry. In this work, a novel ultrathin Laser Induced Graphene (LIG) film with total thickness of only 0.05 mm is synthesized, fabricated and tested for the EMI shielding application. The proposed LIG film, based on the customized conductive material, is fabricated using a pulsed CO 2 laser system. It is demonstrated that the fabricated LIG sample exhibits more than 10 dB total shielding effectiveness (SE T ) in the entire X band. The ratio of SE T / thickness(mm) for the fabricated LIG film is found to be greater than 200, which is phenomenally high as compared to the state of the art EMI shielding materials. Further, the electrical conductivity of the LIG film is measured and this data is utilized to perform simulation using the numerical EM simulator; the CST Microwave Studio for the SE T performances. A close matching is observed between the measured and the simulated SE data. The proposed synthesis scheme appears to be quite promising for design and development of lightweight EMI shielding materials, which can have wide range of applications in industry.