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The propagation of electromagnetic waves in a closed domain with a reflecting boundary amounts, in the eikonal approximation, to the propagation of rays in a billiard. If the inner medium is uniform, then the symplectic reflection map provides the polygonal rays' paths. The linear response theory is used to analyze the stability of any trajectory. The Lyapunov and reversibility error invariant indicators provide an estimate of the sensitivity to a small initial random deviation and to a small random deviation at any reflection, respectively. A family of chaotic billiards is considered to test the chaos detection effectiveness of the above indicators. [ABSTRACT FROM AUTHOR]

In this article, we will show how to improve the standard procedure in the Annex G of IEC 61000-4-21 on the shielding effectiveness (SE) of materials and gaskets through measurements performed in reverberation chambers. We thoroughly analyze and discuss measurement models (MMs), which are already present in the literature including the standardized model. Moreover, we further derive one of these MMs in a different way and introduce a different application, which is suitable to measure high SE values. We apply such MMs and compare results. By the analysis, discussion, and comparisons of measurement results, we clearly provide a robust improvement to the standard measurement procedure. [ABSTRACT FROM AUTHOR]

We present a novel and flexible method to optimize the phase response of reflective metasurfaces (MSs) toward the desired scattering profile. The scattering power is expressed as a spin-chain Hamiltonian using the radar cross section (RCS) formalism. For MSs reflecting an oblique plane wave, an Ising Hamiltonian is obtained. Thereby, the problem of achieving the scattering profile is recast into finding the ground-state solution of the associated Ising Hamiltonian. To rapidly explore the configuration states, we encode the Ising coefficients with quantum annealing (QA) algorithms, taking advantage of the fact that the adiabatic evolution efficiently performs energy minimization in the Ising model. Finally, the optimization problem is solved on the D-Wave 2048-qubit quantum adiabatic optimizer machine for binary phase as well as quadriphase reflective MSs. Even though the work is focused on the phase modulation of MSs, we believe this approach paves the way to fast optimization of reconfigurable intelligent surfaces (RISs) that are modulated in both amplitude and phase for multi-beam generation in and beyond 5G/6G mobile networks. [ABSTRACT FROM AUTHOR]

The effect of a perfectly conducting planar boundary on the average linear momentum (LM), angular momentum (AM), and their power of a time-harmonic statistically isotropic random field is analyzed. These averages are purely imaginary, and their magnitude decreases in a damped oscillatory manner with distance from the boundary. At discrete quasi-periodic distances and frequencies, the average LM and AM attain their free-space value. Implications for the optimal placement or tuning of power and field sensors are analyzed. Conservation of the flux of the mean LM and AM with respect to the difference of the average electric and magnetic energies and the radiation stresses via the Maxwell stress dyadic is demonstrated. The second-order spatial derivatives of differential radiation stress can be directly linked to the electromagnetic energy imbalance. Analytical results are supported by Monte Carlo simulation results. As an application, performance-based estimates for the working volume of a reverberation chamber are obtained. In the context of multiphysics compatibility, mechanical self-stirred reverberation is proposed as an exploitation of electromagnetic stress. [ABSTRACT FROM AUTHOR]

In this study, the authors present the latest developments on the measurements for the shielding effectiveness (SE) of gaskets and materials in reverberation chambers (RCs). A variant method, where the insertion loss of the fixture is achieved from the SE of the fixture with no sample in the aperture is found; it is appropriate for gaskets and for any flat material having a sufficiently high reflectivity at least on one side. A simple and usable condition under which the simplest method for the SE measurements of gaskets and materials in RCs can be used is also given, as well as particular cases where it can be directly applied are shown. This method, whose applicability is enhanced in this study, can be used for gaskets and any flat sample. Such developments simplify measurement setup and associated procedures. Comparisons of results support the methods for the SE measurements of gaskets and material in RCs shown in this study. [ABSTRACT FROM AUTHOR]

Reflection and transmission phenomena associated with high-frequency linear wave incidence on irregular boundaries between adjacent acoustic or electromagnetic media, or upon the irregular free surface of a semi-infinite elastic solid, are studied in two dimensions. Here, an 'irregular' boundary is one for which small-scale undulations of an arbitrary profile are superimposed upon an underlying, smooth curve (which also has an arbitrary profile), with the length scale of the perturbation being prescribed in terms of a certain inverse power of the large wave-number of the incoming wave field. Whether or not the incident field has planar or cylindrical wave-fronts, the associated phase in both cases is linear in the wave-number, but the presence of the boundary irregularity implies the necessity of extra terms, involving fractional powers of the wave-number in the phase of the reflected and transmitted fields. It turns out that there is a unique perturbation scaling for which precisely one extra term in the phase is needed and hence for which a description in terms of a Friedlander–Keller ray expansion in the form as originally presented is appropriate, and these define a 'distinguished' class of perturbed boundaries and are the subject of the current paper. [ABSTRACT FROM AUTHOR]

This paper reviews recent progress in the measurement and modelling of stochastic electromagnetic fields, focusing on propagation approaches based on Wigner functions and the method of moments technique. The respective propagation methods are exemplified by application to measurements of electromagnetic emissions from a stirred, cavity-backed aperture. We discuss early elements of statistical electromagnetics in Heaviside's papers, driven mainly by an analogy of electromagnetic wave propagation with heat transfer. These ideas include concepts of momentum and directionality in the realm of propagation through confined media with irregular boundaries. We then review and extend concepts using Wigner functions to propagate the statistical properties of electromagnetic fields. We discuss in particular how to include polarization in this formalism leading to a Wigner tensor formulation and a relation to an averaged Poynting vector. [ABSTRACT FROM AUTHOR]

Electromagnetic radiation from complex printed circuit boards can occur over a broad frequency bandwidth, ranging from hundreds of megahertz to tens of gigahertz. This is becoming a critical issue for assessment of EMC and interoperability as electronic components become more and more integrated. We use emissions from an enclosure with a single-slot aperture and equipped with operating electronics to exemplify and model such sources. Spatial correlation functions obtained from two-probe measurements are used both to characterize the source and to propagate the emissions. We examine emissions in the submicrowave frequency range, where evanescent decay dominates the measured correlation function at the distances measured. We find that an approximate, diffusion-like propagator describes the measured emissions well. A phase-space approach based on Wigner functions is exploited to develop this approximation and to provide enhanced understanding of the emissions. [ABSTRACT FROM AUTHOR]

Modeling the electromagnetic radiation from modern digital systems—acting effectively as extended stochastic sources as part of a complex architecture—is a challenging task. We follow an approach here based on measuring and propagating field-field autocorrelation functions (ACFs) after suitable averaging. From the modeling side, we use the Wigner transform of the ACFs to describe random wave fields in terms of position and direction of propagation variables. An approximate propagator for the components of the radiated magnetic field is constructed for these ACFs based on a linear flow map. Field-field ACFs at the aperture level are obtained from scanning measurements of complex sources. Distance and spatial resolution of the scanning plane is less than a wavelength from the source plane to capture the imprint of evanescent waves in the near-field ACFs. Near-field scanning and efficient near-to-far-field propagation is carried out and compared with measurements. Results of this study will be useful to assist far-field predictions, source reconstruction, and emission source microscopy. [ABSTRACT FROM PUBLISHER]

We calculate the eigenvalues of an integral operator associated with Prolate Spheroidal Wave Functions (or Slepian functions) by interpreting them as tunnelling probabilities in an analogous quantum problem. Doing so allows us to extend a well-known approximation due to Slepian so that it applies outside an important transition region where these eigenvalues pass from being near unity to being near zero. Study of the eigenvalues has traditionally been associated with problems arising in signal analysis and optics but have more recently found relevance in quantifying the channel strengths available to Multiple-In Multiple-Out (MIMO) radio communication. The approach presented promises easier generalisation to the broader range of geometries possible in the latter context. • Eigenvalues of integral equation are interpreted as tunnelling rates. • Resulting approximation uniformly extends a classical result due to Slepian. • Other classical approximations from Fuchs, Widom achieved as limits. • Approach used allows future extension to more general geometries. • Eigenvalue distribution gives degree-of-freedom estimation for holographic surfaces. [ABSTRACT FROM AUTHOR]

This paper reviews some significant achievements in the research activity and academic career of Paolo Corona, with particular focus on electromagnetic reverberation theory and measurements. An annotated selection is presented for some of his celebrated publications as well as some lesser well-known unpublished works.Some of his recorded views on issues and directions for future research on reverberation chambers are also included. [ABSTRACT FROM AUTHOR]

In this paper, a statistical model for the coupling of electromagnetic radiation into enclosures through apertures is presented. The model gives a unified picture bridging deterministic theories of aperture radiation, and statistical models necessary for capturing the properties of irregular shaped enclosures. A Monte Carlo technique based on random matrix theory is used to predict and study the power transmitted through the aperture into the enclosure. Universal behavior of the net power entering the aperture is found. Results are of interest for predicting the coupling of external radiation through openings in irregular enclosures and reverberation chambers. [ABSTRACT FROM AUTHOR]

A theoretical probability distribution and associated statistics for the coherence bandwidth of an ideal mode-stirred reverberation chamber are derived. The stochastic model assumes and exploits the ergodicity of a dynamic wave chaotic cavity by expressing the coherence bandwidth in terms of the random effective excitation bandwidth and by replacing spatial averaging of transmitter–receiver locations with stir (ensemble) averaging. The theoretical model is validated through comparison with the empirical cumulative distribution function (cdf) extracted from measured S-parameter data from a real chamber, and through simulation using analytical calculations for a fictitious wall-stirred chamber. The results are particularly relevant to the improvement of transmission quality and uncertainty quantification of wireless multipath propagation. [ABSTRACT FROM PUBLISHER]

We derive a probability distribution, confidence intervals and statistics of the quality ( Q) factor of an arbitrarily shaped mode-stirred reverberation chamber, based on ensemble distributions of an idealized random cavity field with assumed perfect stir efficiency. It is shown that Q exhibits a Fisher–Snedecor F-distribution whose degrees of freedom are governed by the number of simultaneously excited cavity modes per stir state. The most probable value of Q is shown to be between a fraction 2/9 and 1 of its mean value, and between a fraction 4/9 and 1 of its asymptotic mean (composite Q) value. The arithmetic mean value is found to exceed the values of most other theoretical metrics for centrality of Q. For a rectangular cavity, we retrieve the known asymptotic expression for Q in the limit of a highly overmoded regime. [ABSTRACT FROM AUTHOR]

A sensor was developed to quantitatively measure perturbations which change the volume of a wave chaotic cavity while leaving its shape intact. The sensors work in the time domain by using either scattering fidelity of the transmitted signals or time-reversal mirrors. The sensors were tested experimentally by inducing volume changing perturbations to a 1m³ mixed chaotic and regular billiard system. Perturbations that caused a volume change that is as small as 54 parts in a million were quantitatively measured. These results were obtained by using electromagnetic waves with a wavelength of about 5 cm; therefore, the sensor is sensitive to extreme sub-wavelength changes of the boundaries of a cavity. The experimental results were compared with finite difference time-domain simulation results, and good agreement was found. Furthermore, the sensor was tested using a frequency-domain approach on a numerical model of the star graph, which is a representative wave chaotic system. These results open up interesting applications such as: monitoring the spatial uniformity of the temperature of a homogeneous cavity during heating up/cooling down procedures, verifying the uniform displacement of a fluid inside a wave chaotic cavity by another fluid, etc. [ABSTRACT FROM AUTHOR]

The flow of electromagnetic wave energy through a chain of coupled cavities is considered. The cavities are assumed to be of sufficiently irregular shape that their eigenmodes are described by random matrix theory. The cavities are coupled by electrically short single mode transmission lines. Approximate expressions for the power coupled into successive cavities are derived, and the predictions are compared with Monte Carlo simulations. The analytic formulas separate into a product of factors. Consequently, the distribution of power in the last cavity of a very long chain approaches lognormal. For lossless cavities, signatures of Anderson localization, similar to those of the conductances of quantum wires, are observed. [ABSTRACT FROM AUTHOR]

This paper presents results of an experimental investigation regarding the statistical distribution of the maximum field and analysis of statistical field inhomogeneities near a cavity wall inside a reverberation chamber. Measurements were performed for both undermoded and overmoded regimes. Departures from ideal isotropic random field behavior at relatively low frequencies were measured by placing a receiving antenna close to one cavity wall. The coexistence of field heterogeneity and anisotropy has been confirmed, together with departures from the ideal statistical distributions of field and energy. Empirical distributions of the maximum value were derived for hybrid (i.e., combined mechanical, frequency, and spatial) mode stirring. The maximum-value distribution is found to be of Fréchet type in undermoded regime and converges to a reverse Weibull distribution in highly overmoded operation, with a transit across the Gumbel distribution when the operation is weakly overmoded. Results exhibit good agreement with previous theoretical and numerical findings. [ABSTRACT FROM AUTHOR]

We calculate and investigate the first four moments of the power received by a short dipole antenna placed inside a reverberation chamber. The analysis is based on the vector angular spectral representation of an idealized electromagnetic random field. It is found that truncating the higher order moments (in particular, the first two invariants) of the replica pairs, considered as an incoherent part, causes a deviation from the ideal negative exponential probability distribution, which is instead found to be a leptokurtic Pearson type-IV distribution with increased skewness. This results in a model of partially coherent random fields received by a real antenna. Using a generalization of Tai's theory, it is demonstrated that the effective aperture of the antenna does not exhibit fluctuations. Implications for the uncertainty and distribution function of the Q-factor of the cavity are analyzed and discussed. [ABSTRACT FROM AUTHOR]

The paper focuses on the reverberation chamber method for the shielding properties evaluation of equipment-level enclosures. The enclosure under test is numerically modeled by an in-house finite-difference time-domain code that is able to predict the field inside the enclosure and the voltage captured by the probe placed inside it. The chamber fields have been modeled by applying the plane-wave superposition. The code is validated by measurements in our reverberation chamber. Subsequently, the effect of probe positioning and length on the induced voltage is analyzed. Finally, the enclosure shielding effectiveness is evaluated by applying two different definitions, and a statistical analysis is carried out, thus allowing an estimation of the measurement uncertainty. [ABSTRACT FROM AUTHOR]

This paper presents a study of coupling between an external field and a metallic enclosure with a long aperture in the frequency range which includes several box resonances. A reverberation chamber (RC) and an anechoic chamber (AC) are considered as a field generation structure. In both cases, a customized FDTD code is used to calculate the current induced by the external field in a loop placed inside the enclosure. In order to simulate the AC facility, a single plane wave is used to represent the test field, whereas for the RC, the field is represented by a proper superposition of random plane waves. Numerical results are experimentally validated. The proposed method is useful to investigate the performance of the enclosure during its early design stage before the realization of a prototype. [ABSTRACT FROM AUTHOR]

Global and local multitrace formulations (MTFs) provide a flexible and efficient method for the modeling of scattering and transmission of time harmonic electromagnetic (EM) waves by composite structures. This contribution extends the domain of applicability of global MTFs to cases where penetrable domains, perfectly conducting domain, and perfectly conducting thin sheets are all part of the design. A novel and easy to implement resonance-free equation to model scattering by perfect conductors is introduced. A Calderón preconditioner designed to limit the number of iterations required for the solution of the discrete system is designed and studied. The accuracy, flexibility, and efficiency of the method are demonstrated on a representative range of examples. [ABSTRACT FROM AUTHOR]

We propose to use Wigner transformation methods as a tool for propagating measured acoustic signals from and towards a source region. We demonstrate the usefulness of the approach both for source reconstruction purposes and as a stable numerical simulation tool with build-in filtering mechanisms. The starting point is a statistical description of the sound field in terms of spatial correlation functions. Using the concept of Wigner transformation – a half Fourier transform method, the correlation function can be associated with a phase space distribution, thus introducing direction or momentum information. A corresponding free-field propagator for Wigner function distributions is derived and the ray-limit of this propagator is discussed. Acoustic data are acquired in an experiment using an 'acoustical camera'; the sound pressure emanating from a vibrating rectangular plate is measured on a 32 × 32 microphone array in coincidence, making it possible to get correlated data with relatively high resolution. Measurements and simulations are compared at different heights above the source plane. It is demonstrated that the Wigner function approach provides a stable tool to propagate correlation data. It is furthermore suitable for nearfield holography where the sound field is propagated back to the plate surface. The directional components encoded in the Wigner function can be used to read off the distance between the source and measurement plane on sub-wavelength scales. [ABSTRACT FROM AUTHOR]

The IEC 61000-4-21 and IEEE 299.1 documents report similar but not equal procedures to measure the shielding effectiveness (SE) of enclosures through the use of reverberation chambers. In this article, it is shown that these two measurement procedures can be merged in a single, enhanced, one. In particular, it is shown that the evaluation of the SE of enclosure in Annex H of IEC 61000-4-21, which exploits only mechanical stirring, can be improved by using the hybrid stirring, which includes also the frequency stirring, thus increasing the number of uncorrelated samples. On the other hand, it is shown that at low frequencies the evaluation of the SE of enclosures based on the definition in IEEE 299.1 can be improved through the use of the maximum values of measured powers rather than the average ones. The single, enhanced, proposed procedure provides more prudent SE values than the two standards at the low frequencies, especially for standard IEEE 299.1. The presented measurement approach is supported by results obtained in three different laboratories. [ABSTRACT FROM AUTHOR]

We describe the contribution of diffractive orbits to semiclassical approximations of Wigner function propagators. These contributions are based on diffractively scattered rays used in the geometrical theory of diffraction (GTD). They provide an extension of well-established approximations of Wigner-function propagators based on rays that propagate by specular reflection and refraction. The wider aim of this approach is to allow for diffractive mechanisms to be accounted for in Eulerian approaches to ray-tracing simulations. Such approaches propagate densities of rays rather than follow rays individually. They promise to be a more efficient means of performing ray-tracing simulations in complex environments with applications in, for example, planning of wireless signal coverage for mobile communication networks. [ABSTRACT FROM AUTHOR]

This work presents over-the-air (OTA) performance, near-field bit-error-ratio (BER), and error vector magnitude (EVM) measurement using software-defined radio (SDR) in the mode-stirred metal enclosure at 5.8 GHz. The metal enclosure is stirred at 5.8 GHz using metallic paddle rotating with uniform speed. Paddle rotation creates a uniform electromagnetic field in the metal enclosure. The electromagnetic field environment in the metal enclosure can be controlled by loading the cavity with absorbing material. Field absorption can be different depending on the amount of absorbing material and location of the absorbers in the metal enclosure. It is shown that signal attenuation increases as we increase the number of absorbers. BER and EVM are measured in this environment and the performance of SDR based digital receiver is analyzed in this environment at RF frequency of 5.8 GHz. [ABSTRACT FROM AUTHOR]

Abstract Diffusion in waveguides with spatially modulated profiles is an important topic in modern electromagnetics and optics. Wave dynamics in the high-frequency asymptotics are governed by classical ray dynamics which can be characterised by looking at the diffusion of particles throughout the channel. We study the transport of particles (rays) in a channel with a sinusoidal profile at different values of the corrugation amplitude. We find that below a certain corrugation level the transport is ballistic, beyond this threshold, a diffusion-like behaviour emerges in the asymptotic limit of large times. In this regime particle transport slows down due to the trapping mechanism in the corrugated regions of the channel. We use the analogy with correlated random walks to discuss the observed transport regimes. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surfaces (RISs) constitute the key enabler for programmable electromagnetic propagation environments and are lately being considered as a candidate physical-layer technology for the demanding connectivity, reliability, localisation, and sustainability requirements of next-generation wireless networks. In this paper, we first present the deployment scenarios for RIS-enabled smart wireless environments that have been recently designed within the ongoing European Union Horizon 2020 RISE-6G project, as well as a network architecture integrating RISs with existing standardised interfaces. We identify various RIS deployment strategies and sketch the core architectural requirements in terms of RIS control and signalling, depending on the RIS hardware architectures and respective capabilities. Furthermore, we introduce and discuss, with the aid of simulations and reflect array measurements, two novel metrics that emerge in the context of RIS-empowered wireless systems: the RIS bandwidth of influence and the RIS area of influence. Their extensive investigation corroborates the need for careful deployment and planning of the RIS technology in future wireless networks. [ABSTRACT FROM AUTHOR]

Abstract: We propose a low observable satellite covered by layered materials. The dielectric properties of the composite materials are analyzed using the coaxial air-line method. Our solution could result in cost-effective applications for satellite stealthness. The particle swarm optimization algorithm is used to design and optimize layered absorbers. The obtained reflection is below −20dB in many frequency subranges, also under an oblique incident condition, within the band 2–18GHz. The optimized layered absorbers are used as a cloak for cube satellites. In particular, we investigated a very simple geometry by using a finite element commercial software in the band from 2 to 18. Finally, the transmission through an aperture on the satellite surface is analyzed. It is highlighted that the optimized layered absorbers attenuate the electric field within the satellite, improving its immunity against electromagnetic interferences. [Copyright &y& Elsevier]

The next generations of wireless networks will work in frequency bands ranging from sub-6 GHz up to 100 GHz. Radio signal propagation differs here in several critical aspects from the behaviour in the microwave frequencies currently used. With wavelengths in the millimetre range (mmWave), both penetration loss and free-space path loss increase, while specular reflection will dominate over diffraction as an important propagation channel. Thus, current channel model protocols used for the generation of mobile networks and based on statistical parameter distributions obtained from measurements become insufficient due to the lack of deterministic information about the surroundings of the base station and the receiver-devices. These challenges call for new modelling tools for channel modelling which work in the short-wavelength/high-frequency limit and incorporate site-specific details—both indoors and outdoors. Typical high-frequency tools used in this context—besides purely statistical approaches—are based on ray-tracing techniques. Ray-tracing can become challenging when multiple reflections dominate. In this context, mesh-based energy flow methods have become popular in recent years. In this study, we compare the two approaches both in terms of accuracy and efficiency and benchmark them against traditional power balance methods. [ABSTRACT FROM AUTHOR]

In this paper, we present an improved model of measurement standard uncertainty of the insertion loss in a reverberation chamber (RC), including frequency stirring. Differently from the previous model, the enhanced one does not require specific conditions on the parameter to be measured. Such an enhancement is applicable for all usable measurement conditions in RCs. Moreover, a majorant is derived, that is obtained under a weak condition on the coefficient of variation of the parameter to be measured. Results from measurements support the validity of both the proposed enhancement and the majorant. [ABSTRACT FROM AUTHOR]

We address the uncertainty of reverberation chamber (RC) measurements in presence of both mechanical and frequency stirring (FS). A base-case model is derived for reverberation fields affected by the measurement uncertainty due to the lack of a perfect statistical uniformity of fields in a RC. It is found that the measurement uncertainty associated with the FS depends on both the total uncorrelated samples and the local insertion loss (IL). The local IL depends on the frequency stirring bandwidth (FSB). The model allows us for obtaining separate measurement uncertainty contributions. Measurements support the achieved uncertainty model. In particular, results show that the dependence on the IL is normally rather weak also when very wide FSBs are used. [ABSTRACT FROM AUTHOR]

We report a new planar antenna design in the shape of a diamond. The performance of the antenna design is initially obtained through simulation, then fabricated, and its performance evaluated through experiment. Experimental characterization of the diamond-shaped monopole antenna shows good agreement with simulation. In comparison with a simple monopole antenna, our diamond-shaped monopole antenna features smaller geometric footprint and displays a higher bandwidth at millimeteric wave frequencies. [ABSTRACT FROM AUTHOR]

In this paper, we propose a multilayer nanostructured composite for broadband shielding applications. Layers disposal, electrical parameters, and thicknesses are optimized through a winning particle optimization algorithm to achieve the minimization of the transmitted waves. The structures are simulated by including the forward/backward scattering matrix formalism in the optimization code. The adopted algorithm is the recently introduced winning particle optimization. Manufacturing of the composites is grounded on the optimization procedure. Thanks to the macroscopic absorption features of such nanostructured layers, very thin and lightweight composites can be produced. Several weight percentages of multiwall carbon nanotubes are considered in composite base material manufacturing, also including 6wt% and 15wt% in order to enhance the electromagnetic shielding performance. Prototypes are tested in the microwave region, showing the reliability of the optimization procedure. [ABSTRACT FROM AUTHOR]

In this paper, we present the design of nanostructured multilayer absorbers, carried out with the aid of a genetic algorithm (GA). Waveguide measurements are performed to recover the dielectric properties of micrographite single-walled carbon nanotube, micrographite walled carbon nanotube, carbon nanofiber, and fullerene-based composite materials. Conductive fillers are uniformly dispersed in an epoxy resin at different weight percentages (1, 3, 5 wt.%). The electromagnetic (EM) analysis is performed embedding the forward/backward propagation matrix formalism in an in-house GA, thus able to carry out optimization upon oblique incidence over a finite angular range. Developed code minimizes both the reflection and the transmission coefficients under the thickness minimization constraint. Comparison between micrographite and nanopowders absorbers is presented and discussed, when a broadband quasi-perfect absorber is achieved among the X-band combining the two filler families, i.e., exhibiting a loss factor greater than 90% in most of the band, for a thickness of about 1 cm. It is demonstrated that the nanofillers with higher aspect ratio mainly contribute to the EM absorption. Findings are of interest in both radar-absorbing material and shielding structures. [ABSTRACT FROM AUTHOR]