Electromagnetic Compatibility Applications Research Articles

Graphene/carbon nanotube aerogels with ultralow filling ratio through perfect cross-linking interface for efficient microwave absorption

Utilizing high-efficiency electrostatic assembly and a scalable freeze-drying technique followed by carbonization, we have developed a series of unique, lightweight, hierarchically porous 1D+2D aerogels containing carbon nanotubes (CNTs) and reduced graphene oxide (rGO). By manipulating the interaction between CNTs and graphene oxide perjurer in cellulose nanofiber (CNF), CNTs can uniformly distribute along the graphene cell walls via an exceptional cross-linking interface in the resultant rGO/CNT aerogels. This arrangement enables abundant heterogeneous interfaces, endowing the aerogels with high conductivity and polarization loss capacity. Moreover, the 1D+2D microstructure of CNT/rGO and the hierarchical pore architecture of the aerogels facilitate multiple scattering, further enhancing their loss capacity toward electromagnetic wave absorption (EMW). Coupled with the optimized impedance matching derived from the adjustable dielectric properties, the aerogels exhibit outstanding EMW absorption with a filling ratio of merely 2 wt%. Specifically, a minimum reflection loss (RLmin) of −49.61 dB and an effective absorption bandwidth (EAB) of 4.16 GHz are achieved. With a filling ratio of 3 wt%, the RLmin reaches −77.51 dB, accompanied by an EAB of 3.84 GHz, surpassing the reported carbon or graphene-based aerogel EMW absorbers. In this work, the ultra-low filling ratio resulting from high conductivity confers a practical design for fabricating lightweight carbon-based aerogels suitable for high-efficiency EMW absorption, manifesting multiple applications in electromagnetic compatibility and aerospace contexts.

Advanced ternary carbon-based hybrid nanocomposites for electromagnetic functional behavior in additive manufacturing

This study explores the processing and performance of acrylonitrile butadiene styrene (ABS)-based carbon ternary hybrid nanocomposites, incorporating carbon nanotubes (CNT), graphene nanoplatelets (GNP), and carbon black (CB), for applications in electromagnetic compatibility (EMC). The effect of nanocomposite processing on electromagnetic properties was evaluated by varying the mixing protocol, either through direct extrusion with simultaneous addition of all constituents or by preparing a master batch followed by dilution. The impact of nanofiller morphology and processing techniques on the behavior of nanocomposites was systematically investigated. Filaments of these nanocomposites were Additive Manufactured via Material Extrusion, and the resulting parts were evaluated for EMI shielding effectiveness (SE) in the X-band frequency range. The study reveals that the morphology, influenced by the processing strategy, significantly impacts the EMI SE properties of the printed samples. Particularly, ternary hybrids 3/3/3 wt% (CNT/GNP/CB) nanocomposites demonstrate promising electrical (0.003 S/cm), electromagnetic (29 dB of total attenuation), and mechanical performance (elastic modulus of 3080 MPa), with a clear advantage observed in those processed via direct extrusion. These nanocomposites were validated as feedstock filaments for 3D printing, and the printed sample exceeds the injection molded behavior for the composition 3/3/3 wt% (CNT/GNP/CB), achieving 40 dB of total attenuation at 11.8 GHz. The findings contribute valuable knowledge into tailoring nanocomposite formulations for additive manufacturing applications in EMI shielding, providing a nuanced understanding of the interplay between processing strategies, nanocomposite morphology, and resulting material properties.

Composite Paints with High Content of Metallic Microparticles for Electromagnetic Shielding Purposes

This paper describes the technological process used to manufacture composite paints with a high content of metallic microparticles (Al and Fe) for automotive electromagnetic compatibility applications. The thickness of the deposited paint layer was larger for paints with a greater metal content, regardless of the plastic support used for paint deposition. The roughness of paint layers with a greater content of metal particles was about 30%–35% higher than that of layers with a lower metal particle content, regardless of the metal type. The surface roughness of paint layers containing Al was at least 2.5-times higher than that of paint layers containing Fe, an aspect that could be explained by the better formulation of the paint containing Fe. The dielectric loss and conductivity values crucially depend on the plastic substrate used, meaning that the dipolar polarization of the substrate enhances the effect of conductive paints. Based on the dielectric properties measured at 10 kHz, the optimal recipe for efficient electromagnetic compatibility was found to be 20 wt.% Fe powder, deposited on a sandblasted polycarbonate (PC) substrate. It is expected that formulations of paints with a high percentage of metallic particles will effectively compete with traditional plastic metallization technologies.

All-liquid frequency selective absorber design with flexibility and wide-angle stability

An all-liquid flexible metamaterial crossing the ultrabroadband range of S, C, X, and Ku bands is reported. This work demonstrates for the first time a frequency selective absorber (FSA) using all-flexible materials, which enables a transmission band of 2.4–4 GHz and a 6–20 GHz ultrawideband absorption. Firstly, liquid metal (LM) as a new functional material with self-healing capability and high reflectivity, based on its metasurface can realize the minimum insertion loss of 0.72 dB at 3.2 GHz. Then, utilizing dielectric resonance and diffraction grating effects of the water-based metasurface, the design can achieve greater than 90% absorption in the frequency band of 6–20 GHz, with a relative bandwidth of 107%. Furthermore, by miniaturizing the design, the FSA exhibits high stability in TM mode with oblique incidence up to 60° and TE mode at 45°. Our design can be fabricated using polydimethylsiloxane lithography and encapsulated with water and LM with a thickness of only 8 mm. Finally, the fabricated FSA are tested by bending to different curvatures, and the good performance indicates its promising applications in electromagnetic stealth, compatibility and wearable devices.

Enhancing Interface Connectivity for Multifunctional Magnetic Carbon Aerogels: An In Situ Growth Strategy of Metal-Organic Frameworks on Cellulose Nanofibrils.

Improving interface connectivity of magnetic nanoparticles in carbon aerogels is crucial, yet challenging for assembling lightweight, elastic, high-performance, and multifunctional carbon architectures. Here, an in situ growth strategy to achieve high dispersion of metal-organic frameworks (MOFs)-anchored cellulose nanofibrils to enhance the interface connection quality is proposed. Followed by a facile freeze-casting and carbonization treatment, sustainable biomimetic porous carbon aerogels with highly dispersed and closely connected MOF-derived magnetic nano-capsules are fabricated. Thanks to the tight interface bonding of nano-capsule microstructure, these aerogels showcase remarkable mechanical robustness and flexibility, tunable electrical conductivity and magnetization intensity, and excellent electromagnetic wave absorption performance. Achieving a reflection loss of -70.8dB and a broadened effective absorption bandwidth of 6.0GHz at a filling fraction of merely 2.2wt.%, leading to a specific reflection loss of -1450dBmm-1, surpassing all carbon-based aerogel absorbers so far reported. Meanwhile, the aerogel manifests high magnetic sensing sensibility and excellent thermal insulation. This work provides an extendable in situ growth strategy for synthesizing MOF-modified cellulose nanofibril structures, thereby promoting the development of high-value-added multifunctional magnetic carbon aerogels for applications in electromagnetic compatibility and protection, thermal management, diversified sensing, Internet of Things devices, and aerospace.

Electric near-field scanning for electronic PCB electromagnetic radiation measurement

This paper introduces a design and test of an electric (E) near-field scanning (NFS) system by using innovative 4-layer miniature probe for electromagnetic compatibility (EMC) application. The probe works in the challenging frequency band up to 12 GHz with spatial resolution lower than 2 mm. The NFS is designed to operate by automation based on PC driven by LabVIEW® interface controlling a vector network analyzer (VNA). The PC communicates with the VNA through the local area network to read and save the measured data emitted by the device under test (DUT). The LabVIEW® interface is designed to control the E-NF positioning motion core by means of STM32® microcontroller. A stepper motor is used to move the E-NF probe along the scanning surface plan. Finally, the NFS is validated by visualizing the E-NF intensity maps generated in real time after calibration with a reference device under test represented by microstrip line and a microwave circuit.

Investigation of electromagnetic shielding effectiveness of nano silver coated stainless steels

This paper presents the shielding effectiveness (SE) of various nanosilver-coated stainless steels (201, 304, 316 and 430), using a coaxial transmission line setup with waveguides and a vector network analyzer (VNA) in accordance with ASTM 4935 standards. The conducted experiments revealed excellent SE outcomes, indicating that the silver-coated stainless steel samples exhibited notably superior SE performance compared to their uncoated counterparts. The importance of SE in electromagnetic compatibility (EMC) applications, particularly in minimizing electromagnetic interference (EMI) and safeguarding sensitive electronic devices, is well acknowledged. This study further explored the shielding effectiveness of a novel hybrid material, nano silver (Ag) coated different stainless steels, with a focus on its potential for improved EMI shielding capabilities. Experimental measurements were conducted in the 5G frequency domain.It was found that nanosilver coating increased the SE of stainless steels by between 5 and 12 dB. This enhancement attributed to the incorporation of nanostructured silver particles on the stainless steel surface, which facilitates enhanced reflection of electromagnetic waves, resulting in superior shielding performance. Moreover, this study underlying the mechanisms of SE through various analyses, including X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). In summary, this research has demonstrated that nano silver coating increases the SE value of materials. This result suggests that all other materials can be used to increase the SE value. The results have implications for advancing electromagnetic shielding technologies and promoting the development of robust EMI shielding solutions in various industrial applications where effective shielding is of paramount importance.

Versatile cellulose nanofibril assisted preparation of ultralight, scalable carbon nanotube aerogel-based electromagnetic wave absorbers with ultrahigh reflection loss

The sustainable cellulose nanofibril (CNF) was efficiently utilized to facilitate the preparation of a type of ultralight, high-porosity carbon nanotube (CNT) hybrid aerogel-based electromagnetic wave (EMW) absorbers. CNF not only serves as a green surfactant to avoid the agglomeration of CNT, but also acts as supporting matrix or binder to promote the construction of porous CNT-based aerogels. Furthermore, the CNF precursor contributes to the generation of CNF-derived nanocarbon (CNFC) for a high-efficiency dielectric modulator, leading to the tuneable electromagnetic parameters and good impedance matching. Combined with the loss capacity of CNFC, the EMW absorption performance of CNT-based aerogels is enhanced. Consequently, the hybrid aerogels show EMW absorption performance involving an effective absorption bandwidth of 3.3 GHz and an ultrahigh reflection loss of −76.46 dB at a filling ratio of 5 wt%, outperforming that of other CNT-based EMW absorbers ever reported. The synergistic effects of multiple EMW absorption mechanisms for the hybrid aerogels were analyzed at length, demonstrating the indispensable roles of the CNF or CNFC in constructing high-efficiency CNT-based EMW absorbers. Combined with the green, sustainable, facile, and scalable preparation approach, the carbon aerogel-based EMW absorbers are highly promising for applications in electromagnetic compatibility or protection and aerospace.

Screen Printed Polarization Independent Microwave Absorber for Wideband RCS Reduction

Designing and deploying a broadband microwave absorber that provides wide bandwidth radar cross section (RCS) reduction for planar and curved surfaces is challenging. We present a resistive ink-based multilayered wideband absorber using a low-priced FR4 substrate to cope with the challenge. The reflection coefficient response of the structure lies beneath −10 dB reference over the frequency span of 1.3–18.6 GHz for the normally incident electromagnetic waves. The multilayered structure incorporates the entire microwave radar frequency span with a relative fractional bandwidth of 173.86%. Moreover, to examine the applicability of the structure for a nonplanar geometrical surface, we further design the structure on a very thin FR4 substrate that can be bent easily. We performed an RCS analysis of the redesigned structure under monostatic and bistatic conditions. The structure thereby exhibits novelty in terms of wider stealth and electromagnetic compatibility applications and also a good counterbalance among different design attributes comprising thickness, bandwidth, and periodicity, unlike the earlier reported work. The proposed prototypes are fabricated and experimentally validated for planar and curved surfaces, respectively. The experimental results depict a good concurrence with the simulated results.

Physico-chemical Characterization of Paint Films with Electromagnetic Properties

Electromagnetic compatibility issues and those generated by these radiations are a major concern for electrical and electronic products, mainly in the fields of communications, information technology, transportation, security and medical services. The paper presents the way to obtain nanostructured paint/plastic/nanopowder paint systems with electromagnetic shielding properties, as well as their characterization by FTIR analysis, DSC and dielectric tests. These systems have Electro-magnetic Interference (EMI)/Electromagnetic Compatibility (EMC) and Electrostatic Discharge (ESD) applications in the manufacture of enclosures for various electronic devices and for the automotive industry. At the laboratory level, 4 non-additive experimental models (EM) coded M1-M4 and 16 additive experimental models coded M5-M20 were obtained. Revolutionary to these materials is the fact that inside they are insulating and, on the outside, they behave like a shield. The results obtained from the dielectric tests performed on the 16 additive systems showed that the samples with a maximum percentage (20 %) of metal nanopowders show the highest values of electrical conductivity. Of the two nanopowders used, that of Fe from samples M11, M12, M19 and M20 which induces the composite higher conductivities than Al nanopowders. The ATR/FTIR spectra of the two paint samples analyzed showed that they were almost identical, suggesting that the paints tested had the same basic chemical structure. DSC analysis showed that pigment paint (V2) has low thermal oxidation stability and lower decomposition temperatures than pigment-free paint (V1), therefore, V2 is less stable under usage conditions, under the influence of normal environmental factors (temperature, humidity, natural or artificial light, etc.) compared to V1.

Universal Statistical Tradeoffs for Shielding Effectiveness Evaluation of Electrically Large Enclosures in Reverberation Chambers

Shielding effectiveness (SE) evaluation of electrically large enclosures within reverberation chambers (RCs) is standardized procedure for electromagnetic compatibility (EMC) applications. In this work the potential relationship between SE and electromagnetic resonances have been investigated with respect to the ambiguity in definition of SE for the international standards, e.g., IEC 61000-4-21 or IEEE Std 299.1. From a statistical point of view, we derive the expansions of SE defined by the ratio of the maxima and the averages respectively. To evaluate SE more prudently as well as to obtain a much smaller uncertainty, we can make the tradeoffs for SE, which should be defined as the ratio of the averages for the overmoded frequency, and the ratio of the maxima for the undermoded using a common criterion aimed to discriminate the electromagnetic field behavior between the undermoded and the overmoded, and also verify the corresponding results by numerical simulations and measurement performed in RC.

Single-Sensor EMI Source Localization Using Time Reversal: An Experimental Validation

The localization of electromagnetic interference (EMI) sources is of high importance in electromagnetic compatibility applications. Recently, a novel localization technique based on the time-reversal cavity (TRC) concept was proposed using only one sensor, and its application to localize EMI sources was validated numerically. In this paper, we present a validation of the proposed time-reversal process in which the forward step of the time-reversal process is performed experimentally and the backward step is carried out via numerical simulations, a realistic scenario which is applicable to practical source localization problems. To the best of the authors’ knowledge, this is the first implementation of a three-dimensional electromagnetic time-reversal process in which the forward signal is provided experimentally while the backward propagation step is carried out numerically. The considered experimental setup is formed by a partially open cavity and two monopole antennas to emulate the EMI source and the sensor (receiving antenna), respectively. Assuming that the location of the source is the feed point of the monopole antenna, the resulting three-dimensional location error in the experimental validation was only 1.49 cm, which is about one-third the length of the monopole antenna, corresponding to about λmin/2 (diffraction limit).

Convergence Analysis of the Currents and Fields Involved in the Method of Auxiliary Sources Applied to Scattering by PEC Cylinders

The method of auxiliary sources (MAS) is an established technique for the numerical solution of electromagnetic shielding and scattering problems exhibiting an increasing interest for the simulation of various electromagnetic compatibility (EMC) applications. In previous works, it was shown that for the problem of transverse magnetic illumination of a perfect electric conducting cylinder by an electric current filament, it is possible for large numbers N of auxiliary sources that the MAS currents diverge and oscillate, while the generated MAS field converges to the exact solution. In this article, we further analyze the convergence issues and oscillations encountered in the MAS by considering the transverse electric case due to excitation by a magnetic current filament. We demonstrate analytically that the convergence/divergence phenomena of the currents and fields also occur in this problem and then study the nature of this divergence in detail. In particular, we prove a large-N asymptotic formula for the divergent MAS currents, which captures accurately the important characteristics of the associated inherent oscillations. Numerical results for noncircular shapes are also presented. The discussed effects must be carefully taken into account in EMC simulations pertaining to cylindrical conductors.

A Simple Power Source Modeling and Experimental Investigation of a Spacecraft for EMC Applications

Simplified modeling of a spacecraft power system is proposed to predict the conducted electromagnetic compatibility (EMC) environment. A key element of the spacecraft conducted environment is the electrical power subsystem, which corresponds to the power source. Since the impedance of the power source has a significant effect on conducted interference, the assessment of power bus impedance is essential to control and manage spacecraft EMC. In the proposed model, all components inside the power system were modeled as simple equivalent circuits with lumped elements. The advantage is that it simplifies the complex power system so that its impedance can be quickly obtained at the early stage of spacecraft system design and development. The model is validated by comparing the calculated results with experimental data. The comparison results between simulation and experiment showed good agreements.

A Frequency Selective Rasorber by Engineering Transverse Standing Waves of Surface Current

The low RCS level out of operating band is urgent for radome while keeping its communication window. To solve this problem, we propose a frequency selective rasorber (FSR) that exhibits a pass-band between two absorption bands in this paper. The surface currents on a finite metallic wire media is analyzed firstly to elaborate transverse standing waves mechanism. High-efficiency and broadband absorption can be achieved by loading lumped resistors at high amplitude of standing waves. By delicately engineering the transverse standing waves versus frequency, a transparent window can be opened within an absorption wideband and it can be modulated by adjusting structural parameters. The transparent window centered around 10.0 GHz in the absorption band from 5.8 GHz to 18.0 GHz. Prototypes were fabricated and measured. Both the simulated and measured results show that for both x- and y-polarized waves, insertion loss of the transparent window at 9.85 GHz is below 0.2 dB while the absorption is above 90% in the two sidebands of 5.8-7.8 GHz and 11.8-18.0 GHz. Furthermore, the rasorber can also work well under oblique incidence angles up to 45 degrees. This work may find wide applications in electromagnetic compatibility, stealthy radomes, etc.

Wideband RCS reduction of thin metallic edges mediated by spoof surface plasmon polaritons

The back-scattering from front edge diffraction contributes significantly to mono-static radar cross section under TE-polarization when the specular reflection of an object is eliminated by elaborate shaping. With the aim to suppress the back-scattering of thin metallic edge, we propose to achieve wideband radar cross section (RCS) reduction by integrating an absorbing structure (AS) in front of the edge. The unit cell of AS is composed of a longitudinal array of metallic strips with linearly decreasing lengths. Under TE-polarized illumination, spoof surface plasmon polariton (SSPP) can be excited with high efficiency. Due to the deep-subwavelength property of SSPP, electromagnetic waves are highly confined around the AS, leading to strong local field enhancement and hence to wideband absorption. In this way, back-scattering of the edge is suppressed and the mono-static RCS can be reduced significantly over wide band. To verify this method, we designed, fabricated and measured a prototype. The results of both simulation and measurement indicate that our proposal can significantly suppress edge scattering, whose RCS reduction more than 10 dB achieves at range of 8.8–17.8 GHz under TE polarization. This work provides a new alternative of suppressing edge diffraction and may find applications in electromagnetic compatibility, radar stealth, etc.

Assessing the Efficacy of a GPU-Based MW-FDTD Method for Calculating Lightning Electromagnetic Fields Over Large-Scale Terrains

This article presents for the first time an OpenACC (Open accelerators)-aided Graphics Processing Unit (GPU)-based approach adopting a 3D moving window finite difference time domain (MW-FDTD) method for calculating lightning electromagnetic fields over large-scale terrains. The efficacy and accuracy of the proposed method are evaluated by comparing its results with the results obtained from a conventional FDTD method. The results show that the GPU-based MW-FDTD method is capable of providing highly accurate results 42 times faster than the conventional CPU-based FDTD method. Moreover, the proposed method required only (2M/N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> ) × 100 = 40%. of the memory needed for carrying out the calculation compared to a conventional FDTD method, where M and N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> are the size of the entire domain in the conventional FDTD method and size of the divided blocks in the MW-FDTD method domain, respectively. The results show the applicability of the MW-FDTD-GPU method for dealing with lightning electromagnetic problems as well as large-scale electromagnetic compatibility (EMC) applications where the efficiency and minimization of the computational time and memory requirements are of great importance.

FDTD modeling and experiments of microfabricated coplanar waveguide probes for electromagnetic compatibility applications

ABSTRACT We present the design, fabrication and experiment of a miniature nonresonant probe based on a coplanar waveguide dedicated to near-field imaging for electromagnetic compatibility applications. Our modeling approach, based on the Finite Difference Time Domain and Finite Element Method, proves that this probe is sensitive to the longitudinal component of the electric field. In addition to its compatibility with integrated circuits, this probe is suitable for wide frequency band applications since it is produced from a micro-metric coplanar line which has no cut-off frequency. We achieved prototypes using the clean room techniques. Using this probe on a precision X-Y scanning table, two-dimensional images of micro-strip line and electric dipole antenna have been successfully constructed. Simulations and measurements results on a microstrip line have shown that the probe is mainly sensitive to the normal electric field. The estimated sensitivity is 30 μV/(V/m).

Aqueous cellulose solution assisted direct exfoliation of graphite to high concentration graphene dispersion

In the present work, high concentration graphene dispersion was prepared by sonication-assisted liquid-phase exfoliation (LPE) using inexpensive and environment-friendly aqueous cellulose solution. The highly efficient exfoliation of starting graphite into graphene was achieved by the noncovalent affinity of cellulose towards graphene. The obtained aqueous graphene sheets exhibited remarkably high concentration of 8.54 mg mL−1 with fewer defects (ID/IG ~ 0.53) and multi-layers structures, which promised a potential ideal candidate for applications in antistatic, corrosion protection, and electromagnetic compatibility.

Suppressing Edge Back-Scattering of Electromagnetic Waves Using Coding Metasurface Purfle

Edge scattering is one of the main scattering sources for metal objects, especially for those with thin front edges. In this paper, we propose to suppress the edge back-scattering of electromagnetic (EM) waves using coding metasurface purfle, which based on the principle of scattering cancellation, rather than absorption. To this end, two split-ring resonators (SRRs) are designed to have a π phase difference, as the 0- and 1-element of the coding metasurface. The coding metasurface is fixed on the front edge of a thin metal plate, and the back-scattering of front edge is significant for EM waves polarized along the edge direction. Due to the anti-phase scattering of the two coding elements, the back-scattering of the edge is suppressed by right of the scattering cancellation along the normal of the edge. Both the simulation and experiment results verify the reduced back-scattering of the flat edge. A maximal reduction of 24dB is attained within the central frequency of about 11 GHz. This work provides a new way of suppressing edge scattering and may find applications in EM compatibility, radar stealth technologies, etc.