Practical Electromagnetic Interference Research Articles

Fabrication of highly conductive polyester fabrics using single-wall carbon nanotubes inks for EMI shielding

Abstract We have fabricated single-wall carbon nanotube (SWCNT)-coated electrically conductive polyester fabric using a low-temperature (LT) dip-and-dry method. Polyester fibers are suitable for industrial applications because of their higher heat resistance. We focused on the surface modification of polyester fibers using N,N-dimethyl-formamide solvent and then improved the adhesion of the SWCNT to polyester fibers. The low sheet resistance of 4.3 ± 0.3 Ω sq−1 was achieved while maintaining the intrinsic flexibility and durability of polyester fabrics by using the LT dip-and-dry method. Moreover, we demonstrated the electromagnetic interference (EMI) shielding using the fabricated electrically conductive polyester fabric. The EMI shielding effectiveness (SE) was measured in the frequency ranges of 8–12 GHz using waveguides and a vector network analyzer. The measured SE of the fabricated electrically conductive polyester fabric was about −34 dB and fulfilled the requirement for practical EMI shielding.

A Practical Solution to Reduce Interference from Led Lights

Abstract The study explores the detection of a harmful, wide-band interference signal, whose origin is a traditional desk LED (light-emitting diode) lamp. The interference signal was noticed on the sensitive solar spectrometer observing system, which was operating at a frequency range between 100 and 300 MHz. The interference signal was so strong and wide-band that it destroyed totally the solar observations. The study introduces two practical EMI (Electromagnetic Interference) reducing methods: ferrite cores and shielding (shielding effectiveness, S.E.). Their theoretical background is presented, and, in addition, these methods are tested in practice. The measurements and tests showed that even simple ferrite core was a very effective method to reduce interference effects. It is important that a suitable setup will be found: a single ferrite core cannot solve a whole problem. This interference problem is very demonstrative and it can be used in educational purposes at an undergraduate level at Metropolia University of Applied Sciences, Finland. This study reveals the fact that standard lamps, which are on the market, do not necessarily follow good EMC (Electromagnetic Compatibility) practices.

Maximized internal scattering in heterostack Ti3C2T x MXene/graphene oxide film for effective electromagnetic interference shielding

Two-dimensional (2D) MXenes have attracted significant attention in electromagnetic interference (EMI) shielding applications due to their excellent metallic conductivity, high surface area, 2D geometry, tunable surface chemistry, and solution processability. In this study, we present a straightforward way of introducing multiple nanoscale interfaces into Ti3C2T x MXenes using insulating graphene oxide (GO) intercalants to enhance internal scattering, resulting in improved EMI shielding effectiveness (SE). The amine-functionalized MXene with positive surface charge and negatively charged GO flakes are electrostatically self-assembled to form a 2D/2D heterostack of MXene/GO nanosheets. The resultant 2D/2D alternating heterostack of MXene/GO bearing multiple internal interfaces with significant impedance mismatch enhances the internal scattering of incident electromagnetic (EM) waves. Interestingly, despite their inferior electrical conductivity, the MXene/GO heterostack films exhibit higher EMI SE values than the randomly mixed hybrid films, and even outperform pristine MXene films. These MXene/GO heterostack films with enhanced absorption of EM waves via the strong internal scattering effect suggest a valuable pathway toward practical EMI shielding with thin and lightweight features.

Ultra-stable graphene aerogels for electromagnetic interference shielding

Graphene aerogels (GAs) are prevailing to solve electromagnetic interference (EMI) issues in next-generation electronic devices. However, the practical EMI shielding application of lightweight GAs is still a great challenge because of their structural instability when confronted with complex conditions. Here, we report a class of ultra-stable GAs with excellent and reliable EMI shielding performances. The GA (ρ = 3.7 mg cm−3) with face-to-face stacked structure exhibits a high shielding effectiveness (SE) of 64.1 dB at the thickness of 1 mm. The specific EMI SE reaches 173,243 dB cm2 g−1, far beyond the previous carbon-based materials. Meanwhile, the structural stability endows the GAs with outstanding resistance to external stimuli, such as mechanical deformation, extreme temperature, flame and underwater environments. The intrinsic conflict of low density and oversized volume is solved by vacuum bagging without structure and performance loss. Our GAs have paved the way for the practical EMI shielding materials and greatly broadened the applied scenes, such as aerospace, warcraft and ocean fields.

Flexible MXene/Graphene oxide films with long-lasting electromagnetic interference shielding performance

MXenes are highly promising as electromagnetic interference (EMI) shielding materials owing to their high mechanical strength, light weight, high electrical conductivity, and processability. However, MXenes readily degrade in humid environments, which has limited further studies on these materials and their commercial application. Herein, we present a feasible strategy for protecting Ti3C2Tx MXene films by coating them with graphene oxide (GO) sheets with sequential filtration method, i.e., filtrating GO into a film firstly, then the MXene is filtered into a film on the top of GO, and finally the filtration is covered with another GO film. GO sheets not only protect Ti3C2Tx MXene from oxidation but also form a heterogeneous interface with it to increase losses and optimize impedance matching between the EMI shield and air. The GO dosage was explored to optimize the process to improve the EMI shielding performance of the GO-coated Ti3C2Tx MXene film. Freestanding films composed of GO/Ti3C2Tx MXene/GO (GMG) layers exhibit relatively stable EMI shielding performance over 70 days. Furthermore, as the GO dosage influences the stability of the GMG film, it was optimized to achieve sufficient coating of the Ti3C2Tx MXene layer with a short processing time to prevent the degradation of the already deposited Ti3C2Tx MXene and GO layers. This strategy based on structural design can lead to the development of low-cost and practical MXene-based EMI shielding materials with long-lasting EMI shielding performance.

Metallized Skeleton of Polymer Foam Based on Metal-Organic Decomposition for High-Performance EMI Shielding.

Highly conductive polymer foam with light weight, flexibility, and high-performance electromagnetic interference (EMI) shielding is highly desired in the fields of aerospace, communication, and high-power electronic equipment, especially in the board-level packaging. However, traditional technology for preparing conductive polymer foam such as electroless plating and electroplating involves serious pollution, a complex fabrication process, and high cost. It is urgent to develop a facile method for the fabrication of highly conductive polymer foam. Herein, we demonstrated a lightweight and flexible silver-wrapped melamine foam (Ag@ME) via in situ sintering of metal-organic decomposition (MOD) at a low temperature (200 °C) on the ME skeleton modified with poly(ethylene imine). The Ag@ME with a continuous 3D conductive network exhibits good compressibility, an excellent conductivity of 158.4 S/m, and a remarkable EMI shielding effectiveness of 63 dB in the broad frequency of 8.2-40 GHz covering X-, Ku-, K-, and Ka-bands, while the volume content is only 2.03 vol %. The attenuation mechanism of Ag@ME for EM waves is systematically investigated by both EM simulation and experimental analysis. Moreover, the practical EMI shielding application of Ag@ME in board-level packaging is demonstrated and it shows outstanding near-field shielding performance. This novel strategy for fabrication of highly conductive polymer foam with low cost and non-pollution could potentially promote the practical applications of Ag@ME in the field of EMI shielding.

Free-standing laser-induced graphene films for high-performance electromagnetic interference shielding

Although laser-induced graphene (LIG) has great advantages in the cost and manufacturing process, it has been seldom reported in the field of electromagnetic interference (EMI) shielding due to its unobtrusive conductivity and the limitation of inherent substrates. In this work, polybenzoxazine is chosen as precursor to fabricate the LIG via a one-step defocused lasing process. As a result of favorable porous structures and high conductivity, the as-produced LIG exhibits the EMI shielding effectiveness up to 24.8 dB in X-band at the thickness of 68 μm. And the EMI shielding effectiveness of LIG/Fe3O4 composite is increased to 32.7 dB at a smaller thickness of 53 μm which is obtained by a solvent-free approach. When considering the thickness and lightweight properties, the absolute shielding effectiveness is also surpassing most of the other carbon-based shielding materials. More importantly, taking advantage of the difference in the thermal expansion coefficient of carbon material and polymeric substrate, we develop a rapid quench-peeling (RQP) strategy for the separation of LIG from polymeric substrate to obtain the free-standing LIG film. Moreover, the structures and properties of LIG are well preserved. The free-standing LIG films after peeling have wider adaptability in practical EMI shielding applications, and also opened up possibilities for use in other fields, such as Joule heating device.

Dual-functional carbonized loofah@GNSs-CNTs reinforced by cyanate ester composite with highly efficient electromagnetic interference shielding and thermal management

Using natural non-polluting raw materials to develop absorption-based electromagnetic interference shielding composites is significantly desirable. Herein, a novel kind of carbonized loofah@graphene nanosheets (GNSs)-carbon nanotubes (CNTs)/epoxy resin modified cyanate ester (CL@GC/CE) composites were successfully prepared through high-temperature carbonization and variable temperature curing process, which show the absorption-based electromagnetic interference (EMI) shielding performance. The as-prepared composites present a favorable electrical conductivity of 32.66 S/cm, exceptional EMI shielding efficiency of 35.57 dB in conjunction with a high absorption coefficient of 0.58. The main reasons for the excellent absorption capacity and EMI shielding performance of the CL@GC/CE composites are the good impedance matching performance of carbonized loofah sponge with a 3D conductive framework, and the multiple reflection scattering and interface polarization effect between the conductive framework and GNSs-CNTs. In view of the remarkable comprehensive properties, the low-cost biomass-derived carbon composites are highly promising materials for practical EMI shielding applications in the fields of telecommunication and aerospace.

Highly conductive graphene film with high-temperature stability for electromagnetic interference shielding

Lightweight, flexible and highly conductive electromagnetic interference (EMI) shielding materials are urgently needed to protect the electronic and telecommunication devices from interference failure. Carbon-based films have attracted much interest to provide EMI shielding with minimal thickness in recent years, particularly exemplified by macroscopic graphene film. However, the inferior electrical conductivity to metal or the un-stability of doped graphene film cannot meet the ever-growing demands for harsh environment applications. Here, we prepare highly conductive copper chloride intercalated graphene film (GF-CuCl2) with high-temperature stability up to 400 °C. The intercalation of CuCl2 significantly improves the hole density, and the achieved electrical conductivity (1.09 × 107 S m−1) is nearly 10 times that of pure graphene film. The ultra-low temperature coefficient of resistance (4.31 × 10−4 K−1) makes GF-CuCl2 electrically stable over a broad temperature range. A 35-μm-thick GF-CuCl2 exhibits an average EMI shielding effectiveness of ∼110 dB from 2 to 18 GHz and ∼126 dB from 8.2 to 12.4 GHz, which is the highest among materials of comparable thickness. Moreover, the EMI shielding capability of GF-CuCl2 shows long-term durability under extreme conditions. All these characteristics demonstrate the GF-CuCl2 is suitable for the practical EMI shielding applications.

Predicting Electromagnetic Interference to a Terminated Wire Using Characteristic Mode Analysis

Electromagnetic coupling to realistic wire configurations exhibit large variations with respect to the frequency, incident angle, and polarization of the interfering signal. In this work, Characteristic Mode Analysis (CMA) is used to calculate the fundamental modes of a terminated wire above an infinite ground plane. Using the properties of the modes, the coupled currents to the wire’s loads are predicted for different incident excitations. Using this simple but practical wire configuration, we show the versatility of CMA in practical electromagnetic interference and coupling applications.

A simple strategy for flexible electromagnetic interference shielding: Hybrid rGO@CB-Reinforced polydimethylsiloxane

In this work, we investigate the electromagnetic interference (EMI) shielding properties of blends of easily available carbon black (CB) with high-surface-area reduced graphene oxide in a polydimethylsiloxane (PDMS) matrix. The chemical composition and morphology of the rGO@CB/PDMS composite are characterized using different techniques such as X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, atomic force microscopy, and field effect scanning electron microscopy. The hybrid filler could effectively improve the electrical conductivity and dielectric loss, and hence the shielding efficiency, and retain its performance even after repeated bending for 100 times. The microwave absorption mechanism of the samples is discussed in detail in terms of their complex permittivity and microstructure. A three-dimensional layered framework is formed within the composite, which in turn leads to multiple reflections of the microwaves at the layer boundaries, subsequently dissipating them as heat due to the presence of conductive CB particles. Because of this, the hybrid rGO@CB/PDMS composite displays superior absorption-dominated shielding property, with a shielding efficiency (SE) of ∼28 dB. The synergetic effect of the hybrid fillers resulting from multiple reflections suggests new pathways for designing flexible shielding materials for practical EMI applications.

Polypyrrole films prepared on self-assembled silane monolayers and applications

Polypyrrole (PPy) films were successfully prepared on the self-assembled silane monolayers (SAMs) for electromagnetic interference (EMI) shielding. X-ray photoelectron spectroscopy was used to estimate the surface properties of SAMs and hydrolytic silane. The deposition process of PPy films on silane SAMs surface was discussed. The PPy films synthesised on SAMs were characterised by scanning electron microscopy, Fourier transform infrared, thermogravimetric analysis and differential scanning calorimetry. The results showed that the uniformity and density of PPy films were improved effectively by using SAMs modification and adding dopants, which could further increase the conductivity and EMI shielding effectiveness (SE) of PPy films. A maximum conductivity of 51·4 S cm–1 and SE value of 37·03 dB for I2 doped PPy films on SAMs has been achieved. The doped PPy films can be used for the practical EMI shielding application for commercial electronic appliances.

3-D Electromagnetic Modeling of EMI Input Filters

In this paper, a novel 3-D electromagnetic modeling approach which enables electromagnetic compatibility (EMC) analysis of power converter systems in an accurate and computationally efficient way is presented. The 3-D electromagnetic modeling approach, implemented in the EMC simulation tool GeckoEMC, is based on two numerical techniques, the partial element equivalent circuit method and the boundary integral method (PEEC-BIM). The developed PEEC-BIM coupled method enables comprehensive EMC analysis taking into account different effects of the PCB layout, self-parasitics, mutual coupling, shielding, etc., which in turn provides a detailed insight into the electromagnetic behavior of power electronic systems in advance to the implementation of hardware prototypes. The modeling features of the GeckoEMC simulation tool for virtual design of electromagnetic interference (EMI) filters and power converters is demonstrated on the examples of a single-phase two-stage EMI filter and a practical EMI filter for a single-phase PFC input stage. Good agreement between the PEEC-BIM simulation and the small signal transfer function measurement results is achieved over a wide frequency range, from dc up to 30 MHz. The EMC simulation environment enables a step-by-step EMC analysis distinguishing the impact of various electromagnetic effects on the EMI filter performance and allowing an optimal EMI filter design.

Synthesis of ferrofluid based nanoarchitectured polypyrrole composites and its application for electromagnetic shielding

The monodispersion of magnetic nanoparticles in conducting polymer is the prerequisite to make a high quality composite for tunable electromagnetic interference (EMI) shielding. To meet this challenge, we have designed and synthesized ferrofluid based nanoarchitectured polypyrrole composites containing Fe3O4 (8–12 nm) via in situ oxidative polymerization. To tune the microwave signals, polypyrrole composites (PFF) with different monomer/ferrofluid weight ratios have been prepared and characterized in microwave frequency domain. A maximum shielding effectiveness value of SEA(max) = 20.4 dB (∼99% attenuation) due to the absorption of microwave has been observed in the frequency range of 12.4–18 GHz and attenuation level varied with ferrofluid loading. The electrical conductivity of PFF composite is of the order of 10−2 S cm−1 order and having superparamagnetic nature with saturation magnetization (Ms) of 5.5 emu g−1. The lightweight PFF composites with high attenuations can provide full control over the atomic structure and are favorable for the practical EMI shielding application for commercial electronic appliances.

Modeling and Design of EMI Noise Separators for Multiphase Power Electronics Systems

This paper first discusses the electromagnetic interference (EMI) noise in multiphase power electronics systems using symmetrical component theory and EMI theory. The theory for multiphase noise separators is developed. Multiphase noise separators are characterized by S-parameters based on symmetrical component theory, S-parameter theory, and EMI theory. A circuit is proposed for multiphase noise separators and techniques are explored for a high-quality design. A prototype is built, tested, and evaluated using the developed theory. The prototype is finally used in a practical EMI measurement.

Synthesis and characterizations of microwave sintered ferrite powders and their composite films for practical applications

Phase pure single phase ferrite powders of (NixR1−x)0.5Zn0.5Fe2O4 (R=Mn, Co, Cu; x=0, 0.5) were manufactured using microwave sintering at 930°C for 10min in air atmosphere. The powders were characterized for their structure, microstructure, thermal, and magnetic properties. Selected powders were used as fillers to prepare their composite films using polymethyl methacrylate polymers as matrix. The composite films were prepared using the melt blending approach and were tested for their microstructure, thermal, and magnetic hysteresis loop as well as 3D magnetic field space mappings using an electromagnetic compatibility scanner. Among the studied ferrites, cobalt doped ferrites and their composites showed the best electromagnetic interference (EMI) shielding effectiveness value and have potential for practical EMI shielding applications.

Towards cost-efficient EMI shielding materials using carbon nanostructure-basednanocomposites

Using a combination of dispersing low-cost carbon nanofibers and a small quantity ofcarbon nanotubes within the polystyrene matrix, we have demonstrated the formation of anovel nanocomposite with superior microstructure and improved electromagneticinterference (EMI) shielding characteristic. This nanocomposite is very promising for use asan effective and practical EMI shielding material owing to its high shielding effectiveness,light weight, low cost, and easy processability.

Studies on electromagnetic interference shielding characteristics of metal nanoparticle- and carbon nanostructure-filled polymer composites in the Ku-band frequency

The dispersion behaviour and electromagnetic interference (EMI) shielding properties were investigated for metal nanoparticle- and carbon nanostructure-filled polymer composites. It was observed that carbon nanostructure-polymer composites exhibited a much higher shielding performance than Ag nanoparticle-polymer composites at the same filler loading. The results also showed that Ag nanoparticle-polymer composites could exhibit an ideal shielding performance only with a very high Ag loading (> 30 wt%). The experimental data exhibited that the shielding effectiveness of the polymer composite containing 5 wt% carbon nanotubes could reach more than 20 dB in the measured frequency region, indicating such composites can be applied to the practical EMI shielding materials. In addition, some possible approaches to further improve the shielding performance of carbon nanotube-polymer composites were proposed and discussed.

Design of Inductor Winding Capacitance Cancellation for EMI Suppression

In this paper, the parasitics in both differential-mode (DM) and common-mode (CM) inductors are first discussed. The methods for both DM and CM inductor winding capacitance cancellation are then proposed. Prototypes are designed and tested, using a network analyzer. Finally, the prototypes are applied to practical power converters and electromagnetic interference (EMI) is measured. Both small signal measurement and practical EMI measurement prove that the proposed methods can efficiently reduce the effects of winding capacitance and therefore improve the inductor's filtering performance