Traditional Electromagnetic Interference Research Articles

Electromagnetic Interference Shielding Films: Structure Design and Prospects.

The popularity of portable and wearable flexible electronic devices, coupled with the rapid advancements in military field, requires electromagnetic interference (EMI) shielding materials with lightweight, thin, and flexible characteristics, which are incomparable for traditional EMI shielding materials. The film materials can fulfill the above requirements, making them among the most promising EMI shielding materials for next-generation electronic devices. Meticulously controlling structure of composite film materials while optimizing the electromagnetic parameters of the constructed components can effectively dissipate and transform electromagnetic wave energy. Herein, the review systematically outlines high-performance EMI shielding composite films through structural design strategies, including homogeneous structure, layered structure, and porous structure. The attenuation mechanism of EMI shielding materials and the evaluation (Schelkunoff theory and calculation theory) of EMI shielding performance are introduced in detail. Moreover, the effect of structure attributes and electromagnetic properties of composite films on the EMI shielding performance is analyzed, while summarizing design criteria and elucidating the relevant EMI shielding mechanism. Finally, the future challenges and potential application prospects of EMI shielding composite films are prospected. This review provides crucial guidance for the construction of advanced EMI shielding films tailored for highly customized and personalized electronic devices in the future.

Multifunctional asymmetric foam with Compression-Enhanced EMI shielding effectiveness exhibits Real-Time tunability of Reflection/Absorption ratio and pressure sensing

Traditional electromagnetic interference (EMI) shielding materials usually have constant shielding effectiveness and fixed absorption/reflection ratio, and cannot respond to the real-time changing shielding requirements of smart wearable electronic devices. Herein, smart asymmetric foams (AF) composed of chromium dioxide decorated graphene (CrO2@G)/thermoplastic polyurethane-poly vinyl alcohol (TP) foams and a eutectic gallium-indium liquid metal (LM)/TP layer were developed via an efficient ‘split conductive modular design/assembly’ strategy. The AF with compressive stress-controlled conductivity can capture and attenuate electromagnetic (EM) waves in the form of absorption-dominated or reflection-dominated by adjusting the compressive strain in real time. The optimized AF achieved a low average reflection coefficient (R) of 0.12 and a minimum value of 0.05, holding the lowest record for LM-based EMI shielding materials with comparable SEt. As the compressive strain increases from 0 to 90 %, the AF alter its SEt from 63.8 ± 3 dB to 92.7 ± 2 dB, while reducing the average EM wave absorption efficiency from 88 % to 39 %, allowing it to be adjusted in real time as needed to block EM waves. Furthermore, the AF demonstrated its application as a strain sensor to monitor human motions. This work provides an effective strategy for the design and preparation of multifunctional smart EMI shielding materials.

Structural Design for EMI Shielding: From Underlying Mechanisms to Common Pitfalls.

Modern human civilization deeply relies on the rapid advancement of cutting-edge electronic systems that have revolutionized communication, education, aviation, and entertainment. However, the electromagnetic interference (EMI) generated by digital systems poses a significant threat to the society, potentially leading to a future crisis. While numerous efforts are made to develop nanotechnological shielding systems to mitigate the detrimental effects of EMI, there is limited focus on creating absorption-dominant shielding solutions. Achieving absorption-dominant EMI shields requires careful structural design engineering, starting from the smallest components and considering the most effective electromagnetic wave attenuating factors. This review offers a comprehensive overview of shielding structures, emphasizing the critical elements of absorption-dominant shielding design, shielding mechanisms, limitations of both traditional and nanotechnological EMI shields, and common misconceptions about the foundational principles of EMI shielding science. This systematic review serves as a scientific guide for designing shielding structures that prioritize absorption, highlighting an often-overlooked aspect of shielding science.

Electromagnetic interference shielding of flexible carboxymethyl cellulose/MWCNT@Fe3O4 composite film with ultralow reflection loss

Nowadays, various high-performance electromagnetic interference (EMI) shielding materials have enormous application potential in electronic field. However, traditional EMI shielding materials often have high conductivity, resulting in the serious mismatch between the impedance of the material surface and the free space, which will cause a large amount of reflection of electromagnetic (EM) waves, leading to secondary reflection pollution. In this paper, we report a novel flexible EMI shielding composite film with extremely low reflection loss and efficient EM wave absorption, which was prepared by assisted self-assembly based on simple vacuum filtration using carboxymethyl cellulose as the matrix and MWCNT@Fe3O4 synthesized by chemical coprecipitation as the composite functional filler. By adjusting the Fe3O4 coating degree of MWCNTs in the filler, the composite film achieved the construction of a conductive network with high Fe3O4 content. Benefit by the good adaptability of conductivity and magnetic permeability, the composite film has good impedance matching ability and microwave absorption performance. The reflection loss of the composite film with the thickness of 28 μm in the X-band was only 0.23 dB, accounting for 1.7 % of the total loss. This work provides new insights for the development of EMI materials and effective mitigation secondary EM wave reflection pollution.

Modeling and Design of Full Electromagnetic Integration of a Symmetrical EMI Filtering Circuit With Flexible Multi-Layer Foil Technique

In a high-frequency power electronic converter with wide-bandgap device, electromagnetic interference (EMI) filter is an essential module for mitigating the conducted EMI issues. However, traditional discrete EMI filter will significantly increase total size and weight of the system. In this article, an UU-core based fully integrated symmetrical EMI filter is proposed using flexible multilayer foil technique, all the common-mode (CM) and differential-mode (DM) filtering components are integrated in the same unit for a more compact design. Moreover, a function-decoupling state is realized between the CM and DM elements, which contributes to predigesting the lumped equivalent CM and DM circuits. Then the parameter design procedure can be simplified. Prototypes of the proposed and other typical types of EMI filters are built for a 100 kHz SiC- <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">mosfet</small> voltage source inverter, contrastive experiments have verified the feasibility and validity of the full electromagnetic integration approach.

Additive manufacturing of carbon nanotube/polylactic acid films with efficient electromagnetic interference shielding and electrical heating performance via fused deposition modeling

In the wake of developments in 5th generation mobile communication technology and Internet of Things, traditional electromagnetic interference (EMI) shielding materials are not satisfied with the booming demand of suppressing electromagnetic pollution. In view of the characteristics of low-cost, easy-operating and functional materials applicability of fused deposition modeling (FDM), in this work, a multifunctional carbon nanotube (CNT)/ polylactic acid (PLA) film with electromagnetic shielding and electric heating properties was prepared by using FDM process. The effects of CNT content, FDM-printed film thickness, and FDM process parameters on electromagnetic shielding performance were studied. The results indicate that the additions of CNT increase the EMI shielding performance by forming the conductive paths in the CNT/PLA FDM-printed films. The EMI shielding value of the 4 wt% CNT/PLA film with a thickness of 4 mm is 68 dB at 12.3Ghz. In addition, the improved electrical conductivity provides the good electric heating performance of the CNT/PLA film. At a safe voltage (16 V), the heating temperature of the 4 wt% and 8 wt% CNT/PLA films reached 67.8 °C and 139 °C, respectively. The good repeatability and stability of CNT/PLA films for electric heating were verified. The obtained CNT/PLA FDM-printed films have excellent electromagnetic shielding and low-voltage electric heating properties by adjusting the CNT contents and the FDM process parameters, which expands the application potential of EMI shielding materials and FDM technology.

A Virtual Impedance Enhancement Based Transformer-Less Active EMI Filter for Conducted EMI Suppression in Power Converters

Due to the successive switching actions in a power electronic system, considerable conducted electromagnetic interference (EMI) is generated. This has been a major concern in designing power converters, which requires additional EMI filtering efforts. Passive EMI filters are the most common solutions to EMI reduction but usually consume a large portion of the volume as well as weight in power converters. Active EMI filters (AEFs) or hybrid EMI filters (HEFs) are considered best candidates over traditional passive EMI filters to achieve higher power density in power converters. The utilization of current transformer to sense or to compensate the EMI noise can increase the volume of an AEF. In this article, a transformer-less AEF, sprung from the concept of virtual impedance enhancement, is proposed. The proposed design features feedforward control with current-sensing-voltage-compensating. The operation principle of the proposed AEF is thoroughly introduced, and its performance is evaluated through simulations and experiments. Experimental results with an ac–dc power converter and a dc–ac inverter show that the proposed AEF can be generally applied to reduce conducted EMI on either ac or dc power lines.

Lightweight and hydrophobic Ni/GO/PVA composite aerogels for ultrahigh performance electromagnetic interference shielding

Abstract Lightweight and high-performance electromagnetic interference (EMI) shielding materials are urgently required to solve increasingly serious radiation pollution. However, traditional lightweight EMI shielding materials usually show low EMI shielding performance, poor mechanical properties, and environmental stability, which greatly limit their practical applications. Herein Ni foam/graphene oxide/polyvinyl alcohol (Ni/GO/PVA) composite aerogels were successfully prepared by a freeze-drying method. The Ni/GO/PVA composite aerogels possessed low density (189 mg cm−3) and high compression strength (172.2 kPa) and modulus (5.5 MPa). The Ni/GO/PVA composite aerogel was hydrophobic, and their contact angle can reach 145.2°. The hydrophobic modification improved the environmental stability of the composite aerogels. Moreover, the Ni/GO/PVA composite aerogels exhibited excellent EMI shielding performance. Their maximum EMI shielding effectiveness (SE) can reach 87 dB at the thickness of 2.0 mm. When the thickness is only 1.0 mm, the EMI SE can still reach 60 dB. The electromagnetic energy absorption and attenuation mechanisms of Ni/GO/PVA composite aerogels include multiple reflection and scattering, dielectric loss, and magnetic loss. This work provides a promising approach for the design and preparation of the lightweight EMI shielding materials with superior EMI SE, which may be applied in various fields such as aircrafts, spacecrafts, drones, and robotics.

An Active EMI Filter in Grounding Circuit for DC Side CM EMI Suppression in Motor Drive System

In this article, an active electromagnetic interference (EMI) filter is designed to reduce the dc side common mode (CM) EMI in motor drive system. Different from the traditional passive EMI filter which is added in the main circuit, the designed active EMI filter (AEF) in this article is added in the grounding circuit which is connected between motor frame and the ground and it can be decoupled from the main circuit. By properly setting the components value, the dc side CM EMI can be suppressed while maintaining a low motor frame voltage. The structure of the AEF is simple and the volume of the AEF can be kept small. The operation principle of the AEF is introduced first and the performance of this AEF is evaluated through simulation. Experiment results verified the effect of this AEF that it can suppress the dc side CM EMI and the motor frame voltage can be kept low.

Microstrip Bandstop Filter for Preventing Conduction Electromagnetic Information Leakage of High-Power Transmission Line

The research of transient electromagnetic pulse emission monitoring technology (TEMPEST) protection is essential. Based on microstrip bandstop filter (MSBSF), a method to prevent electromagnetic information leakage of high-power transmission lines is proposed in this paper. The MSBSF with a high insertion loss and carrying large current in the frequency of 2.40–2.49 GHz is designed, fabricated, and experimentally measured. The fabricated MSBSF with the insertion loss of 38 dB at 2.41–2.49 GHz can carry a current greater than 10A and withstand a voltage of 1.7 kV. Compared with the traditional electromagnetic interference (EMI) filter, the MSBSF has the advantages of preventing conducted electromagnetic information leakage in the high-frequency bands, carrying greater current subject to higher voltage, and possessing lighter weight. The MSBSF may be used to prevent the leakage of high-frequency electromagnetic information of high-power transmission lines.

Improved Methodology for Conducted EMI Assessment of Wide Band-Gap Power Electronics

Electromagnetic interference (EMI) compliance is a requirement for most electronic systems and devices, including power electronics. The emergence of power electronic systems designed with wide band-gap (WBG) semiconductors poses new challenges for compliance. This is due to the high edge rates achievable with WBG devices, coupled with unintentional grounding paths, some of which are introduced galvanically with traditional EMI compliance instrumentation. This makes it beneficial to use isolated measurement methods in place of traditional ground-referenced EMI instruments. This approach is viable in comparison to traditional EMI compliance measurements and can significantly reduce circulating ground currents, which can greatly impact emissions measurement accuracy. This paper proposes a streamlined method for emissions evaluation of power electronics employing an oscilloscope, differential voltage probes, and post-processing software implemented in MATLAB. This proposed method eliminates unintended metrology ground coupling, yields faster full quasi-peak scan times, and minimizes risk of instrumentation damage.

Ultralight, Conductive Ti3C2Tx MXene/PEDOT:PSS Hybrid Aerogels for Electromagnetic Interference Shielding Dominated by the Absorption Mechanism.

MXene aerogels with a porous microstructure are a promising electromagnetic interference (EMI) shielding material due to its low density and excellent electrical conductivity, which has attracted widespread attention. Compared with traditional EMI shielding materials that rely on reflection as the primary mechanism, MXene aerogels with absorption as the dominant mechanism have greater potential for development as a novel EMI shielding material because of its ability to reduce environmental contamination from reflected electromagnetic (EM) waves from materials. In this study, a novel Ti3C2Tx MXene/PEDOT:PSS hybrid aerogel was presented by freeze-drying and thermal annealing using few-layered Ti3C2Tx MXene and the conductive polymer poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS). PEDOT:PSS not only improved the gelling ability of Ti3C2Tx but also successfully established a conductive bridge between MXene nanosheets. The experimental results demonstrated that the hybrid aerogel exhibited an obvious porous microstructure, which was beneficial for the multiple scattering of EM waves within the materials. The EMI shielding effectiveness and specific shielding effectiveness reached up to 59 dB and 10,841 dB·cm2·g-1, respectively, while the SER/SET ratio value was only 0.05, indicating superior wave absorption performance. Furthermore, the good impedance matching, due to the electrical conductance loss and polarization loss effect of the composites, plays a critical role in their excellent wave absorption and EMI shielding performance. Therefore, this work provides a practical approach for designing and fabricating lightweight absorption-dominated EMI shielding materials.

Flexible multilayered aramid nanofiber/silver nanowire films with outstanding thermal durability for electromagnetic interference shielding

Multilayered aramid nanofiber/silver nanowire (ANF/AgNW) films using AgNW as internal conductive layers and ANF as outer protective layers were fabricated via a multiple filtration layer-by-layer process and subsequent hot-pressing. The electromagnetic interference (EMI) shielding and mechanical properties of the multilayered ANF/AgNW films were significantly improved through hydrogen bonding between adjacent layers, and EMI shielding properties were accordingly enhanced owing to the internal multiple reflection of electromagnetic waves between AgNW layers. The 7layer structure ANF/AgNW films exhibited excellent mechanical properties with a tensile strength of 79 MPa and fracture strain of 4.6%, high EMI shielding effectiveness of 63.3 dB, attributing mainly to the synergetic effect of intrinsic mechanical strength of ANF and excellent electrical conductivity of the tightly interconnected AgNW network. In addition, the multilayered films which have excellent stability for EMI shielding properties at high temperature (∼400 °C) are better than traditional polymer-based EMI shielding materials.

EMI filter design for single‐phase grid‐connected inverter with noise source impedance consideration

It is well known that noise source impedance plays a significant role in designing conducted electromagnetic interference (EMI) filters. However, the noise source impedance in a switched-mode power supply is not easy to extract. In this study, the noise source impedance in a single-phase inverter is extracted under operating conditions based on a two-probe approach. First, the noise source modelling and analysis are implemented for the inverter system to illustrate the importance of impedance. Furthermore, the proposed two-probe method is introduced and then validated by several passive components. Proper and straightforward premeasurement calibrations are needed to eliminate the influence of the probes and cables. The approach can accurately extract the common-mode and differential-mode noise source impedances with different configurations according to the characteristics of their propagation paths. Compared with a traditional EMI filter design, the experimental results show that the one designed by the proposed approach can effectively attenuate the conducted EMI noises to meet the requirements with more appropriate and optimised parameters.

Advanced Progress of Optical Wireless Technologies for Power Industry: An Overview

Optical wireless communications have attracted widespread attention in the traditional power industry because of the advantages of large spectrum resources, strong confidentiality, and freedom from traditional electromagnetic interference. This paper mainly summarizes the major classification and frontier development of power industry optical wireless technologies, including the indoor and outdoor channel characteristics of power industry optical wireless communication system, modulation scheme, the performance of hybrid power line, and indoor wireless optical communications system. Furthermore, this article compares domestic and foreign experiments, analyzes parameters for instance transmission rate, and reviews different application scenarios such as power wireless optical positioning and monitoring. In addition, in view of the shortcomings of traditional power technology, optical wireless power transfer technology is proposed and combined with unmanned aerial vehicles to achieve remote communication. At last, the main challenges and possible solutions faced by power industry wireless optical technologies are proposed.

Homogeneous silver nanoparticles decorating 3D carbon nanotube sponges as flexible high-performance electromagnetic shielding composite materials

Nowadays flexible high-performance electromagnetic interference (EMI) shielding materials are greatly demanded in military and daily purpose. To yield high shielding effectiveness (SE), the traditional metallic EMI materials always require a large mass of loading in a composite matrix, which is uneconomic and harmful to the mechanical property of the materials. Herein the homogeneous decoration of Ag nanoparticles on a light-weight and robust carbon nanotube sponge (CNTS) based 3D conductive scaffold is introduced. The flexible Ag/CNTS/PDMS composites exhibit an extremely high and tunable EMI shielding performance with improved mechanical strength and high conductivity. The maximum EMI SE is measured to be even greater than 90 dB in the X-band (8–12 GHz) with a low loading of Ag (3%, wt %) and CNTS (4%, wt %). In addition, the 3D inter-connected pore structure enables EM waves to reflect multiple times inside the Ag/CNTS hybrids which results in a strong absorption ability. The total EMI shielding property can be further conveniently controlled by tuning the Ag-deposition parameters as well as the thickness of the sample. The current approach successfully avoids the dispersion problem of the fillers and will be of great importance in development of high-performance EMI shielding materials.

Active EMI Filter Design With a Modified LCL-LC Filter for Single-Phase Grid-Connected Inverter in Vehicle-to-Grid Application

More and more attention has been gained in the vehicle-to-grid (V2G) system due to its attractive features, such as transferring bidirectional power between electric vehicles and grid, regulating grid voltage/frequency. This paper develops the active electromagnetic interference (EMI) filter (AEF) with significant system volume and weight reduction compared to the traditional passive EMI filter (PEF). While the high-frequency parasitic parameters of the AEF and the restricted loop gain result in limited AEF EMI noise attenuation in the high-frequency range. Thus, an additional passive EMI filter is commonly needed to suppress the EMI noise. For avoiding external passive filter components, the active EMI filter is designed and integrated with a modified LCL-LC filter as a hybrid filter to guarantee EMI noise attenuation. The modified LCL-LC filter can maintain satisfactory harmonic suppression with a higher EMI reduction ability compared to other types of harmonic filters. Based on a single-phase grid-connected inverter, the total harmonic distortion (THD) and the conducted EMI measurement results are compared with the results of traditional LCL, LLCL, LCL-LC filters. The effectiveness of the proposed circuit is verified by simulation and experimental results. The proposed circuit successfully improves the filter design of the inverter in the suppression of harmonics and EMI noise.

Time‐domain low‐frequency non‐periodic transient EMI measurement system

In this study, a time-domain low-frequency non-periodic transient electromagnetic interference (EMI) measurement system is presented. By the use of an antenna, an anti-aliasing filter, and a digital oscilloscope, the radiated emissions measurement specified by electromagnetic compatibility standard MIL-STD-461 is achieved. In the first stage, the antenna receives the radiated emissions of the device under test and the time domain output voltage is acquired in the oscilloscope. Then, to fulfil the spectrum measurement as accurate as an EMI receiver, a spectrum calculating methodology is carried out. Optimised inverse fast Fourier transform procedure for spectrum estimation in the proposed methodology is implemented to reduce the calculation efforts. The proposed EMI measurement technique required only a single time-domain acquisition and no repeatedly continuous scanning was imposed on the frequency measurement of the EMI test receivers. Due to this benefit, scan times are decreased by several orders of magnitude in comparison with a traditional EMI receiver.

The Facile Preparation of Flexible Graphene/Carbon Nanotubes Hybrid Papers for Electromagnetic Interference Shielding

A series of flexible graphene/carbon nanotubes (CNTs) hybrid papers were prepared by a facile impregnation method using cellulose papers as substrate. The impregnation cycles and sequence have a great impact on microstructure, electrical conductivity and electromagnetic interference (EMI) shielding performance of graphene/CNTs hybrid papers. The results showed that the surface of cellulose papers was covered by graphene and CNTs, forming continuous conductive networks. The graphene/CNTs hybrid papers achieved a thickness range of 174.7-253.2 μm and areal density range of 26-35.7 g/m2, which presented a larger advantage than traditional EMI shielding materials. The electrical conductivity was increased from 0.33 S/cm to 7.63 S/cm with the increase of impregnation cycles from 1 to 5. Furthermore, graphene/CNTs hybrid papers delivered a high EMI shielding effectiveness of 22-32 dB in the frequency of 30-1500MHz, which was superior to single graphene or CNTs papers. Moreover, the electrical conductivity and EMI shielding effectiveness of as-prepared graphene/CNTs hybrid papers presented little decline after even bending 100 times at an angle of 180° owing to their excellent flexibility. The graphene/CNTs hybrid papers possess a huge application potential in electromagnetic compatibility (EMC) of electronic device. Key words: graphene; carbon nanotubes; electromagnetic interference shielding; cellulose paper; dielectric polarization

A facile approach for coating Ti3C2Tx on cotton fabric for electromagnetic wave shielding

Electromagnetic interference (EMI) shielding fabric is widely used to deal with radiation pollution. However, the traditional EMI shielding fabrics are limited by their reflection-dominated shielding mechanism, large loading and poor shielding performance. Herein, Ti3C2Tx coated cotton fabrics with low Ti3C2Tx loading (1.5–2.6 mg/cm2) were prepared through a facile vacuum filtration process. Ti3C2Tx coated cotton fabric exhibits excellent electrical conductivity (up to 1570 S/cm), EMI SE (up to 48.9 dB) and superior shielding efficiency (up to 2969 dB cm2/g) with a low Ti3C2Tx loading (2.6 mg/cm2) in the frequency of 2–18 GHz. Especially, Ti3C2Tx coated cotton fabric shows high ratio of absorption shielding efficiency (SEA)/reflection shielding efficiency (SER) (> 9) in the frequency of 2–13.5 GHz, indicating that the dominant shielding mechanism of Ti3C2Tx coated cotton fabrics is microwave absorption of EM radiation. Additionally, the Ti3C2Tx coated cotton fabric exhibits a high tensile strength (up to 70 N) and fracture elongation (up to 18.3%). The result suggests that the Ti3C2Tx coated cotton fabric is a superior absorption-dominated EMI shielding material. The Ti3C2Tx coated cotton fabric with low loading, robust, and highly conductive properties can be regarded as an alternative electromagnetic wave absorbing material.