Investigation of Faraday cage materials with low eddy current and high RF shielding effectiveness for PET/MRI applications

OBJECTIVE

This study aims to evaluate radiofrequency (RF) shielding effectiveness (SE), gradient-induced eddy current, MR susceptibility, and PET photon attenuation of six shielding materials: copper plate, copper tape, carbon fiber fabric, stainless steel mesh, phosphor bronze mesh, and a spray-on conductive coating. 

Approach. We evaluated the six shielding materials by implementing them on identical clear plastic enclosures. We measured the RF SE and eddy current in benchtop experiments (outside of the MR environment) and in a 3T MR scanner. The magnetic susceptibility performance was evaluated in the same MR scanner. Additionally, we measured their effects on PET detectors, including global coincidence time resolution, global energy resolution, and coincidence count rate. 

Main results. The RF SEs for copper plate, copper tape, carbon fiber fabric, stainless steel mesh, phosphor bronze mesh, and conductive coating enclosures were 56.8±5.8, 63.9±4.3, 33.1±11.7, 43.6±4.5, 52.7±4.6, and 47.8±7.1 dB, respectively, in the benchtop experiment. Copper plate and copper tape experienced the most eddy current at 10 kHz in the benchtop experiment and also generated the largest ghosting artifacts in the MR scanner. Stainless steel mesh had the highest mean absolute difference (7.6±0.2 Hz) compared to the reference in the MR susceptibility evaluation. The carbon fiber fabric and phosphor bronze mesh enclosures caused the largest photon attenuation, reducing the coincidence count rate by 3.3 %, while the rest caused less than 2.6 %. 

Significance. The conductive coating proposed in this study is shown to be a high-performance Faraday cage material for PET/MRI applications based on its overall performance in all the experiments conducted in this study, as well as its ease and flexibility of manufacturing. As a result, it will be selected as the Faraday cage material for our second-generation MR-compatible PET insert.

Analysis of Shielding Effectiveness against Electromagnetic Interference (EMI) for Metal-Coated Polymeric Materials

Lightweight materials, such as polymers and composites, are increasingly used in the automotive and aerospace industries. Recently, there has been an increase in the use of these materials, especially in electric vehicles. However, these materials cannot shield sensitive electronics from electromagnetic interference (EMI). The current work investigates the EMI performance of these lightweight materials using an experimental setup based on the ASTM D4935-99 standard and EMI simulation using the ANSYS HFSS. This work studies how metal coating from zinc and aluminum bronze can improve the shielding performance of polymer-based materials, such as polyphenylene sulfide (PPS), polyetheretherketone (PEEK), and polyphthalamide (PPA). Based on the findings of this study, a thin coating (50 μm) of Zn on the surface of PPS and a thin coating of 5 μm and 10 μm of Al-Bronze, respectively, on the surface of PEEK and PPA have indicated an increase in the shielding effectiveness (SE) when subjected to EMI. The shielding effectiveness significantly increased from 7 dB for the uncoated polymer to approximately 40 dB at low frequencies and up to approximately 60 dB at high frequencies for coated polymers. Finally, various approaches are recommended for improving the SE of polymeric materials under the influence of EMI.

Shielding Performance of Electromagnetic Shielding Fabric Implanted with "Split-Ring Resonator"

The electromagnetic shielding (EMS) fabric is an important electromagnetic protection product, which is widely applied in various fields. The improvement of its shielding effectiveness (SE) has always been the focus of research. This article proposes to implant a metamaterial structure of a "split-ring resonator (SRR)" in the EMS fabrics, so that the fabric not only maintains the porous and lightweight characteristics, but also obtains the SE improvement. With the help of the invisible embroidery technology, stainless-steel filaments were used to implant hexagonal SRRs inside the fabric. The effectiveness and influencing factors of the SRR implantation were described by testing the SE of the fabric and analyzing the experimental results. It was concluded that the SRR implantation inside the fabric can effectively improve the SE of the fabric. For the stainless-steel EMS fabric, the increase amplitude of the SE reached between 6 dB and 15 dB in most frequency bands. The overall SE of the fabric showed a decrease trend with the reduction of the outer diameter of the SRR. The decrease trend was sometimes fast and sometimes slow. The decreasing amplitudes were different in various frequency ranges. The number of embroidery threads had a certain effect on the SE of the fabric. When other parameters remained unchanged, the increase of the diameter of the embroidery thread resulted in the increase of the SE of the fabric. However, the overall improvement was not significant. Finally, this article also points out that other influencing factors of the SRR need to be explored, and the failure phenomenon may occur under certain situations. The proposed method has the advantages of the simple process, convenient design, no pore formation, SE improvement retaining the original porous characteristics of the fabric. This paper provides a new idea for the design, production, and development of new EMS fabrics.

Prediction Models of Shielding Effectiveness of Carbon Fibre Reinforced Cement-Based Composites against Electromagnetic Interference

With the rapid development of communication technology as well as a rapid rise in the usage of electronic devices, a growth of concerns over unintentional electromagnetic interference emitted by these devices has been witnessed. Pioneer researchers have deeply studied the relationship between the shielding effectiveness and a few mixed design parameters for cementitious composites incoporating carbon fibres by conducting physical experiments. This paper, therefore, aims to develop and propose a series of prediction models for the shielding effectiveness of cementitious composites involving carbon fibres using frequency and mixed design parameters, such as the water-to-cement ratio, fibre content, sand-to-cement ratio and aspect ratio of the fibres. A multi-variable non-linear regression model and a backpropagation neural network (BPNN) model were developed to meet the different accuracy requirements as well as the complexity requirements. The results showed that the regression model reached an R² of 0.88 with a root mean squared error (RMSE) of 2.3 dB for the testing set while the BPNN model had an R² of 0.96 with an RMSE of 2.64 dB. Both models exhibited a sufficient prediction accuracy, and the results also supported that both the regression and the BPNN model are reasonable for such estimation.

Enhancement of Electromagnetic Wave Shielding Effectiveness by the Incorporation of Carbon Nanofibers-Carbon Microcoils Hybrid into Commercial Carbon Paste for Heating Films

Carbon microcoils (CMCs) were formed on stainless steel substrates using C₂H₂ + SF₆ gas flows in a thermal chemical vapor deposition (CVD) system. The manipulation of the SF₆ gas flow rate and the SF₆ gas flow injection time was carried out to obtain controllable CMC geometries. The change in CMC geometry, especially CMC diameter as a function of SF₆ gas flow injection time, was remarkable. In addition, the incorporation of H₂ gas into the C₂H₂ + SF₆ gas flow system with cyclic SF₆ gas flow caused the formation of the hybrid of carbon nanofibers-carbon microcoils (CNFs-CMCs). The hybrid of CNFs-CMCs was composed of numerous small-sized CNFs, which formed on the CMCs surfaces. The electromagnetic wave shielding effectiveness (SE) of the heating film, made by the hybrids of CNFs-CMCs incorporated carbon paste film, was investigated across operating frequencies in the 1.5-40 GHz range. It was compared to heating films made from commercial carbon paste or the controllable CMCs incorporated carbon paste. Although the electrical conductivity of the native commercial carbon paste was lowered by both the incorporation of the CMCs and the hybrids of CNFs-CMCs, the total SE values of the manufactured heating film increased following the incorporation of these materials. Considering the thickness of the heating film, the presently measured values rank highly among the previously reported total SE values. This dramatic improvement in the total SE values was mainly ascribed to the intrinsic characteristics of CMC and/or the hybrid of CNFs-CMCs contributing to the absorption shielding route of electromagnetic waves.

Electromagnetic Wave Shielding Properties of Amorphous Metallic Fiber-Reinforced High-Strength Concrete Using Waveguides

In this study, high-strength concrete containing hooked-end steel or amorphous metallic fibers was fabricated, and the electrical conductivity and electromagnetic shielding effectiveness were evaluated after 28 and 208 days based on considerations of the influences of the moisture content. Amorphous metallic fibers, which have the same length and length/equivalent diameter ratio as hooked-end steel fibers, were favored for the formation of a conductive network because they can be added in large quantities owing to their low densities. These fibers have a large specific surface area as thin plates. The electromagnetic shielding effectiveness clearly improved as the electrical conductivity increased, and it can be expected that the shielding effectiveness will approach the saturation level when the fiber volume fraction of amorphous metallic fibers exceeds 0.5 vol.%. Meanwhile, it is necessary to reduce the amount of moisture to conservatively evaluate the electromagnetic shielding performance. In particular, when 0.5 vol.% of amorphous metallic fibers was added, a shielding effectiveness of >80 dB (based on a thickness of 300 mm) was achieved at a low moisture content after 208 days. Similar to the electrical conductivity, excellent shielding effectiveness can be expected from amorphous metallic fibers at low contents compared to that provided by hooked-end steel fibers.

Mechanical and Electrical Characteristics of Lightweight Aggregate Concrete Reinforced with Steel Fibers

There is increased interest in applying electromagnetic (EM) shielding to prevent EM interference, which destroys electronic circuits. The EM shielding’s performance is closely related to the electrical conductivity and can be improved by incorporating conductive materials. The weight of a structure can be reduced by incorporating lightweight aggregates and replacing the steel rebars with CFRP rebars. In this study, the effects of lightweight coarse aggregate and CFRP rebars on the mechanical and electrical characteristics of concrete were investigated, considering the steel fibers’ incorporation. The lightweight coarse aggregates decreased the density and strength of concrete and increased the electrical conductivity of the concrete, owing to its metallic contents. The steel fibers further increased the electrical conductivity of the lightweight aggregate concrete. These components improved the EM shielding performance, and the steel fibers showed the best performance by increasing shielding effectiveness by at least 23 dB. The CFRP rebars behaved similarly to steel rebars because of their carbon fiber content. When no steel fiber was mixed, the shielding effectiveness increased by approximately 2.8 times with reduced spacing of CFRP rebars. This study demonstrates that lightweight aggregate concrete reinforced with steel fibers exhibits superior mechanical and electrical characteristics for concrete and construction industries.

Graphene and Iron Reinforced Polymer Composite Electromagnetic Shielding Applications: A Review

With advancements in the automated industry, electromagnetic inferences (EMI) have been increasing over time, causing major distress among the end-users and affecting electronic appliances. The issue is not new and major work has been done, but unfortunately, the issue has not been fully eliminated. Therefore, this review intends to evaluate the previous carried-out studies on electromagnetic shielding materials with the combination of Graphene@Iron, Graphene@Polymer, Iron@Polymer and Graphene@Iron@Polymer composites in X-band frequency range and above to deal with EMI. VOSviewer was also used to perform the keyword analysis which shows how the studies are interconnected. Based on the carried-out review it was observed that the most preferable materials to deal with EMI are polymer-based composites which showed remarkable results. It is because the polymers are flexible and provide better bonding with other materials. Polydimethylsiloxane (PDMS), polyaniline (PANI), polymethyl methacrylate (PMMA) and polyvinylidene fluoride (PVDF) are effective in the X-band frequency range, and PDMS, epoxy, PVDF and PANI provide good shielding effectiveness above the X-band frequency range. However, still, many new combinations need to be examined as mostly the shielding effectiveness was achieved within the X-band frequency range where much work is required in the higher frequency range.

Electromagnetic Shielding Properties of Knitted Fabric Made from Polyamide Threads Coated with Silver

This paper investigates a textile material of low surface mass for its protection against electromagnetic radiation (EMR), which is suitable for composite structures of garments, and for technical and interior applications. The shielding effectiveness against EMR of fabric knitted from polyamide threads coated with silver, measured in the frequency range of 0.9 GHz to 2.4 GHz, indicated a high degree of protection. The key contribution of the paper is the evaluation of the stability of the shielding properties against EM radiation after applying apolar and polar solvents, in synergy with the cyclic process parameters of wet and dry cleaning. The results of the study confirmed the decline in the shielding effectiveness after successive cycles of material treatment with dry and wet cleaning. The effect of wet cleaning in relation to dry cleaning is more apparent, which is due to the damage of the silver coating on the polyamide threads in the knitted fabric.

Relationship between Three-Dimensional Steel Fiber Statistics and Electromagnetic Shielding Effectiveness of High-Performance, Fiber-Reinforced Cementitious Composites

This study aims to investigate the relationship between the steel fibers and the electromagnetic wave shielding effectiveness of a high-performance fiber-reinforced cementitious composite (HPFRCC). The distribution characteristics of the steel fibers and the variation of the electrical conductivity of HPFRCC as a function of the fiber content were quantified based on micro computed tomography (CT) and impedance measurements to determine their correlations with the electromagnetic shielding effectiveness. The impedance results showed that no electrical network was formed in the composite by the steel fibers and it is difficult to manufacture HPFRCC with high-electrical conductivity using steel fibers alone without CNTs or other carbon-based materials. For the steel fiber content of greater than 0.5%, the number of contact points between the steel fibers increased significantly, and the relationship between the fiber content and the number of contact points was observed. Despite the improvement of the electrical conductivity owing to the presence of the steel fibers and to the increase in the contact points between the steel fibers, the shielding effectiveness did not increase further for the steel fiber contents equal or above 1.5%. Consequently, it was found that the factor that controls the shielding effectiveness of HPFRCC is not the electrical network of the steel fibers, but the degree of the dispersion of the individual steel fibers.

Record-High Transparent Electromagnetic Interference Shielding Achieved by Simultaneous Microwave Fabry-Pérot Interference and Optical Antireflection

As a potential risk to human and environmental health, radio frequency (RF) radiation should be studied due to the higher frequencies and larger bandwidths that may be employed. Electromagnetic interference (EMI) shielding materials can prevent exposure to RF radiation, but most of them are visibly opaque. In this work, we propose and fabricate visibly transparent EMI shielding materials using an ultrathin silver layer sandwiched by oxides (SLSO) as building blocks. The samples with a double-sided SLSO (D-SLSO) structure exhibit the highest EMI shielding effectiveness (SE) of 70 dB at 27.6 GHz (>62 dB on average at 4-40 GHz) and a transmittance close to 90% at a visible wavelength of 550 nm, which is comparable with those of polyethylene terephthalate (PET) and glass substrates. The D-SLSO structure plays a dual role: it suppresses optical reflections as antireflection coatings and enhances EMI shielding via Fabry-Pérot interference. In addition, we discuss the origin of the extraordinary frequency dependence of SE, which monotonically increases, contrary to that of conventional metallic mesh. This report describes SLSO-based transparent EMI shielding materials with record-high SE and visible transmittance that provide optoelectronic applications with robust safety and reliability under RF radiation with high and broad frequencies.

Enhanced Shielding Performance of Layered Carbon Fiber Composites Filled with Carbonyl Iron and Carbon Nanotubes in the Koch Curve Fractal Method

Layered carbon fiber composites (CFC) with enhanced shielding effectiveness (SE) were prepared with mixed fillers of carbon nanotubes (CNTs) and carbonyl iron powders (CIPs) in the form of a Koch curve fractal. In the layered composite structure, glass fiber (GF) cloth was used in the wave-transmissive layer (WTL), and the carbon fiber (CF) cloth was used in the supporting layer (SL). Between WTL and SL, CNTs and CIPs were distributed in epoxy resin in the form of a Koch curve fractal to act as an absorbing layer (AL), and copper foil was used as a reflective layer (RL) and bonded at the bottom of the whole composites. The layered structure design and excellent interlayer interface integration obviously improved the SE performance of the CFC. The SE of different samples was investigated, and the results show that, with the increase in the number (n) of Koch curve fractals, the SE of the samples enhanced in the low frequency scope (1-5 GHz). The sample with n = 2 has the highest SE value of 73.8 dB at 2.3 GHz. The shielding performance of the fractal sample filled by CNTs and CIPs simultaneously has a comprehensive improvement in the whole scope of 1-18 GHz, especially for the sample with n = 2. The cumulative bandwidth value of the SE exceeding 55 dB is about 14.3 GHz, accounting for 85% of the whole frequency scope, indicating the composite fabricated in this paper is an electromagnetic shielding material with great prospect.

Synthesis and Electromagnetic Interference Shielding Performance of Ti3SiC2-Based Ceramics Fabricated by Liquid Silicon Infiltration

In this work, Ti₃SiC₂-based ceramics were fabricated by the infiltration of liquid silicon into TiC preform by incorporating a small amount of Al. Al can play a catalytic role to promote the formation of TiC twins before liquid silicon infiltration (LSI), which leads to the increase of transformation efficiency from TiC to Ti₃SiC₂ in the LSI process. When the Al content in the TiC preform increases to 9 wt.%, the volume content of Ti₃SiC₂ reaches 85 vol.%, revealing the high electromagnetic interference shielding effectiveness of 39 dB in the frequency range of 8.2–12.4 GHz. The results indicate that it is an effective way to synthesize Ti₃SiC₂-based ceramics with excellent electromagnetic shielding performance.

Electrical Properties and Electromagnetic Interference Shielding Effectiveness of Interlayered Systems Composed by Carbon Nanotube Filled Carbon Nanofiber Mats and Polymer Composites

The demand for multifunctional requirements in aerospace, military, automobile, sports, and energy applications has encouraged the investigation of new composite materials. This study focuses on the development of multiwall carbon nanotube (MWCNT) filled polypropylene composites and carbon nanofiber composite mats. The developed systems were then used to prepare interlayered composites that exhibited improved electrical conductivity and electromagnetic interference (EMI) shielding efficiency. MWCNT-carbon nanofiber composite mats were developed by centrifugally spinning mixtures of MWCNT suspended in aqueous poly(vinyl alcohol) solutions. The developed nanofibers were then dehydrated under sulfuric acid vapors and then heat treated. Interlayered samples were fabricated using a nanoreinforced polypropylene composite as a matrix and then filled with carbon fiber composite mats. The in-plane and through-plane electrical conductivity of an eight-layered flexible carbon composite (0.65 mm thick) were shown to be 6.1 and 3.0 × 10⁻² S·cm⁻¹, respectively. The EMI shielding effectiveness at 900 MHz increased from 17 dB for the one-layered composite to 52 dB for the eight-layered composite. It was found that the reflection of the electromagnetic waves was the dominating mechanism for EMI shielding in the developed materials. This study opens up new opportunities for the fabrication of novel lightweight materials that are to be used in communication systems.

Measuring the shielding properties of flexible or rigid enclosures for portable electronics

Heaviside, in volume 1 of Electromagnetic theory, considered shielding of conducting materials in the form of attenuation. This treatment is still significant in the understanding of shielding effectiveness. He also considered propagation of electromagnetic waves in free-space. What Heaviside (1850-1925) could never have imagined is that 125 years later, there would be devices we know as mobile phones (or cell phones, handies, etc.) with capabilities beyond the dreams of the great science fiction writers of the day like H. G. Wells (1866-1949) or Jules Verne (1828-1905). More than this, that there would be a need for law enforcement agencies, among others, to use electromagnetically shielded enclosures to protect electronic equipment from communicating with the 'outside world'. Nevertheless, Heaviside's work is still fundamental to the developments discussed here. This paper provides a review of Heaviside's view of shielding and propagation provided in volume 1 of Electromagnetic theory and develops that to the design of new experiments to test the shielding of these portable enclosures in a mode-stirred reverberation chamber, a test environment that relies entirely on reflections from conducting surfaces for its operation.This article is part of the theme issue 'Celebrating 125 years of Oliver Heaviside's 'Electromagnetic Theory''.

Enhanced X-Band Electromagnetic-Interference Shielding Performance of Layer-Structured Fabric-Supported Polyaniline/Cobalt-Nickel Coatings

Despite tremendous efforts, fabrication of lightweight conductive fabrics for high-performance X-band electromagnetic-interference (EMI) shielding remains a daunting technical challenge. We herein report an ingenious and efficient strategy to deposit polyaniline/cobalt-nickel (PANI/Co-Ni) coatings onto lyocell fabrics that involves consecutive steps of in situ polymerization and electroless plating. The PANI-Co-Ni ternary-component system successfully induced a synergistic effect from EM wave-absorption and EM wave-reflection and, moreover, upgraded the match level between magnetic loss and dielectric loss. By the judicious control of polymerization cycles and plating time, low-weight fabric-supported PANI/Co-Ni composites (with PANI and Co-Ni loading of 2.86 and 3.99 mg·cm^-2, respectively) were prepared, which displayed relatively high EMI shielding effectiveness (SE) (33.95-46.22 dB) when compared to their single peers (PANI-coated fabric and Co-Ni-coated fabric) or even the sum of them. Inspired by the so-called "1 + 1 > 2" phenomenon, here we demonstrated that there was an EMI SE enhancement effect in this conductive polymer/metal system that may be associated with interphase chemical and/or physical interactions. Further analysis revealed that this EMI SE enhancement effect was evident under circumstances of relatively low metal content and became weak with the increase of metal content. The mechanisms involved were interpreted through a series of fundamental measurements, including Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM), and vector network analysis (VNA). The linkage between PANI and Co-Ni coatings was in the form of Co-N/Ni-N, which mimics the atomic configuration occurring in cobalt porphyrins. The Co-N/Ni-N configuration strengthened the interphase adhesion and thus resulted in shielding fabrics with high durability for practical applications.

Effects of Carbonization Temperature and Component Ratio on Electromagnetic Interference Shielding Effectiveness of Woodceramics

Woodceramics were fabricated in a vacuum through carbonization of wood powder impregnated with phenol formaldehyde (PF) resin. The effects of carbonization temperature and mass ratio of wood/resin on electromagnetic interference (EMI) shielding effectiveness (SE) and morphology of woodceramics were explored. The PF resin made wood cell walls have the characteristics of glassy carbon. Wood axial tracheid and ray cells were filled with more glassy carbon by increasing addition of PF resin. Moreover, the increase of carbonization temperature was beneficial to improving SE. Woodceramics (mass ratio 1:1) obtained at 1000 °C presented a medium SE level between 30 MHz and 1.5 GHz.