Conductive Shield Research Articles

Lightweight, flexible and superhydrophobic composite nanofiber films inspired by nacre for highly electromagnetic interference shielding

Inspired by the hierarchical structure of nacre, this study prepared a lightweight, flexible, and superhydrophobic polyacrylonitrile (PAN)@SiO2-Ag composite nanofibrous film with high performance electromagnetic-interference shielding via electrospinning. SiO2 incorporated into PAN electro-spun films provided the adhesion site for Ag nanoparticles (AgNPS). AgNPS were then deposited onto the surface of PAN@SiO2 electrospinning nanofibers via facile wet electroless deposition, thus endowing the resulting nanofibers with a core–shell structure. After finishing with a PTDT agent, PAN@SiO2-Ag composite nanofiber films had super hydrophobic property, and their water contact angle reached 156.99°. This scenario also presented high conductivity (approximately 17,788 S/m), average shielding effectiveness (SE), specific SE (SSE), and SSE/t, achieving 82 dB, 367 dB cm3g−1 and 73,478 dB cm2g−1, respectively. This study provides an easy method to prepare bioinspired composite films with high conductive and electromagnetic shielding and high potential applications, such as in wearable and flexible sensors.

Flame-retardant poly(vinyl alcohol)/MXene multilayered films with outstanding electromagnetic interference shielding and thermal conductive performances

With the miniaturized and high-frequency development in electronic products, polymeric films synchronously with high electromagnetic interference (EMI) shielding effectiveness (SE) and thermal conductivity (TC) are urgently needed. In this work, poly (vinyl alcohol)/transition metal carbide (PVA/MXene) films featured with alternating multilayered structure were fabricated through multilayered casting. The continuous MXene layer provided a compact network for conducting heat and electron, endowing the multilayered film with excellent EMI SE and TC synchronously. In particular, the 27-μm-thick PVA/MXene multilayered film (containing 19.5 wt% MXene in total) exhibited an electrical conductivity of 716 S/m, a maximum EMI SE of 44.4 dB and a specific EMI SE (SSEt) of 9343 dB cm2 g−1. Meanwhile, the multilayered film showed a high in-plane TC of 4.57 W/mK, enhanced by almost 23-fold compared with that of neat PVA. Moreover, the multilayered architecture endowed the film with remarkable anti-dripping performance. This work provides a novel and feasible strategy for fabricating flame-retardant polymeric thermal conductive and EMI shielding films, which will have enormous prospect in advanced electrical devices.

Eco-friendly flame retardant and electromagnetic interference shielding cotton fabrics with multi-layered coatings

Considering that the electromagnetic interference (EMI) shielding textiles are deeply affected by the accidental fires, we have designed an eco-friendly flame retardant and EMI shielding cotton fabric. Herein, the cotton fabric, a biomass material, serve as the skeleton and the polyethylenimine/phytic acid (PEI/PA) layer as well as silver nanowires (AgNWs) conductive networks are formed on the surface of cotton fibers through layer-by-layer assembled technology and dip-coating method, which is due to the strong electrostatic interaction and hydrogen bonding effect. The biomass material PA together with PEI functions well to be an effective intumescent flame retardant coating. Besides, the increasing amount of AgNWs constitutes an effective conductive metal shielding layer. Particularly, the cotton fabric with 24.2 wt% of PEI/PA layer and 7.5 wt% of AgNWs network possesses the effective self-extinguishing effect and minimizes the PHRR value about 58.59% of pure cotton fabric. Moreover, a high electrical conductivity of 2416.46 S/m and an impressive EMI shielding effectiveness of 32.98 dB are also achieved over the X-band frequency range with an absorption-dominated mechanism. The excellent flame retardant property and outstanding EMI shielding performance are attributed to the external well-constructed flame retardant layer and interconnected conductive network, which is confirmed by SEM images and EDS mapping images. Besides, it also keeps highly reliable shielding ability during the bending test, washing test and sandpaper abrasion test. Therefore, this flexible flame-retardant EMI shielding textile will benefit the eco-friendly and facile large-scale fabrication of multifunctional textile.

Coreless Transmitting Coils With Conductive Magnetic Shield for Wide-Range Ubiquitous IPT

New coreless transmitting (Tx) coils with a conductive material plate for wide-range ubiquitous inductive power transfer (IPT) zones, i.e., U-IPT zones, where electric devices can be wirelessly charged during operation, are proposed in this paper. Because commercialized IPT systems are only available for short distances of several centimeters and one-to-one charging, the demand is increasing for U-IPT zones in which long-distance wireless charging with three-dimensional (3-D) free-positioning and simultaneous charging of multiple receiving (Rx) coils can be achieved. To satisfy this demand, U-IPT zones should be constructed to have a uniform magnetic field distribution in a wide space, which also poses no risk to the human body. In addition, to generate a uniform magnetic field in a wide 3-D space, such as a single room, the system requires the installation of many Tx coils above the ceilings and behind the walls of the room, and these coils should be capable of high electrical performance to support the efficiency of the entire IPT system and should be of excellent mechanical quality. Therefore, a U-IPT zone should meet the following four criteria: human safety, free-positioning of Rx coils, magnetic field uniformity, and economization. By virtue of a conductive material plate that cancels out the undesired direction of magnetic flux generated from the return wires, the proposed coreless Tx coil does not need any heavy ferromagnetic cores, which can cause nonuniformity of the magnetic field distribution and difficult construction. A prototype coreless Tx coil with the dimensions of 1 m × 1 m × 10 cm was fabricated and experimentally verified for a 1 m × 1 m U-IPT zone. The experimental results showed that 74%, 83%, and 76% high magnetic field uniformity could be achieved for z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> = 25 cm, 50 cm, and 75 cm, respectively, and a 3-D omnidirectional wireless power delivery was achieved, while the guideline of the International Commission on Non-Ionizing Radiation Protection for human safety was satisfied throughout the entire U-IPT zone. Moreover, the weight of the entire system was only 9 kg, enabling easy installation. In the multiple wireless charging experiments, 47 W of power was consumed in total by load resistors, each of them connected to nine Rx coils, respectively, with 32% power efficiency at z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> = 20 cm.

Series Impedance and Losses of Magnetic Field Mitigation Plates for Underground Power Cables

This paper deals with magnetic field mitigation techniques for underground power systems by using conductive or ferromagnetic shielding plates. Two new aspects are considered in this paper beside the shielding effectiveness analysis: the contribution to the series impedance and power losses due to the conducting set formed by the shielding plate/earth return path. A finite thickness ferromagnetic or conductive shielding is assumed buried parallel to the soil/air plane surface in order to model the induction magnetic field mitigation of a power underground cable system in flat configuration. An analytical method, appropriate to deal with possible optimization procedures, is used based on the magnetic vector potential for multilayered configurations where the shielding plate is treated as a different layer. Results for the magnetic field reduction factor at the soil surface are obtained for different shielding materials, different shielding thickness values, as well as different frequency values. Results are validated by employing the finite element analysis.

High-performance flexible electromagnetic shielding polyimide fabric prepared by nickel-tungsten-phosphorus electroless plating

In this paper, functional polyimide (PI) fabric with high electrically conductive and electromagnetic shielding effect was prepared by nickel-tungsten-phosphorus (Ni-W-P) electroless plating. Firstly, a wave-absorbing and conductive polyaniline (PANI) layer was in-situ polymerized on the surface of fabric. Secondly, the PANI reduced the palladium ions to palladium particles acting as catalytically active sites. Finally, Ni-W-P electroless plating was initiated and formed a uniform and dense layer. The features of Ni-W-P alloy layer on PI fabric were characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The thermal stability of the sample was also evaluated by thermogravimetric analysis (TGA). The results showed that the electrical conductivity was 0.08 Ω/sq and the outstanding electromagnetic shielding effectiveness (SE) could reach 103 dB. Moreover, the robust SE performance after multiple ultrasonic washing and bending tests also implied the resultant material had a great potential in the textile protection fields.

Conductive Layer Modeling by Improved Second-Order Artificial Material Single-Layer Method

An improved second-order artificial material single-layer (AMSL) method is proposed to predict the electromagnetic field in the presence of conductive thin layers by the finite-element method (FEM). The AMSL method is based on the replacement of the material physical constants of a conductive shield region with those of an artificial material. The new AMSL physical constants are analytically extracted by equating the equivalent transmission line equations governing the field propagation inside the shield with the FEM solution. This new formulation of the method is a significant improvement of the original AMSL as it is much more robust and accurate for near field solutions, and, above all, it is much more easily implementable in commercial software tools.

High Performance EMI Shielding Materials and Spraying Process Parameters for High Frequency FCBGA Application

Abstract We studied and demonstrated high-performance Ag epoxy composites. A variety of shaped Ag particles were teste to optimize the electrical properties and mechanical reliability. The resulting Ag epoxy composites containing flake-shaped Ag particles showed less than 5×10−7Ω·m electrical conductivity and about 20mΩ series-resistance of PKG daisy chain, which directly corresponded to the excellent shield effectiveness. The shield effectiveness of resulting EMI shielding layer made of Ag and matrix is as high as 60dB, 65dB, 70dB at 5um, 10um, 20um-thick film, respectively by ASTM standard. We studied that how various factors, such as curing temperature, Ag contents, and film thickness, effects the electrical properties of shielding material and FCBGA package. It was found that the resistivity of conductive shielding material and the series-resistance were affected by the curing temperature than the curing time. Additionally, we demonstrated the electrical properties of AgCu epoxy composites.

Conductive, antibacterial, and electromagnetic shielding silver‐plated cotton fabrics activated by dopamine

ABSTRACTA two‐step method was developed in this article to fabricate conductive silver‐plated cotton fabrics, imparting them with antibacterial and electromagnetic shielding properties. Cotton fabric was firstly functionalized by a spontaneous polymerization of dopamine, which acted as an activation and adsorption layer to initiate the following silver plating through the catechol and indole functional groups. The chemical composition of the functional cotton fabric was investigated by X‐ray photoelectron spectroscopy and the surface morphology of the fabric was observed by scanning electron microscopy. The crystalline structure of the silver‐coated cotton fibers was characterized by power X‐ray diffraction, and thermogravimetric analysis of the fabric was also studied to show thermal stability. The homogeneous silver plating was highly conductive with surface resistance about 23.55 mΩ sq.−1 and shielding effectiveness was about 55~95 dB. It also demonstrated excellent and durable antibacterial property against Staphylococcus aureus and Escherichia coli both with reduction percent of bacteria over 99.99%. All of above features made this silver‐plated cotton fabrics a promising candidate as multifunctional textiles. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46766.

Time-Domain Shielding of a Thin Conductive Sheet in the Presence of Pulsed Vertical Dipoles

The classical problem represented by a planar thin conductive shield in the presence of vertical dipole field sources (electric or magnetic) is solved analytically in the time domain via the Cagniard-de Hoop technique. Comparisons with numerical solutions carried out by means of efficient integration algorithms are provided and discussed.

Artificial Material Single Layer to Model the Field Penetration Through Thin Shields in Finite-Elements Analysis

A new artificial material single layer (AMSL) model is presented to solve shielding problem. The field penetration through the conductive shield is described by lossy transmission line equations. The resulting equations are used to numerically synthetize an equivalent material for the shield region having the same geometrical configuration of the original shield, but different specific constants. The AMSL method is very accurate and highly efficient since it allows to discretizing the shield region using only a single layer of finite elements avoiding the fine discretization required by the finite-element method (FEM) to model the skin effect. The most relevant aspect of the proposed procedure is that the AMSL method can be easily implemented in FEM-based commercial software tools.

EXPERIMENTAL VERIFICATION OF QUADRUPOLE MODEL OF THE ELECTRIC FIELD OF A ROTATING MAGNET

We performed an experiment to verify quadrupole model of the electric field of a rotating magnet. It is found that the rotating magnet insulated from the earth and enclosed in a conductive insulated shield produces the potential difference across an air capacitor arranged on the outside of the shield. The field of the electric quadrupole cannot penetrate through the shield, therefore the electric field detected outside the shield is not quadrupole. The effect observed in the experiment can be explained by fictitious electric charge density inside the shield caused by the rotation of the magnet.

Effect of interfacial interaction on rheological, electrically conductive, and electromagnetic shielding properties of polyethylene/GO composites

To regulate interfacial interaction between the polyethylene (PE) and graphene oxide (GO), maleic anhydride grafted high density polyethylene (PE‐g‐MAH) was utilized to enhance interfacial interaction between PE matrix and GO particles. Moreover, as a comparative investigation, γ‐aminopropyltriethoxysilane (KH550) was used to functionalize GO (f‐GO) so as to improve the interfacial interaction between PE matrix and GO particles. Compared to the addition of the PE‐g‐MAH, the f‐GO had better dispersion in the PE/f‐GO composites, indicating that functionalization of the GO with KH550 was the most effective way to improve the dispersion of the GO. However, the gel point for the PE/GO composite was not observed because the fillers network was not formed in the PE/GO composite. Compared to the f‐GO particles, addition of PE‐g‐MAH was efficiency to build network structure of the GO particles so that the electrical conductivity of the PE/GO composites can be effectively improved. Moreover, the electromagnetic interference shielding effectiveness (EMI SE) of the PE/GO composites with addition of PE‐g‐MAH (PE/M‐GO) was consistently higher than that of the PE/f‐GO composites, indicating that the PE‐g‐MAH can effectively improve the EMI SE of the PE/GO composites. In addition, the microwave absorption (SEA) was main shielding mechanism for the PE/f‐GO, PE/M‐GO, and PE/GO composites. POLYM. ENG. SCI., 58:1774–1781, 2018. © 2017 Society of Plastics Engineers

Operator Safety and Field Focality in Aluminum Shielded Transcranial Magnetic Stimulation

This paper aims at verifying the effectiveness of the transcranial magnetic stimulation treatment when a passive shield is introduced for the nursing staff safety. The analysis is developed through a modeling approach, splitting the solution of the field problem into two successive steps. The Duke anatomical model of the Virtual Family dataset is used to model both the patient head and the operator body. The investigations are performed by considering stimulators equipped with a circular spiral coil or a figure-of-eight shaped (FoE or butterfly) winding. The addition of the shield slightly reduces the induced electric field values, while increasing the field focality in the patient brain (especially with the circular coil), preserving the effectiveness of the treatment, anyway. On the operators’ side, the presence of a passive conductive shield significantly reduces the exposure levels.

Fabrication and Preparation of Micro-Coaxial Wires: Electrodeposition of Conductive Gold Shields

Draper is developing a new paradigm in microelectronics packaging, in which the interconnects among components are made, not through the substrate, but rather through micro-coaxial wires. In this paper, we describe the design and fabrication of micro-coaxial wire segments of diameters between 30 μm and 250 μm. The micro-coax comprised a center metal wire, a polymer dielectric layer, and electroplated gold shield. To facilitate integration of the micro-coax on the package, the micro-coax were prepared in ~20 mm segments that are stripped back at the ends to expose < 1 mm of the core wire. To achieve the necessary stripping of the micro-coax shield layer, we have utilized two different seeding and electroplating processes and fixtures. We describe both processes and the fixture design that allowed the scale up in fabrication volume from 0.1 m of micro-coax to 1.2 m of micro-coax per batch.

Magnetic field in an apartment located above 10/0.4 kV substation: levels and mitigation techniques

The paper presents a real case of non-ionising radiation testing in an apartment located directly above a 10/0.4 kV substation in Serbia. In order to check the compliance with national regulations on protection of population from non-ionising radiation, it was necessary to perform measurements of magnetic flux density in the apartment. After the first measurements were performed, the distribution company implemented a mitigation technique by placing a passive conductive shield inside the substation in order to decrease magnetic field levels in the apartment. Measurements performed after the mitigation technique had been implemented have shown that the applied shield had an impact on magnetic field reduction to a certain extent. However, since the obtained shielding factor was not very high, the authors analysed another possible shielding solution which would provide higher shielding factor and consequently lower magnetic field levels in the apartment. Both shielding solutions and the results they provide are presented and analysed.

Fabrication and Preparation of Micro-Coaxial Wires: Electrodeposition of Conductive Shields

We describe the fabrication of micro-coaxial cables with diameters of 25 to 300 micrometers. Draper Laboratory is developing a new microelectronics packaging platform that relies on such microcoax, in place of copper interconnects, for both power and signal distribution among the packaged electronic components. This platform could save design time and fabrication labor over conventional packaging techniques for custom electronics with small production volumes and offers a way to rapid prototype and/or edit circuits. In this work, we focus on the fabrication of microcoax for power distribution. The fabrication process of the metal-dielectric-metal cross-section of the microcoax begins with a commercial metal wire of 18 to 150 micrometer diameter, which is either purchased with a polymer insulation of 1 to 12 micrometer thickness, or is insulated with SiO2 or Al2O3 of 0.1 to 2 micrometer thickness by PECVD or ALD processes. Next, a thin Ti/Au bilayer is applied to the insulated wire by electron beam evaporation and acts both as an adhesive layer and as electrical contact to plate the outer metal shield to its full desired thickness. The metal shield is electroplated using a cyanide-free gold sulfite chemistry that produces a soft satin to bright electrodeposit, meeting Type IIIA of Mil-G-45204 C requirements (i.e., ≥ 99.9 % gold purity and Knoop hardness 90 maximum). Straight DC, temperature of 60 °C, current density of 2 mA/cm2and mild agitation were chosen as parameters for Au electroplating conditions. Gold electrodeposits exhibit very low roughness, good corrosion resistance, excellent solderability, high shine and with evaporated seed metal, good adhesion to the polymer dielectrics. The shield thickness is chosen to give a resistance equal to or less than the resistance of the metal core, e.g., 34 micrometers of plated Au for a 127 micrometer diameter Cu core. The use of the microcoax for packaging requires lengths of microcoax of < 15 mm with the wire tips prepared for electrical connection, i.e., tips where the metal shield ends abruptly leaving the center metal wire exposed for bonding, and so we introduce at periodic intervals along the wire length regions where the outer layers are more easily stripped to expose the metal core. We have accomplished this either by ad hoc placement of a plating-resistant (nail polish or soft-baked photoresist) bead on the seed metal to pattern regions where no shield metal is electrodeposited; or by an evaporation mask during seed metal deposition to pattern regions where neither the metal seed nor the metal shield are deposited. The core metal is then exposed in the beaded or masked regions by wet etching the seed metal, if necessary, and UV laser ablation of the polymer dielectric. In addition to the fabrication processes, we will also discuss the fixturing and handling protocols required for these fine diameter wires. Fixturing is designed to accomplish four criteria: to minimize handling among the various process steps (insulating the wire, e-beam evaporation, electroplating); to pattern the microcoax lengths and abrupt edges to the electrodeposited metal; to make electrical contact to the seed metal during electroplating; and for the necessary volume and yield. We will describe our scale-up from an initial proof-of-concept process that produced 0.1 meters of microcoax of arbitrary segment lengths to a simpler process that produces 2 meters of microcoax of well-defined segment length.

Simultaneous scanning tunneling microscopy and synchrotron X-ray measurements in a gas environment

A combined X-ray and scanning tunneling microscopy (STM) instrument is presented that enables the local detection of X-ray absorption on surfaces in a gas environment. To suppress the collection of ion currents generated in the gas phase, coaxially shielded STM tips were used. The conductive outer shield of the coaxial tips can be biased to deflect ions away from the tip core. When tunneling, the X-ray-induced current is separated from the regular, ‘topographic’ tunneling current using a novel high-speed separation scheme. We demonstrate the capabilities of the instrument by measuring the local X-ray-induced current on Au(1 1 1) in 800 mbar Ar.

DC electrical breakdown dependence on the radial position of specimens within HVDc XLPE cable insulation

Because of temperature gradients and inhomogeneous cooling rates after extrusion, the performances of HVDC XLPE cable insulation at radial position are not uniformly distributed. DC breakdown strength measurements of HVDC XLPE cable insulation specimens in inner insulation (near conductor shield), middle insulation and outer insulation (near insulation shield) have been carried out and show that DC breakdown strength of specimens in middle insulation is relatively lower than that of in inner and outer insulation at 30, 50 and 70 °C. At 90 °C, there is no significant difference of DC breakdown strength of specimens at radial position. Thus the micro performances of XLPE specimens at different radial position have been studied by FTIR, DSC, SEM and XRD. FTIR measurements show that cross-linked by-products (benzyl alcohol and acetophenone) content in middle insulation is higher; DSC measurements shows that crystallinity of specimens in middle insulation is slightly higher; SEM measurements show that the grains of specimens in middle insulation are unevenly distributed and their sizes have obvious difference; the results of XRD measurements show a higher content of by-products, a higher crystallinity and a larger crystalline interplanar spacing (a larger grain size) of specimens in middle insulation, which are consistent with FTIR, DSC and SEM analysis. Therefore, cross-linked by-products, crystallinity and crystal morphology together make DC breakdown strength of specimens in middle insulation lower.

An Integrated Characterization Model and Multiobjective Optimization for the Design of an EV Charger’s Circular Wireless Power Transfer Pads

A good magnetic design of a wireless electric vehicle (EV) charging system requires accurate characterization of the equivalent circuit parameters. This is while considering the effect of the magnetic core and the conductive shielding layers. In the literature, such an analysis is done using 3-D finite element analysis, which makes the design and optimization process time-consuming and computationally expensive. In this paper, an integrated analytical model for the characterization of a circular wireless power transfer EV pads is utilized. This analytical model provides a valuable tool to optimize the design process. This model is utilized when evaluating the objective function for each individual in the multiobjective Pareto Optimality optimization algorithm. The objective is optimizing the pads with three decision variables and four constraints.