Shielding Effectiveness Measurements Research Articles

Novel Carbon Nanotube−Polystyrene Foam Composites for Electromagnetic Interference Shielding

A novel carbon nanotube-polystyrene foam composite has been fabricated successfully. The electromagnetic interference (EMI) shielding effectiveness measurements indicated that such foam composites can be used as very effective, lightweight shielding materials. The correlation between the shielding effectiveness and electrical conductivity and the EMI shielding mechanism of such foam composites are also discussed.

Improved method to graft polyaniline on E‐glass fabric to enhance its electronic conductivity

AbstractA method to enhance the electronic conductivity of polyaniline grafted E‐glass fabric is described. The influence of substituted aromatic sulfonic acids as primary dopants on conductivity of the grafted polyaniline–E‐glass fabrics is studied. The conducting fabrics obtained in this method were characterized by UV‐vis spectroscopy, scanning electron microscopy, X‐ray diffraction study, thermogravimetric analysis, and conductivity. Shielding effectiveness measurements on these Pan–E‐glass fabrics showed that the performance is improved (i.e., 0.01 MHz = 49 dB, 1000 MHz = 7 dB) compared to earlier studies (i.e., 0.05 MHz = 37 dB, 1000 MHz = 1 dB) without pretreatment of fabrics. Possible application of these fabrics, e.g., for dissipation of electrostatic charge, is suggested. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2316–2323, 2005

Polyaniline reinforced conducting E-glass fabric using 4-chloro-3-methyl phenol as secondary dopant for the control of electromagnetic radiations

A method is described to increase the shielding effectiveness (SE) of polyaniline grafted E-glass fabric to control electromagnetic radiations. This process involves the pretreatment of glass fabric with aqueous solution of 10% maleic anhydride prior to grafting of polyaniline by in situ polymerization of aniline. The polyaniline grafted E-glass fabrics treated with polyaniline solution in chloroform is prepared using either p-toluene sulphonic acid (PTSA) or camphor-10-sulphonic acid (CSA) as dopants and 4-chloro-3-methyl phenol (CMC) as secondary dopant to get pore free polyaniline coating of thickness of 100 μm. The resulting pore free conducting fabric of 3 mm thick offered maximum SE of 54 dB at 1000 MHz. The conducting fabrics were characterized by UV–Vis spectroscopy, Conductivity, SEM, XRD, TGA and shielding effectiveness measurements. The SE measurements were carried out using co-axial transmission line method in the frequency range of 0.1–1000 MHz. The study indicates that SE increases with increase in thickness and conductivity of test coupons.

Freestanding conducting polyaniline film for the control of electromagnetic radiations

Abstract Electromagnetic interference is pollution generated due to dense nature of circuitry in electronic devices and is required to be control at its source. Polyaniline is an environmentally stable conducting polymer which can be cast as thin film, which can replace the corrosive metals as a shield for the control of electromagnetic radiations. In this communication we discuss our results on the preparation of flexible freestanding conducting polyaniline film of varied thickness using either p -toluenesulphonic acid (PTSA) or camphor-10-sulphonic acid as a primary dopant and 4-chloro-3-methyl phenol (CMC) as a secondary dopant. The resulting films were characterized by conductivity, scanning electron micrograph and shielding effectiveness measurements (SE). The SE measurements were carried out using co-axial transmission line method in the frequency range of 0.1–1000 MHz. We noticed that only the change of 2% in the shielding effectiveness of these films over the period of 3 years indicating the environmental stability of polyaniline films.

Estimation of the electric parameters of thin electromagnetic shielding materials

AbstractIt is important to know the electric parameters of the shielding material for numerical analysis. The purpose of this report is to estimate electric parameters of thin shielding materials. The electromagnetic field in the vicinity of a horizontal multilayered material with a magnetic dipole source is calculated numerically by a Sommerfeld integral. On the basis of this calculation, we develop a “shielding box” for measuring the shielding effectiveness (SE) with little error. We compare the magnetic SE measured with the shielding box with that obtained by calculation to evaluate this method. Because calculation results are in good agreement with measurement results, we confirm that we can measure magnetic SE of thin shielding materials with this system. Next, we propose a method to estimate unknown electric parameters of shielding materials by using the SE measurement system and the numerical calculation. The electric parameters are derived by iterating numerical calculations to fit the experimental results within 1‐dB error. We estimated the electric parameters of A1 (aluminum) material. Fitted results are in good agreement with the well‐known values, demonstrating the validity of the developed method. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 147(1): 1–9, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.10273

New Figures of Merit for the Characterization of the Performance of Shielding Enclosures

Evaluation and measurement of shielding performance of enclosures and protection structures in general are based on the comparison between the local field values with and without the shield. Apart from some practical problems arising in specific, but relevant, situations like enclosures of small dimensions, such an approach appears rather incomplete and sometime deceitful. Despite this, shielding effectiveness (SE) is a well-established parameter, and it seems that for decades, the attention has been focussed more on how to evaluate and measure the so-called SE, rather on what the goal of any shielding structure is and why each evaluation and measurement should be performed. The main drawback is that SE is a local quantity and its knowledge does not help in the prediction of the real mitigation of undesired effects achieved by means of any shielding structure; undesired effects are mainly due to an integral of an electric or magnetic field, and/or to spatial variations of electric and magnetic field components. In the past, proposals were advanced toward an improved definition and measurement of electromagnetic SE; the proposed new figures of merit were based on the energy (power) penetrating the enclosure, perceived as the key factor for the shielding problem. However, it seems more adequate and correct the direct reference to the mechanism of birth of induced effects, as stemming from Maxwell equations. For these reasons, two new figures of merit are proposed for the comparison of enclosures and shields performance.

The novel technology of the functional fabric composed of polypropylene non-woven selvages, polyester filaments and copper wire

Our process and products were innovative and creative. In order to produce multifunctional fibre products, we combined two or more different kinds of fibres, instead of one single fibre, to spin the ply yarn and weave them into fabrics in the hope that the final products would meet our requirements. The process in this research was innovative and high technical. The ply yarn and fabrics we made possessed high performance and diversity, and they were recyclable and practical. The ply yarn consisting of polypropylene non-woven selvages, copper wires and polyester filaments with a rotor twister possessed superior electrical and mechanical properties due to the natural characteristics of the filaments. The ply yarn was produced under different conditions of twister counts and rotor speeds, and then was woven with a rapier loom. By varying manufacturing parameters, the helix angle and tightness of the twist-wrapped yarn were also changed to enhance the mechanical properties and EMI shielding effectiveness. In this paper, the optimum condition for producing the ply yarn wrapped with metallic filaments was under the rotor speed of 8000 rpm and 2.5 turns/cm, and that with polyester filaments was 6000 rpm and 1.0 turn/cm. After the measurement of electromagnetic shielding effectiveness, we found the fabrics that fabricated with the ply yarn could take as the electromagnetic shielding materials. The weight percentage of the metallic fibre was only 3.40–4.45 wt% and the value of the shielding effectiveness was 10–20 dB.

Size reduction of the door seal structure of a microwave oven by the FD‐TD method

AbstractAssuming a choke groove depth of half the present value, the FD‐TD method is used to obtain a value for the effectiveness of shielding against leakage waves that is very close to the actual value, including higher modes. To reduce computation time, the optimum dimension is first calculated for a TEM mode wave incident on a choke groove with a two‐dimensional cross section. Using the calculated optimal data, a three‐dimensional choke groove with periodic slits is analyzed and evaluated. To further compensate for the degradation of shielding effectiveness due to reduction in size, the case in which a lossy material and the groove are combined is also investigated. A choke based on the results of the analysis gave a measured shielding effectiveness of approximately 31 dB, providing an experimental demonstration of the validity of the analysis. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(10): 73–83, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10190

Shielding effectiveness measurements of materials using nested reverberation chambers

The use of reverberation chambers for determining the shielding effectiveness has the advantage over other techniques in that the reverberation chamber exposes the material to a more realistic environment. That is, in a reverberation chamber, the fields are incident on the material with various polarizations and angles of incidence. There are various reverberation chamber techniques found in the literature and international standards. These techniques can give incorrect results because aperture and cavity-size effects are not correctly accounted for. In fact, we show that for no sample in the aperture, these techniques give a nonzero result for shielding effectiveness. In this paper, we review existing techniques and present a new technique for determining the shielding effectiveness of materials from nested reverberation-chamber measurements. The new approach accounts for aperture, cavity size, and chamber loading effects. Various examples are presented to illustrate the utility of the new approach, and a discussion on edge treatments of the materials is given.

Semi-empirical modeling of apertures for shielding effectiveness simulations

A novel method to include models of complex apertures into the finite-difference time-domain (FDTD) method is presented. Instead of resolving the geometrical details of the aperture, the aperture is treated as a magnetic dipole. The properties of the magnetic dipole moment are determined using the measured transmission cross section of the aperture. This semi-empirical model permits inclusion of complex apertures in FDTD simulations where the smallest dimension of the aperture is only a fraction of the FDTD cell size. Two types of complex apertures positioned in the top panel of a realistic enclosure have been modeled using the semi-empirical model in FDTD. Comparisons between simulated and measured shielding effectiveness of the enclosure are presented, and the results show that complex apertures can indeed be represented by simple magnetic dipoles in shielding effectiveness simulations.

THE NOVEL TECHNOLOGY OF FUNCTIONAL FABRICS COMPOSED OF POLYPROPYLENE NONWOVEN SELVAGE/POLYESTER/STAINLESS STEEL

Nowadays, the Green Environment Protection is popular, and the synthetic fiber nonwoven is recyclable and reusable to fabricate functional products with high additional values. It is because that the synthetic fibers used in the nonwoven industry are almost thermoplastic polymer. In this study, we adopted stainless steel filament as functional metal fiber, polypropylene nonwoven waste as filled material and reinforced it with polyester filament. Our process and products were innovative and creative. In order to produce multifunctional fiber products, we combined two or more different kinds of fibers, instead of one single fiber, to spin the ply yarn and weave them into fabrics in the hope that the final products would meet our requirements. The process in this research was innovative and high technical. The ply yarn and fabrics we made possessed high performance and diversity, and they were recyclable and practical. The functional ply yarn and its fabric responded to the electrical functional demands. The products can be applied on the anti-electrostatic fabric or processed into artificial composites. In this research, the functional ply yarn was produced with an innovative rotor-wrappingtwister. The yarn consisted of polyester filaments, stainless steel filament and polypropylene nonwoven selvages. The speed of the rotor-wrapping-twister and the wrapping counts were the parameters in the manufacturing process. Then the ply yarn was woven into plain fabrics with a rapier loom. Finally, we investigated the tensile properties and maximum breaking strength utilization factors of the fabrics. The maximum breaking strength and elongation of the PS group (core materials were polyester filaments and polypropylene nonwoven selvages, and wrapping material was a stainless steel filament) were better at higher rotor speed (8000 rpm). The influence of the wrapping counts on the tensile properties was different while we used different wrapping materials. After the measurement of electromagnetic shielding effectiveness, we found the fabrics that fabricated with the ply yarn could take as the electromagnetic shielding materials. The weight percentage of the metallic fiber was only 3.52 ∼ 4.58 wt % and the value of the shielding effectiveness was 10 ∼ 25 dB.

Electromagnetic shielding characteristics of optical-fiber feedthroughs

A number of commercially available optical-fiber connector styles ST, SC, and FC were tested to determine the extent to which their use in bulkhead adapter feedthroughs would compromise the shielding of electromagnetic interference for electronic enclosures. Connectors and adapter barrels made from metal, ceramic, and polymer materials were included in the tests. The tests were carried out using a nested reverberation cell and covered a frequency range from 1 to 16 GHz. Although we rely on data acquired by making shielding effectiveness (SE) measurements, we report the results in terms of a transmission cross-section which is the ratio of the power coupled into an enclosure through an aperture to the power per unit area incident on the aperture. The amount of coupling through the feedthroughs we tested varied over 70 dB. The shielding of an all-metal FC connector system was nearly equal to that of a blank reference plate. In some cases, a feedthrough coupled more energy into the enclosure than was coupled through the empty hole required to mount the adapter barrel. Unlike SE, the transmission cross sections do not depend on the volume, shape, or construction materials of the enclosure and can be used to estimate the degradation in the SE for enclosures other than our reference cell. The uncertainties in the reported transmission cross sections are calculated to be /spl plusmn/3 dB and are small compared to the differences between the measured cross sections.

Measurements and simulations of cable shielding against magnetic field induction

Summary form only as given. An experimental setup with loop configurations is applied to measure the performance of cable shielding against the magnetic field induction at power frequencies. Such scheme is preferred for shielding measurements in a small test region to avoid the influences of the ground potential rises and the grounding resistances. A quasi-static two-wire transmission line model has been used to simulate and verify the experimental results of the loop circuits. Besides, to test the application of the loop configurations for practical station-to-station routing of the cables, shielding properties obtained from the loop approach are compared with those of the straight parallel circuits determined by using the Electromagnetic Transients Program (EMTP). In addition, methods for improving the shielding of the magnetic field induced voltages excited from power line faults have been investigated by using the EMTP. An approach to correct the geometrical effects of the loop configurations on the measured shielding effectiveness of the cables for the straight parallel circuits is also proposed. Cables with good shielding performance may be designed and tested by using the methods presented in this paper.

Electromagnetic shielding effectiveness of galvanostatically synthesized conducting polypyrrole films in the 300–2000 MHz frequency range

Both far-field (plane wave) and near field shielding effectiveness (SE) measurements have been conducted on electrochemically synthesized conducting polypyrrole (PPy) films with wide ranging conductivity levels (10 −2 S/cm to 45 S/cm). Co-axial transmission line, TEM test cell and TE 10 waveguide techniques were employed to measure shielding effectiveness as a function of polymer conductivity, frequency and temperature. Highly doped polypyrrole films exhibited shielding levels, above 40 dB from 300 MHz to 2 GHz, which can make them attractive for consideration in shielding applications. However, a loss of 10 to 15 dB in the shielding effectiveness, for the samples aged for a period of two years at room temperature, was observed. SE of PPy films increased with the increase in the dopant concentration and decreased with frequency reaching a plateau at higher frequencies. However, corrected SE values as a function of frequency appeared relatively flat. The measurements made directly on the TEM-t cell would simulate high impedance condition (E-field) due to the capacitive coupling, and use of the correction factors therefore eliminated this condition, giving rise to corrected far-field SE values. Using the theory for plane wave shielding effectiveness of thin material shields, the agreement between the theory and experimental results were tested. Effect of temperature on the plane-wave SE of a lightly doped (0.006 M p-TS) PPy film was also investigated. Results showed significant increase in the SE with temperature. At room temperature the lightly doped PPy film with a dc conductivity of 0.01 S/cm was almost transparent to microwaves with very little reflection or absorption. However as the temperature increased SE increased significantly because of the increase in conductivity of the sample.

Measurement of material shielding effectiveness using a dual TEM cell and vector network analyzer

This paper deals with material shielding effectiveness (SE) measurements made with a system based on a vector network analyzer (VNA) and a dual TEM cell (DTEM). This system allows the separate measurement of the electric and magnetic SE (within the system dynamic range). A description of the measurement system is given together with a summary of the theory used. The limitations of the measuring system are also analyzed and discussed presenting some sample measurements.

The effects of intrinsic test fixture isolation on material shielding effectiveness measurements using nested mode-stirred chambers

The paper evaluates the effects of test fixture isolation when using nested mode-stir chambers for conducting electromagnetic shielding measurements. The nested chamber technique is used by both government and industry to evaluate the electromagnetic attenuating properties of materials as varied as infrared sensor windows to the composites used in the hulls of new ships. Two cases are considered: (1) the test aperture provides little inherent isolation between the two chambers, and (2) the aperture provides reasonably good isolation. It is shown that in the former case, data taken in this fashion can exhibit significant deviation from the latter. A correction factor for the former case is developed. >

Correlation between shielding effectiveness measurements and alternative methods for the characterization of shielding materials

The correlation between different methods for the characterization of shielding materials is discussed. It is found that a good agreement is obtained using basic methods, such as a four-point resistance measurement, or standard shielding effectiveness methods and using other methods allowing a quick control in the field during injection moulding process.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Aperture coupling to a coaxial air line: theory and experiment

Coupling through a circular aperture in the shield of a coaxial air line is studied theoretically and experimentally. Polarizability theory is used to compute the effective dipole moments that excite the coaxial line in the internal region. Measurements of shielding effectiveness were made in a reverberation chamber over wide frequency ranges. Agreement between theory and measurements is generally within +or-10 dB. Recommendations for improvements in the measurements and theory are made for achieving the closer agreement that would be desirable for an artifact standard for shielding effectiveness measurements. >

The influence of the test fixture on shielding effectiveness measurements

In the past, different test cells were used to measure the shielding effectiveness (SE) of materials against electromagnetic radiation, for far-field (or plane wave) conditions. Recently, a new standard was approved. However, some errors may occur, especially in the case of filled conductive plastics, where the conductive layer is not directly accessible from the surface of the material. As well as reporting on some of the difficulties and problems encountered when measuring the SE of this family of materials, the authors propose a different technique for measuring far-field conditions.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The fabrication and characterization of high temperature superconducting magnetic shields

Tubes fabricated of polycrystalline YBa/sub 2/Cu/sub 3/O/sub 7-x/ are characterized, and details of the fabrication procedure are discussed. The microstructure of the tubes determined by scanning electron microscopy and X-ray diffractometry is described. Resistive measurements of T/sub c/ and Delta T/sub c/ have been made. The tubes have also been characterized by means of SQUID (superconducting quantum interference device) magnetometry. The temperature dependence of magnetic fields trapped axially in the tubes has been measured and estimates of penetration depth are given. Moreover, measurements of the transverse shielding effectiveness of the tubes have been made and are compared with theoretical predictions. Studies on flux penetration into the tubes are described. Findings from the microstructure studies are correlated with the observed superconductivity properties. The results on the high-temperature materials are compared to results obtained previously on tubes made from conventional superconductors.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>