Accurate measurement of the true plane-wave shielding effectiveness of thick polymer composite materials via rectangular waveguides

This paper presents a methodology for accurately gauging the true plane wave shielding effectiveness of composite polymer materials via rectangular waveguides. Since the wave propagation of the waveguides is not in the form of plane wave patterns, it is necessary to post-process the S-parameters for the measured data of the waveguide lines to obtain such patterns and ascertain the effectiveness of true plane wave shielding. The authors propose two different methods to achieve this. The first applies simple renormalization of S-parameters, where reference impedance is changed from the value for the waveguide to that for free space, which ensures good accuracy of shielding effectiveness with a small degree of discontinuity across the range of frequencies. The other relies on rigorous extraction of the composite materials' effective permittivity and permeability ascertained from rectangular waveguides; afterward, plane wave shielding effectiveness is calculated analytically and gives very high accuracy. Both procedures assume the given samples are isotropic in character. We validated the accuracy of the methodologies by conducting tests on a set of synthetic samples of 2 mm thickness with unit permittivity and variable conductivity and on a dielectric material of known permittivity (FR4 laminate). The applicability of both methods was further proven by analyzing the isotropic composite materials, a process involving the use of iron particles embedded in a dielectric matrix. The synthetic samples and an FR4 material were tested to check the accuracy of the methods. Based on numerical studies and measurements, we concluded that materials with a shielding effectiveness of up to 25 dB could be measured at a maximum amplitude error of 1 dB to 3dB to a frequency of 18 GHz, depending on the relative permittivity of the material; hence, the first method was suitable for approximation purposes. For maximal accuracy, the second method typically demonstrated an amplitude error of below 0.5 dB to the same frequency across the entire range. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.Czech Science FoundationGrant Agency of the Czech Republic [17-24730S]; Ministry of Education, Youth, and Sports of the Czech Republic-under the programme NPU I [LO1504]; project entitled Support of Sustainability and Development by the Centre for Security, Information and Advanced Technologies [LO1303

Shielding Properties of Cement Composites Filled with Commercial Biochar

The partial substitution of non-renewable materials in cementitious composites with eco-friendly materials is promising not only in terms of cost reduction, but also in improving the composites’ shielding properties. The water and carbon content of a commercial lignin-based biochar is analyzed with thermal gravimetric analysis. Cementitious composite samples of lignin-based biochar with 14 wt.% and 18 wt.% are realized. Good dispersion of the filler in the composites is observed by SEM analysis. The samples are fabricated in order to fit in a rectangular waveguide for measurements of the shielding effectiveness in the X-band. A shielding effectiveness of 15 dB was obtained at a frequency of 10 GHz in the case of composites with 18 wt.% biochar. Full-wave simulations are performed by fitting the measured shielding effectiveness to the simulated shielding effectiveness by varying material properties in the simulator. Analysis of the dimensional tolerances and thickness of the samples is performed with the help of full/wave simulations. Lignin-based biochar is a good candidate for partial substitution of cement in cementitious composites, as the shielding effectiveness of the composites increases substantially

Dielectric, magnetic and electromagnetic shielding properties of Poly-(3,4ethylenedioxythiophene)-maghnite associated with different fillers with any non-canonical shape

A new inverse measuring technique that corrects non-desired sample displacements and can handle any kind of sample shapes is presented. It is applied to the estimation of permittivity and permeability of Poly-(3,4ethylenedioxythiophene)-maghnite (PEDOT-Mag) associated with different additives such as iron, copper, and hydrogen. This electromagnetic characterization has been performed over the 9 to 11 GHz frequency range by comparing the simulated and measured scattering parameters of a partially filled WR-90 waveguide. Additionally, the reflection, absorption multiple reflection losses and the shielding effectiveness of these materials have been calculated. Results show higher values of dielectric constant and loss factor for PEDOT-Mag-copper, than those compounds associated with hydrogen or iron. As expected, the highest permeability values are achieved by PEDOT-Mag-iron. The composite PEDOT-Mag-copper exhibits higher attenuation constant, absorption loss, multiple reflection loss and shielding efficiency values than composites associated with iron or hydrogen. PEDOT-Mag-hydrogen, however, shows the highest reflection loss values

EFFECT OF GRAPHITIC CARBON NANOMODIFIERS ON THE ELECTROMAGNETIC SHIELDING EFFECTIVENESS OF LINEAR LOW DENSITY POLYETHYLENE NANOCOMPOSITES

Conductive polymer composites have become alternative materials for providing electromagnetic and electrostatic shielding where metals are not suitable. In this study, the effect of crystallinity, morphology, concentration and orientation of carbon nanomodifiers on shielding provided by their polyethylene-based composites has been investigated relative to their transport properties. First, the electrical properties and EM SE of composites consisting of heat-treated carbon nanofibers (Pyrograf® -III PR-19 CNF) in a linear low density polyethylene (LLDPE) matrix were assessed. Heat treatment (HT) of CNF at 2500°C significantly improved their graphitic crystallinity and intrinsic transport properties, thereby increasing the EM SE of the nanocomposites. Although the strain-to-failure was about one-third that of pure LLDPE, the absolute value of 180±98% indicates a significant retention of ductility. Second, the influence of the morphology of carbon modifiers on the electrical, thermal and mechanical properties of their composites was investigated. Four heat-treated carbon modifiers were investigated: PR-19 HT carbon nanofibers, multi-walled carbon nanotubes (MWNT HT), helical multi-walled carbon nanotubes (HCNT HT), and pitch-based P-55 carbon fibers (CF). MWHT HT, with the highest aspect ratio, led to the largest composite electrical and thermal conductivities (34 S/m, 1 W/m.K) and EM SE (~24 dB). In contrast, HCNT HT, due to their coiled shape and low aspect ratio, led to a non-percolating microstructure in the composites, which produced poor EM SE (dB). Nonetheless, HCNT HT composites displayed the highest ductility (~250%) and flexibility, which is probably owed to the matrix-modifier mechanical bonding (interlocking) provided by the helical morphology. Using the carbon modifiers that previously led to the best EM SE (i.e., PR-19 HT and MWNT HT), the influence of composite electrical properties on the plane-wave EM SE in the VHF-UHF bands was studied further. Both graphitic nanomodifiers were dispersed in LLDPE matrix to produce a nominally random in-plane modifier orientation. For a concentration of 10 vol% nanomodifiers, EM SE values of 22 dB and 24 dB were obtained for PR-19 HT and MWNT HT nanocomposites (2.5-mm thick), respectively. At a high concentration of 40 vol%, EM SE values as high as 68 dB and 55 dB were respectively attained. Because such nanocomposites possess only moderate electrical conductivity, a model for generally-lossy materials was used to predict the plane-wave EM SE and its components. Based on the material properties of the nanocomposites, the predicted values of EM SE were found to be consistent with the experimental values. Finally, the electrical conductivity and EM SE of nanocomposites that contained 10 vol% of oriented graphitic nanomodifiers (PR-19 HT and MWNT HT) in LLDPE are reported. Micro-filament spinning was used to generate flow-induced orientation of the carbon nanomodifiers. Consequently, the conductivity of the resulting nanocomposites exhibited anisotropy. Thus, the in-plane conductivity in the longitudinal direction (PR-19 HT comp.: ~0.02 S/m; MWNT HT comp.: ~3 S/m) was at least an order of magnitude higher than that along the transverse direction. As measured with a rectangular waveguide (WR510, 1.45-2.2 GHz), the PR-19 HT and MWNT HT oriented nanocomposites (1-mm thick) displayed EM SE values of 0.7±0.4 dB and 3.0±0.8 dB, respectively, when the nanomodifiers were transversely oriented with the polarized electric field. In contrast, when the orientation of the nanomodifiers was parallel with the field, values of 3.2±1.0 dB and 9.0±1.0 dB were obtained, respectively. Therefore, as a result of this anisotropy, as analyzed by polarized electromagnetic waves, the composites displayed anisotropic shielding. (Abstract shortened by UMI.

Millimeter wave transmission systems and related devices

A survey was made of the state-of-the-art in millimeter (20 GHz to 300 GHz) wave transmission systems and related devices. The survey includes summaries of analytical studies and theoretical results that were obtained for various transmission line structures. This material was supplemented by further analysis where appropriate. The transmission line structures are evaluated in terms of electrical performance, ease of manufacture, usefulness for building other devices and compatibility with solid state devices. Descriptions of waveguide transmission lines which have commonly been used in the microwave frequency range are provided along with special attention given to the problems that these guides face when their use is extended into the millimeter wave range. Also, guides which have been introduced specifically to satisfy the requirements of millimeter wave transmission are discussed in detail

EMI measurement and modeling techniques for complex electronic circuits and modules

This dissertation consists of four papers. In the first paper, a combined model for predicting the most critical radiated emissions and total radiated power due to the display signals in a TV by incorporating the main processing board using the Huygens Equivalence theorem and the radiation due to the flex cable based on active probe measurements was developed. In the second paper, a frequency-tunable resonant magnetic field probe was designed in the frequency range 900-2260 MHz for near-field scanning applications for the radio frequency interference studies by using a varactor diode providing the required capacitance and the parasitic inductance of a magnetic field loop (i.e., a parallel LC circuit). Measurement results showed good agreement with the simulated results. In the third paper, a wideband microwave method was developed as a means for rapid detection of slight dissimilarities (including counterfeit) and aging effects in integrated circuits (ICs) based on measuring the complex reflection coefficient of an IC when illuminated with an open-ended rectangular waveguide probe, at K-band (18-26.5 GHz) and Ka-band (26.5-40 GHz) microwave frequencies. In the fourth paper, a method to predict radiated emissions from DC-DC converters with cables attached on the input side to a LISN and on the output side to a DC brushless motor as load based on linear terminal equivalent circuit modeling was demonstrated. The linear terminal equivalent model was extracted using measured input and output side common mode currents for various characterization impedances connected at the input and output terminals of the converter --Abstract, page iv

Carbon Nanotube Composites as Electromagnetic Shielding Materials in GHz Range

Following the development of the new electronic systems and communication networks, the levels of electromagnetic contamination have risen dramatically in the recent years. Every day, new studies appear searching for a way to mitigate the electromagnetic interferences (EMI). At the same time, the rapid evolution of technology forces the field to search for lighter and more efficient materials. The composites using carbon allotropes (such as carbon nanotubes) and polymers as reinforcement are gaining importance, due to the many advantages they exhibit in comparison to the materials that were used until now. A great number of applications require absorption to be the main electromagnetic shielding mechanism, thereby making this review necessary as a way to summarize the latest studies on CNT/polymer composites and how to improve the absorption mechanism by changing the morphology and composition of CNTs

Shielding Effectiveness Measurements of Drywall Panel Coated with Biochar Layers

Shielding against electromagnetic interference (EMI) is a critical issue in civil applications generally solved with metal screens. In recent years, the properties of many composite materials filled with carbon nanotubes or graphene or materials with a carbon-based coating have been analysed with the aim of using them for electromagnetic shielding applications. Among other carbon materials, biochar, derived from biomass and characterized by high carbon content, emerges as a sustainable, renewable, environmentally friendly, and inexpensive material. In this paper, commercial biochar thermally treated at 750 °C is used to coat with several layers common building components such as drywall panel. Shielding effectiveness is measured in the frequency band 1–18 GHz for normal incidence and skew angles 10, 20 and 30 deg in a full anechoic chamber with double ridged, vertically and horizontally polarized broadband horn antennas. The results show that the proposed biochar-coated drywall panels provide a good shielding effectiveness compared to similar solutions, with the advantage of a less expensive and easier to realize building material

Review of applications of the Laboratory for Electromagnetic Compatibility infrastructure

This article provides a thorough description of a range of non-standard application cases in which EMC laboratories can be used other than those traditionally associated with this kind of facilities. The areas covered here include investigations of: wireless and radio systems (such as IoT and broadband radio systems) also that require ultra-high operational dynamic range, emulation of interference-free and/or heavily-multipath propagation environment, shielding effectiveness of cabinets and materials (i.e. thin, light and flexible as textiles as well as heavy and thick such as building construction elements)

Electric and Magnetic Characterization of Materials

none3The knowledge of the electric and magnetic properties of materials over a broadband frequency range is an essential requirement for accurate modelling and design in several engineering applications. The interaction of incident electromagnetic fields with a material can be successfully investigated only when accurate information on the complex permittivity and magnetic permeability is attained. Regardless of the technique used for the measurement, the common challenge is the extraction of the complex relative permittivity and/or magnetic permeability from measured data by expressing the measured quantities as a function of these parameters. The inversion problem to be solved is thus affected by the mathematical model, i.e., the theoretical expressions that relate the electrical and/or magnetic parameters to the measured quantities. The inversion problem can be solved with deterministic or stochastic methods. The complex relative permittivity and magnetic permeability can be determined over the whole frequency range of interest or on a point-by-point basis (at individual frequency points).mixedL. Sandrolini; U. Reggiani; M. ArtioliL. Sandrolini; U. Reggiani; M. Artiol