Electromagnetic Interference Shielding Characteristics Research Articles

Electromagnetic interference shielding characteristics of a core layer-coated fabric with excellent hand-feel characteristics

Electromagnetic shielding fabric (ESF) is a novel electromagnetic shielding product with portability, flexibility, and good mechanical properties. However, the existing ESFs suffer from poor washing fastness of coating and poor comfort performance in terms of hand-feel characteristic. In this study, a core layer-coated yarn (CLCY) was successfully spun using a carboxylic acid-functionalized multi-walled carbon nanotube/polypyrrole/Fe3O4 composite suspension with polyvinyl butyral as an adhesive agent. To better explore the properties, the original fabric and treated fabrics, viz., core layer-coated fabric (CLCF) and surface layer-coated fabric (SLCF), were characterized by several methods. Scanning electron microscopic observations revealed that the coating was on the core layer in CLCF. In addition, the Fourier-transform infrared spectroscopy and X-ray diffraction spectroscopy results revealed that the composition of the coating corresponds with that in the multi-composite suspension. Moreover, the coating of CLCY formed a conductive path with good conductivity in the core layer, but the conductivity of the coating on the surface layer of SLCF deteriorated sharply after washing. Further, compared with the original fabric and SLCF, CLCF has highest breaking strength (after 10 washes), and keeps a relatively good hand-feel characteristic. Finally, the evaluated electromagnetic interference shielding characteristics reveal that the fastness of coating affects the electromagnetic shielding effectiveness, suggesting that the wrapped protection of outside staple fibers in CLCF reduce the loss of coating in the core layer during washing. However, the coating on the surface layer in SLCF could be washed away easily.

Dynamic mechanical analysis and broadband electromagnetic interference shielding characteristics of poly (vinyl alcohol)-poly (4-styrenesulfonic acid)-titanium dioxide nanoparticles based tertiary nanocomposites

ABSTRACTNovel tertiary nanocomposite films comprising of poly (vinyl alcohol) (PVA), poly (4-styrenesulfonic acid) (PSSA) and titanium dioxide (TiO2) nanoparticles (NPS) were prepared using simple solvent casting method. The structural, thermal, morphological, thermo-mechanical and electromagnetic interference (EMI) shielding properties of PVA/PSSA/TiO2 nanocomposite films were investigated. The EMI shielding effectiveness (SE) of PVA/PSSA/TiO2 nanocomposite films in the X and Ku band was found to be 12 dB and 13 dB respectively at 25 wt% TiO2 NPs loading. These results demonstrate the possible applications of PVA/PSSA/TiO2 nanocomposite films as low cost, lightweight and flexible material for EMI shielding.

EMI Shielding Characteristics of Electrically Conductive Polymer Blends of PS/PANI in Microwave and IR Region

Conductive polymeric blends (CPBs) of polystyrene and polyaniline (PS/PANI) were prepared by solution casting method in various compositions. Film thickness of CPBs was achieved ∼ 250 micron. PS/PANI blend films were analyzed for electromagnetic interference (EMI) shielding characteristics in microwave and near-infrared (NIR) regions. PS/PANI blends showed remarkable features. Most mobile telecommunications use GHz frequency range and shielding effectiveness was observed in 9 GHz to 18 GHz. In 9 GHz to 18 GHz frequency range, 45 dB shielding effectiveness was measured. CPBs were also analyzed in the NIR region and showed transmittance of <1%. Microwaves and NIR radiation are the most abundant in the environment and cause damage to human health. Both types of radiation causes serious damage to electronic devices as well.

Impact of pyrolytic carbonaceous nano inerts addition on fracture and electromagnetic interference shielding characteristics of cementitious composites

The fragile behavior of traditional cementitious composites can be tweaked by reinforcing the matrices at nano scale via intrusions of carbonaceous inerts. However, high fabrication cost of these inerts barred their extensive industrial application. In the present study, cost-effective carbonaceous nano-inerts were synthesized via pyrolysis of agricultural wastes in the form of wheat straw and cotton stalk at a temperature of 500 °C in an inert environment. Carbon rich solid residue obtained from pyrolysis was milled to nano size and characterized through energy dispersive X-ray spectroscopy, X-ray diffraction analysis, thermogravimetric analysis, Fourier transform infrared spectroscopy and Raman spectroscopy. Synthesized carbonaceous nano-inerts from wheat straw and cotton stalk have been intruded in to cementitious matrix for the first time in the best knowledge of author, to enhance its fracture characteristics and electromagnetic interference shielding effectiveness. Cement mortar specimens were prepared with the intrusions of carbonaceous nano-inerts by 0.025, 0.05, 0.08, 0.2, 0.5 and 1 wt% of cement in addition mode, after being effectively dispersed in water. Three point bending tests were performed on notched prisms at a very sensitive strain rate of 0.003/min in strain controlled mode with the broken halves analyzed for resistance in compression. Substantial increase of 59.8% in fracture toughness and 44.5% in compression was attained with the addition of 1% carbonized cotton stalk and 0.5% carbonized wheat straw respectively. Moreover, scanning electron micrographs have verified the involved strengthening mechanisms encompassing crack branching, pinning and crack bridging via intruded nano-inerts. Furthermore, shielding against electromagnetic interference was tested in X-band frequency range of 8–12 GHz and maximum improvement of 23.5db and 22.9db was attained with intrusion of carbonized wheat straw and carbonized cotton stalk nano particles respectively.

Polypropylene Nanocomposite Filled with Spinel Ferrite NiFe2O4 Nanoparticles and In-Situ Thermally-Reduced Graphene Oxide for Electromagnetic Interference Shielding Application.

Herein, we presented electromagnetic interference shielding characteristics of NiFe2O4 nanoparticles—in-situ thermally-reduced graphene oxide (RGO)—polypropylene nanocomposites with the variation of reduced graphene oxide content. The structural, morphological, magnetic, and electromagnetic parameters and mechanical characteristics of fabricated nanocomposites were investigated and studied in detail. The controllable composition of NiFe2O4-RGO-Polypropylene nanocomposites exhibited electromagnetic interference (EMI) shielding effectiveness (SE) with a value of 29.4 dB at a thickness of 2 mm. The enhanced EMI shielding properties of nanocomposites with the increase of RGO content could be assigned to enhanced attenuation ability, high conductivity, dipole and interfacial polarization, eddy current loss, and natural resonance. The fabricated lightweight NiFe2O4-RGO-Polypropylene nanocomposites have potential as a high performance electromagnetic interference shielding nanocomposite.

Electrical and electromagnetic interference shielding characteristics of GNP/UHMWPE composites

Conductive polymer composites (CPC) are attractive materials for a wide range of applications because of their weight, corrosion resistivity, design flexibility and low cost. In the present work, the electrical and electromagnetic interference (EMI) shielding characteristics of graphene nanoplatelets (GNP)/ultrahigh molecular weight polyethylene (UHMWPE) composites filled with up to 40 wt% GNP were investigated. In addition, the intrinsic conductivity of the GNP network was estimated based on the statistical power law and the rule of mixtures for randomly oriented filler particles in insulating matrix. Due to the formation of a segregated conductive network at the external surface of UHMWPE powder, an electrical percolation threshold of between 2 and 3 wt% GNP was obtained. At GNP loading of 15 wt%, the composite exhibited an EMI shielding effectiveness of 33 dB, corresponding to 99.95% blocking of the EMI.

Carbon nanotubes and carbon onions for modification of styrene–acrylate copolymer nanocomposites

Styrene acrylate polymer (SAC) nanocomposites with various carbon nanofillers (multi‐walled carbon nanotubes, MWCNT, and onion like carbons, OLCs, annealed at two different temperatures) are manufactured by means of latex based and combined routes. Concentration of the carbon nanofillers is changed in a broad interval starting from 0.01 up to 10 wt%. Elastic, dielectric, and electromagnetic interference (EMI) shielding efficiency of SAC nanocomposites are investigated. Dynamic elastic modulus, electrical conductivity, and EMI shielding efficiency of the investigated SAC nanocomposites increase along with rising nanofiller content. The effect of the addition of anisodiametric MWCNT on the elastic properties as well as EMI shielding characteristics of the SAC nanocomposites is higher than in the case of the addition of OLCs. Modification effectiveness of the polymer matrix in respects to elastic and EMI shielding performance provided by the OLC, annealed at higher temperature, is greater in comparison with the OLC, annealed at lower temperature, generally because of more perfect structure of the first. POLYM. COMPOS., 36:1048–1054, 2015. © 2015 Society of Plastics Engineers

Electromagnetic interference shielding characteristics for orientation angle and number of plies of carbon fiber reinforced plastic

Recently, methods that usea carbon-based filler, a conductive nanomaterial, have been investigated to develop composite fillers containing dielectric materials. In this study, we added geometric changes to a carbon fiber, a typical carbon-based filler material, by differentiating the orientation angle and the number of plies of the fiber. We also studied the electrical and electromagnetic shield characteristics. Based on the orientation angle of , the orientation angle of the carbon fiber was changed between 0, 15, 30, 45, and , and 2, 4, and 6 plies were stacked for each orientation angle. The maximum effect was found when the orientation angle was , which was perpendicular to the electromagnetic wave flow, as compared to , in which case the electrical resistance was small. Therefore, it is verified that the orientation angle has more of an effect on the electromagnetic interference shield performance than the number of plies.

Spin-flop transition, magnetic and microwave absorption properties of α-Fe2O4 spinel type ferrite nanoparticles

We have prepared NiFe2O4, CoFe2O4, Ni0.6Zn0.4Fe2O4 and ZnFe2O4 spinel type ferrite nanoparticles by surfactant-assisted hydrothermal process using cetyltrimethylammonium bromide (CTAB). The spin-flop transition, magnetic, dielectric and permittivity characterizations have been investigated. The spin-flop transition occurs from antiferromagnetic state to mixed state and then ferromagnetic state for Zn doped samples. The spin-flop transition occurs in the temperature range of 50–250K. The ionic conduction, dipolar relaxation, atomic polarization and electronic polarization are the main mechanisms that contribute to the permittivity of a dielectric material. The permittivity increases with increasing frequency. This suggests a resonance behavior, which is expected when the ferrite samples are highly conductive and skin effect become significant. These samples will provide great benefits for electromagnetic applications and electromagnetic interference shielding characteristics.

Synergetic improvement in electromagnetic interference shielding characteristics of polyaniline-coated graphite oxide/γ-Fe2O3/BaTiO3 nanocomposites

Polymer nanocomposites were prepared by in situ polymerization of aniline with graphite oxide (GO), γ-Fe2O3, and BaTiO3 as electromagnetic interference (EMI) shielding materials. GO, γ-Fe2O3, and BaTiO3 nanoparticles were incorporated in the nanocomposites to improve the electromagnetic properties. The nanocomposites showed the significant improvement in both EMI shielding efficiency (SE) and thermal property due to the thermal conductivity of GO, the magnetic effect of γ-Fe2O3, and the electric effect of BaTiO3. The EMI SE of nanocomposites was improved due to the synergetic effect of reflection and absorption of electromagnetic interference by GO, γ-Fe2O3, and BaTiO3 additives.

Electrical properties and EMI shielding characteristics of multiwalled carbon nanotubes filled carbon black-high density polyethylene nanocomposites

Electrically conducting nanocomposites were prepared by melt mixing process using high density polyethylene (HDPE) with 20 wt.% of carbon black (CB) and 0–1 wt.% of multiwalled carbon nanotubes (MWNTs). The effects of MWNTs in HDPE-CB-MWNTs composites were examined using X-ray diffraction and differential scanning calorimeter. DC resistivity (ρ dc), AC conductivity (σ ac), and some dielectric properties and electromagnetic interference (EMI) shielding effectiveness of these composites have been investigated. The results reveal that ρ dc decreases significantly whereas σ ac, , and EMI shielding effectiveness increase with loading of MWNT. The values of , , and σ ac are frequency dependent. Positive temperature coefficient effects are observed to be dominant over temperature range of 60–105 °C and the shielding effectiveness is frequency dependent over the X band (8.2–12.4 GHz).

Electrical conductivity and electromagnetic interference shielding characteristics of multiwalled carbon nanotube filled polyurethane composite films

Multiwalled carbon nanotubes (MWCNTs) were homogeneously dispersed in a pure polyurethane resin by grinding in a planetary ball mill. The structure and surface morphology of the MWCNTs and MWCNT/polyurethane composites were studied by filed emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) methods. The electrical conductivity at room temperature and electromagnetic interference (EMI) shielding effectiveness (SE) of the composite films with different MWCNT loadings were investigated and the measurement of EMI SE was carried out in a frequency range of 8–12 GHz (X-band). The experimental results show that with a low MWCNT concentration the composite films could achieve a high conductivity and their EMI SE has a strong dependence on MWCNT content. For the composite films with 22 wt% of MWCNTs, the EMI SE attained an average value of 20 dB, so that the shielding effect reduced the penetrating power to 1%.

Electromagnetic interference shielding characteristics and shielding effectiveness of polyaniline-coated films

The study aims to investigate the electromagnetic interference (EMI) shielding characteristics and shielding effectiveness (SE) of polyaniline (PANI)-coated films. Free-standing films of emeraldine salt were obtained by PANI-emeraldine base with dode-cylbenzensulfonic acid on a polyethylene terephthalate film. The four-point probe method was employed to measure the electrical resistivity for investigating the electromagnetic characteristics of PANI-coated films. In addition, the SE of the PANI-coated films was measured in two different ways: a flanged coaxial shielding effectiveness test and a shielding effectiveness on the testbed having a box-type chamber equipped with instruments for electromagnetic shielding testing under real conditions. The overall SE measured from experiments was also compared with the approximate SE value calculated from a theoretical method. The present study has shown the possibility of utilizing PANI-coated films as EMI shielding/absorption materials.

Electromagnetic interference shielding effectiveness of graphite‐filled polypropylene and poly(ether imide) based composites

AbstractThe electromagnetic interference shielding characteristics of polypropylene (PP) and poly(ether imide) (PEI) filled with synthetic graphite composites were studied. The thermal properties were characterized by differential scanning calorimetry and thermogravimetric analysis, whereas the morphologies of the composites were studied by scanning electron microscopy. The viscosity measurements were studied by advance rheometry. The measurements of shielding effectiveness (SE) were carried out in the frequency range 8–12 GHz (X‐band range). The return loss and loss due to absorption were also measured as a function of frequency in the X‐band range. It was observed that the SE of the composites was frequency dependent, and it increased with increasing frequency. The SE also increased with increasing filler loading. The PEI‐based composites showed a higher SE compared to that of the PP‐based composites. The correlation between SE and the conductivity of the various composites is also discussed. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Electrical conductivity and electromagnetic interference shielding characteristics of multiwalled carbon nanotube filled polyacrylate composite films

Multiwalled carbon nanotubes (MWCNTs) were homogeneously dispersed in pure acrylic emulsion by ultrasonication to prepare MWCNT/polyacrylate composites applied on building interior wall for electromagnetic interference (EMI) shielding applications. The structure and surface morphology of the MWCNTs and MWCNT/polyacrylate composites were studied by field emission scanning microscopy (FESEM) and transmission electron microscopy (TEM). The electrical conductivity at room temperature and EMI shielding effectiveness (SE) of the composite films on concrete substrate with different MWCNT loadings were investigated and the measurement of EMI SE was carried out in two different frequency ranges of 100–1000 MHz (radio frequency range) and 8.2–12.4 GHz (X-band). The experimental results show that a low mass concentration of MWCNTs could achieve a high conductivity and the EMI SE of the MWCNT/polyacrylate composite films has a strong dependence on MWCNTs content in both two frequency ranges. The SE is higher in X-band than that in radio frequency range. For the composite films with 10 wt.% MWCNTs, the EMI SE of experiment agrees well with that of theoretical prediction in far field.

Studies on electromagnetic interference shielding characteristics of metal nanoparticle- and carbon nanostructure-filled polymer composites in the Ku-band frequency

The dispersion behaviour and electromagnetic interference (EMI) shielding properties were investigated for metal nanoparticle- and carbon nanostructure-filled polymer composites. It was observed that carbon nanostructure-polymer composites exhibited a much higher shielding performance than Ag nanoparticle-polymer composites at the same filler loading. The results also showed that Ag nanoparticle-polymer composites could exhibit an ideal shielding performance only with a very high Ag loading (> 30 wt%). The experimental data exhibited that the shielding effectiveness of the polymer composite containing 5 wt% carbon nanotubes could reach more than 20 dB in the measured frequency region, indicating such composites can be applied to the practical EMI shielding materials. In addition, some possible approaches to further improve the shielding performance of carbon nanotube-polymer composites were proposed and discussed.

Preparation and electromagnetic interference shielding characteristics of novel carbon‐nanotube/siloxane/poly‐(urea urethane) nanocomposites

AbstractPoly(urea urethane) (PUU) with a poly(dimethylsiloxane) soft segment was synthesized. Different types of conductive fillers—carbon nanotube (CNT), silver‐coated carbon nanotube (CNT–Ag), and nickel‐coated carbon nanotube (CNT–Ni)—were blended with PUU to form partially conductive polymer composites. The results showed that highly conductive metals could improve the conductivity of CNTs significantly. When the filler contents were 3, 4, and 5 parts per hundred parts of resin (phr), the PUU/CNT composites possessed electromagnetic interference shielding effectiveness (SE) at 8.5, 28.4, and 26.0 dB as the electromagnetic wave frequencies were 12.3, 16.2, and 15.9 GHz, respectively. SE of the composites that contained CNT–Ni and CNT–Ag increased with the filler loading. At the same modified‐CNT loading, the CNT–Ni‐filled composites had a higher SE than those filled with CNT–Ag. Tensile stresses ranged from 5.7 to 15.6 MPa (a 177.3% increase) when the CNT concentration reached 8 phr. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 345–358, 2005

Electrical Conductivity and Electromagnetic Interference Shielding of Multi-walled Carbon Nanotube Filled Polymer Composites

ABSTRACTMulti-walled carbon nanotube (MWNT) filled polystyrene (PS) composites were synthesized for electromagnetic interference (EMI) shielding applications. SEM images of composites showed the formation of the conducting networks through MWNTs within the PS matrix. The measured DC conductivity of composites increased with increasing MWNT loading, showing a typical percolation behavior. EMI shielding characteristics of MWNT-PS composites were investigated in the frequency range of 8.2–12.4 GHz (X-band). It was observed that the shielding effectiveness (SE) of such composite increased with the increase of MWNT loading. The SE of the composite containing 7 wt% MWNTs could reach more than 26 dB in the measured frequency region.

Method and apparatus to measure electromagnetic interference shielding efficiency and its shielding characteristics in broadband frequency ranges

We have designed and manufactured a flanged coaxial line as a sample holder for measuring the electromagnetic interference (EMI) shielding efficiency (SE) of planar materials in broadband frequency ranges up to 18 GHz. Connecting the samples holder to a vector network analyzer (50 MHz⩽M⩽13.5 GHz), we measured the S (scattering)-parameters and the EMI SE of copper (Cu) as a highly conducting material and emeraldine salt form of polyaniline (PAN–ES) as an intermediately conducting one. The measured EMI SEs of the materials from 50 MHz to 13.5 GHz were compared with those obtained from the conventional ASTM D4935-99 method and theoretical simulation using dc conductivity. We observed that the EMI SEs measured by using both experimental techniques agree with each other in the common frequency range (50 MHz∼1.5 GHz). The EMI shielding characteristics of samples such as the contribution of absorption and reflection to total EMI SE were analyzed through the measured S parameters.

Electromagnetic interference shielding characteristics of fabric complexes coated with conductive polypyrrole and thermally evaporated Ag

Through the chemical coating of polypyrrole (PPy) doped with naphthalene sulfonic acid (NSA) on electrically insulating poly (ethylene terephthalate) (PET) woven fabric, PPy–NSA/PET complexes were synthesized. By using the electrochemical coating of PPy doped anthraquinone-2-sulfonic acid (AQSA) on PPy–NSA/PET complexes, PPy–AQSA/PPy–NSA/PET complexes were synthesized. The silver (Ag) was thermally vacuum evaporated on the surface of PPy–AQSA/PPy–NSA/PET complexes (Ag|PPy–AQSA/PPy–NSA/PET). Electromagnetic interference (EMI) shielding efficiency (SE) and dc conductivity (σdc) of fabric complexes were measured for EMI shielding characteristics and theoretical simulation. The measurement of EMI SE in the frequency range from 50 MHz to 1.5 GHz was performed by using ASTM D4935-99 method. The EMI shielding characteristics such as transmittance, reflectance and absorbance were obtained from the S (scattering)-parameter analysis. We control the contribution of the absorbance or the reflectance to total EMI SE through the coating of conductive PPy and the evaporation Ag.