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Song W.-L.,University of Science and Technology Beijing | Song W.-L.,Beijing Institute of Technology | Song W.-L.,Clemson University | Cao M.-S.,Beijing Institute of Technology | And 7 more authors.
Carbon | Year: 2014

Multilayer graphene/polymer composite films with good mechanical flexibility were fabricated into paraffin-based sandwich structures to evaluate electromagnetic interference (EMI) shielding. Experimental results showed the relationship between electrical properties and shielding performance, demonstrating that electrical properties are significant factors in EMI shielding. Calculation based on electrical conductivity of the composite films was carried out to investigate the fundamental mechanisms of absorption, reflection and multiple-reflections for the polymeric graphene composite films. Both experimental and calculated results indicate that reflection is the dominating shielding mechanism for the as-fabricated polymeric graphene films. The optimization of thickness, skin depth and electrical conductivity in the shielding materials could be highly significant in achieving enhanced EMI shielding. Further improvement in absorption shielding has been achieved by increasing the shielding thickness in order to enhance the overall shielding performance. The optimized shielding effectiveness up to 27 dB suggested effective shielding of the composite films. The implication of the mechanisms for optimizing shielding performance demonstrates significant fundamental basis for designing high-performance EMI shielding composites. The results and techniques also promise a simple and effective approach to achieve light-weight graphene-based composite films for application potentials in EMI shielding coatings. © 2013 Elsevier Ltd. All rights reserved.


Song W.-L.,University of Science and Technology Beijing | Song W.-L.,Beijing Institute of Technology | Cao M.-S.,Beijing Institute of Technology | Qiao B.-B.,Beijing Institute of Technology | And 7 more authors.
Materials Research Bulletin | Year: 2014

The hydrothermal method was utilized to synthesize beta-manganese dioxide (β-MnO2) nanorods. Both the neat bulk samples fabricated from the nano-scale β-MnO2 rods and commercial micron-scale β-MnO2 particles exhibited similar performance in permittivity, electromagnetic interference shielding and microwave absorption. The wax-based composites embedded with the as-prepared β-MnO2 nanorods exhibited greater differences in permittivity, electromagnetic interference shielding and microwave absorption, compared to those embedded with the commercial micron-scale MnO2 particles. The results suggest that neat MnO2 materials are effective in electromagnetic interference shielding and the composites with β-MnO2 nanorods present the highest microwave absorption. Electrical conductivity coupled with size effects was considered as the most significant roles in the variations of permittivity, electromagnetic interference shielding and microwave absorption. The related mechanism associated with reflection and absorption has been discussed. The results have provided potential strategies for designing and achieving high-performance electromagnetic interference shielding and microwave absorbing materials. © 2013 Published by Elsevier Ltd. All rights reserved.


Song W.-L.,University of Science and Technology Beijing | Cao M.-S.,Beijing Institute of Technology | Fan L.-Z.,University of Science and Technology Beijing | Lu M.-M.,Beijing Institute of Technology | And 3 more authors.
Carbon | Year: 2014

We have demonstrated a highly ordered porous carbon (HOPC) as an effective electromagnetic absorber. The unique porous structures allow HOPC to possess high surface area and establish effective three-dimensional (3D) conductive interconnections at very low filler loading, which is responsible for effective electrical loss in terms of dissipating the induced current in the corresponding wax composites. Owing to the 3D porous frame, the wax composites with 1 and 5 wt% HOPC have shown effective bandwidth ∼2 and ∼4.5 GHz, respectively, which is considerably competitive to the performance found in the carbon nanotube- (CNT) and graphene-based composites of much higher filler loadings. This concept based on porous absorbers demonstrates more advantages in the fabrication of lightweight microwave-absorbing materials. Furthermore, the composite with 20 wt% HOPC has exhibited highly effective electromagnetic shielding performance up to 50 dB, which competes well with what has already been achieved in the composites embedded with CNTs and graphene. The fundamental mechanism based on electrical conductivity and complex impedance suggests specific strategies in the achievement of high-performance composites for electromagnetic attenuation and shielding. © 2014 Elsevier Ltd. All rights reserved.


Song W.-L.,University of Science and Technology Beijing | Song W.-L.,Clemson University | Fan L.-Z.,University of Science and Technology Beijing | Cao M.-S.,Beijing Institute of Technology | And 9 more authors.
Journal of Materials Chemistry C | Year: 2014

Ultrathin electromagnetic interference (EMI) shielding materials promise great application potential in portable electronic devices and communication instruments. Lightweight graphene-based materials have been pursued for their exclusive microstructures and unique shielding mechanism. However, the large thickness of the current low-density graphene-based composites still limits their application potential in ultrathin devices. In this work, a novel approach has been taken to use conductive graphene paper (GP) in the fabrication of ultrathin EMI shielding materials. The as-prepared flexible GPs exhibit highly effective shielding capabilities, reaching ∼19.0 dB at ∼0.1 mm in thickness and ∼46.3 dB at ∼0.3 mm in thickness, thus the thinnest GPs having the best shielding performance among graphene-based shielding materials. Double-layered shielding attenuators have been designed and fabricated for a high shielding performance of up to ∼47.7 dB at a GP thickness of ∼0.1 mm. Mechanistically, the high performance should be due to Fabry-Pérot resonance, which is unusual in carbon-based shielding materials. The preparation of conductive GPs of superior shielding performance is relatively simple, amenable to large-scale production of ultrathin materials for EMI shielding and electromagnetic attenuators, with broad applications in lightweight portable electronic devices. This journal is © the Partner Organisations 2014.


Song W.-L.,University of Science and Technology Beijing | Song W.-L.,Beijing Institute of Technology | Cao M.-S.,Beijing Institute of Technology | Hou Z.-L.,Beijing Institute of Technology | And 4 more authors.
Applied Physics A: Materials Science and Processing | Year: 2014

As the development of electronic and communication technology, electromagnetic interference (EMI) shielding and attenuation is an effective strategy to ensure the operation of the electronic devices. Among the materials for high-performance shielding in aerospace industry and related high-temperature working environment, the thermally stable metal oxide semiconductors with narrow band gap are promising candidates. In this work, beta-manganese dioxide (β-MnO2) nanorods were synthesized by a hydrothermal method. The bulk materials of the β-MnO2 were fabricated to evaluate the EMI shielding performance in the temperature range of 20-500 °C between 8.2 and 12.4 GHz (X-band). To understand the mechanisms of high-temperature EMI shielding, the contribution of reflection and absorption to EMI shielding was discussed based on temperature-dependent electrical properties and complex permittivity. Highly sufficient shielding effectiveness greater than 20 dB was observed over all the investigated range, suggesting β-MnO2 nanorods as promising candidates for high-temperature EMI shielding. The results have also established a platform to develop high-temperature EMI shielding materials based on nanoscale semiconductors. © 2014 Springer-Verlag Berlin Heidelberg.

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