Electromagnetic Interference Shielding Effectiveness Performance Research Articles

Influence of PLA/HDPE Ratio and CNT content on the morphology, electrical, and EMI shielding of CNT-filled PLA/HDPE blends

The influence of polylactic acid/high-density polyethylene (PLA/HDPE) volume ratio on the microstructure, electrical resistivity, and electromagnetic interference (EMI) shielding effectiveness (SE) of 1.0 vol% carbon nanotube (CNT) filled PLA/HDPE composites were investigated. Also, the effect of CNT content on the electrical resistivity and EMI SE of 90/10, 50/50, and 10/90 PLA/HDPE blends were studied. The CNT/PLA composite showed superior electrical and EMI SE performance compared with the CNT/HDPE composite. In the PLA/HDPE blends, the nanotubes were selectively localized in the HDPE domain. The EMI SE and electrical conductivity increased with the decrease of HDPE volume fraction in the blend. The 90/10 PLA/HDPE blend exhibited electrical percolation at 0.25 vol% CNT compared to 1.0 vol% for the 10/90 PLA/HDPE blend. At 7.0 vol% CNT and higher, the EMI SE of the 50/50 PLA/HDPE blend showed marginally higher SE than the 90/10 PLA/HDPE blend. The EMI SE was found to be a function of the composite’s electrical resistivity and microstructure.

Graphene Nanoplatelet/Multiwalled Carbon Nanotube/Polypyrrole Hybrid Fillers in Polyurethane Nanohybrids with 3D Conductive Networks for EMI Shielding.

This work reports the preparation of graphene nanoplatelet (GNP)/multiwalled carbon nanotube (MWCNT)/polypyrrole (PPy) hybrid fillers via in situ chemical oxidative polymerization with the addition of a cationic surfactant, hexadecyltrimethylammonium bromide. These hybrid fillers were incorporated into polyurethane (PU) to prepare GNP/MWCNT/PPy/PU nanohybrids. The electrical conductivity of the nanohybrids was synergistically enhanced by the high conductivity of the hybrid fillers. Furthermore, the electromagnetic interference (EMI) shielding effectiveness (SE) was greatly increased by interfacial polarization between the GNPs, MWCNTs, PPy, and PU. The optimal formulation for the preparation of GNP/MWCNT/PPy three-dimensional (3D) nanostructures was determined by optimization experiments. Using this formulation, we successfully prepared GNP/PPy nanolayers (two-dimensional) that are extensively covered by MWCNT/PPy nanowires (one-dimensional), which interconnect to form GNP/MWCNT/PPy 3D nanostructures. When incorporated into a PU matrix to form a nanohybrid, these 3D nanostructures form a continuous network of conductive GNP-PPy-CNT-PPy-GNP paths. The EMI SE of the nanohybrid is 35-40 dB at 30-1800 MHz, which is sufficient to shield over 99.9% of electromagnetic waves. Therefore, this EMI shielding material has excellent prospects for commercial use. In summary, a nanohybrid with excellent EMI SE performance was prepared using a facile and scalable method and was shown to have great commercial potential.

Fiber reinforced thermoplastics compounds for electromagnetic interference shielding applications

Market demands for lightweight and lower cost products drive manufacturers to improve current product portfolios. In the case of electronic devices, the most significant weight originates from the enclosure, traditionally in steel or aluminum, that ensures excellent mechanical and electromagnetic shielding performance. The use of thermoplastics filled with electrically conductive fibers, such as carbon or stainless steel, was investigated as a lightweight and cost-effective alternative to steel sheet for creating electromagnetic interference (EMI) shielding enclosures for electronic devices. This paper presents an EMI shielding analysis workflow for the development of plastic enclosures for an electronic device. The workflow starts by measuring the fiber-reinforced thermoplastic compounds shielding effectiveness (SE) with an experimental method in the 30 MHz–3 GHz frequency band. This analysis helps to filter a vast list of materials with a wide range of shielding performance, 20–100 dB, and allows to obtain empirical data for the second phase of the workflow, computer simulations. Simulations with experimentally adjusted material properties were used to validate the design concept of an enclosure in its early development phase. Results from this study showed that the selected material has better EMI SE performance than a steel sheet venting grid.

Superstructure silver micro-tube composites for ultrahigh electromagnetic wave shielding

Absorption-dominant electromagnetic shielding materials can effectively reduce secondary pollution in the shielding process, and have greater significance in practical applications. Herein, silver (Ag) micro-tubes with superstructure, which were fabricated via using poly(lactic acid) (PLA) fibers as templates, were used to achieve the composites with ultrahigh, lightweight, and absorption-dominant electromagnetic shielding performance. The Ag nanoparticles were firstly deposited on the surface of PLA fibers by chemical reduction. The Ag micro-tubes were obtained by etching the PLA fibers in the core. The Ag nanoparticles were stuck together to form the Ag micro-tubes by polymer chains. The ultrahigh electromagnetic interference (EMI) shielding effectiveness (SE) of ∼110 dB was found in the Ag micro-tubes composed with polydimethylsiloxane or PLA with 1.5 mm in thickness. Due to the micro-tube structure, the composites containing with Ag micro-tubes exhibited absorption dominant shielding mechanism and low density. The absorption coefficient (A) value could reach 0.79 in the composites with Ag micro-tubes. The ultrahigh EMI SE performance and absorption dominant shielding mechanism of the composites was ascribed to the superstructure of the Ag micro-tubes which could efficiently create surface plasmon resonance, electronic vibration, interfacial polarization, capacitance effect and conductive loss. The work provides a new idea for preparing ultrahigh electromagnetic shielding materials with high absorption and low density.

Polydopamine coating improves electromagnetic interference shielding of delignified wood-derived carbon scaffold

Delignified wood (DW) is natural wood’s cellulosic skeleton. It has highly ordered anisotropic architecture, permitting solute accessibility to modify its abundant interior surfaces. Herein, we demonstrate a facile method to coat polydopamine (PDA) conformally on DW’s interior surfaces. The PDA layer not only introduced heteroatom (N), but also facilitated the generation of silver particles by in situ reduction. The prepared DW skeletons were freeze-dried and pyrolyzed at 850/1200 °C to create carbonized DW (CDW) and then embedded in the epoxy matrix to prepare a composite for the application of electromagnetic interference (EMI) shielding. It was found that the PDA coating converted to a highly conductive carbon species on the surface of a DW-derived carbon scaffold. As a result, the PDA modification increased the electrical conductivity (EC) of the plain epoxy/CDW from 0.32 to 0.46 S/m, and accordingly the EMI shielding effectiveness (SE) increased from 18.2 dB for epoxy/CDW to 24.0 dB for epoxy/CDW-PDA, and 30.6 dB for epoxy/CDW-Ag. This work provides a facile and universal methodology to enhance the EC and EMI SE performance of open-porous carbon.

Highly conductive and scalable Ti3C2Tx-coated fabrics for efficient electromagnetic interference shielding

As an increasing number of wireless devices are introduced to our daily lives, long-term environmentally stable conductive fabrics that can shield against electromagnetic radiation are increasingly desired. Herein, conventional cotton and linen fabrics were dip-coated in additive-free, aqueous Ti3C2Tx MXene dyes, which consist of only two-dimensional Ti3C2Tx flakes dispersed in water, to fabricate highly conductive fabrics for electromagnetic interference (EMI) shielding. Ti3C2Tx loading and electrical conductivity of the fabrics increased with the number of dip-coating cycles. After only 4 dip-coating cycles, EMI shielding effectiveness (SE) of Ti3C2Tx-coated (<15 wt%) cotton and linen fabrics reached ∼40 dB over the X-band range. After 24 dip-coating cycles, the total EMI SE increased to ∼80 dB for Ti3C2Tx-coated cotton (54 wt%) and linen (48 wt%) fabrics, which is higher than commercial metal-based conductive fabrics tested in this study. The average EMI SE performance of Ti3C2Tx-coated cotton and linen fabrics only decreased by ∼8% and ∼13%, respectively, after storage under ambient conditions for two years. This work suggests an attractive alternative to current metal-based conductive dyes and provides valuable insights into the development of environmentally stable wearable EMI shielding materials.

Exfoliation and Defect Control of Two-Dimensional Few-Layer MXene Ti3C2Tx for Electromagnetic Interference Shielding Coatings.

Defect-controlled exfoliation of few-layer transition-metal carbide (f-Ti3C2Tx) MXene was demonstrated by optimizing chemical etching conditions, and electromagnetic interference (EMI) shielding coatings were explored. The structural features such as layer morphology, lateral size, layer thickness, defect density, and mechanical stability of the exfoliated f-Ti3C2Tx were strongly dependent on exfoliation conditions. By selecting appropriate exfoliation conditions, moderate etching time leads to the formation of quality f-Ti3C2Tx with lesser defects, whereas longer etching time can break the layer structure and increase defect density, structural misalignment, and oxidative products of f-Ti3C2Tx. The resultant fabricated free-standing flexible f-Ti3C2Tx films exhibited electrical conductivity and electromagnetic interference (EMI) shielding effectiveness (SE) in the X-band of about 3669 ± 33 S/m and 31.97 dB, respectively, at a thickness of 6 μm. The large discrepancy in EMI SE performance between quality (31.97 dB) and defected (3.164 dB) f-Ti3C2Tx sheets is attributed to interconnections between f-Ti3C2Tx nanolaminates interrupted by defects and oxidative products, influencing EMI attenuation ability. Furthermore, the demonstrated solution-processable high-quality f-Ti3C2Tx inks are compatible and, when applied for EM barrier coating on various substrates, including paper, cellulose fabric, and PTFE membranes, exhibited significant EMI shielding performance. Moreover, controlling defects in f-Ti3C2Tx and assembly of heterogeneous disordered carbon-loaded TiO2-Ti3C2Tx ternary hybrid nanostructures from f-Ti3C2Tx by tuning etching conditions could play an enormous role in energy and environmental applications.

Effects of molding conditions on the electromagnetic interference performance of conductive ABS parts

AbstractPolymers filled with conducting fibers to prevent electromagnetic interference (EMI) performance have recently received great attention due to the requirements of 3C (computer, communication, and consumer electronics) products. In the present article, the effect of fiber content and processing parameters, including melt temperature, mold temperature, and injection velocity, on the electromagnetic interference shielding effectiveness (SE) in injection molded ABS polymer composites filled with conductive stainless steel fiber (SSF) was investigated. The influence of fiber orientation and distribution resulting from fiber content and molding conditions on EMI performance was also examined. It was found from measured results that fiber content plays a significant role in influencing part EMI SE performance. SE value can reach the highest values of approximately 40 dB and 60 dB at 1000 MHz frequency for fiber content 7 wt % and 14 wt %, respectively, under the best choice of molding conditions. Higher melt and mold temperature would increase shielding effectiveness due to a more uniform and random fiber orientation. However, higher injection velocity leading to highly‐orientated and less uniform distribution of fiber reduces shielding effectiveness. Among all molding parameters, melt temperature affects SE performance most significantly. Its influence slightly decreases as fiber content increases. Injection speed plays a secondary importance in affecting SE values, and its influence increases as fiber content increases. Upon examination of fiber distribution via optical microscope and subsequent image analysis, it was found that the fiber becomes more densely and random distributed toward the last melt‐filled region, whereas fiber exhibits less concentration around the middle way of the flow path. This can be attributed to the combined effects of fountain flow, frozen layer thickness, and gapwise melt front velocity. The results indicate that molding conditions, instead of fiber content alone, are very important on the SE performance for injection molded SSF filled ABS composites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1072–1080, 2005