柔性基电磁屏蔽材料的研究进展

本文介绍了电磁屏蔽材料的屏蔽原理、电磁屏蔽损耗材料的类型及性能,总结了柔性基电磁屏蔽材料的制备方法及其研究进展。     

柔性基电磁屏蔽材料的研究进展

随着5G通信和物联网的普及,电磁波辐射污染引起了公众的广泛关注.传统的金属电磁屏蔽材料质量高、柔性差难以满足柔性可穿戴电子器件和电子皮肤等领域的需求.因此,质量轻、柔性好的电磁屏蔽材料备受关注.介绍了电磁屏蔽材料的屏蔽原理、电磁屏蔽损耗材料的类型及性能,综述了柔性基电磁屏蔽材料的制备方法及其研究进展.最后,对柔性基电磁屏蔽材料未来的发展方向进行了展望.     

Smart composite materials for self-sensing and self-healing

Abstract

The various methods of self-sensing and self-healing developed within the Composite Systems Innovation Centre, University of Sheffield, are reviewed. Damage sensing using electrical resistance in carbon fibre reinforced composite or using the fibres as optical sensing elements in glass fibre reinforced composite is demonstrated. Amelioration of low level damage is demonstrated in both monolithic composite materials and sandwich structures using direct chemical reactions within the matrix without the use of encapsulants. These reactions can be activated by resistive heating of the material itself. The use of a combination of these techniques could create a truly smart structure able to both sense and repair damage and degradation.     

Multifunctional nanocomposites integrate electromagnetic shielding,thermal, mechanical,and wear resistance properties

The SiC_nws/SiC nanocomposites were in situ synthesized by using nickel carbon foam as catalyst and skeleton. This technique has a series of advantages including simple operation, low cost, and high efficiency. Due to the excellent microwave absorption and thermal properties of SiC_nws, SiC_nws/SiC nanocomposites possess excellent electromagnetic shielding performance with a high SE_T value of 38.3 dB and good thermal properties with thermal conductivity of 13.77 ± 0.098 wm⁻¹k⁻¹ at room temperature. Meanwhile, the bending strength of the nanocomposites is 110.9 ± 7.7 MPa. The friction coefficient of nanocomposites is about 0.26 with a wear speed of about 67 um³/s. Therefore, the nanocomposites integrate many advantages including lightweight (2.0 g/cm³), excellent electromagnetic shielding, good heat conduction, high strength, and wear resistance.     

尖晶石铁氧体材料电磁屏蔽研究进展

描述了尖晶石铁氧体的屏蔽原理,并介绍了共沉淀法、溶胶凝胶法、燃烧法、水热法及溶剂热法等合成尖晶石铁氧体方法。针对尖晶石铁氧体纳米材料存在吸收频带较窄、密度较大等缺点,讨论了金属离子掺杂、聚合物复合改性及碳材料复合改性等方法,以进一步改善和促进尖晶石铁氧体合成的工业化进程。     

Rubber composite materials with the effects of electromagnetic shielding

This work deals with the preparation and properties evaluation of magnetic composites with acrylonitrile butadiene rubber matrix, which are able to shield electromagnetic radiation. In addition to the rubber matrix, these materials contained soft magnetic filler (Li or H40) and ingredients necessary for vulcanization process of prepared rubber compounds (sulfur, accelerator N‐cyclohexyl‐2‐benzothiazole sulfenamide, activators ZnO, and stearin). This study was aimed at the preparation of elastomeric composite materials and evaluation of the influence of ferrite weight fraction on curing characteristics, physical–mechanical, and magnetic properties. The results showed that with increasing content of filler, the moduli, and tensile strength decline. Conversely, elongation at break increased with increasing amount of filler. All composites containing 200 and more phr of ferrite showed sufficient absorption shielding properties, whereas lithium ferrite shows better shielding properties compared with manganese–zinc ferrite H40. POLYM. COMPOS., 37:2933–2939, 2016. © 2015 Society of Plastics Engineers     

Synthesis of urethane acrylate based electromagnetic interference shielding materials

In this work, a new method, consists of synthesis of urethane acrylate (UA) followed by in situ polymerization of pyrrole using cerium (IV) as an oxidant and UV‐curing of the composites, for preparing polypyrrole–UA (PPy–UA) composite films was described. It appeared that dielectric constants of the composites increased with increasing the PPy content and decreased with increasing the frequency from 10^?2 to 10⁷, indicating an interfacial Maxwell–Wagner contribution to the permittivity. An incorporation of a small amount of PPy (15% Py) to UA matrix increased their dielectric constants more than 4 × 10⁴ (41,259) at 10^?2 Hz. So, the incorporation of PPy was very effective for enhancing the dielectric properties of UA matrix. Furthermore, the significant enhancement in dielectric properties (loss tangent and dielectric constant) contributes to the improvement in electromagnetic interference shielding efficiency. Composite films were characterized using Fourier transform infrared attenuated total reflectance (FTIR‐ATR) spectrophotometer and ¹H‐NMR. It was seen that PPy is blended with the UA matrix at the molecular level through H‐bonding interactions. A linear relationship was also observed between the characteristic groups' absorbances of PPy (from FTIR‐ATR) and dielectric constant values (from dielectric spectrometer). © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2013     

Conductive polymer composite materials and their utility in electromagnetic shielding applications

Commercial electronic devices require shielding solutions that ensure electromagnetic compatibility (EMC) while accounting for effects of specific enclosure structural features such as seams, vents, and port dimensions. In practice, suitable EMC materials combine with the device operating characteristics to determine an overall shielding response. To optimally couple plastic design practices with EMC requirements, both polymer materials science and electrical engineering concepts, must be considered. Use of extrinsically conductive polymer (ECP) formulations for electronic applications has advantages in that they can be directly molded to a desired shape and serve to provide the necessary shielding while also meeting mechanical integrity requirements. Shielding and mechanical performance can be varied via filler loading or altered through wall thickness changes to satisfy demands associated with a particular device. Injection‐moldable ECP polycarbonate‐based formulations can attain average shielding effectiveness (SE) levels of ～50–60 dB through 2 GHz at 2‐mm thickness as measured using ASTM D 4935 procedures. These values vary with thickness, and SE improvements of ～10–20 dB are observed when increasing from 1 to 2 mm. Additionally, resultant mechanical properties of shielding composites are strong functions of overall fiber content. These interrelated material and shielding characteristics, which form the basis for filled conductive polymer use within practical enclosure shielding designs, are described. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Carbon nanohorn and graphene nanoplate based polystyrene nanocomposites for superior electromagnetic interference shielding applications

In this article is reported the preparation of carbon nanohorn (CNH)/graphene nanoplates (GNP)/polystyrene (PS) nanocomposites through in‐situ bulk polymerization of styrene monomer in the presence of CNH, followed by the addition of suspension polymerized GNP/PS bead during polymerization of styrene, as next‐generation multifunctional material for high electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) applications. Morphological analysis revealed selective dispersion of CNH in bulk polymerized PS matrix, where GNP/PS beads were randomly distributed. The formation of continuous CNH–CNH conductive path and GNP–CNH–GNP or CNH–GNP–CNH conductive network throughout the PS matrix at exceptionally low loading of CNH (1.0 wt %) and GNP (0.15 wt %) leads to high electrical conductivity (6.24 × 10^?2 S cm^?1) and EMI SE ～(?24.83 dB) when the nanocomposites was prepared in the presence of 75 wt % GNP/PS bead. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42803.     

Synthesis and properties of electromagnetic wave shielding polymer materials with low flammability

Novel polyethylene‐ and polypropylene‐based electromagnetic wave shielding and absorbing composite materials with low combustibility, enhanced thermal and mechanical properties, containing graphite, grinded wood, and fire retardants, were developed and investigated. Flame‐resistance, thermal and mechanical properties of these materials was investigated. Electromagnetic wave reflection coefficients over the frequency range 20–40 GHz were measured; at moderate concentration (10–15%) of functional filler, reflection coefficient can be as low as ?16 dB for PE and ?11 dB for PP composite, respectively. Coke formation mechanism was investigated, the principal role in this process is attributed to aromatization and condensation of aromatic compounds with the formation of polycyclic aromatic systems, an important role of phosphoric acids in accelerating this process was found. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Carbon fiber reinforced composites from industrial waste for microwave absorption and electromagnetic interference shielding applications

Lightweight materials with hybrid microstructures are getting great attention in the area of electromagnetic wave absorption. In the present study, carbon fiber and fly ash reinforced composites are prepared by mixing them with ground granulated blast furnace slag, followed by compaction and sintering at 1000 °C under an argon atmosphere. Akermanite-gehlenite was observed to be the primary crystalline phase present in the prepared samples. Porous composites are obtained with the addition of fly ash and carbon fiber as they inhibit densification. The resultant microstructure has homogeneous carbon fiber dispersion and uniform fly ash anchoring on the matrix phase. This enhanced interface polarization, defect polarization, electron transportation, and impedance matching characteristics of the composites. Hence, the developed composites' microwave absorption and electromagnetic interference shielding properties exhibited an outstanding performance at low thickness with a reflection loss value of ?41.24 dB and total shielding effectiveness of 42.29 dB at the X-band.     

Onion-like carbon for terahertz electromagnetic shielding

It is demonstrated that onion-like carbon (OLC) provides efficient attenuation of the electromagnetic spectrum over the wavelength range 12–230 THz as compared to detonation nanodiamonds (DND) at similar or higher concentrations. Some characteristics of OLC important for the processing of polymer composites such as surface functional groups, zeta-potentials and agglomerate sizes are reported.     

Inorganic nanotubes reinforced polyvinylidene fluoride composites as low-cost electromagnetic interference shielding materials

Novel polymer nanocomposites comprising of MnO₂ nanotubes (MNTs), functionalized multiwalled carbon nanotubes (f-MWCNTs), and polyvinylidene fluoride (PVDF) were synthesized. Homogeneous distribution of f-MWCNTs and MNTs in PVDF matrix were confirmed by field emission scanning electron microscopy. Electrical conductivity measurements were performed on these polymer composites using four probe technique. The addition of 2 wt.% of MNTs (2 wt.%, f-MWCNTs) to PVDF matrix results in an increase in the electrical conductivity from 10^-16S/m to 4.5 × 10^-5S/m (3.2 × 10^-1S/m). Electromagnetic interference shielding effectiveness (EMI SE) was measured with vector network analyzer using waveguide sample holder in X-band frequency range. EMI SE of approximately 20 dB has been obtained with the addition of 5 wt.% MNTs-1 wt.% f-MWCNTs to PVDF in comparison with EMI SE of approximately 18 dB for 7 wt.% of f-MWCNTs indicating the potential use of the present MNT/f-MWCNT/PVDF composite as low-cost EMI shielding materials in X-band region.     

New electromagnetic shielding materials based on viscose‐carbon nanotubes composites

A convenient approach for the preparation of cellulose ‐ carbon nanotubes (CNT) hybrid materials owning electromagnetic shielding properties, based on viscose (V) and TEMPO‐oxidized viscose fibers (VO) is proposed. Viscose ‐ carbon nanotubes (V‐CNT) and TEMPO‐oxidized viscose ‐ carbon nanotubes (VO‐CNT) composites were prepared by embedding carbon nanotubes on the surface of two types of cellulose fibers, that is, viscose and its C₆‐oxidized derivative. The chemical composition, morphology, and thermal stability of the prepared hybrid materials were thoroughly investigated by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analyses. Moreover, electrical properties of the original and composite fibers were assessed. POLYM. ENG. SCI., 59:1499–1506 2019. © 2019 Society of Plastics Engineers     

Lightweight silver@carbon microsphere@graphene (Ag@CMS@GR) composite materials for highly efficiency electromagnetic interference shielding properties

In this article, lightweight silver@carbon microsphere@graphene (Ag@CMS@GR) composite materials were fabricated. First, carbon microsphere (CMS) was prepared by redox hydrothermal method in the presence of FeCl₃ and polyvinyl alcohol. Next, on the surface, silver was deposited to form Ag@CMS particles. And finally, the graphene sheets were added to connect Ag@CMS particles to obtain Ag@CMS@GR composites. Because of the silver nanoparticle may form a conductive pathway, Ag@CMS with relative high content of silver nanoparticles show superior EMI shielding properties. Next, graphene was introduced into Ag@CMS with relative low content of silver particles to form Ag@CMS@GR composites, which is helpful for decreasing the apparent density of composites to around 1.01 g·cm⁻³. And the composites also show good EMI shielding properties. The highest SE and specific SE values of Ag@CMS@GR reached 39.26 dB and 38.87 dB·cm³·g⁻¹ with 5 wt % graphene content. The EMI shielding mechanism of Ag@CMS@GR composites was discussed. It can be potentially used for lightweight EMI shielding applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48459.     

Carbon fiber reinforced polymer metallization via a conductive silver nanowires polyurethane coating for electromagnetic shielding

For electromagnetic shielding in space environment, the metallization of carbon fiber reinforced polymer (CFRP) is required. A specific attention is paid due to the thermal expansion coefficient difference between substrate and metal coating. A surface metallization of a CFRP has been elaborated by electrodeposition. This study presents an original process based on an electrically conductive polymer coating elaborated from a polyurethane matrix filled with a low content of silver nanowires (<10%vol). A continuous and adherent deposit is obtained by an optimization of the electroplating parameters. A minimal volume fraction was determined at 3%vol associated with an applied current density estimated near 0.1 A/dm². The growth speed is 7 μm/h at 0.1 A/dm². The adhesion was checked in severe environmental conditions (−196 to 165°C). The effectiveness shielding obtained with this solution reaches an attenuation value higher than 90 dB between 1 and 26 GHz necessary for space communication applications.     

Rapid preparation,thermal stability and electromagnetic interference shielding properties of two-dimensional Ti3C2 MXene

Two-dimensional (2D) MXenes have attracted much attention due to their unique structural characteristics and novel performance in a variety of functions. The fabrication of 2D Ti₃C₂ MXene by acid etching usually requires a long period of over 10 h. In this work, we report on the rapid preparation, thermal stability and electromagnetic interference (EMI) shielding effectiveness of 2D Ti₃C₂ MXene. With the processing conditions optimized by adjusting the etching time and temperature, Ti₃C₂ MXene with a scattered accordion-like structure has been successfully achieved by etching Ti₃AlC₂ powders with 40% HF at 50 °C for only 0.5 h. The as-synthesized Ti₃C₂ was stable at temperatures up to 300 °C in air, but stable in vacuum at temperatures up to 800 °C. The as-synthesized Ti₃C₂ MXene has good EMI shielding performance. The total shielding effectiveness of Ti₃C₂ in a WAX matrix exceeded 20 dB in the whole frequency ranging from 2 to 18 GHz. The maximum shielding effectiveness value achieved to 34 dB at 18 GHz as the Ti₃C₂ content was up to 70 wt%. This work provides an approach for the large scale preparation of the Ti₃C₂ MXene.     

新型功能性木质电磁屏蔽材料

研究了薄木化学镀铜的生产工艺及所得镀层的电磁屏蔽、装饰性、成本等方面的性能.给出了镀铜液配方及工艺参数.结果表明,单位面积上,化学镀铜的成本远小于铜箔贴面的成本,可节约成本达70%左右.镀铜层均匀连续,具有一定的装饰性.施镀时间在10～15 min之间时,镀铜层的电磁屏蔽效能可达25～40 dB,方块电阻达到0.07Ω/square左右.     

Plastic composites for electromagnetic interference shielding applications

Research in the past eight years has established the ability of polymer composites made with sufficient electrical conductivity to be suitable as shields against electromagnetic interference (EMI). A number of conductive fillers have been used to produce such composites. These include carbon black, carbon fibers, metal fibers, metal flakes, and metal-coated glass fibers. Each filler offers its own set of advantages and disadvantages. An important aspect of developing polymeric composites for EMI shielding applications is measuring their shielding ability in areliable, easy-to-use test facility. Once a reliable test has been developed, basic data relating the bulk conductivity (or surface conductivity of coatings) can be generaated. The objective of this article is to discuss the relative utility of the different types of fillers commonly used, present an analysis of the utility of different testing approaches, and show data correlating volume resistivity with shielding effectiveness.