Electromagnetic interference (EMI) electromagnetic interference caused not only electrical equipment, will also poses a serious threat to human health , and therefore the electromagnetic pollution has been recognized as the following air pollution , water pollution, noise pollution, the fourth-largest public nuisance after . Electromagnetic radiation pollution has caused the world 's attention. Europe, America , Japan and other countries and regions have issued standards and requirements of electromagnetic radiation , such as the U.S. Federal Communications Commission FCC, Technical Association of the German Electrical VDE, Japan VCCI and the UK BS6527 and so on. International Special Committee on Radio Interference CISPR also developed international standards for anti-electromagnetic interference. Electromagnetic radiation hazards , but also makes the world's most populous country - Chinese government attaches great importance since the 1990s , the country has promulgated a number of industry-specific electromagnetic radiation protection , such as " electromagnetic radiation protection" , "Microwave and VHF communications equipment radiation safety requirements "," anti- RF hazards with electric detonators security guidelines ", and in 1998 launched the EMC standards , the use of electromagnetic shielding materials can effectively shield electromagnetic interference , reducing electromagnetic pollution hazards.1. Electromagnetic shielding mechanismElectromagnetic interaction is changing electric and magnetic fields generated by the formation of radiation , the energy in the form of fluctuations spread from near to far . Electromagnetic shielding electromagnetic waves in the mechanism of induced current through the conductors in the conductor , so that the inner conductor can be converted into electromagnetic energy in order to achieve the purpose of shielding . General use shielding effectiveness SE (Shielding Effectiveness) to evaluate the shielding performance electromagnetic shielding materials , according to the theory Schelkunoff electromagnetic shielding , shielding effectiveness into reflective consumption, consumption and multiple reflection absorption consume three parts , with the formula is expressed as : SE = A + R + BA - absorption loss ; B - electromagnetic shielding material in multiple internal reflection losses ; R - is a single reflection of the electromagnetic wave attenuation.2 Status electromagnetic shielding materials research and developmentAccording to the mechanism of the electromagnetic wave shielding electromagnetic shielding material is divided into three categories: reflective, absorptive and absorption , by the application can be divided into a coated composite structure and a category.2.1Electromagnetic shielding paintGold , silver, copper , nickel , carbon, graphite and conductive fine particles to be incorporated into the polymer blend in the conductive coating relative to the original polymer , the electric conductivity is greatly enhanced. Conductive blending process mechanism is more complex, with the effect of conductive filler types and degree of dispersion of the filler in the polymer related. It was found that the presence of " percolation threshold " concentration of filler , insulator below the critical point, the critical concentration is reached , the resistance dropped sharply until the system is stable conduction current exceeds the critical point , the system changed little resistance .Low- cost conductive coating production process is simple , convenient, widely used , depending on the blend , can be divided into silver , carbon-based , copper-based , nickel and so on.Silver conductive coating of high electrical conductivity , excellent shielding performance ( up to 65dB), but limit the scope of expensive , mainly used in the specific domain .Carbon-based coatings are the 1970s by the U.S. military to develop a low density, low cost, relatively poor conductivity, electromagnetic shielding effect is not very satisfactory, is generally used as an antistatic coating.Low resistivity copper-based conductive coating is good , the disadvantage is easily oxidized easily sink greater density , dispersed in the polymer matrix is not good . To prevent oxidation of copper powder , organic compound used , inert metal-coated , or add a reducing agent or other additives and other ingredients in the preparation of the coating process, to obtain a conductive coating having autoxidation . In recent years, with the success of pioneering copper oxidation technology , the rapid development of the copper-based paint .Japan has developed a coating absorbing electromagnetic shielding , with a molecular weight of up to 1,000,000 performance matrix polymer coating protects the metal conductive filler , the filler to prevent the oxidation of copper , so that the shielding performance and more sustainable 10a . Currently the main problem to be solved copper-based paints are: conductive filler in the polymer matrix dispersion , oxidation resistance , and how to reduce the amount of filler .Nickel-based conductive coating affordable , good chemical stability , oxidation problem lighter than copper , Europe and other countries become electromagnetic shielding paint mainstream. In order to improve low conductivity of nickel-based single problem , often copper , nickel mixed coating thickness of 50 ~ 70μm when a volume resistivity of 10-3Ω • cm, 500 ~ 1000MHz shielding effect up to 30 ~ 60dB.One component of electromagnetic shielding has some limitations , it is difficult to achieve broadband shielding. To further enhance the electromagnetic shielding effect , studied multiple composite coating. Literature on 1 ~ 10GHz band electromagnetic shielding coating nickel-base and zinc oxide whiskers micron nickel powder, lead zirconate titanate , SiC, Ni-Zn ferrite as a filler to prepare a coating , composite , high-speed and high absorption preparation low reflection coating electromagnetic shielding material, 10KHz-1GHZ frequency electromagnetic shielding effect of 40dB. Metal foil , paint two sandwich -type electromagnetic shielding materials, in 30 ~ 1000MHz full band performance is better than ordinary paint , in the 400 ~ 1000MHz band , its overall shielding effectiveness of 10dB higher than ordinary paint over the incident electromagnetic wave at 1GHz , its SE up to 70dB.The use of special properties of nano-materials , Nano functional coating is also the current research focus. Electromagnetic radiation from mobile phones human spacing millimeters , will form a strong radiation effects on the human body can not be ignored . Shanghai China "excellent plus" radiation suit developed a nanoscale " electromagnetic shielding materials," as the industry makes the company a minority master the core technology of electromagnetic shielding materials manufacturers , through the use of nanotechnology, radiation suits metal particle size and more small , can improve the ability of radiation , while significantly reducing material waste , greener .2.2 surface coating shielding materialsBy electroless plating , spraying , vacuum plating , or metal- foil method of processing a conductive surface of the insulator , the electromagnetic shielding effect can be achieved . Bonding a metal foil simple process after the copper, nickel , stainless steel, metal foils , etc. The adhesive sheet and the plastic molding , the shielding effect can reach 60 ~ 70dB.Electroless gold plating will usually Cu, Ni plating , etc. to the surface of the material , with good magnetic conductivity, without limitation appearance and other characteristics . Thicker coatings generally have better EMI shielding effectiveness , shielding value of up to 60 ~ 120dB, by blending technology enables the formation of ABS plastic and other engineering plastics alloys, electroplating plastic to make a number of difficult to get to electroplating .Flame spraying , electric arc spraying manner on the surface of aluminum, zinc , copper and other metal layer with a thickness of about 70μm, the electromagnetic shielding effect of up to 70dB, but the disadvantage is between the metal layer and is firmly bonded to the substrate is not easily fall off. Vacuum plating technique using physical vapor deposition of the metal vaporized metal plating layer is then formed on the substrate surface . Magnetron sputtering can also be used in the coating process , a plastic substrate in a process for preparing HIPS Cu / Ni film in the range of 10K ~ 106KHz , a copper layer is 1.0 ~ 4.0μm , the shielding effect of up to 80 ~ 110dB .2.3 fiber composites2.3.1 metalized fabricEach metal coated fibers and textile fibers or textile surface coating on the metal materials generally used for producing the metal fabric can be , so that it has a metallic luster , conductive, electromagnetic shielding function, while maintaining the original textile softness , resistance to bending , folding resistance characteristics. Processes are commonly used wire and mixed with other fibers , spray evaporation , sputtering , electroless plating, plasma treatment .Internationally this study was carried out earlier . 1980s had industrial production , such as the U.S. Matasolg, Germany Baymetex, the Netherlands and Japan Devex Takase dyers , Toray and other companies. Ion fabric is today the world's most advanced sixth generation of electromagnetic radiation shielding materials, low-temperature plasma treatment is continuous surface deposition process for a particular fabric metal processing methods. Japanese company uses low-temperature plasma of fabric processing , low temperature plasma treatment after completion of the surface Al, Ti, Cr, Ni, Cu and other metal processing . This technique can be improved by bonding a base fabric layer and the metal layer is deposited . After treatment of the metal fabric having good mechanical properties and heat resistance , strong adhesion between the fabric and the metal layer . With this method of processing the metal fabric , overcome the shortcomings of both the existence of a weak binding force between the metal layer and a vacuum deposition method fabric, and avoids the problem of waste water treatment chemical plating .2.3.2 composite conductive fiberConductive fibers using vacuum deposition , electroless plating, polymerization , etc., attached to the metal forming the metal fibers in the fiber surface , inside the fiber or metal particles incorporated in the material , and then pumped into the melt or the magnetic permeability of the conductive fibers.The fibers used are stainless steel fibers, copper fibers , iron fibers, carbon fibers , silver plated fibers and glass fiber . Stainless steel fibers with anti- electromagnetic , antistatic , conductive, high temperature and other effects. Stainless steel fibers having a diameter of about 7μm filler resin filling ratio of 6% ( by volume ) up to the shielding effect of 40dB, and the filling factor increases with increasing SE. Currently , stainless steel fibers United States, France , Belgium, Japan and other developed countries have mass production , the production of the finest stainless steel fibers reach 2μm, typically 8 ~ 22μm. Japan launched iron fibers and polypropylene , and polycarbonate resin formed by mixing the plastic shield , wherein the FE-125, iron fiber packing density FE-125MC, FE-125HP3 species is 20% to 27% ( by volume ) , the shielding effect of up to 60 ~ 80dB.Carbon fiber cable acid, salt erosion, expansion coefficient, electrical resistivity 1.5 × 10-3 ~ 3.0 × 10-3Ω • cm. When the carbon fiber as a conductive filler , fiber length , and the extent and amount of the resin adhesive is the key factor for the quality of the conductive material . To improve adhesion with the substrate fiber , carbon fiber filler is often required before the surface oxidation treatment and grafting .USA developed nickel coated graphite fibers shielding materials filled in the ABS resin 20% ( by volume ) , the diameter of 7μm nickel coated graphite fibers , the value in the high 1000MHz SE 80dB. Shinn-Shyong other studies of the adhesive preparation and chemical copper plating , nickel- covered carbon fiber composite ABS shielding effect , the dispersibility of the fiber and the fiber coating and binding good plating showed good EMI shield effect.Copper fiber due to excellent conductivity and with better shielding effect , brass fibers currently used as filler . Japan launched fiber filled brass shielding materials , a filling factor of 10% ( by volume ) when a volume resistivity of less than 10-2Ω • cm, the shielding effect of up to 60dB.Conductive glass fiber glass fiber surface treatment technology and product of the combination , EMITEC fiber is now widely used . Glass fibers can also be made conductive glass sheet , a Japanese company with a diameter 2μm, a length of 100μm plated conductive glass fibers are glass fiber paper , and the resulting paper a good conductive properties of glass can be combined with a resin to prepare as electromagnetic shielding materials. Red abalone rights and other chemical plating method for preparing a glass / Ni, glass / Cu and glass / Cu/Ni-Cu-P3 kind of conductive glass fibers. Double layer structure of glass / Cu / Ni-Cu-P conductive glass fibers , the high electrical conductivity of Cu and Ni-Cu-P plating layer excellent in resistance to oxidation and thermal stability combined with good anti- prepared conductive oxidative and thermal stability is also good metallised glass fiber conductive filler , shielding effect of up to 50 ~ 60dB in the 500MHz.