Microwave Properties Shielding

This chapter intends to explain, beyond the conventional application of EMI shielding, the specificity of conductive polymers for microwave absorption and gives some examples of measured properties. 

Honeywell Oxy Shield nylon/EVOH oxygen-barrier (OB) film s combination of nylon 6 and EVOH delivers a strong mix of benefits the strength, toughness, and flex-crack resistance of nylon with the extremely low oxygen transmission rates, superior fla-vor/odor/aroma-barrier properties, with the outstanding solvent and oil resistance of both nylon and EVOH. The film is microwaveable and recyclable, and does not release harmful substances upon incineration.do 3]... 

P. Chandrasekhar, K. Naishadham, Broadband Microwave Absorption and Shielding Properties of a Poly(Aniline). Synth. Met. 1999,105,115-120. 

P. Saini, M. Arora, Formation Mechanism, Electronic Properties Microwave Shielding by Nano-Structured Polyanihnes Prepared by Template Free Route Using Surfactant Dopants. /. Mater. Chem. A 2013,1, 8926. 

A. R. A. Schettini, D. Khastgir, B. G. Soares, Microwave Dielectric Properties and EMI Shielding Effectiveness of Poly(Styrene-B-Styrene-Butadiene-Styrene) Copolymer Filled with PAni.Dodecylbenzenesulfonic Acid and Carbon Black. Polym. Eng. Sci. 2012, 52, 2041-2048. 

Magnetic nanoparticles are widely used as electromagnetic absorbers in radiation shielding because they have excellent microwave absorption properties. These materials are also used in microwave-based communication systems functioning at frequencies of the order of 109 Hz due to their low crystalline anisotropy [45]. 

There are many applications where the physical properties of a textile substrate are combined with the electrical and shielding properties of polypyrrole. Thus polypyrrole-coated fabrics show excellent dissipation properties. In this way industrial uniforms where explosion-proof conditions or shielding fi om micro-waves are necessary can be fabricated, as well as the use of polypyrrole-coated filters where static charges could cause the explosion of flammable solvents. Other important applications are related to military equipment, as radar-absorbing sheets. The microwave response of those fabrics seems to be ideal for camouflage nets that avoid visual, near-infrared and radar detection. Textile fabrics have also applications in fiber-reinforced composite structures of different resins. 

For example, blends and semi-IPN of polypyrrole and EPDM rubber, prepared by calendering, absorb 85% of microwave radiation in the 10-13 GHz range [167]. Surface deposition of polypyrrole onto poly-(vinylchloride) produced composites with microwave absorption properties in the 0.1-20 GHz frequency range [168]. The same authors also studied the shielding characteristics of blends of polyaniline and poly(3-octylthiophene) with polystyrene and with the copolymer of ethylene and vinyl acetate. For defense purposes, however, a larger frequency range should be covered, but this only encourages continuation of the research. 

In this study, wood fibers modified with nano-sized magnetite have been developed. They show improved electrical conductivity and microwave adsorption ability. Based on these fibers new polymer composites, with special shielding properties against electromagnetic wave,have been obtained. 

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