Title of Invention | "A PROCESS FOR PREPARING FUNCTIONALLY GRADED POLYMERS COMPOSITES MATERIAL HAVING WIDE RANGE OF BAND-GAP IN MICROWAVE ABSORBING RANGE" |
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Abstract | A novel FGPCs have been developed by polymer matrix, nano/micron materials and other chemicals, i.e., accelerator, curing agent, accelerator activator, process oil and antioxidant. The polymers consisting of either natural rubber, polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, ethylene-propylene rubber, ethylene-propylene diene monomer rubber, butyl rubber, halobutyl rubber, nitrile rubber, hydrogenated nitrile rubber, polysulfide elastomer, polyacrylic rubber, neoprene rubber, hypalon rubber, silicone rubber, fluorocarbon rubber, polyurethane rubber, thermoplastic elastomer and/or mixture thereof are used as a matrix. Nano/micron materials i.e., Fe, Co, Ni, NdaFei4B, SmCo5 SrmCoi, BaO.6Fe2O3, SrO.6Fe2O3, Fe 3wt% Si, Fe 4wt% Si, Fe 35wt% Co, Fe 78wt% Ni, Fe 50wt% Ni, MnO.Fe2O3, etc are used to make the FGPCs. The gradation of nano/micron particles comprises a varying particles size and volume fraction in rectangular and cylindrical and other geometries. |
Full Text | FIELD OF THE INVENTION The present invention relates to functionally graded polymeric composite materials having wide range of band-gap in microwave-absorbing range (FGPCs) and method for preparation of the same. BACKGROUND OF THE INVENTION The growth of the electronic and electrical devices is hindered/hampered due to electromagnetic interference (EMI) caused by the high frequency microwave radiation. These EMI problems create false image generation, disruption of electronic and telecommunication systems, clutter on radar, etc To overcome these problems, a profound interest in the microwave absorption technology is developed In this context radar absorbing materials (RAM) are availed/employed to alleviate/mitigate or eliminate the EMI problems due to the high frequency microwave radiation. Generally, conventional microwave absorbers in high frequency region are the dielectric materials like magnetic materials, ceramic materials, etc., which are dispersed in thermoplastics, foams, rubbers, etc. in such a proportion so as to attain/accomplish maximum absorption. Polymeric radar absorbing material (RAM) is an expedient shielding material as it is flexible and can easily be clipped in last two decades. It can easily form into complex shapes with minimal thickness, maintaining the flexibility and weather ability over a wide range of temperature i.e. -50 to 150°C. These are supplanting their metallic and ceramic counterparts because of ease processing, forming and machining, etc., which subsequently follows to feast on other advantages like high production rate, economy of production, etc. Ishino, et al. (Microwave absorber; Ishino, Ken, Watanabe, Takashi, Hashimoto and Yasuo; US 4003840, January 18 1977) have prepared a microwave absorber comprising of a mixture of 0.2 to 0.9 parts by volume of a ferrite powder (maximum size ~ 1.65 mm; MFe2O4 where M is a divalent metal) and 0.8 to 0.1 parts by volume of an organic high molecular compound. Organic high molecular compound can be a thermosetting resin, thermoplastic resin or rubbers selected from certain groups. The attenuation observed was in the range of 500 MHz to 12 GHz for various loadings of the ferrite filler in the matrix. Each combination is suitable over a narrow range of frequency. In addition to this the concentration of ferrite powder in a given composite is constant. Wright (Combined layers in a microwave radiation absorber; R.W. Wright; US 4,012,738; 15th march 1977) have prepared another microwave radiation absorber by combining the layers that comprised of a layer of dielectric material (barium titanate/aluminum flakes) having high dielectric constant, an intermediate layer of a rigid honeycomb structure (low dielectric constant material) and the layer composed of carbonyl iron particles embedded in neoprene backed by the reflecting surface with all the layers parallel and contiguous to each other having combined thickness approximately a quarter wavelength of microwave radiation. Such types of absorbers were particularly well suited for low frequency range i.e. 400-450 MHz. Kanda, et al. (Electromagnetic wave-shielding materials; M. Kanda, T. Hatakeyama, and Y. Morito; US4508640, 2nd April 1985) have produced electromagnetic wave shielding materials that comprised of one or more wave shielding layers and one or more surface layers. The shielding layers comprised of a thermoplastic resin, an aluminum or aluminum alloy and electrically conductive carbon black while the surface layers comprised substantially of thermoplastic resin. The total proportion of carbon black and aluminum was restricted in between 10 to 60 % >by volume. It was observed that by mixing electrically conductive carbon black having shielding effect in MHz frequency region and aluminum having shielding effect in kHz frequency region in the base material, the resulting mixture imparted electromagnetic wave-shielding effect over a wider frequency region even in the region where the shielding effect was almost not detected when the aluminum component or electrically conductive carbon black was used alone. Frequency for the wave absorption ranges from few kHz to 1 GHz. Hiza, et al. (Multi-layered microwave absorber and method of manufacturing the same; M. Hiza, H. Yamazaki, K. Sugihara and T. So; US4923736, 8th may 1990) have formed a multilayered microwave absorber that comprised a plurality of layers with impedance of each layer increases progressively in the direction of incidence of a microwave. The layers were bonded together into an integral sheet structure by a silicone adhesive compound with a coating thickness of 0.1 mm. The structure comprised of the only resinous/rubber layer on the top (low impedance layer), a high impedance layer containing substantial amounts of ferrite or carbon black and the reflection layer containing the same metal. Drawbacks of the invention were the induction of strain in each layer while processing as the thermal coefficient of expansion of each layer will be different and the poor wave absorbing performance. Domnikov et al. (Emi suppression gasket for millimeter waveguides; L. Domnikov, T.S. Fishkin, J.A. Patrick, and G. Garcia; US4932, 12th June 1990) have produced EMI suppression gasket to seal the joint between two millimeter waveguides wherein the inner and outer shields were formed of a selected metal group like Al, Au, Ag, Cu etc. The plate was formed of rubber filled with electrically conductive metallic particles and the volume fraction of particles, a mixture of powder and flakes, was maintained at least 60 %. This gasket can be used to insulate against radio frequency leakage particularly where the microwaves are of very short wavelengths in the order of 1 millimeter (at around 30 GHz) from the waveguides. Lau, et al. (Electromagnetic radiation suppression cover; F.P. Lau, Jr. Yenni, M. Donald, R.W. Seemann, R.J. Kuo; US5,106,437, 21st April 1992) prepared a conformable electromagnetic radiation suppression cover that comprised of one or more absorbing materials and a sealent. The sealent was used to seal and protect the cover from the environment as well as to assist in adherence of the absorber to the reflecting structure. The absorbers typically were of one or more kinds of dissipative particles dispersed in dielectric binder materials. The particles used include metals, magnetic metals, semiconductors, ferrites, and carbon and dielectric binders encompass polymers and ceramics. The reduction in the electromagnetic reflection coefficient observed was not less than 70 % (5.2 dB) and the absorption range for different samples was in between 3-18 GHz. The thickness of the samples was varied between one fortieth to one fourth of the given wavelength range, (i.e. 0.042 to 2.5 cm). Boyer et al. (Microwave absorber for direct surface application; C.E. Boyer, R.J. Kuo, S.M. Logiudice; US 5275880, 4th January 1994) developed an absorber that can directly be used for surface applications, comprised of an absorbing layer bound to one side of the conductive layer and the other side of which was coated with an adhesive which can be directly applied on the surface of the object. The absorbing layer comprised of any of the dissipative particles of metal, graphite, carbon, or ferrite powders and the dielectric binder could be ceramic, polymeric, or elastomeric. Volume loading factors for absorbing materials comprising carbonyl iron microspheres typically from 40 to 65 percent and the range of frequency of wave absorption varies from 2 to 20 GHz for different loadings. Single loading shows narrow range. Yoshinaka et al. (Radio wave absorbing material; M. Yoshinaka, E. Asakura, M. Oku, K. Matsuo and H. Nakamura; US5310598, 10th May 1994) formed a radio wave absorbing material comprised of a) a holding material of synthetic resin/rubber; b) particles or fibers of ferrite, carbon, conductive potassium titanate, silicon carbide, a metal or mixtures of them and c) at least 1 wt. % of zinc oxide whiskers as a radio wave absorbing element. They observed the material to be capable of attenuating radio waves such as VHP, UHF, microwaves, radar waves and millimeter waves over a wide band, most preferably, in the range of 10 GHz to 15 GHz. Reflection attenuation characteristics were measured for a structure of 2 mm thickness containing 100 phr nitrile rubber, 25 phr ZnO whiskers and attenuation of not more than -7 dB was obtained over a wide band (from 10 to 15 GHz). The attenuation is too small. Kolb (Low profile non-electrically-conductive component cover for encasing circuit board components to prevent direct contact of a conformal EMI shield; L.E. Kolb, US6743975, 1st June 2004) has developed nonelectrically- conductive component cover for encasing printed circuit board components to prevent direct contact of a conformal EMI shield. This EMI shield conformed to the surfaces of the components and the circuit board adding little dimensions to it. The shield had low viscosity, high adherence conductive and dielectric coatings formed by conventional spray techniques. The conductive coating prevented significantly all electromagnetic emissions generated by the shielded components from emanating beyond the conformal coating. The dielectric coating was applied to selected locations of the printed circuit board to interpose between the conductive coating and the circuit board to prevent contacts between them. The component cover was formed of PETE, PPS or synthetic rubbers like silicone rubbers, TEFLON, VITON etc. But the frequency range is 30 MHz to 1 GHz). Sakurai (Electromagnetic wave absorbing compositions; I. Sakurai; US 7030172 18th April 2006) has developed an electromagnetic wave absorption composition having a high breakdown voltage wherein the magnetic powder coated with electrically insulating inorganic fines (RF thermal plasma method) was dispersed in a curable organo-polysiloxane as a base polymer. The magnetic powder used was typically of spinel type cubic ferrite and the insulating inorganic fines were selected from the oxides, nitrides, carbides of various elements. The base polymer can be a thermosetting resin, thermoplastic resin, rubber or the like. Such compositions are mainly effective in MHz band. Most of the known microwave-absorbing materials are effective over a small band gap- OBJECTS OF THE INVENTION An object of the present invention is to provide functionally graded composite (FGPCs) materials having wide range of band-gap in microwave-absorbing range and method for preparation the same, in which the concentration of nano/micron sized materials changes from one surface to the opposite surface. Another object of the present invention is to provide functionally graded composite (FGPCs) materials having wide range of band-gap in microwave-absorbing range and method for preparation the same, which is workable over a wide range of frequency. Further object of the present invention is to provide functionally graded composite (FGPCs) materials having wide range of band-gap in microwave-absorbing range and method for preparation the same, which overcomes disadvantage(s) associated with prior art(s). Yet another object of the present invention is to provide functionally graded composite (FGPCs) materials having wide range of band-gap in microwaveabsorbing range and method for preparation the same, which is capable of being made easily with much improved broadband wave absorption and with higher attenuation in the frequency range. Further object of the present invention is to provide functionally graded composite (FGPCs) materials having wide range of band-gap in microwave-absorbing range and method for preparation the same, in which the process is simple. SUMMARY OF THE INVENTION: In the present invention functionally graded polymer composite materials (FGPCs) have been developed. In another embodiment of the present invention, a method has been developed to fabricate functionally graded polymer composites having various shape (Fig 1) and gradation using polymer matrix, nano/micron particles, antioxidant, accelerator, accelerator activator, processing oil and curing agent. In another embodiment of the present invention, various nano/micron particles Fe, Co, Ni, NdaFenB, SmCo5, Sm2Coj7, BaO.6Fe2O3) SrO.6Fe2O3, Fe 3wt% Si, Fe 4wt% Si, Fe 35wt% Co, Fe 78wt% Ni, Fe 50wt% Ni, MnO.Fe2O3, etc are used to make a novel functionally graded polymer composite. Here the concentration of nano/micron particles decreases or increases based on the requirement, but the particle size remains constant in each FGPCs. In another embodiment of the present invention, various nano/micron particles i.e., Fe, Co, Ni, Nd2Fei4B, SmCo5, SmaCoi?, BaO.eFeaOa, SrO.6Fe2O3, Fe 3wt% Si, Fe 4wt% Si, Fe 35wt% Co, Fe 78wt% Ni, Fe 50wt% Ni, MnO.Fe2O3 etc are also used to make FGPCs. Here, the total volume fraction of nano/micron particles in FGPCs is constant but the particle size of nano/micron particles decreases or increases from qne surface to the opposite surface. In another embodiment of the present invention, various mixed nano/micron particles i.e., combination of any two or more following materials, i.e., Fe, Co, Ni, NdaFenB, SmCos, SmaCoi?, BaO,6Fe2C% SrO.6Fe2O3) Fe 3wt% Si, Fe 4wt% Si, Fe 35wt% Co, Fe 78wt% Ni, Fe 50wt% Ni, MnO.Fe2O3, etc are also used to make FGPCs. Here, both concentration and particle size of nano/micron particles decreases or increases at a time. In another embodiment of the present invention, various polymer (elastomer) matrix i.e., natural rubber, styrene-butadiene rubber, polybutadiene rubber, polyisoprene rubber, ethylene propylene rubber, butyl rubber, halobutyl rubber, nitrile rubber, polyacrylic rubber, neoprene rubber, hypalone rubber, silicone rubber, fluorocarbon rubber, polyurethane rubber, etc are used to make a novel FGPCs. In another embodiment of the present invention, various mixed polymer (elastomer) matrix i.e., combination of any two or more of the following rubbers, i.e., natural rubber, styrene-butadiene rubber, polybutadiene rubber, polyisoprene rubber, ethylene propylene rubber, butyl rubber, halobutyl rubber, nitrile rubber, polyacrylic rubber, neoprene rubber, hypalone rubber, silicone rubber, fluorocarbon rubber, polyurethane rubber, etc are used to make a novel FGPCs. In another embodiment of the present invention, various geometries i.e., rectangular, cylindrical, complex geometry, etc are used to make a novel FGPCs using template (Fig. 1). In another embodiment of the present invention, various hollow geometries i.e., rectangular, cylindrical including complex irregular geometry are used to make a novel FGPCs using template (Fig 1). In a next embodiment, a performance study is made in between functionally graded polymer composite, and conventional composite where the distributions of nano/micron particles are uniform through out the matrix. In a last embodiment, a performance study is made in between functionally graded polymer composites where the percentage of nano/micron materials is same and geometry is also same, but the concentration gradient is different. Fig 1: Types of functionally graded polymeric composites. DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO ACCOMPANYING DRAWINGS : -6- This invention provides a functionally graded polymers composite (FGPCs) materials having wide range of band-gap in microwave-absorbing range and method for preparation of the same comprising a polymer matrix, nano/micron materials and other chemicals i.e., antioxidant, accelerator, accelerator activator, processing oil and curing agent. The process for preparation of the same involves the follows steps: Conditioning of Materials Nano/micron sized materials are kept in an oven at a temperature of 50-125°C for 0.5 to 2 hours to remove moisture. Conditioned nano/micron materials are stored in a closed moisture-proof container to make the same cool and then used for weighing and mixing. Antioxidant is in pellet form so it is converted into powder form with the help of mortar and pestle. The rubber and nano/micron sized materials are weighed within a tolerance of ±lg and all other chemicals are weighed within a tolerance of ±0. Ig accuracy. Mixing Mixing of nano/micron materials and other chemicals in polymer matrix is carried out using two-roll mill having rolls of for example 150 mm in diameter at temperature of 50 to 125°C according to the type of polymer. The speed of front roll is in between 10 to 34 rpm and friction ratio between front and rear roll is 1:1.1 to 1: 1.5. The clearance betweerj rolls is adjustable from 0.1 to 12 mm. The formulation of the various mixes is given in Table 1. In these formulations the loading of metal oxide/s, acid/s, antioxidant/s, processing oil/s, accelerator/s and curing agent/s are in the range of 0.01 to 0.2 (vol fraction). Only the major variable is loading and type of nano/micron materials. During mixing, at first polymer is fed into the nip gap of two roll to obtain a thin sheet. Then antioxidant in powder form is added slowly followed by acid. The batch is cut % of the distance across the roll with the help of a knife, and the knife is held at this position until the bank just disappears. This process is continued for about 10 minutes. Then nanomaterials and/or micron sized materials (0.1 to 0.7 vol fraction) tare added evenly across the mill at a uniform rate. Processing oil is added with nanomaterials and/or micron sized materials to get a good distribution of nano/micron materials into the matrix. The materials falling through the nip is collected carefully from the tray and returned back to the mix. The mixing cycle is concluded by passing the rolled batch endwise through the mill six to eight times with an opening of 0.2 mrn to improve the dispersion. Finally the mixed compound is passed four times through the mill at a setting of 0.1 mm, folding it back on itself each time. The batch is removed and kept on the glass sheet, in a closed container to prevent absorption of moisture from the air for 24 hours. After 24 hours accelerator followed by curing agent is added according to the procedure mentioned above. A thin uncured layer ~0.1 mm (even less than 0.1 mm) of the mix is prepared by pressing in between two teflon sheets in the hydraulic press (for few seconds). The inner surfaces of the teflon sheets are coated with coating agent for easy removal of the layer. The volume (thickness) of all the layers of different mixes is made equal by taking different amount of mixes according to the specific gravity of the chemicals. All these layers of different mixes are stacked sequentially with increasing/decreasing amount of nano/micron materials in each layer to form green FGPCs. Curing Curing is carried out in the hydraulic press at a temperature of 100-200°C and a pressure of 1 to 20 MPa which is exerted on the cross sectional area of the cavities of the mold. The green FGPCs are cut into pieces according to the dimension of the mold cavity using template. Before putting the green FGPCs in the mould cavity, the molding surfaces are polished and cleaned with distilled water and again coated with mould releasing agent. The mold is kept at a curing temperature of 100 to 200°C within ± 0.5°C depending on the type of base rubber in the closed press, held at this temperature for at least 20 minute before the green FGPCs are inserted. The temperature of the mold is controlled by means of the temperature controller attached with the press. The press is opened, the green FGPCs are inserted into the mold, and the press is closed in the minimum time possible to prevent excessive cooling of the mold by contact with cool metal surfaces or by exposure to air drafts. A pressure of 1 to 20 MPa is applied and three bumping is given to remove the air bubbles present, if any, for equal time of 15 sec. Finally, a desired pressure is applied and the mold is held for 10 minutes to 8 hours in the press. As soon as the press is opened the cured FGPCs from the mold is removed and cooled in water for 10 to 15 min. The cured FGPCs are conditioned at a temperature of 23±2°C for at least 16 hours before preparing the samples and testing. This invention .provides a functionally graded polymeric composites (FGPCs) comprising a polymer matrix, nano/micron materials and other chemicals i.e., antioxidant, accelerator, accelerator activator, processing oil and curing agent. A process for preparation of a FGPCs comprising the steps of: - nano/micron particles as per user requirement (varies from 0.1 to 0.7 volume fraction) and all other chemicals (volume percentage is constant for these chemicals) are imbedded in the polymer matrix at the semisolid state (i.e., above the glass transition temperature but below the melting point of rubber) by the conventional two roll mixing mill -a thin layer -0.1 mm is prepared from the nano/micron particles imbedded polymer matrix again by two roll mill and hydraulic press at the semisolid state, -this thin nano/micron particles imbedded polymer matrix is optionally coated by coating agent (i.e., silicone spray, soap solution, silicone emulsion solution, stearic acid, polytetrafluoro ethylene, polyvinyl alcohol, etc), - this thin coated/uncoated nano/micron particles imbedded polymer matrix is cut into the required size using template -the cut piece is laminated either increasing or decreasing order as per requirement (shown in Fig 1 ) to get green functionally graded polymer composites -the green graded sheet is kept in the coated mould (coating of the mould is done by any one of these silicone spray, soap solution, silicone emulsion solution, stearic acid, polytetrafluoro ethylene, polyvinyl alcohol) -the mould with green graded sheet is cured for a certain period of time at a specified temperature and pressure to get a cure FGPCs (temperature is applied from one or both sides that depends on the type of FGPCs as shown in Fig 1) -the cured FGPCs is removed from the mould after curing, cooled in room temperature and retained for 24 hours for further characterization. The polymer matrix is selected from the group comprising of natural rubber, polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, ethylenepropylene rubber, ethylene-propylene diene-monomer rubber, butyl rubber, halobutyl rubber, nitrile rubber, hydrogenated nitrile rubber, polysulfide rubber, polyacrylic rubber, neoprene rubber, hypalon rubber, silicone rubber, fluorocarbon rubber, polyurethane rubber, thermoplastic elastomer, and mixture thereof. The polymer matrix natural rubber is selected from the group comprising of standard malaysian rubber (SMR) L, SMR CV, SMR WF, SMR GP, SMR LV, SMR 5, SMR 10, SMR 20, SMR 50, technically specified rubbers (TSR) 5, TSR 10, TSR 20, TSR 50, technically classified rubber, oil extended natural rubber, deproteinized natural rubber, 'peptized natural rubber, skim natural rubber, superior processing natural rubber, heveaplus MG rubber, epoxidized natural rubber, thermoplastic natural rubber, and mixture thereof; the polymer matrix styrene-butadiene rubber is selected from the group comprising of solution styrene-butadiene rubber i.e., SBR 2305, SBR 2304, emulsion styrene-butadiene rubber i.e., cold SBR 1500, cold SBR 1502, hot SBR 100, and mixture thereof; the polymer matrix polybutadiene rubber is selected from the group comprising of cisamer-01, cisamer!220, BR 9000, BR 9004A, BR 9004B, low molecular weight 1, 3 polybutadiene, and mixture thereof; the polymer matrix butyl rubber is selected from the group comprising of IIR-1751, IIR-1751F, IIR-745, Exxon butyl 007, Exxon butyl 065, Exxon butyl 068, Exxon butyl 165, Exxon butyl 268, Exxon butyl 269, Exxon butyl 365, polysar butyl 100, polysar butyl 101, polysar butyl 101-3, polysar butyl 301, polysar butyl 402, and mixture thereof; the polymer matrix ethylene-propylene rubber is selected from the group comprising of dutral- CO-034, dutral-CO-038, dutral-CO-043, dutral-CO-054, dutral-CO-058, dutral-CO- 059, dutral-CO-055, and mixture thereof; the polymer matrix ethylene-propylenediene- monomer • rubber is selected from the group comprising of ethylenepropylene- dicyclopentadiene rubber, ethylene-propylene-ethylidenenorbornene rubber, ethylene-propylene-1, 4 hexadiene rubber, and mixture thereof; the polymer matrix halobutyl rubber is selected from the group comprising of Exxon chlorobutyl 1065, Exxon chlorobutyl 1066, Exxon chlorobutyl 1068, Polysar chlorobutyl 1240, Polysar chlorobutyl 1255, Exxon bromobutyl 2222, Exxon bromobutyl 2233, Exxon bromobutyl 2244, Exxon bromobutyl 2255, Polysar bromobutyl X2, Polysar bromobutyl 2030, and mixture thereof; the polymer matrix nitrile rubber is selected from the group comprising of Krynac-2750, Nipol- 1053, Nipol-1032, Paracril-C, Chemigum-N-3, Krynac-5075, and mixture thereof; the polymer matrix hydrogenated nitrile rubber is selected from the group comprising of zetpol-1010, zetpol-1020, zetpol-2010, zetpol-2020, therban, and mixture thereof; the polymer matrix polyacrylic rubber is selected from the group comprising of hycar-4051, hycar-4052, hycar-4054, vamac-B-124, and mixture thereof; the elastomer matrix neoprene rubber is selected from the group comprising of neoprene-AC, neoprene-AD, neoprene-ADG, neoprene-AF, neoprene-AG, neoprene-FB, neoprene-GN, neoprene-GNA, neoprene-GRT, neoprene-GS, neoprene-GW, neoprene-W, neoprene-W-MI, neoprene-WB, neoprene-WD, neoprene-WHV, neoprene-WHV-100, neoprene-WHV-200, neoprene-WHV-A, neoprene-WK, neoprene-WRT, neoprene-WX, neoprene-TW, neoprene-TW-100, neoprene-TRT, and mixture thereof; the polymer matrix hypalon rubber is selected from the group comprising of hypalon-20, hypalon-30, hypalon-LD-999, hypalon-40S, hypalon-40, hypalon-4085, hypalon-623, hypalon- 45, hypalon-48S, hypalon-48, and mixture thereof; the elastomer matrix silicone rubber is selected from the group comprising of silicone MQ, silicone MPQ, silicone MPVQ, silicone FVQ, and mixture thereof; the polymer matrix fluorocarbon rubber is selected from the group comprising of viton-LM, viton-C- 10, viton-A-35, viton-A, viton-A-HF, viton-E-45, viton-E-60, viton-E-60C, viton-E403, viton-B-50, viton-B, viton-B-70, viton-910, viton-GLT, viton-GF, viton-VTR-4730, .DAI-EL-G-101, DAI-EL-701, DAI-EL-751, DAI-EL-702, DAI-EL- 704, DAI-EL-755, DAI-EL-201, DAI-EL-501, DAI-EL-801, DAI-EL-901, DAI-EL- 902, tecnoflon-FOR-LHF, tecnoflon-NMLB, tecnoflon-NML, tecnoflon-NMB, tecnoflon-NM, tecnoflon-NH, tecnoflon-FOR-45-45BI, tecnoflon-FOR-70-70BI, tecnofion-FOR~45-C-CI, tecnoflon-FOR-60K-Kl, tecnoflon-FOR-50E, tecnoflon-TH, tecnoflon-TN-50, tecnoflon-TN, tecnoflon-FOR-THF, tecnoflon-FOR-TF-50, tecnoflon-FOR-TF, fluorel-2145, fluorel-FC-2175, fluorel-FC-2230, fluorel-FC- 2178, fluorel-FC-2170, fluorel-FC-2173, fluorel-FC-2174, fluorel-FC-2177, fluorel- FC-2176, fluorel-FC-2180, fluorel-FC-81, fluorel-FC-79, fluorel-2152, fluorel-FC- 2182, fluorel-FC-2460, fluorel-FC-2690, fluorel-FC-2480, and mixture thereof, the polymer matrix polyurethane rubber (polyether and polyester type) is selected from the group comprising of FMSC-1035, FMSC-1035T, FMSC-1040, FMSC- 1050, FMSC-1060, FMSC-1066, FMSC-1070, FMSC-1075, FMSC-1080-SLOW, FMSC-1080-FAST, FMSC-1085, FMSC-1090-FAST, FMSC-1090-SLOW, and mixture thereof; the polymer matrix thermoplastic elastomer (polyurethane, polyester, polyamide, styrene-butadiene-styrene, blends, etc) is selected from the group comprising of SBS 1401, SBS 4402, SBS 4452, SBS 1301, SBS 1401-1, SBS 4303, estane-55103, hytrel-40xy, hytrel-63xy, hytrel-72xy, gaflex-547, pebax-2533, pebax-6333, TPR-1600, TPR-1900, TPR-2800, TELCAR-340, SOMEL- 301, SOMEL-601, santoprene, cariflex-TR, solprene-400, stereon, and mixture thereof; the polymer matrix polysulfide elastomer is selected from the group comprising of thiakol-A, thiakol-B, thiakol-FA, thiakol-ST, and mixture thereof. The polymer matrix natural rubber is cured by vulcanizing agent selected from the group comprising of sulphur, hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, diurethane, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix styrene-butadiene rubber is cured by vulcanizing agent selected from the group comprising of sulphur, hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, diurethane, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix polybutadiene rubber is cured by vulcanizing agent selected from the group comprising of sulphur, hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, diurethane, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix butyl rubber is cured by vulcanizing agent selected from the group comprising of sulphur, hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, diurethane, p-quinone dioxime, p-quinone dioxime dibenzoate, phenol-formaldehyde resin, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix ethylene-propylene rubber is cured by vulcanizing agent selected from the group comprising of hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-bis (tbutyl peroxy) hexane, bis(2,4-dichloro-benzoyl) peroxide, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix ethylenepropylene- diene-monomer rubber is cured by vulcanizing agent selected from the group comprising of sulphur, hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, diurethane, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix halo butyl rubber is cured by vulcanizing agent selected from the group comprising of sulphur, hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, zinc oxide, p-quinone dioxime, p-quinone dioxime dibenzoate, phenol-formaldehyde resin, amine, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix nitrile rubber is cured by vulcanizing agent selected from the group comprising of sulphur, hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix hydrogenated nitrile rubber is cured by vulcanizing agent selected from the group comprising of sulphur, hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, dit- butyl peroxide, 2,5-dimethyl-2,5-bis (t-butyl peroxy) hexane, bis(2,4-dichlorobenzoyl) peroxide, tertiary butyl perbenzoate, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix poly aery lie rubber is cured by vulcanizing agent selected from the group comprising of amine, diamine, activated thiol, sulphur, thiourea, trithiocyanuric acid, hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix neoprene rubber is cured by vulcanizing agent selected from the group comprising of magnesium oxide, zinc oxide, lead oxide, iron oxide, titanium oxide, amine, phenol, sulfenamide, thiazoles, thiuram, thiourea, guanidine, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix hypalon rubber is cured by vulcanizing agent selected from the group comprising of magnesium oxide, zinc oxide, lead oxide, iron oxide, titanium oxide, sulphur, hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, N,N'-m-phenylenedimaleimide, amine, phenol, sulfenamide, thiazoles, thiuram, thiourea, guanidine, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix silicone rubber is cured by vulcanizing agent selected from the group comprising of hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, di-t-butyl peroxide, .2,5-dimethyl- 2,5-bis (t-butyl peroxy) hexane, bis(2,4-dichloro-benzoyl) peroxide, tertiary butyl perbenzoate, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix fluorocarbon rubber is cured by vulcanizing agent selected from the group comprising of hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-bis (t-butyl peroxy) hexane, bis(2,4-dichloro-benzoyl) peroxide, tertiary butyl perbenzoate, hexamethylenediamine carbamate, bis(cinnamylidene) hexamethylenediamine, hydroquinone, 4-4'-isopropylidene bisphenol or mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix polyurethane rubber (polyether and polyester type) is cured by vulcanizing agent selected from the group comprising of 1,4-butanediol, 1,4-cyclohexanedimethanol, l,4-bis(2- hydroxyethoxy) benzene, 4,4'methylene-bis(2-chloroaniline), and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); the polymer matrix thermoplastic elastomer (polyurethane, polyester, polyamide, styrene-butadienestyrene, blends, etc) is cured by vulcanizing agent selected from the group comprising of lead oxide, cadmium oxide, zinchydroxide, hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-bis (tbutyl peroxy) hexane, bis(2,4-dichloro-benzoyl) peroxide, tertiary butyl perbenzoate, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction); and the polymer matrix polysulfide elastomer is cured by vulcanizing agent selected from the group comprising of lead oxide, cadmium oxide, zinchydroxide, hydrogen peroxide, dicumyl peroxide, benzoyl peroxide, di-t-butyl peroxide, 2,5-dimethyl-2,5-bis (t-butyl peroxy) hexane, bis(2,4-dichloro-benzoyl) peroxide, tertiary butyl perbenzoate, hexamethylenediamine carbamate, bis(cinnamylidene) hexamethylenediamine, hydroquinone, 4-4'-isopropylidene bisphenol, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction). The polymer matrix comprising of either natural rubber, polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, ethylene-propylene rubber, ethylene-propylene diene monomer rubber, butyl rubber, halobutyl rubber, nitrile rubber, hydrogenated nitrile rubber, polysulfide elastomer, polyacrylic rubber, neoprene rubber, hypalon rubber, silicone rubber, fluorocarbon rubber, polyurethane rubber, thermoplastic elastomer and/or mixture thereof is graded by nano/micron sized particles selected from the group comprising of Fe, Co, Ni, NdaFeuB, SmCos, SmaCoi?, BaO.6Fe2O3, SrO.6Fe2O3, Fe 3wt% Si, Fe 4wt% Si, Fe 35wt% Co, Fe 78wt% Ni, Fe 50wt% Ni, MnO.FeaOa, and mixture thereof which is in the range of 0.1 to 0.7 by volume. The polymer matrix comprising of either natural rubber, polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, ethylene-propylene rubber, ethylene-propylene diene monomer rubber, butyl rubber, halobutyl rubber, nitrile rubber, hydrogenated nitrile rubber, polysulfide elastomer, polyacrylic rubber, neoprene rubber, hypalon rubber, silicone rubber, fluorocarbon rubber, polyurethane rubber, thermoplastic elastomer and/or mixture thereof is further graded by mixed nano/micron particles having same concentration gradient but different particle size i.e 5 nm and 1 to 50 micron and selected from the group comprising of Fe, Co, Ni, Nd2Fei4B, SmCos, SmaCoi?, BaO.GFeaOs, SrO.6Fe2O3, Fe. 3wt% Si, Fe 4wt% Si, Fe 35wt% Co, Fe 78wt% Ni, Fe 50wt% Ni, MnO.Fe2O3, and mixture thereof which is in the range of 0.1 to 0.7 by volume The curing of polymer matrix comprising of either natural rubber, polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, ethylene-propylene rubber, ethylene-propylene diene monomer rubber, butyl rubber, halobutyl rubber, nitrile rubber, hydrogenated nitrile rubber, polysulfide elastomer, polyacrylic rubber, neoprene rubber, hypalon rubber, silicone rubber, fluorocarbon rubber, polyurethane rubber, thermoplastic elastomer and/or mixture thereof is further accelerated by accelerator selected from the group comprising of tert-buttylbenzthiazyl sulphonamide, benzthiazyl 2- sulphenmorpholide, dicyclohexyl benzthiazyl sulphonamide, N-cyclohexyl-2- benzothiazole sulfenamide, 2-mercaptobenzothiazole, 2,2'dibenzothiazyl disulfide, tetramethylthiuram disulfide, zinc dimethyldithiocarbamate, zinc dibutyldithiocarbamate, 4,4'dithiodimorpholine, tellurium diethyldithiocarbamate, dipentamethylene thiuramhexasulfide, tetramethylthiuram monosulfide, ferricdimethyldithiocarbamate, zinc mercaptobenzthiazole, zinc 0,0 dibutylphosphorodithioate, zinc diethyldithiocarbamate, 4-4'dithio dimorpholine, which is in the range of 0.01 to 0.2 (volume fraction) and , and mixture thereof in a ratio of 1 : 99 to 99:1 (by volume). The curing of polymer matrix comprising of either natural rubber, polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, ethylene-propylene rubber, ethylene-propylene diene monomer rubber, butyl rubber, halobutyl rubber, nitrile rubber, hydrogenated nitrile rubber, polysulfide elastomer, polyacrylic rubber, neoprene rubber, hypalon rubber, silicone rubber, fluorocarbon rubber, polyurethane rubber, thermoplastic elastomer and/or mixture thereof is further accelerated by accelerator activator selected from the group comprising of metal oxide and acid which is in the range of 10:1 to 1:10 (by volume). The metal oxide used in accelerator activator is selected from the group comprising of zinc oxide, lead oxide, calcium oxide, magnesium oxide, lead oxide, etc which is in the range of 0.01 to 0.2 (volume fraction). The acid used in accelerator activator is selected from the group comprising of stearic acid, palmitic acid, oleic acid, etc which is in the range of 0.01 to 0.2 (volume fraction). The FGPCs further comprises an antioxidant selected from the group comprising of condensation product of acetone and diphenyl-amine, phenyl-betanapthylamine, blends of diphenyl-p-phenylene diamine and selected arylamine derivatives, blend of arylamines, polymerized 1,2 dihydro 2,2,4-trimethyl quinoline, N~(l,3-dimethylbutyl)-N'-phenyl-p-phenylene-diamine, diaryl para phenylene diamines, 2 mercaptobenzimidazole, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction). The FGPCs further comprises a process oil selected from the group comprising of paraffmic oil, naphthenic oil, aromatic oil, vegetable oil, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction). The nano/micron sized particles and other chemicals imbedded polymer matrix is prepared by mixing the polymer and other compounding ingredients by conventional methods such as open roll mixing using two roll mill and internal mixing kneader, intermix and banbary mixer. The thin polymer layer (before curing) is prepared by two roll mill at a temperature range from about 50°C to about 125°C depending on the type of rubber, and at a friction ratio from about 1:1.1 to about 1:1.5 to selectively produce a thin layer within the range of 0.1 to 10 mm in thickness. The thin polymer layer is optionally coated by one or more coating agent selected from the group comprising of polytetrafluoro ethylene, polyvinyl alcohol, silicone emulsion and detergent/soap solution. The green graded nanocomposites is prepared by laminating of thin polymer layer to produce a rectangular sheet having a thickness within the range of 2 to 1000 mm or unlimited in higher side, or cylindrical shape having a diameter within the range of 10 to 100 mm or unlimited in higher side. The green graded nanocomposites of rectangular/cylindrical shape is cured by hydraulic press in the temperature range of 100°C to about 200°C for 10 minutes to about 8 hours and at pressure in the range of 1 MPa to about 20 MPa. The volume fraction of nano/micron sized materials varies within the range of 0.1 to 0.7 (volume fraction) from the inner surface to outer surface or from outer surface to inner surface (Fig 1) or from outer surface to outer surface i.e., opposite surface (Fig 1). The orifice both regular and irregular, i.e., complex geometry including its dimension (as shown in Figl) were made from one surface to the opposite surface using template; and the concentration of nano/micron sized materials at the inner surface could be varied from 0.01 to 0.2 (volume fraction) depending on the requirement; and the dimension of orifice could be varied using template. Specimen preparation The specimen is cut with the help of sample cutter. Before cutting the specimen, the edges of the die are lubricated with water to facilitate cutting. Thickness of the specimen is measured by means of thickness gauge. Three readings are taken within the gauge length of the specimen, and finally average of the readings is calculated. Width, of the specimens is also measured as the distance between the cutting edges of the blades of the die. Measurement Fig. 2 shows a typical configuration for the measurement of reflection loss over a range of frequency under transmission/ reflection modes wherein the sample is inserted into a segment of a coaxial transmission line. The attenuation in the microwaves is measured in the coaxial transmission line for TEM (transverse electromagnetic waves) propagation mode. Torroidal shaped sample is fitted in the space between the inner and outer conductors of the coaxial line. Then it is backed by the metal (to make it short). Sample is placed exactly at the center of the holder. Torroidal shaped teflon samples are also kept adjacent to the polymer sample to connect the inner conductor perfectly with the two ports. In the case of functionally graded composites (Fig.l), the materials are placed in the holder in such a way that the less filler volume surface should confront/come in the direction of incidence of a microwave. The complex scattering parameter Sn* corresponding to reflection is measured using a Hewlett Packard 8720B network analyzer. The range of frequency swept during measurement is 1-20 GHz. Full two-port calibration is performed on the set-up to eliminate the errors due to directivity, source match, load match and isolation. The effects of sample holder are nullified by de-embedding technique. The similarity between Sn* and 822* and between 812* and 821* for different volume fractions of uniformly distributed polymeric composites shows their reciprocity in the absence of external magnetic field. Scanning Electron Microscopy (SEM) The distribution of nano/micron sized materials in polymer matrix were also determined by using a FEI QUANTA 200 Scanning Electron Microscope (SEM). Prior to SEM studies, the samples were sputter coated with Au-Pd without touching the surface. Sample Microwaves in from port 1 AH diimslom are in mm. Fig. 2: Sample holder assembly Various uniformly dispersed polymeric composites having different volume fractions of the filler (Vf ranging between 0.18 to 0.7) are prepared. Different coordinated sequences/combinations of filler gradations are also prepared wherein the loading is varied from 0.18 to 0.7 along thickness of the sheet and the average volume fraction of the filler is altered to compare these functionally graded polymeric composites (FGPC) with uniformly dispersed polymeric composites (UDPC) (Fig.l). Thickness of the sheet is one of the six parameters that determine the impedance matching condition for zero reflection. For a balanced comparison of UDPC and FGPC, the thickness and an average volume fraction of the filler are maintained constant while preparing both types of sheets. Here, the electromagnetic properties of UDPC and FGPC like e* and p.* will be different even after maintaining the thickness and average filler loading constant, because, the distribution of filler also determines these properties. In FGPC, the filler volume fraction is continuously varying along the thickness direction, so the electromagnetic properties of the FGPC like E* and u* change and hence absorbing properties also change. For a normally incident microwave, lesser the impedance mismatch, lesser the reflection loss will be (absorption will be higher). Both of these microwave-absorbing materials are illuminated by a propagating wave. The absorbers are backed by a metal to reduce the reflection (or to enhance the absorption) through impedance matching. There will be no reflection (total absorption) when the normalized input impedance (Zm) equals the impedance of the free space (Z0). The parameters that determine the impedance matching are ur', ur", er', er", t and frequency of an electromagnetic wave. Smaller the impedance matching degree, closer the values of Zm and Z0 and lesser the reflection loss of radar absorbing material will be. Fig. 3 Variation in the absorption levels of UDPC (uniformly dispersed polymeric composite) with different volume fractions of powders (A: volume fraction of filler varies from 0.05 to 0.35; B: volume fraction of filler varies from 0.39 to 0.52). Fig. 3 (A) shows the variation of reflection loss for uniformly dispersed polymeric composites containing different volume fraction of nano/micron sized powders over the frequency range of 500 MHz to 20 GHz. For much lesser volume fraction of nano/micron sized fillers in the base polymer, reflection loss is negligible. With further increase in the volume fraction of nano/micron sized filler, the maximum attenuation shifts to a higher frequency and simultaneously the maximum absorbing effect increases. At Vf = 0.05, the maximum attenuation of -1.5 dB is observed at a frequency of 6.4 GHz, while at Vf = 0.35, the maximum attenuation of -13.9 dB is observed at 10.4 GHz. The frequency bandwidth for RL GHz for both the cases. Fig. 3(B) shows the maximum microwave absorbing effect (i.e. RL at the peak) and the bandwidth corresponding to RL volume fraction of powder ranging in between 0.39 to 0.43. In UDPC (uniformly dispersed polymeric composite), for a given thickness of 2.5 mm, the maximum absorption of -19 dB at 12.7 GHz and the maximum bandwidth of RL 3.5 GHz ranging in between 11.2 to 14.7 GHz, for the volume fraction of the filler from 0.39 to 0.43 is observed. Wider and deeper the bandwidth is better for the microwave absorbing material. Fig.3 also reveals that for this given thickness of the UDPC (2.5 mm), the frequency 12.7 ± 1 GHz represents the matching frequency with minimum reflection loss at a given filler volume fraction of 0.41 ± 0.2. With further addition of particle's loading, maximum attenuation again shifts to higher frequency range, and maximum absorbing effect decreases. For Vf = 0.46, maximum attenuation of -11.5 dB is observed at a frequency of 15 GHz. Similarly for Vf = 0.52, maximum attenuation of -8.0 dB is observed at a frequency of 15.3 GHz. Again the frequency bandwidth of RL composites containing Vf = 0.46 and Vf = 0.52. From Fig. 3, it is clear that the maximum attenuation and frequency bandwidth of RL proportional to the volume fraction of filler. With increasing the volume fraction of filler, both maximum attenuation and frequency bandwidth increase till it reaches 0.43 and decreases again with further addition of filler. -16- Here a comparison has been made between the composite sheet prepared by uniform dispersion of powder in a polymer and the functionally graded sheet with directional and smooth variation of filler loading in polymer matrix maintaining the same average amount of filler and the thickness as in the homogeneous composite sheet. Fig. 4 Comparison of UDPC (uniformly dispersed polymeric composite) and FGPC (functionally graded polymeric composites) for an equal average volume fraction and thickness (A:V> = 0.35, t = 2.5 mm and B: Vf = 0.39, t = 2.5 mm) Fig. 4 (A) shows the comparison of the reflection loss (microwave absorption) between the uniformly dispersed powder (300 mesh) with volume fraction 0.35 in polymer matrix and the functionally graded sheet wherein the volume fraction of iron powder is varied smoothly along thickness from 0.18 to 0.46 maintaining the average volume fraction of filler in the base material as 0.35. Thickness of both the sheets maintained constant and is 2.5 mm. For Vf = 0.35 in UDPC (uniformly dispersed polymeric composites), frequency bandwidth of RL and the maximum attenuation at 10.4 GHz is -13.9 dB. While for the same average amount of filler volume fraction (Vf = 0.35), FGPC shows different results when the volume fraction of filler is varied from 0.18 to 0.46 along thickness. The maximum attenuation at 10 GHz is -29.6 and the frequency bandwidth of RL 15 dB is 3.8 GHz ranging between 8.7 to 12.5 GHz. The reason for getting different results in UDPC and FGPC for a constant thickness and loading for a normally incident microwave is the impedance mismatching. Closer the normalized input impedance at the surface of the microwave absorbing material to the impedance of the air (377 Q), higher the attenuation/absorption of a microwave will be. Herein, the microstructure and hence the properties of FGPC are changing continuously with varying loading proportion of the filler along the thickness. Similarly, the comparison of reflection loss of UDPC and FGPC for an average filler volume fraction of 0.39 is made in a frequency range of 500 MHz to 20 GHz (Fig. 4(B)). For a normally incident microwave, for a given thickness of 2.5 mm, difference in the attenuation characteristics and frequency bandwidth for RL in Fig. 4(B). The attenuation of microwaves and the frequency bandwidth of RL 15 dB is observed to be maximum for Vf = 0.39 compared to all other types of UDPCs (uniformly dispersed polymeric composites) for a given thickness of 2.5 mrn. The maximum attenuation of -18.8 dB at 12.6 GHz and the frequency bandwidth of 3.5 GHz for RL concentration of -FGPC- is faced front to the normally incident microwaves, maximum attenuation of - 49.5 dB at 12.3 GHz and the frequency bandwidth of RL Fig. 5 Comparison of UDPC (uniformly dispersed polymeric composite) and FGPC (functionally graded polymeric composite) for an equal average volume fraction and thickness (A: Vf = 0.46, t = 2.5 mm and B: Vf = 0.52, t = 2.5 mm) Even for the average volume fraction of iron of 0.46, FGPC outperforms UDPC when attenuation characteristics as well as broadness of the frequency bandwidth are considered as shown in Pig. 5 (A). The maximum attenuation for Vf = 0.46 in UDPC at 15.4 GHz is -11.6 dB and the frequency bandwidth of RL GHz while for FGPC, the maximum attenuation at 9.75 GHz is -18.8 dB and the frequency bandwidth of RL theoretically as well as experimentally proved that higher values of pr', sr' and tan8p results in a thinner absorber. Attenuation of microwave energy occurs due to dielectric and/or magnetic loss of a microwave absorber. For a given thickness, much higher attenuation in the broadband frequency range is observed in the functionally graded polymeric composites compared to the uniformly dispersed composites for a given average loading of filler content. All combination of gradations (volume fraction ranging from 0.18 to 0.56) show better absorption of microwaves in wider frequency range with respect to their uniformly dispersed composites counterpart for a given average volume fractions of the filler. Whereas for an average volume fraction the filler of 0.52, the attenuation characteristics and frequency bandwidth for RL even the resultant FGPC doesn't meet the requisite requirements demanding for the absorber's performance. The UDPC having the filler volume fraction of 0.52, maximum attenuation of -7.8 dB at 15.4 GHz and frequency bandwidth of RL 15 dB is 0 GHz while for the same thickness and loading, in FGPC, maximum attenuation of -15.8 dB at 15.4 GHz and the frequency bandwidth for RL is 1.3 GHz ranging between 14.9 to 16.2 GHz. From the Fig. 5(B), it can be noticed that the initial parts of both the curves are overlapping over each other. The major change in the curves is noticed in the frequency range 10-20 GHz, the range that primarily represents the peaks of the reflection loss curves of UDPC for higher loading of the filler is as shown in Fig. 3. -18- Here, the volume fractioh of the filler in UDPC is 0.52 while in the corresponding FGPC the volume fraction varies from 0.46 to 0.56 that also implies higher loading of the filler throughout the thickness. Thus there is hardly any change in the microwave absorption behaviour (RL curve) of the UDPC and FGPC in the initial parts of the curves (up to 6 GHz). The comparison of UDPC and FGPC is shown in Table 2. Table 2 reveals that the functionally graded polymeric composite shows higher bandwidth as well as higher attenuation for a given volume fraction of the filler and the thickness of the composite. The properties of FGPC are superior to corresponding UDPC even when the matching frequency for the given thickness of UDPC for a given volume fraction of the filler are considered. Maximum attenuation of microwaves is observed to be nearly at the same frequency in both UDPC as well as FGPC (except at Vf = 0.46). Pig. 6 shows the SEM fractographs of different powder loadings in polymer. It is evident that the particles are dispersed uniformly, oriented haphazardly and separated from each other at lower loadings throughout the matrix as shown in Pig. 6 (a, b, c). With increasing powder content in the matrix (see Fig.6: d, e, f) inter-particle distance decreases and the probability for formation of agglomerates becomes more. Fig. 6(d) shows the formation of few agglomerates at Vf = 0.3 and the amount of agglomerates formed increases exorbitantly at Vf =0.35. The irregular fractured surfaces of higher loading composites (Fig. 6: d, e, f) show the distinct phase separation occurred due to agglomerate formation and that phase has been removed from these locations during failure of the material. Fig. 6. (f) also shows highly irregular fractured surface of highly filled (Vf = 0.52) fillerpolymer composites with deep depressions that corresponds to the chipping off of the big agglomerates during fracture. -19- Fig. 6 SEM fractographs of different particle loadings in polymer, (a) Vf = 0.01 (b) Vf = 0.05 (c) Vf = 0.09 (d) Vf = 0.3 (e) Vf = 0.35 (f) Vf = 0.52 EXAMPLES Example A: 20 gm metal oxide/s, 6 gm acid/s, 6 gm antioxidant/s, 1 to 300 gm (interval of 10 gm) nano/micron sized materials (variable), 20 gm processing oil/s, 10 gm curing agent/s and 7 gm accelerator/s are mixed in 350 gm polymer/s at a temperature of 50 to 125°C for 10 to 150 minutes and at friction ratio of 1:1.1 to 1:1.5 by two roll mixing mill. After uniform mixing of all these chemical ingredients in to the matrix, a thin sheet of thickness in the range of 0.1 to 10 mm (based on our requirement) is prepared at a temperature of 50 to 125°C, and at friction ratio of 1:1.1 to 1:1.5 in the same two roll mixing mill. Both sides of this thin sheet/s are optionally coated with coating agents. The coated/uncoated thin sheet is kept in hydraulic press in between two teflon sheet and pressed it again to make a very thin sheet of thickness less than 0.1 mm. The coated/uncoated thin sheets are laminated to the desired thickness to make a green FGPCs either in increasing or decreasing order of nano/micron particles by using template. The split steel die is preheated before putting these green FGPCs in it. The preheating is done in a hydraulic press at a temperature of 100 to 200°C. After temperature is reached close to the desired temperature, the green FGPCs are filled in the die and the other half is placed over it. The temperature of 100 to 200°C and pressure of 1 to 15 MPa and time of 10 minutes to 8 hours are selected to obtained cured FGPCs. The cured FGPCs are taken out from the mould. Measurements of reflection loss over a range of frequency are carried out to know its performance for high tech application. Example B: 32 gin metal oxide/s, 10 gm acid/s, 11 gm antioxidant/s, 1 to 300 gm nano/micron sized material/s (variable, interval of 10 gm), 25 gm processing oil/s, 20 gm curing agent/s and 11 gm accelerator/s are mixed in 700 gm polymer/s at a temperature of 50 to 125°C for 10 to 150 minutes and at friction ratio of 1:1.1 to 1:1.5 by two roll mixing mill. The green FGPCs are prepared as per method described in example 1. The green FGPCs are filled in the die and the other part of the die is placed over it at a temperature of 100 to 200°C wherein the pressure is 1 to 15 MPa. The temperature and pressure are maintained for 10 minutes to 8 hours. The cured FGPCs are taken out from the mould. Now the FGPCs are characterized by reflection loss over a range of frequency carried out to know its performance for high tech application. Example C: 10 gm metal oxide/s, 6 gm acid/s, 5 gm antioxidant/s, 1 to 300 gm nano/micron sized material/s (variable, interval of 10 gm), 10 gm oil/s, 7 gm curing agent/s and 5 gm accelerator/s are mixed in 4 gm polymer/s at a temperature of 50 to 125°C for 10 to 150 minutes and at friction ratio of 1:1.1 to 1:1.5 by two roll mixing mill. The green FGPCs are prepared as per method described in example 1. The green FGPCs are filled in the die and the other part of the die is placed over it at a temperature of 100 to 200°C in which the pressure is 1 to 15 MPa. The temperature and pressure are maintained for 10 minutes to 8 hours and the cured polymer is taken out from the mould. Now the FGPCs is characterized by reflection loss over a range of frequency carried out to know its performance for high tech application. COMMERCIAL POTENTIAL A. Use of microwave electronics by military because of the increased potential for radio frequency (RF) interference. The wallop/impact of the microwave interference on 'military causes various troubles like errors in targeting, reducing system efficiencies etc. Microwave absorbing materials mitigate/attenuate radio wave reflections such as ETC (electronic toll collection system, radar's and TV ghost measures etc. In stealth technology, radar absorbing materials can be of paramount importance. B. A wide range of applications like housing materials for office equipments such as facsimiles, printers; to improve the noise resistance of electronic equipments such as a TV, radio, video system, microwave oven; for communication equipments etc. C. Some applications in automobile industries like control devices in connection with the engine power of a car, speed controller, protective cases, noise prevention of a radio, TV used in cars, panel housings for control instruments etc. D. Cavity resonance problems generally occur due to reduction in the sizes of modules and the demand for enveloping the microwave circuit boards in metallic boxes/cases/housings to offer shielding and to avoid cavity damping interference, the cavity damping absorber materials (cavity damping interference is ascribable to the generation of a standing wave due to stray radiation and the physical properties of the cavity) are applied to the cover of the microwave module. FEATURES OF THE INVENTION (1) A functionally graded polymeric structure is made with and without any adhesive layer between them. (2) The base material used is polymer so it can easily be clipped and confirm to the structure to be shielded as it is highly flexible. (3) Because of the -gradation of nano/micron sized filler in polymer matrix, the criteria required for high permittivity on the front side and high permeability on the rare side is fulfilled. (4) The combination of a) the frequency dependence of loading of the nano/micron sized filler in a dielectric base material (synthetic polymers) and b) the criteria required for high permittivity on the front side and high permeability on the rear side of the structure has led to the evolution of functionally graded polymeric composites. (5) The gradation of nano/micron sized filler along the thickness of the composite sheet has led to the broadband absorption of the unwanted electromagnetic waves and at the same time the accomplishment of the criteria required for higher permittivity on the front side and higher permeability on the rear side of the structure is accomplished for maximum absorption in a given broadband range. (6) The maximum microwave absorption (absorption « 97 %) in a broadband frequency range (~ 9.5 GHz) using a thin, flexible and conformal to the structure to be shielded. ADVANTAGES OF THE PRESENT INVENTION OVER PRIOR ART(S). (1) The primary advantage of employing functionally graded polymeric composites for the attenuation/elimination of the unwanted electromagnetic waves lies in making it possible to adhere all the different layers contiguous and parallel with each other without coating any adhesive between the stacking layers unlike prior art. (2) Attainment of maximum microwave absorption (absorption « 97 %) in a broadband frequency range (~ 9.5 GHz) using a comparatively thin, flexible and conformal sheet that shields the structure. (3) The processing method adopted to prepare the functionally graded polymeric composite (FGPC) is easier with lesser processing cost (cost of forming and machining is not required) that subsequently follows to feast on other advantages like high production rate, economy of production, etc. (4) No separate layer containing high dielectric constant filler in the base material at the front is required. It further reduces the cost of the composite structure. (5) For any possible combination of sequential gradation of filler within a given range, the functionally graded polymeric composite outperforms to its uniformly dispersed counterpart for an equal average loading and thickness. (6) For any given volume fraction and the thickness of the filler, the properties of FGPC are superior compared to the corresponding UDPC (uniformly dispersed polymeric composites) even when the matching frequency for the given thickness of composite is considered. a - Uniformly dispersed polymeric composite; b - Functionally graded polymeric composite FGPC (Vf = 0.35) o.is-o.46 - Functionally graded polymeric composite with average volume fraction of iron powder is 0.35, wherein the volume fraction of the filler is varied from 0.18 to 0.46 along the thickness of the sheet. It is to be noted that the formulation of the present invention is susceptible to modifications, adaptations and changes by those skilled in the art. Such variant formulations are intended to be within the scope of the present invention, which is further set forth under the following claims: WE CLAIM 1. A functionally graded polymeric composite materials having wide range of band-gap in microwave-absorbing range (FGPCs) comprising a polymer matrix, 0.2-0.8 by vol, metal oxide(s), acid(s), antioxidant(s), processing oil(s), accelerator(s) and curing agent(s) are 0.01-0.2 by vol. and nano/micron material(s) is 0.1-0.7 by vol. with respect to the polymer. 2. A process for preparation of functionally graded polymers composite materials having wide range of band-gap in microwave-absorbing range (FGPCs) comprising steps of:- mixing of processing oil(s), nanomaterial(s) and other chemicals in polymer matrix such as herein described, preparation of a thin layer out of the mixture thus obtained followed by lamination of the cut piece to obtain green functionally graded polymers and/or functionally graded polymer nanocomposites, and curing of the green graded sheet in a mould. 3. A process as claimed in claim 2 wherein the mixing is carried out using two-roll mill at a temperature of 50-125°C wherein the speed of front roll is 10-34 rpm and friction ratio between front and rear roll is 1:1.1-1:1.5 to obtain a thin layer of 0.1-10 mm in which the thin layer and the mould is coated with a coating agent such as silicone spray, detergent/soap solution, silicone emulsion solution, stearic acid, polytetrofluoro ethylene, polyvinyl alcohol etc in which the mixing may be carried out by other methods such as internal mixing kneader, intermix and banbary mixer. 4. The FGPCs as claimed in Claim 1 wherein the polymer matrix is selected from the group comprising of natural rubber, polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, ethylene-propylene rubber, ethylene-propylene diene-monomer rubber, butyl rubber, halobutyl rubber, nitrile rubber, hydrogenated nitrile rubber, polysulfide rubber, polyacrylic rubber, neoprene rubber, hypalon rubber, silicone rubber, fluorocarbon rubber, polyurethane rubber, thermoplastic elastomer, and mixture thereof wherein the polymer matrix natural rubber is selected from the group comprising of standard malaysian rubber (SMR) L, SMR CV, SMR WF, SMR GP, SMR LV, SMR 5, SMR 10, SMR 20, SMR 50, technically specified rubbers (TSR) 5, TSR 10, TSR 20, TSR 50, technically classified rubber, oil extended natural rubber, deproteinized natural rubber, peptized natural rubber, skim natural rubber, superior processing natural rubber, heveaplus MG rubber, epoxidized natural rubber, thermoplastic natural rubber, and mixture thereof; the polymer matrix styrene-butadiene rubber is selected from the group comprising of solution styrene-butadiene rubber i.e., SBR 2305, SBR 2304, emulsion styrene-butadiene rubber i.e., cold SBR 1500, cold SBR 1502, hot SBR 100, and mixture thereof; the polymer matrix polybutadiene rubber is selected from the group comprising of cisamer-01, cisamerl220, BR 9000, BR 9004A, BR 9004B, low molecular weight 1, 3 polybutadiene, and mixture thereof; the polymer matrix butyl rubber is selected from the group comprising of IIR-1751, IIR-1751F, IIR-745, Exxon butyl 007, Exxon butyl 065, Exxon butyl 068, Exxon butyl 165, Exxon butyl 268, Exxon butyl 269, Exxon butyl 365, polysar butyl 100, polysar butyl 101, polysar butyl 101-3, polysar butyl 301, polysar butyl 402, and mixture thereof; the polymer matrix ethylene-propylene rubber is selected from the group comprising of dutral-C0-034, dutral-CO-038, dutral-CO-043, dutral-CO-054, dutral-CO-058, dutral-CO-059, dutral-CO-055, and mixture thereof; the polymer matrix ethylene-propylene-diene-monomer rubber is selected from the group comprising of ethylene-propylene-dicyclopentadiene rubber, ethylene-propylene-ethylidenenorbornene rubber, ethylene-propylene-1, 4 hexadiene rubber, and mixture thereof; the polymer matrix halobutyl rubber is selected from the group comprising of Exxon chlorobutyl 1065, Exxon chlorobutyl 1066, Exxon chlorobutyl 1068, Polysar chlorobutyl 1240, Polysar chlorobutyl 1255, Exxon bromobutyl 2222, Exxon bromobutyl 2233, Exxon bromobutyl 2244, Exxon bromobutyl 2255, Polysar bromobutyl X2, Polysar bromobutyl 2030, and mixture thereof; the polymer matrix nitrile rubber is selected from the group comprising of Krynac-2750, Nipol-1053, Nipol-1032, Paracril-C, Chemigum-N-3, Krynac-5075, and mixture thereof; the polymer matrix hydrogenated nitrile rubber is selected from the group comprising of zetpol-1010, zetpol-1020, zetpol-2010, zetpol-2020, therban, and mixture thereof; the polymer matrix polyacrylic rubber is selected from the group comprising of hycar-4051, hycar-4052, hycar-4054, vamac-B-124, and mixture thereof; the elastomer matrix neoprene rubber is selected from the group comprising of neoprene-AC, neoprene-AD, neoprene-ADG, neoprene-AF, neoprene-AG, neoprene-FB, neoprene-GN, neoprene-GNA, neoprene-GRT, neoprene-GS, neoprene-GW, neoprene-W, neoprene-W-MI, neoprene-WB, neoprene-WD, neoprene-WHV, neoprene-WHV-100, neoprene-WHV-200, neoprene-WHV-A, neoprene-WK, neoprene-WRT, neoprene-WX, neoprene-TW, neoprene-TW-100, neoprene-TRT, and mixture thereof; the polymer matrix hypalon rubber is selected from the group comprising of hypalon-20, hypalon-30, hypalon-LD-999, hypalon-40S, hypalon-40, hypalon-4085, hypalon-623, hypalon-45, hypalon-48S, hypalon-48, and mixture thereof; the elastomer matrix silicone rubber is selected from the group comprising of silicone MQ, silicone MPQ, silicone MPVQ, silicone FVQ, and mixture thereof; the polymer matrix fluorocarbon rubber is selected from the group comprising of viton-LM, viton-C-10, viton-A-35, viton-A, viton-A-HF, viton-E-45, viton-E-60, viton-E-60C, viton-E403, viton-B-50, viton-B, viton-B-70, viton-910, viton-GLT, viton-GF, viton-VTR-4730, DAI-EL-G-101, DAI-EL-701, DAI-EL-751, DAI-EL-702, DAI-EL-704, DAI-EL-755, DAI-EL-201, DAI-EL-501, DAI-EL-801, DAI-EL-901, DAI-EL-902, tecnoflon-FOR-LHF, tecnoflon-NMLB, tecnoflon-NML, tecnoflon-NMB, tecnoflon-NM, tecnoflon-NH, tecnoflon-FOR-45-45BI, tecnoflon-FOR-70-70BI, tecnoflon-FOR-45-C-CI, tecnoflon-FOR-60K-KI, tecnoflon-FOR-50E, tecnoflon-TH, tecnoflon-TN-50, tecnoflon-TN, tecnoflon-FOR-THF, tecnoflon-FOR-TF-50, tecnoflon-FOR-TF, fiuorel-2145, fluorel-FC-2175, fluorel-FC-2230, fluorel-FC-2178, fluorel-FC-2170, fluorel-FC-2173, fluorel-FC-2174, fluorel-FC-2177, fluorel-FC-2176, fluorel-FC-2180, fluorel-FC-81, fluorel-FC-79, fluorel-2152, fluorel-FC-2182, fluorel-FC-2460, fluorel-FC-2690, fluorel-FC-2480, and mixture thereof, the polymer matrix polyurethane rubber (polyether and polyester type) is selected from the group comprising of FMSC-1035, FMSC-1035T, FMSC-1040, FMSC-1050, FMSC-1060, FMSC-1066, FMSC-1070, FMSC-1075, FMSC-1080-SLOW, FMSC-1080-FAST, FMSC-1085, FMSC-1090-FAST, FMSC-1090-SLOW, and mixture thereof; the polymer matrix thermoplastic elastomer (polyurethane, polyester, polyamide, styrene-butadiene-styrene, blends, etc) is selected from the group comprising of SBS 1401, SBS 4402, SBS 4452, SBS 1301, SBS 1401-1, SBS 4303, estane-55103, hytrel-40xy, hytrel-63xy, hytrel-72xy, gaflex-547, pebax-2533, pebax-6333, TPR-1600, TPR-1900, TPR-2800, TELCAR-340, SOMEL-301, SOMEL-601, santoprene, cariflex-TR, solprene-400, stereon, and mixture thereof; the polymer matrix polysulfide elastomer is selected from the group comprising of thiakol-A, thiakol-B, thiakol-FA, thiakol-ST, and mixture thereof; 5. The FGPCs as claimed in Claim 1 wherein the polymer matrix comprising of either natural rubber, polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, ethylene-propylene rubber, ethylene-propylene diene monomer rubber, butyl rubber, halobutyl rubber, nitrile rubber, hydrogenated nitrile rubber, polysulfide elastomer, polyacrylic rubber, neoprene rubber, hypalon rubber, silicone rubber, fluorocarbon rubber, polyurethane rubber, thermoplastic elastomer and/or mixture thereof is further graded by mixed carbon nanoparticles having same concentration gradient but different particle size i.e 5 nm and 1 to 50 micron and selected from the group comprising of Fe, Co, Ni, Nd2Fe14B, SmCos, Sm2Co17, BaO.6Fe2O3, SrO.6Fe2O3, Fe 3wt% Si, Fe 4wt% Si, Fe 35wt% Co, Fe 78wt% Ni, Fe 50wt% Ni, MnO.Fe2O3, and mixture thereof which is in the range of 0.1 to 0.7 by volume and wherein the polymer matrix comprising of either natural rubber, polyisoprene rubber, styrene-butadiene rubber, polybutadiene rubber, ethylene-propylene rubber, ethylene-propylene diene monomer rubber, butyl rubber, halobutyl rubber, nitrile rubber, hydrogenated nitrile rubber, polysulfide elastomer, polyacrylic rubber, neoprene rubber, hypalon rubber, silicone rubber, fluorocarbon rubber, polyurethane rubber, thermoplastic elastomer and/or mixture thereof is further graded by mixed carbon nanoparticles having same concentration gradient but different particle size i.e 5 nm and 1 to 50 micron and selected from the group comprising of Fe, Co, Ni, Nd2Fe14B, SmCos, Sm2Co17, BaO.6Fe2O3, SrO.6Fe2O3, Fe 3wt% Si, Fe 4wt% Si, Fe 35wt% Co, Fe 78wt% Ni, Fe 50wt% Ni, MnO.Fe2O3, and mixture thereof which is in the range of 0.1 to 0.7 by volume. 6. The FGPCs as claimed in claim 1, wherein the metal oxide used in accelerator activator is selected from the group comprising of zinc oxide, lead oxide, calcium oxide, magnesium oxide, etc which is in the range of 0.01 to 0.2 (volume fraction) and the acid used in accelerator activator is selected from the group comprising of stearic acid, palmitic acid, oleic acid, etc which is in the range of 0.01 to 0.2 (volume fraction). 7. The FGPCs as claimed in Claim 1, wherein the antioxidant is selected from the group comprising of condensation product of acetone and diphenyl-amine, phenyl-beta-napthylamine, blends of diphenyl-p-phenylene diamine and selected arylamine derivatives, blend of arylamines, polymerized 1,2 dihydro 2,2,4-trimethyl quinoline, N-(l,3-dimethylbutyl)-N'-phenyl-p-phenylene-diamine, diaryl para phenylene diamines, 2 mercaptobenzimidazole, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction) and a process oil is selected from the group comprising of paraffinic oil, naphthenic oil, aromatic oil, vegetable oil, and mixture thereof which is in the range of 0.01 to 0.2 (volume fraction). |
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737-del-2007-Abstract (12-11-2012).pdf
737-DEL-2007-Claims-(06-08-2012).pdf
737-DEL-2007-Correspondence Others-(06-08-2012).pdf
737-del-2007-Correspondence-others (12-11-2012).pdf
737-del-2007-correspondence-others.pdf
737-DEL-2007-Description (Complete)-(06-08-2012).pdf
737-del-2007-description (complete).pdf
737-DEL-2007-Drawings-(06-08-2012).pdf
737-DEL-2007-Form-18-(07-03-2008).pdf
737-DEL-2007-Form-2-(06-08-2012).pdf
737-DEL-2007-Form-3-(06-08-2012).pdf
737-DEL-2007-GPA-(06-08-2012).pdf
Patent Number | 255975 | ||||||||||||
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Indian Patent Application Number | 737/DEL/2007 | ||||||||||||
PG Journal Number | 15/2013 | ||||||||||||
Publication Date | 12-Apr-2013 | ||||||||||||
Grant Date | 10-Apr-2013 | ||||||||||||
Date of Filing | 30-Mar-2007 | ||||||||||||
Name of Patentee | INDIAN INSTITUTE OF TECHNOLOGY | ||||||||||||
Applicant Address | KANPUR,KANPUR-208016,(U.P)INDIA | ||||||||||||
Inventors:
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PCT International Classification Number | C08K7/00 | ||||||||||||
PCT International Application Number | N/A | ||||||||||||
PCT International Filing date | |||||||||||||
PCT Conventions:
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