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electromagnetic radiations protection

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  2. 2. Radiation : The process by which unstable nuclei ofatom emit a quantity of energy, or a particle. This emittedparticle or energy is known as radiation.Classification of radiations:1. Particle radiation (tiny and fast moving material having both energy and weight)2. Electro magnetic radiation (pure energy ) 2
  3. 3. Electromagnetic radiation (EM radiation or EMR) is a form of energyemitted by charged particles, which exhibits wave-like behavior as ittravels through space.EMR has both electric and magnetic field components, which standin a fixed ratio of intensity to each other, and which oscillate in phaseperpendicular to each other and perpendicular to the direction ofenergy and wave propagation. 3
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  5. 5. 1. Electromagnetic waves are propagated by oscillating electric and magnetic fields oscillating at right angles to each other.2. Electromagnetic waves travel with a constant velocity of 3 x 108 ms-1 in vacuum.3. Electromagnetic waves are not deflected by electric or magnetic field4. Electromagnetic waves can show interference or diffraction.5. Electromagnetic waves are transverse waves.6. Electromagnetic waves may be polarized. 5
  6. 6. Natural sources Man made sources cosmic exposure at public places terrestrial occupational exposure internal 6
  7. 7. Broadcast antennas Cell towersDigital TV signals Doppler weather radarElectric trains Over telephone wiresMicrowave beacons PagersPower lines Radio transmittersSatellite radiation Wi-Fi antennasWiring in airplanes Digital displayCell phone chargers Cell phonesCompact fluorescent light (CFL) ComputersCordless phones 7
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  10. 10. Electrical hazards : Strong radiation can induced current capableof delivering an electric shock to persons and animals. It can alsooverload and destroy electrical equipment.Fire hazards : EMR can cause electric currents strong enough tocreate sparks and can ignite flammable material and gases , leadingto an explosion.Biological hazards : EM field can cause dielectric heating ex.Touching and antenna can cause severe burns. 10
  11. 11. EMR can cause cancer , high blood pressure , brain tumors ,headache, leukemia, brain damage etc.WHO facts says that EMR can cause depression , cardiovasculardisorder, reproductive function, developmental disorders,immunological modification etc. but these have lesser chancesthan for child hood leukemia.Electromagnetic interference : it is an unwanted disturbancethat effect the electrical circuit due to EMR emitted from anexternal source .It May interrupt , obstruct or limit the effective performance ofthe circuit. 11
  12. 12. Energy of the incident radiationDepth of penetrationSource of emissionDuration of exposureFrequency of EMR wavesType of EMR wavesDistance from the object 12
  13. 13. It is a process by which a material is able to reduce thetransmission of EMR that effects the humans or equipments.EMS material are used to exclude the unwanted EMR or signals. Italso provide protection against the EM pulses which can disruptneighbouring computers .It provides protection by reducing signals to level at which they nolonger effect equipment or can no longer be received. This isachieved by reflecting and absorbing the radiation. 13
  14. 14. The primary mechanism of EMI shielding is usually reflection.For reflection of the radiation by the shield, the shield must havemobile charge carriers (electrons or holes) which interact with theelectromagnetic fields in the radiation.A secondary mechanism of EMI shielding is usually absorption. Forsignificant absorption of the radiation by the shield, the shieldshould have electric and/or magnetic dipoles which interact with theelectromagnetic fields in the radiation.Other than reflection and absorption, a mechanism of shielding ismultiple reflections, which refer to the reflections at various surfacesor interfaces in the shield. 14
  15. 15. How EMS Works 15
  16. 16. Electromagnetic shielding is used in,Aerospace aviation: In protection of highly advanced avionicequipments.Anti-terrorism: Encryption of relevant secret codes related tonational security.Communication: Safeguarding highly sensitive digital signalprocessing and microwave operating bandDefense: To protect equipment related to military, navy or air force.Information Technology: Protect users from radioactive effects ofcomputers and peripherals.Medical: Prevents interference of electromagnetic waves given outby medical devices especially during critical operations.Transport: For improved performances of automomotiveelectronics luxury devices, vehicle tracking system and detectionsurveillance systems, electric cars etc. 16
  17. 17. 1. Conductive materials2. Nano and micro-carbon black3. Sub micro- and micro-powders of Al, Cu, Ni etc.4. Stainless steel fibers5. Silver-coated polyamide fibres6. Plastic fibre such as poly phenylene vinylene , poly Acetylene(doped form)7. Cellulosic fibers. 17
  18. 18. Reflection /absorption / multi reflection of EM wavesIt should be flexible & light weight.ConductivityCorrosion resistantDurabilityLow cost etc. 18
  19. 19. Material used for EMS include sheet metal mesh , metal form ,Andplasma .Multi layer knitted fabric such as interlock structureTextile Multi layer structureComposite materials for shieldingConductive fabricShielding foil tapesEMI conductive adhesivesMostly conductive fabric are used prepared with differenttechniques. 19
  20. 20. Incorporation of conductive fibres or yarns in to the fabricLamination of conductive layer on to the surface of the fabric suchas conductive coating , spray ,ionic plating .Addition to the conductive fillers such as conductive carbon black,carbon fibre ,metal fibre (stainless steal AL, CU),metal powder andflex to the insulating materialGrafting a conductive polymer such as poly anilines , poly pyrolle, poly vinyl alchol,poly amide on to the fabricCoating of individual fibre by conductive polymerFew examples : Filosano fabric , Flectron , Phantom fabric, Highperformance silver mesh fabric etc. 20
  21. 21. Shielding effectiveness:- It is the ratio of electromagnetic fieldstrength measured without (E0) & with (E1) the tested materialwhen it separates the field source and the receptor. It I s given by SE = Eo /E1Insertion loss (A) : It is a measure of losses in a transmissionsignal cause by the tested material being inserted in to themeasuring channel . It is given by A = Uo/ U1Where Uo = channel out put voltage without tested material U1 = output voltage with tested material 21
  22. 22. For woven fabric :1. Effect of type of material: metals have significantly higher EMS value compare to polymer or cellulosic material Metal > cellulose > polyester (synthetic polymer)2. Effect of no. of apertures : EMS value decreases with increase in no. of holes . However for metals no significance difference is there in shielding.3. Effect of yarn count and thread density : with increase in yarn count the effectiveness increases.4. Effect of no. of fabric layers : the shielding of the material is directly proportional to the thickness of the material. 22
  23. 23. 1. Effect of metal wire diameter: With increase in dia. the shielding effectiveness decreases .2. Effect of knitted structure : Interlock and rib structure have more shielding effectiveness then the plain structure.3. Effect of thickness: Thickness of the knitted fabric shows negligible influence on EMS effectiveness at low to higher frequency.4. Effect of tightness factor : Fabric with higher tightness factor have good shielding effectiveness then lower. 23
  24. 24. Mil –STD 285 :1. Introduced in 19562. This standard has an upper frequency limit of 400 MHz3. Developed for large-enclosure and shelter assessment.IEEE-STD 299:1. Developed by institute of electrical and electronics engg.2. Upper freq. limit 100 GHz.3. This standard is only applicable to an enclosure whose smallest linear dimension is > 2mt.4. It does not apply on small and medium size enclosure . 24
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  27. 27. ASTM-E1851 :1. Developed by the American society for testing and materials .2. It requires freq. range between 140 and 160 KHz and between 14 to 16 MHz.3. Far field shielding measurement between 300 to 500 MHz, 900 to 1000 MHz , and 8.5 and 10.5 GHz are required .4. Used for large enclosure and shelters.VG 95373 part 15 :1. German military standard.2. The freq. range above 30 to 200 MHz3. Minimum antenna to enclosure separation distance of 2.5 mt.4. Only standard applicable to small and medium sized enclosures. 27
  28. 28. ASTM-D 4935 :1. Developed for evaluation of flat thin samples .2. This standard is used for plastic materials .3. Freq. range from 30 MHz to 100 MHz. 28
  29. 29. The EMR are increasing day by day due the increasing use ofelectronics equipment and other sources of EMR . Since the EMR areharmful for us, so it’s a big issue of concern. Due to the newtechnologies and advancement such as use of conductive polymer,multi layer fabrics and composites etc. the EMR hazards can be reduceto some extent. After considering the different parameters ofconstruction for EMS , the effectiveness can be increased . In recentyear conductive fabric considered mainly due to their characteristics offlexibility , lightness and competitive price. 29
  30. 30. 1. R Perumalraj, B.S. Dasaradan and are Nagaswarana, Electrically conductive polymer materials for EMI Shielding, Asian Textile Journal, Jan. 2009 (p- 49 to 57).2. R Perumalraj, B.S. Dasaradan, Electromagnetic shielding fabric, Asian Textile Journal , Oct. 2008 (p-62to 68).3. R Perumalraj , B.S. Dasaradan , Electromagnetic shielding effectiveness of copper core yarn knitted fabric , Indian Journal of Fibre and Textile Research, vol-34 , June 2009 (p-149-154).4. A.Das, V.K. Kothari, A. Kothari and A.Kumar, effect of various parameter on EMS effectiveness of textile fabric , Indian Journal of Fibre and Textile Research, vol-34 , June 2009 (p-144-148).5. K.K.Gupta , S.M. Abbas and A.Srivastava, Microwave interactive fabric: A review , Man Made Textiles in India , Feb 2012 (p-41t0 48).6. P.R.Surwase, EMI shielding Material and measuring methods : A Review , Man Made Textiles in India , Sep. 2011 (p-327 to 330).7. Department of defense, United States of America,MIL – STD 285 .8. V.K. Kothari ,Progress in Textile Science & Technology, vol. 3, (p-396). 30