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Polypyrrole as radar absorbent material(RAM)
- 1. Polypyrrole as Radar Absorbing Material(RAM) By Debajyoti Biswas, Depatment of Electrical Engineering
- 2. Defense and Security Applications of Conducting Polymers Fully Flexible Circuit Boards and Packaging • Health & Environmental Monitoring • Flexible Blast Dosimeters • Chemical Biological Radiation Sensors Distributed Multi-Functional Sensors
- 3. Design of a Stealth Aircraft • General Objectives • Reducing thermal emission from thrust • Reducing radar detection when the aircraft opens its weapons bay • Reducing infra-red and radar detection during adverse weather conditions Limitations • Aerodynamic instability of design : Constant flight correction • Decreasing infrared footprint • Reduction of vulnerability when weapons bay is open • Sensitive skin : RAMs
- 4. Radar Absorbant Material(RAM) • They reduce radar Cross section in detector screen. • Different procedures to reduce radar cross section • No RAM can make any structure invisible.
- 5. Radar Absorbent Materials(RAM) • RAMs absorb radar in various amounts depending on atmos - pheric conditions and different frequencies.[1] • Classifications of RAM Radar Absorbent Materials(RAM) Impedance Matching Resonant Absorbers Pyramidal Absorbers, Tapered Absorbers,.. Combination of Both
- 6. Impedance Matching Absorbers • Cone structures extend perpendicular to surface. • Signal attenuation by 2 ways-1.Scattering(Coherent and Incoherent),2.Absorbtion [2] • High attenuation over wide frequency ranges. • Disadvantages: 1. Thickness & 2. Fragility. http://www.directindustry.com/prod/advanced-electromagnetics/rfi-absorbers-35077-213365.html
- 7. Radar Absorbant Materials: Salisbury Screen • Consists of 3 surfaces- 1. Ground plane: Needs to be concealed 2. Air/Dielectric medium: of precise thickness. 3. Screen: Glossy, resistive. • Working Procedure [2]
- 8. Jaumann Absorber • Two equally-spaced reflective surfaces and a conductive ground plane. • Depends upon the λ/4 spacing between the first reflective surface and the ground plane and between the two reflective surfaces . • Two absorption maxima more bandwidth.[2]
- 9. Conductivity and Radar Absorbtion • Conducting fabric has shielding property against electromagnetic radiation. • From graph below, clearly decreasing resistance provides more Insertion loss, which is equivalent to shielding effectiveness.[6]
- 10. Polypyrrole • Conducting organic polymer, monomer is Pyrrole(퐶4퐻4NH) • PPy is an insulator, but its oxidized derivatives are good electrical conductors.[1]
- 11. Conducting Nature of Polypyrrole[3] As the polymer is partially doped, islands of conducting materials develop Small no. of sites form conducting n/w ; causing dc current density VRH or tunneling induces frequency dependent ac conductivity Higher doping increases n/w density, hence dc conductivity ac conduct - ivity
- 12. Variation of Polypyrrole Conductivity • Better crystalinity= better conductivity. • Sharp peaks in diagram show better crystallinity[7].
- 13. Variation of Polypyrrole Conductivity
- 14. Thermal Stability of Polypyrrole • Polypyrrole has good stability in atmosphere and a wide range of temperature. • Thermogravimetric analysis(TGA) shows that polypyrrole loses weight in more than one distinct stages in air and nitrogen atmosphere.[6]
- 15. Chemical Synthesis of Polypyrrole • When Polypyrrole tubule diameter decrease, conductivity of Polypyrrole tubule increases.[5]
- 17. Delektre Airship with printed electronics • Hull length 1 km and 400 m wide. • Top surface is printed solar panel(200,000 푚2). • Bottom surface is printed re-chargeable battery.[10]
- 18. F-18 Canopy with Eeonomer® • American military jet with radar absorbent characteristics. • Due to static buildup in high altitude air, electronic instruments can get shorted, so use of conducting polymer.[11]
- 19. Summary • Polypyrrole is a conducting organic polymer. • This type of polymer can be used as radar absorbent material(RAM). • This stealth quality varies with various physical parameters. • Can be used to make stealth jet models. • Material tasted in labs and few practical stand-alone aircraft models till now.
- 20. References 1.Polypyrrole:Formation and Use: Paul Saville, Defence R&D Canada – Atlantic :Technical Memorandum DRDC Atlantic TM 2005-004 2.Review of Radar Absorbing Materials: Paul Saville, Defence R&D Canada – Atlantic :Technical Memorandum DRDC Atlantic TM 2005-003 3.Polypyrrole Stability and Coatings for Radar Absorbing Materials: Andrew Leslie,Mike Kopac,Paul Saville: Defence R&D Canada – Atlantic :Technical Memorandum DRDC Atlantic TM 2005-299 4.Development Of New Conductive And Microwave Lossy Materials Involving Conducting Polymer Coatings: Dr. Jamshid Avloni and Dr. Arthur Henn 5.Chemical synthesis of polypyrrole: structure–properties relationship:Duchet, Roger Legras, ,Demoustier-Champagne:Synthetic MetalsVolume 98, Issue 2, 4 December 1998, Pages 113–122 6.Thermal stability of electrochemically prepared polythiophene and polypyrrole:F Mohammad,Calvert,Billingham;1995 7.Novel polypyrrole films with excellent crystallinity and goodhermal stability:Pullarkat P. Jeeju,Sreekanth J. Varma,Puthampadath A. Francis XavierAugustine M. SajimoSankaran JayalekshmiMaterials Chemistry and PhysicsVolume 134, Issues 2–3, 15 June 2012, Pages 803–808 8.On the preparation and multiproperties of the polypyrrole films doped with different ions By: Cheng Guanggui; Ding Jianning; Zhang Zhongqiang; et al.Surface And Interface Analysis Volume: 44 Issue: 7 Pages: 844-850 Published: JUL 2012 9.http://en.wikipedia.org 10.www.delektre.fi/ 11.www.eeonyx.com/
Notas do Editor
- Flexible ckt boards-mount devices on flexible plastic substrates. Also it may be isolated devices attached on a flexible substrate.There will then be a Cu cable between 2 layers. Dosimeter: device that measures exposure to ionizing radiation….Dstributed sensors-many nodes-one control
- --explain everything
- --Radar cross-section (RCS) is a measure of how detectable an object is with a radar. A larger RCS indicates that an object is more easily detected. --RAM –materials to disguise a vehicle or structure from radar detection,no one RAM that is suited to absorption of all radar frequencies
- --Impedance matching absorbers have 3 types-Pyramidal Absorbers, Tapered Absorbers, Matched Absorbers --Tapered loading absorbers-Composed of a slab of lossless & low loss mixtures. -Thinner than pyramidal absorbers but poorer performance.
- --Signal attenuation in 2 ways-Scattering & Absorbtion. --Scattering has 2 parts-1.Coherent scattering: Reflected waves in phase but directed away from receiver 2.Incoherent scattering:Reflected waves back to receiver but out of phase and lower signal strength. --Absorbtion- Cut at angles which maximize no. of bounces & loss of energy Bottom layer conductive foam absorbs that nergy when converted to heat(fan)
- --Radar wave splits n 2 waves-1.reflected from glossy screen,2.passes through dieletrcic but after reflecting at conducting plane comes back after 180 phase shift.When these 2 meet,due to interference signals cancel out each other. --PEC-Perfect Electrically Conducting…………… lossless dielectric of a precise thickness (a quarter of the wavelength of the radar wave to be absorbed)
- --More bandwidth than Sallisbury screen --These absorbers must have all of the layers parallel to each other and the ground plane that they conceal. --are a method of increasing the bandwidth of the Salisbury screen --2 maxima because the wave can resonate at two frequencies. two equally spaced resistive sheets in front of the conducting plane: shown to produce two absorption maxima , thus increasing the bandwidth. --Resistive layers have been formulated using powdered carbon (25 weight %) in a phenol-formaldehyde, cellulose or polyvinyl acetate binder with polyethylene foams as spacers.Silk screening the resistive layers has been shown to produce better control of thickness and resistance
- --The conductivity of Ppy depends on the conditions and reagents used in the oxidation. Conductivities range from 2 to 100 S/cm. --Main application-electronic devices, chemical sensors & drug delivery. --The Nobel Prize in Chemistry was awarded in 2000 for work on conductive polymers including polypyrrole --Most commonly Ppy is prepared by oxidation of pyrrole, which can be achieved using ferric chloride in methanol:n C4H4NH +2FeCl3 → (C4H2NH)n+2 FeCl2 + 2 HCl
- --In undoped states, there is no coducting channel --islands are oxidized sites on the polymer chains; fixed by structural disorder and dopant generally isolated from each other. A small percentage of the sites will form a network --
- --Doping of organic polymer means oxidation or reduction. Oxidation=removes some of delocalized electrons from sp2 hybridized C atoms. Reduxon=adds electron to vacant band.
- -doping,dedoping or redoping of organic polymer-
- --Prototype, multispectral camouflage cover utilizing a PPY-coated net that provides the radar portion of the camouflage and to which the IR and visual components are attached