In this presentation, properties of conducting polymer Polypyrrole (PPy) which may help in radar absorption are discussed. First, some related radar absorbers are studied, then Polypyrrole preparation, source of its conducting nature and changes of this property with different physical properties like crystallinity, thermal stability, ageing and weathering are reviewed
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].
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/
Notes de l'éditeur
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
