Polypyrrole as Radar Absorbing Material(RAM)

By

Debajyoti Biswas,

Depatment of Electrical Engineering

Defense and Security Applications of Conducting Polymers

Fully Flexible Circuit

Boards and Packaging

• Health & Environmental

Monitoring

• Flexible Blast Dosimeters

• Chemical Biological

Radiation Sensors

DistributedMulti-FunctionalSensors

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

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.

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

Pyramidal Absorbers, Tapered Absorbers,..

Resonant Absorbers

Combination of Both

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

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]

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 maximamore bandwidth.[2]

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]

Polypyrrole• Conducting organic polymer, monomer is

Pyrrole(𝐶4𝐻4NH)

• PPy is an insulator, but its oxidized derivatives are good electrical conductors.[1]

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

Variation of Polypyrrole Conductivity

• Better crystalinity= better conductivity.

• Sharp peaks in diagram show better crystallinity[7].

Variation of Polypyrrole Conductivity

Thermal Stability of Polypyrrole• Polypyrrole has good stability in atmosphere and a wide

range of temperature.

• Thermogravimetric analysis(TGA) shows that polypyrroleloses weight in more than one distinct stages in air and nitrogen atmosphere.[6]

Chemical Synthesis of Polypyrrole• When Polypyrrole tubule diameter decrease,

conductivity of Polypyrrole tubule increases.[5]

Weathering of attenuator

Delektre Airship with printed electronics

• Hull length 1 km and 400 m wide.

• Top surface is printed solar panel(200,000 𝑚2).

• Bottom surface is printed re-chargeable battery.[10]

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]

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.

References1.Polypyrrole:Formation and Use: Paul Saville, Defence R&D Canada – Atlantic :Technical Memorandum DRDC Atlantic TM 2005-0042.Review of Radar Absorbing Materials: Paul Saville, Defence R&D Canada – Atlantic :Technical Memorandum DRDC Atlantic TM 2005-0033.Polypyrrole Stability and Coatings for Radar Absorbing Materials: Andrew Leslie,MikeKopac,Paul Saville: Defence R&D Canada – Atlantic :Technical Memorandum DRDC Atlantic TM 2005-2994.Development Of New Conductive And Microwave Lossy Materials Involving Conducting Polymer Coatings: Dr. Jamshid Avloni and Dr. Arthur Henn5.Chemical synthesis of polypyrrole: structure–properties relationship:Duchet, Roger Legras, ,Demoustier-Champagne:Synthetic MetalsVolume 98, Issue 2, 4 December 1998, Pages 113–1226.Thermal stability of electrochemically prepared polythiophene and polypyrrole:FMohammad,Calvert,Billingham;19957.Novel polypyrrole films with excellent crystallinity and goodhermal stability:Pullarkat P. Jeeju,Sreekanth J. Varma,Puthampadath A. Francis XavierAugustine M. SajimoSankaranJayalekshmiMaterials Chemistry and PhysicsVolume 134, Issues 2–3, 15 June 2012, Pages 803–8088.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 20129.http://en.wikipedia.org10.www.delektre.fi/11.www.eeonyx.com/