PLASMA STEALTH Ram Krishna Mohanta 2K14/NSE/13 2nd Sem, M.Tech(NSE) Deptt. Of Applied Physics Delhi Technological University

Contents Radar Cross Section (RCS) What is STEALTH ? Need for RCS reduction Non-Plasma Methods for RCS reduction Limitations of Non-Plasma Methods for RCS reduction What is Plasma Stealth ? Propagation of Electro-Magnetic wave through Plasma Generation of Plasma on Aircraft Advantages of Plasma Stealth Interactive Video [ 04:36s ]

1. Radar Cross Section (RCS) Ability of a target to reflect radar beams in the direction of source Also called as “Radar Backscatter” Larger the RCS, the more easier the detection Depends upon Shape Target material Radar frequency Relative direction to Radar

RCS (σ) = Es= Scattered Electric Field Ei= Incident Electric Field R= Distance from the target RCS = [Geometric Cross section] x [Reflectivity] x [Directivity] Unit of RCS= m2 or dB

SURFACE GEOMETRY RCS b FLAT SURFACE l r CONDUCTING SPHERE r h CYLINDER

2. Stealth A military tactics used to make an object less visible to Radar Low Observable (LO) technology Attempt to greatly reduce the distances at which the target can be detected Passive Electronics Counter-measure

Various methods to achieve “STEALTH” Aircrafts with RCS less than 0.1m2 or -10dBm2 are considered as STEALTHY designs. Reducing Infrared (IR) emission Optimizing Jet Fuels for min. IR emission S-shape nozzle design Cool Air injection into Exhaust Reducing Radio Frequency (RF) Emission Optimizing Airframe for minimum RCS Radar Absorbent Material (RAM) PLASMA STEALTH

Decrease in Received Power Decrease in Detection Range 3.Need for RCS reduction Radar Range Equation: , = Radar Received & Transmitted Power respectively; Watts = Gain of the Transmitter & Receiver Antenna respectively = Wavelength ; m = RCS of the target ; m2 R = Distance to the target; m RCS Reduction Decrease in Received Power Decrease in Detection Range

Conventional aircraft Surface-to-Air Missile Radar 3-5 dBm2 Stealth aircraft Penetration distance by Stealth Aircraft Surface-to-Air Missile Radar -10 dBm2 DETECTION RANGE Comparison of Radar Detection Range Stealth Aircraft vs. Non-Stealth Aircraft

4. Non-Plasma Methods for RCS Reduction Airframe Structure Modification: Tilting the tail surfaces to reduce corner reflections Eliminate the tail completely Eliminate any Uneven surfaces Use of Flat surfaces and sharp edges rather than round edges

Radar Absorbent Material Absorb radiated energy from radar and convert it to heat rather than reflect it back. Materials include dielectric composites and metal fibres containing ferrite isotopes. Iron Ball Paint: Contains microscopic iron spheres that resonate in tune with incoming radio waves and dissipate the majority of their energy as heat.

5. Limitations of Non-Plasma RCS Reduction Airframe Modification: Loss of Maneuverability Limits the Payload capacity If part of Airframe is damaged, Replacement of total structure is needed. Difficult to manufacture Radar Absorbent Material: High Maintenance cost Not all-weather compatible Susceptible to Atmospheric electric discharge

6. Plasma Stealth 1957: Sputnik-1 History of Plasma Stealth: An envelope of plasma is produced around the object to shield its RF signature from Radar. History of Plasma Stealth: American Research 1956: Arnold Eldredge of General Electric “Object Camouflage Method & Apparatus” Project OXCART: Attempt to reduce RCS of a Lockheed A-12 Recon Aircraft Project KEMPSTER: Use of Electron Beam Generator to create a plasma on A-12 Russian Research 1957: Sputnik-1 1999: Dr. Anatoliy Koroteyev 2002 Article: Plasma Stealth tested on Russian Su-27IB Bomber aircraft

Plasma Absorber & Reflector f < High Pass Filter f > Plasma can Reflect, Absorb and Transmit EM wave In Plasma stealth, an envelope of Ionized gas is produced around the object to shield its RF signature from Radar. Depending upon the frequency of Radar (f), Plasma frequency ( ) can be tuned to create a STEALTH effect.

Key to Plasma stealth: Theoretically, Plasma can Absorb all the energy from an incoming EM wave, which implies Complete Stealth and Zero RCS. Propagation of EM Wave through Plasma Wave field gives Energy to particles Particles may absorb fraction of energy as Heat permanently Particles may return fraction of energy to Wave Reduction in intensity of Reflected EM wave

7. Propagation of EM wave through Plasma Interaction of EM wave with Plasma depends mainly upon three Plasma parameters. Plasma frequency; Plasma Temperature; Te Plasma Dielectric constant; As it can be seen by varying Plasma density (n0), both frequency (wp) and dielectric constant ( ) can be varied.

Dispersion relation for collision-less plasma For ; Propagation vector “k” is Imaginary. Wave will reflect back. For ; Propagation Vector “k” is real. Wave will carry energy.

Refractive Index(n) of Plasma: 100% Reflection Over-densed Plasma Plasma Skin depth( ): Depth up to which EM radiation can penetrate

8. Generation of Plasma A. Direct Generation B. Remote Generation Generated inside a container via hollow cathode discharge or capacitive discharge Low Pressure Plasma Better control over Plasma Property Generates a High density Plasma and then expels the plasma to aircraft surface so that it forms a cone structure and surround the whole surface. Similar to re-entry of objects from orbit

9. Advantages of Plasma Stealth Non-Plasma methods for RCS reduction provides a fixed RCS reduction. These techniques are less susceptible, for Radar transmitting with variable transmission frequency. Plasma Stealth techniques provide a Dynamic RCS, that can be varied by tuning the Plasma parameters. Plasma generated at Atmospheric pressure is excellent broadband absorber from VHF to X-band frequency. Reduces drag thereby increasing the aerodynamic performance Better reduction in RCS than other techniques

10. Interactive Video https://www.youtube.com/watch?v=As0Z5ror0BA

References Manipulation of RCS with Plasma; Shen Shou Max Chung, Dept. of Physics, National Tsing Hua University, Taiwan, R.O.C Radar Cross Section Measurement Techniques; V.G. Borkar*, A. Ghosh, R.K. Singh, and N. Chourasia: Defence Science Journal, Vol. 60, No. 2, March 2010, pp. 204-212 Plasma cloud generation technology for stealth applications; Fiszer, Michal and Jerzy Gruszczynski, Journal of Electronic Defence, June 2002. Study and Optimization of Plasma-Based Radar Cross Section Reduction Using Three-Dimensional Computations; Bhaskar Chaudhury & Shashank Chaturvedi (2009), IEEE Transactions on Plasma Science 37 (11): 2116–2127

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