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http://flux.aps.org/meetings/YR98/BAPSD ... 00009.html
A Conceptual Study of
Stealth Plasma Antenna *
Weng Lock Kang, Mark Rader, and Igor Alexeff
UTK Plasma Science Laboratory
Department of Electrical and Computer Engineering
University of Tennessee
Knoxville, TN 37996-2100
The University of Tennessee Plasma Science Laboratory had
involved in the studies of cloaking application of plasma
discharge in the past. It had been shown that cloaking could be
achieved by modifying the frequency of the propagating r.f.
signal using a pulse plasma discharge. Two frequency shifting
mechanisms were studied, one by using the plasma a:; a
nonphysical plunger to upshift the frequency (I), the other by
the phase velocity increase to change the frequency of the
incoming radiation (2).
We are recently however involved in the conceptual study of
stealth plasma antenna. Stealth plasma antenna achieves its
cloaking property without depending on frequency shifting. It
depends instead on the behavior of an electromagnetic wave
propagating in the plasma medium.
We have actually demonstrated that it is feasible to constriict
an antenna out of a glass tube filled with low-pressure gas,
such as a fluorescent tube (3). When the gas is ionized, %we
have an efficient, highly directional receiving and transmitting
antenna. When the gas de-ionizes, the structure reverts tci a
simple structure of a glass tube, with negligible radar crosssection,
rendering it the stealth or cloaking property.
* Supported in part by AFOSR
1. I. Alexeff, F. Dyer, and Mark Rader, "Frequency
Modulation of Free Space R.F. Signal," IEEE Internatiorial
Conference on Plasma Science, ISBN 0-7803-0147-1 (199 I),
p.86
2. Mark Rader, "Frequency Modification of RF Signals Using
an Ionized Gas," Ph.D. dissertation, The University of
Tennessee, May 1991.
3. W.L. Kang, M. Rader, and I. Alexeff, "A Microwave Plasma
Closing Switch and Stealth Plasma Antenna," IEEIE
International Conference on Plasma Science, ISBN 0-7803-
2669-5 (1995), p.141.
Acknowledgments
This work was supported in part by AFOSR Grant F49620-
94-1-0054 and AFOSR AASERT Award F49620-93-1-0465
References
[l] W. Shen, J. E. Scharer, IV. T. Lam, B. G. Porter and K . L.
Kelly, "Properties of a VUV Laser Created Plasma Sheet
for a Microwave Reflector", Journal of Applied Physics.
October 1995.
IEEE TRANSACTIONS ON PLASMA SCIENCE, VOL. 33, NO. 6, DECEMBER 2005
Three-Dimensional Computation of Reduction in
Radar Cross Section Using Plasma Shielding
Bhaskar Chaudhury and Shashank Chaturvedi
Abstract—We have performed three-dimensional (3-D) finite-
difference time-domain (FDTD) simulations for calculating
microwave scattering from metallic objects shielded by a plasma
shroud. Such simulations are of interest for plasma-based stealth
technology. The simulations yield a reasonable match with experimental
measurements. A physical interpretation has also been
provided for these results, in terms of the flow of electromagnetic
power. Such an analysis is only possible using the detailed
spatio-temporal evolution of electromagnetic fields that is provided
by the FDTD method. We find that apart from absorption,
the bending of waves toward regions of lower plasma density plays
an important role in determining the extent of backscatter. This
has major implications for plasma stealth applications, which have
heretofore assumed that plasma absorption is the main mechanism.
Also, bending could actually enhance radar scattering in
directions oblique to the incident direction.We have also identified
situations where 3-D simulations become necessary, and other
situations where a composite one–dimensional simulation may be
enough. This has practical relevance since it could help reduce the
demand for computational resources while modeling large objects
like aircraft.
Index Terms—Absorption, electromagnetic wave, finite-difference
time-domain (FDTD), plasma, radar cross section (RCS).
.....
Existing “low observable” (stealth) designs of aircraft tend to
make use of special aircraft shapes, or of microwave-absorbing
coatings, in order to reduce the RCS. However, there are situations
where these techniques may not be effective, such as the
use of a wide range of frequencies in radar [2].
A collisional unmagnetized plasma, which has a complex dielectric
constant, can be used as a good absorber of electromagnetic
waves over a wide range of frequencies. This absorption
leads to a reduction in the RCS over a wide frequency range
[3]. When an electromagnetic wave enters a weakly-ionized
plasma, it is subjected to absorption as well as scattering [4].
Absorption arises from loss of energy of the wave due to energy
transfer to charged particles, and subsequently to neutral
particles (atoms and molecules) by elastic and inelastic collisions.
Wave scattering is due to spatial variation of the refractive
index, such as during the transition from free space to a plasma,
as well as density variation within the plasma. For a plasma to
act as an efficient absorber over a wide range of frequencies,
without significant reflection of the incident signal, three conditions
must be satisfied by both the electron density level and
its spatial variation [3]. First, the electron density should be sufficiently
high near the target whose RCS is sought to be reduced.
Second, this density should falloff with increasing distance from
the target. Third, the electron–ion and electron–neutral collision
rates should be sufficiently high to result in significant wave absorption.
Experimental development in this area must be supported by
systematic computer simulation work for three reasons. First,
it is necessary to maximize the effectiveness of plasma absorption
over a wide frequency range. This requires selection of the
plasma dimensions, the electron and neutral density levels in
the plasma, and the spatial profiles of these densities. This optimization
can be done through detailed three-dimensional (3-D)
electromagnetics simulation for the actual object dimensions.
Second, it is known that different parts of an object (e.g., aircraft)
contribute different amounts to the RCS. This means that
a significant reduction in RCS may be obtained by only creating
the plasma around the portions that contribute most to RCS.
This, too, must be studied in detail through 3-D electromagnetics
simulations. Third, such a plasma must be sustained by a
constant input of power from some external source. Hence, the
parameters of the plasma need to be carefully chosen, in order
to minimize the power consumption required for a given RCS
reduction.
Accurate calculation of the RCS for complex shapes, and
its modification in the presence of plasma, is thus critical for
plasma stealth applications. The present work reflects the first
step in this direction.
The RCS refers to far-field measurements. However, we
could not locate published experimental data for RCS in the
presence of plasma. Such data is available, however, for the
near-field. Hence, as a first step, we have validated our 3-D
electromagnetic wave scattering/absorption calculations for
plasma-shielded objects against experimental and analytical
results in the near-field region.
.....
bios:
Shashank Chaturvedi was born in New Delhi,
India, in 1962. He received the B.Tech. degree in
chemical engineering from the Indian Institute of
Technology, Delhi, India, in 1985, and the Ph.D.
degree in chemical engineering from Princeton
University, Princeton, NJ, in 1989.
He has since been working at the Institute for
Plasma Research, Gandhinagar, India. For several
years, he worked on computer modeling of different
fusion reactor configurations, including tokamaks.
Over the past ten years, he has been involved in
the modeling of pulsed-power systems, including pulsed electromagnetics,
radiation-hydrodynamics, MHD simulations, and shock waves.
Bhaskar Chaudhury was born in Giridih, India, on
November 16, 1978. He received the B.Sc. degree in
physics from Vinoba Bhave University, Hazaribagh,
India, and the M.Sc. degree in applied physics from
Sikkim Manipal Institute of Technology, Gangtok,
India. He is currently working toward the Ph.D.
degree at the Institute for Plasma Research, Gandhinagar,
India.
His current interests include computational electromagnetics
and wave propagation in plasmas.
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