Daniel Gogny and RCS
RCS problematics
• Mid eighties: Soviet anti ballistic missile program :
radar system
Hen house
Pillbox
RCS Problematics
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Detection distance (RCS)-4
Drastic RCS reduction mandatory
Ambitious program, initially in Aquitaine research center
Collective effort in RCS (diffraction of EM waves) computation
and diffraction physics
• All centers contributed
RCS computing
• King computer of mid eighties was Cray X-MP, delivering less
than 1 Gflops peak
• Y-MP much better: > 2 Gflops,but it was not enough…
X-MP
Y-MP
RCS computing
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Wave diffraction : oscillatory solution
Mesh size : a fraction of wavelength
The higher the frequency, the smaller the mesh size
We had to develop two types of computer codes
– Purely numerical, well suited to low frequencies
– High frequencies, based on asymptotic methods
Asymptotic methods
• Generalization of Geometrical Optics to other diffraction phenomena,
such as diffracted or creeping rays
• The so called Geometrical Theory of Diffraction (Keller) and Physical
Theory of Diffraction (Ufimtsev) were designed for objects with edges, but
edges diffracts to much and must not appear on low RCS objects
• Methods devoted to computation
of low RCS objects required
• We needed some collaborations
• Hopefully Daniel was with us
Collaborations
• How to initiate collaboration in a field where you are not
known ?
• Some scientists were outstanding in the field of
electromagnetics, but how to convince them to collaborate
(even the first step : how to speak to them was not so evident…)
• The Y-MP equivalent EM scientist (several hundreds of
papers)
Raj Mittra, head of
Urbana Champaign
EM Lab
Collaborations
• Looks great, but how to get in touch with this semi-god
• We dreamt of doing this, Daniel did it A formula that sums up a part of
• How exactly : I do not know
Daniel elegance and fine sens of
humour…
• Daniel told me that it had been « a bit difficult »…
• But in 1990, Mittra came in CESTA and collaboration started
• From 1990 to mid nineties, very fruitful collaboration with Mittra
and his lab
• Other nice collaborations with « Science et Tech » fine team of
physicists : Rouet, Averbuch, Béllissard and mathematicians :
Bardos, Balabanne, Lebeau, also initiated by Daniel Gogny
• We were allowed (and even incited…) to publish papers (not only to
write secret reports…)
Collaborations
• I am indebted to Daniel and Patricia also for that
Translation
Patricia
+Daniel’s
physical
insights
We also
benefited
from interaction
with Mittra
Working on diffraction’s physics
• Daniel Gogny also worked on different subjects in
diffraction physics applied to RCS
• Diffraction by periodic materials (the name
« metamaterial » was not yet coined)
• Diffraction by ionized gases
• Helical structures : presentation by Frédéric
• Analogy between creeping rays and Regge poles
Conclusion
• Remembrance of a period of intense scientific and technical activity
to meet a challenge that was (and perhaps still is) quite hard
• Daniel Gogny came and helped us a lot, by working with us, and by
allowing us to access to leading scientists we had not even dared to
approach
• Though he was himself initially far from the field of
electromagnetism, his outstanding scientific stature, and his
charismatic personnality allowed him (and us…) to succeed
• I focused the talk on what was the most important from my point of
view : his contribution was so wide in scope that lot of other things
could be said