Low-observable "stealth" aircraft technology was developed
in the 1970s and deployed in the 1980s. The general idea
was revealed to the public in 1988.
Physics places some severe limits on what is possible.
Note two distinct goals:
a) No radiation scattered directly back against the
incident wave.
b) No radiation scattered in any direction.
Goal (a) is kinda sorta achievable under some conditions.
Goal (b) is physically impossible for a passive opaque
object.
Anybody who knows about wave mechanics knows this. There
were half-hearted attempts to keep it secret ... but the
cat is out of the bag, and has been for a while now. Even
wikipedia (hardly a source for cutting-edge technology)
discusses numerous kinds of anti-stealth technology: https://en.wikipedia.org/wiki/Stealth_aircraft#Limitations
It makes an interesting open-ended physics exercise.
If your students want to know what physicists do in the
real world, ask them to use what they know about wave
mechanics to design a system that can detect and locate
the enemy's stealth aircraft. How many ways of doing
it can you think of?
At this level of detail, my favorites are:
a) Multistatic radar (transmitters located far away
from the receivers) so that we are looking at angles
other that direct back-scatter.
b) Long-wave radar. It is mathematically impossible
to make an absorber that is thin compared to the
wavelength. Try it sometime, in a ripple tank or
otherwise. Or think about the theory: Feynman
volume II chapter 32.
c) Combinations of the above.
In particular, imagine what I call OtH/2 i.e. half
over-the-horizon radar. Station huge HF transmitters
a couple of hundred miles inland, then put receivers
along the borders and coastlines. That means the
illumination bounces down from the ionosphere, so
there is good geometry for detecting the scattered
waves.
To achieve decent resolution, long-wave radar requires
enormous antennas, for the obvious physics reasons.
That's a problem for airborne radar sets, but not for
ground-based systems. Just deploy thousands of small
sub-receivers, and phase lock them à la NRAO VLA.
Since they are passive receivers, it is hard for
enemy countermeasures to target them.
Ditto for an aircraft carrier battle group. Put a
sub-receiver on each ship in the group, and phase
lock them.
At the next level of detail, it would be a colossal
mistake to think that the adversary will not adapt
to what you are doing. The foregoing discussion
applies to a /passive absorber/ but there is no law
that says the enemy has to be passive. At longer
wavelengths, it gets easier and easier to perform
active cancellation: http://defenseelectronicsmag.com/systems-amp-subsystems/assemble-active-cancellation-stealth-system
So the eternal cat-and-mouse game continues.
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This is definitely real-world physics. Although phys-l
isn't the optimal forum to discuss policy, we can note
in passing that there are trillion-dollar policy issues
surrounding the F-35. Its "stealth capability" has been
touted as a major selling point. Alas the average Member
of Congress has no way of knowing what that really means.
The vendor has overpromised and underdelivered on every
other key aspect of the program, so it makes sense to
be skeptical.
Sure, the F-35 is invisible to typical 1980s-style
radars ... but the 1980s have been over for a while
now ... and I've seen reports that the F-35 shows up
just fine on 1940s-style long-wave radar. I don't
know exactly what will happen in the next few years,
but I do know that merely chanting the words "stealth
capability" does not answer the question.