I really shouldn't have said "same general idea as a mirror". Should have qualified that with "parabolic".A material with a different but constant homogeneous reflective index throughout will 'bend' waves in a straight line. Very simplified explanation wave bends/scatters at discontinuities in electromagnetic properties (which is often in most cases also where there are physical discontinuities, such as the boundary between water and air, or glass),
View attachment 19437
The Luneburg lens makes use of layered varying reflective index in it's material to bend and refocus waves from a given direction on a same point. It is in effect introducing gradually varying discontinuities to shepard waves towards a desired redistribution. The blue hue in the pic below shows the gradual varying of reflective index in the material to bend parallel rays (and we can assume waves emitted from a source a long enough distance away to be arriving in parallel, i.e. if the distance between emitter and receiver is very large compared to the effective emitting aperture ) incoming from a given direction to a point on the opposite inner surface of the sphere.
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In the above pic, if we line the point at 'a' with a reflective material (like plating the underside of a mirror), we can reflective everything that concentrates at 'a' back towards the direction of 'A', since the wave lines now traces from a to A going out the same way it came in. This modifies the lens into a radar reflector. If we plate the arc region between a and b then all signal coming from the orientation range from A to B will be reflect back as if we have directed a corner reflector in the needed direction in each case. Of course the plated region from A to B will obstruct waves arriving from that direction and not allowing the lens to work properly for these cases. However we can always position it so that those regions faces direction where signals are not likely to arrive, such as the belly of the plane. And the fact that these parts are coated with reflective material means they will still reflect/scatter quite well, just not in a controlled and focused way.
That's my quick and amateurish explanation.
J-20 5th Gen Fighter Thread V
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I really shouldn't have said "same general idea as a mirror". Should have qualified that with "parabolic".
I was chiding my own use of the mirror analogy, not yours! Sorry!
Does anyone know whether Jefferey Lin (co-author) has an account on our site?
skywatcher?
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That's me, all right!
Holy Cow!
outstanding article Jeffrey, I agree with most of it, and its nice to be able to "talk back" to such an outstanding author, I have a small issue with design philosophy on the J-20 as opposed to the F-35, of course LockMart and Chengdu are going to do things a little differently, and there is no proto-type numbered 2014, at least that we have seen??
and when you are talking about the AFA's symposium, it would be a "mischaracterization" to say General "Hawk" Carlisle is "spooked" by the latest super wazoo long range Chinese missile, in fact the Chinese engineers and designers are likely very flattered that such a "worthy" as "Hawk" is taking them seriously and encouraging our own team to develop a similarly capable weapon. In fact I would characterize Gen Carlisle's reaction as "respect", that is in no way tantamount to "spooked".
I would imagine the only thing that has ever "spooked" Gen Carlisle is the BHO team capping F-22 production at 187, in fact I would imagine he was rather more "pissed", brat.
Mind = blown.
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