Standing Bear wrote:
On Tuesday 24 October 2006 04:06, Harry Veeder wrote:
They must be reverse engineering a
crashed Romulan spaceship.
;-)
Harry
Terry Blanton wrote:
http://news.bbc.co.uk/1/hi/sci/tech/6064620.stm
Experts create invisibility cloak
By Paul Rincon
Science reporter, BBC News
A US-British team of scientists has successfully tested a cloak of
invisibility in the laboratory.
The device mostly hid a small copper cylinder from microwaves in tests
at Duke University, North Carolina.
It works by deflecting the microwaves around the object and restoring
them on the other side, as if they had passed through empty space.
<more>
Bet these things are being built and fitted to RAF birds as you read this!
I don't think this one's actually useful for cloaking, even if it could
be extended to cover an entire airplane (and if the mechanism could be
carried aboard the plane).
The problem is that the only advantage of "true invisibility" over a
really good coat of "black paint" comes when someone could otherwise see
you by observing your silhouette (like an X-ray or shadow play). If
they observe you only by shining a "flashlight beam" on you, when you're
placed against a non-reflective background (such as the sky), then black
paint works just as well as "true invisibility".
Since this particular scheme currently works only in the radar range, we
need to look at how radar works -- it doesn't see silhouettes, and
what's more it doesn't use ambient radiation. Rather, it shines a
"flashlight beam" on the target and looks at the reflected radiation.
So, "black paint" -- (part of) Stealth bomber technology -- works just
as well as active invisibility when dealing with radar. The other part
of Stealth bomber technology, which is (apparently!) to bounce the
radiation off in just a few random directions which _usually_ won't
include the radar receiver on the ground (hence hard edges and flat
planes, rather than smooth curves which would reflect
omnidirectionally), works because there isn't any ambient radar
radiation to speak of.
With visible light, the story changes -- we often observe things against
bright backgrounds (such as sky), so silhouettes are useful for seeing
things. A perfectly black object can be seen by the things it occludes.
And lots of flat planes, to assure that the beam will hardly ever
bounce directly back to the observer, doesn't help with visible light
because there's so much ambient visible light around that _some_
lightsource will always be positioned so as to "light up" the object as
seen by the observer. So "true invisibility" would make a huge
difference in the visible spectrum. But this gadget is far, far from
working in visible light, as I understand it.
Standing Bear
