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2007-01-12 Science & Technology

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Posted by 3dc 2007-01-12 10:14|| || Front Page|| [2 views since 2007-05-07] Top

#1 The mathematics predicts that the size of the electromagnetic fields go to infinity at the surface of the cloaked region, possibly wrecking the invisibility.

I think infinite EM fields will do more than wreck the cloaking field.

Posted by Rob Crawford">Rob Crawford 2007-01-12 11:11|| http://www.kloognome.com/]">[http://www.kloognome.com/] 2007-01-12 11:11|| Front Page Top

#2 The size (3 dimensions) of the EM fields go to infinity at the surface (2 dimensions) of the cloaked region?

Babble.

Posted by mojo">mojo 2007-01-12 11:15|| 2007-01-12 11:15|| Front Page Top

#3 Klaatu barada nikto

Here let me illustrate the tricky bit of cloaking

Posted by RD 2007-01-12 11:50|| 2007-01-12 11:50|| Front Page Top

#4 The paper with the maths is here for those who want to wade through it.

Posted by occasional observer 2007-01-12 12:16|| 2007-01-12 12:16|| Front Page Top

#5 oo you outed me as a fraud!

>;-)

Posted by RD 2007-01-12 12:18|| 2007-01-12 12:18|| Front Page Top

#6 If the calculations say it goes to infinity, someone missed a sign change error, or forgot to add in a minor factor when setting up the equation. It'll come out in the rechecking, although likely the outside world will never hear about it.

Posted by trailing wife 2007-01-12 12:22|| 2007-01-12 12:22|| Front Page Top

#7 Klaatu barada nikto

RD, you have my attention but I wasn't planning on destroying the earth today. Not enough bandwidth.

Get on my Notes calendar and block out some time. Maybe late next week.

Posted by GORT 2007-01-12 12:29|| 2007-01-12 12:29|| Front Page Top

#8 IIUC, the 'infinity' issue arises thus:

Prior mathematics seemed to prove that there would always be some component of light/electromagnetic energy which would not be perfectly reflected, hence invisibility is impossible even at a given wavelength for objects which are active transmitters.

Greenleaf et al show that those maths depend on the assumption of upper and lower bounds on components of the associated tensors. That assumption does not hold under certain boundary conditions on the materials' surface and therefore it is theoretically possible to create a perfect reflectivity for any object at a given wavelength.

Posted by occasional observer 2007-01-12 12:41|| 2007-01-12 12:41|| Front Page Top

#9 "neglecting dispersion"

Posted by James">James 2007-01-12 12:41|| http://idontknowbut.blogspot.com]">[http://idontknowbut.blogspot.com] 2007-01-12 12:41|| Front Page Top

#10 In any case, an imperfect cloak would be useful in that you could see out. If it was 90% effective, it would be like looking at "The Predator" in Schwarzenegger's movie. Looking out from a 90% effective cloak would be like looking through sunglasses, I suppose. And that is only for visible light. If you wanted to, you could see out just fine using night vision goggles or something.

Posted by gorb 2007-01-12 13:40|| 2007-01-12 13:40|| Front Page Top

#11 It's all pretty clear to me.

Posted by Shipman 2007-01-12 14:09|| 2007-01-12 14:09|| Front Page Top

#12 Maxwell's equations said that a simple copper disk like the one Smith used could be cloaked without a problem, but anything that emitted electromagnetic waves...

Erm? Unless it's at absolute zero, that copper disk is going to be emitting electromagnetic waves. I'm emitting them as we speak.

Greenleaf's team determined that a more complicated phenomenon arises when using Maxwell's equations, leading to a "blow up" (an unexpected infinite behavior) of the electromagnetic fields.

Pish posh. A little renormalization will take care of that.

Posted by Angie Schultz 2007-01-12 16:25|| 2007-01-12 16:25|| Front Page Top

#13

"It's a FAAAAKE!!!!"

Posted by Mizzou Mafia 2007-01-12 20:16|| 2007-01-12 20:16|| Front Page Top

23:48 Mike N.
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