Terahertz Shielding

[Citizen]

Hello Folks.

 

I'm an electronics specialist but not in the field of RF / emitted energy and I have a question for those who might have more intimate knowledge.

 

Using a common microwave oven as an example:

The oven operates at 2.45 ghz with a wavelength of approx. 122mm. The metal mesh / screen inside the door allows sight into the chamber but disallows microwaves from escaping because the holes in the screen are too small for the microwaves to propagate through (roughly 1 to 1.5mm openings)

 

Now let's move to Terahertz radiation with wavelengths ranging from 0.1mm to 1.0mm. What size opening would disallow these waves to pass? I would expect a copper mesh with openings of 0.05mm would suffice?

 

Any help is greatly appreciated!

[Klaynos]

You need to scale everything. So you would need a mesh 1000 times finer for the shortest wavelengths. You also need to bear two other things into the equation, firstly metals are further from the perfect electrical conductor in the thz regime, and for a broadband source you need to be careful to avoid spoof surface plasmon modes which will give you a very strong transmission around a small frequency range.

[John Cuthber]

I think tinfoil hats work just as well with THz radiation as they do with GHz stuff.

[Citizen]

I think tinfoil hats work just as well with THz radiation as they do with GHz stuff.

 

Ha!

 

Well, I was thinking about modifying some carry-on bags to be unscannable by sewing in an additional liner of common copper mesh used for filtration but after a cursory search the smallest openings I could find were in the 0.05mm range.

 

If the smallest wavelength is 0.1mm, I would have expected an opening of 0.05mm would prevent passage or possibly allow limited pass-through for a bleedover effect but as I said, this is not my expertise and I am quite certain that there are variables I have not accounted for in my assumption.

[Klaynos]

Airports will treat such bags as suspicious.

[Citizen]

Airports will treat such bags as suspicious.

 

Of course they will. They can peer inside if they desire with old fashioned eyeballs. =)

 

So the question remains open. Can such a liner, sewn into carry-on luggage, reflect Thz away?

[Mr Skeptic]

Well, I was thinking about modifying some carry-on bags to be unscannable by sewing in an additional liner of common copper mesh used for filtration but after a cursory search the smallest openings I could find were in the 0.05mm range.

 

I am quite certain that there are variables I have not accounted for in my assumption.

 

I think the biggest variable you're forgetting is that when the bag turns out to be unscannable security will pretty much be forced to hand-search it. Most likely they will search it very carefully and pass each of the items individually through their detector. That and they'll be very upset at you.

[Klaynos]

Of course they will. They can peer inside if they desire with old fashioned eyeballs. =)

 

So the question remains open. Can such a liner, sewn into carry-on luggage, reflect Thz away?

 

Yes, trivially, at THz frequencies you need only a very very very thin layer of metal to reflect 100% as the metal is a very close approximation to a perfect electrical conductor.

 

Or they might just go down the controlled explosion route, when you will be very upset at them... Either way, you loose.

[John Cuthber]

You certainly used to be able to buy lead lined bags for film and such. That would block everything from radio waves to xrays (and it would thin any gammas down a bit too.)

Why bother?

All you would do would be piss off the customs/ immigration officers.

Is that ever a good idea?

[Citizen]

Yes, trivially, at THz frequencies you need only a very very very thin layer of metal to reflect 100% as the metal is a very close approximation to a perfect electrical conductor.

 

Or they might just go down the controlled explosion route, when you will be very upset at them... Either way, you loose.

 

That can be translated as a 'yes'? That the copper, aluminum, stainless or brass mesh will successfully prevent THz from passing through?

 

 

Also, to address several comments that have been posted: I am fully aware that proceeding with this experiment will almost certainly result in excessive scrutiny by the TSA but that is my objective.

 

 

Amendment IV

The right of the people to be secure in their persons, houses, papers, and effects,

against unreasonable searches and seizures, shall not be violated, and no Warrants

shall issue, but upon probable cause, supported by Oath or affirmation, and particularly

describing the place to be searched, and the persons or things to be seized.

[Mr Skeptic]

Oh, I see. You're one of the people who takes our most important laws literally.

 

Um, taking a plane is voluntary and in order to take the plane you must consent to be searched. Oh, and apparently you can't just leave the airport if they do decide to search you, cause I guess that's suspicious or something.

[zparqi]

You might want to consider a material made from carbon nano-tubes which have the property of shielding those frequencies as they are fairly conductive. This has the added benefit of NOT being an obvious shielding material which would be completely incongruous with a 'luggage' application. These materials containing vacuum deposited metals particles might be more appropriate.

 

http://www.metalcoat...CFDatasheet.pdf

Metal Plated Conductive Carbon fibers (MPCC)

 

http://en.wikipedia....atrix_composite

 

 

Might even consider using the relatively cheap reflective products here: http://compositeenvisions.com/

Edited January 18, 2012 by zparqi

[John Cuthber]

"This has the added benefit of NOT being an obvious shielding material which would be completely incongruous with a 'luggage' application. "

Yeah, picture the scene at the airport.

2 customs officials checking bags

 

"Hey Fred."

"Yep,"

"You know this new scanner thingy they got"

"The terahertz one? yes, why do you ask"

"How much did it cost?"

"about a zillion dollars, why?"

"Because I can't see what's in this bloke's bag"

" don't worry- that's not obvious shielding- it's perfectly normal for baggage to be opaque to terrahertz radiation- that's why we use it. Nothing incongruous there"

"Thanks"

(Turns to passenger)

"OK, Mr Bin Laden , carry on."