Understanding the Metal Mesh Effect on Microwaves

[E92M3]

I know that the metal mesh on the microwave oven door can block microwaves because the holes are much smaller than the wavelengths. It is the same reason why some radio telescopes can be made with a mesh. What is this effect called?

 

[litup]

I believe the effect is called "Faraday shield" where a conducting sphere would cause RF to basically turn into currents flowing outside the skin and keeping the rf from penetrating. It works in reverse also, as long as the holes in such a skin is a lot smalled in diameter than the wavelength of the radiation being shielded.

 

[skeptic2]

While a mesh with holes much smaller than the wavelength provides very good shielding it still is not as good as a solid metal shield. I read a book on this about 20 years ago and remember it even had formulas to calculate the amount of radiation that still passes through, but unfortunately I can't even remember the name of the book.

 

[litup]

While a mesh with holes much smaller than the wavelength provides very good shielding it still is not as good as a solid metal shield. I read a book on this about 20 years ago and remember it even had formulas to calculate the amount of radiation that still passes through, but unfortunately I can't even remember the name of the book.

I think smaller than wavelength holes in a conductor subject to EM radiation of any wavelength can produce plasmons, surface effect conduction that can allow some energy to penetrate even though it is theoretically too small a hole for normal radiation to penetrate.

That effect has been used to make sub-wavelength resolution microscopes, for instance.

 

[microwaveguru]

I know that the metal mesh on the microwave oven door can block microwaves because the holes are much smaller than the wavelengths. It is the same reason why some radio telescopes can be made with a mesh. What is this effect called?

It is called a "waveguide beyond cutoff"

 

[skeptic2]

It is called a "waveguide beyond cutoff"

Thanks, I think it may have.

 

[litup]

It is called a "waveguide beyond cutoff"

Sub-wavelength waveguide?

Here is one discussion of holes in shielding material, like the holes in microwave oven front window shield:

http://www.interferencetechnology.com/technologies/shielding/forums.html?tx_mmforum_pi1%5Baction%5D=list_post&tx_mmforum_pi1%5Btid%5D=105

 

[chrisbaird]

I would call the object a Faraday shield or part of a Faraday cage: http://en.wikipedia.org/wiki/Faraday_cage

The effect could be called a waveguide below the cutoff frequency.