I Wavelength and size of holes or grating

[merlyn]

Could someone explain to be the reason why size of the hole or grating in the case of Faraday cage is what determines if the screen or grating is opaque or transparent? I'm pretty sure it has something to do with interference patterns in classical physics.

Thank you all in advanced.

 

[PeroK]

Have you looked for an existing answer online?

 

[merlyn]

Yes. I didn't know how to phrase the question.
I thought I could get a more succinct and definitive answer here.

 

[PeroK]

Yes. I didn't know how to phrase the question.
I thought I could get a more succinct and definitive answer here.

It's probably best to be more precise about what you don't understand about what you've read.

 

[merlyn]

It's probably best to be more precise about what you don't understand about what you've read.

I just wanted the basic mechanism explained, or at least a reference.
Should I look under defraction, reflection or perhaps slit experiment ?

 

[tech99]

Could someone explain to be the reason why size of the hole or grating in the case of Faraday cage is what determines if the screen or grating is opaque or transparent? I'm pretty sure it has something to do with interference patterns in classical physics.

Thank you all in advanced.

It needs to be somewhat smaller than half a wavelength diameter to block radiation. Not to do with diffraction.

 

[merlyn]

It needs to be somewhat smaller than half a wavelength diameter to block radiation. Not to do with diffraction.

Wonderful...Why? What are the physics?

 

[tech99]

The hole behaves as a very short piece of metallic waveguide. If it is smaller than certain critical dimensions it is cut-off and will not support propagation of a wave.
Another way to look at is that large holes create surface impedance which reduces the flow of current in the surface, which is necessary for reflection.
And another way to look at it is that resonant slots will radiate as they deflect surface currents around them.

 

[merlyn]

The hole behaves as a very short piece of metallic waveguide. If it is smaller than certain critical dimensions it is cut-off and will not support propagation of a wave.
Another way to look at is that large holes create surface impedance which reduces the flow of current in the surface, which is necessary for reflection.
And another way to look at it is that resonant slots will radiate as they deflect surface currents around them.

Do you have any references which I can explore further?

 

[sophiecentaur]

resonant slots will radiate

Could it be resonance? The effect doesn't have a peak; it's just a high pass function.

One way of looking at it is that the network of conductors changes the Impedance presented to the incident wave. At a low enough frequency, the grid looks just like a metal plate (Z=0) and is a perfect reflector.