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Author Topic: How fine must a mesh be to screen out voltage?  (Read 3317 times)

Offline Atomic-S

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How fine must a mesh be to screen out voltage?
« on: 13/05/2010 05:51:23 »
Given a charged flat conductor at potential V, and a wire mesh on both sides at potential 0 located a distance D away from the plate, let the whole apparatus be immersed in an electrolyte. What is the maximum spacing S of the wires that make up the mesh, such that at any point (far enough away from the edge of the plate that we do not have to consider edge effects), within the liquid but outside the assembly (that is, at a distance greater than D from the plate), the absolute value of the potential will not be greater than |V|/100?


 

Offline Geezer

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How fine must a mesh be to screen out voltage?
« Reply #1 on: 13/05/2010 06:47:48 »
We give up.

What's the answer?
 

Offline RD

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How fine must a mesh be to screen out voltage?
« Reply #2 on: 13/05/2010 15:33:09 »
If it's an alternating voltage then the shielding is frequency dependent ...



http://www.eetasia.com/ARTICLES/2000DEC/2000DEC01_RFD_ID_TA.PDF?SOURCES=DOWNLOAD

There a couple of typos on that table:
 the -26db hole size for 3GHz should be 2.5mm, (like the mesh on the door of a microwave oven).

« Last Edit: 13/05/2010 16:58:08 by RD »
 

Offline Geezer

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How fine must a mesh be to screen out voltage?
« Reply #3 on: 13/05/2010 16:31:50 »
If the electrolyte is conductive, won't that mess things up a bit?
 

Offline techmind

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How fine must a mesh be to screen out voltage?
« Reply #4 on: 14/05/2010 22:38:19 »
RD, maybe I'm being a pedant, but you quote mesh sizes for blocking electro-magnetic radiation. You can generate alternating current electric fields without an associated magnetic field - which don't propagate like radiowaves, and (I thought) otherwise behaved much like static electric fields.

If you had a whip-aerial which was but a small fraction of the resonant quarter-wave in length, you won't get much current (and thus magnetic component) - just a local non-radiative E-field. Surely you could 'shield' this using the same calculations as you would for a static DC field?


What do you think?
 
 

Offline Atomic-S

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How fine must a mesh be to screen out voltage?
« Reply #5 on: 29/05/2010 05:18:21 »
Quote
If it's an alternating voltage then the shielding is frequency dependent ...
Interesting, but a bit off of my question, which was actually aimed at the DC situation, or AC of low enough frequency that the wavelength is much longer than the dimensions in question.

Quote
If the electrolyte is conductive, won't that mess things up a bit?
Very probably; the electolyte is a key feature of the question. And yes, conductive electrolytes are contemplated (although not so conductivs as to create a dead short, e.g. mercury).

Quote
If you had a whip-aerial which was but a small fraction of the resonant quarter-wave in length, you won't get much current (and thus magnetic component) - just a local non-radiative E-field. Surely you could 'shield' this using the same calculations as you would for a static DC field?
I think you are correct; however the system is to be in an electrolyte. I am not sure whether the presence or absence of the electrolyte affects the mesh dimension; but it certainly affects the impedance at the test point, which for some purposes matters.
 

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How fine must a mesh be to screen out voltage?
« Reply #5 on: 29/05/2010 05:18:21 »

 

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