The projector shielding. Could you make it clear for me?

Discussion in 'General Electronics Chat' started by DaniilL, Jul 28, 2014.

  1. DaniilL

    Thread Starter New Member

    Jul 28, 2014
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    Hello
    I plan to make a system like that (the pictures at the bottom of the page there):
    http://www.asilo.com/aztap1/
    Because I have got an allergy on electro-magnetic radiation, in other words electro sensitivity. As you see the author of that project has put the projector in the metallic case. He is an engineer and has made all using the knowledge available now in that area for science. And because of this, as I remember he claims that he reached attenuation of 80 dB in that project. I understand electronics very little, but get something from this book:
    Controlling Radiated Emissions by Design
    Michel Mardiguian
    http://us.bookzz.org/g/Michel Mardiguian
    I would like to make it that way (If I don’t understand right something in the technology of shielding or do not to take something into account, please tell me what exactly).
    I will order welding of the box from 2 mm steel with dimensions 40x40x60 cm with welding of the seams the same way as for gas pipes. Is the size of the box right? I hope that the big volume of air inside of it will give enough possibility for cooling. The opening for the projector beam will be with a lengthened hole (a metal tube), which should be three times longer than the diameter of the opening. I am not sure that the projector which I buy will be able to get through this tube without loss. First probably I will need to experiment with a cardboard model, so that the projector beam can go through it fully and then order. What is better, a smaller in diameter opening, but the tube (waveguide) will be shorter too, or a bigger opening, but the tube will be longer, related to the diameter of the opening? As I remember when ratio is 1 / 3, the effectiveness of a round opening is 90 db. But its dimensions nevertheless I imagine have importance too, and the smaller the better, is that right?
    Ventilation will be passive, I hope that this same opening will be enough for that, because I plan to buy a projector with little power, on LEDs (27 or 60 W). I don’t know here which to get, the one that has 300 Lm beam, but with less well focusing or another one that has 500-700 Lm which is more powerful, what is not desirable, but with better focusing, I need an advice here. On the top will be an opening for putting the projector inside (is there any importance on what it will lie there?) Again, It will be covered with steel, the gasket will be made from something like metal mesh going around perimeter (which of them exactly is here more suitable, can I take any mesh whatsoever (for example mesh for ordinary dishwashing?) In the place of the contact the surface will be rubbed down and cleaned to a metallic sheen (with abrasive paper for example); all this gets tightly squeezed up together on bolts, their rods can be welded to the case. Bolts are outside the perimeter of the gasket. Will this rods work like an antenna, in the book above, author tells that in the case of metalized plastic, long, protruding screws must be avoided because they can become radiating antennae (page 246),but what with that in my case, is that also true in the case I present here? There will be two apertures at the box bottom for the power and HDMI-cables. As I understood both cables should be putted in something like metal corrugated pipe, which should be tightly pressed down to the case with bolts on gasket the same way as the top cover. Is it also needed here to make a tube(waveguide)? Can the cables go together through the same duct and the same opening in the box, or they should be separated? (I have not understood it from the book, too difficult) The computer will be situated in another room. HDMI- cables will be 20 m long; is it needed to shield all of their length, or it is enough to shield only the part that will be in the main room. Leakages in another room will not be so important. The opposite end of cable shield should be grounded also as I understood.
    As to material used, will the 2 mm steel be effective approximately the same way through all the spectrum of frequencies as other metals. I cannot understand that from graphs which even give self-contradicting impression, possibly because of misunderstanding. I read that it is better (or what?) when the metal sheet is multilayered, at least for example 1 mm steel and 0,025 mm copper? What a difference I actually get here for my project? I need preferably to shield through all the spectrum of frequencies, because I do not know exactly which of them are affecting me. And how it is practically… the steel box can be welded in my country (in my parts) by usual weldors (by the way, is the 2 mm too thick, the shielding properties depending on the thickness as well), but what to do with copper? May be wrap this box afterwards additionally with thick aluminum or copper foil, or maybe you know where to buy prefabricated sheets already prepared specially for this purpose? Would it be possible to cover this finished box somehow afterwards also with copper or it will be needed to start from the beginning? All this details I think have an importance, may be without addressing them shielding can become useless.
    Reflected waves? they don’t evaporate by themselves and disappear as opposed to absorbed waves, so gradually the high frequencies (in the case of only steel present in the shield without copper) they will be rereflected all the time until they go out from the opening for the projector beam, is not that so? How then the shielding effectiveness by reflection actually works?
     
  2. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Too much to read..

    Something about putting a small projector into a metal box..
    All I have to say is cooling WILL be an issue if you don't have adequate ventillation holes or sufficient surface area for radiation.

    And I can't believe someone has electrosensitivity enough to have to justify putting every darn piece of electronics into a metal box.

    I'd suggest wrapping everything in aluminum foil and then just ground it..
    http://www.cnccookbook.com/img/OthersProjects/NoiseProof.jpg
     
  3. AlphaDesign888

    New Member

    Jul 27, 2014
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    I want 50 bucks to read all of that :eek:
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    DaniilL, welcome to AAC.

    Here are some tips for effective communication on on-line forums.

    If you want folks to read your initial post, make it short and sweet. Give us the lowdown in four sentences or fewer. You can always expand on the details in a subsequent post.

    Also, make your subject title descriptive. Make efficient use of the limited title space. "Could you make it clear for me?" doesn't help much.
     
  5. Johann

    Senior Member

    Nov 27, 2006
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    Yep! I agree! Anyway, effective screening does not imply making the metal box waterproof! It MAY HAVE ventilation holes (as long as they are not individually to big).
     
  6. kubeek

    AAC Fanatic!

    Sep 20, 2005
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    I´d suggest wrapping the OP in aluminium foil, and then grounding.

    Beware that conductive foil only dampens the electrostatic part of EM fields, the magnetic fields will remain completely unaffected.
    Also there is so much EM radiation all around you that you should be dead already, you should seek some very deep underground shelter to get the best shielding.
     
    Last edited: Jul 29, 2014
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  7. AlphaDesign888

    New Member

    Jul 27, 2014
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    I studied an unit called Applied Reasoning some years back. It teaches you how to write an argument. You first begin with the conclusion, and then have reasons to support your argument. You end up with very clear communication in your essay.
     
  8. alfacliff

    Well-Known Member

    Dec 13, 2013
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    shielding the projector will not stop all electromagnetic radiation, all cables going into or out of the shield will have to be filtered to stop conducted noise. the power cord can radiate a lot, and the video cable (if used) can too. test equpiment and high end radio manufacturers used to use coper plated steel for their cases and chasis.
    if you really want to go to a lot of trouble, lookup "tempest" the shielding for computers, monitors and other equipment under tempest specs is incredable.
     
  9. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Yeah .. thats why hes talking about steel tubing around all the cables,etc..
    Seems overkill to me but I can't imagine the extent of his "illness"
     
  10. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    The underground shelter could also be deadly. Wouldn't that put him closer to the Earth's electromagnetic core?:p
     
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  11. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
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    This condition is called EHS - Electromagnetic HyperSensitivy. It is described in this Wikipedia article http://en.m.wikipedia.org/wiki/Electromagnetic_hypersensitivity

    It is not a recognized medical diagnosis. Several studies suggest it is more likely a psychological condition related to a placebo effect. Several blind studies of self reported patients could not recognize the existence of EMR.

    Other interesting references follow.
    http://www.emrsafety.8m.net/newbook.htm
    http://www.dailymail.co.uk/femail/article-450995/The-woman-needs-veil-protection-modern-life.html
     
  12. alfacliff

    Well-Known Member

    Dec 13, 2013
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    steel tubes around the wires would not be as effective as normal shielding and filtering. think of the shielding for a standard good quality rf signal generator, double shielding, effective bypassing, feed through caps, and such. for extreme shielding, RCA used to make a riciever for the 500 khz emergency frequency that was required by the fcc to be monitored all the time the sstation was transmitting to assure no interference to emergency comms. how about a 500 khz reciever that blocks a 50 kw broadcast station located at the station? now thats shielding.
     
  13. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    So the remedies for this condition are basically the same as the protection from alien brain probes.. TINFOIL hats :D
    Then add on a tinfoil tuxedo and out on the town you go.
     
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  14. Alec_t

    AAC Fanatic!

    Sep 17, 2013
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    Unfortunately, screening the projector is only a small part of the solution. You are constantly being bombarded with EM radiation from various sources outside your control, e.g cosmic radiation, cell-phone masts, TV masts .....
    Perhaps you could wear a good old-fashioned suit of armour (or at least a chain-mail tunic) and attach a grounding strap to it? ;)
     
  15. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    I can't help myself..
    [​IMG]
     
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  16. DaniilL

    Thread Starter New Member

    Jul 28, 2014
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    Thank you, but what is normal cable shielding? How it differs from my original plan? I have looked up “tempest” but found only that this is a standard, and have not found a firm that can make an enclosure of the kind I am talking here about.
     
  17. DaniilL

    Thread Starter New Member

    Jul 28, 2014
    3
    0
    Unfortunately, all is not so simple here.

    In my particular state what makes problems for me are the computer, TV, and other powerful computational electronics. If nothing of this sort is in near proximity of me then all is OK as to myself.
     
    Last edited: Jul 30, 2014
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