Dan74
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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
**broken link removed**
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?
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
**broken link removed**
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?