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#1
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shielding
What material can be used for shield against potentially dangerous
levels of radio waves. Lets say outside my bedroom is a radio communication device. What material could stop the waves from entering. Cement? Lead? How thick? |
#2
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shielding
Aluminium Siding -and- Aluminium Screened Windows Speaking of aluminum screen, I previously tried a little experiment. Just one layer of screen isn't enough, if I make a cylnder of screen, 5-6 layers thick, then place my cell phone inside the signal is lost completly. 2-3 layers cause loss of a few bars. I'm not sure if it is a result of blocking the signal or just scrambling it. |
#3
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shielding
On Oct 9, 8:28 pm, wrote:
On Oct 9, 12:18 pm, RHF wrote: On Oct 9, 10:00 am, billy wrote: What material can be used for shield against potentially dangerous levels of radio waves. Lets say outside my bedroom is a radio communication device. What material could stop the waves from entering. Cement? Lead? How thick? Aluminium Siding -and- Aluminium Screened Windows I have a MSEE, but E&M is not my specialty. However, since aluminum is not a ferous material, I believe the H wave will penetrate it. RF shielding paint is generally nickle for that reason. I don't recall if "mu metal" is ferous or not. Turn your degree in! Faraday cages, AKA screen rooms, are used to isolated a space from the outside world. They use copper mesh, with the junctions welded, and achieve isolations of from 80dB up to ~120dB, more dB isolation requiring multiple "walls". Think nested Russian dolls. A RF/EM "wave" consists of both E and H fields. Any conductive case with completely conductive seams and walls will stop any RF/EM field. Take a cookie tin. With unpainted top and bottom join edges. Put an FM radio inside tuned to the strongest FM local staiton. As you put the top on the signal will go away. Works for AM/MW/Cell phones as well. Over in alt.survival we have several ongoing threads about how to protect electronics in a nuclear or solar EMP event. The better answer would be "why do you think you have dangerous levels of RF impinging your home/bedroom?" And "What frequencies do you think are present?" Higher frequencies mean shorter wavelengths, which mean any openings have to become smaller and minor joint imperfections become more important. IE A friend has a home recording studio. He lives within a mile of a pretty powerful AM/MW station. He was getting some interference in spite of serious efforts to filter the RF at the input to his mixer. At my suggestion he built a screen room of 'chicken wire'. Rat wire would have been better but the larger wire knocked the signals intensity down enought so it was not a problem. His room isn't really RF tight, a good radio will still pick up the stronger local MW stations, they are all very weak. A not perfect screen room but effective enough for his needs. Cellphones, TVs, FRS HTs and FM radio are fairly uneffected. Rat wire with it's 1/4" grid would kill everything below microwave, if you could build a good enough door. Terry |
#4
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shielding
billy wrote:
What material can be used for shield against potentially dangerous levels of radio waves. Lets say outside my bedroom is a radio communication device. What material could stop the waves from entering. Cement? Lead? How thick? here ya go. http://www.ericisgreat.com/tinfoilhats/ Drifter... |
#5
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shielding
On Oct 9, 6:37 pm, wrote:
On Oct 9, 8:28 pm, wrote: On Oct 9, 12:18 pm, RHF wrote: On Oct 9, 10:00 am, billy wrote: What material can be used for shield against potentially dangerous levels of radio waves. Lets say outside my bedroom is a radio communication device. What material could stop the waves from entering. Cement? Lead? How thick? Aluminium Siding -and- Aluminium Screened Windows I have a MSEE, but E&M is not my specialty. However, since aluminum is not a ferous material, I believe the H wave will penetrate it. RF shielding paint is generally nickle for that reason. I don't recall if "mu metal" is ferous or not. Turn your degree in! Faraday cages, AKA screen rooms, are used to isolated a space from the outside world. They use copper mesh, with the junctions welded, and achieve isolations of from 80dB up to ~120dB, more dB isolation requiring multiple "walls". Think nested Russian dolls. A RF/EM "wave" consists of both E and H fields. Any conductive case with completely conductive seams and walls will stop any RF/EM field. [snip] Not any. Skin depth comes into play so that any Faraday cage is going to have a lower cut-off frequency below which attenuation falls off. The size of holes set an upper cut-off frequency above which attenuation falls off. A Faraday cage, therefore, looks like a band- stop filter for RF/EM fields - the thicker the walls and the smaller the holes, the wider the bandwidth.. Tom |
#6
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shielding
On Oct 9, 1:42 pm, billy wrote:
Aluminium Siding -and- Aluminium Screened Windows Speaking of aluminum screen, I previously tried a little experiment. Just one layer of screen isn't enough, if I make a cylnder of screen, 5-6 layers thick, then place my cell phone inside the signal is lost completly. 2-3 layers cause loss of a few bars. I'm not sure if it is a result of blocking the signal or just scrambling it. Why do you state "potentially dangerous levels of radio waves" ? |
#7
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shielding
On Oct 9, 3:37 pm, wrote:
On Oct 9, 8:28 pm, wrote: On Oct 9, 12:18 pm, RHF wrote: On Oct 9, 10:00 am, billy wrote: What material can be used for shield against potentially dangerous levels of radio waves. Lets say outside my bedroom is a radio communication device. What material could stop the waves from entering. Cement? Lead? How thick? Aluminium Siding -and- Aluminium Screened Windows I have a MSEE, but E&M is not my specialty. However, since aluminum is not a ferous material, I believe the H wave will penetrate it. RF shielding paint is generally nickle for that reason. I don't recall if "mu metal" is ferous or not. Turn your degree in! Faraday cages, AKA screen rooms, are used to isolated a space from the outside world. They use copper mesh, with the junctions welded, and achieve isolations of from 80dB up to ~120dB, more dB isolation requiring multiple "walls". Think nested Russian dolls. A RF/EM "wave" consists of both E and H fields. Any conductive case with completely conductive seams and walls will stop any RF/EM field. Take a cookie tin. With unpainted top and bottom join edges. Put an FM radio inside tuned to the strongest FM local staiton. As you put the top on the signal will go away. Works for AM/MW/Cell phones as well. Over in alt.survival we have several ongoing threads about how to protect electronics in a nuclear or solar EMP event. The better answer would be "why do you think you have dangerous levels of RF impinging your home/bedroom?" And "What frequencies do you think are present?" Higher frequencies mean shorter wavelengths, which mean any openings have to become smaller and minor joint imperfections become more important. IE A friend has a home recording studio. He lives within a mile of a pretty powerful AM/MW station. He was getting some interference in spite of serious efforts to filter the RF at the input to his mixer. At my suggestion he built a screen room of 'chicken wire'. Rat wire would have been better but the larger wire knocked the signals intensity down enought so it was not a problem. His room isn't really RF tight, a good radio will still pick up the stronger local MW stations, they are all very weak. A not perfect screen room but effective enough for his needs. Cellphones, TVs, FRS HTs and FM radio are fairly uneffected. Rat wire with it's 1/4" grid would kill everything below microwave, if you could build a good enough door. Terry Like I said E&M isn't my thing; rather I know analog IC design. Somehow managed to pass two classes in E&M, and even knew how to do Smitch charts. I'm not quite convinced that aluminum shielding is all you need. Good audio transformers use mu-metal shields. I thought the Faraday shield only blocks the E, not H. Doing some googling, this website agrees with me: http://www.williamson-labs.com/480_shi.htm This is the nickle spray I use for shielding: http://www.mgchemicals.com/products/841.html There is a chart of non-ferous and ferous shielding, with the ferous shield being 20db better at times. |
#8
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shielding
On Tue, 09 Oct 2007 17:00:13 -0000, billy
wrote: What material can be used for shield against potentially dangerous levels of radio waves. Lets say outside my bedroom is a radio communication device. What material could stop the waves from entering. Cement? Lead? How thick? You need to fabricate one of these devices ............. immediately! http://zapatopi.net/afdb/ |
#9
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shielding
On Oct 10, 1:15 am, RHF wrote:
On Oct 9, 12:18 pm, RHF wrote: On Oct 9, 10:00 am, billy wrote: What material can be used for shield against potentially dangerous levels of radio waves. Lets say outside my bedroom is a radio communication device. What material could stop the waves from entering. Cement? Lead? How thick? - Aluminium Siding -and- Aluminium Screened Windows Follow-up Comment : These are a beginning and most likely the lowest cost first step. Plus they are the least intrusive and when viewed from the exterior will not look like urban blight. M...Sushi suggests "This is the nickle spray I use for shielding:http://www.mgchemicals.com/products/841.html There is a chart of non-ferous and ferous shielding, with the ferous shield being 20db better at times." CAUTION - Before using it on Interior Walls in Living Spaces be sure to consult the MSDS Information for the Product and the contact the Manufacture as to it's Safe Uses. ~ RHF . That paint is used for shield small plastic cases, not walls, though it is available as a brus hon product. My comment is the ferrous shielding is more effective. This again goes back to E&M,but my recollection is a non-ferous shield only stops E, not H. A ferrous shield, being electrically conductive as well, stops both fields. Like I said, E&M is not my field of specialty, just my 2 cents. |
#10
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shielding
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