[ARCHIVED THREAD] - Microwave For EMP (Page 1 of 2)
Posted: 12/21/2010 9:13:57 AM EDT
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I was looking at my old microwave and it occurred to me that it might make a decent faraday cage. What does everyone think?
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It is a great faraday cage. For microwaves (2.45 GHz - wavelengh of 12.2 cm) ETA: try it.... put a phone with wifi in your microwave..... Wifi should be killed nearly instantly.... and in my case most of the cell signal was also attenuated, its not perfect. If something is small enough to fit into a microwave in the first place... Why would you have to put it into a microwave to protect it from EMP? |
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I was looking at my old microwave and it occurred to me that it might make a decent faraday cage. What does everyone think? Thanks. No offense. It's a dumb idea that won't work - add to the fact you really don't have to worry about EMPs. Well, I wouldn't say you won't have to worry abt EMP... Just that most of the silly reasons posted here the last few weeks wouldn't count for much. The real reason you would need to worry abt EMP is because if it ever happened, we're probably in for a lot worse issues than EMP. Like a full on nuclear war. |
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Quoted: Quoted: It is a great faraday cage. For microwaves (2.45 GHz - wavelengh of 12.2 cm) ETA: try it.... put a phone with wifi in your microwave..... Wifi should be killed nearly instantly.... and in my case most of the cell signal was also attenuated, its not perfect. If something is small enough to fit into a microwave in the first place... Why would you have to put it into a microwave to protect it from EMP? Who said I was protecting my phone from EMP.... I really more worried about this...  burns my frikkin' city down everytime Really OP... EMP is overrated. Unplug your stuff and it'll likely be fine... beyond that no one knows so its best to prepare for more realistic eventualities, like floods, tornados, hurricanes, droughts, fires, unemployment and economic distress. |
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I didn't ask if anyone thought the threat was real. I just asked as to whether the idea would work.
As far as : [/quote] Really OP... EMP is overrated. Unplug your stuff and it'll likely be fine... beyond that no one knows so its best to prepare for more realistic eventualities, like floods, tornados, hurricanes, droughts, fires, unemployment and economic distress. [/quote] Can't flood here. The last tornado that went through here wasn't heard until the last minute because of the traffic noise so there's not a whole lot that can be done about that. Working on power. Can't do much about a drought. Can't afford more insurance(fire). I'm disabled and on SS. I have a year's worth of supplies. So, I would say that I'm better off than 95% of the country. And, from what I've read, the power cord would act as an antenna to absorb more of the pulse waves to amplify the effect on the device. However, from the info and history I have studied, I believe EMP is a threat. It may come from a nuke or it may come from the sun or it may not come at all. Hopefully not. But that is why we prep. For the unknown happenstances. If I can hedge my bets by storing some electronics safely, I say it's foolish not to. I'm sure we didn't think it was possible the Japanese were going to attack us at Pearl Harbor. I'm sure they didn't think a single bomb was going to flatten an entire city. Look at the Flash Gordon radio programs and comics from the 1920s. Much of the impossible is happening today. Just because you don't think something is possible doesn't mean it isn't. That said, things are changing and not for the better. If this were to happen, it could be a game changer. Causing repercussions that could take years to get back to any kind of modern normalcy. The solar event in, I believe, 1859 wrecked havoc with the telegraph lines and stations. If it were to happen now, what would happen to the chips and micro circuitry? If the power lines would act as an antenna, what would happen to the transformers? Even if nothing was affected other than the transformers, that could mean no electrical grid for the 3-5+ years to replace them from Europe or Asia. |
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I was looking at my old microwave and it occurred to me that it might make a decent faraday cage. What does everyone think? Thanks. Some are pretty leaky. There are detectors designed to test microwave ovens for leaks.....Radio Shack used to sell a cheap hand-held one. if the emitter still works and you're curious you could probably test it. The lower the emissions, the better the faraday cage. At a minimum it'll tell you if you're getting unsafe RF exposure while nuking a cheese sandwich. |
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It won't work. The holes are too big.
The holes are too big for what???? Why???? I suspect he's referring to the wavelengths for which a microwave's shielding is effective: microwaves. You can't just simply assume that other wavelengths, like the kind that make up the rest of our Doomsday EMP, will be shielded to the same degree. |
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I suspect he's referring to the wavelengths for which a microwave's shielding is effective: microwaves. You can't just simply assume that other wavelengths, like the kind that make up the rest of our Doomsday EMP, will be shielded to the same degree. It's reasonable to believe though that it will be effective at the design frequency as well as lower frequencies. The peak energy of a high altitude NEMP pulse is in the range of 100kHz - 1MHz and there is little energy above 100MHz. If you're experiencing EMP at 2.4gHz, EMP is the least of your problems. |
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Guys, look...
A microwave oven uses an 'RF gasket' that is a capacitive area around the perimeter of the door that is 'tuned' by its width and gap spacing to attenuate energy in the 2.4 gHz band and works IN BOTH DIRECTIONS, energy coming from the inside of the oven and energy [like potential EMP] getting into the oven. The 'gasket' works very well with an attenuation at the designed frequency of 50 dB I'd guess. [I've got the equipment to measure this if I ever feel the need] This tuning is rather broad but likely starts rolling off about 5% from the 2400 mc center frequency. At lower frequencies say below 100 mc where EMP energy is found, the door seal is about as useful as an empty BOB. If you don't believe this, take an AM/FM radio and turn it up in both bands and stick it into oven. It'll play just fine. So the BAD NEWS is a microwave oven offers little protection to an EMP event. The GOOD NEWS is that for small devices, no protection is needed in most cases unless you have long wire antennas attached to the device Now if putting your stuff into a microwave makes you FEEL better, by all means get busy doing it. |
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If something is small enough to fit into a microwave in the first place... Why would you have to put it into a microwave to protect it from EMP? This question is worth repeating, because it exposes the fallacy of using a "Faraday cage" to protect against HEMP: Just about anything that's small enough to fit inside a Faraday cage is too small to be damaged by HEMP anyway. Small device = very short conductors = very little HEMP intercepted = very little chance of damage |
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Oh geeze.... Are you being skeptical? Because I've seen it being recomended by someone, I can't recall if it was DOD, or someone doning a review of the literature type study. Makes sense it would work. I've seen some pretty nice screen rooms made of copper foil PCB boards. Nothing lab grade, but good enough to tune common carrier pagers, which is almost impossable in an open enviroment. |
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Oh geeze.... Are you being skeptical? Because I've seen it being recomended by someone, I can't recall if it was DOD, or someone doning a review of the literature type study. Makes sense it would work. I've seen some pretty nice screen rooms made of copper foil PCB boards. Nothing lab grade, but good enough to tune common carrier pagers, which is almost impossable in an open enviroment. No, I use al foil often for RF shielding and development. In fact I'm experimenting with some pagers right now for a miniature repeater. Very familiar with your issue. My comment was that considering the size of something that could be easily wrapped in a qty of foil that someone would have in their BOB, etc, it would be pointless to do it because of the tons of info in this thread [and on other threads] explaining that small devices without long conductors connected to them aren't at risk in the first place. It's as if folks chime in without getting a grounding [grin] on the meat of a thread. See the next post? 
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Popcorn cans make good faraday cages. At this time of year they're easy to find too. I just use the wire brush on my dremel tool to remove all of the paint on mating surfaces between the lid and the can. Yes they do if you put LOTS of aluminium foil around the lid and can. Buy why do you need a Faraday cage??? |
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Popcorn cans make good faraday cages. At this time of year they're easy to find too. I just use the wire brush on my dremel tool to remove all of the paint on mating surfaces between the lid and the can. Yes they do if you put LOTS of aluminium foil around the lid and can. Buy why do you need a Faraday cage??? These are the 5 gallon metal cans––no need to put foil around it. |
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Popcorn cans make good faraday cages. At this time of year they're easy to find too. I just use the wire brush on my dremel tool to remove all of the paint on mating surfaces between the lid and the can. Yes they do if you put LOTS of aluminium foil around the lid and can. Buy why do you need a Faraday cage??? These are the 5 gallon metal cans––no need to put foil around it. Why not? |
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I'm sure the metal of the can alone provides 80 to 100 dB of isolation. Why would you need more? How can you be sure of 80 dB isolation with just a lid contact that has been Dremeled clean? At what frequency would you get that sort of isolation? At what position in the can? |
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I'm sure the metal of the can alone provides 80 to 100 dB of isolation. Why would you need more? How can you be sure of 80 dB isolation with just a lid contact that has been Dremeled clean? At what frequency would you get that sort of isolation? At what position in the can? Those numbers would be typical based on isolation specifications for shielded anechoic chambers with simple single layer metalic shielding. IIRC those numbers apply from about 100MHz to 5GHz or so. The cans that I have have about a 1/2" overlap between the lid and the can that is very tight. Nothing much will be getting through that. What makes you think that it wouldn't have that isolation? |
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Oh geeze.... Are you being skeptical? Because I've seen it being recomended by someone, I can't recall if it was DOD, or someone doning a review of the literature type study. Makes sense it would work. I've seen some pretty nice screen rooms made of copper foil PCB boards. Nothing lab grade, but good enough to tune common carrier pagers, which is almost impossable in an open enviroment. No, I use al foil often for RF shielding and development. In fact I'm experimenting with some pagers right now for a miniature repeater. Very familiar with your issue. My comment was that considering the size of something that could be easily wrapped in a qty of foil that someone would have in their BOB, etc, it would be pointless to do it because of the tons of info in this thread [and on other threads] explaining that small devices without long conductors connected to them aren't at risk in the first place. It's as if folks chime in without getting a grounding [grin] on the meat of a thread. See the next post?
LOL And then YOU suggest glomming on aluminum foil to improve the isolation 
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Oh geeze.... Are you being skeptical? Because I've seen it being recomended by someone, I can't recall if it was DOD, or someone doning a review of the literature type study. Makes sense it would work. I've seen some pretty nice screen rooms made of copper foil PCB boards. Nothing lab grade, but good enough to tune common carrier pagers, which is almost impossable in an open enviroment. No, I use al foil often for RF shielding and development. In fact I'm experimenting with some pagers right now for a miniature repeater. Very familiar with your issue. My comment was that considering the size of something that could be easily wrapped in a qty of foil that someone would have in their BOB, etc, it would be pointless to do it because of the tons of info in this thread [and on other threads] explaining that small devices without long conductors connected to them aren't at risk in the first place. It's as if folks chime in without getting a grounding [grin] on the meat of a thread. See the next post?
LOL And then YOU suggest glomming on aluminum foil to improve the isolation 
So why do you need a Faraday cage??? |
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Those numbers would be typical based on isolation specifications for shielded anechoic chambers with simple single layer metalic shielding. IIRC those numbers apply from about 100MHz to 5GHz or so. The cans that I have have about a 1/2" overlap between the lid and the can that is very tight. Nothing much will be getting through that. What makes you think that it wouldn't have that isolation? Because odds are the lid is only making contact in 5 or 6 or 12 places which introduces discontinuities in the surface which causes currents to flow on both the inside and outside. it's analgous to a EMC shielded cabnet where the bulkhead plate isn't screwed down 9but otherwise making contact., or if the gasket is removed from the door. You still get a lot of shielding, but not 80 dB. In fact I've never seen 80 dB on a cabinet without phosphor bronze spring fingers rather then the wire mesh gasket. You realize 80 dB means one hundredth of a millionith of the original power. |
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Oh geeze.... Are you being skeptical? Because I've seen it being recomended by someone, I can't recall if it was DOD, or someone doning a review of the literature type study. Makes sense it would work. I've seen some pretty nice screen rooms made of copper foil PCB boards. Nothing lab grade, but good enough to tune common carrier pagers, which is almost impossable in an open enviroment. No, I use al foil often for RF shielding and development. In fact I'm experimenting with some pagers right now for a miniature repeater. Very familiar with your issue. My comment was that considering the size of something that could be easily wrapped in a qty of foil that someone would have in their BOB, etc, it would be pointless to do it because of the tons of info in this thread [and on other threads] explaining that small devices without long conductors connected to them aren't at risk in the first place. It's as if folks chime in without getting a grounding [grin] on the meat of a thread. See the next post?
LOL And then YOU suggest glomming on aluminum foil to improve the isolation
So why do you need a Faraday cage??? Good question. I'm not convinced that EMP represents a threat to devices NOT connected to either an antenna or power lines. I'm not 100% convinced that it is not a threat either. |
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Those numbers would be typical based on isolation specifications for shielded anechoic chambers with simple single layer metalic shielding. IIRC those numbers apply from about 100MHz to 5GHz or so. The cans that I have have about a 1/2" overlap between the lid and the can that is very tight. Nothing much will be getting through that. What makes you think that it wouldn't have that isolation? Because odds are the lid is only making contact in 5 or 6 or 12 places which introduces discontinuities in the surface which causes currents to flow on both the inside and outside. it's analgous to a EMC shielded cabnet where the bulkhead plate isn't screwed down 9but otherwise making contact., or if the gasket is removed from the door. You still get a lot of shielding, but not 80 dB. In fact I've never seen 80 dB on a cabinet without phosphor bronze spring fingers rather then the wire mesh gasket. You realize 80 dB means one hundredth of a millionith of the original power. Yep, I know exactly what it means. |
| I just re read your post. The 80dB you mention is from 100 Mhz to 5 Ghz. Thats bordering on the don't care range from EMP. At at least the higher end of those frequencies, you might get great capacitive coupling across the popcorn lid, but you won't from 100 KHz to 100 Mhz. In this range you need good physical contact, or something with a lot of capactance like Al or Cu tape. |
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Also, don't overlook the waveguide cutoff effect of a 'wavefront' entering a waveguide.
Putting a "receiver" [any device that could be damaged by a large enough pulse at low frequencies -not saying such a pulse could be generated in the context of HEMP] deeper into a waveguide [in this case a closed one on one end, that is a popcorn can] will attenuate RF effectively. Older RF sig gens [that still leave warm fuzzies in my tummy  , I had 2 as a kid my Father found somewhere and one I was able to retune to 2M and the commercial band and the other worked on 6M] used so called 'piston' attenuators and typically they were an approx 1 inch dia tube with a coupling link at one end and a sliding piston with a coupling link at the other. They drifted like a SOB though... Was I happy to get my first HP 8660C...
50 dB atten was easily and accurately obtained in about 4 inches of movement and the sig gens were useful below a microvolt. The piston atten distance/power relationship [scale cal] is logarithmic. So, what I'm saying, is that any long metal container like the popcorn oil can may very well have sufficient attenuation for the 'imaginary' EMP pulse just a foot or two from the open end. NO LID IS NEEDED... [ I was pulling your tail 357  ]
...possibily, if the device is put at the bottom of the can and no conductors pass into the waveguide that could couple energy. To reduce energy at lower frequencies, stack two cans. The goal is tall and narrow. My microwave books are at a different location, maybe I'll remember to look up the formula or find it with a Google search. Another thing, an EMP pulse isn't likely going to be the strongest radiation in the first place, and maybe only a 10 or 20 dB reduction would be enough to protect a susceptible device. 10 or 20 dB is a 1/10 and 1/100 power reduction. That's a LOT. [My SO has conked out  from all the Christmas eve activity today. It all starts again in the AM!]
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To do a practical experiment [and bypass the HI-IQ idiot theory] to see and evaluate waveguide cutoff effects, take a popcorn can and suspend an AM/FM radio on some paracord and introduce it into the can.
You should see a reduction of signal strength as you lower the radio. Try both bands. If you have a radio with a SS meter that works on the AM bands, that would be a good one to try. [Not that any of the EMP groupies here will...  ]
I don't have a metal can here or I would do the experiment precisely with a spectrum analyzer. Hmmm, I think I have a metal Blitz fuel can that's empty. maybe will try tomorrow. A metal fuel can should make a great protective shield for small electrical devices that are a few miles from an EMP event!
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Say you wanted to protect a watch, Eotech, or walkie talkie from this MYTHICAL EMP RISK.
All you have to do is pick up some aluminium dryer vent pipe, stretch a piece out for about 2 1/2 feet and put the device to be protected in the middle of the tube. You DON'T, I said DON'T, have to close the ends. But hey, whatever blows your dress up, it won't hurt anything... Th-hh-aa-at's it F-oo-oks. This will attenuate signals in the frequencies of interest greatly. No silly Faraday cage needed. 
No ground  needed.
Now can we all forget this EMP nonsense? OH-OH It's 12PM Christmas Eve. All our lights should be going off and the power plants should be blowing up soon if that guy's claims have any truth. Hot Dog, fasten your seat belts! |
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To do a practical experiment [and bypass the HI-IQ idiot theory] to see and evaluate waveguide cutoff effects, take a popcorn can and suspend an AM/FM radio on some paracord and introduce it into the can. You should see a reduction of signal strength as you lower the radio. Try both bands. If you have a radio with a SS meter that works on the AM bands, that would be a good one to try. [Not that any of the EMP groupies here will... ]
I don't have a metal can here or I would do the experiment precisely with a spectrum analyzer. Hmmm, I think I have a metal Blitz fuel can that's empty. maybe will try tomorrow. A metal fuel can should make a great protective shield for small electrical devices that are a few miles from an EMP event! I did an experiment similar to what you describe. The results were, well, underwhelming. My back of the envelope calculations indicate about 25 dB reduction at UHF (70 cm). It looks like a popcorn can is not so good. |
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To do a practical experiment [and bypass the HI-IQ idiot theory] to see and evaluate waveguide cutoff effects, take a popcorn can and suspend an AM/FM radio on some paracord and introduce it into the can. You should see a reduction of signal strength as you lower the radio. Try both bands. If you have a radio with a SS meter that works on the AM bands, that would be a good one to try. [Not that any of the EMP groupies here will... ]
I don't have a metal can here or I would do the experiment precisely with a spectrum analyzer. Hmmm, I think I have a metal Blitz fuel can that's empty. maybe will try tomorrow. A metal fuel can should make a great protective shield for small electrical devices that are a few miles from an EMP event! I did an experiment similar to what you describe. The results were, well, underwhelming. My back of the envelope calculations indicate about 25 dB reduction at UHF (70 cm). It looks like a popcorn can is not so good. UHF isn't where you need attenuation. Try down around 1 mHz with an AM radio. Actually a 25 dB reduction is probably all you need [for the MYTHICAL EMP of course-[ wink]. |
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To do a practical experiment [and bypass the HI-IQ idiot theory] to see and evaluate waveguide cutoff effects, take a popcorn can and suspend an AM/FM radio on some paracord and introduce it into the can. You should see a reduction of signal strength as you lower the radio. Try both bands. If you have a radio with a SS meter that works on the AM bands, that would be a good one to try. [Not that any of the EMP groupies here will... ]
I don't have a metal can here or I would do the experiment precisely with a spectrum analyzer. Hmmm, I think I have a metal Blitz fuel can that's empty. maybe will try tomorrow. A metal fuel can should make a great protective shield for small electrical devices that are a few miles from an EMP event! I did an experiment similar to what you describe. The results were, well, underwhelming. My back of the envelope calculations indicate about 25 dB reduction at UHF (70 cm). It looks like a popcorn can is not so good. UHF isn't where you need attenuation. Try down around 1 mHz with an AM radio. Actually a 25 dB reduction is probably all you need [for the MYTHICAL EMP of course-[ wink]. I'll try it at AM when I go back to work and have access to better equipment. |