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I found this pretty awesome explanation for why a microwave oven doesn't block cell phone reception: http://skeptics.stackexchange.com/a/5410 http://skeptics.st

by tszyn 13y ago

I found this pretty awesome explanation for why a microwave oven doesn't block cell phone reception: http://skeptics.stackexchange.com/a/5410 http://skeptics.stackexchange.com/a/5410 Clearly, this whole "cell phone in a fridge" thing is a clever attempt to make Snowden lose his nerd cred.

rmccue 13y ago
A solid box of metal is going to be a pretty effective Faraday cage regardless of what (sane^) frequency you're using. Microwaves on the other hand are specifically designed to be Faraday cages, so they're tailored specifically to the frequency they're blocking. (How exactly they do this I'm not quite sure, given that the frequency of a phone and the frequency of phones is quite similar.) ^: Where "sane" means "not gamma waves"
- anotherhue 13y ago
  Microwaves aren't Faraday cages as it's too difficult to manufacture a perfect seal, instead the size of the holes in the door act as a tuned RF choke.
  - sliverstorm 13y ago
    Why on earth would you need a "perfect" seal?
    - anotherhue 13y ago
      People sometimes like to watch the food being cooked, for one. At KW levels of power a few dB is still enough to do harm. Lots of nasty reports in the medical literature of this type of exposure, typically unlucky repairmen. The eye has very poor heat dissipation mechanisms, and they showed in the 70's the RF exposure could cause cataracts in rabbits. (I think dogs were exposed too -- it was a new field, so they didn't know what would happen) https://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4502597 https://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=45025...
      - sliverstorm 13y ago
        Not an RF engineer here, though I know a few- is a nearly-but-not-quite-perfect Faraday cage really only going to attenuate a few dB?
        anotherhue 13y ago
        I meant to say that if a small portion of the energy leaked through, it would still be enough to be concerned about. Most cages will provide very good, though imperfect shielding, but cages of that quality are economically unviable for home purposes. I recall reading that they were subject to failure from every day wear and tear too, which would be hard to spot until it was dangerous. The chokes are just a more practical design.
        marshray 13y ago
        It all depends^TM, mostly on the wavelength and the size and shape of the gap and the phase of the moon. dB is a logarithmic scale, so this kind of back-of-the-envelope reasoning is sometimes made easier and sometimes counterintuitive.
        anotherhue 13y ago
        I meant to say that if a small portion of the energy leaked through, it would still be enough to be concerned about. Most cages will provide very good, though imperfect shielding, but cages of that quality are economically unviable for home purposes. I recall reading that they were subject to failure from every day wear and tear too, which would be hard to spot until it was dangerous. The chokes are just a more practical design.
      - deleted 13y ago
        [deleted]
- davidcuddeback 13y ago
  > the frequency of a phone and the frequency of phones is quite similar (I'm assuming you meant frequency of a phone and microwave oven.) That's not quite accurate. Cell phones use many frequency bands [1]. I only see one frequency on the list (2500 MHz) that is close to the frequency used by consumer microwave ovens (2.45 GHz) [2]. I don't think 2100 MHz is close enough to be attenuated by a microwave oven, but of course I'm just speculating because it depends on the design of the oven's shielding. Don't forget that phones switch to a frequency on which they have signal. If you don't have 4G coverage, your phone will use 3G, etc. These operate at different frequencies. So attenuating one or two of the frequencies on the list is probably not good enough. [1] https://en.wikipedia.org/wiki/Cellular_frequencies https://en.wikipedia.org/wiki/Cellular_frequencies [2] https://en.wikipedia.org/wiki/Microwave_oven#Principles https://en.wikipedia.org/wiki/Microwave_oven#Principles
  - rmccue 13y ago
    > I don't think 2100 MHz is close enough to be attenuated by a microwave oven, but of course I'm just speculating because it depends on the design of the oven's shielding. I assumed that the design was that of a Faraday cage, which blocks the frequency it's designed for and all lower frequencies. anotherhue noted however that it's a tuned RF choke, which will only block a certain frequency. For reference, I'm in Australia with a 3G phone on Optus, so the frequencies here are a little less scattered [1]. [1]: http://whirlpool.net.au/wiki/mobile_phone_frequencies http://whirlpool.net.au/wiki/mobile_phone_frequencies

by tszyn 13y ago

rmccue 13y ago

A solid box of metal is going to be a pretty effective Faraday cage regardless of what (sane^) frequency you're using. Microwaves on the other hand are specifically designed to be Faraday cages, so they're tailored specifically to the frequency they're blocking. (How exactly they do this I'm not quite sure, given that the frequency of a phone and the frequency of phones is quite similar.) ^: Where "sane" means "not gamma waves"

anotherhue 13y ago
Microwaves aren't Faraday cages as it's too difficult to manufacture a perfect seal, instead the size of the holes in the door act as a tuned RF choke.
- sliverstorm 13y ago
  Why on earth would you need a "perfect" seal?
  - anotherhue 13y ago
    People sometimes like to watch the food being cooked, for one. At KW levels of power a few dB is still enough to do harm. Lots of nasty reports in the medical literature of this type of exposure, typically unlucky repairmen. The eye has very poor heat dissipation mechanisms, and they showed in the 70's the RF exposure could cause cataracts in rabbits. (I think dogs were exposed too -- it was a new field, so they didn't know what would happen) https://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4502597 https://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=45025...
    - sliverstorm 13y ago
      Not an RF engineer here, though I know a few- is a nearly-but-not-quite-perfect Faraday cage really only going to attenuate a few dB?
      - anotherhue 13y ago
        I meant to say that if a small portion of the energy leaked through, it would still be enough to be concerned about. Most cages will provide very good, though imperfect shielding, but cages of that quality are economically unviable for home purposes. I recall reading that they were subject to failure from every day wear and tear too, which would be hard to spot until it was dangerous. The chokes are just a more practical design.
      - marshray 13y ago
        It all depends^TM, mostly on the wavelength and the size and shape of the gap and the phase of the moon. dB is a logarithmic scale, so this kind of back-of-the-envelope reasoning is sometimes made easier and sometimes counterintuitive.
      - anotherhue 13y ago
        I meant to say that if a small portion of the energy leaked through, it would still be enough to be concerned about. Most cages will provide very good, though imperfect shielding, but cages of that quality are economically unviable for home purposes. I recall reading that they were subject to failure from every day wear and tear too, which would be hard to spot until it was dangerous. The chokes are just a more practical design.
    - deleted 13y ago
      [deleted]
davidcuddeback 13y ago
> the frequency of a phone and the frequency of phones is quite similar (I'm assuming you meant frequency of a phone and microwave oven.) That's not quite accurate. Cell phones use many frequency bands [1]. I only see one frequency on the list (2500 MHz) that is close to the frequency used by consumer microwave ovens (2.45 GHz) [2]. I don't think 2100 MHz is close enough to be attenuated by a microwave oven, but of course I'm just speculating because it depends on the design of the oven's shielding. Don't forget that phones switch to a frequency on which they have signal. If you don't have 4G coverage, your phone will use 3G, etc. These operate at different frequencies. So attenuating one or two of the frequencies on the list is probably not good enough. [1] https://en.wikipedia.org/wiki/Cellular_frequencies https://en.wikipedia.org/wiki/Cellular_frequencies [2] https://en.wikipedia.org/wiki/Microwave_oven#Principles https://en.wikipedia.org/wiki/Microwave_oven#Principles
- rmccue 13y ago
  > I don't think 2100 MHz is close enough to be attenuated by a microwave oven, but of course I'm just speculating because it depends on the design of the oven's shielding. I assumed that the design was that of a Faraday cage, which blocks the frequency it's designed for and all lower frequencies. anotherhue noted however that it's a tuned RF choke, which will only block a certain frequency. For reference, I'm in Australia with a 3G phone on Optus, so the frequencies here are a little less scattered [1]. [1]: http://whirlpool.net.au/wiki/mobile_phone_frequencies http://whirlpool.net.au/wiki/mobile_phone_frequencies