On 18 Sep 1999 16:47:49 +0200 naddy@mips.rhein-neckar.de (Christian
Weisgerber) writes:
> Brian D Williams <talon57@well.com> wrote:
>
> > This of course is why you have a perforated metal screen in the
> > front of your microwave oven, the wavelength is larger than the
> > openings in the mesh, so they can't escape and you can safely
> watch> > so you don't burn your mac'n'cheese.....
>
> Yep.
>
> So why does my mobile phone (GSM ~900MHz) continue to work when
> placed inside my microwave oven (2.4GHz presumably)?
>
> --
> Christian "naddy" Weisgerber
> naddy@mips.rhein-neckar.de
Good question. Microwave ovens work at 2450 MHz, which is a resonance frequency of the water molecule. Most food has a lot of water in it, so that frequency is generally effective at heating food.
Check the signal strength meter on the cell phone when it is outside the oven. If it indicates a very strong signal, you may be so close to the cell site base that the attenuation of the signal by the oven box is not sufficient to stop the phone from working. GSM phones periodically announce their presence to the cell site, about once a minute, I think, and if the cell site does not get a strong enough signal from the cell phone it marks the number as temporarily out of service.
People with heart pacemakers are warned to stay away from operating microwave ovens. That is evidence that the shielding effect of those ovens is not perfect. Another experiment which might be interesting to try is to put an AM radio or an FM radio in the oven box. I have not tried this, but I suspect that the radios will continue to work if they are tuned to a strong signal. Even inexpensive radio receivers usually have automatic gain control capability with a dynamic range of 60 or 80 or more decibels. So if the signal strength inside the box is a million times less (60 db less) than outside the box, the radio might still work, provided the signal strength outside the box is great enough. Interestingly, the normal range of human hearing is even greater than that, about 100 decibels or more.
Just in case, I should state the following, obvious as it may be: Do not turn the oven on when electronic equipment is inside the oven.
Ron Kean
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