Bit of an applied physics question here, to do with microwave ovens and the grille in the door through which you can see.

My understanding has been that the grille works because the waveform of the microwave photons is too large to physically fit through the holes. Visible light, with a much higher frequency, passes through easily. It has also been my understanding that microwave radiation is non-ionizing, and while you might have a Very Bad Day™ if you got in the way of a kilowatt magnetron’s output, it’s going to be mostly surface burns and tissue damage from heat. You’re not going to “be on anti-cancer meds for the rest of your life,” as The Expanse puts it.

I recently had an interaction in which a self-described “expert in RF” informed me that there is no such thing as the wave of a photon having physical size, and the grille works only because it’s a Faraday cage. (Is this even mutually-exclusive??) He also said that microwave radiation is extremely dangerous and “you can do some serious DNA damage with just a little bit of light cooking”. He asserted that the walls and door/grille of a microwave oven do not block the microwave radiation per se, but merely attenuate it, and that the FCC specifies acceptable attenuation levels. His assertion is that if the magnetron’s output power goes out of spec, then the unintended output also goes out of spec and quickly becomes very dangerous to be around.

His explanation doesn’t square with what I’ve heard about microwaves over the years, but neither myself nor, I suspect, he, is an expert in the underlying physics. I was hoping someone might be able to set the record straight on this exciting issue. :-)

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    $\begingroup$ Microwaves are electromagnetic radiation. Light also is electromagnetic radiation---the same exact phenomenon. Ask your expert, "how come the Faraday cage keeps the microwaves in, while letting some of the light get through?" $\endgroup$ Commented Jan 31, 2019 at 23:53
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    $\begingroup$ Your friend is not an expert in rf. That kind of summarizes it. $\endgroup$
    – Jon Custer
    Commented Feb 1, 2019 at 0:01
  • $\begingroup$ When you have a health concern, it is always a great idea to check with strangers online. How could they possibly be wrong? sciencealert.com/… $\endgroup$
    – safesphere
    Commented Feb 1, 2019 at 2:09

1 Answer 1


The effectiveness of a metal mesh screen at blocking radio-frequency electromagnetic waves is a direct function of the size of the holes in the mesh compared to the wavelength of those waves. Microwaves ovens produce radiation with a frequency of about 2.4 gigahertz, corresponding to a wavelength of about 12 centimeters. The holes in the window mesh of a microwave oven are small enough relative to this that the mesh window acts for all intents and purposes like a mirror to 12cm microwaves: they hit it and bounce off, and almost nothing escapes through the holes.

So your "RF expert" does not know what he is talking about.


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