[admiralspoo]

It depends on the frequency. The brain is mostly water, but there are clear differences in the dielectric constant of air, the skull (bone) and the sweet delicious gray matter inside the cavity. By tuning the frequency of the waves, you can set up resonances in the cavity.

For a related effect, see https://www.youtube.com/watch?v=wCrtk-pyP0I

[01100011]

From the report:

"Frey reported these symptoms with an RF source transmitting at 1.3GHz(which provides the greatest absorption depth into cortical tissue)..."

So they are implying that not all RF is stopped by the skin and some does penetrate deep enough to reach the brain. I don't suppose it will be long until some shortsighted YouTuber tries this as the experiment would not be hard to replicate at all.

[ajsnigrutin]

Due to skin effect, most of the power is absorbed in the outer layers (skin mostly), and that causes 'warm/hot/burning' feeling, before doing anything else to your body.

[K0balt]

That's not what the "skin effect" refers to, and penetration of tissue / heating is completely dependent on frequency.

[xxpor]

Hm resonance inside the skull isn't something I'd considered, that's a fair point.

[CamperBob2]

Because it's not an issue. A bag of saltwater makes a really terrible resonant cavity.

[emmelaich]

You'd think grapes would make a poor resonant cavity too. But you can create plasma with grapes in a microwave oven.

[CamperBob2]

Yes, and that's precisely because they are so lossy. It's not a resonant effect. You're just taking advantage of the grape's cross section being roughly a quarter-wavelength at 2.4 GHz, which allows the magnetron to dump a ton of power into it.

It's analogous to using a couple of forks to operate a pickle from 120V.

[MacsHeadroom]

>roughly a quarter length

Is that not resonance?

[CamperBob2]

The same thing would happen with an ideal resistor whose leads formed a dipole of the right length, so no.

[the_only_law]

Before I act like an idiot and go do this, is there any significant safety risk or major risk to the equipment in doing this?

[CamperBob2]

Should be fine as long as you put a cup of water in the microwave alongside the grape. They aren't really meant to run empty, and microwaving a single grape would be basically running it empty.