Sometimes, when I’m really cold, it can take over an hour to warm me up, even with a heating blanket. The quickest solution, a hot shower, feels really inefficient with all the heat going down the drain.
That got me thinking about microwaves. They heat food (partly) from the inside, contrary to simple infrared radiation.
Could we safely do that with people?
I found a Reddit thread where a non-lethal weapon and people getting eye damage because they stayed too long in front of a radar dish.
Could some sort of device be made that would warm specific areas (say, a hand or a leg) without endangering sensitive areas like the eyes?
Would it actually warm someone up from the inside? Would it be possible to make it safe?
Would it present advantages in cases of hypothermia, compared to heated IV fluids?
TL;DR: Yes, but the ways in which it could go wrong if done incorrectly mean it is essentially guaranteed to be deemed never worth the risk.
Microwaves don’t heat food “from the inside” necessarily, but from a depth that the microwaves manage to penetrate into it. In the cases of the microwave frequencies used in domestic appliances, that translates to around 4cm, give or take a small amount. So you would theoretically be able to heat your subject subcutaneously down to that depth. Note that the surface would also get heated in the process. There are fancy formulae to determine what the graph looks like of energy imparted to water (for sake of argument) in what proportion at what depth, but I won’t get into that here. This may or may not be useful for some manner of non-supervillian related purpose, but I can’t think of what that might be off the top of my head.
If the question is, “does exposure to microwaves cause any kind of freaky health effects, cause cancer, or induce mutant superpowers over and above just heating up the subject,” the answer insofar as we can determine is no.
However, it is absolutely possible to cause a wide array of boring old regular injuries up to an including death by, not to put too fine a point on it, cooking people. It’s very easy to bring water and other liquids to a boil by heating via microwave, for instance, and doing that inside the subject’s skin is probably a recipe for disaster. You would have to be able to accurately control the amount of energy imparted on the subject, and you would need some compelling reason why you’d have to do that via microwave versus innumerable more traditional methods many of which are inherently fail-safe, like just immersing them in warm water.