Isn’t all radiation– from colours we can see all the way to microwave and nuclear – just the frequency of wavelengths? Like radio is light waves? So microwaves being a longer wavelength, when it passes through different materials (say, plastics) it can be sped up* and distorted, bringing it into the spectrum of UV light?
I don’t know, I’m not a physicist, but that would be my guess. I’d love for someone with knowledge to educate me here.