Makes so much more sense than ultrasonics. Microwaves have the advantage of extremely short wavelengths which means they behave in a truly confusing fashion from the perspective of normal humans. I built a microwave fixture once for testing; it didn't work at first because my ground lugs were not equilaterally spaced around the lug which caused an impedance mismatch at 15 GHz or some shit. You can also beam super high frequency stuff at a surface and under the right circumstances, with the right carrier wave witchcraft, you can cause the harmonics to be more useful. Sennheiser had a "speaker" for sale for a while that you could bathe a wall in tweaky ultrasound and have program audio reflect back (it was like the 4th subharmonic of the parent waveform). But it had a range measured in feet. Acoustic energy is a lot more finicky than emf when it comes to range.