Microwave Voice to Skull actually certified as proven by the US Army. You will see a lot of references to things being possible but pay attention to where they say that in one experiment the words from one to ten were successfully transmitted to the test subjects head via microwave and microphones next to the persons head was not able to pickup the sound.
US Army Voice to Skull Studies and Proof Declassified
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(Mod Edit) The link has been fixed.