Has anyone heard of this? From the quick research it's frequency in various tones that mess with your brainwaves. There have been studies on binaural beats. You can find some of the frequencies on YouTube but the mp3's/cd's are very expensive. [video=youtube;d1akBw6G180]http://www.youtube.com/watch?v=d1akBw6G180[/video] The Gates Of Hades, also called The Gates Of Hell, is the most popular and looks downright unpleasant.
Depending on the frequency, some induce terrifying nightmares, but you're still in a conscious state. While some "iDosers" get high off of it.
Japan uses something similar to silence protest crowds. They echo sounds back instantly and the sound scrambles your brain in a way that prevents you from being able to speak. DHS also is stocking up on these weapons.