It's not the first crowd control tool to use sound waves, but Raytheon's patent for a new type of riot shield that produces low frequency sound waves to disrupt the respiratory tract and hinder breathing, sounds a little scary.
Crowd control tools like the LRAD Sound Cannon emit bursts of loud and annoying sounds that can induce headaches and nausea. But Raytheon's non-lethal pressure shield creates a pulsed pressure wave that resonates the upper respiratory tract of a human, hindering breathing and eventually incapacitating the target. The patent points out that the sound waves being generated are actually not that powerful, so while protestors might collapse from a lack of oxygen reaching their brains, their eardrums won't be damaged in the process. Phew!
And like Roman soldiers joining their shields to form a large impenetrable wall, these new riot shields can actually be networked together to form a larger acoustical horn, vastly improving their range, power, and effectiveness. There's no word on what the long-term medical implications might be if you find yourself on the wrong side of one of these shields. But I imagine the unpleasant experience is not unlike being force choked from afar by Darth Vader. [Google Patents via New Scientist]