Riot shields could scatter crowds with 'wall of sound'

RIOT shields that project a wall of sound to disperse crowds will reduce violent clashes with police, according to a patent filed by defence firm Raytheon of Waltham, Massachusetts.

The device looks similar to existing riot shields, but it incorporates an acoustic horn that generates a pressure pulse. Police in the US already use acoustic devices for crowd control purposes that emit a loud, unpleasant noise.

The new shield described by Raytheon produces a low-frequency sound which resonates with the respiratory tract, making it hard to breathe. According to the patent, the intensity could be increased from causing discomfort to the point where targets become "temporarily incapacitated".

Acoustic devices haven't seen wide adoption because their range is limited to a few tens of metres. The patent gets around this by introducing a "cohort mode" in which many shields are wirelessly networked so their output covers a wide area, like Roman legionaries locking their shields together. One shield acts as a master which controls the others, so that the acoustic beams combine effectively.

Raytheon declined to comment on the work.

"We do not have sufficient technical detail yet to determine if there are any hidden medical implications," says Steve Wright of Leeds Metropolitan University in the UK. "These are always a concern because of the risk to sensitive bodily functions such as hearing, or even inducing panic attacks in asthmatics."

The biggest danger, he warns, is that the technology would be used for political control. "If authorities in Egypt or Syria had this, would they use it for dispersal or to shove crowds into potentially lethal harm's way?"

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