by kleinbl00

A smaller emitter placed even more closely, perhaps in someone’s pillow, might do the trick, said Dr. Qin. But it’s hard to believe such a device could escape attention. In theory, a building could be packed with small emitters; however, experts called it unlikely.

And while ultrasound can cause many of the symptoms reported, there’s no evidence that it can cause mild brain injury.

“I know of no acoustic effect that can cause concussion symptoms,” Dr. Altmann said. “Sound going through the air cannot shake your head.”

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