Last year, US and Canadian diplomats and their families in Cuba suffered from weird illnesses that led many to speculate about a "sonic weapon" of some kind. After analyzing a reported audio clip of the mysterious sound released by the AP (below), University of Michigan computer scientist Kevin Fu and his Zhejiang University colleagues Wenyuan Xu and Chen Yan suggest that the source may have been accidental interference between ultrasonic signals. From IEEE Spectrum:
There are existing sources of ultrasound in office environments, such as room-occupancy sensors. “Maybe there was also an ultrasonic jammer in the room and an ultrasonic transmitter,” (Fu) suggests. “Each device might have been placed there by a different party, completely unaware of the other.”
One thing the investigation didn’t explore was whether the AP audio could have produced the wide range of symptoms, including brain damage, that afflicted embassy workers. “We know that audible signals can cause pain, but we didn’t look at the physiological effects beyond that,” Fu says. At press time, the FBI had yet to announce the results of its investigation. A panel of Cuban scientists and medical doctors, meanwhile, concluded that a “collective psychogenic disorder” brought on by stress may have been at work.
Fadel Adib, a professor at MIT who specializes in wireless technology for sensing and communications, calls the study by Fu and his colleagues “a creative take on what might have happened.” Adib, who wasn’t involved in the research but reviewed the results, adds that wireless signals can and do interact with one another. “And if that happens, you’ll hear signals you wouldn’t expect to hear,” he says. “Given all the possible explanations, this definitely seems the most plausible and the most technically feasible.”
Fu is careful to offer a caveat: “Of course, we don’t know for certain this was the cause. But bad engineering just seems much more likely than a sonic weapon.”
And for more: "How We Reverse Engineered the Cuban “Sonic Weapon” Attack"