A few months ago, several members of the U.S. Embassy in Cuba had apparently suffered some strange kind of attack. Multiple members of the embassy’s staff claimed a variety of symptoms from headaches to brain damage, and investigators were unable to determine what was going on.
The strange collection of symptoms combined with the lack of any sort of device that could have caused such symptoms has stymied investigators for months. Doctors had analyzed the brains of the victims and discovered ‘anomalies’ but no clear cause, and repeated sweeps of their hotel rooms turned up no weapons, devices, or anything else suspicious.
More broadly, many scientists struggled to think of anything that could have been responsible, even theoretically. The evidence gathered suggests some sort of sonic or acoustic weapon, but not such weapon exists. Multiple researchers went on record saying that such injuries from acoustics were not possible.
However, the Associated Press that was supposedly heard by victims of the embassy attacks, with the implication that the sound itself—or a device emitting the sound—was responsible for the injuries. Again, the sound evaded detection or analysis. However, this time a group of researchers has possibly managed to uncover a clue.
Reverse-engineering the audio sample, researchers from the University of Michigan and Zhejiang University an effect called intermodulation distortion, which happens when two signals at different frequencies combine to create new signals occurring at the sums or differences between the two original signals. For instance, two signals at 25 kHz and 32 kHz could combine to produce a signal of 7 kHz, similar to the one in the AP video.
The is that two different devices in the victims’ hotel rooms produced ultrasonic waves at these frequencies, and that those signals combined via intermodulation distortion to produce the noise recorded in the AP video. Crucially, this would explain why some victims heard a noise and others did not, as intermodulation distortion is highly localized.
But this still doesn’t explain any of the wide variety of symptoms experienced by the victims. It’s unlikely that the noise itself could have caused the brain damage and concussion-related symptoms experienced by many of the embassy staff, but it might be possible that the devices producing the ultrasonic waves could somehow trigger those injuries a different way.
This mystery is still a long way from being solved, but there’s a chance this analysis could help investigators find the solution. At the very least, it’s a solid hypothesis that investigators and other scientists can test, which is better than nothing.