Starting in 2016, various (mostly American and Canadian) diplomatic personnel have reported bizarre health effects (https://www.pbs.org/newshour/politics/the-mysterious-cuba-sonic-attacks-are-still-puzzling-investigators), with symptoms so strange they were often not believed (https://globalnews.ca/news/3945259/cuba-sonic-mysterious-attacks-canada-investigation/), and which are potentially even linked brain abnormalities (https://www.theguardian.com/world/2017/dec/06/us-embassy-attack-cuba-brain-abnormalities-victims) in affected personnel. The Cuban government has (I'd suggest plausibly) denied (https://www.cnn.com/2017/10/28/politics/cuba-names-sonic-attacks/index.html) any responsibility for the strange "attacks", and there seems to be no immediately obvious medical explanation for the symptoms.
In the official IEEE publication Spectrum
, two enterprising US & Chinese professors and a grad student have put up a fascinating article (https://spectrum.ieee.org/semiconductors/devices/how-we-reverse-engineered-the-cuban-sonic-weapon-attack) providing a plausible explanation for the combination of audible noise and (potentially) detrimental health effects that might be linked to exposure to high powered ultrasonic devices, and most saliently, why
ultrasonic devices would be used in a diplomatic context (to quash and/or engage in eavesdropping). In essence, their explanation boils down to Intermodulation Distortion causing the audible effects. Their Spectrum article is essentially distilling bits of their research paper manuscript (pdf direct link) (https://spqr.eecs.umich.edu/papers/YanFuXu-Cuba-CSE-TR-001-18.pdf), (much of) the abstract of which I'll quote below:
We created a proof of concept eavesdropping device to
exfiltrate information by AM modulation over an inaudible ultrasonic carrier. When a second
inaudible ultrasonic source interfered with the primary inaudible ultrasonic source, intermodu-
lation distortion created audible byproducts that share spectral characteristics with audio from
the AP news. Our conclusion is that if ultrasound played a role in harming diplomats in Cuba,
then a plausible cause is intermodulation distortion between ultrasonic signals that unintention-
ally synthesize audible tones. In other words, acoustic interference without malicious intent to
cause harm could have led to the audible sensations in Cuba.
There has been at least one investigation, by Cuba. (It was naturally limited by a lack of cooperation by the U.S.,which may or may not have been justified.)
I would be interested in the reaction of those investigators, and vice versa, as to how this could in fact be done physically in the place where this allegedly happened. And how the effect was accomplished through numerous normal physical barriers and then affected some while not affecting others.