A team of computer scientists from the University of Michigan’s Security and Privacy Research Group may have found the solution to the mystery of so-called “sonic attacks” on U.S. diplomats in Cuba.  The leaders of.the team were electrical engineering and computer science professors Kevin Fu of the University of Michigan and Wenyuan Xu from Zhejiang University. 
New Theory for “Sonic Attacks” 
In an article they simplified their project by answering the following four questions:
- What is ultrasound useful for? Ultrasound – high-frequency sound waves human ears can’t hear—are useful, for example, in medical devices to examine fetuses during pregnancy or in occupancy sensors to detect movement.
- What can go wrong with ultrasound? Examples: electronic hearing aids converting ultrasonic occupancy sensors into audible sounds and ultrasonic signals secretly activating voice-control systems.
- Should people worry about ultrasound causing bodily harm? There’s little evidence of ultrasound causing bodily harm without prolonged, direct physical contact at high intensity.
- What might have happened inCuba? The true cause could have been equipment trying to listen in on the diplomats’ and visitors’ conversations. No single ultrasonic tone would do this, but combining more than one can create audible byproduct sounds, including by accident. To test this theory they created an eavesdropping device that would record audible conversations and transmit the recordings to a nearby surveillance team over an inaudible ultrasonic link. When we placed a second inaudible ultrasonic device in the area, we were able to create interference – technically called “intermodulation distortion” – between the two signals that made similar sounds to those recorded in Cuba.”
The Introduction of their 80-page research report elaborates on the above answer to the first question by stating, “There are many potential sources of ultrasound in office, home, and hotel environments. Energy efficient buildings often use ultrasonic room occupancy sensors in every room (Figure 1). Ultrasonic emitters can repel rodents and other pests. HVAC systems and other utilities with pumps or compressors can vibrate entire buildings. Certain burglar alarm sensors, security cameras, and automated doors use ultrasound for detection of movement.” (Emphasis added.) 
There 80-page research paper’s Conclusion states,“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 unintentionally synthesize audible tones. In other words, acoustic interference without malicious intent to cause harm could have led to the audible sensations in Cuba.” The conclusion of the research paper itself also states, “our experiments do not eliminate the possibility of malicious intent to harm diplomats.” (Emphasis in original.)
“This is a variation of what I have always thought,” James Cason, a former top U.S. diplomat in Havana, told el Nuevo Herald. “It explains the sonic part, that no one was spotted planting new devices inside the homes and doing it from the outside would require something huge.”
As a non-electrical engineer who has been carefully following the news about the medical problems experienced by some U.S. diplomats Cuba, this research paper offers a new possible explanation of what happened in what many accounts call “acoustic attacks” in Cuba. This theory deserves further investigation.
If I correctly understand this theory, the audible sound similar to that heard in Cuba requires at least two ultrasound sources that interfere with each other and this suggests that the audible sound was accidental and not intended. This supports Cuba’s consistent assertion that it did not intend to do anything to harm the American diplomats, an assertion that makes obvious sense from Cuba’s own self-interest of avoiding antagonizing the U.S.
One of the ultrasound sources in their research was one “that would record audible conversations and transmit the recordings to a nearby surveillance team over an inaudible ultrasonic link.” Why was this device chosen? Was it the only device that would produce the comparable interference when combined with another ultrasonic source? Or are there other possible ultrasound devices? In any event, what country or company was the source of this ultrasound in Cuba? Cuba? A secret U.S. agency? A third country?
If one of the ultrasound devices in Cuba was one for eavesdropping and if Cuba was the user of such device, the U.S. would still have a legitimate complaint against Cuba. But a wide reading of materials about the U.S. and Cuba suggests that the U.S. always has assumed that Cuba was and is always attempting to spy on U.S. diplomats on the island.
I hope this theory is confirmed by others as it should eliminate the supposed reason for the U.S.’ reducing the staffing of its Havana Embassy, issuing the travel advisory that U.S. citizens should reconsider any plans to travel to Cuba and expelling Cuban diplomats from Washington, D.C.
Other comments from readers are especially welcome on these and related issues.
 See posts listed in the “U.S. Diplomats Medical Problems in Cuba, 2016-2018” section in List of Posts to dwkcommentaries—Topical: CUBA.
 Professor Fu at an apparent young age already has an impressive resume and in October 2017 received a University of Michigan Regent’s Award for Distinguished Public Service. (Craig, Kevin Fu recognized with Regents’ Award for Distinguished Public Service, Univ. Michigan CSE News (Oct. 9, 2017).
 Fu & Xu,, Can sound be used was a weapon? 4 questions answered, The Conversation (Mar. 1, 2018); Yan, Fu & Xu, On Cuba, Diplomats, Ultrasound, and Intermodulation Distortion (Mar. 1, 2018) (80-page report); Moore, Cuba “sonic attacks”; a covert accident? Univ. Michigan CSE News (Mar. 2, 2018); Torres, Computer scientists may have solved the mystery behind the ‘sonic attacks’ in Cuba, Miami Herald (Mar. 2, 2018).
 A prior post reported about American teens hearing high-pitched sounds at the Havana Airport that apparently came from a “Zonic” device, whose Spanish manufacturer described it as “an “ultrasound animal repeller” that “makes the stay of birds, reptiles, and rodents uncomfortable” by emitting “vibrations of high frequency (ultrasounds), alternating between ranges for different animals, so that they will never nest.”