On Cuba, Diplomats, Ultrasound, and Intermodulation Distortion. Yan, C., Fu, K., & Xu, W. Technical Report University of Michigan Tech Report CSE-TR-001-18, 2018.
On Cuba, Diplomats, Ultrasound, and Intermodulation Distortion [pdf]Paper  On Cuba, Diplomats, Ultrasound, and Intermodulation Distortion [pdf]Website  abstract   bibtex   
This technical report analyzes how ultrasound could have led to the AP news recordings of metallic sounds reportedly heard by diplomats in Cuba. Beginning with screen shots of the acoustic spectral plots from the AP news, we reverse engineered ultrasonic signals that could lead to those outcomes as a result of intermodulation distortion and non-linearities of the acoustic transmission medium. 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 unintentionally synthesize audible tones. In other words, acoustic interference without malicious intent to cause harm could have led to the audible sensations in Cuba.
@techreport{
 title = {On Cuba, Diplomats, Ultrasound, and Intermodulation Distortion},
 type = {techreport},
 year = {2018},
 websites = {https://spqr.eecs.umich.edu/papers/YanFuXu-Cuba-CSE-TR-001-18.pdf},
 institution = {University of Michigan Tech Report CSE-TR-001-18},
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 abstract = {This technical report analyzes how ultrasound could have led to the AP news recordings of metallic sounds reportedly heard by diplomats in Cuba. Beginning with screen shots of the acoustic spectral plots from the AP news, we reverse engineered ultrasonic signals that could lead to those outcomes as a result of intermodulation distortion and non-linearities of the acoustic transmission medium. 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 unintentionally synthesize audible tones. In other words, acoustic interference without malicious intent to cause harm could have led to the audible sensations in Cuba.},
 bibtype = {techreport},
 author = {Yan, Chen and Fu, Kevin and Xu, Wenyuan}
}
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