Possibly. There have been many advances in acoustics, especially in the application of ultrasound, that may explain that incident in Cuba.
In 2017, US diplomatic staff began to suffer mysterious traumatic injuries that have now been dubbed “Havana syndrome” by the US and Canadian media. The diplomats stationed in Cuba initially referred to the phenomenon as “The Thing“ whereas University of Pennsylvania specialists who examined victims brought back from Cuba gave it the name "Immaculate Concussion".
So far, it has affected US and Canadian diplomatic staff in Cuba and US diplomatic staff in China. The symptoms are more serious than just hearing loss and have since been confirmed to constitute a form of brain damage. The physical symptoms are:
(from initial reports) “hearing, cognitive, visual, balance, sleep and other problems”.
(from Senate congressional hearings) “sharp ear pain, headaches, ringing in one ear, vertigo, disorientation, attention issues and signs consistent with mild traumatic brain injury or concussion”.
(from an State Department email alert to US embassy staff in China) “dizziness, headaches, tinnitus, fatigue, cognitive issues, visual problems, ear complaints and hearing loss, as well as difficulty sleeping”.
The official response (Cuban incidents)
The official response (Chinese incidents)
The Associated Press has obtained a recording of what some U.S. Embassy workers heard in Havana in a series of unnerving incidents later deemed to be deliberate attacks. The recording, released Thursday by the AP, is the first disseminated publicly of the many taken in Cuba of mysterious sounds that led investigators initially to suspect a sonic weapon.
The recordings themselves are not believed to be dangerous to those who listen. Sound experts and physicians say they know of no sound that can cause physical damage when played for short durations at normal levels through standard equipment like a cellphone or computer.
The sound seemed to manifest in pulses of varying lengths — seven seconds, 12 seconds, two seconds — with some sustained periods of several minutes or more. Then there would be silence for a second, or 13 seconds, or four seconds, before the sound abruptly started again.
A closer examination of one recording reveals it’s not just a single sound. Roughly 20 or more different frequencies, or pitches, are embedded in it, the AP discovered using a spectrum analyzer, which measures a signal’s frequency and amplitude.
To the ear, the multiple frequencies can sound a bit like dissonant keys on a piano being struck all at once. Plotted on a graph, the Havana sound forms a series of “peaks” that jump up from a baseline, like spikes or fingers on a hand.
“There are about 20 peaks, and they seem to be equally spaced. All these peaks correspond to a different frequency,” said Kausik Sarkar, an acoustics expert and engineering professor at The George Washington University who reviewed the recording with the AP.
The multiple peaks could be accounted for if the alleged sonic device is a phased array speaker made of multiple ultrasound transducers. Phased array speakers are used to "steer" and "aim" sounds without actually changing the position of the speakers. Phased arrays work by exploiting acoustic interference timed in order to propel a wave in a particular direction.
Besides the discordant phase effect little else is known about the sound itself.
Clinical features of “Havana syndrome” (July 2019):
Mean whole brain white matter volume was significantly smaller in patients compared with controls, with no significant difference in the whole brain gray matter volume.
There were significantly greater ventral diencephalon and cerebellar gray matter volumes and significantly smaller frontal, occipital, and parietal lobe white matter volumes; significantly lower mean diffusivity in the inferior vermis of the cerebellum; and significantly lower mean functional connectivity in the auditory subnetwork and visuospatial subnetwork but not in the executive control subnetwork.
This profile is close to leukariosis, a kind of white matter disease caused by, ordinarily hypertensive, injury to small blood vessels that supply cortical white matter around the parietal lobes. Leukariosis is a precursor to the dementia known as “Binswanger’s disease” but the progression doesn't always happen.
We now know that the injury is real. The US and Canadian reaction has been to accuse Cuba of foul play, to expel Cuban diplomats and to repatriate non-essential staff as well as family members to the home country. This reaction is consistent with a real perceived threat. There is obviously something hurting these diplomats but there's no evidence that the cause was a "sonic bomb".
Sound can be used to cause harm to humans in a variety of ways.
Injury to the inner ear. Loud sounds can rupture parts of the inner ear. This is a well known cause of hearing loss. According to the National Institute on Deafness and Other Communication Disorders, sounds above 85 dBA are potentially injurious but this figure is sensitive to the frequency of the sound. High decibel sounds dissipate too quickly to make for effective weapons. Their range is too short.
High-intensity focused ultrasound (HIFU) ablation
Ultrasound focused by a lens to a high pressure is capable of causing injury inside the body at the focal point. This technique is called high intensity ultrasound therapy and is used to treat small tumors non-invasively. In therapy, the mechanism used is usually hyperthermic (and therefore cannot be the cause of Havana syndrome) but can also be mechanical. Mechanically, lesions can be opened inside an organ via acoustic cavitation of bodily fluids. The high energy sound waves disturb bodily fluids causing bubbling. The increased pressure inside a sac or vessel will open a lesion.
High intensity ultrasound necessary for concussion could be achieved by using an array system of ultrasound transducers. This is consistent with descriptions of the injury as immaculate (focused) concussion by specialists.
Concussive force starts above 85 g-force with the average concussion being at 95 g-force.
Sonosensitisers and Sonodynamic therapy
In medicine, sonosensitisers are chemicals that, in solution, oxidize when treated with frequencies of sound. The chemical phenomenon is known as acoustic cavitation and its use biomedically is known as sonodynamic therapy. Sonosensitisers are often chemicals that release reactive ions that cause chain reactions that release chemicals toxic to cells. Many are also photosensitisers. An example is Copper Cysteamine which releases the Cu+ supercation that reacts with water to produce reactive oxygen species that cause necrotic cell death.
Doctors can deliver these cytotoxins to targeted tissues by conjugating the individual nanoparticles with antibodies. This is known as immunochemical passive targeting. Adapting these cytotoxic drugs for oral delivery is feasible, less harmful copolymerizing medicines have been, but is not practiced in cancer therapy because of the dangers. In addition, other sound-sensitive nanoparticles exist that rely on piezoelectric principles to cause cell death. This is the same technology used in leadless, batteryless pacemakers. Finally, there are also antibodies that bind to small vessel endothelial cells in the central nervous system. These are supposed to be used for drug delivery behind the blood–brain barrier.
A nation-state actor, if so inclined, could repurpose medical innovations in order to manufacture a sound-responsive poison that causes "mild traumatic brain injury" deleterious to white matter. This explanation is consistent with the claims of former NSA officer, Mike Beck, who claims have developed Parkinson's disease, along with a colleague while stationed in China. Beck thought a microwave weapon might be responsible. This explanation is undermined, however, because specialists who inspected the first returnees from Cuba reportedly found no evidence of a toxin.