With the Houston deluge, this is not the time for a serious post. If you’re curious enough to want more detail on how I thought about the Havana attacks, this is bedtime reading — for super techies.

My reaction to the initial report, by CNN on August 14, was the possibility of a case of mass hysteria. Wikipedia lists remarkable incidents, but mass hysteria need not be remarkable. It can be quite subtle. Numerous incidents involve faux “outbreaks” of a disease. It tends to occur in small, closed social communities, of which English-speaking legations in Cuba are an obvious example.

Perhaps a member of of this group came down with an undiagnosed inner ear infection, leading to a sense of pressure and tinnitus. Suppose the tenure of this individual began before the thaw. This person may have suffered Cuban harassment at that time, of the tire-slashing and super-gluing kind. “Justifiable paranoia” occurs. As the saying goes, “Even paranoids have real enemies.” Under conditions of tension and isolation, this could be enough to spark hysteria. And the medical findings? Preexisting conditions.

So I did not go at it as if it was real. It might have all petered out. But the reports persisted, with larger numbers of affected individuals. The F.B.I. has the expertise, and external consultants have no doubt been employed, to address the above. Although it is worth noting, mass hysteria has occasionally fooled experts, at least for a while.

So, assuming it is real, what is it? The Guardian consulted a  real expert, Tim Leighton, who thinks ultrasonics would be difficult. Quoting,

Leighton, who has studied the safety of ultrasound and measures to avoid its potential adverse effects on humans, said he would like to see more “prosaic possibilities” such as drugs or poison ruled out before being persuaded of the sonic weapon theory.

Leighton thinks a weapon that can work at a distance would have to be car-sized. I disagree. Another expert, Cleveland, refers to commercially available technology. Quoting,

Cleveland said that building an ultrasound emitter would not be hard. “You can buy transducers on the internet that emit these frequencies,” he said. “Anybody with a bit of engineering background could put one together.”

At that level, yes. But basic physics and some antenna theory suggests that it is possible to do much better. To do so would require the resources of a top-tier state, of which there are only a few. The mathematics of electronically scanned radar, at which the Russians are very good, is a good jumping off point. It also requires advanced materials science and condensed matter physics, so it is in no way easy.

Cleveland is correct that the effects could conceivably be produced by low doses of something not thoroughly studied in the West, like the Novichok toxins. But I chose to key off the F.B.I. theory that this was sonic. It’s the only reasonable choice for open source analysis. And there is one reported characteristic of the attacks that conforms with neither Cleveland’s off-the-shelf parts, or poison.

This was noted in (CNN) Sonic attacks in Cuba hit more diplomats than earlier reported, officials say. Quoting,

Other attacks made a deafeningly loud sound similar to the buzzing created by insects or metal scraping across a floor, but the source of the sound could not be identified, the two US officials said.

This is highly significant. We know that sound and light are both waves. Light can travel in a vacuum. Sound requires air. If you hold two flashlights, one in each hand,  and cross the beams, they pass through each other without influencing each other. This is because, in the normal world, the vacuum is linear.

The same is almost true with sound, but not quite. In normal circumstances, sound mixes up with sound to make new sounds. This is because air is not linear, and neither are the objects it encounters. Since 2000, this has been exploited in two ways:

• A method of projecting private sound to a distant person using two ultrasonic frequencies aimed at that person. The frequencies combine by nonlinear mixing, on the ear of the targeted individual, to produce sound audible only to that person.
• An ultra directional microphone. (Google Patents) A directional microphone system includes an ultrasonic emitter and receiver. The emitter directs a beam of ultrasound at the audio source with sufficient intensity that non-linear air effects cause non-linear interactions between the ultrasonic sound and the source’s sonic sound.

So we see that multiple frequencies of ultrasound can create audible sounds, and a single frequency of ultrasound can retrieve audible sound  from a somewhat distant person. That an ultrasonic, ultradirectional microphone is possible is probably the cause of theories of CNN “experts”:

There are other possibilities, including environmental factors, said experts like Sharon Weinberger, a journalist, and the author of “The Imagineers of War: The Untold Story of DARPA.” Others, such as former Foreign Service Officer James Lewis, point to the possibility of human error, in particular a surveillance operation gone wrong.

The implication is that a microphone using an ultrasonic beam was maladjusted or broken, causing the “attack.” But the patent describes a microphone of very limited and specific use, when the monitor and the subject are separated by unobstructed air. Under that circumstance, and only that, does the microphone have an advantage over other directional microphones. Perhaps because of this stringent limitation, this design is not offered on the open market. It has no use interior to a dwelling.

There’s more, but there are more days of deluge. So I will supply more bedtime reading another night.