If you’ve been paying attention to the news, you may have seen a series of articles about American officials in Cuba. 21 employees appear to have suffered a bizarre array of injuries, ranging from hearing loss to dizziness to concussion-like traumatic brain injuries. Some officials reported hearing disturbing sounds in the embassy and in their hotel rooms. Reports range from clicking to grinding, humming or even growling. One staff member described being awakened by a terrifyingly loud sound, only to have it disappear as soon as he moved away from his bed. When I got back to bed, the mysterious sound returned.
Cuba has denied any wrongdoing. However, the US has already taken action – expelling two Cuban diplomats from the US in May. The question, however, is what exactly may have caused these injuries. The press went wild with theories about sonic weapons, hidden bugs and electronic devices, poisons, you name it. Even Julian Assange opined, stating that “The range of symptoms suggests this is a pathogen combined with paranoia in an isolated diplomatic corps.”
So what’s going on? Strange incidents? Cloak and dagger gone wrong? Mass hysteria at the US State Department or something else entirely?
The most common theory being floated is some kind of auditory or sonic weapon. Acoustic (ultrasonic) non-lethal weapons such as Long Range Acoustic Device (LRAD) are well known for their use by law enforcement to disperse protests or on ocean-going vessels to deter pirates and conservationists. LRAD devices emit an extremely strong focused beam of sound. Usually the sound is a siren, but the system can also be used as a giant megaphone. Everyone on the beam is motivated to get off it.
The main thing about LRAD devices is that they are not small or light. Even with ultrasound you can’t beat physics. Making a lot of noise means vibrating a lot of air. This requires a relatively large speaker. The smallest portable device weighs about fifteen kilograms. Since the LRAD still vibrates the air, it won’t work very well through walls. LRAD-style devices aren’t very secret either. They emit a beam 30 to 60 degrees wide, so they are definitely not a sonic laser. They also have a lot of spillage — operators behind the device must always wear hearing protection.
Unwrap your tinfoil hat
One theory that I haven’t seen spread much is microwave auditory effect. This is a phenomenon where RF energy directed at a human head is converted into sound perceptible by the target. The first paper published on the effect was by Alan H. Frey in 1961. Frey worked at General Electric’s Center for Advanced Electronics at Cornell University in New York.
I should note that microwave here refers to the wavelength of the radio frequency signal being transmitted. On the same subject : SDR for Assessing Wireless Device and Network Security. Microwaves include any signal from 1 meter wavelength (300 MHz) to 3 mm wavelength (100 GHz)
Frey’s paper describes how test subjects were able to hear buzzing, clicking, hissing and even tapping when transmitters were aimed at their skulls. Strangely, some of the test subjects were partially deaf and could still hear the microwave sounds. What’s more, subjects can feel the effects of the microwave beam. Depending on the transmitter settings, the subjects felt a “hard blow to the head.” Further changes to the transmitter resulted in subjects reporting a “tingling” sensation.
The purpose of the article was to draw attention to the phenomenon. Frey didn’t have the resources to fully investigate the microwave hearing effect, so he wanted others to start working on it. It’s the scientific equivalent of saying “Hey, that’s cool, you should check it out!”
If you haven’t guessed yet, the power levels required to hear microwave sounds were quite high. Frey uses several transmitters with different power levels. The transmitters were pulsed, like magnetrons, so while the average power was low, the peak power was high.
As an example, the weakest transmitter used by Frey was able to output a power density of 4 w/m² at 1310 Mhz. The peak power is 2670 w/m². The US guideline for human exposure at this frequency is 6.55 w/m². Another transmitter used by Frey measured 71 w/m² at 425 MHz, peaking at 2540 w/m². Compare this to the FCC guideline of 2 w/m² at this frequency.
What exactly causes RF energy to be converted into sound? The mechanism behind the microwave hearing effect has not been scientifically proven. The leading theory is that pulsed radio frequency energy heats the tissues of the inner ear, causing them to expand rapidly. These expansions cause tiny shock waves that are then interpreted as sounds by the brain.
Frey noted that “one can protect with a 2-inch square piece of fly netting, part of [temple] and completely cuts out RF sound.” The fly screen would be the fine metal grid used in screen doors. Frey may not have known it, but he was providing all the evidence the tin hat crowd needed.
Of course, technology like this can’t exist without someone trying to make a weapon out of it. In the early 2000s, the US Navy funded research on Mob Excess Deterrent Using Silent Audio (MEDUSA). It was a “less lethal weapon” that would use the microwave sound effect for crowd control. It uses an electronically controlled antenna that allows it to transmit a wide or narrow radio frequency beam. MEDUSA can even “project” multiple targets simultaneously.
MEDUSA never became a combat weapon. Initial results from the project were promising, but there were questions about its safety. At the high power levels used, could microshock waves actually damage sensitive brain tissue? What about RF exposure to sensitive neurons? In the end, the project was canceled.
Back to the present day, could the microwave hearing effect be at play in Cuba? This is quite possible. The technology is definitely there – the effect has been demonstrated with transmitters since the 1960s. With enough power and a narrow-beam antenna, attackers wouldn’t even need to be in the same room or building as their targets. Power levels high enough to be heard or even cause pain can also cause dizziness, nausea and even traumatic brain damage. All we can do is await the results of ongoing investigations and keep a tin hat handy.
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