Microwave Weapons are Prime Suspect in Ills of U.S. Embassy Workers

Last Saturday, The New York Times published an article by Pulitzer Prize-winning science writer William Broad with the headline “Microwave Weapons are Prime Suspect in Ills of U.S. Embassy Workers.”

Doctors and scientists say microwave strikes may have caused sonic delusions and very real brain damage among embassy staff and family members.

The article has made quite a splash; I even heard about it on the news.

This topic is relevant to Intermediate Physics for Medicine and Biology, so I’ll address it in this post. I hesitate, however, because the science is uncertain and the topic of electromagnetic effects on health is fraught with conspiracy theories and voodoo science. Yet, the issue has more than academic importance; U.S.-Cuban relations suffered because of these unexplained health effects. So, reluctantly, I wade in.
I begin with a report from last March in the prestigious Journal of the American Medical Association (JAMA) by Swanson et al. about “Neurological Manifestations Among US Government Personnel Reporting Directional Audible and Sensory Phenomena in Havana, Cuba” (Volume 319, Pages 1125–1133).

• Question: Are there neurological manifestations associated with reports of audible and sensory phenomena among US government personnel in Havana, Cuba? 
• Findings: In this case series of 21 individuals exposed to directional audible and sensory phenomena, a constellation of acute and persistent signs and symptoms were identified, in the absence of an associated history of blunt head trauma. Following exposure, patients experienced cognitive, vestibular, and oculomotor dysfunction, along with auditory symptoms, sleep abnormalities, and headache. 
• Meaning: The unique circumstances of these patients and the consistency of the clinical manifestations raised concern for a novel mechanism of a possible acquired brain injury from a directional exposure of undetermined etiology.

The article’s claim of cognitive dysfunction has been hotly debated. A post in the blog Neuroskeptic was….er….skeptical. It concludes

Overall … the JAMA paper is pretty weak. Clearly, something has happened to make these 21 people experience so many unpleasant symptoms, but at present I don’t think we can rule out the possibility that the cause is psychological in nature.

Last week’s New York Times article was triggered by the recently proposed hypothesis that microwaves are responsible for these health issues. Russ Hobbie and I discuss the biological effects of electric and magnetic fields in Section 9.10 of IPMB. We focus on the potential of microwaves to induce tumors, and conclude that nonthermal mechanisms are implausible. In other words, radiofrequency fields can heat tissue—just like in your microwave oven—but they don’t cause cancer. The hypothesis touted in the Times article, however, is a thermal mechanism: a thermoelastic pressure wave sensed as sound by part of the inner ear called the cochlea.

Hearing induced by microwaves has been studied for years, and is known as the “Frey effect” after Allen Frey, who first reported it. A 2007 article in the journal Health Physics by James Lin and Zhangwei Wang (Volume 92, Pages 621-628) describes this phenomenon.

Hearing of Microwave Pulses by Humans and Animals: Effects, Mechanism, and Thresholds

The hearing of microwave pulses is a unique exception to the airborne or bone-conducted sound energy normally encountered in human auditory perception. The hearing apparatus commonly responds to airborne or bone-conducted acoustic or sound pressure waves in the audible frequency range. But the hearing of microwave pulses involves electromagnetic waves whose frequency ranges from hundreds of MHz to tens of GHz. Since electromagnetic waves (e.g., light) are seen but not heard, the report of auditory perception of microwave pulses was at once astonishing and intriguing. Moreover, it stood in sharp contrast to the responses associated with continuous-wave microwave radiation. Experimental and theoretical studies have shown that the microwave auditory phenomenon does not arise from an interaction of microwave pulses directly with the auditory nerves or neurons along the auditory neurophysiological pathways of the central nervous system. Instead, the microwave pulse, upon absorption by soft tissues in the head, launches a thermoelastic wave of acoustic pressure that travels by bone conduction to the inner ear. There, it activates the cochlear receptors via the same process involved for normal hearing. Aside from tissue heating, microwave auditory effect is the most widely accepted biological effect of microwave radiation with a known mechanism of interaction: the thermoelastic theory. The phenomenon, mechanism, power requirement, pressure amplitude, and auditory thresholds of microwave hearing are discussed in this paper. A specific emphasis is placed on human exposures to wireless communication fields and magnetic resonance imaging (MRI) coils.

Their introduction gives some useful numbers.

The microwave auditory phenomenon or microwave hearing effect pertains to the hearing of short-pulse, modulated microwave energy at high peak power by humans and laboratory animals (Frey 1961, 1962; Guy et al.1975a, b; Lin 1978, 1980, 2004). The effect can arise, for example, at an incident energy density threshold of 400 mJ m^-2 for a single, 10-µs-wide pulse of 2,450 MHz microwave energy, incident on the head of a human subject (Guy et al. 1975a, b; Lin 1978). It has been shown to occur at a specific absorption rate (SAR) threshold of 1.6 kW kg^-1 for a single 10-µs-wide pulse of 2,450 MHz microwave energy. A single microwave pulse can be perceived as an acoustic click or knocking sound, and a train of microwave pulses to the head can be sensed as an audible tune, with a pitch corresponding to the pulse repetition rate (Lin 1978).

The temperature increase caused by such a microwave pulse is rapid (microseconds) and tiny (microdegrees Celsius), and the associated pressure is small (tenths of a Pascal, or equivalently millionths of an atmosphere). People can hear these sounds because the cochlea is so sensitive.

One reason that microwaves might be a more plausible mechanism than sound waves for the apparent embassy attacks is acoustic impedance, discussed in Chapter 13 of IPMB. Air and water have very different impedances. When a sound wave impinges on a person, most of the acoustic energy is lost by reflection, and little (perhaps one part in a thousand) enters the fluid-filled body. Animals have evolved elaborate structures in the middle ear to mitigate this acoustic mismatch. However, a pressure wave caused by microwave heating originates inside the ear. No energy is lost by sound reflecting from the air-tissue interface.

I am no expert on thermoelastic effects, but it seems plausible that they could be responsible for the perception of sound by embassy workers in Cuba. By modifying the shape and frequency of the microwave pulses, you might even induce sounds more distinct than vague clicks. However, I don’t know how you get from little noises to brain damage and cognitive dysfunction. My brain isn’t damaged by listening to clicky sounds. Either there is more to this that I don’t understand, or—as neuroskeptic speculates—the rest of the cause is “psychological in nature.”

Right now, our country could use a hard-nosed scientist or engineer expert in the bioeffects of microwave radiation to look into this problem. Where have you gone John Moulder and Ken Foster? We need you!