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By Greg Lapin, N9GL
Chairman, ARRL RF Safety Committee
March 28, 2001
I had planned to continue the discussion of athermal effects of RF energy. In the interim, the US military announced the development of a new RF weapon for crowd control purposes. Let's examine this new issue.
Last month I had said that I would continue the discussion of athermal effects of RF energy. In the interim, the US military announced the development of a new RF weapon that it developed for crowd control purposes. I received a number of outraged email messages from hams that thought that this application of RF was an abomination. I also read several misstatements of facts in the press. As a result, I am putting aside the continuing discussion of athermal effects in order to examine this new issue.
The concept of using electromagnetic energy as a weapon is not new. Nikola Tesla proposed such a weapon in 1931. The military has since done much research into such "death rays," though they have always been deemed impractical. The generation of enough electromagnetic energy to hurt people on a battlefield is far more difficult than using the energy that is stored chemically in gunpowder.
One technology that became popular during the 1980s and has since progressed is the "rail gun." This device fires a solid projectile like a standard gun, but instead of being driven by an explosion of gunpowder, electromagnetic energy is used to generate a huge magnetic force. The projectile is fired at much higher speeds than a bullet attains from a gun barrel. However, the power supply required to generate this type of force is not exactly portable. One early rail gun used a power supply that was two stories tall and generated 1.6 million amperes of current. Another rail gun project used 14,000 car batteries, which were used to generate a five-second pulse of 2.5 million amperes of current.
If you search Internet for "electromagnetic weapons" you find an amazing array of Web sites that are concerned with conspiracy theories (which brings to mind the very fine movie of the same name). The most prevalent is the fear that the government is using electromagnetic energy for mind control. Perhaps that explains the behavior of some otherwise reasonable hams when they get involved in a pileup on the air.
The US military's new weapon--which they call an Active Denial System, or ADS--makes use of the properties of electromagnetic energy that generate heat, much like a microwave oven, at frequencies that do not penetrate deep enough to damage tissue. The frequencies used are in the 100-GHz range, and the penetration depth is reported to be 1/64-inch into a liquid-based medium, such as human tissue. The energy passes through dry substances, such as clothing, with very little attenuation. After 10 years of research and an expenditure of $40 million, scientists and engineers working on this project came up with the correct combination of frequency, power density, and exposure duration to cause a painful sensation without actually damaging tissue.
Of course, an announcement such as this brings all kinds of experts out of the woodwork. One well-known figure, who manages to get himself in front of the press whenever an RF energy issue comes up, decried the danger of athermal effects: "We've known that many forms of microwaves at levels below heating can cause significant health effects in the long term," this individual said. The absurdity of this statement is obvious. The announcement was about a weapon designed to produce a heating effect. What does this have to do with athermal effects? Furthermore, there has never been any evidence that athermal effects cause any biological harm at all.
Statements such as this are, at the very least, irresponsible. Even if such harm is ever proven--and let me again emphasize that there is a lot of research that has not shown any such thing--the minimal exposures from this device are unlikely to cause it. Consider ionizing energy such as X-rays, that is known to have the potential to damage tissue and cause cancer. We do not consider the very small risk of biological damage from short exposures to X-rays to be unacceptable.
What is wrong with using electromagnetic energy as the military suggests? Consider what it is designed to replace. The authorities currently have to resort to rubber bullets and tear gas to control unruly crowds. When soldiers are faced with civilians who are throwing rocks and Molotov cocktails at them, they often respond with lethal force. In the recent movie Rules of Engagement, Marines protecting a US Embassy in a hostile country kill a plaza filled with civilians, including women and children. In the movie, the crowd at first was unruly. Then, things escalated to throwing rocks, followed by heaving burning bottles of gasoline, and finally--as it turns out--shooting guns at the embassy. Granted, this was fiction, but would a non-lethal electromagnetic weapon have prevented the massacre in that kind of situation? It certainly would have made for a dull movie.
Some people have mentioned danger to the eyes from such exposure. This is certainly a possibility. The parameters of the RF energy that have been described in press releases lead me to estimate that this energy would not penetrate far beyond the eyelids, so closing one's eyes would probably be protection enough against damage to the cornea or lens. Since human eyes are recessed in the skull, the pain to the orbit would most likely cause a natural closing of the eyelids before damage to the structures in the eyeball could occur. Even if long-term damage occurs, such as cataracts, medical science has come up with a cure for this malady. Many people who have had cataract surgery see better afterwards than they ever did.
The few dangers that exist in the use of ADS technology are dwarfed by the extreme dangers posed by the alternatives. Rubber bullets can maim and kill. Tear gas and pepper spray can damage the sensitive tissues of the eyes and lungs. If non-lethal electromagnetic weapons are used as designed, they are far preferable to the use of these other methods.
The military also has proposed other positive applications for ADS technology. One of these is to form a portable invisible fence around sensitive areas. The suggestion has been made that surrounding ships in port with this energy might have prevented the October 2000 terrorist bombing of the USS Cole in Yemen.
As with all weapons, technology provides antidotes. If an electromagnetic energy weapon is put into general use, you can be sure that we will soon see tinfoil-lined clothing and attenuation shields. It is not hard to shield against RF energy; ham are experts at this skill. Of course, people who are stupid enough to throw rocks at men with guns may not be able to figure this out.
As hams, we like to think of RF energy as a beneficial thing. It is a miracle of nature that allows us to communicate with the world. To use the same energy to hurt people certainly seems to be a misuse of the technology that we love. However, after looking at the alternatives, I believe that the military has settled on the best of several bad alternatives. "Set phasers on stun."
Editor's note: Greg Lapin, N9GL, started working in the RF safety world after spending many years first studying cardiac function imaging and then brain tumor kinetics. He serves as chairman of the ARRL RF safety Committee and as a member of the IEEE Committee on Man and Radiation. A former professor of Biomedical Engineering and Neurology at Northwestern University, Lapin now works as a consulting professional engineer in the electronics industry. He was first licensed while a teenager in 1969 and continues to be fascinated by virtually all aspects of Amateur Radio. One of his many interests is electronic design, and he is the author of Chapter 8, "Analog Signal Theory and Components" in The ARRL Handbook for Radio Amateurs. His non-ham interests include making things grow in his garden and serving as commissioner of the local children's softball league. At other times--when he is not working or helping his kids with their homework--you might find him with the local emergency services agency, climbing his tower, building a new QRP rig, playing with his APRS setup, responding to QSL cards, going off on a DXpedition, or trying to get that "new one." You can reach him by email at g.lapin@ieee.org.
