Microwave Engineering Europe - December 2007 - (Page 11) MILITARY/AEROSPACE 11 Heat ray a focus for concern By Peter Clarke, EE Times Europe & The U.S. authorities have taken more than 15 years to research the use of the heating effect of millimeter waves as an antipersonnel weapon, so plenty of due diligence should have been done that the Silent Guardian system brought to market by Raytheon Co. is both non-lethal and effective. On the surface it seems like the stuff of science-fiction; a non-lethal directional heat ray that causes angry crowds to disperse and makes insurgents run for cover. However, there are some things in the documentation of the heat-ray weapon that suggests it is technology looking for a problem to solve and this observer has concerns over the further development and deployment of the system. One particular concern is that Silent Guardian uses a convergent, focused beam. The pitch from Raytheon’s datasheet on Silent Guardian is that the heat-ray produces an “intolerable heating sensation” in the top 1/64 of an inch of the skin but that it “does not cause injury because of the shallow penetration depth of the millimeter wave.” The datasheet also discusses a focused beam and shows a convergent beam coming from a millimeterwave antenna. However, what is not disclosed is the effect of the beam hitting the human eye or the effect of prolonged exposure. Also we are not told the energy density of the beam or what happens when that energy is focused to a point. It is the same as the sun in whose parallel rays it can be pleasant to bathe. But when those same rays are focused they produce dramatic heating effects. For example a simple magnifying glass can be used to set fire to paper or grass. According to reports from the Air Force Research Laboratory (Kirtland, New Mexico) in 2001, a two-second burst of energy from a millimeter wave system can heat the skin to a temperature of 130 degrees F. But what does a 10 second burst of energy do to the skin? Or one minute? And what is not clear from that account is whether that was measured with a divergent or convergent beam, because the information at that time was classified. A divergent beam could be engineered for safety so that the closer protagonists came to the source the greater the energy flux and the more painful their exposure the millimeter waves. This would be a form of self-limiting device. But a bigger concern is that after spending tens of millions of dollars in development - $40 million by AFRL up to 2001 – the system just won’t work very well. Raytheon claims the Silent Guardian fills the gap between “shout and shoot” but the riotous, protesting insurgent masses may find thick clothing, balaclava helmets and gloves quite effective at nullifying the heat ray. They may find objects they can use as shields. This emphasizes that the Silent Guardian is likely to be most effective where the victim is unable to cover his or her skin or move out of the way of the beam. As a result all that money will have been spent on a weapon that may not be good at its primary function, but that would be unsurpassed as a means of torture. A series of mirrors used to collect and redirect sunlight to temporarily inconvenience marauding rioters, protesters, insurgents and opposing armies might not work on a cloudy day - but it has been used in warfare since biblical times. It is a lot cheaper to develop than a millimeter-wave heat ray system and may be equally effective Article reprinted courtesy of EE Times Europe. & & Microwave Engineering ● December 2007 ● www.mwee.com 011_MWEE.indd Sec1:11 23/11/07 11:02:40 http://www.rohde-schwarz.com/ad/fsu67 http://www.ohde-schwartz.com/ad/fsu67 http://www.mwee.com
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