Airport Passenger Screening Using Millimeter Wave Machines Compliance with Guidelines (2017) / Chapter Skim
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3 Radiation Protection Standards
3 Radiation Protection Standards
Pages 23-38
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The chapter lays out the details for dosimetry aspects for millimeter wave advanced imaging technology (AIT) and for health effects of millimeter wave AIT, specifically, the interaction of AIT millimeter waves with tissues, before describing the relevant standards.
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HEALTH EFFECTS OF MILLIMETER WAVES FROM AIT There have been many scientific studies investigating the correlation between exposure to non-ionizing radiation and subsequent health effects. Because of the widespread use of cell phones operating in the 1 to 5 GHz range, many of these studies have focused on this radio frequency (RF)
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The power level of 26 GHz waves entering tissue will decrease to approximately 13 percent of the surface value at a depth of approximately 0.65 mm.2 Because of the shallow, penetrative nature of the waves in this frequency range, the organs of concern are the skin and the eye. The well understood deterministic effect on tissues in this frequency range is heating resulting from currents induced by the electric field interaction with con ductive tissue, which is largely due to the interaction of the electromagnetic waves 1 National Council on Radiation Protection and Measurements, 1998, "Commentary No.
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In a living organism, heating of tissues may be offset by blood flow to the immediate vicinity, which acts as a cooling mechanism. Therefore poorly perfused organs, such as some structures of the eye, may be at greater risk of thermal damage from a given exposure than other well-perfused regions of the body.3 STRUCTURE OF THE HUMAN EYE The adult human eye (Figure 3.1)
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One 2012 animal study investigated the ocular damage threshold in rabbits for millimeter waves with a frequency of 40 GHz and found that permanent ocu lar changes began to occur at incident power density levels between 100 and 200 mW/cm2 (1,000 and 2,000 W/m2 ) , with transient changes observed at 100 mW/cm2 (1,000 W/m2 )
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Le Quement, and Y Le Drean, 2011, Millimeter-wave interactions with the human body: State of knowledge and recent advances, International Journal of Microwave and Wireless Technologies 3(2)
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, there is little in the published record regarding health effect phenomena. Additionally, few studies consider the low levels of exposures in the range of the stated power density for 9 T
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Rather than relying on incident power density (or SAR calculations) as a safety metric, they suggested monitoring the skin temperature with magnetic resonance imaging–based measures to directly monitor the thermal effects of millimeter wave, particularly for near-field consideration with millimeter wave mobile handsets.1 Gapeyev et al.
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Ziskin, 2003, Local heating of human skin by millimeter waves: A kinetics study, Bioelectromagnetics 24(8)
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. Among the most influential guidelines for the use and application of millimeter waves are those set by the International Commission on Non-Ionizing Radiation Protection (ICNIRP)
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have stated in the Journal of Radiological Protection that the RF exposure limits published by various organizations are similar to one another in terms of power density (W/m2) across the RF spectrum and are based on the principle of protecting individuals against potentially adverse effects resulting from tissue heating.15 An extensive literature of animal experimentation indicates disrupted food behavior when the SAR is above about 4 W kg−1 for roughly an 14 Federal Communications Commission, 2006, Order in the Matter of SafeView, Inc.
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. SOURCE: IEEE Std C95.1-2005-IEEE Standard for Safety Levels with Respect to Human Expo sure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz.
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based on "limited evidence" from both human and animal studies, the weight of evidence has not risen to a level that would change the basis for RF exposure limits.18 As was made clear in the previous section, the scientific data on possible health effects of millimeter waves is sparse. Aside from thermal effects, little is known about mechanisms that may govern millimeter wave interactions with biological systems.
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As can be seen in Table 3.1, limits set on average power density fields are remarkably consistent. The main differences arise from differences in averaging time; ranging from about 3 to 6 min to 30 min.
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In the United States, the main federal agency responsible for RF health and safety is the FCC, with the FDA responsible for medical devices and radiation emitting products. The RF exposure limits published by various organizations are similar to one another in terms of power density (W/m2)
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Limits on peak pulsed-RF fields vary substantially. Finding 3.4: Limits set on average power density fields are set as 10 W/m2.
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