INTERNATIONAL COMMISSION ON NON‐IONIZING RADIATION PROTECTIONICNIRP STATEMENTON HEALTH ISSUES ASSOCIATED WITH MILLIMETERWAVE WHOLE BODY IMAGING TECHNOLOGYPUBLISHED IN: HEALTH PHYSICS 102(1):81‐82; 2012

ICNIRP PUBLICATION – 2012

ICNIRP Guidelines

ICNIRP STATEMENT—HEALTH ISSUES ASSOCIATED WITHMILLIMETER WAVE WHOLE BODY IMAGING TECHNOLOGYInternational Commission on Non-Ionizing Radiation Protection*INTRODUCTIONA NEW generation of whole-body image scanners has
been installed in many airports and other security
checkpoints worldwide. They are capable of detectingweapons or objects made of any type of material thatare being worn or are concealed by clothing at a shortrange or at distances of a few meters, within a defined
scanning zone.
Active scanners emit electromagnetic waves at frequencies in the tens of gigahertz (GHz or 109 Hz) or the
microwave region and form an image by processing thewaves scattered by the object or person being scanned. It
is noteworthy that scanners designed to passively detect
the broadband microwave radiation emitted by the human body do not expose the body to electromagneticwaves.
At the frequencies used by these scanners, theenergy per photon (quantum energy of GHz radiation) is
not sufficient to break chemical bonds or to ionize atoms
or molecules. Thus, the scanners use non-ionizing radiation, unlike traditional x-ray backscatter machines,
which use ionizing radiation.
The typical parameters of the active scanners involve 10 to 100 mW of total output power from antennas
operating at 30 to 100 GHz. They take about 2 to 5 s tocomplete a multi-directional scan of the subject. Thesescanners are also referred to as millimeter wave (mmwave) body scanners because at this frequency thewavelength is between 3 and 10 mm in air.
These scanners can image through a subject’s clothing and detect concealed weapons, explosives, or suspicious articles and display them along with detailed
images of the surface anatomy. For the general public,* ICNIRP Secretariat, c/o Gunde Ziegelberger, c/o Bundesamt für
Strahlenschutz, Ingolstaedter Landstrasse 1, 85764 Oberschleissheim,
Germany.
The authors declare no conflict of interest.
For correspondence or reprints contact info@icnirp.org.
0017-9078/12/0
Copyright © 2011 Health Physics Society

DOI: 10.1097/HP.0b013e31823a1278
www.health-physics.com

the scans involve a brief exposure time. However, foroccupational situations during manufacturing, testing andinstallation, repeated exposures or extended exposure
durations may occur. The scientific data on possible
effects and health implications of mm waves are sparse.
Aside from thermal interactions, little is known about
mm wave interactions with biological systems or themechanisms that may govern any direct interaction.
The objective of this statement is to address thepossible adverse health effects from exposure to mmwaves used in whole body electronic security scanners.
The statement includes an assessment of the applicabilityof currently available exposure guidelines.
INDUCED FIELDS AND ENERGY DEPOSITIONAt the frequencies of mm waves, the induced fields
and energy deposition in biological media can be determined in much the same manner as for other nonionizing spectra if the permittivity of relevant tissues atthese frequencies is known. Between 30 to 100 GHz, thebehavior of relative permittivity follows those of thelower frequencies. Specifically, the real and imaginaryparts of the complex relative permittivity for skin tissues
decrease from 20 to 6 and 20 to 12, respectively.
However, the skin tissue is not homogeneous but
consists of a multilayer of stratum corneum (SC), epidermis, and dermis and varies according to body location; for example, forearm and palm skin have thin andthick SC, respectively. In general, at mm wave frequency
the permittivity of skin is governed by cutaneous freewater contents.
The specific absorption rate (SAR) of the mm wave
energy increases with frequency. Calculations of mm
wave transmission for skin on the forearm showed anincrease from 55% to 65% between 30 and 90 GHz(Alexseev and Ziskin 2007; Alexseev et al. 2008). It isnoteworthy that a thick SC in the palm causes an increasein transmission as a result of the layer matching phenomenon at higher mm wave frequencies. Power transmission coefficient for skin on the forearm showed an81

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increase from 55% to 65%. However, at the highest
frequencies the SAR in the deeper regions of the skin
may become lower because of the reduced penetration
depth at these frequencies. For example, the penetration
depth of a plane-wave field decreases from 0.8 to 0.4 mm
and 1.2 to 0.7 mm for skin on the forearm and palm,respectively.
GUIDELINES FOR LIMITING EXPOSURE
The ICNIRP recommends guidelines for limiting
human exposure that pertain to frequencies over theentire non-ionizing radiation spectrum (ICNIRP 1998,2009). For radio frequency electromagnetic fields between 10 to 300 GHz, the existing guideline for thegeneral public is 10 W m⫺2 averaged over a certain timeinterval that decreases with increasing frequency (6 minat 10 GHz and 10 s at 300 GHz). In addition, for pulsed
fields, the peak incident power density averaged over thepulse width may not exceed 10 kW m⫺2. The corresponding values are 50 W m⫺2 and 50 kW m⫺2, respectively,
for occupational exposures. These values are based on
the avoidance of adverse effects caused by mild wholebody heat stress and/or tissue damage caused by excessive localized heating.
It is noted that mm wave body scanners operate inpulse modes. The power levels employed by these mmwave body scanners are low but can generate power
densities up to 1.0 kW m⫺2 for a pulsed field averaged
over the pulse width. The resulting human exposures areJanuary 2012, Volume 102, Number 1

about a tenth of currently recommended guidelines forthe general public.

Acknowledgments—The support received by ICNIRP from the Australian
Radiation Protection and Nuclear Safety Agency, the International Radiation Protection Association, the European Commission, and the German
Federal Ministry for the Environment, Nature Conservation and Nuclear
Safety is gratefully acknowledged.
During the preparation of this statement, drafted under the leadershipof the ICNIRP SC3 Chair, James C. Lin, the composition of the International Commission on Non-Ionizing Radiation Protection was as follows:
P. Vecchia, Chairman (Italy), R. Matthes, Vice-Chairman (Germany), M.
Feychting (Sweden), A. Green (Australia), K. Jokela (Finland), J. Lin(United States of America), K. Schulmeister (Austria), Z. Sienkiewicz(United Kingdom), A. Peralta (The Philippines), P. Söderberg (Sweden),
B. Stuck (United States of America), A. Swerdlow (United Kingdom), E.
Van Rongen (The Netherlands), B. Veyret (France), G. Ziegelberger,
Scientific Secretary (Austria).

All ICNIRP members are requested to fill in and update asnecessary a declaration of personal interests. Those documents areavailable online at www.icnirp.org/cv.htm.

REFERENCES
Alekseev SI, Ziskin MC. Human skin permittivity determinedby millimeter wave reflection measurements. Bioelectromagnetics 28:331–339; 2007.
Alekseev SI, Radzievsky AA, Logani MK, Ziskin MC. Millimeter wave dosimetry of human skin. Bioelectromagnetics
29:65–70; 2008.
ICNIRP. Guidelines for limiting exposure to time-varying
electric, magnetic, and electromagnetic fields (up to 300GHz). Health Phys 74:494 –522; 1998.
ICNIRP. Statement on the “Guidelines for limiting exposure totime-varying electric, magnetic and electromagnetic fields(up to 300 GHz).” Health Phys 97:257–259; 2009.
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