Underestimation of EMF/NIR Exposure for Children for Mobile Telephones and for Electronic Article Survellance(EAS) Systems

1
Underestimation of EMF/NIR Exposure for Children
for Mobile Telephones and for Electronic Article
Survellance(EAS) Systems

• Om P. Gandhi
• Department of Electrical Computer Engineering
• University of Utah
• Salt Lake City, UT 84112 U.S.A.

Invited paper presented at the International NIR
and Health Workshop- Brazil, May 18,19,2009.
2
Some Pertinent Publications

1. O. P. Gandhi, G. Lazzi and C. M. Furse,
   Electromagnetic Absorption in the Human Head and
   Neck for Mobile Phones at 835 1900 MHz, IEEE
   Trans on Microwave Theory Techniques, Vol.
   44(10), pp. 1884-1897, 1996.
2. O. P. Gandhi and G. Kang, Some Present Problems
   and a Proposed Experimental Phantom for SAR
   Compliance Testing of Cellular Telephones at 835
   and 1900 MHz, Physics in Medicine Biology,
   Vol. 47, pp. 1501-1518, 2002.
3. O. P. Gandhi and G. Kang, Inaccuracies of a
   Plastic Pinna SAM for SAR Testing of Cellular
   Telephones Against IEEE and ICNIRP Safety
   Guidelines, IEEE Trans. On Microwave Theory
   Techniques, Vol. 52(8), pp. 2004-2012, 2004.

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Pertinent Publications - Continued

1. O. P. Gandhi, Electromagnetic Fields Human
   Safety Issues, Annual Review of Biomedical
   Engineering, Vol. 4, pp. 211-234, 2002.
2. O. P. Gandhi and G. Kang, Calculation of
   Induced Current Densities for Humans by Magnetic
   Fields from Electronic Article Surveillance
   Devices, Physics in Medicine Biology, Vol. 46,
   pp. 2759-2771, 2001.
3. G. Kang and O. P. Gandhi, SARs for
   Pocket-Mounted Mobile Telephones at 835 and 1900
   MHz, Physics in Medicine Biology, Vol. 47, pp.
   4301-4313, 2002.

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In order to study the effect of head size and
pinna thickness on the absorption of
electro-magnetic energy radiated by cell phones,
we have used

• Two different anatomic models of the head (The
  Utah Model and the Visible Man Model), and
• 11.1 larger and -9.1 smaller versions of the
  above two models i.e. a total of six anatomical
  models.
• The smaller versions of the head models were used
  to correspond to the smaller heads of the adults
  as well as the children.

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Continued .

• Different thicknesses of pinnas of the head
  models (20, 14, 10, and 6 mm) to correspond to
  the various individuals as well as thinner pinnas
  of children.
• Different sizes/tilt angles of cell phone
  antennas and handsets (2 types of antennas, three
  sizes of handsets).
• Two frequencies 1900 and 835 MHz.

Gandhi Kang, Phys. Med. Biol., 47, 1501-18,
2002. Gandhi Kang, IEEE Trans. MTT, 52(8),
2004-12, 2004.
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(b) The "Visible Man" model
(a) The Utah Model
Fig. 1. A visualization of the two
anatomically-based 30º-tilted head models used
for SAR calculations.
Gandhi Kang, Phys. Med. Biol., 47, 1501-18,
2002.
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Table 1. The calculated peak 1-g SARs for two
models of the human head for an irradiated power
of 125 mW at 1900 MHz.
Gandhi Kang, Physics in Med Biol., 47,
1501-18, 2002.
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Table 2. The calculated peak 1-g SARs for two
models of the human head for an irradiated power
of 600 mW at 835 MHz.
Gandhi Kang, Physics in Med Biol., 47,
1501-18, 2002.
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Note that the peak 1-g SARs for both the body
tissue and the brain increase monotonically with
the reducing head size (and pinna thickness) for
both of the head models (Utah and Visible Man),
all handset dimensions and the antennas i.e.
monopoles as well as helices.
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Fig. 2. SAR distribution of Utah head model at
1900 MHz. (a) 11.1 larger, (b) average, and (c)
smaller.
Gandhi Kang, Phys. Med. Biol., 47, 1501-18,
2002.
11
Fig. 3. SAR distribution of Utah head model at
835 MHz. (a) 11.1 larger, (b) average, and (c)
9.09 smaller.
Gandhi Kang, Phys. Med. Biol., 47, 1501-18,
2002.
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These figures calculated for the human heads of
various sizes are consistent with the results
reported for head models of adults and children
(Gandhi et al., IEEE MTT, 44, 1884-97, 1996) in
that there is a deeper penetration of absorbed
energy for the smaller heads compared to that for
the larger heads, both for 1900 and 835 MHz of
radiated fields.
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Effect of the pinna thickness on the brain and
body tissue SAR is given in the following table
Table 3. The calculated peak 1-g body tissue and
brain SARs for the Utah Model of the head.
Assumed is a handset of dimensions 22 x 42 x 122
mm held at an angle of 30º relative to the head.
Frequency (MHz) (irradiated power in mW) Antenna length (mm) Tissue Pinna thickness (mm) Pinna thickness (mm) Pinna thickness (mm) Pinna thickness (mm)
Frequency (MHz) (irradiated power in mW) Antenna length (mm) Tissue 20 14 10 6
Frequency (MHz) (irradiated power in mW) Antenna length (mm) Tissue Peak 1-g SAR Peak 1-g SAR Peak 1-g SAR Peak 1-g SAR
1900 (125 mW) 40 Body tissue Brain 0.51 0.20 0.83 0.27 1.02 0.33 1.29 0.46
835 (600 mW) 80 Body tissue Brain 2.44 0.85 2.95 1.06 3.20 1.24 3.50 1.37
Gandhi Kang, Physics in Med Biol., 47,
1501-18, 2002.
14
As expected, both the body tissue and brain SARs
increase monotonically with the reducing pinna
thickness (e.g. for the children). This is due
to the closer placement of the radiating antenna
to the body tissues and to the brain.
15
We have also reported Gandhi Kang, IEEE Trans.
MTT, 52, 2004-12, 2004 that use of a plastic
pinna for the specific anthropomorphic
mannequin (SAM) head model used for SAR
compliance testing of cell phones underestimates
both the peak 1-g SAR as well as the 10-g SAR
required for ICNIRP Guidelines by a factor of
1.6-2.0 or more, even for adults. We have also
reported that use of the so-called Visible Man
Model based on the CT scans of a fairly husky
(105 kg) mans cadaver tends to underestimate
both the peak 1- and 10-g SARs. This problem is
further compounded by the fact that SARs are
higher for children as compared to adults.
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(a) Side view.
(b) Cut through reference plane R passing through
mouth M.
(c) A cut 30 mm below plane R.
Fig. 4. SAM head model with three cross-sectional
cuts defining the 5-10 mm thickness of the
plastic shell. (Source IEEE Std., 1528, 2005)
Gandhi, IEEE Trans. on Microwave Theory
Techniques, 52(8), 2004.
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Table 4. Comparison of peak 1- and 10-g SARs
obtained for SAM and Anatomic Models for the
cheek and 15º-tilted positions of the 22 x 42
x 122 mm handsets with different antennas. The
SARs are normalized to a radiated power of 600 mW
at 835 MHz.
Antenna Axial Length mm Peak 1-g SAR (W/kg) Peak 1-g SAR (W/kg) Peak 1-g SAR (W/kg) Peak 1-g SAR (W/kg)
Antenna Axial Length mm SAM 5-10 mm plastic pinna Utah Model, 6 mm-thick pinna Utah Model, 14 mm-thick pinna Visible Man, 6 mm-thick pinna
Cheek Position 80 mm monopole 3.30 10.82 9.58 6.43
Cheek Position 20 mm helix 4.18 14.40 14.51 9.07
15?-Tilted position 80 mm monopole 2.49 10.90 8.80 7.12
15?-Tilted position 20 mm helix 2.65 14.96 12.96 9.95
Peak 10-g SAR (W/kg) Peak 10-g SAR (W/kg) Peak 10-g SAR (W/kg) Peak 10-g SAR (W/kg) Peak 10-g SAR (W/kg) Peak 10-g SAR (W/kg)
Cheek Position 80 mm monopole 2.36 3.67 4.55 2.34
Cheek Position 20 mm helix 3.03 4.79 6.61 3.21
15?-Tilted position 80 mm monopole 1.69 3.83 4.46 3.17
15?-Tilted position 20 mm helix 1.77 5.06 5.94 4.15
Gandhi, IEEE Trans. on Microwave Theory
Techniques, 52(8), 2004-12, 2004.
18
Table 5. Comparison of peak 1- and 10-g SARs
obtained for SAM and anatomic models for the
cheek and 15º-tilted positions of the 22 x 42
x 122 mm handsets with different antennas. The
SARs are normalized to a radiated power of 125 mW
at 1900 MHz.
Antenna Axial Length mm Peak 1-g SAR (W/kg) Peak 1-g SAR (W/kg) Peak 1-g SAR (W/kg) Peak 1-g SAR (W/kg)
Antenna Axial Length mm SAM 5-10 mm plastic pinna Utah Model, 6 mm-thick pinna Utah Model, 14 mm-thick pinna Visible Man, 6 mm-thick pinna
Cheek Position 80 mm monopole 0.73 2.05 2.31 1.97
Cheek Position 20 mm helix 0.93 2.24 2.54 2.66
15?-Tilted position 80 mm monopole 1.13 3.06 3.00 3.06
15?-Tilted position 20 mm helix 1.30 3.52 3.45 3.96
Peak 10-g SAR (W/kg) Peak 10-g SAR (W/kg) Peak 10-g SAR (W/kg) Peak 10-g SAR (W/kg) Peak 10-g SAR (W/kg) Peak 10-g SAR (W/kg)
Cheek Position 80 mm monopole 0.49 0.85 1.04 0.90
Cheek Position 20 mm helix 0.59 0.94 1.16 1.02
15?-Tilted position 80 mm monopole 0.74 1.16 1.33 1.36
15?-Tilted position 20 mm helix 0.82 1.34 1.52 1.61
Gandhi, IEEE Trans. on Microwave Theory
Techniques, 52(8), 2004-12, 2004.
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10-g SAR, Visible Man Model, cheek position,
frequency 1900 MHz Radiated power 125 mW
Fig. 5. Variation of peak 10-g SAR as a function
of separation from the absorptive tissues.
Handset of dimensions 22 x 42 x 122 mm.
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10-g SAR, Utah Model, 15º-tilted position,
frequency 1900 MHz Radiated power 125 mW
Fig. 6. Variation of peak 10-g SAR as a function
of separation from the absorptive tissues.
Handset of dimensions 22 x 42 x 122 mm.
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1-g SAR, Utah Model, 15º-tilted position,
frequency 835 MHz Radiated power 600 mW
Fig. 7. Variation of peak 1-g SAR as a function
of separation from the absorptive tissues.
Handset of dimensions 22 x 42 x 122 mm.
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The underestimation of SAR by SAM is due to the
fact that the cell phone under test is physically
separated from the tissue-simulant head model of
SAM by several millimeters. It has been
repeatedly shown both computationally and
experimentally that each additional millimeter
of physical separation of the radiating source
from the tissue-simulant model results in an
underestimation of SAR by 13-15. Thus, a factor
of 2 or more underestimation of SAR by the SAM
SAR com-pliance model is understandable because
of the 6-10 mm thickness of the plastic pinna
used for SAM.
Kang and Gandhi, Phys. Med. Biol., 47, 4301-13,
2002. Gandhi Kang, IEEE-MTT, 52, 2004-12, 2004.
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Electronic Article Surveillance (EAS) Systems

• Being introduced into stores, libraries, and
  hospitals to prevent theft of items.
• Use alternating magnetic fields (at frequencies
  of several kHz to several MHz.
• May take the form of one- or two-sided panels of
  current-carrying loops near the exit door, loops
  hidden in the floor or under the checkout
  counters.
• We have used the impedance method to calculate
  induced current densities for 1mm resolution
  anatomical models of adult and scaled models of
  10- and 5-year old children.

Gandhi Kang, Phys. Med. Biology, 46, 2759-71,
2001.
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Fig. 8. A few representative EAS systems.
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Table 6. Some typical external dimensions and
derived voxel sizes used for the anatomic models
of the male adult and 10- and 5-year old boys.
Gandhi Kang, Phys. Med. Biol., 47, 2759-71,
2001.
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(c) 5-year old boy
(a) Adult male
(b) 10-year old boy
Fig. 9. The three anatomic models used for
calculations of induced electric fields and
current densities.
Gandhi Kang, Phys. Med. Biol., 47, 2759-71,
2001.
27
From Gandhi Kang, Phys. Med. Biol., 46,
2759-71, 2001.
Fig. 10. Top view of the schematic of an assumed
magnetic deactivator coil and the placement of
the human model relative to it. All dimensions
are in cm.
28
From Gandhi Kang, Phys. Med. Biol., 46,
2759-71, 2001.
Fig. 11. An assumed EAS system using a pair of
rectangular coils with an overlap of 10 cm. The
lower rung of the bottom coil is assumed to be 20
cm off the ground plane. The marked dimensions
are in cm.
29
From Gandhi Kang, Phys. Med. Biol., 46,
2759-71, 2001.
Along the y-axis from y 40 cm (frontal plane of
the body) to y 70 cm.
Fig. 12. The calculated variations of the
magnetic fields with distance y from the center
of the deactivator solenoid and for the vertical
z-axis passing through the front of the human
model (y 40 cm) at the edge of the table.
30
From Gandhi Kang, Phys. Med. Biol., 46,
2759-71, 2001.
Along the vertical z-axis passing through the
front of the model.
Fig. 13. The calculated variations of the
magnetic fields with distance y from the center
of the deactivator solenoid and for the vertical
z-axis passing through the front of the human
model (y 40 cm) at the edge of the table.
31
From Gandhi Kang, Phys. Med. Biol., 46,
2759-71, 2001.
Along line passing through the
center of the coils of the EAS system.
Fig. 14. The calculated variations of the
magnetic fields with distance y along line
passing through the center of the EAS coils
and for a vertical line at a distance x 20
cm (y 0) from the plane of the EAS panel.
32
From Gandhi Kang, Phys. Med. Biol., 46,
2759-71, 2001.
Along the vertical line at a distance x
20 cm (y 0) from the plane
Fig. 15. The calculated variations of the
magnetic fields with distance y along line
passing through the center of the EAS coils
and for a vertical line at a distance x 20
cm (y 0) from the plane of the EAS panel.
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Assumed for the calculation of induced current
densities for the various parts of the body is
Frequency (F) of 1 kHz, 50,000 A turns rms for
the 85 cm high table top deactivator,
and Frequency of 30 kHz, 100 A turns for a second
panel type EAS system.
ICNIRP Basic Restriction for max
area- averaged current density J for CNS tissues
(brain and spinal cord)
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Table 7. The calculated organ-averaged and
maximum 1 cm2 area-averaged current densities (J)
for the CNS tissues for the models of the adult
and 10- and 5-year old children for the 1 kHz
magnetic deactivator.
Organ Adult 10-year old child 5-year old child
Organ J(mA m-2) J(mA m-2) J(mA m-2)
Brain Pineal gland Organ-averaged Maximum (1 cm-2) Organ-averaged Maximum (1 cm-2) 0.15 0.48 0.02 --- 0.66 2.02 0.10 --- 1.77 4.46 0.51 ---
Gandhi Kang, Phys. Med. Biol., 47, 2759-71,
2001.
35
Table 8. The calculated organ-averaged and
maximum 1 cm2 area-averaged current density (J)
for the CNS tissues for the models of the adult
and 10- and 5-year old children for the 30 kHz
EAS pass-by system.
Organ Adult 10-year old child 5-year old child
Organ J(mA m-2) J(mA m-2) J(mA m-2)
Brain Pineal gland Organ-averaged Maximum (1 cm-2) Organ-averaged Maximum (1 cm-2) 4.75 17.63 0.92 --- 23.20 64.64 17.42 --- 40.70 98.93 36.27 ---
Gandhi Kang, Phys. Med. Biol., 47, 2759-71,
2001.
36
The point to note is that higher current
densities are induced for the CNS tissues of the
10- and 5-year old children for both of the
assumed EAS systems.
This is due to the fact that the head of the
taller adult is considerably above the
deactivator or the pass-by EAS panel and is thus
in the weaker magnetic field region.
The heads of the shorter children, on the other
hand, are in higher magnetic fields. The maximum
induced J for the children may exceed ICNIRP
basic restrictions if sufficiently strong
magnetic fields are used.
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Conclusions for Mobile Telephones

• Use of six different anatomical models (two
  different head shapes and three different scaled
  versions i.e. average, larger, and smaller
  versions of each, shows that the peak 1-g SAR for
  the brain for the smaller models representative
  of children may be up to 220 at 1900 MHz and
  144 at 835 MHz of the SARs of the larger models.
• This is due to the thinner pinna and the skull
  for the smaller models which results in closer
  placement of the mobile telephones to the brain
  of children.

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Conclusions -- Continued

• Use of the SAM (standard anthropomorphic
  mannequin) model with a 5-10 mm thick plastic
  spacer in the shape of pinna chosen by industry
  for SAR compliance testing results in an
  artificial, more distant placement of the mobile
  telephone from the tissue-simulating fluid of
  SAM. This gives an SAR that is up to two or more
  times smaller than for the anatomic models of the
  adult head, and an even larger underestimation of
  the SAR for the heads of children.

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Conclusions -- Continued

• In Europe, compliance of the maximum magnetic
  fields induced current densities for the CNS
  tissues (brain and the spinal cord) against
  ICNIRP guidelines is required for all EAS
  systems.
• Because of the larger height, the adult head is
  generally in the weaker magnetic field region
  resulting in lower induced current densities for
  the brain for adults.
• The heads of children, on the other hand, are in
  the stronger magnetic field regions resulting in
  higher induced currents for the brain as compared
  to adults.