# Anticipated Impact of Hand-Hold Position on the Electromagnetic Interaction of Different Antenna Types/Positions and a Human in Cellular Communications

Authors: Salah I. Al-Mously; Marai M. Abousetta
Journal: International Journal of Antennas and Propagation
 (2008)

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## Abstract

This paper is intended to investigate intensely the impact of multipossible hand-hold positions
on the electromagnetic (EM) interaction of handset antennas and a human by using a finite-difference
time-domain (FDTD) method. Candy-bar handsets with different external and internal
antenna positions operating in the GSM900, GSM1800/DCS, and UMTS/IMT-2000 bands are
hereby simulated with configuration of the most parts in order to achieve the commercially
available handset model design. Homogeneous and heterogeneous phantoms both are used to
simulate the human head, whereas, a semirealistic model with three different tissues is designed
to simulate a human hand holding a set. Both of the antenna performance including the total
isotropic sensitivity (TIS) and the specific absorption rate (SAR) in tissues are examined for the
different suggested applicable cases, where various positions of antenna, handset and hand are
considered in simulations.
This simulation study determines that both of the antenna performance and the SAR in tissues
significantly alter owing to the positioning of the handset against user's head at different hand
levels; where a maximum alteration is observed due to the exposure of handset with internal
antenna, as compared with the handset having external antenna.


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## Body

## 1. Introduction

The  possible health  hazard of cellular communication
handsets  due to their electromagnetic (EM) interaction with human and the means
of reducing the impact of this interaction have appeared as a public concern. It is  noticeable that while using
cellular handset in close proximity to head, many factors may affect on the EM
interaction, among them is the hand-hold
position.Measuring the specific absorption rate (SAR) in human
head exposed to the handset antenna radiation, most standards (IEEE-1528, EN
50360/1, IEC 62209, ARIB STD-T56, FCC, ACA) [1–7] ignore considering the use of
hand model due to the various possible hand-hold positions and the worst-case
SAR value is obtained without the use of a hand model. However, the hand-hold
has a considerable impact on the handset antenna performance which can be altered according to the antenna
type/position and hand-hold position. Hence, it is highly significant to anticipate
the EM interaction of handset antennas and a human head taking into account the
different possible hand-hold positions.Although over the
last fifteen years many authors have investigated the interaction between
the EM field radiated by the cellular hand-held and human head [8–23], nothing has
been published yet about the hand effect on the EM interaction after examining
both antenna performance and the SAR in tissues, by taking into consideration
the effects of different operating frequencies, different antenna types, and
different positions  of the hand, antenna, and handset against head.In [8–12], user’s hand was simulated by a simple block
model, where in [8], the model consists of one tissue (muscle), whereas in [9–12],
the models consisted of two tissues (bone and muscle). In [13, 14], a hand with
typical handset holding model was simulated with one tissue approximating the
average hand tissues relative permittivity. In [15], user’s hand was simulated
by a 3D anatomical model with eleven tissues, based on its real geometry
acquired by an MR scan. A homogeneous 3D model was used in [16] to simulate the
user’s hand, whereas a realistic model with two tissues (bone and muscle) was
used in [17]. A simplified model of a hand grasping a cellular phone was
presented in [18], where the hand model can be digitally moved while grasping
the handset with external antenna. A thin
rubber glove filled with a muscle simulating liquid was used in [14, 15] to
conduct the experimental measurement of the hand impact beside the simulation, whereas
in [19], PVC tubes filled with a lossy liquid at the cheek left position
was used to conduct the measurement at both 900 and 1800 MHz. In [20–22], a
semirealistic model with three tissues (bone, muscle, and skin) was designed
and used to simulate the user’s hand, whereas in [23], a realistic model of
three tissues was generated and used.Specifically in [12–14, 16, 17, 22, 23], the effect of
hand-hold positions was considered in evaluating the EM interaction and was
observed as follows.(1) In [12], two different block
models of the hand holding the handset at 900 and 1800 MHz were examined. A
simple model of shorted-patch antenna in different orientations over a metal
plate (chassis) with 3.6 mm thickness all were used to simulate the handset.
The EM interaction between MRI-based head model with six tissues and the
handset were investigated for different chassis lengths. Both the antenna
specifications and SAR in tissues were computed due to sliding the hand on the
handset at different positions. A single handset position with respect to head
was considered. Only the patch antenna was examined, where the different
possible antenna positions were ignored.(2) In [13], both homogeneous and
heterogeneous (seven tissues) head models are involved in computing the maximum
local SAR in tissues at 900 and 1500 MHz. A typical hand model with one tissue
sliding on a handset was used, where the handset was modeled by a simple metal
box with a monopole and dipole antenna. The maximum local SAR in head was
calculated due to different hand-hold positions and different distances between
handset and head. The internal antenna was not examined and the different
possible antenna positions on the handset were not considered. The antenna
performance due to the hand-hold alteration was not presented.(3) In [14], two different right-hand-hold
positions were considered with two different handset models (one with a
right-side monopole and the other with a rectangular patch antenna) against
head at cheek position and operating at 1747 MHz. Only the antenna
performance was evaluated for different antenna orientations, where both
experimental and numerical techniques have been conducted. A fiberglass torso
phantom of brain/muscle simulating liquid and a thin rubber glove filled with
the same liquid were used in measurements, whereas a homogeneous torso plus
hand phantom was used in simulations. The different possible antenna positions
were not examined in that study.(4) In [16], three different
right-hand-hold positions were considered using a clam-shell phone with a
left-side external antenna. Based on the phone type, a cheek position
was considered. The simulation was conducted at 1880 MHz, where only the
antenna performance of the handset against specific
anthropomorphic mannequin (SAM) was examined.(5) In [17], eight right-hand-hold
positions sliding on the handset with internal antenna were considered. Only
the antenna performance was evaluated at 925 and 1795 MHz with no human-head
involvement in computation.(6) In [22], two applicable extremes
of hand holding for a candy-bar handset with external antenna close to head at cheek and tilt positions and operating at 900 MHz were considered.
That work did not take into consideration the EM interaction of, firstly, the
internal-type antenna, secondly, the possible antenna positions, thirdly, the
possible different operating frequencies, and fourthly, the effect of tissues
inhomogeneity using an MRI-based head model.(7) In [23], the performance of a
realistic commercial quad-band clamshell-type handset with different external
antennas was predicted under various usage patterns. The EM interaction of
handset and SAM phantom was computed and measured at 1880 MHz, where three
different hand-hold positions were examined. The values of SAR in tissues due
to the considered different usage patterns were not presented and the effects
of head-tissues inhomogeneity as well as the different possible antenna
types/positions were ignored.In this research, a semirealistic right-hand model with
three tissues [20–22] is designed to determine the impact of the hand-hold
position on the EM interaction between handset antennas and human. Heterogeneous
anatomically correct model of twenty five different tissues as well as
homogeneous SAM phantom are used to simulate the user’s head.In view of the fact that the external antenna position on a
handset has a considerable impact on the EM interaction [20], twelve
single-band handset models having different
antenna types/positions are designed and simulated to find out the
available commercial models design. The earlier six models are with external
antennas positioned on the left and right side and operating at 900, 1800, and
2025 MHz, whereas the later six models are with internal antennas positioned at
top and bottom of the handset and operating at 900, 1800, and 2025 MHz.The prediction of the EM interaction is based on evaluating
the handset antenna performance including the total isotropic sensitivity (TIS)
as well as the SAR and power absorbed in tissues.
Bothcheek and tilt positions of the handset against head are examined
in compliance with the IEEE-standard 1528 [1].All simulations are achieved at 900, 1800, and 2025 MHz,
which represent the GSM-family standards including E-GSM900 (880–960 MHz),
GSM1800/DCS (1710–1880 MHz), and
UMTS/IMT-2000 (1885–2200 MHz),
respectively. For the later, the frequency of 2025 MHz represents the upper
edge of the transmitting band of the IMT-2000 (1885–2025 MHz) also
within the range of UMTS band.


## 2. Fdtd Modeling

The finite-difference
time-domain (FDTD) method proposed by Yee in 1966 [24] is a direct solution of
Maxwell’s curl equations in the time domain: (1)▿×H=∂∂tεE+σEE,▿×E=−∂∂tμH−σHH, where ε and μ are the electric and magnetic properties of
the material, respectively; σE and σH are the electric and magnetic conductivity,
respectively; and the electric (E)
and magnetic (H) field components
are positioned as [25] (2)E=(ExEyEz),H=(HxHyHz). Maxwell’s curl equations are
discretized using a 2nd-order finite-difference approximation in both space and
time in an equidistantly spaced mesh, where E and H are
calculated at alternating discrete points in time using a leap-frog algorithm
[24, 25]. Although FDTD technique has some limitations [26], its robustness, its suitability for handling
complex problems composed of any number of subvolumes and its general independence of material compositions make it more popular than other
techniques and the most applied in EM solver platforms. SEMCAD X (ver. 12.4 JUNGFAU) simulation platform [27] is selected
for simulating these work cases due to its handling, functionality, and
features for highly detailed CAD models as well as efficient FDTD solver for
simulating advanced applications. SEMCAD
X is a 3D full wave simulation environment based on the FDTD method.


### 2.1. Handset Model with External Antenna

For the handset with external antenna, a candy-bar handset
operating at 900 MHz [22] is adopted and redesigned to produce six different
models with left- and right-side external-antenna operating at 900, 1800, and
2025 MHz. The handset with the left-side antenna will be referred later as
model-A1, whereas the handset with the right-side antenna will be referred as
model-A2. The maximum dimensions of the handset with external antenna
(excluding the antenna height) are 104 mm × 43 mm × 16.5 mm (length × width ×
thickness), whereas the multilayer PCB dimensions are 97 mm × 37 mm × 1 mm.The considered electromechanical parts of the
proposed handset models with external and internal antennas areantenna, external
antenna cover, PCB, shields, LCD and its holder, housing parts, keypad and
buttons, battery and battery contacts, and connectors. Table 1 shows the
dielectric material parameters used for simulations [22, 23, 26].Table 1
The main dielectric parts of the
handset CAD models and the corresponding material parameters.
Partεrσ (S/m)Antenna
cover and bushing2.50.003PCB
dielectric4.50.07LCD
glass4.50.01LCD
dielectric3.00.01Housing
and covers3.50.02Keypad/buttons3.50.02Battery
case3.50.02A short-whip antenna top-loaded with a small
cylinder [21, 22, 28] is suggested. A matching of 15.25 nH lumped element is
needed at 900 MHz [22], whereas at 1800 and 2025 MHz, the antenna is well tuned
and no matching is considered. The antenna has been tilted back by (8°)
to reduce the EM interaction with head. Figure 1 shows the SEMCAD
X representation of
model-A1 with the antenna configuration and its dimensions at the adopted
frequencies, that is, 900, 1800, and 2025 MHz.Figure 1
TheSEMCAD X representation of
the handset with external antenna (model-A1) showing the numerical antenna
structure and its dimensions at 900, 1800, and 2025 MHz.


### 2.2. Handset Model with Internal Antenna

Many
techniques were suggested to make the microstrip patch antenna (MPA) suitable
in size for the mobile communication terminals. One of the effective ways to
reduce the patch size of the microstrip antenna is to introduce a shorting pin
at the edge of the
patch [29]. An overview and a survey on the compact patch antenna including the
antennas with shorting pin are detailed in [30]. The performance of the
probe-fed single and stacked shorted-patch antennas due to the EM interaction
with the human were investigated in [11, 12], where the possible different
antenna positions were not examined.In this
work, a semirealistic handset model using
a single-band probe-fed rectangular patch antenna with shorting plate at the
edge is designed. Six different handset models are simulated with top and
bottom-mounted patch antennas operating at different frequencies, that is, 900,
1800, and 2025 MHz.The handset parts and components are not located identically
in all models due to the different antenna position and size regarding each
different operating frequency. Figure2 demonstrates the SEMCAD X representation of handset model-B1, where different parts and components are
shown in different views. Figure 3 shows the structure of the rectangular patch
antenna with shorting plate. The plastic back-cover of the handset touches the
patch antenna, where no air gap exists between them. The maximum physical
dimensions of the handset with internal patch antenna are 110 mm × 44 mm × 13 mm, whereas; the multilayer PCB dimensions are 97 mm × 37 mm × 1 mm. The
dimensions of the patch antenna at 900, 1800, and 1800 MHz are illustrated in
Figure 3, where the width of the shorting plate is 3.5 mm.TheSEMCAD X representation of
the handset with internal antenna (model-B1) showing different components and
parts in different views.
(a)(b)(c)(d)Figure 3
The numerical structure of the rectangular patch antenna with shorting
plate, used for the handset with internal antenna, and its dimensions at 900,
1800, and 2025 MHz.


### 2.3. Hand Model

A semirealistic hand model consisting of three
tissues (skin, muscle, and bone) [20–22] is designed with two common different
holding positions referred later as hand1 and hand2. Hand1 is grasping the lower
part of the handset, whereas hand2 is grasping the upper part of the handset. These proposed
hand-holds represent the two applicable extremes
of hand holding. The electrical properties and densities of the hand tissues
are given in Table 2.Table 2
Values of hand, HR-EFH, and SAM
material parameters (relative permittivityεr,
electrical conductivity σ, density ρ) used for simulations at 900, 1800, and 2025 MHz.
Hand Tissue900 MHz1800 MHz2025 MHzρ (kg/m3)εrσ (S/m)εrσ (S/m)εrσ (S/m)Hand skin41.410.8738.871.1838.531.281100Hand muscle55.030.9453.551.3453.261.471041Hand bone12.450.1411.780.2811.640.311990HR-EFH
Tissueεrσ (S/m)εrσ (S/m)εrσ (S/m)ρ (kg/m3)Air1.0000.001.000.0001.000.0001.16Blood vessel44.780.7043.341.0743.061.181050Bone (ramus of mandible)12.450.1411.780.2811.640.311990Brain/gray matter52.730.9450.081.3949.651.531039Brain/white matter38.890.5937.010.9136.701.011043Cerebellum49.441.2646.111.7145.621.841040Cerebro Spinal Fluid (CSF)68.642.4167.202.9266.873.091007Ear (cartilage)42.650.7840.221.2939.701.441100Eye-cornea55.241.3952.771.8652.342.001032Eye-lens46.570.7945.351.1545.101.261090Eye-vitreous body68.901.6468.572.0368.462.171009Fat (average infiltrated)11.330.1111.020.1910.950.22916Jaw bone (mandible)12.450.1411.780.2811.640.311990Mastoid cells (bones)5.500.045.3700.075.3400.08980Midbrain (mesencephalon)45.790.7643.001.2043.001.001039Muscles55.030.9453.551.3453.261.471041Nasal cavity (mucous membrane)46.080.8443.851.2343.481.351050Parotid gland59.681.0458.141.5057.811.651050Skin41.410.8738.871.1838.531.281100Skull16.620.2415.560.4315.350.491645Spinal cord32.530.5730.870.8430.600.921038Spine12.450.1411.780.2811.640.311990Thalamus45.790.7643.001.2043.001.001039Tongue55.270.9453.571.3753.231.511041Ventricles (brain)68.642.4167.202.9266.873.091007SAM phantom materialεrσ (S/m)εrσ (S/m)εrσ (S/m)ρ (kg/m3)SAM head shell5.00.00165.00.00165.00.00161030SAM head liquid41.50.9740.01.440.01.41030


### 2.4. Head Model

A heterogeneous high-resolution European female head (HR-EFH) model with pressed ears
[31], available with Schmidt & Partner Engineering AG (SPEAG, Zurich, Switzerland) [27],
is used. This MRI-based model consists of 121 different slices, with slice
thicknesses of 1 mm (ear region) and 3 mm and a transverse spatial resolution
of 0.2 mm. Twenty five different tissues are recognized and their electrical
properties and densities are given in Table 2. Head and hand tissue properties
are set according to material properties and densities database in [27] and to those
given in [32], where both are based on [33].For comparison, an SAM phantom developed by
different standard committees [1, 3–6] is also used to simulate the human head.
The electrical properties of the SAM materials are defined in [1, 34] and given
in Table 2.Figure4 exhibits different holding positions of the handset
models close to HR-EFH at cheek position indicating the coordinate
system, where the acoustic output is set opposite to earpiece center in
compliance with IEEE Std. 1528 [1]. Due to different antenna types/positions
considered in simulations, the distances between the antennas feed points and
the nearest head-tissue voxel also differ. According to the acoustic output
position at the origin point (x=0,y=0,andz=0mm) and with the different coordinate systems
arrangement for each antenna type (Figure 4), the antenna feed position is at (x=17,y=−11,andz=−8.5mm) for model-A1; at (x=−17,y=−11,andz=−8.5mm) for model-A2, whereas it is at (x=15,y=−3,andz=5.4mm) for model-B1; and at (x=15,y=−89.5,andz=5.4mm) for model-B2.Different CAD representations of the handset in hand against HR-EFH atcheek position: (a) Model-A2 in hand1 (bone only), (b) Model-A1 in hand2 (bone only),
(c) Model-B1 in hand1, and (d) Model-B1 in hand2.
(a)(b)(c)(d)


## 2.1. Handset Model with External Antenna

For the handset with external antenna, a candy-bar handset
operating at 900 MHz [22] is adopted and redesigned to produce six different
models with left- and right-side external-antenna operating at 900, 1800, and
2025 MHz. The handset with the left-side antenna will be referred later as
model-A1, whereas the handset with the right-side antenna will be referred as
model-A2. The maximum dimensions of the handset with external antenna
(excluding the antenna height) are 104 mm × 43 mm × 16.5 mm (length × width ×
thickness), whereas the multilayer PCB dimensions are 97 mm × 37 mm × 1 mm.The considered electromechanical parts of the
proposed handset models with external and internal antennas areantenna, external
antenna cover, PCB, shields, LCD and its holder, housing parts, keypad and
buttons, battery and battery contacts, and connectors. Table 1 shows the
dielectric material parameters used for simulations [22, 23, 26].Table 1
The main dielectric parts of the
handset CAD models and the corresponding material parameters.
Partεrσ (S/m)Antenna
cover and bushing2.50.003PCB
dielectric4.50.07LCD
glass4.50.01LCD
dielectric3.00.01Housing
and covers3.50.02Keypad/buttons3.50.02Battery
case3.50.02A short-whip antenna top-loaded with a small
cylinder [21, 22, 28] is suggested. A matching of 15.25 nH lumped element is
needed at 900 MHz [22], whereas at 1800 and 2025 MHz, the antenna is well tuned
and no matching is considered. The antenna has been tilted back by (8°)
to reduce the EM interaction with head. Figure 1 shows the SEMCAD
X representation of
model-A1 with the antenna configuration and its dimensions at the adopted
frequencies, that is, 900, 1800, and 2025 MHz.Figure 1
TheSEMCAD X representation of
the handset with external antenna (model-A1) showing the numerical antenna
structure and its dimensions at 900, 1800, and 2025 MHz.


## 2.2. Handset Model with Internal Antenna

Many
techniques were suggested to make the microstrip patch antenna (MPA) suitable
in size for the mobile communication terminals. One of the effective ways to
reduce the patch size of the microstrip antenna is to introduce a shorting pin
at the edge of the
patch [29]. An overview and a survey on the compact patch antenna including the
antennas with shorting pin are detailed in [30]. The performance of the
probe-fed single and stacked shorted-patch antennas due to the EM interaction
with the human were investigated in [11, 12], where the possible different
antenna positions were not examined.In this
work, a semirealistic handset model using
a single-band probe-fed rectangular patch antenna with shorting plate at the
edge is designed. Six different handset models are simulated with top and
bottom-mounted patch antennas operating at different frequencies, that is, 900,
1800, and 2025 MHz.The handset parts and components are not located identically
in all models due to the different antenna position and size regarding each
different operating frequency. Figure2 demonstrates the SEMCAD X representation of handset model-B1, where different parts and components are
shown in different views. Figure 3 shows the structure of the rectangular patch
antenna with shorting plate. The plastic back-cover of the handset touches the
patch antenna, where no air gap exists between them. The maximum physical
dimensions of the handset with internal patch antenna are 110 mm × 44 mm × 13 mm, whereas; the multilayer PCB dimensions are 97 mm × 37 mm × 1 mm. The
dimensions of the patch antenna at 900, 1800, and 1800 MHz are illustrated in
Figure 3, where the width of the shorting plate is 3.5 mm.TheSEMCAD X representation of
the handset with internal antenna (model-B1) showing different components and
parts in different views.
(a)(b)(c)(d)Figure 3
The numerical structure of the rectangular patch antenna with shorting
plate, used for the handset with internal antenna, and its dimensions at 900,
1800, and 2025 MHz.


## 2.3. Hand Model

A semirealistic hand model consisting of three
tissues (skin, muscle, and bone) [20–22] is designed with two common different
holding positions referred later as hand1 and hand2. Hand1 is grasping the lower
part of the handset, whereas hand2 is grasping the upper part of the handset. These proposed
hand-holds represent the two applicable extremes
of hand holding. The electrical properties and densities of the hand tissues
are given in Table 2.Table 2
Values of hand, HR-EFH, and SAM
material parameters (relative permittivityεr,
electrical conductivity σ, density ρ) used for simulations at 900, 1800, and 2025 MHz.
Hand Tissue900 MHz1800 MHz2025 MHzρ (kg/m3)εrσ (S/m)εrσ (S/m)εrσ (S/m)Hand skin41.410.8738.871.1838.531.281100Hand muscle55.030.9453.551.3453.261.471041Hand bone12.450.1411.780.2811.640.311990HR-EFH
Tissueεrσ (S/m)εrσ (S/m)εrσ (S/m)ρ (kg/m3)Air1.0000.001.000.0001.000.0001.16Blood vessel44.780.7043.341.0743.061.181050Bone (ramus of mandible)12.450.1411.780.2811.640.311990Brain/gray matter52.730.9450.081.3949.651.531039Brain/white matter38.890.5937.010.9136.701.011043Cerebellum49.441.2646.111.7145.621.841040Cerebro Spinal Fluid (CSF)68.642.4167.202.9266.873.091007Ear (cartilage)42.650.7840.221.2939.701.441100Eye-cornea55.241.3952.771.8652.342.001032Eye-lens46.570.7945.351.1545.101.261090Eye-vitreous body68.901.6468.572.0368.462.171009Fat (average infiltrated)11.330.1111.020.1910.950.22916Jaw bone (mandible)12.450.1411.780.2811.640.311990Mastoid cells (bones)5.500.045.3700.075.3400.08980Midbrain (mesencephalon)45.790.7643.001.2043.001.001039Muscles55.030.9453.551.3453.261.471041Nasal cavity (mucous membrane)46.080.8443.851.2343.481.351050Parotid gland59.681.0458.141.5057.811.651050Skin41.410.8738.871.1838.531.281100Skull16.620.2415.560.4315.350.491645Spinal cord32.530.5730.870.8430.600.921038Spine12.450.1411.780.2811.640.311990Thalamus45.790.7643.001.2043.001.001039Tongue55.270.9453.571.3753.231.511041Ventricles (brain)68.642.4167.202.9266.873.091007SAM phantom materialεrσ (S/m)εrσ (S/m)εrσ (S/m)ρ (kg/m3)SAM head shell5.00.00165.00.00165.00.00161030SAM head liquid41.50.9740.01.440.01.41030


## 2.4. Head Model

A heterogeneous high-resolution European female head (HR-EFH) model with pressed ears
[31], available with Schmidt & Partner Engineering AG (SPEAG, Zurich, Switzerland) [27],
is used. This MRI-based model consists of 121 different slices, with slice
thicknesses of 1 mm (ear region) and 3 mm and a transverse spatial resolution
of 0.2 mm. Twenty five different tissues are recognized and their electrical
properties and densities are given in Table 2. Head and hand tissue properties
are set according to material properties and densities database in [27] and to those
given in [32], where both are based on [33].For comparison, an SAM phantom developed by
different standard committees [1, 3–6] is also used to simulate the human head.
The electrical properties of the SAM materials are defined in [1, 34] and given
in Table 2.Figure4 exhibits different holding positions of the handset
models close to HR-EFH at cheek position indicating the coordinate
system, where the acoustic output is set opposite to earpiece center in
compliance with IEEE Std. 1528 [1]. Due to different antenna types/positions
considered in simulations, the distances between the antennas feed points and
the nearest head-tissue voxel also differ. According to the acoustic output
position at the origin point (x=0,y=0,andz=0mm) and with the different coordinate systems
arrangement for each antenna type (Figure 4), the antenna feed position is at (x=17,y=−11,andz=−8.5mm) for model-A1; at (x=−17,y=−11,andz=−8.5mm) for model-A2, whereas it is at (x=15,y=−3,andz=5.4mm) for model-B1; and at (x=15,y=−89.5,andz=5.4mm) for model-B2.Different CAD representations of the handset in hand against HR-EFH atcheek position: (a) Model-A2 in hand1 (bone only), (b) Model-A1 in hand2 (bone only),
(c) Model-B1 in hand1, and (d) Model-B1 in hand2.
(a)(b)(c)(d)


## 3. Fdtd-Grid Generation and Simulation Parameters

The simulation platformSEMCAD
X incorporates automated heterogeneous grid generation, which automatically
adapts the mesh to a specific setup. The most crucial parts with respect to
grid resolution are the antenna, as well as the PCB with its thin PEC ground
layers (110 μm thickness).To align the simulated handset components to the
FDTD grid accurately, a minimum spatial resolution of0.5×0.5×0.5mm3 and a maximum spatial
resolution of 10×10×10mm3 in the x, y, and z directions are chosen for simulating
the handset in hand close to head. Depending on the case complexity, a refining
factor of (5–20) with grading
ratio of (1.2-1.3) is used for
the solid regions during the simulations. The simulations assume a steady-state
voltage at 900, 1800, and 2025 MHz, with a feed point of 50 Ohm voltage source
of 0.5 mm physical gap. The absorbing boundary conditions (ABCs) are set as a uniaxial
perfectly matched layer (UPML) mode with a very high strength thickness, where
minimum level of absorption at the outer boundary is (>99.9%) [27].Table3 lists the total number of FDTD-grid cells
required to simulate the handset models in free space and in hand close to head
at different positions operating at 900, 1800, and 2025 MHz.Table 3
The generated FDTD grid cell size of the studied
handset models in free space and in hand close to HR-EFH at different positions
operating at 900, 1800, and
2025 MHz.
FDTD-grid cell size (Mcells)900 MHz1800 MHz2025 MHzHandset modelA1A2A1A2A1A2In free
space0.733720.733720.479250.479250.891130.89113HR-EFHCheekHand119.84119.905518.0718.199812.902713.1749Hand218.51318.708516.620816.284211.851412.3738TiltHand120.756120.963919.340119.266518.921318.695Hand219.618119.626217.85217.655217.444817.4434Handset modelB1B2B1B2B1B2In free
space1.1761.207551.043781.229121.043781.08768HR-EFHCheekHand119.418418.798719.213719.936219.076919.0168Hand217.670317.613817.177119.024217.116418.2577TiltHand121.859422.078520.977621.9321.193121.4403Hand220.379820.852419.088219.797919.297919.4936


## 4. Em Interaction between Handset and Human

The EM
interaction between handset antenna and human is evaluated, firstly, by
assessing the effect of human head and hand on the handset antenna performance
through computing the antenna parameters including the input impedance(Zin), |S11| in dB, radiation efficiency (ηrad), total efficiency (ηtot), and the total
isotropic sensitivity (TIS), secondly, by assessing the impact of antenna EM
radiation on head and hand through computing the SAR and power absorption in tissues.


### 4.1. Antenna Performance

The results in Table4 show the computed antenna
parameters including Zin, |S11| in dB, ηrad, and ηtot of the handset models at 900 MHz under
different usage patterns in a presence of HR-EFH model, whereas the results in Tables 5 and 6 show the antenna
parameters at 1800 and 2025 MHz, respectively. The ηtot is given by (3)ηtot=ηmisηrad, where ηmis represents the mismatch efficiency and equal
to (4)ηmis=(1−|S11|2). Figure 5 illustrates the 3D far-field radiation
pattern of the handset model-A1 in free space as well as in hand1 close to head
(SAM and HR-EFH) at cheek position
and operating at 900, 1800, and 2025 MHz, whereas Figure 6 illustrates the 3D far-field
radiation pattern of the handset model-B1 in the same conditions. In both
Figures 5 and 6, the antenna feeding source position considered as the origin
of the antenna pattern coordinate system, that is, x=0,y=0,andz=0mm.Table 4
Computational results of the
antenna input impedance,Zin,|S11| in dB, radiation efficiency, ηrad, and total efficiency, ηtot, for different handset setups at 900 MHz.
ParameterFrequency/900 MHzZin (Ohm)|S11| (dB)ηrad (%)ηtot (%)Handset modelA1A2A1A2A1A2A1A2No
headIn free space44.5
+ j0.8644.5
+ j0.86−24.4−24.477.877.877.677.6In hand149.2
− j8.1751.3
− j9.55−21.6−20.589.860.387.259.8In hand278.5
+ j37.458.36
− j3.5−9.1−21.530.736.526.936.3HR-EFHCheekHand142.7
+ j4.6342.6
+ j4.27−20.6−20.818.721.218.521.0Hand257.7
+ j46.944.1
+ j10.9−7.9−17.610.310.78.6010.6TiltHand148.1
+ j2.2547.0
− j0.49−30.4−30.129.130.729.130.7Hand266.7
+ j46.752.2
+ j10.1−8.1−19.916.217.113.616.9Handset modelB1B2B1B2B1B2B1B2No
headIn free space49.6 – j11.750.6 – j6.92−18.7−23.283.283.982.183.5In hand160.4 – j0.3224.4
+ j11.7−20.5−8.564.562.663.953.8In hand217.0
+ j36.217.7
+ j34.6−3.8−4.135.537.520.923.0HR-EFHCheekHand157.7 – j17.530.1
+ j13.5−15.1−10.625.535.624.732.5Hand222.6
+ j 32.617.9
+ j32.6−5.4−4.314.619.810.412.5TiltHand157.2 –  j13.430.3+14.3−17.0−10.537.944.537.140.5Hand219.6
+ j32.915.4
+ j33.9−4.7−3.619.427.412.815.5Table 5
Computational results of the
antenna input impedance,Zin,|S11| in dB, radiation
efficiency, ηrad, and total efficiency, ηtot, for different handset setups at 1800 MHz.
ParameterFrequency/1800 MHzZin (Ohm)|S11| (dB)ηrad (%)ηtot (%)Handset modelA1A2A1A2A1A2A1A2No
headIn free space38.7 + j9.9238.7 + j9.92−15.5−15.589.889.887.387.3In hand138.5 + j9.0756.2 + j0.82−15.6−24.652.262.150.861.9In hand298.7 + j26.441.7 + j5.52−8.7−19.327.842.424.841.9HR-EFHCheekHand143.9 + j17.961.7 + j18.1−14.1−14.417.530.116.829.0Hand2106 + j47.245.6 + j16.3−7.0−15.29.620.07.619.4TiltHand143.7 + j22.564.1 + j22.0−12.3−13.020.130.118.928.6Hand2106 + j50.344.5 + j18.2−6.8−14.111.119.18.818.3Handset modelB1B2B1B2B1B2B1B2No
headIn free space33.3 – j9.9738.9 – j8.72−12.7−16.090.086.485.184.2In hand136.7 – j6.1358.7
+ j23.3−15.5−13.054.041.252.439.1In hand249.2
+ j36.542.9
+ j6.88−9.2−19.531.137.227.436.7HR-EFHCheekHand137.9
+ j7.6461.1
+ j25.5−15.8−12.322.922.922.321.5Hand248.6
+ j52.052.8
+ j6.65−6.6−23.115.613.912.213.8TiltHand132.9 – j1.2559.3
+ j24.9−13.6−12.524.426.523.325.0Hand242.0
+ j41.440.3
+ j9.6−7.6−16.517.722.314.621. 8Table 6
Computational results of the
antenna input impedance,Zin,|S11| in dB, radiation
efficiency, ηrad, and total efficiency, ηtot, for different handset setups at 2025 MHz.
ParameterFrequency/2025 MHzZin (Ohm)|S11| (dB)ηrad (%)ηtot (%)Handset modelA1A2A1A2A1A2A1A2No headIn free space41.8 + j12.341.8 + j12.3−15.9−15.992.092.089.689.6In hand137.6 + j11.249.4 + j2.06−14.4−33.355.465.553.565.4In hand272.4 + j28.436.4 + j10.1−10.8−14.232.046.129.344.3HR-EFHCheekHand142.3 + j16.861.5 + j8.64−14.1−17.819.132.018.431.4Hand282.8 + j40.945.4 + j17.0−8.5−14.810.519.09.018.3TiltHand143.6 + j20.960.1 + j9.4−12.8−18.122.333.021.132.5Hand282.1 + j44.645.7 + j18.1−8.1−14.411.920.110.119.3Handset modelB1B2B1B2B1B2B1B2No headIn free space42.7 – j1.8045.5
+ j4.0−21.8−23.994.694.094.093.6In hand149.4 – j0.3370.1
+ j36.5−43.1−9.667.032.867.029.2In hand273.4
+ j62.750.6
+ j25.3−6.3−12.233.038.625.336.3HR-EFHCheekHand149.9
+ j5.5073.2
+ j38.6−25.2−9.126.816.726.714.6Hand274.5
+ j75.059.3
+ J21.1−5.3−13.712.016.68.515.4TiltHand140.7
+ j2.9272.6
+ j37.6−19.3−9.328.820.928.518.5Hand263.4
+ J67.550.4
+ j38.6−5.6−9.114.225.010.323.2The three-dimensional far-field radiation patterns of the handset
model-A1 in free space, in hand1 close to SAM and in hand1 close to HR-EFH at
900, 1800, and 2025 MHz.
(a)
Model-A1 in free-space, 900 MHz(b)
Model-A1 in free-space, 1800 MHz(c)
Model-A1 in free-space, 2025 MHz(d)
Model-A1 in hand1 close to SAM,cheek-position, 900 MHz(e)
Model-A1 in hand1 close to SAM,cheek-position, 1800 MHz(f)
Model-A1 in hand1 close to SAM,cheek-position, 2025 MHz(g)
Model-A1 in hand1 close to
HR-EFH,cheek-position, 900 MHz(h)
Model-A1 in hand1 close to
HR-EFH,cheek-position, 1800 MHz(i)
Model-A1 in hand1 close to
HR-EFH,cheek-position, 2025 MHzThe three-dimensional far-field radiation beam patterns of the handset
model-B1 in free space, in hand1 close to SAM and in hand1 close to HR-EFH at
900, 1800, and 2025 MHz.
(a)
Model-B1 in free-space, 900 MHz(b)
Model-B1 in free-space, 1800 MHz(c)
Model-B1 in free-space, 2025 MHz(d)
Model-B1 in hand1 close to SAM,cheek-position, 900 MHz(e)
Model-B1 in hand1 close to SAM,cheek-position, 1800 MHz(f)
Model-B1 in hand1 close to SAM,cheek-position, 2025 MHz(g)
Model-B1 in hand1 close to
HR-EFH,cheek-position, 900 MHz(h)
Model-B1 in hand1 close to
HR-EFH,cheek-position, 1800 MHz(i)
Model-B1 in hand1 close to
HR-EFH,cheek-position, 2025 MHz


### 4.2. Total Isotropic Sensitivity

The TIS
is a measure of the handset receiving performance, where both TIS and total
radiated power (TRP) together determine effectiveness of the handset as a piece
of radio equipment, in particular, the maximum range at which the handset can
operate from the base station with some given level of performance [35]. As
compared with the normal receiver sensitivity in GSM900, a typical
specification for the TIS is around 10-dB higher in talk position [36]. The TIS
can be measured in reverberation chamber with a definition formula given in
[37]. In [38], the sensitivity of a commercially available GSM900 phone in
receiving mode was measured in reverberation chamber for different handset
setups, that is, in free space and against head phantom. Using SEMCAD X, the computed TIS values for
the proposed handset models under different usage patterns are computed as listed
in Table 7.Table 7
The total isotropic sensitivity
(TIS) levels of the handset models for different setups at 900, 1800, and 2025 MHz.
TIS (dBm)900 MHz1800 MHz2025 MHzHandset modelA1A2A1A2A1A2In free space−104.9−104.9−105.4−105.4−105.5−105.5In hand1−103.6−103.8−103.1−103.9−103.3−104.2In hand2−100.3−101.6−99.8−102.2−100.7−102.5HR−EFHCheekHand1−98.7−99.2−98.3−100.6−98.7−101.0Hand2−95.4−96.3−94.9−98.9−95.6−98.6TiltHand1−100.6−100.9−98.8−100.6−99.3−101.1Hand2−97.4−98.3−95.5−98.7−96.0−98.9Handset modelB1B2B1B2B1B2In free space−105.2−105.2−105.3−105.3−105.7−105.7In hand1−104.2−103.3−103.2−101.9−104.3−100.7In hand2−99.1−99.6−100.4−101.7−100−101.6HR-EFHCheekHand1−100−101.1−99.5−99.3−100.3−97.
7Hand2−96.2−97.0−96.9−97.4−95.2−97.
9TiltHand1−101.7−102.1−99.7−100−100.6−98.7Hand2−97.1−97.9−97.7−99.4−96.2−99.
7


### 4.3. Sar and Power Absorption Computation in Tissue

The influence
of the EM wave irradiation on the living body is measured by evaluating the SAR,
where SAR is defined as the amount of EM energy absorption in the unit mass as
follows [39]: (5)SAR=σEρ|E|2. Here, σE (S/m) represents
the electric conductivity, E (V/m) the rms electric
field strength, and ρ (kg/m3)
the mass density of the tissue. An algorithm based on SCC34/SC2/WG2
computational dosimetry (IEEE-1529 [40]), the spatial-peak SAR(x,y,z,f0) can be computed over any required mass by using SEMCAD X platform.The spatial-peak SAR should be evaluated in a cubical volume of the body
tissues that is within 5% of the required mass [27]. The averaged-peak SAR (spatial-peak
SAR [IEEE-1529]) can be specified over a cube of 1 g and 10 g mass, and
normalized to a certain source power. Referred to the IEEE standard C95.1b-2004
[41] (for low-power devices, uncontrolled environment), the antenna input power is set as 0.6 W at 900 MHz and 0.125 W
at both 1800 and 2025 MHz for all handset setups.The computed values of the peak SAR (averaged
over 1 g and 10 g) and power absorption in tissues owing to handsets exposure in
different conditions at 900, 1800, and 2025 MHz are listed in Tables8, 9, and
10, respectively.Table 8
Pooled statistics of peak 1 and
10 g SAR in tissues, radiated power, absorbed power in tissues, dielectric loss,
and power budget error for the handset models in hand closed to HR-EFH at
different positions operating at 900 MHz.
Handset modelFrequency/900 MHzA1A2B1B2Hand positionhand1hand2hand1hand2hand1hand2hand1hand2Antenna input power (mW)600600600600600600600600Cheek-positionSAR1g in head (W/kg)3.382.522.772.514.873.232.213.07SAR10g in head (W/kg)1.901.762.011.942.522.371.742.42SAR1g in hand (W/kg)1.545.161.463.620.796.374.065.47Radiated power (mW)111.051.6125.963.4148.662.6194.875.2Absorbed power in head (mW)250.4209.1247.3214.7280.3229.3183.3245.3Absorption rate in head (%)41.734.841.235.
846.738.230.540.
9Absorbed power in hand (mW)97.5208.386.4182.648.6260.2146.2229.8Dielectric loss (mW)135.0119.6134.5131.5115.636.163.736.9Power budget error (%)1.011.900.981.301.151.941.992.13Tilt-positionSAR1g in head (W/kg)2.611.992.041.903.192.040.911.52SAR10g in head (W/kg)1.100.971.171.101.451.360.731.20SAR1g in hand (W/kg)1.865.111.724.401.127.004.257.30Radiated power (mW)174.481.9184.3101.4222.776.9243.393.1Absorbed power in head (mW)184.6159.2185.3160.6193.8195.6130.3166.0Absorption rate in head (%)30.826.530.926.832.332.621.727.7Absorbed power in hand (mW)114.0237.199.4213.577.0280.0159.0291.4Dielectric loss (mW)122.5110.0126.2117.3104.835.063.938.7Power budget error (%)0.751.970.801.190.282.080.581.80Table 9
Pooled statistics of peak 1 and
10 g SAR in tissues, radiated power, absorbed power in tissues, dielectric loss,
and power budget error for the handset models in hand closed to HR-EFH at
different positions operating at 1800 MHz.
Handset modelFrequency/1800 MHzA1A2B1B2Hand positionhand1hand2hand1hand2hand1hand2hand1hand2Antenna input power (mW)125125125125125125125125Cheek-positionSAR1g in head (W/kg)1.480.851.161.102.671.810.841.49SAR10g in head (W/kg)0.660.410.670.551.740.850.510.90SAR1g in hand (W/kg)1.283.871.212.010.841.821.651.06Radiated power (mW)21.09.5536.224.227.915.326.917.3Absorbed power in head (mW)53.736.245.738.961.744.627.847.7Absorption rate in head (%)43.029.036.631.249.435.722.338.2Absorbed power in hand (mW)36.663.931.150.024.358.260.847.0Dielectric loss (mW)13.412.811.811.410.95.309.3012.3Power budget error (%)0.182.000.160.330.101.270.120.58Tilt-positionSAR1g in head (W/kg)1.540.890.931.062.461.660.420.77SAR10g in head (W/kg)0.600.350.530.491.100.720.260.45SAR1g in hand (W/kg)1.253.801.602.241.122.171.941.36Radiated power (mW)23.611.035.722.929.218.331.327.2Absorbed power in head (mW)50.535.742.436.152.237.917.426.8Absorption rate in head (%)40.428.634.028.941.830.413.921.4Absorbed power in hand (mW)37.063.134.253.629.760.365.158.0Dielectric loss (mW)13.212.712.011.413.66.4610.612.8Power budget error (%)0.441.960.540.740.211.620.450.17Table 10
Pooled statistics of peak 1 and 10 g SAR in tissues, radiated power,
absorbed power in tissues, dielectric loss, and power budget error for the
handset models in hand closed to HR-EFH at different positions operating at
2025 MHz.
Handset modelFrequency/2025 MHzA1A2B1B2Hand positionhand1hand2hand1hand2hand1hand2hand1hand2Antenna input power (mW)125125125125125125125125Cheek-positionSAR1g in head (W/kg)1.851.091.391.643.782.400.711.32SAR10g in head (W/kg)0.770.500.770.781.701.150.430.80SAR1g in hand (W/kg)2.124.101.981.950.582.101.832.17Radiated power (mW)23.011.339.322.933.410.618.319.2Absorbed power in head (mW)53.736.744.843.768.649.426.044.0Absorption rate in head (%)43.029.335.835.054.939.520.835.2Absorbed power in hand (mW)36.764.430.047.314.559.368.051.0Dielectric loss (mW)11.010.010.710.88.003.1010.410.0Power budget error (%)0.482.000.140.120.362.061.860.62Tilt-positionSAR1g in head (W/kg)1.911.151.171.583.802.200.380.71SAR10g in head (W/kg)0.670.420.600.691.540.930.230.40SAR1g in hand (W/kg)2.174.182.311.980.922.162.102.72Radiated power (mW)26.412.640.624.235.612.923.129.0Absorbed power in head (mW)50.735.040.840.159.043.217.626.2Absorption rate in head (%)40.628.032.632.047.234.
614.121.0Absorbed power in hand (mW)36.864.932.950.122.062.771.558.0Dielectric loss (mW)10.89.89.810.28.23.610.69.8Power budget error (%)0.182.120.70.380.132.061.781.60Figures7 and 8 indicate the sliced-distribution
of the averaged-peak SAR1g in the HR-EFH tissues exposed to EM
radiation of handset models-A1 and A2 under different usage patterns at 900 and
1800 MHz, respectively, whereas, Figures 9 and 10 indicate the sliced-distribution
of the averaged peak SAR1g due to handset models-B1 and B2 exposure under
the same usage patterns at 900 and 1800 MHz, respectively.Sliced distribution of the averaged-peakSAR1g in the
yz-plane, normalized to 0.6 W input power, of the HR-EFH at different positions
due to the exposure at 900 MHz of (a) handset model-A1 and (b) handset
model-A2.
(a)(b)Sliced distribution of the averaged-peakSAR1g in the
yz-plane, normalized to 0.125 W input power, of the HR-EFH at different
positions due to the exposure at 1800 MHz of (a) handset model-A1 and (b)
handset model-A2.
(a)(b)Sliced distribution of the averaged-peakSAR1g in the
yz-plane, normalized to 0.6 W input power, of the HR-EFH at different positions
due to the exposure at 900 MHz of (a) handset model-B1 and (b) handset
model-B2.
(a)(b)Sliced distribution of the averaged-peakSAR1g in the
yz-plane, normalized to 0.125 W input power, of the HR-EFH at different
positions due to the exposure at 1800 MHz of (a) handset model-B1 and (b)
handset model-B2.
(a)(b)


## 4.1. Antenna Performance

The results in Table4 show the computed antenna
parameters including Zin, |S11| in dB, ηrad, and ηtot of the handset models at 900 MHz under
different usage patterns in a presence of HR-EFH model, whereas the results in Tables 5 and 6 show the antenna
parameters at 1800 and 2025 MHz, respectively. The ηtot is given by (3)ηtot=ηmisηrad, where ηmis represents the mismatch efficiency and equal
to (4)ηmis=(1−|S11|2). Figure 5 illustrates the 3D far-field radiation
pattern of the handset model-A1 in free space as well as in hand1 close to head
(SAM and HR-EFH) at cheek position
and operating at 900, 1800, and 2025 MHz, whereas Figure 6 illustrates the 3D far-field
radiation pattern of the handset model-B1 in the same conditions. In both
Figures 5 and 6, the antenna feeding source position considered as the origin
of the antenna pattern coordinate system, that is, x=0,y=0,andz=0mm.Table 4
Computational results of the
antenna input impedance,Zin,|S11| in dB, radiation efficiency, ηrad, and total efficiency, ηtot, for different handset setups at 900 MHz.
ParameterFrequency/900 MHzZin (Ohm)|S11| (dB)ηrad (%)ηtot (%)Handset modelA1A2A1A2A1A2A1A2No
headIn free space44.5
+ j0.8644.5
+ j0.86−24.4−24.477.877.877.677.6In hand149.2
− j8.1751.3
− j9.55−21.6−20.589.860.387.259.8In hand278.5
+ j37.458.36
− j3.5−9.1−21.530.736.526.936.3HR-EFHCheekHand142.7
+ j4.6342.6
+ j4.27−20.6−20.818.721.218.521.0Hand257.7
+ j46.944.1
+ j10.9−7.9−17.610.310.78.6010.6TiltHand148.1
+ j2.2547.0
− j0.49−30.4−30.129.130.729.130.7Hand266.7
+ j46.752.2
+ j10.1−8.1−19.916.217.113.616.9Handset modelB1B2B1B2B1B2B1B2No
headIn free space49.6 – j11.750.6 – j6.92−18.7−23.283.283.982.183.5In hand160.4 – j0.3224.4
+ j11.7−20.5−8.564.562.663.953.8In hand217.0
+ j36.217.7
+ j34.6−3.8−4.135.537.520.923.0HR-EFHCheekHand157.7 – j17.530.1
+ j13.5−15.1−10.625.535.624.732.5Hand222.6
+ j 32.617.9
+ j32.6−5.4−4.314.619.810.412.5TiltHand157.2 –  j13.430.3+14.3−17.0−10.537.944.537.140.5Hand219.6
+ j32.915.4
+ j33.9−4.7−3.619.427.412.815.5Table 5
Computational results of the
antenna input impedance,Zin,|S11| in dB, radiation
efficiency, ηrad, and total efficiency, ηtot, for different handset setups at 1800 MHz.
ParameterFrequency/1800 MHzZin (Ohm)|S11| (dB)ηrad (%)ηtot (%)Handset modelA1A2A1A2A1A2A1A2No
headIn free space38.7 + j9.9238.7 + j9.92−15.5−15.589.889.887.387.3In hand138.5 + j9.0756.2 + j0.82−15.6−24.652.262.150.861.9In hand298.7 + j26.441.7 + j5.52−8.7−19.327.842.424.841.9HR-EFHCheekHand143.9 + j17.961.7 + j18.1−14.1−14.417.530.116.829.0Hand2106 + j47.245.6 + j16.3−7.0−15.29.620.07.619.4TiltHand143.7 + j22.564.1 + j22.0−12.3−13.020.130.118.928.6Hand2106 + j50.344.5 + j18.2−6.8−14.111.119.18.818.3Handset modelB1B2B1B2B1B2B1B2No
headIn free space33.3 – j9.9738.9 – j8.72−12.7−16.090.086.485.184.2In hand136.7 – j6.1358.7
+ j23.3−15.5−13.054.041.252.439.1In hand249.2
+ j36.542.9
+ j6.88−9.2−19.531.137.227.436.7HR-EFHCheekHand137.9
+ j7.6461.1
+ j25.5−15.8−12.322.922.922.321.5Hand248.6
+ j52.052.8
+ j6.65−6.6−23.115.613.912.213.8TiltHand132.9 – j1.2559.3
+ j24.9−13.6−12.524.426.523.325.0Hand242.0
+ j41.440.3
+ j9.6−7.6−16.517.722.314.621. 8Table 6
Computational results of the
antenna input impedance,Zin,|S11| in dB, radiation
efficiency, ηrad, and total efficiency, ηtot, for different handset setups at 2025 MHz.
ParameterFrequency/2025 MHzZin (Ohm)|S11| (dB)ηrad (%)ηtot (%)Handset modelA1A2A1A2A1A2A1A2No headIn free space41.8 + j12.341.8 + j12.3−15.9−15.992.092.089.689.6In hand137.6 + j11.249.4 + j2.06−14.4−33.355.465.553.565.4In hand272.4 + j28.436.4 + j10.1−10.8−14.232.046.129.344.3HR-EFHCheekHand142.3 + j16.861.5 + j8.64−14.1−17.819.132.018.431.4Hand282.8 + j40.945.4 + j17.0−8.5−14.810.519.09.018.3TiltHand143.6 + j20.960.1 + j9.4−12.8−18.122.333.021.132.5Hand282.1 + j44.645.7 + j18.1−8.1−14.411.920.110.119.3Handset modelB1B2B1B2B1B2B1B2No headIn free space42.7 – j1.8045.5
+ j4.0−21.8−23.994.694.094.093.6In hand149.4 – j0.3370.1
+ j36.5−43.1−9.667.032.867.029.2In hand273.4
+ j62.750.6
+ j25.3−6.3−12.233.038.625.336.3HR-EFHCheekHand149.9
+ j5.5073.2
+ j38.6−25.2−9.126.816.726.714.6Hand274.5
+ j75.059.3
+ J21.1−5.3−13.712.016.68.515.4TiltHand140.7
+ j2.9272.6
+ j37.6−19.3−9.328.820.928.518.5Hand263.4
+ J67.550.4
+ j38.6−5.6−9.114.225.010.323.2The three-dimensional far-field radiation patterns of the handset
model-A1 in free space, in hand1 close to SAM and in hand1 close to HR-EFH at
900, 1800, and 2025 MHz.
(a)
Model-A1 in free-space, 900 MHz(b)
Model-A1 in free-space, 1800 MHz(c)
Model-A1 in free-space, 2025 MHz(d)
Model-A1 in hand1 close to SAM,cheek-position, 900 MHz(e)
Model-A1 in hand1 close to SAM,cheek-position, 1800 MHz(f)
Model-A1 in hand1 close to SAM,cheek-position, 2025 MHz(g)
Model-A1 in hand1 close to
HR-EFH,cheek-position, 900 MHz(h)
Model-A1 in hand1 close to
HR-EFH,cheek-position, 1800 MHz(i)
Model-A1 in hand1 close to
HR-EFH,cheek-position, 2025 MHzThe three-dimensional far-field radiation beam patterns of the handset
model-B1 in free space, in hand1 close to SAM and in hand1 close to HR-EFH at
900, 1800, and 2025 MHz.
(a)
Model-B1 in free-space, 900 MHz(b)
Model-B1 in free-space, 1800 MHz(c)
Model-B1 in free-space, 2025 MHz(d)
Model-B1 in hand1 close to SAM,cheek-position, 900 MHz(e)
Model-B1 in hand1 close to SAM,cheek-position, 1800 MHz(f)
Model-B1 in hand1 close to SAM,cheek-position, 2025 MHz(g)
Model-B1 in hand1 close to
HR-EFH,cheek-position, 900 MHz(h)
Model-B1 in hand1 close to
HR-EFH,cheek-position, 1800 MHz(i)
Model-B1 in hand1 close to
HR-EFH,cheek-position, 2025 MHz


## 4.2. Total Isotropic Sensitivity

The TIS
is a measure of the handset receiving performance, where both TIS and total
radiated power (TRP) together determine effectiveness of the handset as a piece
of radio equipment, in particular, the maximum range at which the handset can
operate from the base station with some given level of performance [35]. As
compared with the normal receiver sensitivity in GSM900, a typical
specification for the TIS is around 10-dB higher in talk position [36]. The TIS
can be measured in reverberation chamber with a definition formula given in
[37]. In [38], the sensitivity of a commercially available GSM900 phone in
receiving mode was measured in reverberation chamber for different handset
setups, that is, in free space and against head phantom. Using SEMCAD X, the computed TIS values for
the proposed handset models under different usage patterns are computed as listed
in Table 7.Table 7
The total isotropic sensitivity
(TIS) levels of the handset models for different setups at 900, 1800, and 2025 MHz.
TIS (dBm)900 MHz1800 MHz2025 MHzHandset modelA1A2A1A2A1A2In free space−104.9−104.9−105.4−105.4−105.5−105.5In hand1−103.6−103.8−103.1−103.9−103.3−104.2In hand2−100.3−101.6−99.8−102.2−100.7−102.5HR−EFHCheekHand1−98.7−99.2−98.3−100.6−98.7−101.0Hand2−95.4−96.3−94.9−98.9−95.6−98.6TiltHand1−100.6−100.9−98.8−100.6−99.3−101.1Hand2−97.4−98.3−95.5−98.7−96.0−98.9Handset modelB1B2B1B2B1B2In free space−105.2−105.2−105.3−105.3−105.7−105.7In hand1−104.2−103.3−103.2−101.9−104.3−100.7In hand2−99.1−99.6−100.4−101.7−100−101.6HR-EFHCheekHand1−100−101.1−99.5−99.3−100.3−97.
7Hand2−96.2−97.0−96.9−97.4−95.2−97.
9TiltHand1−101.7−102.1−99.7−100−100.6−98.7Hand2−97.1−97.9−97.7−99.4−96.2−99.
7


## 4.3. Sar and Power Absorption Computation in Tissue

The influence
of the EM wave irradiation on the living body is measured by evaluating the SAR,
where SAR is defined as the amount of EM energy absorption in the unit mass as
follows [39]: (5)SAR=σEρ|E|2. Here, σE (S/m) represents
the electric conductivity, E (V/m) the rms electric
field strength, and ρ (kg/m3)
the mass density of the tissue. An algorithm based on SCC34/SC2/WG2
computational dosimetry (IEEE-1529 [40]), the spatial-peak SAR(x,y,z,f0) can be computed over any required mass by using SEMCAD X platform.The spatial-peak SAR should be evaluated in a cubical volume of the body
tissues that is within 5% of the required mass [27]. The averaged-peak SAR (spatial-peak
SAR [IEEE-1529]) can be specified over a cube of 1 g and 10 g mass, and
normalized to a certain source power. Referred to the IEEE standard C95.1b-2004
[41] (for low-power devices, uncontrolled environment), the antenna input power is set as 0.6 W at 900 MHz and 0.125 W
at both 1800 and 2025 MHz for all handset setups.The computed values of the peak SAR (averaged
over 1 g and 10 g) and power absorption in tissues owing to handsets exposure in
different conditions at 900, 1800, and 2025 MHz are listed in Tables8, 9, and
10, respectively.Table 8
Pooled statistics of peak 1 and
10 g SAR in tissues, radiated power, absorbed power in tissues, dielectric loss,
and power budget error for the handset models in hand closed to HR-EFH at
different positions operating at 900 MHz.
Handset modelFrequency/900 MHzA1A2B1B2Hand positionhand1hand2hand1hand2hand1hand2hand1hand2Antenna input power (mW)600600600600600600600600Cheek-positionSAR1g in head (W/kg)3.382.522.772.514.873.232.213.07SAR10g in head (W/kg)1.901.762.011.942.522.371.742.42SAR1g in hand (W/kg)1.545.161.463.620.796.374.065.47Radiated power (mW)111.051.6125.963.4148.662.6194.875.2Absorbed power in head (mW)250.4209.1247.3214.7280.3229.3183.3245.3Absorption rate in head (%)41.734.841.235.
846.738.230.540.
9Absorbed power in hand (mW)97.5208.386.4182.648.6260.2146.2229.8Dielectric loss (mW)135.0119.6134.5131.5115.636.163.736.9Power budget error (%)1.011.900.981.301.151.941.992.13Tilt-positionSAR1g in head (W/kg)2.611.992.041.903.192.040.911.52SAR10g in head (W/kg)1.100.971.171.101.451.360.731.20SAR1g in hand (W/kg)1.865.111.724.401.127.004.257.30Radiated power (mW)174.481.9184.3101.4222.776.9243.393.1Absorbed power in head (mW)184.6159.2185.3160.6193.8195.6130.3166.0Absorption rate in head (%)30.826.530.926.832.332.621.727.7Absorbed power in hand (mW)114.0237.199.4213.577.0280.0159.0291.4Dielectric loss (mW)122.5110.0126.2117.3104.835.063.938.7Power budget error (%)0.751.970.801.190.282.080.581.80Table 9
Pooled statistics of peak 1 and
10 g SAR in tissues, radiated power, absorbed power in tissues, dielectric loss,
and power budget error for the handset models in hand closed to HR-EFH at
different positions operating at 1800 MHz.
Handset modelFrequency/1800 MHzA1A2B1B2Hand positionhand1hand2hand1hand2hand1hand2hand1hand2Antenna input power (mW)125125125125125125125125Cheek-positionSAR1g in head (W/kg)1.480.851.161.102.671.810.841.49SAR10g in head (W/kg)0.660.410.670.551.740.850.510.90SAR1g in hand (W/kg)1.283.871.212.010.841.821.651.06Radiated power (mW)21.09.5536.224.227.915.326.917.3Absorbed power in head (mW)53.736.245.738.961.744.627.847.7Absorption rate in head (%)43.029.036.631.249.435.722.338.2Absorbed power in hand (mW)36.663.931.150.024.358.260.847.0Dielectric loss (mW)13.412.811.811.410.95.309.3012.3Power budget error (%)0.182.000.160.330.101.270.120.58Tilt-positionSAR1g in head (W/kg)1.540.890.931.062.461.660.420.77SAR10g in head (W/kg)0.600.350.530.491.100.720.260.45SAR1g in hand (W/kg)1.253.801.602.241.122.171.941.36Radiated power (mW)23.611.035.722.929.218.331.327.2Absorbed power in head (mW)50.535.742.436.152.237.917.426.8Absorption rate in head (%)40.428.634.028.941.830.413.921.4Absorbed power in hand (mW)37.063.134.253.629.760.365.158.0Dielectric loss (mW)13.212.712.011.413.66.4610.612.8Power budget error (%)0.441.960.540.740.211.620.450.17Table 10
Pooled statistics of peak 1 and 10 g SAR in tissues, radiated power,
absorbed power in tissues, dielectric loss, and power budget error for the
handset models in hand closed to HR-EFH at different positions operating at
2025 MHz.
Handset modelFrequency/2025 MHzA1A2B1B2Hand positionhand1hand2hand1hand2hand1hand2hand1hand2Antenna input power (mW)125125125125125125125125Cheek-positionSAR1g in head (W/kg)1.851.091.391.643.782.400.711.32SAR10g in head (W/kg)0.770.500.770.781.701.150.430.80SAR1g in hand (W/kg)2.124.101.981.950.582.101.832.17Radiated power (mW)23.011.339.322.933.410.618.319.2Absorbed power in head (mW)53.736.744.843.768.649.426.044.0Absorption rate in head (%)43.029.335.835.054.939.520.835.2Absorbed power in hand (mW)36.764.430.047.314.559.368.051.0Dielectric loss (mW)11.010.010.710.88.003.1010.410.0Power budget error (%)0.482.000.140.120.362.061.860.62Tilt-positionSAR1g in head (W/kg)1.911.151.171.583.802.200.380.71SAR10g in head (W/kg)0.670.420.600.691.540.930.230.40SAR1g in hand (W/kg)2.174.182.311.980.922.162.102.72Radiated power (mW)26.412.640.624.235.612.923.129.0Absorbed power in head (mW)50.735.040.840.159.043.217.626.2Absorption rate in head (%)40.628.032.632.047.234.
614.121.0Absorbed power in hand (mW)36.864.932.950.122.062.771.558.0Dielectric loss (mW)10.89.89.810.28.23.610.69.8Power budget error (%)0.182.120.70.380.132.061.781.60Figures7 and 8 indicate the sliced-distribution
of the averaged-peak SAR1g in the HR-EFH tissues exposed to EM
radiation of handset models-A1 and A2 under different usage patterns at 900 and
1800 MHz, respectively, whereas, Figures 9 and 10 indicate the sliced-distribution
of the averaged peak SAR1g due to handset models-B1 and B2 exposure under
the same usage patterns at 900 and 1800 MHz, respectively.Sliced distribution of the averaged-peakSAR1g in the
yz-plane, normalized to 0.6 W input power, of the HR-EFH at different positions
due to the exposure at 900 MHz of (a) handset model-A1 and (b) handset
model-A2.
(a)(b)Sliced distribution of the averaged-peakSAR1g in the
yz-plane, normalized to 0.125 W input power, of the HR-EFH at different
positions due to the exposure at 1800 MHz of (a) handset model-A1 and (b)
handset model-A2.
(a)(b)Sliced distribution of the averaged-peakSAR1g in the
yz-plane, normalized to 0.6 W input power, of the HR-EFH at different positions
due to the exposure at 900 MHz of (a) handset model-B1 and (b) handset
model-B2.
(a)(b)Sliced distribution of the averaged-peakSAR1g in the
yz-plane, normalized to 0.125 W input power, of the HR-EFH at different
positions due to the exposure at 1800 MHz of (a) handset model-B1 and (b)
handset model-B2.
(a)(b)


## 5. Power Budget Error

The power
budget error is defined as(6)Powerbudgeterror=|Pin−(Prad+Pabs+PLoss)|Pin,(7)PLoss=Pd+Pc, where Pin is
the input power, Prad the
radiation power, Pabs the
absorbed power in tissues, and PLoss the
total power loss. PLoss includes
the dielectric loss Pd and the
metallic ohmic-loss Pc. Since all metal parts are considered as PEC
in simulations, thus Pc=0 and PLoss=Pd. However, (6) was defined by [21, 22, 42] as the computation error. Even with (6) equals zero, numerical errors,
and geometry errors could be still inherent to the numerical analysis. Tables 8–10 list the power
budget error values for both handset types in different conditions and at
different frequencies.


## 6. Discussion

The hand impact on the EM interaction between
handset antennas and human is investigated profoundly in this paper. Owing to
hand-hold alteration under different usage patterns, handsets with external and
internal antennas show a significant deviation in their performance as well as
in their EM radiation impact on head. Although the user’s hand has a negative
impact on the antenna performance of a handset in-use, changing its position
may reduce the amount of the SAR and power absorption in head tissues.


### 6.1. Antenna Performance

The results listed in Tables4–7 manifest that
the hand-hold position has a considerable impact on the handset antenna
matching, antenna radiation efficiency, and the TIS. The impact of hand at
different positions on the antenna performance (excluding the TIS) was already
presented by [12, 14, 16, 22, 23]. However, this impact may vary depending on
many factors, that is, antenna type/position, handset position with respect to
head, and the operating frequency, concluded as follows.(1) The significant degradation in internal patch antenna
performance due to the different hand positions, as compared with the external
antenna, is because the patch antenna is sandwiched between hand and head
tissues during the practical usage, where the hand tissues act as the antenna
upper dielectric layers. This may shift the tuning frequency as well as
decrease the radiation efficiency.(2) Based on the relation between the
absolute difference in antenna total efficiency due to hand-hold alteration
(from hand1 to hand2) and the antenna/handset position, as shown in Figure11, internal
antenna exhibits more variation in total efficiency values than external
antenna. The maximum absolute difference (25%) is recorded at 900 MHz for
model-B2 against HR-EFH at tilt position. The direction of arrows shown in Figure 11 indicates whether the
total efficiency increases (↑) or decreases (↓) while shifting the hand from
hand1 to hand2. This arrow's indication is also applicable for the TIS and SAR
in Figures 12 and 13, respectively.Absolute difference in the antenna total efficiency owing to hand-hold alteration
at different antenna/handset positions against HR-EFH in GSM900, GSM1800, and
UMTS/IMT-2000 bands.
(a)
Models-A1 and A2 against HR-EFH(b)
Models-B1 and B2 against HR-EFHAbsolute difference in the TIS levels owing to hand-hold alteration at
different antenna/handset positions against HR-EFH in GSM900, GSM1800, and
UMTS/IMT-2000 bands.
(a)
Models-A1 and A2 against HR-EFH(b)
Models-B1 and B2 against HR-EFHPercentage difference in the averaged-peakSAR1g values in
HR-EFH, owing to hand-hold alteration, at different antenna/handset positions in
GSM900, GSM1800, and UMTS/IMT2000 bands.
(a)
Models-A1 and A2 against HR-EFH(b)
Models-B1 and B2 against HR-EFH(3) Although the interference of the
external noisy components (i.e., display and camera, as well as their
associated feed circuits) is not considered in simulation, the drop in TIS
specification of handsets while in-use, as shown in Table7, is caused by
antenna total efficiency decrease due to hand impact. Simulating the handsets
having external antennas, the maximum TIS level of −94.9 dBm is obtained for
model-A1 in hand2 against HR-EFH at cheek position operating at 1800 MHZ, where a minimum total efficiency of 7.6% is recorded, whereas simulating
the handsets having internal antennas, the maximum TIS level of −95.2 dBm is
obtained for model-B1 in hand2 against HR-EFH at cheek position
operating at 2025 MHZ, where a minimum total efficiency of 8.5% is recorded. It
is obvious that the maximum TIS level is around 10 dB higher for the above-mentioned
handsets while in-use, as compared with them in free space.(4) Figure12 illustrates the
absolute difference in TIS levels due to hand-hold alteration at different
antenna/handset positions against the HR-EFH as depicted in Table 7. It is
vivid that handsets with internal antennas exhibit more variation in their TIS
levels than handsets with external antennas, where a maximum difference (5.1 dBm) is recorded at 2025 MHz for model-B1 at cheek position. A maximum difference (5.1 dBm) is also recorded due
to the hand-hold alteration at 900 MHz for model-B1 just in hand.(5) Figures11 and 12 demonstrate that hand2 always has
more impact on antenna performance including the TIS than hand1, except for
model-B2 against HR-EFH at cheek and tilt positions, while operating at 2025 MHz.


### 6.2. Sar and Power Loss in Tissues

Tables8–10 reveal that due
to the exposure of the handset in hand close to HR-EFH at different positions
and operating frequencies, both the averaged-peak
SAR1g and power absorption in tissues may vary considerably according
to hand-hold position, observed as follows.(1)
More SAR
variation in HR-EFH tissues is perceived owing to the internal antenna
exposure, as compared with the external antenna exposure. Figure13 shows the
relation of the percentage of spatial-peak SAR1g difference values
in HR-EFH tissues due to hand-hold alteration versus antenna/handset position
at 900, 1800, and 2025 MHz. The percentage difference of SAR in
HR-EFH tissues while shifting the hand from hand1 to hand2 is defined as (8)%DifferenceinSAR=(SARinHR−EFHwithhand2SARinHR−EFHwithhand1−1)×100. A maximum
percentage difference in SAR (86.8%) is recorded for model-B2 at cheek position and operating at 2025 MHz
(Figure 13(b)) which
represents twice the maximum value of that recorded in cases of handsets having
external antenna (Figure 13(a)).(2) The direction of arrows shown in
Figure13(b) indicates that shifting of the hand-hold from hand1 to hand2 may
result in the decrease of spatial-peak SAR1g in HR-EFH tissues if exposed
to model-B1 EM radiation at different positions and frequencies, whereas the
same shift may increase the spatial-peak SAR1g when exposed to
model-B2. This SAR behavior due to the hand-hold shifting is also applicable
when the head exposes  to the EM radiation of handset models-A1 and A2,
respectively, (Figure 13(a)) but with minor difference in some exceptional
cases with model-A2. It is because of the antenna is located on top of the handset and the distance
between its feeding position and the nearest head tissue being almost the same while using
both model-A1 and model-A2.(3) In [12], shifting the hand-hold
from the lower part of the chassis (hand position = 60 mm) to the upper part
(hand position = 0 mm), which is to some extent the same hand-hold alteration proposed
in this study, the spatial-peak SAR1g in head got decreased from 6 W/kg to 4 W/kg at 900 MHz, and from 5.5 W/kg to 3.5 W/kg at 1800 MHz. The
corresponding percentage differences in SAR (8) are −33.3% and −36.3%,
respectively. Although different hand/handset models used in this study, as
compared with those in [12], the above percentage differences in SAR values nearly
coincide with the results drawn in Figure 13(b) for model-B1 at cheek and tilt positions operating at 900 and 1800 MHz. Relative to the head,
the chase in [12] was tilted (74°)from
the vertical and (10°) from the ear toward the cheek.(4) It is clear from Figure13 that
the operating frequency has a considerable effect on the SAR values in head
tissues while shifting the hand-hold with different handset position and
different antenna types/positions. Moreover, the considerable effect of the
frequency change is also noticed in both antenna total efficiency and TIS shown
in Figures 11 and 12, respectively, where this effect appears stronger in
cases of internal antennas than cases of external antennas.(5) The percentage values of power
absorption in head (SAM and HR-EFH) at different antenna/handset positions in
GSM900, GSM1800, and UMTS/IMT-2000 bands are narrated and illustrated in Figure14. The percentage power absorption is given by (9)%Powerabsorptionintissue=Powerabsorptionintissue(W)Antennainputpower(W)×100. Both SAM and HR-EFH absorb more power with
hand1 than with hand2, when exposed to the EM radiation of handset with
external antenna in different conditions. This is also true when the head was exposed to the EM
radiation of the handset with internal antenna model-B1, whereas with model-B2,
head-tissues absorb less power with hand1 than with hand2. It is because both antenna
and its feeding positions are at the upper part of the models-A1, A2, and B1,
and shifting the hand from hand1 to hand2 will cover the antenna, whereas both
antenna and its feeding positions are at the lower part of model-B2 and
shifting the hand from hand1 to hand2 will uncover the patch antenna. Covering
the antenna by user’s hand may increase the power absorption in hand tissues
and decrease it in head tissues.Percentage power absorption in head tissues at different antenna/handset
positions in GSM900, GSM1800, and UMTS/IMT-2000 bands.
(a)
Models-A1 and A2 at 900 MHz(b)
Models-B1 and B2 at 900 MHz(c)
Models-A1 and A2 at 1800 MHz(d)
Models-B1 and B2 at 1800 MHz(e)
Models-A1 and A2 at 2025 MHz(f)
Models-B1 and B2 at 2025 MHz(6) To some context, the power absorption in hand tissues
behaves inversely to that in head.


#### 6.3. Power Loss in Handset Materials

The power loss in handset materials is corresponded
to the dielectric loss (since all the metal parts are considered as PEC in
simulations and consequently the metallic ohmic-loss equal to zero). Tables8–10 give the
dielectric loss values for the twelve handset models in different usage
patterns. Although both handset models with internal and external antennas use
the same material properties for their components and parts, they have
different volumes of dielectric materials and consequently different amounts of
dielectric loss. However, it
is obvious that the hand-hold alteration has a significant effect on the
dielectric loss amount of the handsets having internal antennas, as compared
with the handsets having external antennas; it is because of their different
antenna types and positions. The percentage difference in the dielectric loss
values owing to hand-hold alteration can be defined as (10)%DifferenceinPd=(Pdwithhand2Pdwithhand1−1)×100.The dielectric loss of the
handset with internal antenna gets decreased while shifting the hand from hand1
to hand2, where a maximum percentage difference of −68.8% is recorded at 900 MHz for model-B1 atcheek position,
whereas no more than −11.4% is recorded for model-A1 at the same frequency and
position. The negative sign of the percentage values indicates that hand2 has
more impact than hand1.


#### 6.4. Comparison between Sam and He-Efh Simulation Effects

Many researchers have investigated the SAR in
both SAM- and MRI-based human head due to the handset antennas exposure. Study
by some researchers concluded that SAM underestimates SAR in adult MRI-based head,
whereas, some other researchers concluded that SAM overestimates SAR in MRI-based adult head.
Simultaneously, some researchers have presented mixed results. Light has been shed
in detail on all these three states in [34] indicating the potential causes of
discrepancies.The simulations carried out in
this work bring to light SAR difference in SAM and HR-EFH as explained here. According
to the adopted handset positions with respect to head, inclusion of the pinna
in the 1 and 10 g SAR averaging volumes for the HR-EFH and the database used to
define the tissues parameters, the SAM has always been found underestimating
SAR in HR-EFH by a factor ranging from 1.0 to 2.0, with the exception of the
handset models being atcheek positions and operating at 900 MHz, where SAM overestimates SAR in HR-EFH by a
factor ranging from 1.0 to 1.4. The SAR results and its behavior in both SAM
and HR-EFH owing to handsets exposure at different setups coincide with those presented
by the (IEEE SCC-34/SC-2/WG-2) [34] while considering all tissue including the
pinna for the MRI-based adult head.SAM and HR-EFH get different
SAR values and absorb different amount of powers because of the differences
between their volumes, masses, and homogeneities. The volume and mass of the
SAM phantom are approximately 5825cm3 and 6.018 kg (considering a
homogeneous density of 1030 kg/m3), respectively, whereas, volume
and mass of the HR-EFH model are approximately 4063cm3 and 4.7158 kg,
respectively. The accuracy of volume and mass calculation depends on the
FDTD-grid spatial resolution and number of cells.Figures5 and 6 expose an
inconsiderable difference in the antenna far-field radiation pattern because of
the presence of heterogeneous head tissues (HR-EFH), as compared to the
homogeneous tissues (SAM).


#### 6.5. Power Budget Error

For the same FDTD-grid setting, handset in hand
close to HR-EFH needs more number of grid cells to be simulated, as compared
with handset close to SAM. It is true even with duplicating the refining factor
of SAM solid regions (shell and liquid). It is because of homogeneous property
of the SAM phantom in which the spatial resolution along the head tissue gradually
increases from the minimum to maximum in short distance at each axis. As concerning
the heterogeneous HR-EFH model, the minimum spatial resolution has no big
chances to reach the maximum value at each axis owing to the existence of the twenty
five different tissues. Consequently, for the same FDTD-grid setting, the power
budget error in cases with the HR-EFH is less than in cases with the SAM. As
revealed in Tables8–10, the power
budget errors in simulations are around 2%.


#### 6.6. Computational Requirements

All computations were performed
on a 2 GHz Intel centrino Laptop machine (Dell, inspiron-630 m) with 2 GB memory
and a 1.6 GHz dual core Intel Pentium machine (Acer, Aspire M1600) with 4 GB
memory.The
runtime and memory requirements depend on the simulation space as well as the
refinement factor for each solid region. Less memory and runtime were required
for the handset simulation in free space, whereas more memory and runtime were
required for the handset in hand close to head. The maximum number of FDTD-grid
cells that can be achieved with the adopted simulating machines is about 24 Mcells, where a hardware accelerator aXware [27] is not used. The machine memories were
enough to achieve all simulations where the runtimes were about 1–10 hours
depending on the total number of grid cells.


## 6.1. Antenna Performance

The results listed in Tables4–7 manifest that
the hand-hold position has a considerable impact on the handset antenna
matching, antenna radiation efficiency, and the TIS. The impact of hand at
different positions on the antenna performance (excluding the TIS) was already
presented by [12, 14, 16, 22, 23]. However, this impact may vary depending on
many factors, that is, antenna type/position, handset position with respect to
head, and the operating frequency, concluded as follows.(1) The significant degradation in internal patch antenna
performance due to the different hand positions, as compared with the external
antenna, is because the patch antenna is sandwiched between hand and head
tissues during the practical usage, where the hand tissues act as the antenna
upper dielectric layers. This may shift the tuning frequency as well as
decrease the radiation efficiency.(2) Based on the relation between the
absolute difference in antenna total efficiency due to hand-hold alteration
(from hand1 to hand2) and the antenna/handset position, as shown in Figure11, internal
antenna exhibits more variation in total efficiency values than external
antenna. The maximum absolute difference (25%) is recorded at 900 MHz for
model-B2 against HR-EFH at tilt position. The direction of arrows shown in Figure 11 indicates whether the
total efficiency increases (↑) or decreases (↓) while shifting the hand from
hand1 to hand2. This arrow's indication is also applicable for the TIS and SAR
in Figures 12 and 13, respectively.Absolute difference in the antenna total efficiency owing to hand-hold alteration
at different antenna/handset positions against HR-EFH in GSM900, GSM1800, and
UMTS/IMT-2000 bands.
(a)
Models-A1 and A2 against HR-EFH(b)
Models-B1 and B2 against HR-EFHAbsolute difference in the TIS levels owing to hand-hold alteration at
different antenna/handset positions against HR-EFH in GSM900, GSM1800, and
UMTS/IMT-2000 bands.
(a)
Models-A1 and A2 against HR-EFH(b)
Models-B1 and B2 against HR-EFHPercentage difference in the averaged-peakSAR1g values in
HR-EFH, owing to hand-hold alteration, at different antenna/handset positions in
GSM900, GSM1800, and UMTS/IMT2000 bands.
(a)
Models-A1 and A2 against HR-EFH(b)
Models-B1 and B2 against HR-EFH(3) Although the interference of the
external noisy components (i.e., display and camera, as well as their
associated feed circuits) is not considered in simulation, the drop in TIS
specification of handsets while in-use, as shown in Table7, is caused by
antenna total efficiency decrease due to hand impact. Simulating the handsets
having external antennas, the maximum TIS level of −94.9 dBm is obtained for
model-A1 in hand2 against HR-EFH at cheek position operating at 1800 MHZ, where a minimum total efficiency of 7.6% is recorded, whereas simulating
the handsets having internal antennas, the maximum TIS level of −95.2 dBm is
obtained for model-B1 in hand2 against HR-EFH at cheek position
operating at 2025 MHZ, where a minimum total efficiency of 8.5% is recorded. It
is obvious that the maximum TIS level is around 10 dB higher for the above-mentioned
handsets while in-use, as compared with them in free space.(4) Figure12 illustrates the
absolute difference in TIS levels due to hand-hold alteration at different
antenna/handset positions against the HR-EFH as depicted in Table 7. It is
vivid that handsets with internal antennas exhibit more variation in their TIS
levels than handsets with external antennas, where a maximum difference (5.1 dBm) is recorded at 2025 MHz for model-B1 at cheek position. A maximum difference (5.1 dBm) is also recorded due
to the hand-hold alteration at 900 MHz for model-B1 just in hand.(5) Figures11 and 12 demonstrate that hand2 always has
more impact on antenna performance including the TIS than hand1, except for
model-B2 against HR-EFH at cheek and tilt positions, while operating at 2025 MHz.


## 6.2. Sar and Power Loss in Tissues

Tables8–10 reveal that due
to the exposure of the handset in hand close to HR-EFH at different positions
and operating frequencies, both the averaged-peak
SAR1g and power absorption in tissues may vary considerably according
to hand-hold position, observed as follows.(1)
More SAR
variation in HR-EFH tissues is perceived owing to the internal antenna
exposure, as compared with the external antenna exposure. Figure13 shows the
relation of the percentage of spatial-peak SAR1g difference values
in HR-EFH tissues due to hand-hold alteration versus antenna/handset position
at 900, 1800, and 2025 MHz. The percentage difference of SAR in
HR-EFH tissues while shifting the hand from hand1 to hand2 is defined as (8)%DifferenceinSAR=(SARinHR−EFHwithhand2SARinHR−EFHwithhand1−1)×100. A maximum
percentage difference in SAR (86.8%) is recorded for model-B2 at cheek position and operating at 2025 MHz
(Figure 13(b)) which
represents twice the maximum value of that recorded in cases of handsets having
external antenna (Figure 13(a)).(2) The direction of arrows shown in
Figure13(b) indicates that shifting of the hand-hold from hand1 to hand2 may
result in the decrease of spatial-peak SAR1g in HR-EFH tissues if exposed
to model-B1 EM radiation at different positions and frequencies, whereas the
same shift may increase the spatial-peak SAR1g when exposed to
model-B2. This SAR behavior due to the hand-hold shifting is also applicable
when the head exposes  to the EM radiation of handset models-A1 and A2,
respectively, (Figure 13(a)) but with minor difference in some exceptional
cases with model-A2. It is because of the antenna is located on top of the handset and the distance
between its feeding position and the nearest head tissue being almost the same while using
both model-A1 and model-A2.(3) In [12], shifting the hand-hold
from the lower part of the chassis (hand position = 60 mm) to the upper part
(hand position = 0 mm), which is to some extent the same hand-hold alteration proposed
in this study, the spatial-peak SAR1g in head got decreased from 6 W/kg to 4 W/kg at 900 MHz, and from 5.5 W/kg to 3.5 W/kg at 1800 MHz. The
corresponding percentage differences in SAR (8) are −33.3% and −36.3%,
respectively. Although different hand/handset models used in this study, as
compared with those in [12], the above percentage differences in SAR values nearly
coincide with the results drawn in Figure 13(b) for model-B1 at cheek and tilt positions operating at 900 and 1800 MHz. Relative to the head,
the chase in [12] was tilted (74°)from
the vertical and (10°) from the ear toward the cheek.(4) It is clear from Figure13 that
the operating frequency has a considerable effect on the SAR values in head
tissues while shifting the hand-hold with different handset position and
different antenna types/positions. Moreover, the considerable effect of the
frequency change is also noticed in both antenna total efficiency and TIS shown
in Figures 11 and 12, respectively, where this effect appears stronger in
cases of internal antennas than cases of external antennas.(5) The percentage values of power
absorption in head (SAM and HR-EFH) at different antenna/handset positions in
GSM900, GSM1800, and UMTS/IMT-2000 bands are narrated and illustrated in Figure14. The percentage power absorption is given by (9)%Powerabsorptionintissue=Powerabsorptionintissue(W)Antennainputpower(W)×100. Both SAM and HR-EFH absorb more power with
hand1 than with hand2, when exposed to the EM radiation of handset with
external antenna in different conditions. This is also true when the head was exposed to the EM
radiation of the handset with internal antenna model-B1, whereas with model-B2,
head-tissues absorb less power with hand1 than with hand2. It is because both antenna
and its feeding positions are at the upper part of the models-A1, A2, and B1,
and shifting the hand from hand1 to hand2 will cover the antenna, whereas both
antenna and its feeding positions are at the lower part of model-B2 and
shifting the hand from hand1 to hand2 will uncover the patch antenna. Covering
the antenna by user’s hand may increase the power absorption in hand tissues
and decrease it in head tissues.Percentage power absorption in head tissues at different antenna/handset
positions in GSM900, GSM1800, and UMTS/IMT-2000 bands.
(a)
Models-A1 and A2 at 900 MHz(b)
Models-B1 and B2 at 900 MHz(c)
Models-A1 and A2 at 1800 MHz(d)
Models-B1 and B2 at 1800 MHz(e)
Models-A1 and A2 at 2025 MHz(f)
Models-B1 and B2 at 2025 MHz(6) To some context, the power absorption in hand tissues
behaves inversely to that in head.


### 6.3. Power Loss in Handset Materials

The power loss in handset materials is corresponded
to the dielectric loss (since all the metal parts are considered as PEC in
simulations and consequently the metallic ohmic-loss equal to zero). Tables8–10 give the
dielectric loss values for the twelve handset models in different usage
patterns. Although both handset models with internal and external antennas use
the same material properties for their components and parts, they have
different volumes of dielectric materials and consequently different amounts of
dielectric loss. However, it
is obvious that the hand-hold alteration has a significant effect on the
dielectric loss amount of the handsets having internal antennas, as compared
with the handsets having external antennas; it is because of their different
antenna types and positions. The percentage difference in the dielectric loss
values owing to hand-hold alteration can be defined as (10)%DifferenceinPd=(Pdwithhand2Pdwithhand1−1)×100.The dielectric loss of the
handset with internal antenna gets decreased while shifting the hand from hand1
to hand2, where a maximum percentage difference of −68.8% is recorded at 900 MHz for model-B1 atcheek position,
whereas no more than −11.4% is recorded for model-A1 at the same frequency and
position. The negative sign of the percentage values indicates that hand2 has
more impact than hand1.


### 6.4. Comparison between Sam and He-Efh Simulation Effects

Many researchers have investigated the SAR in
both SAM- and MRI-based human head due to the handset antennas exposure. Study
by some researchers concluded that SAM underestimates SAR in adult MRI-based head,
whereas, some other researchers concluded that SAM overestimates SAR in MRI-based adult head.
Simultaneously, some researchers have presented mixed results. Light has been shed
in detail on all these three states in [34] indicating the potential causes of
discrepancies.The simulations carried out in
this work bring to light SAR difference in SAM and HR-EFH as explained here. According
to the adopted handset positions with respect to head, inclusion of the pinna
in the 1 and 10 g SAR averaging volumes for the HR-EFH and the database used to
define the tissues parameters, the SAM has always been found underestimating
SAR in HR-EFH by a factor ranging from 1.0 to 2.0, with the exception of the
handset models being atcheek positions and operating at 900 MHz, where SAM overestimates SAR in HR-EFH by a
factor ranging from 1.0 to 1.4. The SAR results and its behavior in both SAM
and HR-EFH owing to handsets exposure at different setups coincide with those presented
by the (IEEE SCC-34/SC-2/WG-2) [34] while considering all tissue including the
pinna for the MRI-based adult head.SAM and HR-EFH get different
SAR values and absorb different amount of powers because of the differences
between their volumes, masses, and homogeneities. The volume and mass of the
SAM phantom are approximately 5825cm3 and 6.018 kg (considering a
homogeneous density of 1030 kg/m3), respectively, whereas, volume
and mass of the HR-EFH model are approximately 4063cm3 and 4.7158 kg,
respectively. The accuracy of volume and mass calculation depends on the
FDTD-grid spatial resolution and number of cells.Figures5 and 6 expose an
inconsiderable difference in the antenna far-field radiation pattern because of
the presence of heterogeneous head tissues (HR-EFH), as compared to the
homogeneous tissues (SAM).


### 6.5. Power Budget Error

For the same FDTD-grid setting, handset in hand
close to HR-EFH needs more number of grid cells to be simulated, as compared
with handset close to SAM. It is true even with duplicating the refining factor
of SAM solid regions (shell and liquid). It is because of homogeneous property
of the SAM phantom in which the spatial resolution along the head tissue gradually
increases from the minimum to maximum in short distance at each axis. As concerning
the heterogeneous HR-EFH model, the minimum spatial resolution has no big
chances to reach the maximum value at each axis owing to the existence of the twenty
five different tissues. Consequently, for the same FDTD-grid setting, the power
budget error in cases with the HR-EFH is less than in cases with the SAM. As
revealed in Tables8–10, the power
budget errors in simulations are around 2%.


### 6.6. Computational Requirements

All computations were performed
on a 2 GHz Intel centrino Laptop machine (Dell, inspiron-630 m) with 2 GB memory
and a 1.6 GHz dual core Intel Pentium machine (Acer, Aspire M1600) with 4 GB
memory.The
runtime and memory requirements depend on the simulation space as well as the
refinement factor for each solid region. Less memory and runtime were required
for the handset simulation in free space, whereas more memory and runtime were
required for the handset in hand close to head. The maximum number of FDTD-grid
cells that can be achieved with the adopted simulating machines is about 24 Mcells, where a hardware accelerator aXware [27] is not used. The machine memories were
enough to achieve all simulations where the runtimes were about 1–10 hours
depending on the total number of grid cells.


## 6.3. Power Loss in Handset Materials

The power loss in handset materials is corresponded
to the dielectric loss (since all the metal parts are considered as PEC in
simulations and consequently the metallic ohmic-loss equal to zero). Tables8–10 give the
dielectric loss values for the twelve handset models in different usage
patterns. Although both handset models with internal and external antennas use
the same material properties for their components and parts, they have
different volumes of dielectric materials and consequently different amounts of
dielectric loss. However, it
is obvious that the hand-hold alteration has a significant effect on the
dielectric loss amount of the handsets having internal antennas, as compared
with the handsets having external antennas; it is because of their different
antenna types and positions. The percentage difference in the dielectric loss
values owing to hand-hold alteration can be defined as (10)%DifferenceinPd=(Pdwithhand2Pdwithhand1−1)×100.The dielectric loss of the
handset with internal antenna gets decreased while shifting the hand from hand1
to hand2, where a maximum percentage difference of −68.8% is recorded at 900 MHz for model-B1 atcheek position,
whereas no more than −11.4% is recorded for model-A1 at the same frequency and
position. The negative sign of the percentage values indicates that hand2 has
more impact than hand1.


## 6.4. Comparison between Sam and He-Efh Simulation Effects

Many researchers have investigated the SAR in
both SAM- and MRI-based human head due to the handset antennas exposure. Study
by some researchers concluded that SAM underestimates SAR in adult MRI-based head,
whereas, some other researchers concluded that SAM overestimates SAR in MRI-based adult head.
Simultaneously, some researchers have presented mixed results. Light has been shed
in detail on all these three states in [34] indicating the potential causes of
discrepancies.The simulations carried out in
this work bring to light SAR difference in SAM and HR-EFH as explained here. According
to the adopted handset positions with respect to head, inclusion of the pinna
in the 1 and 10 g SAR averaging volumes for the HR-EFH and the database used to
define the tissues parameters, the SAM has always been found underestimating
SAR in HR-EFH by a factor ranging from 1.0 to 2.0, with the exception of the
handset models being atcheek positions and operating at 900 MHz, where SAM overestimates SAR in HR-EFH by a
factor ranging from 1.0 to 1.4. The SAR results and its behavior in both SAM
and HR-EFH owing to handsets exposure at different setups coincide with those presented
by the (IEEE SCC-34/SC-2/WG-2) [34] while considering all tissue including the
pinna for the MRI-based adult head.SAM and HR-EFH get different
SAR values and absorb different amount of powers because of the differences
between their volumes, masses, and homogeneities. The volume and mass of the
SAM phantom are approximately 5825cm3 and 6.018 kg (considering a
homogeneous density of 1030 kg/m3), respectively, whereas, volume
and mass of the HR-EFH model are approximately 4063cm3 and 4.7158 kg,
respectively. The accuracy of volume and mass calculation depends on the
FDTD-grid spatial resolution and number of cells.Figures5 and 6 expose an
inconsiderable difference in the antenna far-field radiation pattern because of
the presence of heterogeneous head tissues (HR-EFH), as compared to the
homogeneous tissues (SAM).


## 6.5. Power Budget Error

For the same FDTD-grid setting, handset in hand
close to HR-EFH needs more number of grid cells to be simulated, as compared
with handset close to SAM. It is true even with duplicating the refining factor
of SAM solid regions (shell and liquid). It is because of homogeneous property
of the SAM phantom in which the spatial resolution along the head tissue gradually
increases from the minimum to maximum in short distance at each axis. As concerning
the heterogeneous HR-EFH model, the minimum spatial resolution has no big
chances to reach the maximum value at each axis owing to the existence of the twenty
five different tissues. Consequently, for the same FDTD-grid setting, the power
budget error in cases with the HR-EFH is less than in cases with the SAM. As
revealed in Tables8–10, the power
budget errors in simulations are around 2%.


## 6.6. Computational Requirements

All computations were performed
on a 2 GHz Intel centrino Laptop machine (Dell, inspiron-630 m) with 2 GB memory
and a 1.6 GHz dual core Intel Pentium machine (Acer, Aspire M1600) with 4 GB
memory.The
runtime and memory requirements depend on the simulation space as well as the
refinement factor for each solid region. Less memory and runtime were required
for the handset simulation in free space, whereas more memory and runtime were
required for the handset in hand close to head. The maximum number of FDTD-grid
cells that can be achieved with the adopted simulating machines is about 24 Mcells, where a hardware accelerator aXware [27] is not used. The machine memories were
enough to achieve all simulations where the runtimes were about 1–10 hours
depending on the total number of grid cells.


## 7. Conclusioin

On the
bases of the handset, hand, and head models used in this research, it has been significantly
elaborated that the hand-hold position has a considerable impact on the EM
interaction between cellular handset and human. Other related factors such as the
operating frequency, antenna type/position, and the handset position against
head were assessed while anticipating the hand impact. To achieve realistic in-use
conditions, different candy-bar handset models having external and internal
antennas operating in GSM900, GSM1800, and UMTS/IMT-2000 bands were simulated, whereas
semirealistic hand model of three tissues, MRI-based adult female head model of
twenty five tissues, and SAM phantom were selected for evaluating the EM
interaction. Owing to the hand-hold alteration, more differences in values of
the antenna total efficiency, total isotropic sensitivity, and both SAR and
power absorption in tissues were recorded with the handset models having
internal patch antenna, as compared with the handset models having external
loaded short-whip antenna. This paper showed interesting results; in a certain
usage pattern of a handset having left-side external antenna, the maximum
percentage difference of spatial-peakSAR1g values in head due to
the right hand-hold alteration may reach over 42%, whereas it may reach over
86% with the handset having bottom-mounted internal patch antenna. The power
budget errors in the proposed simulations were around 2%.



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*Source: 102759-2009-01-04.xml*