SAR reduction in the modelled human head for the mobile phone using different material shields
Dutta et al. Hum. Cent. Comput. Inf. Sci.
SAR reduction in the modelled human head for the mobile phone using different material shields
Prabir Kumar Dutta 0
Pappu Vankata Yasoda Jayasree 0
Viriyala Satya Surya Narayana Srinivasa Baba 1
0 Department of ECE, GITAM Institute of Technology, GITAM University , Visakhapatnam, A.P. , India
1 Department of ECE, College of Engineering, Andhra University , Visakhapatnam, A.P. , India
Every mobile phone emits radio frequency electromagnetic energy. The amount of this energy absorbed by the human head is measured by the specific absorption rate (SAR). There are standard limits, according to which phones sold should be below certain SAR level. To maintain these limits, shields can be used for the mobile phones. In this paper using ANSYS HFSS, modelling of the human head is done. The modern mobile phone design is used for simulation. SAR distribution is measured for different layers of the head due to exposure to radiation from the mobile phone operating at GSM-1800 frequency band. The performance of the mobile phone antenna due to different shields is observed. Proper shielding material properties are found.
-
SAR = σ E2
2ρ
(1)
where σ is the Conductivity of body tissue (S/m), ρ is the density of body tissue (kg/m3),
E is the RMS value of the electric field strength in the tissue (V/m). SAR tests are
performed for only 6 min of mobile phone usage, but practically, studies have shown that
people use mobile phones for more than hours.
Over the years, a lot of attention have been paid to the analysis of SAR in the human
head due to the complexity and large scale involved in this kind of problems. Recently,
research efforts have been devoted to the reduction of peak SAR in the human head
for handset applications. Mobile phone antenna performance gets affected due to the
human head has been investigated in many published papers [
10–14
]. The impact of
mobile phones on the human head can be measured using SAR [
13–18
]. The radiation
from the mobile phones can be reduced using a shield that results in the decrease of
SAR. However, this shield affects the performance of the mobile phone antenna. Proper
shield material is to be selected such that it reduces the radiation while maintaining a
good quality of signal transfer and reception from the mobile phone.
Global system for mobile communications (GSM) is a standard developed by the
European Telecommunications Standards Institute (ETSI) to describe protocols for
second-generation (2G) digital cellular networks used by mobile phones. In Africa, Europe,
Middle East and Asia, most of the providers use 900 and 1800 MHz bands. The
GSM900 system uses the frequency band (890–915) MHz for uplink and the band (935–960)
MHz for downlink. While, the GSM-1800 system uses the frequency band (1710–1785)
MHz for uplink and the band (1805–1880) MHz for downlink. In GSM systems, up to
eight users share the same frequency channel, and each phone transmits only one-eighth
of the time as the time division multiple access (TDMA) is used, so the average power
is one-eighth of the peak power. GSM-900 phones have a peak power of 2 W, and as the
maximum average power is one-eighth of the peak power. Hence, the GSM-900 mobile
phones radiate an average power of 250 mW. GSM-1800 phones have a peak power of
1 W; hence the GSM-1800 mobile phones radiate an average power of 125 mW [
19
]. In
this paper, the mobile phone is designed to operate in GSM-1800 frequency band.
Some research was done in this area, where the old models of mobile phones with
dipole and helix antennas were used [
20–22
]. The mobile phone models discussed in
those papers are not used in this modern time. In a paper [
21
], aluminium was used as
the shield, but using conductive materials as the shield will degrade the mobile phone
antenna performance.
In this paper, modern type of mobile phone with the shield is tested. With the help of
HFSS, 3D head model is designed. SAR in the human head is measured. In a modern
mobile phone, Planar Inverted-F Antenna (PIFA) is used. The advantage of PIFA is that
they are compact in size and have small back lobes, which make them ideal for mobile
phone antennas. A mobile phone equipped with PIFA is analyzed.
Simulation Model
Head Model
The Head model used in this paper consists of four layers (skin, fat, skull, and brain)
having dimensions 15 cm wide, 25 cm high, and the thickness of each layer is shown in the
Fig. 1 [
19
]. Layers of the head are considered as flat layers because when mobile phones
are used practically, it is placed with the face in such a way that it looks flat with the
head. Only vertical half of the head is considered in the model to save simulation time.
The human head biological tissues can be considered as lossy dielectric materials whose
conductivity and relative permittivity depend on frequency. The properties of different
layers of the head that are used are shown in Table 1 [
1
].
Phone Model
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