VOL. 12, NO. 6, MARCH 2017
ISSN 1819-6608
ARPN Journal of Engineering and Applied Sciences
©2006-2017 Asian Research Publishing Network (ARPN). All rights reserved.
www.arpnjournals.com
TEXTILE ANTENNA WITH Z SHAPE EBG STRUCTURE
FOR SAR REDUCTION
M. Ramesh1, V. Rajya Lakshmi2 and P. Mallikarjuna Rao3
1
Department of Electrical and Computer Engineering, Gandhi Institute of Technology and Management, Visakhapatnam, India
Department of Electrical and Computer Engineering, Anil Neerukonda Institute of Technology and Sciences, Visakhapatnam, India
3
Department of Electrical and Computer Engineering, Andhra University, Visakhapatnam, India
E-Mail: [email protected]
2
ABSTRACT
This paper presents the design of Textile antenna embedded with Z shape Electromagnetic Band Gap (EBG)
Structure. The textile antenna is designed using rectangular shape patch with Hexagonal slot. Jeans fabric is being used as
substrate. Return loss, Specific Absorption Rate (SAR) value and impedance bandwidth are investigated using HFSS
simulator.
Keywords: textile antenna, electromagnetic band gap, specific absorption rate.
1. INTRODUCTION
The ever - growing miniaturization of electronic
devices combined with wearable antennas leads to creation
of wide range of applications. The wireless connectivity is
used for connecting body worn devices and to establish
body to body communication. The Antennas are the basic
components for providing the WBAN and WPAN services
in to wireless heterogeneous networks [1-2]. The WPAN
and WBAN involve the range of Body Centric Wireless
Communication (BCWC). The communication is
established from off body to on body and vice versa using
body centric communication. The Antennas must be small
size, lightweight and support high data rate for WBAN
applications [3].
The conventional textile antennas suffer from
surface waves and narrow bandwidth. In Textile antennas,
varieties of commercial fabrics are available with small
thickness and low dielectric constant that are used as
substrate in antenna design. Textile antennas are
comfortable and flexible to wear on human body
compared with microstrip antennas because textile
antennas are made with conductive and non-conductive
fabrics [4]. In [5], felt fabric used as substrate for dual
band textile antenna.
In BCWC, the EM waves incident on Human
body. The EM properties of body tissues change with type
of tissue and frequency [6]. The phantom model is used in
the analysis of radio waves around and inside human body
at ISM band [7].
Textile antennas are near to human body then
body absorbs more EM energy, it creates hazards to
human body. How much power is absorbed by tissues can
be calculated using SAR [8].
SAR =
(1)
σE𝑖 2
International
Electro
technical
Commission
(IEC),European Union and it is less than or equal to
1.6W/kg over 1g of tissue for FCC.
To reduce SAR a reflector element is used in the
middle of antenna and human head which reduces the
absorption of EM energy by human body and achieved a
70% decrease in SAR [9]. In [10], authors deployed split
ring resonator for the same scenario to reduce SAR in the
dual band. Using the property of metamaterial, which is
useful in decreasing the SAR, a new design structure of
metamaterial antenna called square meta material antenna
is designed, the performance of SMM is verified by
varying the permittivity of the meta material by keeping
the permeability a constant and observed that SAR has
reached a better value for a permittivity of -3 and
permeability is 1[11]. SAR performance is analyzed with
ferrite materials for tri-band antenna [12]. Two types of
EBG structures are used to reduce the SAR value that is
interdigitated EBG and square EBG with via [13]. Double
band textile antennas are designed using felt substrate on
dual square EBG and SAR reduction is observed in the
Human Head [14].The combination of Auxiliary Antenna
Elements with ferrite shields also reduce the SAR value
[15].
In view of the above discussion, an attempt has
been made to reduce the SAR by employing Z shaped
EBG. This paper has been organized as follows: In section
II, the schematic view and dimensions of proposed
antenna are listed. In section III, simulated results of the
proposed antenna with EBG and without EBG embedded
with phantom model are shown. In section IV, conclusions
are given.
2. ANTENNA DESIGN AND IMPLEMENTATION
ρ
conductivity of body tissue in S/m,Ei Electric field strength in the tissue in V/m, σ - Density of
body tissue in kg/m3.The Limit of SAR value is less than
or equal to 2 W/kg averaged over the 10 g of tissue for
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VOL. 12, NO. 6, MARCH 2017
ISSN 1819-6608
ARPN Journal of Engineering and Applied Sciences
©2006-2017 Asian Research Publishing Network (ARPN). All rights reserved.
www.arpnjournals.com
Table-1. Electrical properties of tissues at 2.5GHz [6].
Skin
Thickness
(mm)
2
εr
37.9
Loss
tangent
0.28
σ(S/m)
Fat
4
5.27
0.14
0.10
Muscle
8
52.61
0.24
1.77
Layer
1.48
2.3 IMPLEMENTATION EBG STRUCTURE
Figure-1. Schematic of textile Antenna a) top view b) side
view without EBG c) side with EBG.
2.1. PROPOSED TEXTILE ANTENNA WITHOUT
EBG
Figure-1(a) represents geometry of the patch with
feed line. The microstrip antenna consist of three layers
ground, substrate and patch respectively. Figure-1(b)
shows the side view of textile antenna without EBG
structure. The Textile antenna is implemented using jeans
as a substrate because it is very comfortable to wear. Here,
ground size is 60 x 60 mm, substrate dimensions are Ws
=60mm, Ls=60mm and thickness is 1.5mm with dielectric
constant εr =1.6 and loss tangent is 0.023[4].The patch
length L=42 mm, width W=38mm.Here hexagonal slot is
used on patch, the distance between any two opposite
branches is a=8.8 mm and it has six branches, the length of
each branch is 5mm.
l
s
Figure-3. Structure of Z shape EBG array.
Here, we proposed new design of Z shape EBG
structure and size of array is 3x4. The Dimensions of the Z
shape EBG unit cell is shown in Figure-3. The size of Z
shape patch width w= 12 mm, length l= 17 mm and
substrate thickness is 1mm.Here jeans fabric is used as
substrate. The width of Z shape rectangular patch is
w=12mm, the space between adjacent cells is s =2mm, so
the periodicity of Z shape EBG structure is p = w +
s=14mm.
2.4. TEXTILE ANTENNA WITH EBG
Figure-2. Proposed textile antenna without
phantom model.
Initially, the textile antenna is not combined with
phantom model of human body that is shown in Figure-2.
The human body absorbs some amount of radiation that is
represented using SAR value.
2.2. PHANTOM MODEL
The electrical properties of phantom model are
shown in Table I. Here square phantom model is used. It
consists of three layers: skin, Fat and muscle respectively.
This model is kept 2mm distance from the ground plane of
textile antenna.
Figure-4. Textile antenna with EBG and phantom model.
The textile antenna uses same dimensions
proposed in Figure-1(a) but integrated with Z shape EBG
structure. The Textile Antenna is embedded with Z shape
EBG structure that is shown in Figure 4.In this analysis
3x4 EBG structure is used. Here four layers are used that
is shown in Figure-1(c), Bottom layer is ground,
substrate1, EBG structure, substrate2 and patch
respectively. Here two substrates are jeans fabric. The Z
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VOL. 12, NO. 6, MARCH 2017
ISSN 1819-6608
ARPN Journal of Engineering and Applied Sciences
©2006-2017 Asian Research Publishing Network (ARPN). All rights reserved.
www.arpnjournals.com
3. RESULTS AND ANALYSIS
Name
X
.
Y
HFSSDesign1
m1 0.00
2.5000 -13.8297
m2 2.5520 -10.0206
m3 2.4000 -10.0671
ANSOFT
Curve Info
S11
Setup1 : Sw eep
Name
X
Y
.
ANSOFT
m1 2.5930 -90.0853
m2 2.3600 90.9469
m4 150.00
2.5040 -0.0924
Phase Reflection [deg]
shape EBG structure is positioned 1mm distance from
Ground plane. Next the patch is positioned 0.5mm
distance from EBG. The overall height between ground
and patch of antenna is 1.5mm.
Curve Info
phase
Set : Sw eep
100.00
m2
50.00
m4
0.00
-50.00
m1
-100.00
-2.00
-150.00
Name
Delta(X)
d( m1,m2)
-0.2330
1.08
Delta(Y)
Slope(Y)
181.0322
-776.9623
1.50
2.00
InvSlope(Y)
-0.0013
-6.00
2.50
3.00
Frequency [GHz]
3.50
3.91
Figure-7. Phase reflection of Z shape EBG.
-8.00
m2
m3
-10.00
-12.00
m1
-14.00
Delta(X)
1.00Delta(Y)
-0.1520
-0.0465
Name
Slope(Y)
d( m2,m3)
0.3058
InvSlope(Y)
1.50
3.2704
2.00
2.50
3.00
Frequency [GHz]
3.50
4.00
Figure-5. Return loss of antenna without EBG and
phantom model.
Name
All the simulations are done using Ansoft HFSS
simulator. The simulated return loss graph of conventional
Textile antenna without EBG and phantom model is
shown in Figure-5. The textile antenna resonates at 2.5
GHz frequency with return loss -13.82dB and impedance
bandwidth (-10dB) is 155MHz.
Name
X
.
Y
ANSOFT
m10.00
2.5000 -7.7371
The simulated phase reflection of Z shape EBG
structure is shown in Figure-7. The Phase reflection
changes continuously from +900 to -900 in this interval
frequency changes from 2.36 GHz to 2.59 GHz, it cross 00
Reflection phase line at 2.5GHz frequency. It acts as EBG
in this interval.
X
Y
m1 0.00
2.5000 -20.2994
m2 2.1455 -10.0658
m3-2.50
2.7719 -10.1447
Curve Info
(S(1,1)
Setup1 : Sw eep
-5.00
Return Loss dB
Return Loss [dB]
-4.00
-7.50
m2
-10.00
-12.50
-15.00
-17.50
Curve Info
S11
Setup1 : Sw eep
-1.00
m1
-20.00
-22.50
1.00
1.50
2.00
Return loss [dB]
-2.00
2.50
3.00
3.50
Frequency [GHz]
4.00
4.50
5.00
Figure-8. Return loss of textile antenna with EBG on
phantom model.
-3.00
-4.00
-5.00
-6.00
-7.00
m1
-8.00
1.00
m3
1.50
2.00
2.50
3.00
3.50
Frequency [GHz]
4.00
4.50
5.00
Figure-8 shows simulated return loss of the
textile antenna is integrated with Z shape EBG structure
on phantom model. The antenna resonates at 2.5GHz with
return loss -20.29dB.The impedance bandwidth is 630
MHz from 2.14 GHz to 2.77 GHz.
Radiation Pattern 2
Figure-6. Return loss of textile antenna without EBG on
phantom model.
HFSSDesign1
0
-30
ANSOFT
Curve Info
dB(GainTotal)
Setup1 : LastAdaptive
Freq='2.4GHz' Phi='0deg'
30
dB(GainTotal)
Setup1 : LastAdaptive
Freq='2.4GHz' Phi='90deg'
-7.00
-14.00
-60
The Textile antenna is positioned on phantom
model and distance of 2 mm is maintained between them.
Figure-6 shows characteristic of antenna is effected by
human body. Here, the textile antenna resonates at 2.5GHz
with return loss -7.73dB and SAR value is 8.9 W/kg
averaged over 10 g of tissue.
60
-21.00
-28.00
-90
90
-120
120
-150
150
-180
Figure-9. Far field radiation pattern of antenna with EBG
on phantom model.
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VOL. 12, NO. 6, MARCH 2017
ISSN 1819-6608
ARPN Journal of Engineering and Applied Sciences
©2006-2017 Asian Research Publishing Network (ARPN). All rights reserved.
www.arpnjournals.com
The simulated far-field pattern of textile antenna
with EBG structure on phantom model shown in Figure-9.
Due to EBG structure, the back radiation is reduced.
3.1. SAR ANALYSIS
[5] S.Zhu and R.Langley. 2007. Dual band wearable
antennas over EBG substrate. The Institution of
Engineering and Technology, Electronics Letters.
43(3): 2.
[6] Gabriel C. 1996. Compilation of the Dielectric
Properties of Body Tissues at RF and Microwave
Frequencies. Brooks Air Force Technical Report,
AL/OE-TR-1996-0037.
[7] P. Salonen, Y. Rahmat-Samii, and M. Kivikoski.
2004. Wearable Antennas in the Vicinity of Human
Body. Antennas and Propagation Society International
Symposium. IEEE467-470.
[8] IEEE C95.1-2005. IEEE Standard for Safety Levels
with Respect to Human Exposure to Radio Frequency
Electromagnetic Fields, 3 kHz to 300 GHz. IEEE
International Committee on Electromagnetic Safety
(SCC39), IEEE-SA Standards Board, 3 October 2005.
Figure-10. SAR value for proposed antenna.
Figure-10 shows simulated SAR value of textile
antenna with EBG structure on the surface of phantom
model. The SAR value is 1.26 W/kg averaged over 10 g of
tissue at 0.3Watts of input power. For the textile antenna
without EBG, SAR value is 8.9 W/kg. The SAR value is
reduced by
. − . 6
.
x
= 85.8%
[9] A. Hirata, T. Adachi, and T. Shiozawa. 2004. Folded
loop antenna with a reflector for mobile handsets at
2.0 GHz. Microwave and Optical Technology Letters.
40(4): 272-275.
[10] J.-N. Hwang, F.-C. Chen. 2006. Reduction of the
Peak SAR in the Human Head With Metamaterial.
IEEE. 54(12): 3763-3770.
(2)
4. CONCLUSIONS
The proposed Textile antenna is embedded with
Z shape EBG structure used for wearable applications. The
proposed textile antenna reduced SAR value by 85.8%
compared with textile antenna without Z shape EBG.
Moreover, the impedance bandwidth is improved 75.3%
and return loss also increased.
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