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Advances in Wireless and Mobile Communications.
ISSN 0973-6972 Volume 10, Number 5 (2017), pp. 735-745
© Research India Publications
http://www.ripublication.com
Analysis of Different Performance Parameters of
Bodywearable Antenna- A Review
Kanav Badhan
UIET, Panjab University, Chandigarh 160017
Jaget Singh
UIET, Panjab University, Chandigarh 160017
Abstract
Body-worn antenna is ideally used in military, mobile communication and
healthcare applications. Planar structure, compactness, flexible construction
material, good radiation efficiency and bandwidth are some of the specific
requirements for body-worn- antennas. The right choice of antenna design is
important to minimize the losses because the body also deteriorates the
performance of antenna. The shape of the patch and properties of dielectric
substrate like thickness directly effects the performance of simple microstrip
patch antenna. Therefore it is important to know how these aspects influence
the performance of body-wearable antenna. This paper presents a review of
the various dielectric substrate used in wearable antenna design, effect of
human body on antenna performance and various shapes and techniques used
in literature to minimize unwanted effects. Various dielectric substrates can be
used in body-wearable antenna design. Generally, textile materials are used,
because they reduce the surface wave losses and enhance the radiation
efficiency and bandwidth of antenna. Human body limits the performance of
antenna significantly. The human body plays a very significant role in antenna
performance. Human body being a lossy medium which reduces the
performance of antenna. Various microstrip patch shapes and diversity
techniques have been proposed by the researchers to improve the impedance
bandwidth and radiation efficiency. The metamaterial technology improves
the overall performance of the antenna and reduces the body Specific
Absorption Rate (SAR) values. The performance of proposed shapes can also
be tested on different textile substrates and metamaterials.
Keywords: Bodywearable Antenna, Textile Substrates, Metamaterial, Return
Loss, Impedance Bandwidth.
736 Kanav Badhan and Jaget Singh
I. INTRODUCTION
The body centric wireless communication has drawn the attention of researchers in
the present era. The body worn antennas are widely used for these type of
communications and have received much attention in commercial sports,
entertainment and healthcare applications [1]. Body worn antenna may be made from
textiles [2-5] or may be worn as a button antenna[6]. The wearable antenna may be
operating on single or dual frequencies. For body worn applications the antennas
should be of small size, light weight, consumes less power, almost maintenance free,
and with no installation cost. The compact size, low cost, easy fabrication makes
microstrip patch antenna highly suitable and comfortable on body surface. But the
reduction of the size of the antenna leads to reduced performance of the antenna such
as poor efficiency, impedance and bandwidth. Hence design of a wearable antenna is
quite challenging [7].
Wearable antennas are usually placed in human torso or arm. The human body acts as
a lossy medium which degrades the performance of wearable antenna [8]. In order to
design a bodywearable antenna the design parameters and different dielectric
properties of substrates should be clearly studied. Also the effect of body on antenna
parameters needs to be understood. These parameters should be optimized according
to body-worn applications. To improve the bodywearable antenna performance,
various techniques have been proposed by the researchers like selecting thick and
high dielectric substrates materials, various radiating microstrip patch shapes, slotting
in patch to improve bandwidth, the array of antennas etc. The wearable antenna may
use the combination of these techniques to give favorable performance in the vicinity
of the human body. This paper presents a brief review of design parameters of patch
antennas, different types of dielectric substrate materials and patch shapes along with
their performance analysis.
The remaining paper is organized as, section II presents the analysis of various
dielectric substrates for bodywearable antennas, effect of body on antenna
performance are discussed in section III, Section IV outlines the different shapes of
microstrip patch used in literature for body worn applications and finally we conclude
in section V.
II. ANALYSIS OF VARIOUS DIELECTRIC SUBSTRATES FOR
BODYWEARABLE ANTENNAS
The microstrip patch antenna consists of a radiating patch etched on a dielectric
substrate and a ground plane as shown in figure 1<insert figure 1 here>. The radiating
patch is made of gold or copper and can be of any possible shape. The dielectric
substrate is a main component of patch antenna. Before selecting the dielectric
substrate different design criteria’s like permittivity, loss tangent, thickness of
dielectric, electrical surface resistivity of conductive dielectric fabric, the moisture
content of fabric should be considered. Generally the dielectric properties rely upon
Analysis of Different Performance Parameters of Bodywearable Antenna.. 737
temperature, frequency, surface roughness, moisture content, purity and homogeneity
[9].
The dielectric constant value for the fabrication of patch antenna should be in between
2.2≤ εr ≤12 [10]. For textile materials like flectron, zelt, shieldit etc. dielectric
constant should be less than 2 because lower εr decreases losses occurred by surface
waves and enhances the spatial waves and improves impedance bandwidth of an
antenna. The amount of power converted into heat in the material is called loss
tangent or dissipation factor denoted by tanδ. If loss tangent value is high losses will
be high and radiation efficiency will decrease [10].
The thickness of dielectric substrate should be in between 0.003λ< h <0.005λ [10]
where λ is operating wavelength of an antenna. The selection of thickness of substrate
is a trade off between bandwidth and efficiency [11]. A thick substrate with low value
of relative permittivity results in larger patch size and if same relative permittivity is
chosen with same thin substrate the patch size decreases [12].
In literature, ample of work has been done on different substrates. Various dielectric
substrates have been proposed by the researchers. Air with least dielectric constant of
1 gives the return loss of -22.644 and benzocyclobutane which has dielectric constant
of 2.6 shows return loss of -18.1248 [13]. The Duroid 6010 with dielectric constant of
10.7 is used in phased array configuration of 1*4 at 1.35 GHz and it shows optimized
results [14]. FR4 epoxy is widely used substrate in microstrip patch antenna design. P.
Kumar et al. used rectangular patch antenna with FR4 epoxy resin at 2.45 GHz [16].
The calculated gain of patch antenna is 3.954 dB and the author concluded that it is
well suited for body centric communication.
Fractal shape microstrip patch antenna is implemented using foam substrate. Using
foam substrate the size of the antenna reduces to 84%. B.T.P. Madhav et al. [14]
demonstrated that RT-Duroid gives better performance in terms of gain, directivity
than LCP substrate but it is costlier than LCP.
Nowadays the microstrip patch antennas are fabricated on textile substrates. For
textile antenna design, the conductive fabric should have low and stable electrical
surface resistance. Also, It should be flexible and homogenous over entire area. The
moisture content of the fabric should also be considered. The author in [15] described
that zelt which is high quality nylon based substrate is highly suitable for body
wearable applications due to its durability. The author compared the performance of
proposed zelt antenna with conventional FR4 antenna. The gain of zelt antenna was
0.5dB higher than FR4 antenna. The proposed antenna was found suitable to be
mounted on human body. It shows better return loss and radiation pattern
performance. Nylon has a medium dielectric constant of 3.6. The work demonstrates
that the antenna fabricated using nylon as a substrate resonates at 989MHz with return
loss of -35.42 dB and a gain of 6.1 dB. S. Sankaralingam et al. compared the
performance characteristics of wearable circular zelt, flectron and shieldit patch
antenna on polyester substrate in both free space environment and human body
vicinity [9].
The table 1 shows the performance characteristics of these proposed antennas. It is
clear from the table that zelt antenna gives best performance.
738 Kanav Badhan and Jaget Singh
Table1: Performance charactersistics of zelt, flectron and s0hielded antennas.[8]
The author in [17] proposed a 3D foldable antenna using flexible Kapton substrate.
The results show the excellent performance of upto 75% radiation efficiency with -
8dB return loss. Hence, the antenna is highly suitable for body worn wireless devices.
The author in [18] gives a complete survey of textile materials in wearable antenna
designs. The various textile materials and their electrical properties viz. moisture
content, assemblage on human body and their selection criteria are studied. The textile
materials used for wearable antenna design are also discussed.
Table 2 shows the comparison of the textile materials. From the Table it is clear that
for Bluetooth applications, polyamide spacer fabrics, woollen felt and PDMS
performs better.
III. EFFECT OF HUMAN BODY ON ANTENNA PERFORMANCE
The human body acts as an irregular shaped medium. The body has a frequency
dependent conductivity and permittivity. Due to high permittivity of body tissues
resonant frequency of an antenna changes. It acts as a lossy medium and it reduces the
gain of the body worn antenna at lower operating frequencies. Hence for body worn
devices the electrical properties of body tissues and their interactions with the antenna
should be studied before designing the wearable antenna. In literature various
simplified body models like homogenous model, 3 layer model and complex 3D body
models are discussed [19]. The layer model of human tissue is shown in figure 2. In
this model the effect of outermost body tissue is also acknowledged. This model has
three layers: skin, fat and muscle and the antenna is to be placed on top layer.
Analysis of Different Performance Parameters of Bodywearable Antenna.. 739
Figure 2: 3 Layer Body Model
Skin and muscles have high water content that adversely affects the operating
wavelength of the antenna [20]. Skin has homogeneous design. It has inhomogeneous
dielectric properties. Muscles have average dielectric properties and fat has poor
dielectric properties. Table 3 shows the electrical properties of various tissues at
6.5GHz and 8GHz provided by National Research Council [21].
The placement of antenna on human body has a crucial effect on performance. When
antenna is placed on triceps and thighs that have average skin and fat thickness it
performs better. When it is placed on site with less thickness like forehead and wrist,
its performance deteriorates [22]. As operating frequency increases, permittivity
decreases which leads to better reflection away from the body and hence antenna
performance boosts. Table 4 shows the performance of antenna at various sites at 4.6
GHz and 8 GHz.
Table 2. Comparison of various dielectric materials [18]
Application Dielectric material
Conductive
materials
Material h(mm) ∈r
tanδ
Performance
GSM
(900MHz)
and
Bluetooth(2.
4GHz)
Unspecified
material
0.236 3.29 0.0004
-
Acceptable
WLAN
(2.4GHz)
Fleece fabric 3 1.04 - Knitted copper
fabric
Acceptable
GPS(1.5GHz
)
Cordura
0.5 Betwee
n 1.1
and 1.7
-
Copper tape Good
ISM(2.4
GHz) and
GPS (1.5
GHz)
Fleece fabric 2.56 1.25
-
Flectron Acceptable to Good
ISM(900Mh
z)
Polyurethane
protective Foam
11 1.16 0.01 Flectron Acceptable
740 Kanav Badhan and Jaget Singh
WLAN (2.4
GHz and 5.8
GHz)
Felt
1.1 1.30 0.02 Zelt Acceptable
ISM(2.4
GHz)
Cotton/Polyeste
r
2.808 1.6 0.02 Flectron/Condu
ctive ink
Good
Not specific
(2-2.4 GHz)
Polydimethylsil
oxane (PDMS)
- 3.0-13 0.02 Embroidered
conductive
fibric
Good
Bluetooth
(2.4GHz)
Polyamide
spacer
fabric
6 1.14 Negligible Silver-copper-
nickel plated
woven fabric
Good
Bluetooth
(2.4GHz)
Woollen felt 3.5 1.45 0.02 Silver copper
nickel plated
woven fabric
Good
Table 3. Dielectric properties of skin, fat and muscles [22]
Tissue Layer εr σ(S/m) Tanθ (Loss
Tangent)
Skin 34.5 4.3 0.347
Fat 4.8 0.33 0.191
Muscle 47.5 5.8 0.338
Table 4. The performance of antenna at various body sites at 4.6 Ghz and 8 Ghz [22]
Anatomical Site Total Gain
(dB)
Radiation
Efficency (%)
SAR e-3
(W/kg)
Forehead 2.0/6.3 26.5/47.7 2.7/4.1
Neck 1.6/6.0 22.8/47.1 2.3/4.1
Biceps 4.5/7.3 41.2/58.5 2.8/4.5
Triceps 4.8/7.3 41.4/56.8 2.9/4.6
Chest 4.4/6.5 39.7/53.3 2.9/4.3
Wrist 4.0/3.9 40.9/38.2 2.5/4.3
Abdomen 4.6/5.0 44.1/45.8 2.7/4.4
Anterior Thigh 4.8/6.7 41.7/55 3.0/4.4
Posterior Thigh 5.2/6.3 44.7/52.4 3.0/5.2
Calf 4.7/7.0 41.8/56.3 2.9/4.5
Analysis of Different Performance Parameters of Bodywearable Antenna.. 741
IV. WEARABLE ANTENNA DESIGNS
The body worn antenna design must have few requisites like invisible on the body,
omni-directional radiation pattern, tuning adjustment to compensate for body effect,
high gain etc. To meet above requirements some recently proposed wearable antenna
design are discussed in this section.
1. Rectangular Patch antenna The author M. Wozniak et al. designed a rectangular patch antenna and tested the
designed antenna in the vicinity of human body and it is simulated using CST
software. The performance analysis revealed that the S11 parameter was -33dB and
the proposed antenna can be used for GSM 1800 applications. Various disadvantages
of this design are stiffness, narrow bandwidth (2%), high fabrication cost [23].
2. 3D Folded Slot antenna:
T.Thai et al. proposed a 3D folded slot antenna at 2.4 GHz for body worn
applications. The designed antenna showed an excellent performance of 75%
radiation efficiency with -8 db return loss. The proposed antenna has high bandwidth
and data rate and it is well suited for wearable applications [17].
3. Dual Band Coplanar Antenna on EBG substrate:
S. Jhu et al. described the dual band coplanar patch antenna integrated with
electromagnetic band gap substrate. The antenna operates at the 2.5 GHz and 5 GHz
bands. Due to high impedance surface provided by EBG (Electromagnetic Band Gap),
back radiation reduces. The author also studied the electromagnetic properties of
different textiles and discussed the textile material suitable for body wearable design.
The author compared the proposed antenna with rectangular patch antenna and results
showed that the proposed antenna has an operating bandwidth of 4% at 2.4 GHz and
10% at 5.5 GHz. Rectangular patch antenna has bandwidth of 2.5% at 2.45 GHz and
4.6% at 5.5GHz, hence proposed antenna performs better. The proposed antenna
reduces back radiation and SAR by a factor of 20. The author also analyzed the
bending performance of antenna and measurements revealed that antenna is tolerant
to bending in either E-plane or H-plane but only when worn around arms and legs
[15].
4. Circular Patch Antennas:
The circular patch antenna using three textile materials namely Flectron, Zelt and
Shieldit are presented by S. Sannkaralingam et al . These antennas are mounted on the
vicinity of the human body, their impedance and radiation characteristics at 2.4Ghz
are analysed. The author concluded that Zelt antenna has highest radiation efficiency
of 79.1% as compared to Flectron (61%)and Shieldit antennas (57%). Gain of Zelt
antenna can have maximum value of 6.92 db. The simulations showed that proposed
wearable antennas have required characteristics and impedance and it is highly
suitable for bluetooth applications [8].
742 Kanav Badhan and Jaget Singh
5. Omnidirectional Vest Mounted Bodywearable Antenna:
The author presented a omnidirectional bodywearable vest mounted antenna for UHF
operations. The proposed design have 79*41*28mm3 compact diversity module and
four antennas for omnidirectional radiation pattern. The performance of designed
antenna is evaluated under indoor environment and with several human activities. The
gain of 21db was achieved in a mutipath indoor environment. The proposed antenna
with diversity performed better than single whip monopole antenna [24].
6. Circular Patch Low Profile Antenna:
T.Bjornien et al. designed a circular patch head worn antenna with a thickness of 7
mm in 5.8 GHz ISM band. The author outlined the ellipsoid head model so that the
antenna is efficiently optimized. It is concluded that the antenna has zero dbi gain and
radiation efficiency of 76% and SAR is below the International Commission on Non-Ionizing Radiation Protection (ICNIRB) and Federal Communications Commission
(FCC) limits [25].
7. Swastika Slot UWB Patch Antenna: V.Kumar et.al investigated the performance of Swastika slot patch antenna for UWB
applications at 3.1 and 10.6 GHz the dimensions of the antenna was 27*27*1.6mm
.The antenna has a gain of 6.43 db at 11 GHz and 1.77/5.6 db at UWB. Antenna
radiation efficiency is varied from 81.3 % to 90.67 % also slotting and notching in the
radiating patch improves the impedance bandwidth and radiation pattern of antenna
[7].
8. Fractal body worn metamaterial antenna :
Metamaterial technology reduces the size of the antenna by using DGS. The gain,
return loss, bandwidth improves by using metamaterial technology in antenna design.
Especially for the significant reduction of SAR values metamaterial can be used. The
author concluded that antenna with low SAR can be designed by fractal model with
metamaterial used as a ground plane or substrate [26].
9. Latex based AMC backed endfire antenna:
The author K. Aggarwal et al. proposed a first latex based end-fire antenna at 2.45
GHz with AMC backed metamaterial surface. The author designed a yagi-uda
antenna. The proposed antenna gives significant performance with a gain of 0.12 dBi
and has improved on body radiation efficiency of 78.97 [27].
10. Planer Inverted “F” antenna (PIFA): Nowadays, planer inverted “F” shape antenna is gaining popularity for body wearable
applications due to their significant reduction in body SAR values. The author
presented a PIFA with metamaterial surface for body SAR reduction. The proposed
design consists of AMC structure that acts as a PMC and it controls the radiation
Analysis of Different Performance Parameters of Bodywearable Antenna.. 743
pattern of the antenna and hence designed antenna is capable of preventing hazardous
EM radiation from human body [28].
V. CONCLUSION
From this paper, we conclude that bodyworn antennas are useful for many
applications like military, medical and sports. The main challenges in bodywearable
antenna design include compactness, flexibility, durability, high gain and bandwidth ,
good radiation efficiency and low body SAR are the main challenges in the
bodywearable antenna design . The main performance characteristics of these
antennas are mainly the choice of substrate, its thickness, geometry of the patch. It is
reviewed that substrates with lower value of permittivity increases the resonance
frequency of antenna and improves gains and efficiency. The substrate thickness
should be chosen such that the geometry of antenna remains compact and efficiency
of antenna improves. The conductive textile materials electromagnetic properties,
their placement on human bodies, bending performance, moisture content should also
be studied in order to minimize the losses. Slotting and notching in radiating patch
improves the bandwidth and radiation efficiency. Therefore various shapes of patch
with slots and notches can be designed with these key techniques. The performance of
proposed shapes can also be tested on different textile substrates. Metamaterials
significantly reduces the body SAR and improves the performance of antenna in terms
of gain, return loss, bandwidth and efficiency. The wearable antenna design may also
consist of combination of mentioned techniques. The right technique should be
chosen such that the antenna gives the optimum performance for bodywearable
applications. Also, most of the work has been done on ISM band so, we can also test
the performance of body worn antenna on UWB frequencies. The wearable antennas
has many challenges in their design but no matter how, they still have a bright future
specifically for medical and healthcare applications.
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