The document discusses the design requirements and characteristics of wearable antennas. It begins by outlining the key requirements of wearable antennas including size compatibility, proximity to the human body, specific absorption rate, bending/twisting effects, and permittivity/permeability considerations. It then reviews various substrate materials that can be used for microstrip wearable antennas including PTFE, polystyrene, and composites. Several previous studies on wearable antenna designs and materials are summarized. The document concludes by stating that wearable antenna design must carefully consider human body effects to optimize performance while meeting safety standards.

1. Design Engineering
ISSN: 0011-9342
Issue: 5 | Pages: 861 - 868
[861]
A Review on Substrate Requirements and
Characteristics of Wearable Antenna
1
S.Saranya, 2
B.Sharmila, 3
AL.Chockalingam, 4
K.Mohanraj
1,2
Sri Ramakrishna Engineering College, 3
M.Kumarasamy college of Engineering, 4
Sri Sairam
Engineering College
1
saranya.s@srec.ac.in,2
sharmila.rajesh@srec.ac.in, 3
chockalingamal.eee@mkce.ac.in,
4
mohanraj.ice@sairam.edu.in
Abstract:
The antennas which are designed in a manner to operate when they are worn or textile fabricated
is entitled as Wearable antennas. In recent communication trends like Internet of Things (IOT)
these wearable antennas engage themselves in decisive roles where the data connectivity
between smart devices is made achievable across the world. They can be worn by fabricating it
in any textile material and the demand for wearable antennas are increasing widely in the areas
like Medical applications, smart gadgets, remote monitoring and Defense applications. The
antenna designated for wearable application should posses the characteristics like size
compatibility, low specific absorption rate (SAR), better efficiency, flexibility to withstand the
bending and twisting effect in the fabric. Antenna should also be able to survive the loss due to
near field effect of human body since they act as a lossy material which absorbs energy from
electromagnetic waves resulting in large reduction of antenna efficiency. Microstrip antenna is
one of the best suited antennas for the above mentioned requirement since it is easy to fabricate
in the textile material, conformal in nature and can be hidden in the clothing. This paper is
broadly arranged into three categories which describes about the requirements of wearable
antennas, study of substrate characteristics and review of different substrate materials used in
microstrip antenna which can be used in wearable application.
Keywords: Body area network (BAN), Internet of Things (IOT), specific absorption rate (SAR),
Microstrip antenna, conformal antenna

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I. INTRODUCTION
Wireless network of wearable computing device which is made more feasible by new
advancements in technologies like compact size, lightweight, extremely low power utilization
and proficient surveil wearable sensors are termed as body area networks (BANs) . BANs are
those in which sensors endlessly keep track of human’s biological or functional behavior. The
WBAN faces many limitations like characteristics of physical layer plays a vital role, the path
loss estimation within different nodes of the body and delay spread prediction. These
characteristics of WBAN require a detailed knowledge on the propagation of EM waves and the
behavioral characteristics of antenna in the near field region of human body.
The wireless Body area networks may have a wide variety of trending application in thrust realm
namely physical fitness observation and so on as mentioned earlier but to satisfy these
applications the WBAN has to overcome many challenging issues by considering the following
criterias deployed with the sensors like SAR, Power Efficiency, Inter and intra sensor
communication protocols, routing protocols, network backbone and so on.
II. THE DESIGN REQUIREMENTS OF WEARABLE ANTENNA
The wearable antenna should be designed by considering the following factors like low profile,
near field effect of human body, specific absorption rate, dielectric permittivity, Bending and
twisting effect of the textile worn antenna thereby producing a better efficiency and gain.
Size compatibility: Wearable antennas should satisfy the requirements like low profile including
light weight, smaller volume and easy fabrication. These requirements are fulfilled by the
microstrip antennas except they operate in narrow bandwidth and high frequency. These
drawbacks can be overcome by modifying the thickness of the substrate, introducing different
feeding techniques, cutting slots, altering the impedance matching techniques and including
multiple resonators in microstrip antenna based on the application of wearable device.
Proximity to human body: Human body has the properties similar to dielectric material. The
performance characteristics of the on body and off body antennas differ in many aspects. In

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wearable devices the antenna is placed in near field to the human body which is the reactive zone
or non-radiative phase and the effective transmission take place after the transition zone in the
far field medium resulting in a more lossy transmission.
SAR: The SAR with respect to EM waves or energy is given by the E filed inside the human
tissue. It can be best described in the equation as
𝑺𝑨𝑹 =
𝟏
𝑽
𝝈(𝒓) 𝑬(𝒓) 𝟐
𝝆(𝒓)
𝒅𝒓
𝒔𝒂𝒎𝒑𝒍𝒆
Where
𝜎 - Electrical conductivity of the sample tissue
E - RMS electric field
𝜌 - Density of the sample tissue
𝑉 - Volume of the sample tissue
The FCC has fixed the SAR limit below 1.6 W/Kg per 1 gm of human tissue and average value
of 2 W/Kg per 10 gm of sample tissue.
Bending and twisting effect: The wearable antenna when embedded or fabricated in the textile
material is expected to undergo bending and twisting effects [1]. These effects of bending and
twisting should be checked in axial, radial and tangential directions to ensure maximum
efficiency. The design should be in such a manner that these effects don’t produce any change in
the radiation pattern and reflection coefficient.
Permittivity and Permeability:
The speed of electromagnetic radiation is also same as that of the light which is dependent on the
factors like permittivity and permeability in free space. They tend to slower the speed of EM
waves and decrease the wavelength. Hence wearable material of the antenna has to be chosen in
such a way with low values of permittivity and permeability [4] to achieve higher wavelength
based on different application requirements of wearable device.

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III. SUBSTRATE CHARACTERISTICS IN MICROSTRIP ANTENNA
The basic rule addressing the design of microstrip antenna lies in the substrate selection. The
dielectric materials are preferred as a substrate to provide mechanical strength to the antenna
which may affect the electrical property of it. The important substrate properties like dielectric
constant and loss tangent their behavior with different parameters has to be considered. The wide
range of substrates in the microstrip antenna can be grouped or classified under few major
streams of substrates namely:
1. Ceramic
2. Semiconductor
3. Ferrimagnetic
4. Synthetic
5. Composite Material
The flexible or wearable antenna mainly falls under the composite material category.
Considering the wearable nature of the antenna and keeping flexibility as a major concern the
following materials like Polytetrafluoroethylene (PTFE), polystyrene, polyolefin, polyphenylene,
alumina, sapphire, quartz, ferromagnetic and rutile can be more suited for different wearable
applications. These materials satisfy the conformal nature of the Antennas. The properties of few
substrate materials are listed below:
TABLE I : Characteristics of Substrates at 10 GHz
Substrate material Dielectric constant Loss tangent
Polytetrafluoroethylene 2.1 0.0004
polystyrene 2.4–2.7 0.0004
glass microfiber : 4E-4
polyolefin 2.30 0.0003
Polyphenylene 2.55 0.0016

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Alumina - 99.5% 9.8 0.0004
sapphire 9.4, 1.6 0.0001
quartz 3.8 0.0004
IV. LITERATURE SURVEY
A review on the previous wearable antenna was carried out to obtain a clear outline about the
behavior of different material for variety of applications and their drawbacks can be analyzed.
Rui Pei, et.al. explains about the wearable antenna used for medical application [1]. In this
paper analysis was performed at 2.4 GHz with the help of two different antennas, former one
was with the FR4 substrate on a rectangular shaped patch and the later one was using the soft
textile material with the same design. The study of textile material with the relative permittivity
(𝛆r) ranging from 1.5 to 2.2 was carried out with the materials like cotton, wool, Elano-wool,
viscose and polyester.
The boon and bane of the simulations performed are ordered respectively. The conventional
rectangular patch would meet the design requirements for the wearable system with high gain
but with the added cost for the copper material used. The bending effect of the antenna has very
minimal effect in the parameters like reflection coefficient and radiation pattern. The antenna
has to be simulated in a more complex environment similar to human phantom model and the
SAR value on the human body should be considered. The bending effect was considered only in
the axial direction whereas the radial and tangential directions also have to be analyzed.
Hadi Bahramiabarghouei, et.al proposed a wearable antenna [2] specialized for breast cancer
detection within the frequency band of 2- 4 GHz. It should satisfy the requirements like low
profile, biocompatible and dual polarization. The Spiral shaped antenna was designed and
embedded on the array to enable the surface current in both the directions. The substrate was
designed with the thickness of 0.05-mm and the material was chosen as Kapton polyimide. The
value of 3.5 was its estimated relative permittivity. The proposed antenna serves as

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biocompatible component because of the superstrate layer protecting both antennas hence
making it safe on human body. Future work planned for this methodology will be to implement
it on patients with a prototype for improved microwave imaging.
Sherif R.Zahran, et.al proposed a monopole wearable antenna [5] for Ultra wide band (UWB)
with flexible substrate satisfying robustness thermal endurance and can perform at its best with
extreme bending. The substrate used was Rogers Ultralam 3850 with LCP (Liquid Crystalline
Polymer) which should meet the requirement of 2.9 as its dielectric constant and 0.0025 as its
required loss tangent value. The frequency range of 4 GHz to 10.6 GHz was observed as its
operational bandwidth which satisfies almost 80% of ultra wide band range. The radiation
pattern observed was also Omni directional in nature except at higher frequencies. The analysis
of Specific absorption rate (SAR) has to be performed in human phantom model.
Albert Sabban proposed a metamaterial antenna and fractal antenna [6] with wearable
characteristic. These antennas have compact size and multiband application. The gain and
directivity was enhanced by introducing a SRR (Split Ring Resonator) by 2.5dB rather than
using an ordinary patch antenna. The methodology also shows that the effective area of the
fractal antenna is appreciably high than the regular printed antenna. The antenna is dual
polarized and its mounted in the belt for testing in patients. The SAR analysis and proximity of
human body has to be considered for analysis.
Abd Rahman, N.H, et.al elucidated the implementation of textile antenna on the surface of
human body [7]. Unlike the previous works he also took the human body effect into
consideration and how it affects the performance of the wearable application more precisely in
terms of frequency shift and efficiency. In the design perspective the electro textile had the
properties like electrical conductivity 2.2 x 10^4 s/m and fabric composition of 83% copper and
17% polyester. In spite of copper being the main component of the e-textile material the
conductivity is lower because of the non conductive polyester. Hence the ideal performance is
not achieved.
V. SUMMARY
The portal devices has distinct fault finding components known as wearable antennas
henceforth utmost care is necessary in designing them with human body in the near field region.
The study was carried out in such a way initially the requirements of the wearable antenna was

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listed and the major classifications of the substrate was also discussed by listing few substrate
parameters. The survey on previous works shows that the performance criteria like bandwidth,
Gain, efficiency has to be maintained based on the application needs thereby maintaining the
specific absorption rate under the norms and having a low profile design with conformal
antenna. However the trade off in the performance characteristics has to be chosen based on
the wearable application needs.
ACKNOWLEDGEMENT
I would like to express my special thanks of gratitude to the management, the principal and the
Head of the Department of Electronics and communication Engineering of Sri Ramakrishna
Engineering College, Coimbatore for providing facilities and research guidance in our
Department.
REFERENCES
[1] R. Pei, J. Wang, M. Leach, Z. Wang, S. Lee and E. G. Lim, "Wearable antenna design for
bioinformation," 2016 IEEE Conference on Computational Intelligence in Bioinformatics
and Computational Biology (CIBCB), Chiang Mai, Thailand, 2016, pp. 1-4, doi:
10.1109/CIBCB.2016.7758129.
[2] H. Bahramiabarghouei, E. Porter, A. Santorelli, B. Gosselin, M. Popović and L. A.
Rusch, "Flexible 16 Antenna Array for Microwave Breast Cancer Detection," in IEEE
Transactions on Biomedical Engineering, vol. 62, no. 10, pp. 2516-2525, Oct. 2015, doi:
10.1109/TBME.2015.2434956.
[3] Saqib Hussain , et.al. “Design of Wearable Patch Antenna for Wireless Body Area
Networks” on (IJACSA) International Journal of Advanced Computer Science and
Applications, Vol. 9, No. 9, 2018 PP:146 – 151.
[4] El Gharbi, M.; Fernández-García, R.; Ahyoud, S.; Gil, I. A Review of Flexible Wearable
Antenna Sensors: Design, Fabrication Methods, and Applications. Materials 2020, 13,
3781. https://doi.org/10.3390/ma13173781
[5] S. R. Zahran, A. Gaafar and M. A. Abdalla, "A flexible UWB low profile antenna for
wearable applications," 2016 IEEE International Symposium on Antennas and

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Propagation (APSURSI), Fajardo, PR, USA, 2016, pp. 1931-1932, doi:
10.1109/APS.2016.7696672.
[6] A. Sabban, "Small wearable antennas for wireless communication and medical
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[7] Abd Rahman, N.H.; Yamada, Y.; Amin Nordin, M.S. Analysis on the Effects of the
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[8] Microstrip Antenna Design Handbook by Ramesh Garg, Prakash Bhartia, Inder Bahl and
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