Flexible Miniaturized UWB CPW II- shaped Slot
Antenna for Wireless Body Area Network (WBAN) Applications Amal AFYF I
,
,'
'* , Larbi BELLARBI ' , Fatima RIOUCH
2,
Anouar ACHOUR 4 Mohamed.Adel SENNOUNI
"
Abdelhamid ERRACHID
3,
Electrical Engineering Laboratory (LGE), Higher National School of Technical Education (ENSETI ENSIAS) Rabat, Morocco 2
STRS Laboratory, National Institute of Post and Telecommunications (INPT). Rabat Morocco 3
Institute of Analytic Sciences (ISA) Lyon University-France 4
LITEN Laboratory of FST-Settat-Morocco
( * )
[email protected];
[email protected] Abstract-A
flexible microstrip antenna printed on a Kapton
design, low cost, easy system implant etc. So the design should
Polymide substrate, excited by a CPW feed line, and operated in
be such that antennas performance is not deteriorated even if
S-band at 3.5GHz, is successfully validated. Unlike previous
they are bent. During last few years researchers have been
flexible antennas, this structure offers a very thin thickness (O.16mm) with overall dimensions of 36x25 mm2 that assure an
working on various aspects in wearable antenna designs.
easy integration into clothes and wireless body area network
(WBAN)
systems. Modeling and performance evaluation of the
proposed antenna in term of return loss, voltage standing wave ratio,
radiation
pattern,
and current distribution have been
carried out using CST -MW STUDIO Software. Keywords-Flexible
Microstrip
Antenna;
Some researchers have proposed flexible antennas which can be easily integrated into clothing [6-19]. This paper is organized as follows: Section II and III respectively introduce,
Design Procedures and Simulation
Results for the proposed antenna. Conclusion is shown in
Kapton
Polymide;
S
Section
IV.
As
antenna
in
subsequent
optimization
STUDIO.
simulations with CST Microwave Studio [8]. I.
of
described
Band; Wireless Body Area Network (WBAN) Systems; CST-MW
TABLET.
INTRODUCTION
structures
market
analysis,
the
revenue
of
Professional & Amateur Sport Training
flexible Wearable WBAN
300 billion USD in 2028 [1]. Their light weight, low-cost
Asthma
manufacturing, ease of fabrication, and the availability of
Sleep staging
flexible
substrates
(i.e.:
papers,
textiles,
and
Medical
Wearable Health Monitoring Implant WBAN
plastics) make flexible electronics an appealing candidate for
Diabetes Control Cardiovascular Detection
the next generation of consumer electronics [2]. Moreover, recent
developments
in
miniaturized
and
flexible
Cancer Detection
energy
Remote control of
storage and self-powered wireless components paved the road
Ambient Assisted Living (AAL)
Medical Devices
for the commercialization of such systems [3]. Consistently,
Patient Monitoring Tele-medicine Systems
the new wireless protocols for body area networks (WBANs)
Real Time Streaming
are highly attractive as future solutions for a wide ranging applications
including,
military,
health
care,
by
Battle Management
electronics is estimated to be 30 billion USD in 2017 and over
inexpensive
the
out
Soldier Fatigue Assessment and
Recent years have witnessed a great deal of interest from to
sections,
carried
WBAN ApPLICATIONS
both academia and industry in the field of flexible electronics. According
was
Entertainment Applications
sport
Emergency(non-medical)
Non-Medical
entertainment and many others have been categorized into two
Emotion Detection
main areas by the IEEE 802.15.6 standard. These two areas are
Secure Authentication
medical and non-medical (Conswner Electronics) [4-5]; shown
Personal information sharing
in Table I. While talking about wireless body area networks, suddenly it comes into mind that how the signals would be
II.
communicated? Well, an antenna, which is a fundamental part of the network, is the answer for this. Flexible antenna is one of the most fascinating and cutting edge research areas of modern era. It provides a wearable interface between human and the machine. Since we are talking about wearable antennas, it is necessary to mention here that antennas for such applications should possess certain properties like light weight, confonnal
52
A. To
ANTENNA DESIGN
Choice of antenna substrate comply
with
flexible
technologies,
integrated
components need to be highly flexible and mechanically robust; they also have to exhibit high tolerance levels in tenns of bending repeatability and thermal endurance. A lot of design approaches of flexible and confonnal antennas were reported
978-1-4673-8096-6/15/$31.00 ©201 5 IEEE
in
the
literature
including
Electro-textile [9],
paper-based A
[10], fluidic [11], and synthesized flexible substrates [12]. Kapton Polyimide film was chosen as the antenna substrate due to its good balance of physical, chemical, and electrical properties with a low loss factor over a wide frequency range ( tan ()
=
0.002 ). Furthermore, Kapton Polyimide offers a
very low profile (50.8 fJm) yet very strength
of
165
MPa
at
73°F,
a
robust
with
dielectric
a
tensile
strength
of
3500-7000 volts/mil, and a temperature rating of -65 to 150°C [13]. Other Polymer based and synthesized flexible substrates have been also used in several designs [14-15].
Choice offeed technique
B.
It is worth mentioning that there are several techniques used to characterize the electromagnetic properties of thin and flexible films/substrates such as: the near field microscopy, Co planar Waveguide CPW approach, differential open resonator method, and goniometric time domain spectroscopy method [16-17]. However, in this work, Co-Planar Waveguide (CPW) Fig.l. The proposed flexible CPW antenna
is preferred over other feeding techniques since no via holes or shorting
pins are
involved,
in addition to several useful
characteristics such as: low radiation losses, larger bandwidth, improved impedance matching, and more importantly, both radiating element and ground plane are printed on the same side of the substrate, which promotes low fabrication cost and
The table below presents the various parameters of the antenna shown in the Fig.l. TABLE I!.
PHYSICAL DIMENSIONS OF THE ANTENNA
complexity. C.
Antenna parameters
In this paper a flexible CPW rectangular antenna 3 (25X36XO.16 mm ) with a II- shaped slot in the medium of the radiator and two tuning stubs is developed. The extremely thin Kapton-substrate Hs used in the design makes the antenna suitable for being implemented or pasted on clothes. Fig.l shows the geometry shape of the proposed antenna. The ungrounded antenna is etched on Kapton Polyimide substrate with a thickness of Hs and dielectric constant of 3.4. in order to maintain the flexibility of the antenna the excitation is made through a 50n CPW feed line. Then by using optimization solver in CST-MW Studio several optimization processes was applied until we got the desired performances of the antenna. Table
below
presents
the
optimized
parameters
of
the
developed antenna.
D.
RESULTS AND DISCUSSION
To show the effect of the structure geometry, we have started from a simple rectangular patch (Antenna a), and by adding respectively a II- shaped slot (Antenna b), and tuning stubs we arrived to model the proposed design (Antenna c), Fig.2
53
VSWR (a)
(b)
(c)
Fig. 2. The geometric shape of the CPW rectangular antenna: (a) simple rectangular antenna,(b) CPW rectangular antenna with IT-shaped slot in the radiator,and (c) CPW rectangular antenna with two antiparallel tuning stubs in the ground and IT-shaped slots in the radiator. Fig. 4. The simulated VSWR of the three antenna structures
This section mainly presents the major simulation results of the designed antenna. From Fig.3 it is seen that the antenna (c) has a good impedance matching with a return loss of about -32dB at the operating frequency of 3.SGHz. Moreover the antenna shows a broadband propriety with an impedance bandwidth of about S70MHz which is from 3.23GHz to 3.7SGHz as shown in Fig.3. Further Fig.4 shows the obtained simulated Voltage Standing Wave Ratio (VSWR). From the graph it's clear that at 3.SGHz the antenna provides a
In Fig.S, the simulated variation of the antenna input impedance versus frequency of the developed antenna can be seen. the
It is observed that the antenna is quit well matched to SO n
impedance. Then at the operating frequency of
3.SGHz, the average value of the resistance (real part) is SO Ohms, also the average value of the reactance (imaginary part) is O-Ohms which provides the adequate input impedance matching at the desired resonant frequency.
minimum VSWR of about 1.0S (less than 2), which is within the recommended range. The obtained result indicates that the transmitter and antenna are well matched and a maximum possible amount of energy is absorbed at the input terminal
Return Loss (dB)
with a minimum reflected power.
Fig. 5. Simulated antenna impedance (Ohm) vs. frequency of the proposed CPW antenna
Current distribution determines how the current flows on the patch antenna. Fig. 6 demonstrates these results. We observe
a
high
strength
of
current
radiates
along
the
transmission line, the edges of tuning stubs, and the IT-shaped Fig. 3. Simulated return loss of the different antenna structures
54
slot.
Gain (dB) Fig. 6. Current density at 3. 51 GHz
The radiation pattern taken for the far-field at 3.51GHz is indicated by the 3D view in Fig.7. The directivity of the Fig. 9. Simulated antenna gain vs Frequency
proposed antenna is about 3dBi. Further, Fig.8 indicates that the antenna provides a directional behavior in both E-plan (a)
III.
and H-plan (b).
CONCLUSION
A newly miniaturized CPW antenna structure has been successfully designed and simulated via CST Microwave Studio. The performance criteria extracted from the software includes Return Loss, YSWR, Radiation Pattern, and Surface Currents, provide clear indication that the proposed design is suitable for WBAN applications; due to its good matching input impedance at the operating frequency of 3.5GHz and its broadband propriety. Further, the miniaturized size of the developed antenna with the enhanced gain of 4dB that exhibits at 3.5GHz, are good features for such applications. Future work will focused to explore the accuracy issues observed here for the inclusion of the body phantom in the simulation model before the realization stage and measurement tests. REFERENCES
Fig. 7. 3D radiation pattern at 3. 51GHz
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