IET Microwaves, Antennas & Propagation

Research Article

e-Textile embroidered wearable near-field ISSN 1751-8725

Received on 1st December 2017
Revised 11th August 2018
communication RFID antennas Accepted on 5th September 2018
E-First on 15th October 2018
doi: 10.1049/iet-map.2018.5435
www.ietdl.org

Yutong Jiang1 , Lulu Xu2, Kewen Pan1, Ting Leng1, Yi Li2, Laith Danoon1, Zhirun Hu1
1School of Electrical and Electronic Engineering, The University of Manchester, Oxford Road, Manchester, UK
2School of Materials, The University of Manchester, Oxford Road, Manchester, UK
E-mail: yutong.jiang@manchester.ac.uk

Abstract: Wearable e-textile near-field communication (NFC) radio-frequency identification (RFID) antennas fully integrated
with garments using embroidery techniques, which enables everyday clothing to become connective to wireless communication
systems, is presented. The e-textile wearable antennas have been designed through full electromagnetic wave simulation
based on the electrical properties of conductive threads and textile substrates at the high frequency band, allocated for NFC
wireless communications. The e-textile wearable NFC antenna performance under mechanical bending as well as human body
effects have been experimentally studied and evaluated; the antennas can operate under significantly bending angle and body
effects attributed to its broad operating bandwidth. This is highly desirable and distinguished to conventional NFC antennas; the
proposed e-textile wearable NFC antennas can be placed almost any place on clothes and still capable to communicate at the
desired operating frequency of 13.56 MHz. The maximum read range of the e-textile wearable NFC tags is measured to be
around 5.6 cm, being compatible to typical commercially available metallic NFC tags. The e-textile wearable NFC tags can lead
to numerous potential applications such as information exchange, personal security, health monitoring and Internet of Things.

1 Introduction while the reading of UHF RFIDs requires specific receiving

antenna with relatively large sizes [12].
In recent years, near field communication (NFC) has become Among existing NFC tag antenna research, Iqbal and Saeed
increasingly popular in commodity market and believed to be one [13] have analysed metal NFC circuit performance regarding to
of the technologies that would realise the ubiquitous connectivity various resonant frequencies and return loss presented with
between the virtual internet world and the physical world for simulation results only, and Del-Rio-Ruiz and Lopez-Garde [14]
Internet of Things (IoTs) applications. The main function of an have mainly discussed how textile based NFC circuits
NFC system is contactless communication between NFC tag and measurements respond to different types of substrate material. In
reader without the requirement of any external battery. The first this paper, NFC RFID antennas integrated with garment using
development of NFC tags can be traced back to 1970 when it was embroidery technology are proposed, designed, fabricated,
called ‘short-range radio-telemetry for electronic identification measured and characterised. Different from previous research, our
using modulated backscatter’ [1]. Till this day, NFC technology work focuses on design and performance of purely textile-based
has been applied in numerous fields such as, ID cards, debit/credit NFC tags regarding to the specific requirements for daily
cards, itemised commodities and hotel room keys [2]. wearables, for instance, when an NFC tag is bent from body
The operating frequency of an NFC antenna is typically set at movements, the resonant frequency shifts away from 13.56 MHz,
13.56 MHz. A passive NFC tag operates by the transmitted power which could easily result in communication failure. To prevent this,
from the reader [3]. Magnetic induction coupling is applied the NFC structure in this work is designed to achieve an operating
between the tag antenna and the reader antenna within a short bandwidth that is considerably wider than commercial ones. In
distance to draw its necessary operating power for the IC chip on fabrication, conductive threads with fairly low resistivity are
the tag from the reader's electromagnetic field. NFC antennas integrated seamlessly with skin-friendly textile material, such as
possess a working distance that is typically around a couple of cm cotton, which possesses the flexibility to be easily applied to
to a few tens of cm and a data transfer rate around 424 kbits/s for everyday garments. Microchips are bonded on the NFC antennas,
which the maximum value is up to 848 kbits/s [4]. which contain the information to be accessed by an NFC reader
The application of NFC tags for wearable wireless wirelessly. The novel e-textile wearable NFC tags are expected to
communications has been challenging since existing antenna lead to numerous potential applications within the fields such as
fabrication methods, including chemical etching and screen information exchange, personal security, health monitoring and
printing, are not particularly suitable for close-fitting wearables [5]. IoTs [15, 16].
Recently, researchers have developed various types of textile This paper is structured as follows. Section 2 will discuss the
antennas that realise off-body communications, such as patch design methodology of e-textile wearable NFC antennas, material
antennas applied in protective clothing for firefighters and basic selections and embroidery technique. In Section 3, measurements
attachments for normal garments [6, 7]. Wearable ultra-high of the fabricated NFC tags are presented together with their RF
frequency (UHF) radio-frequency identification (RFID) antennas performance evaluation (S-parameters) under various degrees of
have also been developed and implemented on smart textiles for bending. Furthermore, the wireless reading measurements of the
various applications, such as body-centric sensing and apnea NFC tags including the effects of bending and human body contact
detection and the maximum read range is up to 16 m for patch are provided. Section 4 summarises the key results and findings.
UHF RFID antenna circuits with microchip connections [8–11].
Very different from UHF RFIDs, NFC RFIDs have limited read
range usually within a few centimetres, which are preferred in
more personal applications that require high security levels.
Moreover, NFC RFIDs can be read by NFC-enabled smartphones

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2 Design methods and procedures
2.1 NFC design and simulation
For a passive NFC tag, the read range depends on the minimum
transmitted power needed to operate the tag circuitry. Therefore,
the main challenges in the design process are (i) to minimise the
power dissipated by the antenna and (ii) to maximise the
conversion efficiency between the electromagnetic power from the
reader and the DC power consumed by the tag [3].
Fig. 1 presents a simplified equivalent circuit for the microchip Fig. 1 Equivalent circuit model of an NFC-microchip matching network
and antenna, where the antenna is designed to conjugately match
the microchip. The antenna inductance Lant can be derived from the
following equation [17]:

1
Lant = (1)
(2π f r)2Cchip

where f r stands for the circuit resonant frequency and Cchip stands
for the chip capacitance.
Commercially available metallic NFC tags are usually designed
with narrow bandwidth and Q factor around 30–40 in order to
achieve high transmitting efficiency [18]. However, textile-based
NFC tags especially require relatively wide operating bandwidth to
be able to tolerate clothing shape change and human body effects.
The proposed NFC structure is designed and optimised to meet this
requirement.
The NFC antennas in this work have been designed in a shape
of rectangular spiral coil. The antenna dimensions are optimised
with the antenna inductance according to (2) [17], based on which
the preliminary layout of the NFC antenna is built for full wave
simulation

d
Lant = K1 μ0N 2 (2)
1 + K2 p

where d is the coil diameter which is the mean value of the outer
and inner diameters of the coil (dout and din); note: for a square
shaped coil, dout and din, respectively, represent the outer and inner
lengths of the edges which are highlighted in Fig. 2. N is the
number of turns; K1 and K2 are parameters that depend on the
layout, which are, respectively, 2.34 and 2.75 for square line
inductors [12]; µ0 is the free space permeability and p = (dout −
din)/(dout + din).
Fig. 2 CST model of designed NFC RFID antenna and simulated results
Figs. 2a and b present the NFC antenna layout created with (a) Model front view, (b) Cross-section cutting plane, (c) Simulated reflection
CST Microwave Studio [19]. The antenna is fed by a discrete port coefficient (S11) from the CST model
that connects both ends of the NFC coil. The cross-section of the
thread is assumed to be circle with radius of 0.25 mm. The choice
of threads and yarns for these NFC RFID antennas is a trade-off 2.2 Fabrication
between their electrical and mechanical properties. In other words, Thirty NFC antenna prototypes embroidered on cotton substrate,
they are selected to be not only conductive but also structurally made with conductive yarns coated with several types of metals,
stable under possible bending [20]. In order to meet these including silver, stainless steel and aluminium, have been designed
requirements, threads used to construct NFC antennas are chosen and fabricated on cotton. Four samples of these circuits are shown
as polyamide threads coated with silver. Although metal wire in Fig. 3. Among all the coating materials, silver and stainless steel
threads have also been considered in the design process due to their are believed to be the best choices for such conductive yarns to
relatively low resistivity, their toughness and electrical stability are apply on wearables [22, 23]. Due to the high inertness of these two
rather low and less suitable for textile circuits. The thread used in types of metal, they would not be much affected by sweat or
this work has a resistivity of 17.2 Ω/m, which is an order higher moisture from the user. Moreover, silver and stainless steel have a
than aluminium used for commercial metallic NFC antennas. high resistance against water and low concentrated acid so that the
Cotton (Er = 2.31) has been chosen as substrate material due to its textile circuit would be applicable to dry cleaning and even mild
comfort level to human skin. NXP SL2S2102FTB microchip has water cleaning.
been chosen in this work. The chip input capacitance is 97 pF at Fig. 4 illustrates two embroidery techniques, back stitch and
13.56 MHz. satin stitch, in fabricating NFC antennas, respectively. Both
Fig. 2c illustrates simulated reflection coefficient (S11) of the antennas were constructed using stainless steel coated nylon
optimised NFC antenna in the Smith chart. The NFC antenna threads. From the perspective of the stability of the structure, satin
model has impedance of 16.71 + j120.32 Ω at 13.56 MHz, which stitch is better than back stitch since it is more difficult to be
indicates an antenna inductance of 1.41 μH. The imaginary part snapped or ripped off. However, due to the fact that the satin stitch
conjugately matches the microchip (SL2S2102FTB) input requires much longer threads for the same antenna size, the DC
reactance −j121 Ω, and the chip resistance is large enough to be resistance of the antenna in Fig. 4b is measured as 70 Ω, which is
considered as an open circuit and therefore to be ignored in the much higher than the one in Fig. 4a that is 11.6 Ω. For this very
connection with tag coil [21]. reason, back stitch is used in this work.

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 Table 1 NFC antenna parameters
Length, mm Width, mm Spacing between Number of turns
turns, mm
49.5 49.5 1.9 4

Fig. 3 Selected NFC antenna samples

Fig. 6 Measured reflection coefficient S11 in Smith chart format

(a) Antenna coil measurements, (b) Antenna connected with matching circuit

are fabricated for the purpose of performance comparison. The

antenna dimensions are listed in Table 1. Figs. 5a and b show
antenna coils made with silver coated nylon conductive threads
with 0.5 mm thickness (Arduino Flux Workshop) and stainless
steel coated conductive threads with 0.3 mm thickness
(BEKAERT) by back stitch embroidery technique. The DC
resistance of the antenna is measured as 9.9 and 21.6 Ω,
respectively. A copper NFC tag with on FR4 substrate (Er = 4.7)
with a line width of 0.5 mm and a thickness of 17.5 μm is
presented in Fig. 5c as copper is one of the most common material
in commercial NFC manufacture, the DC resistance of which is
Fig. 4 Stainless steel coated NFC antennas observed under a microscope
only 2.2 Ω.
corresponding to two different fabrication techniques
The antenna is designed to be matched up with an NXP
(a) Back stitch technique, (b) Satin stitch technique
microchip SL2S2102FTB which can be regarded as purely
capacitive. Referring to Fig. 1, only the imaginary parts between
the microchip and antenna can be matched conjugately as the coil
antenna cannot be lossless. To realise the best power transmitting
efficiency the microchip series resistance (∼0) and antenna
resistance need to be as close as possible [24]. Therefore, silver-
coated conductive threads are preferred rather than those with
stainless steel coatings due to a lower resistivity.

3.2 Bandwidth
In order to verify the resonant frequency and bandwidth of the
NFC tag antennas, S-parameters of the antenna were measured
using Keysight Fieldfox VNA N9918A.
Fig. 6a shows the S11 of the silver-coated textile antenna coil in
the Smith chart, the antenna has measured the impedance of 13.5 +
j119.5 Ω at 13.56 MHz, which is fairly close to the designed value
(16.7 + j120.3 Ω). The coil inductance calculated from this
measurement is 1.4 μH.
The quality factor of the antenna can be calculated from the
measured resistance and inductance using the following equation
[25]:

2π f rLant
Q= (3)
R

Fig. 5 NFC antenna prototypes

where f r is the antenna resonant frequency and Lant and R are the
(a) Silver coated conductive threads embroidered with cotton, (b) Stainless steel coil inductance and resistance, respectively. The Q factor of the
coated conductive threads embroidered with cotton, (c) Copper on PCB proposed textile NFC tag is 8.85.
In order to test the tag performance at the operating frequency, a
3 Results and discussion matching circuit consisted with a resistor (36 Ω) and a capacitor
(97 pF) is connected in series with the antenna coil. The capacitor
3.1 DC characteristics value is chosen as the input capacitance of the microchip so that
the imaginary part is matched to zero, and the purpose of the series
In Fig. 5, three NFC RFID antennas with the same structure are
resistor is to match the circuit impedance with the VNA input
presented, where Fig. 5a is the proposed circuit and Figs. 5b and c
impedance (50 Ω) in order to minimise reflected power at the
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 Fig. 9 Measured S11 magnitudes for four different bending cases shown in
Fig. 7 S11 results of NFC circuits made of e-textile and copper in Fig. 8 and without bending
magnitude (dB) against frequency
3.3 Bending test
Table 2 Experimental result comparison between NFC tags
manufactured with e-textile and copper To integrate e-textile NFC RFID antennas into close-fitting
Material Silver Stainless steel Copper garments, it is essential to ensure it has stable electrical properties,
coated coated such as operating efficiency and read range, when the antenna is
under natural human body movements. Since the antenna is applied
DC resistance, Ω 9.9 21.6 2.2
to a cotton substrate which can be easily bent out of shape, natural
network impedance at 13.5 + j119.5 26.2 + j124.5 2.5 + j119.2 bending seems to be the factor that would most likely affect the
13.56 MHz, Ω antenna operation. Therefore, it is necessary to determine how the
Q factor 8.85 4.75 47.7 antenna performance would change with different bending.
maximum transmitted 32.52 32.03 38.09 Fig. 8 illustrates bending tests of the NFC antenna using U-bend
energy, dB method [27] where four plastic cylinders with different diameters
10 dB bandwidth, MHz 3.787 3.794 3.610 are applied for the NFC antenna to be bent around. The measured
S11 magnitude and impedance with and without bending are shown
in Fig. 9 and Table 3, respectively.
As presented in Fig. 9, the resonance frequency and operational
bandwidth of the NFC antenna change slightly as the bending
increases. However, due to the broad bandwidth of the antenna, the
shift of resonant frequency would not affect the RFID reading as
long as 13.56 MHz still falls within the 10 dB bandwidth.
In Table 3, Z(fc) represents the matched antenna impedance at
each central frequency for different bending. The imaginary part of
the antenna impedance decreases as the bending increases, which
indicates gradual decrements of the antenna inductance. This is due
to the fact that when the antenna is no longer planar but bent
Fig. 8 Antenna bent around four cylinders with decreasing diameters of around the cylinder, the current flowing in the opposing sides of
(a) 35 mm, (b) 28 mm, (c) 23 mm, (d) 17 mm the antenna is drawn closer to each other, thus the electromagnetic
field exists on both sides of the circuit which tend to introduce
resonant point. The circuit impedance after matching is presented extra electrical coupling that cancels out the inductance of the
in Fig. 6b, where the admittance is almost entirely cancelled out antenna. Consequently, the NFC resonance frequency goes up as
and the resistance is matched to ∼50 Ω. the antenna inductance decreases.
Fig. 7 depicts the measured S11 magnitude of the three NFC
antennas shown in Fig. 5. The detailed comparison results are 3.4 Power transmission and wireless reading
listed in Table 2. All three antennas resonate around 13.56 MHz as
designed with return loss of −32.52, −32.03 and −38.09 dB, After the NFC antenna is connected with a microchip, the
respectively. The 10 dB bandwidth results of the textile antennas contactless antenna verification method described in [17] is
coated with silver (3.787 MHz) and stainless steel (3.794 MHz) are performed to determine the NFC antenna power transmission
slightly wider than the one of copper antenna (3.61 MHz), which is pattern during wireless measurements as presented in Fig. 10a.
also considerably wider than that of commercial NFC tag antennas From the measurements shown in Fig. 10b, the detected voltage
[26]. The wide bandwidth is a critical parameter for wearable levels with an oscilloscope are higher than the source voltage
applications as the resonant frequency of the antenna shifts when (0.25 V), which means the magnetic field produced by the
the garment bends. For a narrow band antenna, the shift of the generator coil induces a current flow in the NFC tag, and the
resonance frequency will cause the tag unreadable by NFC readers. magnetic field generated from this current is captured by the
oscilloscope coil. At tag resonant frequency, the current flowing
In Table 2, the Q factor of copper NFC circuit is considerably into the tag antenna is maximised. As a result, the proposed NFC
higher than the ones made with metal-coated conductive threads antenna is able to achieve the maximum transmitted power at 13.6
since the power transmitting efficiency is directly related to the MHz, showing the antenna is well tuned.
antenna resistance. Considering a trade-off between the working In order to measure the NFC tag read range, a microchip (NXP
efficiency and operating bandwidth required for textile integrated SL2S2102FTB) has been connected to the NFC antenna as shown
circuits, the proposed silver coated e-textile based NFC antenna is in Fig. 11a.
fairly applicable. A USB-connected Texas Instruments reader (TRF7970A) is
used for the read range measurement. The experimental setup for
tag reading is presented in Fig. 11b, where the reader is held
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Table 3 Results for bending tests
bending diameter, mm N/A 35 28 23 17
fc, MHZ 13.56 13.82 14.10 14.23 14.64
return loss, dB −32.52 −29.91 −31.1 −30.54 −32.42
Z(fc), Ω 49.6 − j3.5 51.9 − j8.9 50.5 − j11.8 50.9 − j14.6 50.4 − j20.2

Fig. 11 Read distance measurements

(a) Fabricated e-textile wearable NFC RFID tag, (b) Tag reading experimental setup,
(c) NFC tag detected by the RFID reader (facing forward), (d) NFC tag detected by the
RFID reader (facing backward)

going through the antenna coil. Nonetheless, due to the wide

bandwidth of the antenna, the NFC tag is able to be read within
0.5 cm even though the tag is almost completely folded (180°
bending angle).
Fig. 10 Contactless antenna verification
(a) Measurement setup, (b) Detected voltage level versus frequency
3.5 Effects of human body
horizontally above the tag with a laboratory stand and the distance In order to ensure the e-textile wearable NFC RFID tag is fully
between is measured with an electrical vernier caliper. It is crucial functional in daily use, it is necessary to take measurements with
that no metal surface is near the tag or the reader, otherwise the human skin contact. In existing research, Salonen et al. [28] have
read distance would be affected. Once an NFC tag is held within a presented that how vicinity of skin affects the performance of
certain range of the reader, the red LED on the reader goes on as wearable patch antennas. Since the NFC coil in this paper is
shown in Figs. 11c and d, meaning the RFID data has been seamlessly integrated with very light substrate, direct skin contact
received by the reader. can easily occur.
Both forward and backward facing directions were tested in the Among all conditions listed in Table 4, the tag is mostly
measurements, between which hardly any difference has been reduced by direct skin contact. This is due to the fact that
observed. The best read range of the NFC RFID tag is 5.57 cm, transmitted EM energy is partially absorbed by body tissue layers,
comparing to the read distance of a commercial aluminium NFC which leads to a slight reduction in the tag current [29].
tag (ST25TA64K) tested with the same reader which is 8.17 cm;
such results are satisfying for an NFC tag that aims for short range
reading. 4 Conclusion
A simple bending test has also been applied in order to observe This paper has presented the design and fabrication process of
the read range limits of the tag, where a V-bend method has been novel e-textile wearable NFC antennas which are fully integrated
carried out [27] as shown in Figs. 12a and b. The bending angles with garment, enabling truly ubiquitous wireless connectivity to
are setup with an electrical angle meter and maintained with scotch everyday clothing. The NFC tags perform well under bending and
tapes and plastic tweezers during measurements. The results are human body effects. The 10 dB bandwidth of the fabricated NFC
presented in Fig. 12c, showing how the read range is affected by antenna is 3.787 MHz and the quality factor is 8.85. The broad
increasing degree of bending. operation bandwidth of the e-textile NFC RFID tags proposed in
As the antenna working frequency shifts further from its this work is highly desirable for smart textile due to its flexibility
original point with increasing degrees of bending, the reflected towards bending and can potentially lead to numerous applications,
power from the NFC tag gradually decreases. Consequently, the such as personal security, health and wellbeing monitoring, big
read range of the tag is shortened since there is less magnetic flux data and IoTs.

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 [7] Chen, S., Kaufmann, T., Ranasinghe, D., et al.: ‘A modular textile antenna
design using snap-on buttons for wearable applications’, IEEE Trans.
Antennas Propag., 2016, 64, (3), pp. 894–903
[8] Koski, K., Sydänheimo, L., Rahmat-Samii, Y., et al.: ‘Fundamental
characteristics of electro-textiles in wearable UHF RFID patch antennas for
body-centric sensing systems’, IEEE Trans. Antennas Propag., 2014, 62, (12),
pp. 6454–6462
[9] Mongan,, W.M., Rasheed,, I., Ved, K., et al.: ‘Real-time detection of apnea
via signal processing of time-series properties of RFID-based smart
garments’. 2016 IEEE Signal Processing in Medicine and Biology Symp.
(SPMB), Philadelphia, PA, USA, 2016, pp. 1–6
[10] Virkki, J., Wei, Z., Liu, A., et al.: ‘Wearable passive E-textile UHF RFID tag
based on a slotted patch antenna with sewn ground and microchip
interconnections’, Int. J. Antennas. Propag., 2017, 2017, pp. 1–8
[11] Ginestet, G., Brechet, N., Torres, J., et al.: ‘Embroidered antenna-microchip
interconnections and contour antennas in passive UHF RFID textile tags’,
IEEE Antennas Wirel. Propag. Lett., 2017, 16, pp. 1205–1208
[12] Nikitin, P., Rao, K.: ‘Theory and measurement of backscattering from RFID
tags’, IEEE Antennas Propag. Mag., 2006, 48, (6), pp. 212–218
[13] Iqbal, R., Saeed, M.: ‘Wearable near field communication ring antenna for
mobile communication’. Int. Conf. Open Source Systems and Technologies,
Lahore, Pakistan, 2014
[14] Del-Rio-Ruiz, R., Lopez-Garde, J.: ‘Design and performance analysis of a
purely textile spiral antenna for on-body NFC applications’. IEEE MTT-S Int.
Microwave Workshop Series on Advanced Materials and Processes, Pavia,
Italy, 2017
[15] Shaikh, F., Zeadally, S., Exposito, E.: ‘Enabling technologies for green
internet of things’, IEEE Syst. J., 2017, 11, (2), pp. 983–994
[16] Atzori, L., Iera, A., Morabito, G.: ‘The internet of things: a survey’, Comput.
Netw., 2010, 54, (15), pp. 2787–2805
[17] ‘How to design a 13.56 MHz customized tag antenna’. AN2866 Application
note, 2009. Available at: http://www.ebvnews.ru/doc/AN15284.pdf, accessed
10 March 2017
Fig. 12 Wireless bending test [18] ‘RF430CL330H practical antenna design Guide’ Texas Instruments,
(a) 120° V-bend setup, (b) Tag read with 120° bend angle, (c) NFC tag read range SLOA197, 2014.
decreases with increasing degree of bending [19] Cst.com.: ‘CST MICROWAVE STUDIO® – 3D EM Simulation Software’,
2017. Available at: https://www.cst.com/products/cstmws, accessed 26
November 2017
Table 4 NFC read range with different levels of skin contact [20] Post, E., Orth, M., Russo, P., et al.: ‘E-broidery: design and fabrication of
Condition Read range, cm textile-based computing’, IBM Syst. J., 2000, 39, (3.4), pp. 840–860
direct skin contact 5.3 [21] Farnell.com. 2017. Available at: http://www.farnell.com/datasheets/
1683422.pdf?
vicinity of skin without touching (1 mm) 5.5 _ga=2.61107945.41218670.1493817437-1811059628.1491485357, accessed
thin cotton layer (0.5 mm thickness) between skin 5.5 26 November 2017
[22] Atwa, Y., Maheshwari, N., Goldthorpe, I.: ‘Silver nanowire coated threads for
and tag electrically conductive textiles’, J. Mater. Chem. C, 2015, 3, (16), pp. 3908–
without skin contact 5.6 3912
[23] Joseph, S., Mcclure, J., Chianelli, R., et al.: ‘Conducting polymer-coated
stainless steel bipolar plates for proton exchange membrane fuel cells
(PEMFC)’, Int. J. Hydrog. Energy, 2005, 30, (12), pp. 1339–1344
5 References [24] Rahola, J.: ‘Power waves and conjugate matching’, IEEE Trans. Circuits Syst.
II, Express Briefs, 2008, 55, (1), pp. 92–96
[1] Landt, J.: ‘The history of RFID’. IEEE Potentials, 2005, 24, (4), pp. 8–11 [25] AN11535: ‘Measurement and tuning of a NFC and reader IC antenna with a
[2] Coskun, V., Ok, K., Ozdenizci, B.: ‘Near field communication (NFC)’ (Wiley, MiniVNA’, 2014, 291991
Somerset, 2011, 1st edn.) [26] Lee, Y.: ‘RFID coil design’ (Microchip Technol. Inc. Appl. Note, Chandler,
[3] Roselli, L.: ‘Green RFID systems’ (Cambridge University Press, Cambridge, Arizona, USA, 1998)
United Kingdom, 2014, 1st edn.), p. 8 [27] ASTM E290-14: ‘Standard test methods for bend testing of material for
[4] Curran, K., Millar, A., Mc Garvey, C.: ‘Near field communication’, Int. J. ductility’, ASTM International, West Conshohocken, PA, 2014, https://
Electr. Comput. Eng. (IJECE), 2012, 2, (3), pp. 371–372 doi.org/10.1520/E0290-14
[5] Choi, E., Park, J., Kim, B., et al.: ‘Fabrication of electrodes and near-field [28] Salonen, P., Rahmnat-Sarnii, Y., Kivikoski, M.: ‘Wearable antennas in the
communication tags based on screen printing of silver seed patterns and vicinity of human body’. IEEE Int. Symp. Antennas and Propagation Digest,
copper electroless plating’, Int. J. Prec. Eng. Manuf., 2015, 16, (10), pp. Monterey, CA, USA, vol. 1, 20–25 June 2004, pp. 467–470
2199–2204 [29] Klemm, M., Troester, G.: ‘EM energy absorption in the human body tissues
[6] Hertleer, C., Rogier, H., Vallozzi, L., et al.: ‘A textile antenna for off-body due to UWB antennas’, Prog. Electromagn. Res., 2006, 62, pp. 261–280
communication integrated into protective clothing for firefighters’, IEEE
Trans. Antennas Propag., 2009, 57, (4), pp. 919–925

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