frequency signature chipless rfid tag with enhanced data
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Frequency signature chiplessRFID tag with enhanced datacapacity
Bilal Aslam1a), Umar Hasan Khan1, Ayesha Habib1,Yasar Amin1,2, and Hannu Tenhunen2,31 ACTSENA, Department of Telecommunication Engineering,
University of Engineering and Technology, Taxila-47050, Punjab, Pakistan2 iPack VINN Excellence Center, Royal Institute of Technology (KTH),
Isafjordsgatn 39, Stockholm, SE-16440, Sweden3 TUCS, Department of Information Technology, University of Turku,
Turku-20520, Finland
a) bilal.aslam@uettaxila.edu.pk
Abstract: Frequency signature chipless RFID tag based on spurline reso-
nator is presented in this letter. Resonant response of spurline is explained by
analyzing the surface current distribution. Chipless tag consists of a data
encoding circuit and two cross polarised monopole antennas. The tag has a
data capacity of 16 bits in the range 2.13 to 4.1GHz. Data capacity of data
encoding circuit is enhanced by repositioning the spurlines. The prototype of
the tag is fabricated on FR4 substrate. Developed tag can be used for cost
effective identification of items in the industry.
Keywords: frequency signature, data encoding circuit, bandstop character-
istics, chipless tag
Classification: Microwave and millimeter wave devices, circuits, and
systems
References
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[2] I. Cuinas, R. Newan, M. Trebar and A. Melcon: IEEE Antennas Propag. Mag.56 [2] (2014) 196. DOI:10.1109/MAP.2014.6837090
[3] A. Arbit, Y. Oren and A. Wool: IEEE Pervasive Comput. 13 [2] (2014) 52.DOI:10.1109/MPRV.2014.22
[4] Y. Feng, L. Xie, Q. Chen and L. R. Zheng: IEEE Sensors J. 15 (2015) 3201.DOI:10.1109/JSEN.2014.2385154
[5] E. Amin, S. Bhuiyan, N. Karmarkar and B. Jensen: IEEE Sensors J. 14 (2014)140. DOI:10.1109/JSEN.2013.2278560
[6] A. Ramos, A. Lazaro, R. Villarino and D. Girbau: IEEE RFID-TA (2014) 165.DOI:10.1109/RFID-TA.2014.6934221
[7] P. Kalansuriya, N. C. Karmakar and E. Viterbo: IEEE Trans. Microw. TheoryTechn. 60 (2012) 4187. DOI:10.1109/TMTT.2012.2222920
[8] R. Rezaiesarlak and M. Manteghi: IEEE Trans. Antennas Propag. 62 (2014)898. DOI:10.1109/TAP.2013.2290998
[9] S. R. Choudhury, S. K. Parui and S. Das: IJEAT 3 [1] (2013).
© IEICE 2015DOI: 10.1587/elex.12.20150623Received July 16, 2015Accepted August 10, 2015Publicized August 26, 2015Copyedited September 10, 2015
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LETTER IEICE Electronics Express, Vol.12, No.17, 1–6
[10] M. Sumi, R. Dinesh, C. M. Nijas, S. Mridula and P. Mohanan: Radio Eng. 24[4] (2014).
1 Introduction
Passive radio frequency identification (RFID) is becoming increasingly popular in
many areas of supply chain because of reliability and affordability [1, 2, 3]. Over
the past three decades, the price of silicon chips has gone down exponentially
resulting in a considerable reduction in cost of the chip based RFID tags. However,
the chip based RFID tags are not yet economical enough to completely replace the
barcodes for item level tagging [4, 5]. Chipless RFID tags can be a more convenient
choice for item level tagging. The chipless RFID tags are also expected to possess
higher read range as no RF power from the reader signal is utilized to power up the
chip.
The core component of chipless RFID tags is the data encoding circuit. The two
main data encoding techniques being used include time domain signature [6, 7] and
frequency signature [8, 9, 10]. Frequency signature technique is more popular as it
offers better coding capacity.
Multi-resonator structures are employed to encode the data in frequency
signature technique. Spurline resonator is a common structure used for data
encoding [9, 10]. A single spurline is essentially a bandstop filter, and a combi-
nation of such spurlines can create the desired frequency signature. [9] achieved the
frequency signature by placing multiple spurlines adjacent to each other in a log
periodic pattern. Such configuration does not support high data capacity per unit
area. [10] addressed this issue by arranging the spurlines in the lower left and lower
right corners. In this letter, the prospects of improving the data capacity per unit
area further are discussed by placing the spurlines in the lower left and upper right
corners.
2 Spurline resonator
Spurline is a structure exhibiting bandstop characteristics. It consists of an L shaped
slot cut into a microstrip line and are shown in Fig. 1. Important parameters of the
spurline are the slot length L and the slot width s. Fifty ohm lines shown in the
Fig. 1 form input and output ports. Spurline can be modelled as a parallel RLC
which explains it’s bandstop characteristics at resonance [10].
Fig. 1. Spurline resonator.© IEICE 2015DOI: 10.1587/elex.12.20150623Received July 16, 2015Accepted August 10, 2015Publicized August 26, 2015Copyedited September 10, 2015
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IEICE Electronics Express, Vol.12, No.17, 1–6
Stopband frequency is controlled by slot length L which is approximately a
quarter of the guided wavelength at the resonant frequency.
L ¼ �g4
ð1ÞWhere �g is the guided wavelength and is given by
�g ¼ �
"eff¼ �
"rþ12
þ "r�12
ffiffiffiffiffiffiffiffiffiffi
1þ12 hw
p ð2Þ
"eff is the effective dielectric constant; h is the thickness of the dielectric and w
is the width of the microstrip line. Bandwidth of the stopband is controlled by the
slot width s. Narrow slot results in a narrow stopband and vice-versa [10]. Width of
the fifty ohm lines (H2) is set using the microstrip synthesis equation.
Design parameters of the spurline resonator of Fig. 1 are: W ¼ 26mm; H1 ¼6mm; L ¼ 16:5mm; s ¼ 0:5mm and H2 ¼ 3:4mm. Substrate with permittivity
3.55, thickness 1.524mm and loss tangent 0.0027 is used. Simulated transmission
response is shown by solid line in Fig. 2. A band notch at 3.08GHz is observed. If
the open end of the slot is closed then the resonant notch is shifted to a higher
frequency [10]. This fact is depicted by shifting of the notch to 4.88GHz shown by
dotted line in Fig. 2. Presence or absence of a notch at a certain frequency can be
utilized for data encoding, which is the basis of frequency signature technique. A
spurline resonator can, therefore, encode 1 data bit.
Surface current distribution of the spurline resonator at resonant frequency is
plotted in Fig. 3. Current distribution is concentrated heavily around the closed end
of the slot giving inductive effect. Similarly, current distribution vanishes inside
and close to the open end of the slot giving a capacitive effect. When the open end
is closed, the capacitive effect reduces This explains the shifting of resonance to a
higher frequency when the slot is closed.
Fig. 2. Frequency signature of spurline resonator.
© IEICE 2015DOI: 10.1587/elex.12.20150623Received July 16, 2015Accepted August 10, 2015Publicized August 26, 2015Copyedited September 10, 2015
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IEICE Electronics Express, Vol.12, No.17, 1–6
3 Data encoding structure
An 8 bit data encoding structure in the 2.38 to 4.04GHz frequency range using
spurline resonators was presented in [10]. In the proposed structure, the data
capacity per unit area is doubled by repositioning the spurlines. Proposed structure
is shown in Fig. 4.
Spurlines of the lower left corner (L1–L8) correspond to the least significant
data byte and the spurlines of the upper right corner (L9–L16) correspond to the
most significant data byte. Corresponding lengths are listed in Table I and are set
according to Eq. (1). Other design parameters are: W ¼ 44mm; H ¼ 12mm; Wp ¼3:4mm; l1 ¼ 22m and l2 ¼ 4mm. Each spurline is 0.3mm wide and separated by
distance of 0.3mm to the adjacent spurline.
Proposed structure is designed on FR4 substrate with a thickness of 1.524mm.
Fig. 5 shows the fabricated prototype and it’s associated results. Good agreement
between simulated and measured results is observed. 16 equally spaced resonant
notches are observed in the 2.13 to 4.1GHz frequency band. Each notch encodes a
unique data bit.
Fig. 3. Surface current distribution of spurline resonator.
Fig. 4. 16-bit data encoding structure.
Table I. Optimum spurline lengths for data encoding
(mm) L1 L2 L3 L4 L5 L6 L7 L8
23 21.7 20.4 19.1 18.1 17.4 16.5 15.9
(mm) L9 L10 L11 L12 L13 L14 L15 L16
15.6 15 14.3 13.7 13.3 12.5 12.3 11.6
© IEICE 2015DOI: 10.1587/elex.12.20150623Received July 16, 2015Accepted August 10, 2015Publicized August 26, 2015Copyedited September 10, 2015
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4 Chipless RFID tag design
Complete chipless RFID tag also require antennas working in the operative
frequency range for transmitting and receiving the signals from the reader. A
UWB monopole antenna and it’s reflection response is shown in Fig. 6. Effective
aperture efficiency of monopole antenna is optimized to achieve high gain which
results in improved readrange that is significantly higher than the previously
published results [10]. Full chipless RFID tag with integrated antennas and it’s
transmission response is shown in Fig. 7.
Fig. 5. Simulated and measured 16-bit frequency signature.
Fig. 6. Reflection coefficient of monopole antenna.
© IEICE 2015DOI: 10.1587/elex.12.20150623Received July 16, 2015Accepted August 10, 2015Publicized August 26, 2015Copyedited September 10, 2015
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5 Conclusion
A novel data encoding approach using spurline resonators is proposed. Proposed
approach offers enhanced data capacity. A 16-bit data encoding circuit is designed
and tested. Design of a full 16-bit chipless RFID tag is also presented. The chipless
RFID tag is an economical alternative to the conventional barcode. High gain
antennas are used to prolong the read range.
Acknowledgments
This work was financially supported by Vinnova (The Swedish Governmental
Agency for Innovation Systems) and University of Engineering and Techonology
Taxila, Pakistan through the Vinn Excellence centers program and ACTSENA
research group funding, respectively.
Fig. 7. 16-bit chipless RFID tag and its frequency response.
© IEICE 2015DOI: 10.1587/elex.12.20150623Received July 16, 2015Accepted August 10, 2015Publicized August 26, 2015Copyedited September 10, 2015
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