Frequency signature chipless RFID tag with enhanced data ...

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) [email protected]

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

[1] M. Chen, W. Luo, Z. Mo, S. Chen and Y. Fang: IEEE/ACM Trans. Networking(2015). DOI:10.1109/TNET.2014.2386318

[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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IEICE Electronics Express, Vol.12, No.17, 1–6

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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