Frequency Signature Chipless RFID Tag With Enhanced Data Capacity

Transcription

1 This article has been accepted and published on J-STAGE in advance of copyediting. Content is final as presented. IEICE Electronics Express, Vol.*, No.*, 1 6 Frequency Signature Chipless RFID Tag With Enhanced Data Capacity Bilal Aslam 1a), Umar Hasan Khan 1, Ayesha Habib 1, Yasar Amin 1,2 and Hannu Tenhunen 2,3 1 ACTSENA, Department of Telecommunication Engineering, University of Engineering and Technology, Taxila-47050, Punjab, Pakistan. 2 ipack VINN Excellence Center, Royal Institute of Technology (KTH) Isafjordsgatn 39, Stockholm, SE-16440, Sweden. 3 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 resonator 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 characteristics, Chipless tag Classification: Microwave and millimetre wave devices, circuits, and systems References IEICE 2015 DOI: /elex Received July 16, 2015 Accepted August 10, 2015 Publicized August 26, 2015 [1] M. Chen, W. Luo, Z. Mo, S. Chen and Y. Fang, An Efficient Tag Search Protocol in Large-Scale RFID Systems With Noisy Channel, IEEE/ACM Trans. Networking,, [2] I. Cuinas, R. Newan, M. Trebar, and A. Melcon, RFID-Based Traceability Along the Food-Production Chain, IEEE Antennas Propag. Mag., vol. 56, no. 2, April [3] A. Arbit, Y. Oren and A. Wool, A Secure Supply-Chain RFID System that Respects Your Privacy, IEEE Pervasive Comput., vol. 13, no. 2, May [4] Y. Feng, L. Xie, Q. Chen and L. R. Zheng, Low-cost Printed Chipless RFID Humidity Sensor Tag for Intelligent Packaging, IEEE Sens. J., vol. 15, no. 6, June [5] E. Amin, S. Bhuiyan, N. Karmarkar and B. Jensen, Development of a Low Cost Printable Chipless RFID Humidity Sensor, IEEE Sens. J., vol. 14, no. 1, Jan [6] A. Ramos, A. Lazaro, R. Villarino and D. Girbau, Time-Domain UWB RFID tags for smart floor applications, IEEE RFID-TA,

2 [7] P. Kalansuriya, N. C. Karmakar, and E. Viterbo, On the Detection of Frequency-Spectra-Based Chipless RFID Using UWB Impulsed Interrogation, IEEE Trans. Microwave Theory Tech., vol. 60, no. 12, pp , Dec [8] R. Rezaiesarlak, and M. Manteghi, Complex-Naural-Resonance-Based Design of Chipless RFID Tag for High Density Data, IEEE Trans. Antennas Propag., vol. 62, no. 2, Feb [9] S. R. Choudhury, S. Kr. Parui and S. Das, Design of a Compact Wideband Log Periodic Spur Line Bandstop Filter, IJEAT, vol. 3, no. 1, October [10] Sumi, M., R. Dinesh, C. M. Nijas, S. Mridula, and P. Mohanan, Frequency Coded Chipless RFID Tag using Spurline Resonators, Radio Eng., vol. 24, no. 4, Introduction Passive radio frequency identification (RFID) is becoming increasingly popular in many areas of supply chain because of reliability and affordability [1-3]. 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 [8-10]. 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 combination 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 2

3 be modelled as a parallel RLC which explains its bandstop characteristics at resonance [10]. Fig. 1. Spurline resonator. Stopband frequency is controlled by slot length L which is approximately a quarter of the guided wavelength at the resonant frequency. L = λ g 4 Where λ g is the guided wavelength and is given by (1) λ g = λ ε eff = λ ε r εr h w ε 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 (H 2 ) is set using the microstrip synthesis equation. (2) Fig. 2. Frequency signature of spurline resonator. Design parameters of the spurline resonator of Fig. 1 are: W=26mm; H 1 =6mm; L=16.5mm; s=0.5mm and H 2 =3.4mm. Substrate with permittivity 3.55, thickness 1.524mm and loss tangent is used. Simulated 3

4 transmission response is shown by solid line in Fig. 2. A band notch at 3.08 GHz 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 4.88 GHz 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. 3. Surface current distribution of spurline resonator. 3 Data Encoding Structure An 8 bit data encoding structure in the 2.38 to 4.04 GHz 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. Fig bit data encoding structure. Spurlines of the lower left corner (L 1 -L 8 ) correspond to the least significant data byte and the spurlines of the upper right corner (L 9 -L 16 ) 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=44mm; 4

5 Fig. 5. Simulated and measured 16-bit frequency signature. H=12mm; W p =3.4mm;l 1 =22m and l 2 =4mm. Each spurline is 0.3mm wide and separated by distance of 0.3mm to the adjacent spurline. Table I. Optimum spurline lengths for data encoding (mm) L1 L2 L3 L4 L5 L6 L7 L (mm) L9 L10 L11 L12 L13 L14 L15 L 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. 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 Conclusion A novel data encoding approach using spurline resonators is proposed. Proposed approach offers enhanced data capacity. A 16-bit data encoding cir- 5

6 Fig. 6. Reflection coefficient of monopole antenna. Fig bit chipless RFID tag and its frequency response. cuit 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 ACT- SENA research group funding, respectively. 6