Bending Dipole Design of Passive UHF RFID Tag Antenna for CD / DVD Discs Wai Tong Luk1and Kai Ning Yung2 1
Wireless Communications Research Center, City University of Hong Kong, Hong Kong
2
Wireless Communications Research Center, City University of Hong Kong, Hong Kong 1
[email protected] 2
[email protected]
Introduction Multimedia materials are playing an important role in our life especially in libraries, music and video shops, etc. They mainly are the CD or DVD Rom for storing audio and video information in digital format. More and more library systems, inventory systems or cashier systems are changing from barcode to HF RFID or even UHF RFID gradually. However, there is no any Passive UHF RFID Tag for CD or DVD in product market that performs the read range more than 2 meters from reading with RFID reader and 7dBi antenna. But UHF RFID tag antenna performance strongly depends on the impedance of the chip [1]. Read range is one of the indicators to evaluating the performance of the tag antenna. The size of the tag will affect the gain and bandwidth of tag performance [2]. CD or DVD Discs are made from a 1.2 mm thick disc of polycarbonate plastic, with a thin layer of aluminum to make a reflective surface. This layer is metallic and will affect the tag performance. The conventional planar passive UHF RFID tags will be degrade in performance when attached to metallic objects [3] like CD or DVD discs, so it is difficult to perform its read range more than 2 meters but small in size. The bending folded dipole double meander-type or ring-type tag antenna performs about 0.4 meters in maximum read range only [4]. In this paper, we will present the tailor-made design of UHF RFID tag antennas to identifying each of CD or DVD discs. Bending Dipole Design The proposed design is implemented with these steps [2]: 1) Select the application and define tag requirements To indentify each of the CD or DVD discs, the tag antenna is designed in the circular region of 12 to 36 mm in diameter on the central region of the CD or DVD with free from metallization. 2) Determine the materials for antenna construction The proposed tag antenna is label on the 1.2 mm thick disc of polycarbonate plastic in this region with the dielectric constant of 2.78. 3) Determine RF impedance of packaged ASIC
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The tag IC is used the Philips SL3S10 01 FTT UCODE EPC G2 TSSOP8 Package with the input impedance in 867 MHz is 22 – j404 Ω and 915MHz is 16 – j380 Ω. 4) Identify the type of antenna and its parameters To fulfill the size which can be fit in the region of 12 to 36 mm circular sector of the CD or DVD disc, a bending dipole design is proposed and optimized with matching input impedance [5] and shown in Figure 1. 5) Perform parametric study and optimization The tag designed is to perform a longer read range, place it in small area and tune the matching circuit more easily, so the bending dipole design is chosen. As the dielectric permittivity of CD or DVD disc will change the complex impedance Z = R + jX of the tag antenna port, it can be tuned the conjugate impedance by changing the dimensions of the matching section to match with input impedance of the tag IC. If the space is smaller, the resonance frequency will shift to higher frequency range as it affects the imaginary part of the input impedance. If the width of the dipoles is changed, it affects the real part of the input impedance mainly. The simulation result of the real part and imaginary part of Z-parameters are shown in Figure 2 and it matches imaginary part of input impedance (3.00 + j379.01Ω) perfectly in 915 MHz but not match well (2.32 + j336.82Ω) in 867 MHz. Figure 3 and 4 shows the simulation result of the antenna pattern in 3D View with RCS (Radar Cross Section) by the Zeland IE3D version 11.5, it shows the radiation direction is along z axis. Sample Results To evaluate the proposed tag antenna, Figure 5 and 6 showed the sampled fabricated antennas. The reader is chosen CSL-461 4-Port EPC Class 1 Gen 2 UHF RFID Reader with about 7 dBi circular polarized antenna (30dBm RF Power) for testing the tag performance. The radiation pattern of the tag antenna is measured and shown in Figure 7 and 8 by taken the maximum read range value for each direction of the tag antenna with RFID reader in the anechoic chamber. Figure 8 shows that the measured read range of this proposed antennas are about 3.5 meters along the z axis of the tag antenna in maximum. Conclusion The proposed tag antenna for identification of the CD or DVD discs was presented. It performs a longer read range and can be adjusted of the dimensions of the matching section in the tag antenna for optimizing direct match with internal impedance of IC chip by comparing with the double meander-type or ring-type antenna design [4]. Measured Data shown in Figure 7 and 8 agreed with the simulated result shown in Figure 3 and 4.
Acknowledgements: The work described in this article was supported by a grant from (9667007) CityU Applied R & D Funding (ARD) and entitled “A Custom-made RFID System for Libraries”. References [1] Nikitin, P.V. and Rao, K.V.S., Performance limitations of passive UHF RFID systems, Antennas and Propagation Society International Symposium 2006, IEEE, 9-14 July 2006, pp:1011-1014, ISBN: 1-4244-0123-2. [2] K. V. Seshagiri Rao, Pavel V. Nikitin and Sander F. Lam, Antenna Design for UHF RFID Tags: A Review and a Practical Application, IEEE Transactions on Antennas and Propagation ON, vol. 53, no. 12, Dec 2005. [3] Karthik Narayanan Moncombu Ramakrishnan, Performance Benchmarks for Passive UHF RFID Tags, Master Thesis, Guindy – Anna University,Chennai, India, 2003. [4] Andrenko, A.S., Kai, M., Maniwa, T., Yamagajo, T., Compact printed-on-CD UHF RFID Tag Antennas, IEEE Antennas and Propagation International Symposium, 2007, pp.5455-5458, ISBN: 978-1-4244-0877-1. [5] Xianming Qing and Ning Yang, A Folded Dipole Antenna for RFID, Antennas and Propagation Society International Symposium, 2004. IEEE, 20-25 June 2004, Volume: 1, pp97- 100, ISBN: 0-7803-8302-8. Figures
Im
Re
Figure 1. The Design of Passive UHF RFID
Figure 2. The real part and imaginary part
Tag Antenna for CD / DVD discs
of Z-parameters of the proposed antenna
y x
Figure 3. Antenna Pattern in 3D view
Figure 5. Fabricated Proposed Antenna in DVD disc
Figure 7. Measured Tag Antenna Pattern of x-y plane
Figure 4. Antenna Pattern in front view
Figure 6. Fabricated Proposed Antenna in CD disc
Figure 8. Measured Tag Antenna Pattern of x-y plane
