To improve HF detection of small RFID tags, a Distributed Diameter Coil (DDC) resonator is included in the reader coil. The key ideas of detection improvement are twofold: using a resonator with Magnetic Resonant Coupling (MRC) and modifying the distribution of diameter and current for each loop of the DDC resonator. These factors allow the magnetic coupling to increase between the reader and the smaller tag, especially in our case where the effective area of the tag is below 0,1% of the reader coil surface. Numerical simulations are carried out using HFSS to confirm the enhancement of the mutual coupling between the tag and the reader coil: the coupling coefficient is used in double-loop coupling (the case of the coupling of two loops), when a third loop (resonator) is inserted. The optimization of the magnetic coupling between a large reader and a small tag with resonator could be realized in changing first the sub-coil diameters, and then the sub-coil number of turns. One figure of merit to quantify the ability of surface detection is defined. A 15% improvement of detection surface in Horizontal Mode is measured at 1 cm of the reader plane in comparison with a conventional coil. Experimental detection measurements on real structures are described to validate statements.
2. Mirbozorgi, S., H. Bahrami, M. Sawan, and B. Gosselin, "A smart cage with uniform wireless power distribution in 3D for enabling long-term experiments with freely moving animals," IEEE Transactions on Biomedical Circuits and Systems, Vol. 10, No. 2, 424-434, 2016.
3. Diet, A., et al., "Detection tube for small HF RFID tags, based on mutual coupling with a coil resonator," IEEE European Microwave Week (EuMC), 375-378, Sept. 2015.
4. Diet, A., C. Conessa, Y. Le Bihan, F. Alves, M. Grzeskowiak, M. Benamara, and G. Lissorgues, "LF RFID chequered loop antenna for pebble detection and area localization," IEEE European Microwave Week (EMC), 41-44, Oct. 2016.
5. Zeng, Y., B. Clerckx, and R. Zhang, "Communicatios and signals design for wireless power transmission," IEEE Transactions on Communications, Vol. 65, No. 5, 2264-2290, 2017.
6. Bito, J., S. Jeong, and M. M. Tentzeris, "Heuristic passive and active matching circuit design method for wireless power transfer for moving objects," Wireless Power Transfer (WPT), 1-4, May 2006.
7. Hwang, H., J. Moon, B. Lee, C. Jeong, and S. Kim, "An analysis of magnetic resonance coupling effects on wireless power transfer by coil inductance and placement," IEEE Transactions on Consumer Electronics, Vol. 60, No. 2, 203-209, 2014.
8. Fotopoulou, K. and B. W. Flynn, "Wireless power transfer in loosely coupled links: Coil misalignment model," IEEE Transactions on Magnetics, Vol. 47, No. 2, 416-430, 2011.
9. Mirbozorgi, S. A., P. Yeon, and M. Ghovanloo, "Robust wireless power transmission to mm-sized free-floating distributed implants," IEEE Transactions on Biomedical Circuites and System, Vol. 11, No. 3, 692-702, 2017.
10. Waters, B. H., B. J. Mahoney, G. Lee, and J. R. Smith, "Optimal coil size ratios for wireless power transfer applications," IEEE International Symposium on Circuits and Systems (ISCAS), 2045-2048, Jun. 2014.
11. Shi, X. and J. R. Smith, "Large area wireless power via a planar array of coupled resonators," IEEE International Workshop on Antenna Technology (iWAT), 200-203, Mar. 2016.
12. Choi, B. H., E. S. Lee, Y. H. Sohn, G. C. Jang, and C. T. Rim, "Six degrees of freedom mobile inductive power transfer by crossed dipole Tx and Rx coils," IEEE Transactions on Power Electronics, Vol. 31, No. 4, 3252-3272, 2016.
13. Kamineni, A., G.-A. Covic, and J.-T. Boys, "Analysis of coplanar intermediate coil structures in inductive power transfer systems," IEEE Transactions on Consumer Electronics, Vol. 30, No. 11, 6141-6154, 2015.
14. Sharma, A., I. J. Garcia Zuazola, A. Gupta, A. Perallos, and J. C. Batchelor, "Non-uniformly distributed-turns coil antenna for enhanced H-field in HF-RFID," IEEE Antennas and Wireless Propagation Letters, Vol. 61, No. 10, 4900-4907, 2013.
15. Benamara, M., M. Grzeskowiak, G. Lissorgues, A. Diet, Y. Le Bihan, and C. Conessa, "Calculation of the equivalent mutual impedance in complex HF RFID systems," IEEE International Conference of Applied Electromagnetics and Communications (ICECOM), Sept. 2016.
16. Diet, A., M. Grzeskowiak, Y. Le Bihan, M. Biancheri-Astier, M. Lahrar, C. Conessa, M. Benamara, G. Lissorgues, and F. Alves, "Improvement of RFID HF tags detection with a distributed diameter coil," IEEE Antennas and Wireless Propagation Letter, Vol. 15, 1943-1946, 2016.
17., , http://www.ansys.com/Products/Simulation+Technology/Electronics/Signal+Integrity/ANSYS+HFSS.
18. Finkerseller, A., RFID Handbook, Carl Hanser Verlag, Munchen, Germany, 2002.
19., , http://www.nxp.com/products/identification-and-security/smart-labeland-tag-ics/icode:MC_4202.
20., , sttID for 13.56 MHz Long Range Reader / Writer SIL-212. http://www.stt-rfid.com/node/101.
21. Diet, A., M. Biancheri-Astier, Y. Le Bihan, C. Conessa, F. Alves, M. Grzeskowiak, M. Benamara, and G. Lissorgues, "Design of 1 cm2 coils for HF RFID instruments tracking with detection range improvement," IEEE International Conference on RFID Technology & Application (RFID-TA), 2017.
22. Lee, H., S. Kang, Y. Kim, and C. Jung, "Small-sized metallic and transparent film resonators for MR-WPT system," IEEE Electronics Letters, Vol. 52, No. 8, 650-652, 2016.
23. Kang, S.-H., V.-T. Nguyen, and C.-W. Jung, "Analysis of MR-WPT using planar textile resonators for wearable applications," IET Microwaves, Antennas and Propagation, Vol. 10, No. 14, 1541-1546, 2016.