1. On The Effect of Mutual Coupling on LF and UHF Tags Implemented in Dual Frequency RFID Applications Gregory J. Owen Benjamin D. Braaten* Robert M. Nelson Dustin Vaselaar North Dakota State University Cherish Bauer-Reich Jacob Glower Michael Reich Aaron Reinholz

2. Topics  Introduction  Dual frequency tag  Test setup  Test results  Discussion  Conclusion North Dakota State University

3. Introduction  Interest in RFID has recently grown tremendously in many areas [1]-[5]:  supply chain management [6]-[8]  RFID security [9]-[10]  UHF antenna design [11]  back-scattering analysis [12]-[14]  dual frequency applications  Types of systems [1]  passive  semi-passive  active North Dakota State University

4. Introduction  On a passive tag the antenna is typically connected directly to the rectifier.  thus antenna impedance and rectifier impedance directly effect the read range  Antenna characteristics (gain, input impedance and resonant frequency) can be effected by nearby conducting and non-conducting objects [15]-[21]:  Weather-proof enclosures  Surface placement of tag  Other RFID tags (i.e., dual-frequency tags) North Dakota State University

5. Introduction  Several advantages are gained by using a weather-proof enclosure [18]:  Protection against heat, physical damage, and the environment (moisture, sun)  Dual-frequency implementation  Several examples include:  Electronic car tolling [22]  Livestock tracking [23]-[24] North Dakota State University

6. A Little Background  The max theoretical read range of a passive RFID tag can be written as (using Friis’s eqn.) [25]: where North Dakota State University

7. The Dual-Frequency Tag and Test Setup North Dakota State University (902-928MHz)(125.4-134kHz)

8. Test Setup North Dakota State University

9. Test Results North Dakota State University (reminder) LF tag

10. Test Results North Dakota State University (reminder) M-tag [33]

11. Test Results North Dakota State University (reminder) Squiggle Tag [33]

12. Test Results North Dakota State University (reminder) Rampart tag [29]

13. Discussion North Dakota State University  Table 3 showed that a LF tag placed directly on the M-tag reduced the read range by 67.27%.  Table 4 showed that the LF tag placed near the squiggle tag reduced the read range by 91.84%.  The Rampart-line was less affected by the LF tag.

14. Discussion North Dakota State University  In all cases by moving the LF tag to the edge of the UHF tags the read range could be recovered.  The trade-off to moving the LF tag to the edge of the UHF tag is a larger footprint.

15. Conclusion North Dakota State University  A dual frequency (UHF and LF) tag has been introduced.  The read range of each tag was determined in the presence of mutual coupling.  In several instances the read range of the UHF tag was substantially decreased (91.84%).

16. Conclusion North Dakota State University  In all instances is was shown that most of the read range could be recovered by moving the LF tag to the same plane of the UHF tag

17. Questions Thank you for listening North Dakota State University

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