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The Practicality of Multi-Tag RFID Systems

The Practicality of Multi-Tag RFID Systems. Leonid Bolotnyy Scott Krize Gabriel Robins. Department of Computer Science University of Virginia. passive. semi-passive. active. Introduction. RFID. Tags types:. Frequencies: Low (125KHz), High (13.56MHz), UHF (915MHz). Coupling methods:.

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The Practicality of Multi-Tag RFID Systems

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  1. The Practicality of Multi-Tag RFID Systems Leonid BolotnyyScott KrizeGabriel Robins Department of Computer ScienceUniversity of Virginia

  2. passive semi-passive active Introduction • RFID • Tags types: • Frequencies: Low (125KHz), High (13.56MHz), UHF (915MHz) • Coupling methods: signal signal reader antenna Inductive coupling Backscatter coupling

  3. Radar invented - 1935 • EAS invented - early 1960’s • First RFID patent filed - 1973 • First RFID book published - 1999 • Auto-ID Center formed - 1999 • EPCglobal formed - 2004 • First RFID game marketed - 2006 History

  4. Object Identification • Bar-codes vs. RFID • line-of-sight • scanning rate • Unreliability of object detection • radio noise is ubiquitous • temperature and humidity • objects/readers moving speed • liquids and metals are opaque to RF • milk, water, juice • metal-foil wrappers • object occlusion • number of objects grouped together • tag variability and receptivity • tag aging

  5. Case Studies • Defense Logistics Agency trials (2001) • 3% of moving objects did not reach destination • 20% of tags recorded at every checkpoint • 2% of a tag type detected at 1 checkpoint • some tags registered on arrival but not departure • Wal-Mart experiments (2005) • 90% tag detection at case level • 95% detection on conveyor belts • 66% detection inside fully loaded pallets

  6. Multi-Tag RFID UseMultiple tags per object to increase reliability of object detection/identification

  7. B-field • Optimal Tag Placement: 4 β 3 2 1 The Power of an Angle • Inductive coupling: voltage ~ sin(β), distance ~ (power)1/6 • Far-field propagation: voltage ~ sin2(β), distance ~ (power)1/2

  8. Equipment and Setup • Equipment • 4 linear antennas by Alien Technology • 4 circular antennas by Alien Technology • 4 circular antennas by ThingMagic • Setup • empty room • 20 solid non-metallic & 20 metallic and liquid objects • tags positioned perpendicular to each other • tags spaced apart • software drivers

  9. Experiments • Read all tags in reader’s field • Randomly shuffle objects • Compute average detection rates • Variables • reader type • antenna type • tag type • antenna power • object type • number of objects • number of tags per object • tags’ orientation • tags’ receptivity

  10. 1Tag: 58% 2Tags: 79% 3Tags: 89% 4Tags: 93% Linear Antennas

  11. 1Tag: 75% 2Tags: 94% 3Tags: 98% 4Tags: 100% Circular Antennas

  12. Power = 31.6dBm 1 0.9 0.8 0.7 0.6 0.5 Detection Probability 0.4 0.3 Δ= 5.2% Δ=14.4% Δ=19.8% 0.2 0.1 Δ= 6.9% Δ=21.3% 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Object Number Linear Antennas vs. Multi-tags 2 Readers, 2 Tags 84.5% 1 Reader, 2 Tags 79.3% 2 Readers, 1 Tag 64.9% 1 Reader, 1 Tag 58.0%

  13. Δ= 5.2% Δ=8.4% Δ= 15.1% Δ=18.3% 2 Readers, 2 Tags 99.4% 1 Reader, 2 Tags 94.2% Δ=3.2% 2 Readers, 1 Tag 91.0% 1 Reader, 1 Tag 75.9% Circular Antennas vs. Multi-Tags Power = 31.6dBm 1 0.9 0.8 0.7 Detection Probability 0.6 0.5 0.4 0.3 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 Object Number

  14. 1 Tag 2 Tags 3 Tags 4 Tags Power • Decrease in detection with decrease in power • More rapid decrease in detection for circular antennas

  15. Uni-polar tags Bi-polar tags Importance of Tag Orientation

  16. Controlling Variables • Radio noise • Tag variability • Reader variability • Reader power level • Distance to objects &type, # of antennas

  17. Circular Antenna 1 0.9 0.8 0.7 0.6 Detection Probability 0.5 0.4 0.3 0.2 0.1 0 1 2 3 4 Number of Tags Power=31.6dBm, No Liquids/Metals Power=31.6dBm, With Liquids/Metals Power=27.6dBm, No Liquids/Metals Power=27.6dBm, With Liquids/Metals Detection in Presence of Metals & Liquids • Decrease in solid/non-liquid object detection • Significant at low power • Similar results for linear antennas

  18. Power=31.6dBm, Circular Antennas Power=31.6dBm, Linear Antennas Power=27.6dBm, Circular Antennas 0.9 Power=27.6dBm, Linear Antennas 0.8 0.7 0.6 0.5 Detection Probability 0.4 0.3 0.2 0.1 0 1 Tag 2 Tags 3 Tags 1 Tag 2 Tags 3 Tags 1 Tag 2 Tags 3 Tags Antenna #1 Antenna #2 Antenna #1 and #2 Number of Tags Multi-Tags on Metals and Liquids • Low detection probabilities • Drop in detection at low power • Linear antennas outperform circular • Multi-tags better than multiple readers

  19. Metals & Liquids ∆ : 3%-13% Varying Number of Objects Experiment 1: 15 solid non-metallic & 15 liquids and metals Experiment 2: 20 solid non-metallic & 20 liquids and metals

  20. Detection Delta

  21. Anti-Collision Algorithms Algorithm Redundant Tags Connected-Tags * Assuming tags communicate to form a single response ** If all tags are detected

  22. Reliability Availability Localization Safety Applications of Multi-Tags

  23. Security Theft Prevention Tagging Bulk Materials Packaging More Applications

  24. Year Cost Economics of Multi-Tags • Rapid decrease in passive tag cost • 5 cent tag expected in 2008 • 1 penny tag in a few years

  25. Cost Trends Time

  26. Business Case for RFID • Costs & benefits (business case) • Moore’s law • higher employee productivity • reduction in workforce • automated business processes • workforce reduction • Tag manufacturing yield and testing • 30% of chips damaged during manufacturing • 15% damaged during printing [U.S. GAO] • 20% tag failure rate in field [RFIDJournal] • 5% of tags purchased marked defective

  27. Increase in RFID tag demand Decrease in RFID tag cost RFID Tag Demand • Demand drivers • tag cost • desire to stay competitive • Cost effective tag design techniques • memory design (self-adaptive silicon) • assembly technology (fluidic self assembly) • antenna design (antenna material)

  28. Conclusion • Unreliability of object detection • radio noise is ubiquitous • temperature and humidity • objects/readers moving speed • liquids and metals are opaque to RF • milk, water, juice • metal-foil wrappers • object occlusion • number of objects grouped together • tag variability and receptivity • tag aging • Many useful applications • Favorable economics

  29. Generalized “Yoking Proofs” RFID Multi-Tags 3 PUF Inter-Tag Communication Our Research

  30. Thank You Questions?

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