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TagMaster Training 2013 RFID Theory

TagMaster Training 2013 RFID Theory. Contents. Definition of RFID Different types of RFID History of RFID RFID System Radio Waves Radio Regulations Safety and Health. Definition of RFID.

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TagMaster Training 2013 RFID Theory

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  1. TagMaster Training 2013 RFID Theory TagMaster AB

  2. Contents • Definition of RFID • Different types of RFID • History of RFID • RFID System • Radio Waves • Radio Regulations • Safety and Health TagMaster AB

  3. Definition of RFID ”Radio-frequency identification (RFID) is a technology that uses communication via radio waves to exchange data between a reader and an electronic tag attached to an object, for the purpose of identification and tracking.” (Wikipedia) TagMaster AB

  4. Classification of RFID Systems • Frequency • 125/134 kHz • 13.56 MHz • 860-960 MHz • 2.4 GHz • 5.2-5.8 GHz • Tag Power Source • Passive • Semi-passive • Active • Tag-Reader Protocol • Requirements • Standard or Proprietary TagMaster AB

  5. RFID Frequencies • LF and HF systems are short range systems (1 cm – 3 m). They are for example used in proximity cards for access control and for tracking of animals and library books. • UHF and SHF systems have longer read range (5 m - 50 m) and are mainly used for item tracking and identification. • TagMaster provides systems for 860-960 MHz and 2.45GHz. 860-960 MHz 2.45 GHz 13.56 MHz 5.8 GHz 125-134 kHz LF MF HF VHF UHF SHF 30 kHz 300 kHz 3 MHz 30 MHz 300 MHz 3 GHz 30 GHz TagMaster AB

  6. Passive Semi-Passive Active No transmitter (backscattering) No battery (powered from RF field) No transmitter (backscattering) Battery to power logic Active transmitter Battery to power logic and radio Passive, Semi-Passive, and Active Tags Exercise: 1. Compare with a flashlight and a mirror 2. How does this affect tag price, lifetime, lifetime predictability & read range? TagMaster AB

  7. Tag-Reader Protocols • The protocol defines how the reader and the tag communicates • Compromise of different requirements • Maximum number of tags that can be read "simultaneously" • Time it takes to read a single or a large number of tags • Data rate between tag and reader • Maximum number of readers in close proximity • Power consumption of tag • Reading range • Standard or Proprietary • Standard procotols such as EPC Gen 2 makes it possible to buy readers and tags from different manufacturers. This can make things cheaper but not always optimized for specific requirements. • Proprietary systems can be optimized for special applications. TagMaster AB

  8. History of RFID - Part 1 (History of Radio) 1865 James Clerk Maxwell theoretically predicted the existence of electromagnetic waves 1888 Heinrich Hertz is credited with being the first to produce and detect such waves at radio frequencies 1893 Nikola Tesla first demonstrated the feasibility of wireless communications 1895 Guglielmo Marconi developed commercial workable radio communication TagMaster AB

  9. History of RFID - Part 2 1935 Robert Watson-Watt got a British patent for radar 1940 The first IFF (Identification Friend or Foe) system was developed in Germany 1945 Léon Theremin invented “The Thing”, a passive listening device used by the Soviet Union to spy on the American embassy 1948 Harry Stockman presented a paper titled "Communication by Means of Reflected Power 1973 Mario Cardullo got a US patent for a passive transponder; the first true ancestor of modern RFID Replica of “The Thing” Radar/IFF Cardullo’s patent Stockman’s Triple Turret Reflector TagMaster AB

  10. RFID System Properties • The main components of an RFID system are readers and tags (sometimes called interrogators and transponers) • The reader is connected to an external system. The external system may be a PC but can also be a simple garage door opener. • RFID systems can be classified in a number of ways:frequency, power source, air protocol, etc. TagMaster AB

  11. Antenna Detuning • A tag antenna is tuned to receive radio waves of a particular frequency • When a tag is placed on an object the antenna may be detuned • Objects containing metal and/or water can be problematic • All tags do not work on all materials, but… • … it is possible to design tags that work on e.g. metal or close to water A tag that should not be mounted on metal A tag that can be mounted on metal TagMaster AB

  12. The graphs on this page show the reader output power (­30dBm) required to read an EPC Gen 2 tag at different frequencies (860­-960MHz) The tag is the same in both graphs Optimized for EU frequencies (865.6­867.6MHz) Optimized for metal mounting In one of the graphs the tag is mounted on metal, in the other the tag is in free air. Exercise: In which graph is the tag mounted on metal? Antenna Detuning - Example TagMaster AB

  13. Power Units • Output power for RFID readers are expressed in different ways • ERP (Effective Radiated Power) • relative to a dipole antenna (the simplest real antenna) • EIRP (Equivalent Isotropically Radiated Power) • relative to a theoretical isotropic antenna • Power values can be converted • PEIRP = PERP 1.64 Theoretical isotropic antenna Dipole antenna TagMaster AB

  14. Read and Write Ranges • Read and write ranges depend on both the reader and the tag. • Main parameters • Reader output power and frequency • ID-tag antenna characteristics (and output power for active systems) • Reader receiver sensitivity 1 3 2 TagMaster's 2.45 GHz Semi-passive System TagMaster AB

  15. Communication Lobe • The communication lobe is the area (in free space) where the tag can be read. It is dependent of both reader and tag. TagMaster AB

  16. Communication Lobe Example • Example of communication lobe on a site (marked directly on asphalt) TagMaster AB

  17. Reading Probability • Reading probability drops from 100% to 0% at the lobe edge Reading probability Perfect read Practical read 100 % Seldom/No read 0 1.5 3 4.5 6 7.5 Distance [m] TagMaster AB

  18. Reading Probability • An actual measurement of the reading probability TagMaster AB

  19. Passing Speed • In high-speed applications, the maximum passing speed is obtained by maximizing the time the tag is readable by the reader. • A fast train with tags mounted on the side should pass the reader such that the tags pass through the widest part of the lobe. TagMaster AB

  20. Passing Speed • TagMaster systems support passing speeds of several hundred km/h. TagMaster AB

  21. Passing Speed • In some cases (e.g. if a vehicle has a front-mounted tag) the time in the lobe can be maximized like this. TagMaster AB

  22. Radio Waves • Radio waves are electromagnetic waves with many similarities to light (and some important differences). • Electromagnetic waves are self-propagating with electric and magnetic components oscillating in phase perpendicular to each other and perpendicular to the direction of energy propagation. TagMaster AB

  23. Frequency Spectrum  = Gamma rays HX = Hard X-rays SX = Soft X-rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultrahigh frequency VHF = Very high frequency HF = High frequency MF = Medium frequency LF = Low frequency VLF = Very low frequency VF = Voice frequency ELF = Extremely low frequency Radio waves TagMaster AB

  24. When two or more waves traverse the same space, the net amplitude at each point is the sum of the amplitudes of the individual waves. Superposition Principle TagMaster AB

  25. Interference • Frequency bands used for RFID are also used by other systems • 2.45 GHz WLAN, Bluetooth, microwave ovens • 865-868 MHz (EU) Cordless phones (CT2) • 902-928 MHz (US) Cordless phones, intercoms, radio modems • These systems may interfere with the RFID system TagMaster AB

  26. Reflection/Absorption/Attenuation • When an electromagnetic wave hits an object, part of it is reflected, part of it is absorbed and part of it continues attenuated • Light and radio waves behave differently • Cardboard blocks light but is transparent to radio waves • Water is transparent to light but blocks radio waves • Metal mainly reflects radio waves • It is not possible to read through metal • The reflected wave may interfere with non-reflected waves • Water mainly absorbs radio waves • It is not possible to read through water (humans are 60% water) • Absorption is higher for higer frequencies • Glass attenuates radio waves • The read range of a tag may be reduced if it isplaced behind a windscreen TagMaster AB

  27. Water Absorption 106 105 104 103 102 101 Absorption Coefficient (cm-1) 100 10-1 10-2 10-3 10-4 10-5 1012 1018 104 1010 1016 1022 108 1014 1020 106 102 Frequency (Hz) Image based on data from "Classical Electrodynamics", J. D. Jackson TagMaster AB

  28. Positive and Negative Identification • Positive identification  the user wants to be identified • Negative identification  the user does not want to be identified • RFID works well in the positive case • In the negative case it is often possible to hide the tag • Cover the tag with your hand • Put the tagged object in a metal bag TagMaster AB

  29. Radio waves that reach a tag by different paths interfere. In some spots the waves will cancel out each other. The locations of these dead spots are frequency dependent. Frequency hopping can be used to move the spots around. Compared to a passive tag, a semi-passive tag is less sensitive to dead spots as it does not use the RF energy to power the internal electronics. Multipath Propagation TagMaster AB

  30. Frequency Hopping (FHSS) • When Frequency Hopping is enabled, the reader changes its frequency at short intervals • Frequency Hopping eliminates most problems • Problems caused by reflections • Problems caused by interference from other systems (WLAN, etc.) • Frequency Hopping is most efficient in wide frequency bands. • Frequency Hopping is enabled by default! No FHSS FHSS TagMaster AB

  31. Radio waves are polarized RFID tag antennas are linearly polarized. For optimal performance the tag must be rotated in the same way as the electrical field. TagMaster’s RFID readers use circular polarization to make it possible to read tags with any rotation. Polarization TagMaster AB

  32. Polarization and Ground Reflections • Light reflected from a horizontal surface such as water is horizontally polarized. Polarized sun glasses block horizontally polarized light to reduce the glare. • Radio waves behave in the same way • A horizontal tag is more sensitive to ground reflections. • Multipath interference may create holes and islands in the lobe. • The maximum read range may be longer with a horizontal tag. • A vertical tag gives a morewell defined lobe. Lobe with horizontal tag Lobe with vertical tag TagMaster AB

  33. End TagMaster AB

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