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  • 1. RFID Systems and Operating Principles University of Houston Bauer College of Business Spring 2007 Presentation Source: RFID Handbook, Chapter 3
  • 2. Overview
    • Please read Chapter 3 of the RFID Handbook for this section
    • RFID Systems can be categorized based on:
      • Operating principles
      • Frequency
  • 3. CLASSIFICATION BY OPERATING PRINCIPLE
  • 4. LC Circuit
    • An LC circuit consists of an inductor, represented by the letter L, and a capacitor, represented by the letter C. When connected together, an electrical current can alternate between them.
    • The resonance effect occurs when inductive and capacitive reactances are equal. The word resonance refers to a class of phenomena in which a small driving perturbation gives rise to a large effect in the system.
    • Applications of Resonance:
      • Tuning: LC circuits are set at resonance for a particular carrier frequency
      • Voltage Magnification
      • Current Magnification
      • Load Impedence
  • 5.  
  • 6. Electronic Article Surveillance (EAS)
  • 7. Why EAS?
    • RFID = Identification + EAS
    • Shoplifters steal more than US$10 billion a year from U.S. retailers ($60 billion worldwide)
    • Shoplifting means:
      • lost sales
      • higher inventory costs
      • tighter margins
  • 8. 1-Bit Transponders
    • A bit is the smallest unit of information that can have only two states:
      • “1” = “transponder in interrogating zone”
      • “0” = “no transponder in interrogating zone”
  • 9. EAS system architecture
    • Reader antenna
    • Security element (tag)
    • Deactivation device
    • Activator device
  • 10.  
  • 11. Radio Frequency
    • Components:
      • The radio frequency (RF) uses LC resonant circuits adjusted to a particular frequency
      • Tags: Modern Systems employ coils etched between foils in the form of a stick-on label
  • 12. Radio Frequency
    • Operation:
      • The reader generates a magnetic field in the radio frequency range
      • When tag is moves into the vicinity of the magnetic alternating field, energy from the alternating field induces voltage in the tag’s coil ( Faraday’s Law )
      • If the frequency of the reader’s field corresponds with the frequency of the tag’s circuit, the tag’s circuit produces a sympathetic oscillation (also starts to oscillate)
  • 13. Radio Frequency
    • Operation:
      • The current that that flows in the tag’s circuit, as a result of the sympathetic oscillation, ultimately acts against its cause – the magnetic field of the reader
      • This “resistance” leads to a small voltage drop in the reader’s coil and ultimately leads to decrease in magnetic field strength
      • To ensure better detection rate, the reader may “sweep” across frequencies: 8.2 MHz+- 10%
  • 14.  
  • 15.  
  • 16. Radio Frequency
    • Deactivation
      • Item is placed into deactivator
      • Deactivator generates a sufficiently high magnetic field that the induced voltage destroys the foil capacitor of the circuit
      • Capacitors are designed with intentional short-circuit points, called “dimples”
      • The breakdown of the capacitor is irreversible
  • 17. Radio Frequency
    • Problems:
      • The detection rate can be as low as 70%
      • The detection rate is heavily influenced by certain materials (especially metal) – affect the resonant frequency of the coil
      • Both reader antenna and tag must have adequate size to ensure adequate data transmission
  • 18.  
  • 19. Microwave
    • Operation:
      • Exploits the generation of “ Harmonics ” by components (e.g. capacitance diodes)
      • The harmonic of a sinusoidal voltage A with a frequency fA is a sinusoidal voltage B, whose frequency fB is an integer multiple of fA
      • Tag receives frequency wave from the reader and “multiplies” the frequency and sends it back to the reader
      • After receiving the “multiplied” frequency signal, the sensor is able to detect the presence of the tag. (E.g. the sensor tuned to the second harmonic triggers alarm when it detects that frequency)
  • 20.  
  • 21. Microwave
    • Advantages:
      • If the signal is modulated (ASK, FSK), then interference from other signals can be prevented – the harmonic is also modulated
      • Microwave EAS systems are less sensitive to metal parts – typical frequencies used are 915 MHz (Europe), 2.45GHz, or 5.6 GHz
      • Microwave systems are typically used to protect textiles
  • 22.  
  • 23. Frequency Divider
    • Operation:
      • Operates in the long wave range at 100-135.5 kHz
      • Tag derives power from the magnetic field; frequency received from the reader is divided by two by the microchip and send back to the reader
      • The signal is half the original frequency - subharmonic
      • Signal can be modulated (ASK or FSK) to filter interference
      • Tag has to be removed from a product after purchase
  • 24. Electromagnetic EAS
    • Operate using strong magnetic fields in range of10-20kHz
    • Due to the extremely low frequency, they are the only systems suitable for products containing metal
    • Signal contains summation of differential frequency of the extra signals by superimposing additional signals with higher frequencies over main signal
    • The tags are usually in the form of self-adhesive magnetic strips with lengths ranging from 2cm to 20cm
    • To deactivate: cashier runs a strong permanent magnet along the metal strip  magnetization of the element. Can be reactivated any number of times.
    • However, system performance depends on tag position
  • 25.  
  • 26. Acoustomagnetics
    • Tags come in the form of small, thin plastic boxes
    • The box contains two metal strips
      • Hard metal strip
      • Strip made from amorphous metal (can vibrate)
      • Ferromagnetic substances are “ magnetostrictive ” – change in length due to magnetization
    • The strip vibrates at high amplitude at resonant frequency of the system
    • The strip continues to oscillate even after the reader’s field is switched off - like a tuning fork. Hence, itself generates a magnetic alternating field that can be detected by security system  higher sensitivity.
    • To deactivate the tag, it has to be demagnetized
  • 27.  
  • 28. Transmission Procedures
    • HDX: data transfer from the transponder to the reader alternates with data transfer from the reader to the transponder
    • FDX: data transfer from the transponder to the reader takes place at the same time as the data transfer from the reader to the transponder
    • SEQ: transfer of energy from the reader takes place for a limited period of time. Data transfers occur in between these energy pulses
  • 29. FDX, HDX, SEQ Source: RFID Handbook
  • 30. Advantages of SEQ Systems
    • The available operating voltage is up to twice that of a comparable half/full duplex systems
    • The energy available to the chip can take, theoretically any value
  • 31. Inductive coupling
    • Almost always operated passively
    • Frequency range used (wavelength): <135 KHz (2400 m), 13.56 MHz (22.1 m)
    • Components
      • Electronic data-carrying device – Microchip
      • Large coil area – Antenna
  • 32. Inductive coupling
    • Operation:
      • Reader’s antenna coil generates a strong EM field, which penetrates cross-section of coil
      • Because frequency used is >>> distance between reader and transponder’s antennae, the EM field can be treated as a simple magnetic alternating field  Voltage generated by Inductance
      • Circuit resonates at transmission frequency of reader – very high current generated in reader by resonance step-up which produce required field strengths for operation
      • The two coils can also be interpreted as a transformer (distance between coils < 0.16 λ – transponder is in Near Field
  • 33. Inductive coupling
      • Efficiency of power transfer between reader and transponder is proportional to:
        • Operating frequency
        • Number of windings (higher frequencies need lower windings)
        • Area enclosed by transponder coils
        • Distance between two coils
      • Data Transfer from Transponder  Reader
        • Load Modulation : switching a load resistor on and off at the transponder’s antenna controlled by data – changes voltage and hence, amplitude
        • Sensitivity : Two modulation sidebands sent along with main signal (subcarriers), or subharmonics used
  • 34. Inductive coupling
  • 35. Electromagnetic backscatter coupling
    • Operated at UHF frequencies: 868 MHz (Europe) and 915 MHz (USA); and microwave frequencies: 2.5 GHz and 5.8 GHz
    • Used for long-range systems
      • Gap between reader and transponder > 1m
    • To achieve ranges of >15m – backscatter transponders have backup batteries to supply power
    • To maximize battery power, “stand-by” mode used when transponder moves out of range of reader
    • The battery of an active transponder never provides power for the transmission of data between transponder and reader. Exclusively serves for supply to microchip.
  • 36. Electromagnetic backscatter coupling
    • Data transmission  Reader
      • Modulated reflection cross-section
        • Efficiency by which objects reflect EM waves – “ Reflection cross-section ”. Objects that are in resonance with wave front that hits them have large reflection cross-section
        • Proportion of incoming power is reflected. The reflection characteristics are influenced by altering the load connected to the antenna in time with the data stream to be transmitted. The amplitude of reflected power is thus modulated
        • The reader has a “ directional coupler ” which differentiates between forward and backward signals
  • 37. Close coupling
    • Ranges between 0.1 cm – 1 cm
    • Transponder inserted into reader or placed on marked surface (“touch and go”)
    • Allows transponder coil to be precisely positioned in air gap of a ring-shaped or U-shaped core
    • High freq AC in reader generates high freq magnetic field in core and air gap – which provides power supply to chip in transponder
  • 38. Close coupling
    • Frequencies in range 1- 10 MHz used
    • In contrast to inductively coupled or microwave systems, the efficiency of power transfer is very good
    • Suited for operation of chips with high power consumption – microprocessors (need 10 mW for operation)
    • Contact-less smart cards – ISO 10536
  • 39. Close coupling
    • Data transfer transponder  reader
      • Magnetic coupling: Load modulation with subcarrier used for magnetically coupled data transfer. Frequency and modulation specified in ISO 10536 standard
      • Capacitive coupling: Plate capacitors in reader and transponders arranged so that they are exactly parallel to one another – defined in ISO 10536
  • 40. Electrical coupling
    • Uses electrostatic fields for transmission of energy and data
    • Load modulation used to transfer data from transponder to reader
  • 41. Data Transfer from Reader
    • All known digital modulation procedures used
      • ASK: Amplitude shift keying (most used)
      • FSK: Frequency shift keying
      • PSK: Phase shift keying
  • 42. CLASSIFICATION BY FREQUENCY
  • 43. Basic Types of RFID Systems Railroad car monitoring Toll collection systems Long read range High reading speed Line of sight required (Microwave) Expensive High UHF: 850-950MHz Microwave: 2.4 – 5.8 GHz Access Control Smart Cards Short to medium read range Potentially inexpensive Medium reading range Medium 10-15 MHz Access control Animal/Human identification Inventory Control Short to medium read range, inexpensive, low reading speed Low 100-500 kHz Typical Applications Characteristics Frequency Band
  • 44. Agenda
    • 13.56MHz RFID Systems (HF)
      • Operating principles are similar to LF
    • 400-1000MHz RFID Systems (UHF)
    • 2.4GHz RFID Systems (Microwave)
  • 45. How to select an appropriate RFID System?
    • For each application, there is an appropriate RFID system in terms of:
      • Operating principles
        • Frequency
        • Range
        • Coupling
      • Functionality
        • Read-only
        • Read-write
        • Motion-detection
      • Physical form:
        • Stationary readers
        • Handheld Readers
        • Tunnels, Gates
      • Cost
  • 46. 13.56MHz RFID Systems Library RFID System from Tagsys Tag Circulation Desk Station Programming Station Security Gate
  • 47. 13.56MHz – Operating Principles
    • Mostly passive – no battery
      • Low cost
      • Longer life-time
    • Inductive coupling is used for data transmission
  • 48. 13.56MHz – Operating Principles
    • RF field at 13.56MHz is not absorbed by water or human tissue
    • Sensitive to metal parts in the operating zone (this applies to all RFID systems)
    • As the magnetic field has vector characteristics, tag orientation influences performance of the system (distance)
      • Rotating fields
    • Since inductive RFID systems are operated in the near field, interference from adjacent systems is lower compared to other systems
  • 49. 13.56MHz - Tags
    • Tags are available in different shapes and have different functionality
    • A few turns (<10) of antenna are sufficient to produce a passive tag  low cost
  • 50. 13.56MHz –Shape of Tags
    • ISO Cards (ISO 14443, ISO 15693)
    • Durable industrial tags
    • Thin and flexible smart labels
  • 51. 13.56MHz –Functionality
    • Memory size (from 64 bit - ID tags to several Kbytes)
    • Memory types: ROM, WORM/OTP, R/RW
    • Security mechanisms can be implemented
    • Multi-tag capability – several tags can be read at once
  • 52. 13.56MHz – Readers
    • Range
      • “Proximity” (<100 mm)
        • Handheld devices, printers, terminals
        • Small size, low cost
      • “Vicinity” (<1.5m)
        • More complex
        • Higher power consumption
      • “Medium range” (<400 mm)
  • 53. 13.56MHz –Physical Form of Readers
    • Application
      • Mobile
      • Stationary
  • 54. 13.56MHz –Readers
    • Readers can have several antennas to allow for:
      • Greater operating range
      • Greater volume/area coverage
      • Random tag orientation
  • 55. 13.56MHz – Conveyor Performance
    • A reader that reads 10 to 30 tags per second  Successful tagging of items on a conveyor running at 3 meters/sec and spaced 0.10 m
  • 56. 13.56MHz – Overall Performance
    • Application fit is the key
      • Memory size, security level
    • Smaller operating distances allow faster data transmission, longer operating distances impose lower transmission speed
    • Greater resistance to noise
      • Outside of the ISM band
  • 57. 400-1000 MHz UHF RFID-Systems (UHF)
  • 58.
    • Uses EM Propagation
    • The amount of energy collected is a function of the aperture of the receiving antenna, which in simple terms is related to the wavelength of the received signal
    • Operating range is dependent on the radiant power of the reader, the operating frequency, and the size of a tag antenna
    400-1000 MHz UHF RFID-Systems Operating Principles
  • 59. 400-1000 MHz UHF RFID-Systems Wave Properties
    • EM waves are related to light and behave in a similar manner
    • EM waves can be reflected off radio conductive reflective surfaces, refracted as they pass the barrier between dissimilar electric media, or detracted around a sharp edge
    • UHF waves have shorter waves and, thus, are more effected when passing objects
  • 60. 400-1000 MHz UHF RFID-Systems Penetration into Liquids
    • EM waves penetrate into different liquids, depending on the electrical conductivity of the liquid
    • Water has high conductivity  will reflect and absorb the signal
    • Oil and petroleum liquids have low conductivity  will allow EM to pass
  • 61. 400-1000 MHz UHF RFID Range
    • Read range depends on:
      • Transmitter (reader) power
      • Energy requirements of the tags (for passive tags)
      • Absorption factor of materials to which the tag is attached
      • Tag size
        • The smaller the tag, the smaller the energy capture area, the shorter the read range
  • 62. 400-1000 MHz UHF RFID Interference
    • Electrical noise from motors, florescent lights, etc is minimal at UHF
    • Noise from other RFID systems, mobile phones, etc.
    • Frequency Hoping Spread Spectrum (FHSS) can reduce interference
  • 63. 400-1000 MHz UHF RFID Read Direction
    • UHF allows for directional antennas
    • This allows to direct the signal to particular groups of tags
  • 64.
    • Orientation of the tag antenna with respect to the reader’s antenna will impact range (not important for some systems)
    Tag Orientation
  • 65. 2450 MHz RFID Systems
  • 66. 2450 MHz RFID Systems
    • Microwave RFID systems have been in wide-spread use for over 10 years in transportation applications
      • Rail car tracking
      • Toll collection
      • Vehicle access control
  • 67. 2450 MHz RFID Systems Operating Principles
    • Modulated backscatter
    • Microwave systems operate in the “far field”  long range systems
    • Microwave signals are attenuated and reflected by materials containing water or human tissue and are reflected by metallic objects
      • It is possible to design tags that work on metallic objects
    • Line of sight is not required for operations
  • 68. 2450 MHz RFID Systems Operating Principles
    • UHF and microwave signals easily penetrate wood, paper, cardboard, clothing, paint, dirt, and similar materials
    • Because of short wave length and reflective properties of metal, high reading readability can be achieved in metal-intensive environments
    • Sensitive to orientation
      • Rotating antennas can solve the problem
  • 69. 2450 MHz RFID Systems Operating Principles
    • UHF and Microwave systems are allocated many MHz of spectrum  independent operation of different systems, less interference
    • Microwave systems have a proven record of reliability
  • 70. 2450 MHz RFID Systems Physical Form of Tags
    • Tags come in various forms
    • Tags are smaller than their LF and HF counterparts
    • 3 major types of tags
      • EZ pass type
      • Tags for logistical purposes
      • Thin and flexible smart labels
  • 71. 2450 MHz RFID Systems Tags
    • From 64 bits to several Kbytes
    • ROM, OTP, R/RW
    • All required security levels can be realized
    • Multiple tags can be read in the same zone
  • 72. 2450 MHz RFID Systems Readers
    • “Proximity”
    • “Vicinity”
    • Handheld
    • Stationary
  • 73. 2450 MHz RFID Systems Performance
    • Compared to inductive systems, the UHF and microwave systems can have longer range, higher data rates, smaller antennas, more flexibility in form factors and antenna design
    • Object penetration and no line-of-sight readability can be better for LF systems
  • 74. Conclusion
    • Operating principles impact:
      • Appropriateness of a particular RFID system for a particular application
      • Vulnerabilities of RFID systems
        • Interference
        • Security attack