Inductive Coupling
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Inductive Coupling

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Inductive Coupling Presentation Transcript

  • 1. Overview of RFID System Characteristics
    • Operating Frequency
    • Method of Coupling
    • Transmission Range
    • Data Storage Capacity
    • Power Supply (Active, Passive)
    • Read Only / Read-Write
    • Transmission Types (HDX, FDX, SEQ)
  • 2. Method of Coupling
    • All RFID systems have two basic ways of exchanging information:
      • (1) inductive coupling 
      • or
      • (2) electromagnetic backscatter
  • 3. Inductive Coupling
    • Operating Frequency: 13,56 MHz (HF)
      • Also 135 kHz
    • Transmission Range: <1 meter
    • Data Storage Capacity: up to 100 KB
      • EEPROM memory
    • Power Supply: Passive
    • Both Read Only and Read-Write
    • Transmission Types: HDX, FDX, SEQ
  • 4. Inductive Coupling Inductive coupling means that the transponder and the antenna are coupled by the magnetic flux through both coils, much like a transformer. All the energy used in the tag is drawn from the primary coil of the antenna.
  • 5. Inductance
    • Electromagnetic induction is the production of voltage across a conductor situated in a changing magnetic flux.
    • Faraday found that the voltage produced around a closed path conductor is proportional to the rate of change of the magnetic flux through any surface bounded by that path.
    Faraday's law:
  • 6. Oscillator
    • A capacitor and an inductor connected together form an oscillator. Both capacitors and inductors store energy.
    A capacitor stores energy in the form of an electrostatic field an inductor stores energy in a magnetic field
    • Once the capacitor is charged:
    • The capacitor will start to discharge through the inductor. As it does,
    • the inductor will create a magnetic field.
    • Once the capacitor discharges, the inductor will try to keep the current
    • in the circuit moving, so it will charge up the other plate of the capacitor.
    • Once the inductor's field collapses, the capacitor has been recharged
    • (but with the opposite polarity), so it discharges again through the inductor.
  • 7. Resonators
    • The antenna coil of the transponder and the capacitor form a resonant circuit tuned to the transmission frequency of the reader. The voltage U at the transponder coil reaches a maximum due to resonance in the circuit.
      • This is way a radio receiver works
    • The efficiency of power transfer between the antenna coil of the reader and the transponder is proportional to:
      • the operating frequency f
      • the number of windings n
      • the area A enclosed by the transponder coil
      • the angle of the two coils relative to each other
      • the distance between the two coils.
  • 8. The rest of the picture
    • The energy in the coil can is harvested using diodes and capacitors (C 2 ) to rectify the current.
    LC circuit oscillator
  • 9. Method of Coupling
    • All RFID systems have two basic ways of exchanging information:
      • (1) inductive coupling
      • or
      • (2) electromagnetic backscatter 
  • 10. Backscatter Coupling
    • Operating Frequency: 915MHz (UHF), 2.5 GHz & 5.8 GHz (Microwave)
      • Also 868MHz (Europe)
    • Transmission Range: > 1 meter
    • Data Storage Capacity: high bandwidth
    • Power Supply: p assive, semi-passive, active
    • Both r ead only and read-write, etc
    • Transmission Types: HDX, FDX, SEQ
  • 11. What is backscatter
    • Electromagnetic backscatter is quite similar to radars.
    • Depending on its characteristics, an antenna reflects part of an incoming electromagnetic wave back to the sender.
    • Electromagnetic wave are reflected by most objects that are larger than half the wavelength.
    • The efficiency of reflection is particularly large for antennas that are in resonance with the incoming waves.
      • The short wavelengths of UHF facilitate the construction of antennas with smaller dimensions and greater efficiency.
  • 12. Far field not near field
    • Opposite to inductive coupling, electromagnetic backscatter works beyond the near field.
    • The energy available at the transponder is found by calculating the free space path loss a F between the reader and the transponder.
    • a F = −147 . 6 + 20 log (r) + 20 log (f ) − 10 log (G T ) − 10 log (G R )
  • 13. How it works
    • The power reflected from the transponder is radiated into free space. A small proportion of this (free space attenuation) is picked up by the reader’s antenna.
    • The reflected signal travels into the antenna connection of the reader in the backwards direction and can be decoupled using a directional coupler.