Inductive Coupling


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Inductive Coupling

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