Overview of RFID System Characteristics

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 (C2) 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: passive, semi-passive, active • Both read 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 aF between the reader and the transponder. aF = −147.6 + 20 log(r) + 20 log(f ) − 10 log(GT) − 10 log(GR)

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.