Physics of RFID

1
Physics of RFID

• University of Houston
• Bauer College of Business
• Summer 2008

2
Why study physics of RFID?

• Vulnerabilities of RFID systems
• Operation
• Security

3
Electromagnetism

• Electromagnetism unified framework for
  understanding electricity, magnetism, and the
  relationship between them
• A charge creates an electric field
• When the charge starts moving, it creates
  magnetic field
• Electric force and magnetic force are intimately
  related, so together they are called
  Electromagnetic (EM) force

4
Faradays Law

• Any change in the magnetic environment of a coil
  of wire will cause a voltage to be "induced" in
  the coil
• Change could be produced by
• Changing the magnetic field strength
• Moving a magnet toward or away from the coil
• moving the coil into or out of the magnetic field
• rotating the coil relative to the magnet, etc.

Source http//hyperphysics.phy-astr.gsu.edu/hbase
/electric/farlaw.html
5
Coupling
6
Carrier Frequencies

• Wave - a disturbance of some kind (e.g. EM
  disturbance)
• Frequency - property of radio waves used to
  transmit data

7
(No Transcript)
8
(No Transcript)
9
Carrier Frequency

• RFID systems may use a particular frequency band
  depending on
• Application
• Legislature
• Cost considerations

10
Frequency Bands
11
Wave Adventures

• EM waves can be
• Reflected off radio conductive reflective
  surfaces
• Refracted as they pass the barrier between
  dissimilar media
• Detracted around a sharp edge
• Absorbed
• UHF waves have shorter waves and, thus, are more
  affected when passing objects

12
Absorption

• When electromagnetic energy passes through any
  substance other than a vacuum, some of the energy
  is absorbed and is converted to heat
• Attenuation of radio signals (by absorption)
  depends on the characteristics of the material
  through which the EM wave propagates
• Differing from UHF- and µW-systems, the RF field
  at LF is not absorbed by water or human tissue,
  which allows operation through water or human
  beings. The influence of water or moisture on the
  performance is negligible.

13
Reflection

• Reflection can be helpful by causing the waves to
  be redirected around objects
• Reflection can also cause a problem if a direct
  wave meets with a reflected wave with an opposite
  phase ? wave cancellation can occur resulting a
  no-read situation
• Multiple antennas can solve the problem

14
Reflection
15
Refraction

• Refraction the change of direction of a wave
  due to them entering a new medium (Wikipedia)

16
(No Transcript)
17
Diffraction

• Diffraction - the spreading out of waves as they
  pass a sharp corner

18
Antenna
Source Asif and Mandviwalla, 2005
19
Range

• Range the working distance between a tag and a
  reader

Range
20
Range and Power Levels

• The range that can be achieved in an RFID system
  is determined by
• The power available at the reader
• The power available within the tag
• The environmental conditions and structures
• More important at higher frequencies than at
  lower frequencies

21
Conclusion

• Theory vs. practice
• Active RFID systems