RFID Systems and Operating Principles

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RFID Systems and Operating Principles

• Vlad Krotov
• DISC 4397 Section 12977
• University of Houston
• Bauer College of Business
• Spring 2005
• Presentation Source Finkenzeller, 2003
• Image Source Checkpoint Systems

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Announcements

• Feb 7 class (Monday) will be held
• in room 290G

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Last class

• 13.56MHz RFID Systems (HF)
• 400-1000MHz RFID Systems (UHF)
• 2.4GHz RFID Systems (Microwave)

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Electronic Article Surveillance (EAS)
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Why EAS?

• Shoplifters steal more than US10 billion a year
  from U.S. retailers (60 billion worldwide)
• Shoplifting means
• lost sales
• higher inventory costs
• tighter margins

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Source Checkpoint Systems, 2005
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Evolution of EAS

• RFID Identification EAS
• Most RFID system (identification) also carry the
  functionality for theft prevention
• Shrinkage reduction
• POS
• Warehouse

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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

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EAS system architecture

• Reader antenna
• Security element (tag)
• Deactivation device
• Activator device

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Radio Frequency

• 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

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Radio Frequency

• 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 tags
  coil (Faradays Law)
• If the frequency of the readers field
  corresponds with the frequency of the tags
  circuit, the tags circuit produces a sympathetic
  oscillation (also starts to oscillate)

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Radio Frequency

• The current that that flows in the tags 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 readers coil and ultimately leads to
  decrease in magnetic field strength
• To ensure better detection rate, the reader may
  sweep across frequencies

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Radio Frequency

• In order to deactivate an item, the item is
  placed into deactivator
• Deactivator generates a sufficiently high
  magnetic field that the induced voltage destroys
  the foil capacitor of the circuit
• The breakdown of the capacitor is irreversible

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Radio Frequency

• The detection rate can be as low as 70
• The detection rate is heavily influenced by
  certain materials (especially metal)
• Both reader antenna and tag must have adequate
  size to ensure adequate data transmission

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Microwave

• Tag received frequency wave from the reader
• Then the tag multiplies the frequency and sends
  it back to the reader
• After receiving the multiplied frequency
  signal, the system is able to detect the presence
  of the tag

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Microwave

• If the signal is modulated (ASK, FSK), then
  interference from other signals can be prevented
• Microwave EAS systems are less sensitive to metal
  parts
• Microwave systems are typically used to protect
  textiles

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Frequency Divider

• The procedure operates in the long wave range at
  100-125.5 kHz
• Tag contains a microchip and a resonant circuit
  coil made of wound copper
• The resonant circuit is made to resonate at the
  operating frequency of the EAS system
• Tag derives power from the magnetic field
• The frequency received from the reader is divided
  by two by the microchip and send back to the
  reader
• The tag has to be removed from a product after
  purchase

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Electromagnetic EAS

• This type of EAS operates using strong magnetic
  fields in the range from 10 Hz to around 20kHz
• Tag contains a strip of a soft magnetic metal
• Through magnetization, the strip emits osculation
  at the frequency of the system
• The tags are usually in the form of self-adhesive
  magnetic strips with lengths ranging from 2cm to
  20cm
• To deactivate a tag, the cashier runs a strong
  permanent magnet along the metal strip ?
  magnetization of the element
• Due to the extremely low frequency,
  electromagnetic systems are the only systems
  suitable for products containing metal
• However, system performance depends on tag
  position

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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)
• The strip vibrates at the frequency of the system
• One advantage of this system is the strip
  continues to oscillate even after the readers
  field is switched off ? higher sensitivity of the
  system
• To deactivate the tag, it has to be demagnetized

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Transmission Procedures

• In the half duplex procedure (HDX) the data
  transfer from the transponder to the reader
  alternates with data transfer from the reader to
  the transponder
• In the full duplex procedure (FDX) the data
  transfer from the transponder to the reader takes
  place at the same time as the data transfer from
  the reader to the transponder
• In the sequential systems (SEQ), the transfer of
  energy from the reader takes place for a limited
  period of time. Data transfers occur in between
  these energy pulses

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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

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Data Transmission

• AKS amplitude shift keying
• FSK frequency shift keying
• PSK phase shift keying
• Most systems use ASK

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