RFID Systems and Operating Principles

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RFID Systems and Operating Principles

• University of Houston
• Bauer College of Business
• Spring 2007
• Presentation Source RFID Handbook, Chapter 3

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Overview

• Please read Chapter 3 of the RFID Handbook for
  this section
• RFID Systems can be categorized based on
• Operating principles
• Frequency

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CLASSIFICATION BY OPERATING PRINCIPLE
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LC Circuit

• An LC circuit consists of an inductor,
  represented by the letter L, and a capacitor,
  represented by the letter C. When connected
  together, an electrical current can alternate
  between them.
• The resonance effect occurs when inductive and
  capacitive reactances are equal. The word
  resonance refers to a class of phenomena in which
  a small driving perturbation gives rise to a
  large effect in the system.
• Applications of Resonance
• Tuning LC circuits are set at resonance for a
  particular carrier frequency
• Voltage Magnification
• Current Magnification
• Load Impedence

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Electronic Article Surveillance (EAS)
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Why EAS?

• RFID Identification 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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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

• Components
• 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

• Operation
• 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

• Operation
• 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 8.2 MHz- 10

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Radio Frequency

• Deactivation
• Item is placed into deactivator
• Deactivator generates a sufficiently high
  magnetic field that the induced voltage destroys
  the foil capacitor of the circuit
• Capacitors are designed with intentional
  short-circuit points, called dimples
• The breakdown of the capacitor is irreversible

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Radio Frequency

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

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Microwave

• Operation
• Exploits the generation of Harmonics by
  components (e.g. capacitance diodes)
• The harmonic of a sinusoidal voltage A with a
  frequency fA is a sinusoidal voltage B, whose
  frequency fB is an integer multiple of fA
• Tag receives frequency wave from the reader and
  multiplies the frequency and sends it back to
  the reader
• After receiving the multiplied frequency
  signal, the sensor is able to detect the presence
  of the tag. (E.g. the sensor tuned to the second
  harmonic triggers alarm when it detects that
  frequency)

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Microwave

• Advantages
• If the signal is modulated (ASK, FSK), then
  interference from other signals can be prevented
  the harmonic is also modulated
• Microwave EAS systems are less sensitive to metal
  parts typical frequencies used are 915 MHz
  (Europe), 2.45GHz, or 5.6 GHz
• Microwave systems are typically used to protect
  textiles

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Frequency Divider

• Operation
• Operates in the long wave range at 100-135.5 kHz
• Tag derives power from the magnetic field
  frequency received from the reader is divided by
  two by the microchip and send back to the reader
• The signal is half the original frequency -
  subharmonic
• Signal can be modulated (ASK or FSK) to filter
  interference
• Tag has to be removed from a product after
  purchase

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Electromagnetic EAS

• Operate using strong magnetic fields in range
  of10-20kHz
• Due to the extremely low frequency, they are the
  only systems suitable for products containing
  metal
• Signal contains summation of differential
  frequency of the extra signals by superimposing
  additional signals with higher frequencies over
  main signal
• The tags are usually in the form of self-adhesive
  magnetic strips with lengths ranging from 2cm to
  20cm
• To deactivate cashier runs a strong permanent
  magnet along the metal strip ? magnetization of
  the element. Can be reactivated any number of
  times.
• 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)
• Ferromagnetic substances are magnetostrictive
  change in length due to magnetization
• The strip vibrates at high amplitude at resonant
  frequency of the system
• The strip continues to oscillate even after the
  readers field is switched off - like a tuning
  fork. Hence, itself generates a magnetic
  alternating field that can be detected by
  security system? higher sensitivity.
• To deactivate the tag, it has to be demagnetized

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Transmission Procedures

• HDX data transfer from the transponder to the
  reader alternates with data transfer from the
  reader to the transponder
• FDX data transfer from the transponder to the
  reader takes place at the same time as the data
  transfer from the reader to the transponder
• SEQ 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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FDX, HDX, SEQ
Source RFID Handbook
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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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Inductive coupling

• Almost always operated passively
• Frequency range used (wavelength) lt135 KHz (2400
  m), 13.56 MHz (22.1 m)
• Components
• Electronic data-carrying device Microchip
• Large coil area Antenna

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Inductive coupling

• Operation
• Readers antenna coil generates a strong EM
  field, which penetrates cross-section of coil
• Because frequency used is gtgtgt distance between
  reader and transponders antennae, the EM field
  can be treated as a simple magnetic alternating
  field ? Voltage generated by Inductance
• Circuit resonates at transmission frequency of
  reader very high current generated in reader by
  resonance step-up which produce required field
  strengths for operation
• The two coils can also be interpreted as a
  transformer (distance between coils lt 0.16 ?
  transponder is in Near Field

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Inductive coupling

• Efficiency of power transfer between reader and
  transponder is proportional to
• Operating frequency
• Number of windings (higher frequencies need lower
  windings)
• Area enclosed by transponder coils
• Distance between two coils
• Data Transfer from Transponder ? Reader
• Load Modulation switching a load resistor on and
  off at the transponders antenna controlled by
  data changes voltage and hence, amplitude
• Sensitivity Two modulation sidebands sent along
  with main signal (subcarriers), or subharmonics
  used

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Inductive coupling
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Electromagnetic backscatter coupling

• Operated at UHF frequencies 868 MHz (Europe) and
  915 MHz (USA) and microwave frequencies 2.5 GHz
  and 5.8 GHz
• Used for long-range systems
• Gap between reader and transponder gt 1m
• To achieve ranges of gt15m backscatter
  transponders have backup batteries to supply
  power
• To maximize battery power, stand-by mode used
  when transponder moves out of range of reader
• The battery of an active transponder never
  provides power for the transmission of data
  between transponder and reader. Exclusively
  serves for supply to microchip.

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Electromagnetic backscatter coupling

• Data transmission ? Reader
• Modulated reflection cross-section
• Efficiency by which objects reflect EM waves
  Reflection cross-section. Objects that are in
  resonance with wave front that hits them have
  large reflection cross-section
• Proportion of incoming power is reflected. The
  reflection characteristics are influenced by
  altering the load connected to the antenna in
  time with the data stream to be transmitted. The
  amplitude of reflected power is thus modulated
• The reader has a directional coupler which
  differentiates between forward and backward
  signals

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Close coupling

• Ranges between 0.1 cm 1 cm
• Transponder inserted into reader or placed on
  marked surface (touch and go)
• Allows transponder coil to be precisely
  positioned in air gap of a ring-shaped or
  U-shaped core
• High freq AC in reader generates high freq
  magnetic field in core and air gap which
  provides power supply to chip in transponder

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Close coupling

• Frequencies in range 1- 10 MHz used
• In contrast to inductively coupled or microwave
  systems, the efficiency of power transfer is very
  good
• Suited for operation of chips with high power
  consumption microprocessors (need 10 mW for
  operation)
• Contact-less smart cards ISO 10536

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Close coupling

• Data transfer transponder ? reader
• Magnetic coupling Load modulation with
  subcarrier used for magnetically coupled data
  transfer. Frequency and modulation specified in
  ISO 10536 standard
• Capacitive coupling Plate capacitors in reader
  and transponders arranged so that they are
  exactly parallel to one another defined in ISO
  10536

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Electrical coupling

• Uses electrostatic fields for transmission of
  energy and data
• Load modulation used to transfer data from
  transponder to reader

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Data Transfer from Reader

• All known digital modulation procedures used
• ASK Amplitude shift keying (most used)
• FSK Frequency shift keying
• PSK Phase shift keying

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CLASSIFICATION BY FREQUENCY
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Basic Types of RFID Systems
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Agenda

• 13.56MHz RFID Systems (HF)
• Operating principles are similar to LF
• 400-1000MHz RFID Systems (UHF)
• 2.4GHz RFID Systems (Microwave)

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How to select an appropriate RFID System?

• For each application, there is an appropriate
  RFID system in terms of
• Operating principles
• Frequency
• Range
• Coupling
• Functionality
• Read-only
• Read-write
• Motion-detection
• Physical form
• Stationary readers
• Handheld Readers
• Tunnels, Gates
• Cost

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13.56MHz RFID Systems
Library RFID System from Tagsys
Tag
Circulation Desk Station
Programming Station
Security Gate
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13.56MHz Operating Principles

• Mostly passive no battery
• Low cost
• Longer life-time
• Inductive coupling is used for data transmission

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13.56MHz Operating Principles

• RF field at 13.56MHz is not absorbed by water or
  human tissue
• Sensitive to metal parts in the operating zone
  (this applies to all RFID systems)
• As the magnetic field has vector characteristics,
  tag orientation influences performance of the
  system (distance)
• Rotating fields
• Since inductive RFID systems are operated in the
  near field, interference from adjacent systems is
  lower compared to other systems

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13.56MHz - Tags

• Tags are available in different shapes and have
  different functionality
• A few turns (lt10) of antenna are sufficient to
  produce a passive tag ? low cost

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13.56MHz Shape of Tags

• ISO Cards (ISO 14443, ISO 15693)
• Durable industrial tags
• Thin and flexible smart labels

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13.56MHz Functionality

• Memory size (from 64 bit - ID tags to several
  Kbytes)
• Memory types ROM, WORM/OTP, R/RW
• Security mechanisms can be implemented
• Multi-tag capability several tags can be read
  at once

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13.56MHz Readers

• Range
• Proximity (lt100 mm)
• Handheld devices, printers, terminals
• Small size, low cost
• Vicinity (lt1.5m)
• More complex
• Higher power consumption
• Medium range (lt400 mm)

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13.56MHz Physical Form of Readers

• Application
• Mobile
• Stationary

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13.56MHz Readers

• Readers can have several antennas to allow for
• Greater operating range
• Greater volume/area coverage
• Random tag orientation

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13.56MHz Conveyor Performance

• A reader that reads 10 to 30 tags per second ?
  Successful tagging of items on a conveyor running
  at 3 meters/sec and spaced 0.10 m

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13.56MHz Overall Performance

• Application fit is the key
• Memory size, security level
• Smaller operating distances allow faster data
  transmission, longer operating distances impose
  lower transmission speed
• Greater resistance to noise
• Outside of the ISM band

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400-1000 MHz UHF RFID-Systems (UHF)
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400-1000 MHz UHF RFID-SystemsOperating Principles

• Uses EM Propagation
• The amount of energy collected is a function of
  the aperture of the receiving antenna, which in
  simple terms is related to the wavelength of the
  received signal
• Operating range is dependent on the radiant power
  of the reader, the operating frequency, and the
  size of a tag antenna

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400-1000 MHz UHF RFID-SystemsWave Properties

• EM waves are related to light and behave in a
  similar manner
• EM waves can be reflected off radio conductive
  reflective surfaces, refracted as they pass the
  barrier between dissimilar electric media, or
  detracted around a sharp edge
• UHF waves have shorter waves and, thus, are more
  effected when passing objects

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400-1000 MHz UHF RFID-SystemsPenetration into
Liquids

• EM waves penetrate into different liquids,
  depending on the electrical conductivity of the
  liquid
• Water has high conductivity ? will reflect and
  absorb the signal
• Oil and petroleum liquids have low conductivity
  ? will allow EM to pass

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400-1000 MHz UHF RFIDRange

• Read range depends on
• Transmitter (reader) power
• Energy requirements of the tags (for passive
  tags)
• Absorption factor of materials to which the tag
  is attached
• Tag size
• The smaller the tag, the smaller the energy
  capture area, the shorter the read range

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400-1000 MHz UHF RFIDInterference

• Electrical noise from motors, florescent lights,
  etc is minimal at UHF
• Noise from other RFID systems, mobile phones,
  etc.
• Frequency Hoping Spread Spectrum (FHSS) can
  reduce interference

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400-1000 MHz UHF RFIDRead Direction

• UHF allows for directional antennas
• This allows to direct the signal to particular
  groups of tags

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Tag Orientation

• Orientation of the tag antenna with respect to
  the readers antenna will impact range (not
  important for some systems)

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2450 MHz RFID Systems
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2450 MHz RFID Systems

• Microwave RFID systems have been in wide-spread
  use for over 10 years in transportation
  applications
• Rail car tracking
• Toll collection
• Vehicle access control

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2450 MHz RFID SystemsOperating Principles

• Modulated backscatter
• Microwave systems operate in the far field ?
  long range systems
• Microwave signals are attenuated and reflected by
  materials containing water or human tissue and
  are reflected by metallic objects
• It is possible to design tags that work on
  metallic objects
• Line of sight is not required for operations

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2450 MHz RFID SystemsOperating Principles

• UHF and microwave signals easily penetrate wood,
  paper, cardboard, clothing, paint, dirt, and
  similar materials
• Because of short wave length and reflective
  properties of metal, high reading readability can
  be achieved in metal-intensive environments
• Sensitive to orientation
• Rotating antennas can solve the problem

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2450 MHz RFID SystemsOperating Principles

• UHF and Microwave systems are allocated many MHz
  of spectrum ? independent operation of different
  systems, less interference
• Microwave systems have a proven record of
  reliability

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2450 MHz RFID SystemsPhysical Form of Tags

• Tags come in various forms
• Tags are smaller than their LF and HF
  counterparts
• 3 major types of tags
• EZ pass type
• Tags for logistical purposes
• Thin and flexible smart labels

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2450 MHz RFID SystemsTags

• From 64 bits to several Kbytes
• ROM, OTP, R/RW
• All required security levels can be realized
• Multiple tags can be read in the same zone

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2450 MHz RFID SystemsReaders

• Proximity
• Vicinity
• Handheld
• Stationary

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2450 MHz RFID SystemsPerformance

• Compared to inductive systems, the UHF and
  microwave systems can have longer range, higher
  data rates, smaller antennas, more flexibility in
  form factors and antenna design
• Object penetration and no line-of-sight
  readability can be better for LF systems

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Conclusion

• Operating principles impact
• Appropriateness of a particular RFID system for a
  particular application
• Vulnerabilities of RFID systems
• Interference
• Security attack