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RFID Systems and Operating Principles
Vlad KrotovVlad Krotov
DISC 4397 – Section 12977DISC 4397 – Section 12977 University of HoustonUniversity of Houston
Bauer College of BusinessBauer College of BusinessSpring 2005Spring 2005
Presentation Source: AIM Global, 2000Presentation Source: AIM Global, 2000
Basic Types of RFID Systems
Frequency Band Characteristics Typical Applications
Low
100-500 kHz
Short to medium read range, inexpensive, low reading speed
Access control
Animal/Human identification
Inventory Control
Medium
10-15 MHz
Short to medium read range
Potentially inexpensive
Medium reading range
Access Control
Smart Cards
High
UHF: 850-950MHz
Microwave: 2.4 – 5.8 GHz
Long read range
High reading speed
Line of sight required (Microwave)
Expensive
Railroad car monitoring
Toll collection systems
Agenda
• 13.56MHz RFID Systems (HF)– Operating principles are similar to LF
• 400-1000MHz RFID Systems (UHF)
• 2.4GHz RFID Systems (Microwave)
Why study operating principles?
• Selecting an RFID system that is most appropriate for your business
Why study operating principles?
• Business process/RFID system alignment
• According to Michel Porter’s (2001) poor understanding of capabilities offered by e-commerce is what caused, in part, the dot-com crash in 2000
How to select an appropriate RFID System?
• For each application, there is an appropriate RFID system in terms of:– Operating principles
• Frequency• Range• Coupling• etc.
– Functionality• Read-only• Read-write• Motion-detection• Etc.
– Physical form:• Stationary readers• Handheld Readers• Etc.
– Cost
13.56MHz RFID SystemsLibrary RFID System from Tagsys
Tag
Circulation Desk Station
Programming Station
Inventory Reader
Security Gate
13.56MHz – Operating Principles
• Mostly passive – no battery– Low cost– Longer life-time
• Inductive coupling is used for data transmission
13.56MHz – Operating Principles Inductive coupling
• An antenna of the reader generates a magnetic field
• The field induces voltage in the coil of the tag and supplies the tag with energy (Faraday’s Law)
13.56MHz – Operating Principles Inductive coupling
Faraday’s Law
• Any change in the magnetic environment of a coil of wire will cause a voltage to be "induced" in the coil
• No matter how the change is produced, the voltage will be generated:– The 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.
• Implications? – Interference from “magnets”
Source: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html
13.56MHz – Operating Principles Inductive coupling
• Data transmission from the reader to the tag is done by changing one parameter of the transmitting field (amplitude, frequency or phase)
13.56MHz – Operating Principles Inductive coupling
• Information transmission from the tag to the reader is done by changing amplitude or phase
data
13.56MHz – Operating Principles Inductive coupling
Source: AIM Global, 2000
13.56MHz – Operating Principles
• 13.56MHz are proximity systems• Operating distance is usually equal the
diameter of the reader antenna• For distances longer than this value, the
field strength decreases exponentially (1/d^3)
• The required transmission power increases with the sixth exponent of the distance (d^6)
Distance
Fie
ld S
tren
gth
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
13.56MHz – Operating Principles Tags
• Tags are available in different shapes and have different functionality
• A few turns (<10) of antenna are sufficient to produce a passive tag low cost
13.56MHz – Operating Principles Shape of Tags
• ISO Cards (ISO 14443, ISO 15693)
• Durable industrial tags
• Thin and flexible smart labels
13.56MHz – Operating Principles Tag 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
13.56MHz – Operating Principles Readers
• “Proximity” (<1m)– Handheld devices, printers, terminals– Small size, low cost
• “Vicinity” (<1.5m)– More complex– Higher power consumption
• “Medium range” (<4m)
13.56MHz – Operating Principles Physical Form of Readers
• Mobile
• Stationary
13.56MHz – Operating Principles Physical Form of Readers
• Readers can have several antennas to allow for:– Greater operating range– Greater volume/area coverage– Random tag orientation
13.56MHz – Operating PrinciplesConveyor Performance
• A reader that reads 10 to 30 tags per second Successful tagging of items on a conveyor running at 3 m/s and spaced 0.10 m
13.56MHz – Operating PrinciplesOverall 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
400-1000 MHz UHF RFID-Systems (UHF)
400-1000 MHz UHF RFID-SystemsOperating Principles
• Electromagnetic wave propagation is used for data transmission (and powering transponders in the case of passive tags)
• The reader transmits an electromagnetic (EM) wave which propagates outward
• The amount of energy available is decreasing (1/d^2) as the distance from the reader increases
400-1000 MHz UHF RFID-SystemsOperating Principles
• 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
400-1000 MHz UHF RFID-SystemsOperating Principles
400-1000 MHz UHF RFID-SystemsOperating Principles
• Operating range is dependent on the radiant power of the reader, the operating frequency, and the size of a tag antenna
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
400-1000 MHz UHF RFID-SystemsWave Properties - Reflection
• EM waves can be reflected off any conductive or partially conductive surface, such as metal, water, concrete, etc.
• 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
400-1000 MHz UHF RFID-SystemsWave Properties - Reflection
400-1000 MHz UHF RFID-SystemsWave Properties - Refraction
• Refraction – the change of direction of a wave due to them entering a new medium (Wikipedia)
400-1000 MHz UHF RFID-SystemsWave Properties - Refraction
400-1000 MHz UHF RFID-SystemsWave Properties - Diffraction
• Diffraction - the spreading out of waves as they pass a sharp corner
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
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
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
400-1000 MHz UHF RFIDRead Direction
• UHF allows for directional antennas
• This allows to direct the signal to particular groups of tags
• Orientation of the tag antenna with respect to the reader’s antenna will impact range (not important for some systems)
Tag Orientation
2450 MHz RFID Systems
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
2450 MHz RFID SystemsOperating Principles
• Energy and data transmission using propagating radio signals– Same as in long-range radio communications
• An antenna of the reader generates a propagating radio wave, which is reflected by the antenna of the tag
• A passive tag converts the signal into voltage supply
• Data transmission from the reader to the tag is done by changing amplitude, frequency, or phase of the transmitting field
2450 MHz RFID SystemsOperating Principles
• The return transmission from the tag is accomplished by changing the load of the amplitude and/or phase of the signal modulated backscatter
• Alternatively, a signal of different frequency can be generated, modulated, and transmitted to the reader – “Active RF transmitter tags”
2450 MHz RFID SystemsOperating Principles
• 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
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 meatal-intensive environments
• Sensitive to orientation– Rotating antennas can solve the problem
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
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
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
2450 MHz RFID SystemsReaders
• “Proximity”
• “Vicinity”
• Handheld
• Stationary
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
Conclusion
• Chose the systems which is most appropriate for your application