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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

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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