RFID Systems and Operating Principles 2

8/3/2019 RFID Systems and Operating Principles 2

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RFID Systems and Operating

PrinciplesVlad Krotov

DISC 4397 Section 12977

University of HoustonBauer College of Business

Spring 2005

Presentation Source: Finkenzeller, 2003Image Source: Checkpoint Systems


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Announcements:

Feb 7 class (Monday) will be heldin 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

(EA

S)


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Why EAS?

Shoplifters steal more than US$10 billion ayear from U.S. retailers ($60 billionworldwide)

Shoplifting means:

lost sales

higher inventory costs

tighter margins


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Source: Checkpoint Systems, 2005


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Evolution ofEAS

RFID = Identification + EAS

Most RFID system (identification) also

carry the functionality for theft prevention Shrinkage reduction:

POS

W

arehouse


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1-Bit Transponders

A bit is the smallest unit of information thatcan 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 LCresonant circuits adjusted to a particularfrequency

Tags: Modern Systems employ coilsetched between foils in the form of a stick-on label


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Radio Frequency

The reader generates a magnetic field in theradio frequency range

When tag is moves into the vicinity of the

magnetic alternating field, energy from thealternating 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 tagscircuit produces a sympathetic oscillation (alsostarts to oscillate)


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Radio Frequency

The current that that flows in the tags circuit, asa result of the sympathetic oscillation, ultimatelyacts against its cause the magnetic field of the

reader This resistance leads to a small voltage drop in

the readers coil and ultimately leads todecrease in magnetic field strength

To ensure better detection rate, the reader maysweep across frequencies


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Radio Frequency

In order to deactivate an item, the item isplaced into deactivator

Deactivator generates a sufficiently highmagnetic field that the induced voltagedestroys the foil capacitor of the circuit

The breakdown of the capacitor isirreversible


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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 datatransmission


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Microwave

Tag received frequency wave from thereader

Then the tag multiplies the frequencyand sends it back to the reader

After receiving the multiplied frequencysignal, the system is able to detect thepresence of the tag


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Microwave

If the signal is modulated (ASK, FSK),then interference from other signals canbe prevented

Microwave EAS systems are less sensitiveto metal parts

Microwave systems are typically used toprotect 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 coilmade of wound copper

The resonant circuit is made to resonate at theoperating 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 inthe 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-adhesivemagnetic strips with lengths ranging from 2cm to 20cm

To deactivate a tag, the cashier runs a strong permanentmagnet along the metal strip magnetization of theelement

Due to the extremely low frequency, electromagnetic

systems are the only systems suitable for productscontaining metal However, system performance depends on tag position


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Acoustomagnetics

Tags come in the form of small, thin plasticboxes

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 thesystem To deactivate the tag, it has to be demagnetized


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Transmission Procedures

In the half duplex procedure (HDX) the datatransfer from the transponder to the readeralternates with data transfer from the reader tothe transponder

In the full duplex procedure (FDX) the datatransfer from the transponder to the reader takesplace at the same time as the data transfer fromthe reader to the transponder

In the sequential systems (SEQ), the transferof energy from the reader takes place for alimited period of time. Data transfers occur inbetween these energy pulses


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Advantages of SEQ Systems

The available operating voltage is up totwice that of a comparable half/full duplexsystems

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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RFID Systems and Operating Principles 2

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