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• Use an electronic microchip with data storage capacity of up to a few kilobytes
Data-carrying device : Data transfer between the transponder and a reader
Full Duplex(FDX)
Half Duplex(HDX)
Transponder Reader
HDX
FDX
• < 30MHz• Load modulation • Simple circuitry• Harmonic Procedure
Similar to the modulated
cross-section procedure in
radar technology
• Sub-harmonic Procedure
Sequential System(SEQ)
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• Down link : data transfer from the reader to the transponder
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Power supply to passive transponders
Reader
Transponder
Magnetic field H
Rectification
DC Power Generation
weak transformer-type coupling
Resonance Capacitor
Resonance
Capacitor
135 kHz Typical 100-1000 windings
13.56MHz Typical 3-10 windings
trimming cap. to compensate for resonance frequency manufacturing tolerances
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Different designs of inductively coupled transponders. The photo shows half finished transponders, i.e. transponders before injection into a plastic housing (reproduced by permission of AmaTech GmbH & Co. KG, D-Pfronten)
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Reader for inductively coupled transponder in the frequency range <135 kHz
with integral antenna (reproduced by permission of easy-key System, micron, Halbergmoos)
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: transponderreader
Load modulation
Binary Code Signal, subcarrier freq. (fs)
TransponderMagnetic field H
signal Modulation
product by load modulation with
subcarrierGeneration of load modulation in the transponder by switching the drain-source resistance of an FET on the chip.
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Example : circuit-load modulation with subcarrier
13.56MHz
Subcarrier(212 kHz)
/64Divider
NAND
Full-wave
Rectifier
SW w.r.t output of IC3a
Q : TP 가 Reader 기로 너무 가까이 가면 ?
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Example : Subharmonic Procedure
128 kHz
64 kHz
Subcarrier (64 kHz)
128 kHz
Basic circuit of a transponder with subharmonic back frequency
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Long-range systemsRFID systems in which the gap between reader and transponder is greater than 1m
UHF frequencies :868 MHz (Europe), 915MHz (USA)908.5~914MHz (Korea)
Microwave frequencies :2.5GHz, 5.8GHz
Short Wavelength
ANT size & Efficiency
Q : RFID 의 인식거리를 넓히고자 한다 . 사용 주파수와 인식거리와의 관계는 ?
Free space path loss
Free space path loss aF at different frequencies and distances.
the transponder’s antenna gain : 1.64 (dipole),
the reader’s antenna gain : 1 (isotropic)
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antenna
Lithium batteries
Active transponder for the frequency range 2.45 GHz.
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reflection cross-sectionThe efficiency with which an object reflects electromagnetic waves.
Operating principle of a backscatter transponder.
The impedance of the chip is ‘modulated’ by switching the chip’s FET
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2 Full and Half Duplex Procedure
ranges between 0.1 cm and a maximum of 1 cm. Close coupling systems
Close coupling transponder in an insertion reader with magnetic coupling coils
• frequency range : 1-10MHz• Efficiency : Very good
The mechanical and electrical parameters of contactless close coupling chip cards standard, ISO 10536
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Magnetic Coupling
Capacitive Coupling
Load Modulation in close coupling systems
Plate capacitors are constructed from coupling surfaces isolated from one another.
Capacitive coupling in close coupling systems
ElectricalField E
Reader’s coupling surface
Transponder’s coupling surface
: transponderreader
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Capacitive coupling
An electrically coupled system
1m 의 거리에서 전극 크기 a×b=4.5cm×7cm
( 스마트 카드에 대응하는 형태 ) 를 갖는 트랜스폰더 읽기를 위해 필요한 전극 전압 (f=125kHz)
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2 Full and Half Duplex Procedure
Equivalent circuit diagram of an electrically coupled RFID system
3.2.5 Data Transfer : Reader Transponder
• ASK: amplitude shift keying• FSK: frequency shift keying• PSK: phase shift keying
Because of the simplicity of demodulation, the majority of systems use ASK modulation.
: transponderreader
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