Tag Antenna Design for Passive UHF RFID System

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RFI In The Name Of God DTag Antenna Design for Passive UHF RFID System Click to edit Master subtitle style Presentor: H. Razaghian5/6/12

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What is RFID?

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Radio-Frequency Identification (RFID) A technology for communication via radio waves between a reader and a tag attached to an object for the two purpose: Identification Click to edit Tracking Master subtitle style

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History of RFID

Roots of RFID technology traced back to world war II. The Germans discovered that if pilots rolled their planes as returned to base, change the radio signal reflected back.

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Under Watson-Watt, the British developed the first active identify friend subtitle style Click to edit Master or foe(IFF) system.

Harry Stockman published a paper Communications by Means of Reflected Power in October 1948.

Considerable advances in microelectronics, embedded software, and RF integrated circuits 5/6/12 44

Components of the RFID System

RFID Reader(Transceiver)

-Can read and write data to tag

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RFID Tag(Transponder)

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Located on the object

-Contains the information of the identified Click to edit Master subtitle style -Distributes the information between other data processing system.

Data Processing Subsystem

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Simple Block Diagram of an RFID System

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RFID Reader

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The reader sometimes called an interrogator or scanner sends and receives RF data to and from tag via antenna.Click contain: The reader to edit Master subtitle style RF transceiver module (transmitter and receiver) signal processor and controller unit coupling element (antenna) serial data interface to a host system.

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Reader AnatomyDigital Signal Processor (DSP)

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Network Processor


Power Supply

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915MHz Radio

13.56MHz Radio 88

Types of Readers

Readers can be at a fixed point - Assembly line - Store entrance - Shipping

Fixed such as Reader

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Assembly line

ReadersClick to also be mobile/handheld can edit Master subtitle style

Material (Records boxes loaded and identify boxes Tracking as they are removed)5/6/12 Handheld Wireless Reader 99

Shipping Bill of Portal Lading

Some Examples of RFID Reader

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RFID Tag

The tag acts as a programmable data-carrying device Components of tag 1) Coupling element(antenna) 2) low-power CMOS IC

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Tag Block Diagram

RFI DControl Logic (Finite State machine) Memory Cells

Antenn a

Power Supply Tx Modulator


Rx Demodulato r

Tag Integrated Circuit (IC)5/6/12

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Types of Tags1.

Active tag, which has a battery that supplies power to all functions.

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Semipassive tag, which has a battery used only to power the tag IC, and not for communication. Passive tag, which has no battery on it.Click to edit Master subtitle style

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The absence of a power supply makes: - much cheaper - more smaller than active tags

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RFID Tag Memory

Read-only tags - Tag ID is assigned at the factory during manufacturing 1) can never be changed 2) No additional data can be assigned to the tag Write once, read many (WORM) tags - Data written once, e.g., during packing or manufacturing Click to edit Master subtitle style 1) tag is locked once data is written 2) similar to a compact disc or DVD Read/Write - Tag data can be changed over time 1) Part or all of the data section can be locked5/6/12

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Performance of system

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Performance of system

Reader transmits a modulated RF signal to the Tag

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The application specific integrated circuit (ASIC) chip receives power from antenna

Chip responds by varying its input impedance and thus modulate the backscattered signal

Chip impedance switches between two states: - matched to the antenna (chip collects power in this state) - strongly mismatched


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Operational Frequencies

Low frequency (LF) (125-134KHz)

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High frequency (HF) (13.56MHz) -they are based on magnetic flux coupling among the reader,s and tag,s coils

Ultra-high frequency (UHF) (860-960MHz)Click to edit Master subtitle style

Microwave frequency (2.45GHz and 5.8GHz) -they are based on electromagnetic interaction among the reader,s and tag,s antenna

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Types of Power Transfer from Reader to the Tag

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Magnetic induction (near-field RFID) Electromagnetic (EM) wave capture (far-field RFID)

These two designs take advantage of the EM properties associatedsubtitle style RF antenna, the Click to edit Master with an Near-field and the Far-field.

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Near-field Power/Communication Mechanism for RFID

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Near-field RFID

Basis of near-field coupling between a reader and , tag is:

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Faraday s principle of magnetic induction

Using Induction for power coupling from reader to tag

modulation.

Click to edit in near-field Technique used Master subtitle styleRFID is Load

The range for magnetic induction approximates to: C/2f where C is speed of light and f is the frequency.5/6/12

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Far-field Power/Communication Mechanism for RFID

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Far-field RFID

Basis of far-field coupling between a reader and tag is:

Electromagnetic (EM) wave propagation

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Using EM wave capture for power transfer from reader to tag

scattering.

Technique used Master subtitle style Click to edit in far-field RFID is Back

Tags that use far-field principles operate at greater than 100MHz typically in UHF and Microwave bands.5/6/12

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Antenna for Passive Tag

Antenna determines the performance of a tag

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A suitable RFID tag antenna must have the following characteristics:

1) Be small enough and have very high efficiency Click to edit Master subtitle style 2) Be very cheap 3) Normally, have matching polarization with reader antenna 4) Must provide good impedance matching

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Antenna Passive Tag Design

The most important tag performance characteristic is read rang Read range : maximum distance which reader can detect the backscattered signal ,s tag Friis free-space formula

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PtGt (Under R P hypothesis of 4 Gr = t polarization 4Ra h 0 matching) Rc 2 Zc 5/6/12 2424 = 1

Impedance Matching

Circuit Model of a RFID Tag

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Click to edit Master subtitle style Adding an external matching network with lumped elements is prohibitive in tags due to cost and fabrication issues. Antenna must be directly matched to the ASIC

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Qualitative behavior of antenna impedance, chip impedance, and read range as function of frequency

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1)T match

Methods for Conjugate Impedance Matching

RFI D2Zt(1+ )2ZA 2Zt + (1+)2ZA

Zi n =Equivalent circuit Click to edit is connected antenna source Master subtitle styleto

a second dipole of

length al the parameters a,b and w can be adjusted to match the Zchip

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2) Inductively coupled loop


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Equivalent Click coupled small style Inductively to edit Master subtitle loop circuit

(2fM Zin ZLoo )2 Z = p+ A Rin(f0) = (2f0M)2/RA(f0)

proximity to the radiating body 2f0Lloop The strength of the coupling and added reactance, controlled by d and shape of the loop

placed at = close a Xin(f0)

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3) Meandering


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Useful for tag fabricated with dipoles Useful for size reduction

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Types of Antenna with Impedance Matching

Meandering and T-match

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Tmatch Click to edit Master subtitle style

Meandering and 5/6/12 inductively

Meandering with

Meanderi ng

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RFID Advantages over Barcode

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No line of sight required for reading Each tag can carry a lot of data (read/write) UPC(Barcodes) require optical reader to read whereasClick to edit Master subtitle style radio waves RFID reader reads via Passive tags have a virtually unlimited lifetime Active tags can be read from great distances

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RFI [1] RFID Journal, The History of RFID D TechnologyReferences[2] R. Want, An Introduction to RFID Technology , Pervasive Computing, IEEE Journals, vol. 5, pp. 25-33, Feb. 2006. Click to edit Master subtitle style [3] K. V. S. Rao, Pavel V. Nikitin, S. F. Lam, Impedance Matching Concepts in RFID Transponder Design, Fourth IEEE Workshop on Automatic Identification Advanced Technologies, AutoID05, pp.39-42, 2005 5/6/12 3232

http://www.rfidjournal.com/article/articleview

RFI DIs the Question?Click to edit Master subtitle style

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RFI DThank you for your attentionClick to edit Master subtitle style

Hamed Razaghian

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Tag Antenna Design for Passive UHF RFID System