Antenna Positioning Analysis and

Dual-Frequency Antenna Design of High Frequency Ratio for

Advanced Electronic Code Responding Labels

Kin Seong LeongAuto-ID Laboratory, School of Electrical and Electronic

Engineering, The University of Adelaide.

2

Something about Myself

• Bachelor in Engineering (Electrical and Electronic) (2003)

• Research Assistant (2004)

• Ph.D. in Engineering (2005 – 2007)

3

Research Supervisors

• Prof. Peter H. Cole (Supervisor)

• Prof. Bevan D. Bates (Co-Supervisor)

• Dr. Samuel P. Mickan (Previous Co-Supervisor)

4

Special Notes

• Research carried out during the candidature period.

• Technical depth adjusted to fit in the allocated time.

• All discussion welcome after this presentation.

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Organisation of Presentation

• Research Background

• Antenna Positioning Analysis

• RFID Tag Antenna Design

• Dual-frequency RFID Tag Antenna Design

• Conclusion and Future Work.

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Background of Research

• Radio Frequency Identification (RFID)– Enable supply chain automation.– Pallet level tagging.

• Item level tagging– Each and every item has its own tag with

unique ID.– Tag is usually passive.

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Background of RFID

• A simple RFID system:

8

Frequency Bands in RFID

• LF (<135 kHz)

• HF (13.56 MHz)

• UHF (860 – 960 MHz)

• Microwave (2.45 GHz)

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Areas of Interest

• Areas of interest:– Antenna design for Item level tagging.– EMC regulation.– RFID system deployment.

• Engineering discipline (IEEE):– Antennas and Propagation– Electromagnetic Compatibility– Microwave Theory and Techniques

Antenna Positioning Analysis

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Challenges

• Dense reader environment.

• Reader collision problem.

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Modeling

• Simple path loss

• More complex model

• MATLAB simulator

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Simulation

• Input: – Position of antenna(s)– Elevation of antenna(s)– Radiation pattern – Transmitted power– Solution space

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Simulation

• Output:6dBi

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Multi-Channel Simulation

• Antennas operating certain channels away from channel of interest.

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Experiments

• Determine n:

• Locations:

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Contributions

Simulation Software

Second Carrier Sensing

Development of Reader Synchronisation

Sources of Error in Simulation

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Sources of Simulation ErrorSources of Simulation Error

Simulation Model

Reflection, Refraction, and Diffraction

Radiation Pattern of Antenna

Simulation Result Interpretation and Analysis

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Reader Synchronisation

• European EN 302 208– “Listen Before Talk” Provision.

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Listen Before Talk (LBT)

• ETSI EN 302 208– 865 to 868 MHz– 200 kHz channels– 2W ERP – only 10 channels– LBT

• Listen for 5 ms– Various thresholds

– 2W ERP, threshold is -96 dBm

• Use sub-band for 4s

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Listen Before Talk (LBT)

• Limited deployment of reader antenna.

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Reader Synchronisation

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Fine-tuning Methods

• Reducing the overall time for talking. • Reducing the power output. • Use of external sensors.• The use of RF opaque or RF absorbing

materials• Dynamic Channel Assignments

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Sub-band 2

Sub-band 4

Sub-band 6

Sub-band 8

Sub-band 10

Case Study

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Case Study

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R F A b s o r b i n g M a t e r i a l s

2 8 4 1 0 6 2 8 4 1 0 6 2 8

Case Study

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C h a n n e l

8 2 6 1 0 4 8 2 6 1 0 4 8 2 C h a n n e l

2 8 4 1 0 6 2 8 4 1 0 6 2 8

Case Study

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Second Carrier Sensing

• RFID Tags– Passive– Low Cost

• “Confused” when more than one reader attempts to interrogate.

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Second Carrier Sensing

Reader ready to transmit

First Carrier Sensing

Choose a channel

Channel Occupied?

Random wait

Yes No

Second Carrier Sensing

Lower than

Threshold?

YesNo

Reader Transmits

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Second Carrier Sensing

• Investigate suitable threshold values for common antenna positions:

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Half Way Review

• First part: Antenna Positioning Analysis– Development of Simulation Software– Investigation on

• Sources of simulation errors

• RFID Regulations• RFID Deployment• Reader Synchronisation• Threshold of Second Carrier Sensing

Design of RFID Tag Antenna

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Design Steps

• HF tag:– 13.56MHz– Inductive coil to resonate with chip input

capacitance at 13.56 MHz.

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Design Steps

• UHF Tag:– Within 860 – 960 MHz.– Impedance match with chip impedance.

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Design Steps

• Simulation– Ansoft High Frequency Structure Simulator

(HFSS)• 3D Full-wave Electromagnetic Field Simulation

• Finite Element Method (FEM)

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Design Steps

• HFSS Scripting

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Design Steps

• Prototyping– HFSS export: dxf format– ISO-Pro milling software

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Design Steps

• Measurement– Impedance measurement

• Use of BALUN• Direct measurement

• Cable shielding

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Design Steps

• Tag Fabrication– Antenna combined with RFID chip.

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Design Steps

• Deployment

HF Tag Antenna Design

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An RFID Tag for Pig

• A circular tag with holes in middle.

• Encapsulated in plastic casing.

• Attached to the ears of pigs.

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HF Pig Tag

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HF Pig Tag

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HF Wine Closure Tag

UHF Tag Antenna Design

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Joint Research

• UHF RFID tag antenna design.– Beer Keg Tag Antenna– Wine Closure Tag Antenna– Animal Tag Antenna

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UHF Beer Keg Tag

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UHF Wine Closure Tag

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UHF Animal Tag

Design of Dual-Frequency RFID Tag Antenna

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Frequency Bands in RFID

• LF (<135 kHz)

• HF (13.56 MHz)

• UHF (860 – 960 MHz)

• Microwave (2.45 GHz)

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HF vs UHF

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Proposal Formulation

Merge HF and UHF

Dual Frequency Antenna

(With frequency ratio ≈ 70)

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Current Technology

• Microstrip patch antenna– Too low frequency ratio (< 5).

• Common aperture antenna– Dual feed point

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Brain Storming

• 3 Methodologies:– Making a HF antenna operates in UHF.– Making an UHF antenna operates in HF.– Merging a HF antenna and an UHF

antenna.

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Design Aim (1)

• Antenna impedance equals to the complement of the input impedance of the RFID chip at UHF operation– Design frequency: 960 MHz– Chip impedance: 17 - j150Ω – Design aim: 17 + j150Ω

• A resonance point at HF.– Parallel resonance.– Zero reactance and infinite resistance.

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Design Aim (2)

• A single feed antenna.– Avoid modification on existing chip

• Reasonable antenna size and cost.

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Merging

• Merging a HF antenna and an UHF antenna.

• Idea:– A HF multi-turn coil antenna.– A UHF planar dipole.– A transmission line to separate both the

above antennas.

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A Simple HF RFID Antenna

• A multi-turn planar spiral antenna.

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A Simple UHF RFID Antenna

• A dipole with matching network.– RFID chip is usually capacitive. The matching

network is to transform the antenna into inductive to enable conjugate matching.

Final Design

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Chip

Final Design (1)

• Transmission line to transfer the HF coil antenna impedance to very high value (ideally open circuit).

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Final Design (2)

• Overlapping loops to provide high capacitance.

Chip

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Final Design (3)

• A gap to prevent the UHF antenna shorting the HF antenna. A patch on the bottom provides path for UHF operation.

Chip

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Final Design (4)

• DC path for rectifier circuit (some type as specified by IC designer).

Chip

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Simulation

• Using Ansoft HFSS

• Simulated impedance (at 960 MHz):– 24 + j143Ω– Very near to the target of 17 + j150Ω

• Resonance near 13.56 MHz

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Fabrication

• On double-sided FR4

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Measurement Setup

SMA Connector(At the chip location)

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HF Testing

• Transmission measurement: Resonance at HF.

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UHF Testing (1)

• Impedance measurement: Matching impedance with respect to RFID chip.

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UHF Testing (2)

• At 960 MHz:– 50 + j135Ω

• Balance to unbalance problem– BALUN needed.

• Pattern in good agreement

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Miniaturisation

• Similar idea.

• Key characteristics retained:

• Merge a HF and a UHF antennas.

• Transmission line to separate both antennas.

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Final Design

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New Features (1)

• Relocation of UHF dipole.• Inside the HF coil.

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New Features (2)

• Miniaturisation of HF coil.• The new HF coil is reduced from 98 mm

by 65 mm to 81 mm by 58 mm, gap is 0.5 mm and track width is 1 mm.

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New Features (3)

• Miniaturisation of UHF dipole• To fit in the smaller HF coil antenna.

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New Features (4)

• HF not affecting UHF over a broader bandwidth.• The HF antenna is not exactly a short

circuit for the entire band of UHF.

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New Features (4)

• HF not affecting UHF over a broader bandwidth.• Uses high characteristic impedance

coplanar strips (CPS).

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New Features (4)

• HF not affecting UHF over a broader bandwidth.

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New Features (5)

• The coupling effect between UHF and HF antenna.• The coupling between antennas

becomes more serious.

• Fine-tuning required.

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New Features (6)

• Structure optimised• HF coil tilted.

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Testing

• HF: Maximum read range.

• UHF: Up to 2m.

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UHF in HF

• HF chip requires high inductance which is not possibly provided by a small UHF antenna.

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HF in UHF

• HF antenna resonates at HF and impedance match at UHF.

• Problem: Extremely lossy.– Peak directivity of 3.5. (Simulation)– Peak gain of only 0.0004. (Simulation)

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Alternative Methods

• Stacking HF and UHF coil antenna.

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Review

• Second part:Design of dual-frequency tag antenna– Design of HF and UHF tag antennas.– Investigation on measuring technique.– Design of dual-frequency tag antennas.

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Possible Research Extension

• Dual-frequency RFID protocol.

• Dual-frequency chip design.

Conclusion

90

Acknowledgement

• My supervisors (Prof. Peter H. Cole, Prof. Bevan D. Bates, Dr. Samuel P. Mickan)

• Mun Leng Ng

• Geoff, Rob and Pavel.

Questions?