RFMTC11GÄVLE OCTOBER 4–5th 2011

Impact of Moisture Content on RFID Antenna Performance for Wood-Log Monitoring

Sohil Shahabi Ghahfarokhi, Sathyaveer Prasad, Danial TayariUniversity of Gävle

Sohil.shahabi@gmail.com, prdsar@hig.se, danial.tayari@gmail.com

October 4, 2011

Presentation outline• Traditional wood supply chain

• RFID in wood supply chain

• Challenges of using RFID in wood supply chain

• Effect of moisture content on the dielectric constant of wood

• Parameters for RFID tag performance evaluation

• Antenna design

• Simulation results

• Reader range calculations

• Summary

• Questions

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Traditional Wood Supply Chain

Designated Area

CutterLogged

Area

CollectorsPiles/Stacks

of logTransport

Factory

Stamping

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RFID in Wood Supply Chain

Designated Area

CutterLogged

Area

CollectorsPiles/Stacks

of logTransport

Factory

RFIDRFID

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Challenges of using RFID in wood supply chain

• The whole process should be completed 3-5 weeks.

• Processing time can go up to 15 weeks during winter.

• During these 15 weeks, moisture content may vary due to environmental factors like sun, rain, snow, etc.,

• Hence, it influences the RFID tag and reader performance.

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Effect of Moisture Content on the Dielectric Constant of Wood• Moisture content of wood: the weight of water expressed as a

fraction ,usually a percentage, of the weight of oven dry wood.

• Dielectric constant

• Loss tangent

Ref: G.I. Torgovnikov, Dielectric properties of wood and wood based material., Springer series in wood

science, Berlin Springer-Vlg cop, 1993.

 

Moisture content Dielectric constant Loss tangent

5% 1.8 0.08

10% 2.1 0.11

20% 3.2 0.17

30% 4.5 0.20

40% 5.3 0.19

80% 8.8 0.15

120% 12.3 0.11

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Ref: Choo, J.; Ryoo, J.; Hong, J.; , "Novel RFID tag antenna with stability to material," Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE , vol., no., pp.1-4, 5-11 July 2008.

Parameters for RFID tag performance evaluation

• RFID Antenna Parameters – Return Loss

– Directivity

– Radiation Efficiency

• RFID performance is evaluated by computing the maximum reader range

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Max. reading range [Ref] defined using Friis transmission formula:

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Antenna Design• Designed in HFSS• Folded Dipole• Polyamide Casing• Operating Frequency: 867 MHZ• Dielectric Constant of wood: 3.2

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Simulation Results

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Return loss of designed antenna at different dielectric constants

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Simulation ResultsRadiation efficiency vs. Directivity at different dielectric constants

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Reader Range Calculation

Reader Parameters (XCODEEIU9050)

Antenna Parameters (From Simulation Results)

Return Loss (ηreader)= -10 dB Radiation efficiency(Effreader)= 0.8 Directivity (Dreader) = 0 dBiTransmitted Power (Pt )=29.5dBmPolarization efficiency = 1

Return Loss (ηtag)Radiation Efficiency (Efftag)Directivity (Dtag)

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Max. reading range defined using Friis transmission formula:

Reader Range Calculations

εr Loss tangent

Moisture Content

ηtag

(dB)

Dtag Efftag Max. Range

(m)

%change

2.1 0.11 10% -3.7 2.23 30% 1.8 10%

3.2 0.17 20% -5.9 2.36 27% 2 -

4.5 0.2 30% -5 2.5 22% 1.78 11%

5.3 0.19 40% -4.6 2.56 22% 1.76 12%

8.8 0.15 80% -3.2 2.19 27% 1.61 20%

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A= Reader range for desired dielectric constant

B= Reader range for εr =3.2

Summary

• Increase of moisture content decreases the resonating frequency and increases the return loss of the RFID antenna. Hence the maximum reader range decreases up to 20%.

• Variation of maximum reader range may increase the overall cost of the wood supply chain and also reduces the reliability.

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Questions

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