Jin-Kyu Byun and Dong-Uk Shim

Jin-Kyu Byun and Dong-Uk ShimEME Research Team

Electronics and Telecommunications Research Institute

Analysis of EMF DistributionAround UHF RFID Reader

2007. 9. 6.

2::: ETRI, The Future Wave ::: EME Research Team

IT R&D Global Leader

Electromagnetic Fields from RFID (EAS) Systems

Increasing deployment of RFID/EAS systems in everyday life

Public concerns about possible health issues by EMF

Increase in other wireless applications and services (WiBro, DMB, W-LAN)

2007 Int. Workshop on Biological Effects of EMF

Need to monitor and assess EMF emissions from RFID arises

Standard for evaluation of human exposure to EMF from EAS and RFID



Standards and Regulations

EN 50357: Basic Standard for EAS and RFID systems

EC recommendation 1999/519/EC: general public exposure evaluation is not mandatory (after installation)

EN 50364: Product standard for EAS and RFID systems

Spatial averaging

Measurement and analysis to show compliance with reference level and basic restrictions

IEC 62369-1 (CDV) : Evaluation of exposure to EMF from EAS and RFID systems

Draft is based on EN standards, will replace EN standards when completed


European Standards



Standards and Regulations

902-928 MHz band:

Power limitation : 1 W (6dBi Gain, 4 W EIRP)

433.5-434.5 MHz band:

For container identification at ports and harbors

High power (50 W) is allowed : occupational exposure

13.56 MHz :

Field strength limitation: 10,000 uV/m at 30 m (EMC consideration)

According to FCC, it is manufacturer’s responsibility to ensure RFID system is compliant with FCC regulations

However, if installed system does not comply with FCC regulations, the system cannot be used and should be modified


FCC regulations



Assessment of EMF from RFID Reader

Numerical modeling of RFID reader antenna for FDTD calculation:

FDTD simulation for reactive near field region

Calculation of gain and radiation pattern


Antenna modeling for FDTD calculation

Measurements to show compliance with reference levels:

If measured values exceed reference levels, SAR measurement should be made

Field measurement around RFID reader

Using flat phantom and tissue-equivalent liquid

Measurement at different distances from phantom

SAR measurement using flat phantom



Structure and Performance of RFID Antenna


Wilkinson Power divider and quarter wavelength path difference to get circular polarization

Antenna Gain : 6.34 dBi

Radiation pattern shows -3dB beam width of about 60o

Patch antenna with 2 patches perpendicular to each other



For all directions (360o) around RFID reader with 15o between radial lines

Measurement at 0.3, 0.5, 1, and 1.5 meter at each radial lines

For main beam direction (right in front of antenna), additional measurements are made from 0.1~1.5 m with 0.1 m separation between measuring points

Field measurement around RFID reader

SAMSYS MP9320 UHF long-range reader:

910-914 MHz frequency range

RF power : 1 W

Antenna Gain : 6±5 dBi


RFID reader

NARDA SRM-3000:

Isotropic measurement with tri-axial probe

E-field probe

Measurement position

::: ETRI, The Future Wave ::: EME Research Team


120

130

140

0

30

60

90

120

150

180

210

240

270

300

330

120

130

140

30 cm 50 cm 1 m 1.5 m

Angle (o)

Ele

ctr

ic F

ield

(d

B u

V/m

)

RFID E-Field Measurement Result

Measurement of E-field from RFID reader in Anechoic Chamber

Measured E-field around RFID reader

Measured field distribution does not exactly coincide with calculated antenna pattern, because measurements are not made in far-field region

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0.0 0.5 1.0 1.50

10

20

30

40

50

60

70E

lect

ric

Fie

ld (

V/m

)

Distance (m)

0.12

RFID E-field Measurement Result

Measured E-field along main beam direction

As distance is increased, E-field approaches 1/r dependence

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IT R&D Global LeaderSAR measurement of RFID reader

SAR measurement setup

Reader: RFID KIS-KIT 1000U

910~914 MHz, 1 W power, 6 dBi, reading distance=3 m

10

FlatPhantom

ReaderModule

PowerModule

Reader Antenna

Distance (d)



SAR hotspot appears near the middle of the left-half plane

SAR measurement of RFID reader

SAR distribution and peak location

d=0 cm

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d=5 cm

d=10 cm d=15 cm



When d>20 cm, peak location is irregular and there is little difference between max and min SAR value

SAR measurement of RFID reader

SAR distribution and peak location

d=20 cm

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d=25 cm

d=30 cm d=50 cm



Plot of 1 g peak SAR and 10 g peak SAR

Each measurement was repeated 3 times, and min and max values were discarded

Flat phantom dimension: 80 cm × 50 cm × 21 cm, shell thickness= 6 mm

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1.251

0.12 0.1160.064 0.05 0.042

0.939

0.277

0.730

0.556

0.174

0.084 0.080 0.057 0.029 0.0190.000

0.200

0.400

0.600

0.800

1.000

1.200

밀착 5 10 15 20 25 30 50

시험 거리 d (cm)

SA

R(W

/kg)

1g SAR

10g SAR

Distance d (cm)

adjacent (0)



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From d=10 cm, the SAR values decrease dramatically, and when d>20 cm, the measurements are not meaningful considering probe characteristics

Distance between RFID reader protective case and antenna should be noted (about 1 cm)

Maximum local SAR: 1.25 W/kg (1g, adjacent)

Measurement uncertainty: ±10%

SAR measurement results



Conclusions

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Numerical analysis of RFID antenna and E-field measurement show most power is contained within main beam of the antenna (60o width)

SAR measurement using flat phantom show even when RFID reader is in contact with flat phantom shell, the peak local SAR (1 g) does not exceed 1.6 W/kg

EMF distribution around UHF RFID reader

Various exposure situations with multiple RFID readers should be studied

Devices that emit multiple frequencies

Simultaneous exposure with other wireless services/devices

Further study

Jin-Kyu Byun and Dong-Uk Shim

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