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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
3::: ETRI, The Future Wave ::: EME Research Team
IT R&D Global Leader
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
2007 Int. Workshop on Biological Effects of EMF
European Standards
4::: ETRI, The Future Wave ::: EME Research Team
IT R&D Global Leader
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
2007 Int. Workshop on Biological Effects of EMF
FCC regulations
5::: ETRI, The Future Wave ::: EME Research Team
IT R&D Global Leader
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
2007 Int. Workshop on Biological Effects of EMF
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
6::: ETRI, The Future Wave ::: EME Research Team
IT R&D Global Leader
Structure and Performance of RFID Antenna
2007 Int. Workshop on Biological Effects of EMF
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
7::: ETRI, The Future Wave ::: EME Research Team
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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
2007 Int. Workshop on Biological Effects of EMF
RFID reader
NARDA SRM-3000:
Isotropic measurement with tri-axial probe
E-field probe
Measurement position
::: ETRI, The Future Wave ::: EME Research Team
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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
8
::: ETRI, The Future Wave ::: EME Research Team
IT R&D Global Leader
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
9
::: ETRI, The Future Wave ::: EME Research Team
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)
::: ETRI, The Future Wave ::: EME Research Team
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SAR hotspot appears near the middle of the left-half plane
SAR measurement of RFID reader
SAR distribution and peak location
d=0 cm
11
d=5 cm
d=10 cm d=15 cm
::: ETRI, The Future Wave ::: EME Research Team
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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
12
d=25 cm
d=30 cm d=50 cm
::: ETRI, The Future Wave ::: EME Research Team
IT R&D Global LeaderSAR measurement of RFID reader
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
13
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)
::: ETRI, The Future Wave ::: EME Research Team
IT R&D Global LeaderSAR measurement of RFID reader
14
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
::: ETRI, The Future Wave ::: EME Research Team
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Conclusions
15
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