Around UHF RFID Reader

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27 Νοε 2013 (πριν από 3 χρόνια και 8 μήνες)

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Jin
-
Kyu Byun and Dong
-
Uk Shim

EME Research Team

Electronics and Telecommunications Research Institute

Analysis of EMF Distribution

Around UHF RFID Reader

2007. 9. 6.


::: ETRI, The Future Wave :::

EME Research Team

IT R&D Global Leader

1

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

::: ETRI, The Future Wave :::

EME Research Team

IT R&D Global Leader

2

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

::: ETRI, The Future Wave :::

EME Research Team

IT R&D Global Leader

3

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

::: ETRI, The Future Wave :::

EME Research Team

IT R&D Global Leader

4

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

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EME Research Team

IT R&D Global Leader

5

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 60
o





Patch antenna with 2 patches perpendicular to each other

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EME Research Team

IT R&D Global Leader

6


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

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

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EME Research Team

IT R&D Global Leader

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
)
Electric Field (dB uV/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

7

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EME Research Team

IT R&D Global Leader

0.0
0.5
1.0
1.5
0
10
20
30
40
50
60
70
Electric Field (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

8

::: ETRI, The Future Wave :::

EME Research Team

IT R&D Global Leader

SAR measurement of RFID reader

SAR measurement setup


Reader: RFID KIS
-
KIT 1000U


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

9

Flat

Phantom

Reader

Module

Power

Module

Reader Antenna

Distance (
d
)

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EME Research Team

IT R&D Global Leader



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

SAR measurement of RFID reader

SAR distribution and peak location


d
=0 cm

10


d
=5 cm


d
=10 cm


d
=15 cm

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EME Research Team

IT R&D Global Leader



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

11


d
=25 cm


d
=30 cm


d
=50 cm

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EME Research Team

IT R&D Global Leader

SAR 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

12

1.251
0.12
0.116
0.064
0.05
0.042
0.939
0.277
0.730
0.556
0.174
0.084
0.080
0.057
0.029
0.019
0.000
0.200
0.400
0.600
0.800
1.000
1.200
밀착
5
10
15
20
25
30
50
시험

거리

d
(cm)
SAR(W/kg)
1g SAR
10g SAR
Distance
d

(cm)

adjacent (0)

::: ETRI, The Future Wave :::

EME Research Team

IT R&D Global Leader

SAR measurement of RFID reader

13


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

IT R&D Global Leader

Conclusions

14


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

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