Jin-Kyu Byun and Dong-Uk Shim EME Research Team

1. Analysis of EMF Distribution Around UHF RFID Reader Jin-Kyu Byun and Dong-Uk Shim EME Research Team Electronics and Telecommunications Research Institute 2007. 9. 6.

2. 2007 Int. Workshop on Biological Effects of EMF 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) • Need to monitor and assess EMF emissions from RFID arises • Standard for evaluation of human exposure to EMF from EAS and RFID

3. 2007 Int. Workshop on Biological Effects of EMF Standards and Regulations • European Standards • 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

4. 2007 Int. Workshop on Biological Effects of EMF Standards and Regulations • FCC 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

5. 2007 Int. Workshop on Biological Effects of EMF Assessment of EMF from RFID Reader • Antenna modeling for FDTD calculation • Numerical modeling of RFID reader antenna for FDTD calculation: • FDTD simulation for reactive near field region • Calculation of gain and radiation pattern • Field measurement around RFID reader • Measurements to show compliance with reference levels: • If measured values exceed reference levels, SAR measurement should be made • SAR measurement using flat phantom • Using flat phantom and tissue-equivalent liquid • Measurement at different distances from phantom

6. 2007 Int. Workshop on Biological Effects of EMF Structure and Performance of RFID Antenna • Patch antenna with 2 patches perpendicular to each other • 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

7. 2007 Int. Workshop on Biological Effects of EMF Field measurement around RFID reader • RFID reader • SAMSYS MP9320 UHF long-range reader: • 910-914 MHz frequency range • RF power : 1 W • Antenna Gain : 6±5 dBi • E-field probe • NARDA SRM-3000: • Isotropic measurement with tri-axial probe • Measurement position • 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

8. 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

9. RFID E-field Measurement Result Measured E-field along main beam direction • As distance is increased, E-field approaches 1/r dependence 8

10. SAR measurement of RFID reader SAR measurement setup Flat Phantom Distance (d) Reader Antenna Reader Module Power Module • Reader: RFID KIS-KIT 1000U • 910~914 MHz, 1 W power, 6 dBi, reading distance=3 m 9

11. SAR measurement of RFID reader SAR distribution and peak location • d=0 cm • d=5 cm • d=10 cm • d=15 cm • SAR hotspot appears near the middle of the left-half plane 10

12. SAR measurement of RFID reader SAR distribution and peak location • d=20 cm • d=25 cm • d=30 cm • d=50 cm • When d>20 cm, peak location is irregular and there is little difference between max and min SAR value 11

13. SAR measurement of RFID reader Plot of 1 g peak SAR and 10 g peak SAR adjacent (0) Distance d (cm) • 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

14. SAR measurement of RFID reader • SAR measurement results • 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% 13

15. Conclusions • EMF distribution around UHF RFID reader • 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 • Further study • Various exposure situations with multiple RFID readers should be studied • Devices that emit multiple frequencies • Simultaneous exposure with other wireless services/devices 14