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Jin-Kyu Byun and Dong-Uk Shim

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Jin-Kyu Byun and Dong-Uk Shim

  1. 1. 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.
  2. 2. Electromagnetic Fields from RFID (EAS) Systems <ul><li>Increasing deployment of RFID/EAS systems in everyday life </li></ul><ul><li>Public concerns about possible health issues by EMF </li></ul><ul><li>Increase in other wireless applications and services (WiBro, DMB, W-LAN) </li></ul>2007 Int. Workshop on Biological Effects of EMF <ul><li>Need to monitor and assess EMF emissions from RFID arises </li></ul><ul><li>Standard for evaluation of human exposure to EMF from EAS and RFID </li></ul>
  3. 3. Standards and Regulations <ul><li>EN 50357: Basic Standard for EAS and RFID systems </li></ul><ul><ul><li>EC recommendation 1999/519/EC: general public exposure evaluation is not mandatory (after installation) </li></ul></ul><ul><li>EN 50364: Product standard for EAS and RFID systems </li></ul><ul><ul><li>Spatial averaging </li></ul></ul><ul><ul><li>Measurement and analysis to show compliance with reference level and basic restrictions </li></ul></ul><ul><li>IEC 62369-1 (CDV) : Evaluation of exposure to EMF from EAS and RFID systems </li></ul><ul><ul><li>Draft is based on EN standards, will replace EN standards when completed </li></ul></ul>2007 Int. Workshop on Biological Effects of EMF <ul><li>European Standards </li></ul>
  4. 4. Standards and Regulations <ul><li>902-928 MHz band: </li></ul><ul><ul><li>Power limitation : 1 W (6dBi Gain, 4 W EIRP) </li></ul></ul><ul><li>433.5-434.5 MHz band: </li></ul><ul><ul><li>For container identification at ports and harbors </li></ul></ul><ul><ul><li>High power (50 W) is allowed : occupational exposure </li></ul></ul><ul><li>13.56 MHz : </li></ul><ul><ul><li>Field strength limitation: 10,000 uV/m at 30 m (EMC consideration) </li></ul></ul><ul><li>According to FCC, it is manufacturer’s responsibility to ensure RFID system is compliant with FCC regulations </li></ul><ul><ul><li>However, if installed system does not comply with FCC regulations, the system cannot be used and should be modified </li></ul></ul>2007 Int. Workshop on Biological Effects of EMF <ul><li>FCC regulations </li></ul>
  5. 5. Assessment of EMF from RFID Reader <ul><li>Numerical modeling of RFID reader antenna for FDTD calculation: </li></ul><ul><ul><li>FDTD simulation for reactive near field region </li></ul></ul><ul><ul><li>Calculation of gain and radiation pattern </li></ul></ul>2007 Int. Workshop on Biological Effects of EMF <ul><li>Antenna modeling for FDTD calculation </li></ul><ul><li>Measurements to show compliance with reference levels: </li></ul><ul><ul><li>If measured values exceed reference levels, SAR measurement should be made </li></ul></ul><ul><li>Field measurement around RFID reader </li></ul><ul><li>Using flat phantom and tissue-equivalent liquid </li></ul><ul><ul><li>Measurement at different distances from phantom </li></ul></ul><ul><li>SAR measurement using flat phantom </li></ul>
  6. 6. Structure and Performance of RFID Antenna 2007 Int. Workshop on Biological Effects of EMF <ul><li>Wilkinson Power divider and quarter wavelength path difference to get circular polarization </li></ul><ul><li>Antenna Gain : 6.34 dBi </li></ul><ul><ul><li>Radiation pattern shows -3dB beam width of about 60 o </li></ul></ul><ul><li>Patch antenna with 2 patches perpendicular to each other </li></ul>
  7. 7. <ul><li>For all directions (360 o ) around RFID reader with 15 o between radial lines </li></ul><ul><ul><li>Measurement at 0.3, 0.5, 1, and 1.5 meter at each radial lines </li></ul></ul><ul><ul><li>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 </li></ul></ul>Field measurement around RFID reader <ul><li>SAMSYS MP9320 UHF long-range reader: </li></ul><ul><ul><li>910-914 MHz frequency range </li></ul></ul><ul><ul><li>RF power : 1 W </li></ul></ul><ul><ul><li>Antenna Gain : 6±5 dBi </li></ul></ul>2007 Int. Workshop on Biological Effects of EMF <ul><li>RFID reader </li></ul><ul><li>NARDA SRM-3000: </li></ul><ul><ul><li>Isotropic measurement with tri-axial probe </li></ul></ul><ul><li>E-field probe </li></ul><ul><li>Measurement position </li></ul>
  8. 8. RFID E-Field Measurement Result Measurement of E-field from RFID reader in Anechoic Chamber Measured E-field around RFID reader <ul><li>Measured field distribution does not exactly coincide with calculated antenna pattern, because measurements are not made in far-field region </li></ul>
  9. 9. RFID E-field Measurement Result Measured E-field along main beam direction <ul><li>As distance is increased, E-field approaches 1/r dependence </li></ul>
  10. 10. SAR measurement of RFID reader SAR measurement setup <ul><li>Reader: RFID KIS-KIT 1000U </li></ul><ul><li>910~914 MHz, 1 W power, 6 dBi, reading distance=3 m </li></ul>Flat Phantom Reader Module Power Module Reader Antenna Distance ( d )
  11. 11. SAR measurement of RFID reader <ul><ul><li>SAR hotspot appears near the middle of the left-half plane </li></ul></ul>SAR distribution and peak location <ul><li>d =0 cm </li></ul><ul><li>d =5 cm </li></ul><ul><li>d =10 cm </li></ul><ul><li>d =15 cm </li></ul>
  12. 12. SAR measurement of RFID reader <ul><ul><li>When d >20 cm, peak location is irregular and there is little difference between max and min SAR value </li></ul></ul>SAR distribution and peak location <ul><li>d =20 cm </li></ul><ul><li>d =25 cm </li></ul><ul><li>d =30 cm </li></ul><ul><li>d =50 cm </li></ul>
  13. 13. SAR measurement of RFID reader Plot of 1 g peak SAR and 10 g peak SAR <ul><li>Each measurement was repeated 3 times, and min and max values were discarded </li></ul><ul><li>Flat phantom dimension: 80 cm  50 cm  21 cm, shell thickness= 6 mm </li></ul>Distance d (cm) adjacent (0)
  14. 14. SAR measurement of RFID reader <ul><li>From d =10 cm, the SAR values decrease dramatically, and when d >20 cm, the measurements are not meaningful considering probe characteristics </li></ul><ul><li>Distance between RFID reader protective case and antenna should be noted (about 1 cm) </li></ul><ul><li>Maximum local SAR: 1.25 W/kg (1g, adjacent) </li></ul><ul><li>Measurement uncertainty: ±10% </li></ul><ul><li>SAR measurement results </li></ul>
  15. 15. Conclusions <ul><li>Numerical analysis of RFID antenna and E-field measurement show most power is contained within main beam of the antenna (60 o width) </li></ul><ul><li>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 </li></ul><ul><li>EMF distribution around UHF RFID reader </li></ul><ul><li>Various exposure situations with multiple RFID readers should be studied </li></ul><ul><li>Devices that emit multiple frequencies </li></ul><ul><li>Simultaneous exposure with other wireless services/devices </li></ul><ul><li>Further study </li></ul>

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