1. Bioelectromagnetics ECEN 5341/4341 Lecture 3 1. Environmental and Occupationally Encountered Electromagnetic Fields 2. The objective is to get a feel for the size of both the natural fields we are exposed to and the size of the fields that we are now exposed to resulting from the wide spread use of electricity. 1

2. Atmospheric Sources 1. Direct Current and ELF (0 to 3khz) 2. Earths DC Magnetic Fields 24μT to 65μT variation up to about 1μT with the Northern Lights over several minutes 3. Electric fields DC 100 to 300V/m with the earth negative. Up to 100kV/m in thunderstorms. 2

3. Natural EM Power Density at the Earths Surface 3

4. B Field for Underwater Cable 4 Normal load 400A shielded so no E field outside

5. High Voltage AC Lines 5 Standards in US limit Fields to 1 to 5kV/m

6. Magnetic fields from Power Lines as a Function of Distance 6

7. The Effects of Power Pole Configurations and Phasing on Magnetic Fields 7

8. Fourier Spectrum of A Current Wave Form 8

9. Typical Magnetic Field Exposure Levels At Home 9

10. Variations in Magnetic Field Exposures Over the Course of a Day 10

11. Some Current Wave Forms 11

12. The Fourier Spectra of 1.7 12

13. Magnetic Fields Around Appliances 13

14. Some Typical Magnetic and Electric Field Strengths vs. Distance 14

15. Wave Shapes Near Fluorescent Light 15

16. Common Exposures 16

17. Exposures on Electric Trains 17

18. Electric Field Scaling and Induced Currents 18

19. Electric and Magnetic Induced Current Densities 19

20. Internally Generated Voltages 20

21. Sources of Intermediate and Radio Frequency Fields 1. Scanners, Libraries, Airport Security 920MHz, B = 10µT and Deactivate at 50-60Hz 500µT 2. Video Display Terminals, VDT, Cathode Ray Tubes CRT Up to 20KV inside the Tube, ≈10V/m at 0.5m 21

22. Computer Display Fields 1 22

23. RF Sources 2. RF heaters for sealing plastic etc. 3. RF Transmission Short Wave 2 -27MHz 3-20V/m at 10’s of meters. 4. Radio TV 5. Base Stations and Cell Phones 23

24. TV and Base Stations 24

25. Exposure Levels 1. US average about 50µW/m 2 to 100µW/m 2 2. We have measure E =1 to 2 V/m in Boulder, peak 10 mW 3. Peak Power from transmitter about50 KW 4. Radar Peak at Megawatts, over the horizon 25

26. Frequencies 26