Lecture 3 Assignment 1. In addition to reading through Chapter 1 and starting chapter 2 read one paper on the exposures that you get from a low frequency source and write up a one page summary. Also you should start looking for papers on a topic you want to follow up on. 2. Be prepared to talk about what you have read for about 5 minutes in class on Wednesday. 3. People we do not get to on Wednesday will be asked to talk on Friday. 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. 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. 3

Natural EM Power Density at the Earths Surface 4

B Field for Underwater Cable 5 Normal load 400A shielded so no E field outside

High Voltage AC Lines 6 Standards in US limit Fields to 1 to 5kV/m

Magnetic fields from Power Lines as a Function of Distance 7

The Effects of Power Pole Configurations and Phasing on Magnetic Fields 8

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Some Typical Magnetic and Electric Field Strengths vs. Distance 10

Fourier Spectrum of A Current Wave Form 11

Typical Magnetic Field Exposure Levels At Home 12

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Variations with time of Day 14

Variations in Magnetic Field Exposures Over the Course of a Day 15

Some Current Wave Forms 16

The Fourier Spectra of

Magnetic Fields Around Appliances 18

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Wave Shapes Near Fluorescent Light 20

Common Exposures 21

Exposures on Electric Trains 22

Electric Field Scaling and Induced Currents 23

Induced Electric Fields 24

A More Complete Model 25

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Electric and Magnetic Induced Current Densities 27

Internally Generated Voltages 28

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 29

Computer Display Fields 1 30

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 31

TV and Base Stations 32

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 power density < 10 mW/m 2 3. Peak Power from transmitter about50 KW 4. Radar Peak at Megawatts, over the horizon 33

Frequencies 34