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.
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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
Normal load 400A shielded so no E field outside
5
High Voltage AC Lines
Standards in US limit Fields to 1 to 5kV/m
6
Magnetic fields from Power Lines as a Function of
Distance
7
The Effects of Power Pole Configurations and
Phasing on Magnetic Fields
8
1
9
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
1
13
Variations with time of Day
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Variations in Magnetic Field Exposures Over the
Course of a Day
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Some Current Wave Forms
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The Fourier Spectra of 1.7
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Magnetic Fields Around Appliances
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1
19
Wave Shapes Near Fluorescent Light
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Common Exposures
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Exposures on Electric Trains
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Electric Field Scaling and Induced Currents
23
Induced Electric Fields
24
A More Complete Model
25
1
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Electric and Magnetic Induced Current Densities
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Internally Generated Voltages
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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
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Computer Display Fields
1
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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
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TV and Base Stations
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Exposure Levels
 1. US average about 50µW/m2 to 100µW/m2
 2. We have measure E =1 to 2 V/m in Boulder, peak
power density < 10 mW/m2
 3. Peak Power from transmitter about50 KW
 4. Radar Peak at Megawatts, over the horizon
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Frequencies
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