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.

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Atmospheric Sources1. 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.

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Natural EM Power Density at the Earths Surface

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B Field for Underwater Cable

4Normal load 400A shielded so no E field outside

High Voltage AC Lines

5Standards in US limit Fields to 1 to 5kV/m

Magnetic fields from Power Lines as a Function of Distance

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The Effects of Power Pole Configurations and Phasing on Magnetic Fields

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Fourier Spectrum of A Current Wave Form

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Typical Magnetic Field Exposure LevelsAt Home

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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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Some Typical Magnetic and Electric Field Strengths vs. Distance

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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

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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 Security920MHz , B = 10µT and Deactivate at 50-60Hz

500µT2. 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 Fields1

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RF Sources2. 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 Levels1. US average about 50µW/m2 to 100µW/m2

2. We have measure E =1 to 2 V/m in Boulder, peak 10 mW

3. Peak Power from transmitter about50 KW4. Radar Peak at Megawatts, over the

horizon

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Frequencies

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