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Lecture 3 Assignment

This assignment includes reading on electromagnetic exposures from low frequency sources and summarizing a chosen topic. Explore environmental and occupational electromagnetic fields, field sizes, natural sources, and exposure standards. Dive into types of fields, power and magnetic density, measurements for bio-effects, and common transmitters. Learn about RF and microwave sources, diathermy devices, and associated exposure levels. Enhance understanding of induced currents, power emissions, and safety standards in various frequency ranges.

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Lecture 3 Assignment

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  1. Lecture 3 Assignment • 1. In addition to reading through Chapter 1 , 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 and write a one page summary of it. • 2. This is due Wednesday

  2. Bioelectromagnetics ECEN 5341/4341 Lecture 3-4 • 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.

  3. Atmospheric Sources • 1. Static and ELF (0 to 3khz) • 2. Earth’s Static Magnetic Fields range from 24μT to 65μT with variation up to about 1μT with the Northern Lights over several minutes • 3. Electric fields Static 100 to 300V/m with the earth negative. Up to 100kV/m in thunderstorms.

  4. Natural EM Power Density at the Earths Surface

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

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

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

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

  9. 1

  10. Some Typical Magnetic and Electric Field Strengths vs. Distance (Error 1mG=0.1µT)

  11. Fourier Spectrum of A Current Wave Form

  12. Typical Magnetic Field Exposure LevelsAt Home

  13. 1

  14. Variations with time of Day

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

  16. Some Current Wave Forms

  17. The Fourier Spectra of Figure 1.7

  18. Magnetic Fields Around Appliances

  19. 1

  20. Wave Shapes Near Fluorescent Light

  21. Common Exposures

  22. Exposures on Electric Trains

  23. Electric Field Scaling and Induced Currents

  24. Induced Electric Fields

  25. A More Complete Model

  26. 1

  27. Electric and Magnetic Induced Current Densities

  28. Internally Generated Voltages

  29. 1

  30. IF and RF Exposure Measurements • Intermediate Frequencies, IF 3kHz 10MHz • Radio Frequencies, RF, 10MHz 300GHz • These are approximate frequency ranges and overlap. • Bio-effects standards below 10MHz are set on nerve stimulation . Above 10MHz they are set on the basis of heating and temperature rise of ½ oC • As the temperature rise depends on the shape of the biological material, the conductivity, the dielectric constant, the incident power density, frequency and time we go to other measurements that are related but easier to measure.

  31. Measureable Quantities • Power density , PD, S in watts/m2 • Electric Fields in V/m • Specific Absorption Rate SAR • Magnetic field H in A/m • Magnetic Flux Density B in Tesla/m2 • In general the power emitted from a source decreases as 1/rn at large distances from the source. In the far field n=2 or for r >>λ and free space.

  32. Some Common Transmitters.

  33. 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

  34. Computer Display Fields • 1

  35. 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, WiFi

  36. RF and MicrowaveSources • 1 Microwave oven leakage 20 V/m (at an average distance of 20 cm) (Mantiply et al., 1997; Plets et al., 2016) • 2 Dielectric Heaters 27 MHz, average E-field levels around 400 V/m and maximum values up to 2,000 V/m (Hitchcock and Patterson, 1995). Magnetic fields of approximately 1 A/m are also present around the sealer. • 3. Plastic heaters Typical frequencies used by these devices range from 4 to 50 MHz. Mean exposure levels range from 30 to 300 V/m for electric fields and 0.1 to 0.7 A/m for magnetic fields (Joyner and Bangay, 1986; Stuchly et al., 1980)

  37. RF and Microwave Sources • Induction heaters use eddy currents to heat metals or semiconductors by generating a strong alternating magnetic field inside a coil. Frequencies in the RF range can reach 27 MHz although lower frequency units (50 Hz) are also commonly used, which produce stronger magnetic fields with deeper penetration. Magnetic field mean exposure levels associated with RF units are about 0.6 A/m at the operator position, where mean electric field levels are about 50 V/m. Lower frequency units can lead to higher exposure levels around the operator, with magnetic field mean exposures about 5 A/m and electric field mean levels about 300 V/m (Allen et al., 1994; Cooper, 2002; Floderus et al., 2002; Mantiply et al., 1997)

  38. Diathermy Devices • The most common technologies used are continuous or pulsed shortwave (13.56 or 27.12 MHz) and microwave (915 MHz or 2.45 GHz) diathermy. Average electric field levels at about one meter from the source are approximately 60 V/m for pulsed shortwave devices and 300 V/m for continuous shortwave systems. Average magnetic field levels are about 0.20 and 0.70 A/m, respectably. However, maximum exposure levels can reach up to 5,000 V/m for electric fields and 10 A/m for magnetic fields (Allen et al., 1994; Mantiply et al., 1997; Martin et al., 1990; Mild, 1980; Shah and Farrow, 2013; Stuchly et al., 1982).

  39. Cell Phone • 1. Base station transmitting antennas are formed of vertical arrays of collinear dipoles phased to give a narrow beam width (typically between 7 and 10 degrees). • 2. Mean electric fields of an operator can range from around 0.5 V/m, while working on the ground near the mast, to around 13 V/m, while working on the mast (Cleveland et al., 1995; Cooper et al., 2004) Mean electric field strength values are around 500 V/m near the antenna, although maximum levels up to 1,000 V/m are possible (Bernhardt and Matthes, 1992; Mantiply et al., 1997). Mean magnetic field strength levels are around 0.2 A/m, but maximum levels can reach up to 1 A/m (Vermeeren et al., 2015).

  40. RF Environments • The majority of measurements tend to be below 1 V/m and only around 0.1% are above 20 V/m. The strictest reference level established by this legislation for environmental (residential) exposure is 28 V/m, which corresponds with the limit set for the 10-400 MHz frequency, typically associated with FM radio and VHF TV broadcasting.

  41. TV and Base Stations

  42. 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

  43. Frequencies

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