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Determination of Power Absorption in Man Exposed to High Frequency Electromagnetic Fields by Thermographic Measurements on Scale Models

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Arthur W. Guy, Michael D. Webb, Carrol C. Sorensen · 1976

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Human bodies can absorb 5.63 W/kg from 31 MHz radiation at modest field strengths, confirming frequency-dependent absorption patterns.

Plain English Summary

Summary written for general audiences

Researchers used thermographic measurements on scale models to determine how much radiofrequency energy the human body absorbs when exposed to high frequency electromagnetic fields. They found that exposure to 31 MHz radiation at 10 mW/cm² could produce peak absorption rates as high as 5.63 W/kg in humans. The study confirmed that power absorption increases with the square of frequency below 31 MHz.

Why This Matters

This 1976 study represents foundational research in understanding how human bodies absorb electromagnetic energy, establishing measurement techniques still used today. The finding that 31 MHz radiation at relatively modest field strengths can produce absorption rates of 5.63 W/kg is significant because it demonstrates how efficiently the human body can absorb RF energy at certain frequencies. What makes this particularly relevant is that many modern devices operate in frequency ranges where similar absorption patterns occur. The research methodology using scale models and thermographic imaging became a standard approach for SAR (Specific Absorption Rate) measurements that now guide safety limits for wireless devices. The confirmation that absorption increases with frequency squared below 31 MHz helps explain why regulatory agencies pay close attention to frequency-specific exposure limits.

Figures from the Original Paper

Diagrams extracted from the original research document.

diagramPage 2 - Fig. 1: Exposure of phantom scale model of man in a resonant cavity.
p. 2 of the original PDF
diagramPage 3 - Photograph of cavity exposure system (Fig. 3)
p. 3 of the original PDF
chartPage 4 - Figure 5. Electrical conductivity of phantom muscle as a function of NaCl and TX 150 content (measured at 23°C).
p. 4 of the original PDF
diagramPage 6 - AI-described figure: Fig. 6 illustrates thermograms and calculated peak absorbed power density for a scale model man exposed to electric fields at 24.1 MHz.
p. 6 of the original PDF
diagramPage 8 - AI-described figure: Figures showing scale model thermograms and calculated peak absorbed power density for a 70-kg ellipsoid exposed to electromagnetic fields, with various intensity scans and profile scans.
p. 8 of the original PDF
diagramPage 9 - AI-described figure: Figures showing scale model thermograms and measured peak absorbed power densities for a human subject exposed to an electric field.
p. 9 of the original PDF
diagramPage 10 - AI-described figure: Fig. 11 displays scale model thermograms and measured peak absorbed power densities for a 70-kg human model exposed to a magnetic field, showing intensity scans and profile scans at various points.
p. 10 of the original PDF

Exposure Information

Specific exposure levels were not quantified in this study.

Cite This Study
Arthur W. Guy, Michael D. Webb, Carrol C. Sorensen (1976). Determination of Power Absorption in Man Exposed to High Frequency Electromagnetic Fields by Thermographic Measurements on Scale Models.
Show BibTeX
@article{determination_of_power_absorption_in_man_exposed_to_high_frequency_electromagnet_g5071,
  author = {Arthur W. Guy and Michael D. Webb and Carrol C. Sorensen},
  title = {Determination of Power Absorption in Man Exposed to High Frequency Electromagnetic Fields by Thermographic Measurements on Scale Models},
  year = {1976},
  
  
}
No DOI on file for this study.

Quick Questions About This Study

The study found that 31 MHz radiation at 10 mW/cm² field strength could produce peak power absorption densities as high as 5.63 W/kg in the human body using thermographic measurements on scale models.
The research confirmed that electromagnetic power absorption in the human body increases as the square of the frequency for frequencies below 31 MHz, matching theoretical predictions for this frequency range.
Researchers used thermographic measurements on scale models of humans exposed to scaled-up frequencies in a VHF resonant cavity to determine power absorption patterns that would occur in full-scale humans.
Scale models allowed researchers to safely study power absorption patterns by using higher frequencies and field strengths that produced measurable thermal effects, then scaling the results down to predict human exposure effects.
The study used 10 mW/cm² field strength in their VHF resonant cavity system to generate sufficient power absorption for accurate thermographic measurement of the heating patterns in the scale models.