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Power Deposition in a Spherical Model of Man Exposed to 1-20-MHz Electromagnetic Fields

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James C. Lin, Arthur W. Guy, Curtis C. Johnson · 1973

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1973 theoretical study found extremely low power absorption from 1-20 MHz fields, suggesting thermal safety levels could exceed microwave standards.

Plain English Summary

Summary written for general audiences

This 1973 theoretical study used spherical models to calculate how much radiofrequency energy the human body absorbs when exposed to electromagnetic fields between 1-20 MHz. The researchers found that at these frequencies, power absorption is extremely low - less than 2.5×10⁻³ milliwatts per gram of body tissue per milliwatt of incident radiation. The study suggested that thermal safety levels for HF frequencies could be much higher than the 10 mW/cm² recommended for microwaves.

Why This Matters

This foundational research from 1973 established early theoretical models for understanding how the human body absorbs radiofrequency energy, particularly in the HF band that includes AM radio and some industrial heating applications. What makes this study significant is its demonstration that magnetic field measurements are crucial for assessing exposure risks at these frequencies - a principle that remains relevant today as we evaluate EMF exposure from various sources. The finding that power absorption at 1-20 MHz is orders of magnitude lower than microwave frequencies helped shape early safety standards, though we now understand that biological effects aren't solely determined by thermal heating. The reality is that this theoretical modeling work laid important groundwork for EMF dosimetry, but modern research has revealed non-thermal biological mechanisms that weren't considered in these early thermal-based safety assessments.

Exposure Information

Specific exposure levels were not quantified in this study.

Cite This Study
James C. Lin, Arthur W. Guy, Curtis C. Johnson (1973). Power Deposition in a Spherical Model of Man Exposed to 1-20-MHz Electromagnetic Fields.
Show BibTeX
@article{power_deposition_in_a_spherical_model_of_man_exposed_to_1_20_mhz_electromagnetic_g6413,
  author = {James C. Lin and Arthur W. Guy and Curtis C. Johnson},
  title = {Power Deposition in a Spherical Model of Man Exposed to 1-20-MHz Electromagnetic Fields},
  year = {1973},
  
  
}

Quick Questions About This Study

The study examined electromagnetic fields between 1-20 MHz, which includes the HF (high frequency) band used for AM radio broadcasting and some industrial applications. This frequency range is much lower than cell phone frequencies.
According to the theoretical calculations, a 70-kg person absorbs less than 2.5×10⁻³ milliwatts per gram of body tissue for each milliwatt per square centimeter of incident 20 MHz radiation - an extremely small amount.
The study showed that for field impedances less than 120π Ω, magnetically induced energy absorption predominates over electric field effects. This means H-field measurements are essential for accurately estimating HF exposure hazards.
The spherical model calculations suggested that thermal safe-exposure levels for the HF band (1-20 MHz) could be many orders of magnitude higher than the 10 mW/cm² level recommended for microwaves.
Researchers used spherical models of the human body and described induced electric fields inside the model using a combination of quasi-static electric and magnetic induction solutions for both plane wave and near-field exposures.