THE MECHANISM OF ABSORPTION OF ULTRAHIGH FREQUENCY ELECTROMAGNETIC ENERGY IN TISSUES, AS RELATED TO THE PROBLEM OF TOLERANCE DOSAGE
Herman P. Schwan, Kam Li · 1955
This 1956 study pioneered the scientific understanding of how human tissues absorb RF energy and safe exposure limits.
Plain English Summary
This 1956 technical report by Friend, Finch, and Schwan investigated how human tissues absorb ultra-high frequency electromagnetic energy and what levels might be considered safe for exposure. The researchers examined the physical mechanisms behind tissue heating from RF energy and worked to establish tolerance dosage guidelines. This represents some of the earliest scientific work on determining safe exposure limits for electromagnetic radiation.
Why This Matters
This 1956 research represents a foundational moment in EMF safety science, when researchers first began systematically studying how our bodies absorb radiofrequency energy. What makes this work particularly significant is its focus on 'tolerance dosage' - essentially asking the critical question of how much RF exposure is too much. The science demonstrates that even nearly 70 years ago, researchers recognized the need to understand tissue absorption mechanisms to protect human health.
The reality is that this early work laid the groundwork for today's specific absorption rate (SAR) limits used to regulate cell phones and other wireless devices. However, modern RF exposures from smartphones, WiFi, and 5G networks are far more complex and ubiquitous than anything these 1950s researchers could have imagined. While their focus on tissue heating mechanisms was scientifically sound, we now understand that biological effects can occur through non-thermal pathways as well.
Figures from the Original Paper
Diagram extracted from the original research document.
Exposure Information
Specific exposure levels were not quantified in this study. Duration: not specified
Study Details
To determine the percentage of airborne radiation absorbed by the human body and where the absorbed energy is transformed into heat, particularly focusing on the effects of frequency, skin thickness, and subcutaneous fat thickness on energy absorption and heat distribution.
A semitheoretical approach was used. From reflection coefficients obtained by exposure of tissue lay...
At low frequencies well below 1000 MHz and at high frequencies well above 3000 MHz, the percentage o...
Conservative estimates of tolerable amounts of energy should be based on possible 100 percent absorption for frequencies between 1000 and 3000 MHz. For frequencies below 1000 MHz, most of the radiant energy is transformed into heat in the deep tissues, making it more dangerous than high frequency radiation. For frequencies above 3000 MHz, predominant surface heating occurs, making it less dangerous. A tolerance dosage of 0.01 Watt/cm2 is recommended for the total frequency range, with higher figures expected for frequencies above 3000 MHz when more is known about heat regulation mechanisms.
Show BibTeX
@article{the_mechanism_of_absorption_of_ultrahigh_frequency_electromagnetic_energy_in_tis_g3873,
author = {Herman P. Schwan and Kam Li},
title = {THE MECHANISM OF ABSORPTION OF ULTRAHIGH FREQUENCY ELECTROMAGNETIC ENERGY IN TISSUES, AS RELATED TO THE PROBLEM OF TOLERANCE DOSAGE},
year = {1955},
}