Measurement of RF Power-Absorption in Biological Specimens (10 to 100 MHz)
Frank M. Greene · 1977
A method measures RF power absorbed by biological specimens by comparing forward and reflected power on the feed line to the NBS Near-Field Synthesizer operating at 10 to 100 MHz.
Plain English Summary
The exact measurement point on the feed line is not critical, and measurements can be made at full operating power without interrupting exposure tests. In an example with 100 watts forward power and 11.1 watts reflected power, the specimen absorbed 44.4 watts, which is half the load power. The absorbed power can never exceed half the forward power, reaching this maximum when reflected power is 25 percent of forward power.
Why This Matters
The synthesizer operates inside a doubly-shielded copper room with at least 60 dB shielding efficiency, making radiation losses negligible. Before testing, each field generator is tuned to present a 50-ohm load with zero reflected power, then retuned for minimum reflected power after the specimen is inserted. The method does not require the RF sources to be matched to their feed lines because only the ratio of reflected to forward power matters. Measurement sensitivity increases with absorbed power and can be improved by starting with an input impedance higher than 50 ohms.
Finding
The method has the advantage that the exact measuring point on the feed line is not critical, as it is with methods employing direct impedance measurements, and that the required measurements can be made without interfering with the exposure tests.
In their words
“The method has the advantage that the exact measuring point on the feed line is not critical, as it is with methods employing direct impedance measurements, and that the required measurements can be made without interfering with the exposure tests.”
Exposure Information
Specific exposure levels were not quantified in this study.
Show BibTeX
@article{measurement_of_rf_power_absorption_in_biological_specimens_10_to_100_mhz__g4030,
author = {Frank M. Greene},
title = {Measurement of RF Power-Absorption in Biological Specimens (10 to 100 MHz)},
year = {1977},
}