Value chain · CLM-1348
In plain terms
People feel microwave warmth only at fairly high strengths: tens of milliwatts per square centimetre for a second or so on the forehead, and less if more of the body is exposed. Pain needs tens of times more. So feeling nothing does not mean a person is below the limit.
The claim as recorded
The 1972 Proceedings of the IEEE review tabulates human thresholds for sensing microwave heat. On a 37 cm2 area of the forehead, warmth was felt within 1 s at 58.6 mW/cm2 at 3 GHz and 21.0 mW/cm2 at 10 GHz, and within 4 s at 33.5 and 12.6 mW/cm2. If the whole face were exposed, the warmth threshold at 10 GHz was estimated at 4-6 mW/cm2 within 5 s. At 3 GHz on 9.5 cm2 of forearm, the pain threshold ranged from 3.1 W/cm2 for 20 s to 830 mW/cm2 for exposures over 3 minutes, and was 560 mW/cm2 for 3 minutes on 53 cm2. In a separate test, a forehead at 74 mW/cm2 of 3 GHz took 15 to 73 s to notice warmth. The review suggests that skin perception may give a warning before injurious exposure.
Evidence behind this: T2, a peer-reviewed review compiling cited human sensation experiments. The thresholds are other laboratories' measurements, which the review reports.
Scope and limits
The frequencies are 3 and 10 GHz, not the 2.45 or 5.8 GHz of power-beam designs, and no scaling law is given. The areas are small patches, not whole-body exposure. The whole-face figure is an estimate that assumes uniform skin sensitivity, and the review notes that it may be somewhat low. Our comparison, not the paper's: the 1978 reference beam centre of 23 mW/cm2 (230 W/m2, register value) is just above the 1 s forehead warmth threshold at 10 GHz and below the 3 GHz value. The 1 mW/cm2 rectenna edge is below all thresholds listed, so a person there would get no warning by sensation. The review's view that perception is a protection factor is its own. Its own warmth-threshold figures show that sensation comes only at or above the 10 mW/cm2 limit of the time, except for the whole-face estimate.
What it assumes
No assumptions are recorded against this claim.
Where it comes from
PDF p.25 / printed 411, Table XII (render): 3000 MHz 58.6, 46.0, 33.5 mW/cm2 and 10,000 MHz 21.0, 16.7, 12.6 mW/cm2 at 1, 2 and 4 s, over 37 cm2 of forehead; 74 mW/cm2 at 3000 MHz, reaction time "varied between 15 and 73 s". PDF p.26 / printed 412: whole-face threshold at 10,000 MHz "would be 4-6 mW/cm2 within 5 s"; pain "ranges from 830 mW/cm2 for exposures longer than 3 min to 3.1 W/cm2 for a 20-s exposure period"; 560 mW/cm2 for a 3-min exposure on 53 cm2; perception "may provide a protection factor" (paraphrase outside the quotes).
Basis: mW/cm2 incident at 3 GHz and 10 GHz; exposure seconds; exposed skin area cm2
Related records
- Answers question
- QST-001 not published in this release
Cite this
energyaperture.com/c/clm-1348
CLM-1348, Energy Aperture, as of 1972-04.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-705
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