CALC-002

Does ICNIRP's averaging reduce the design figure?

Feeds CLM-0009. This is the step that decides QST-001, so it is the one most in need of challenge.

The question. ICNIRP Table 5 reference levels are "averaged over 30 min and the whole body". An averaged limit can be met by a source whose instantaneous or local peak is far higher. Does that apply here?

Time averaging. The limit averages over 30 minutes. A power satellite beams continuously under normal operation, so over any 30-minute window the time-averaged incident power density equals the instantaneous value. No reduction.

Spatial averaging. The limit averages over the whole body, so a reduction requires the incident power density to vary substantially across a human body.

Rectenna major axis:     13 km    = 1.3e4 m
Human body height scale:            ~1.8 m

Ratio:                   1.3e4 / 1.8 = ~7.2e3

The illuminated region is roughly four orders of magnitude larger than a body. A beam profile that varies smoothly over kilometres is effectively uniform over 1.8 m, so the whole-body spatial average equals the local value. No meaningful reduction.

Result: the averaging conditions do not reduce the design figure. The comparison between the 230-245 W/m2 design peak and the 10 W/m2 reference level is therefore valid at the beam centre.

Where this fails, stated plainly. Two assumptions carry it, and neither is sourced:

1. The beam is continuous. If it were pulsed or duty-cycled, the 30-minute average would fall in proportion to the duty cycle. None of the five documents reviewed states a duty cycle. 2. The profile varies over kilometres, not metres. If the design used fine spatial structure - an interference pattern with metre-scale nulls, say - the whole-body average could be well below the peak. Nothing reviewed suggests this, but nothing rules it out either.

Both assumptions must be tested against a source before this calculation supports anything public. A verifier should attack these two points first.

Cite this