Value chain · CLM-1133
In plain terms
The exposure limits the paper cites at this frequency are 10 watts per square metre for the public, 50 for workers and 100 on military sites. Their pulsed test averaged below those everywhere except right beside the dish's feed; but had the 100 kW run continuously, the 100 W/m2 zone would have skimmed within three metres of the ground for nearly four kilometres, which is why the receiver itself has to be big enough to catch the beam, and why aircraft overhead are a separate question.
The claim as recorded
NRL 2022 states that "Time-averaged RF power density levels at 10 GHz are restricted by international agreement" to "10 W/m2 for the general public, 50 W/m2 for occupational exposure, and 100 W/m2 for military workplaces", citing ICNIRP 2020, IEEE C95.1-2019 and IEEE C95.1-2345-2014; that the pulsed Blossom Point transmitter's "time-average radiated power only reaches these levels of concern in the immediate vicinity of the reflector's feed"; and, for a simulation "assuming a continuous 100 kW source and no rectenna blockage" at 0.1 degree tilt, scaled from the measured pulsed waveform at 1046 m, that "the boundary of the 100 W/m2" "exposure zone is within 3 m altitude (relative to the elevation at the transmitter) for distances within 3.7 km of the source", so that "adequately sizing the rectenna to block this field at ground level would thus be important for minimizing RF exposure concerns further down range", with "significant field strength at altitudes > 40 m" where aircraft exposure is handled by "estimated duration of aircraft exposure during flight, as for the HUSIR system".
Evidence behind this: T2 for the simulated exposure map (scaled from a measured pulsed waveform, continuous power assumed); the three limit values are the standards' and are T1 in those instruments, cited here through SRC-270 only.
Scope and limits
A SIMULATION FOR A SOURCE THAT DID NOT RUN CONTINUOUSLY, WITH THE RECTENNA REMOVED; no measured exposure figure exists in the paper ("dosimet" and "SAR" absent), and only the 100 W/m2 boundary is described in words, the 10 and 50 W/m2 zones being crop readings. X-band terrestrial grazing geometry over 6.5 km; the numbers do not transfer to a 2.45 or 5.8 GHz beam from orbit, which arrives from above and has no down-range zone of this shape. IEEE C95.1-2345-2014 is not held and is cited here only as SRC-270 cites it.
What it assumes
"International agreement" is the authors' description of ICNIRP plus two IEEE standards; the register's own readings of ICNIRP 2020 (CLM-0008) give the same 10 and 50 W/m2.
Where it comes from
PDF 6 / printed 33: time-averaged RF power density levels at 10 GHz are, the paper says, restricted by international agreement (its [24] to [26]) "to 10 W/m2 for the general public, 50 W/m2 for occupational exposure, and 100 W/m2 for military workplaces" (normalised); because of its low duty factor, the paper says, the Blossom Point transmitter's time-average radiated power reaches these levels of concern only in the immediate vicinity of the reflector's feed (R1); Fig. 15 maps these safety limits in the elevation plane assuming continuous transmit power (normalised); "For this simulation, the transmitter tilt angle is 0.1" (normalised) deg; the results are scaled from measured observations of the pulsed waveform at a distance of 1046 m (normalised); "the boundary of the 100 W/m2" (raw) "exposure zone is within 3 m altitude (relative to the elevation at the transmitter) for distances within 3.7 km of the source" (normalised); sizing the rectenna adequately to block this field at ground level would thus, the paper says, be important for minimising RF exposure concerns further down range (R1); "significant field strength at altitudes > 40 m" (R1); where safety concerns are typically addressed, it says, by the estimated duration of aircraft exposure during flight, as for the HUSIR system (its [27]) (R1); Fig. 15 caption "assuming a continuous 100 kW source and no rectenna blockage" (normalised). PDF 13: [24] ICNIRP 2020 guidelines, Health Phys. 118(5) 483-524 (R2); [25] IEEE Std C95.1-2019, Oct. 2019, the IEEE standard for safety levels with respect to human exposure to electric, magnetic and electromagnetic fields, 0 Hz to 300 GHz (normalised); [26] "IEEE Standard for Military Workplaces" (raw), "IEEE Std C95.1-2345-2014, May 2014" (normalised); [27] T. A. Cott, "RF radiation environment over Millstone hill," MIT Lincoln Laboratory Tech. Rep. 1141, Dec. 2019 (normalised). Fig. 15 crop (render readings): colour scale to 1,400 W/m2; upper 100 W/m2 boundary from about 6 m at the transmitter to about 45 m at 6.5 km, 50 W/m2 to about 50 m, 10 W/m2 off the 60 m top of the plot between 4.5 and 6.5 km; lower 100 W/m2 boundary about 2 m out to 1.5 km, about 3 m near 3.7 km, about 8 m at 6.5 km. Recomputed: duty 1 us x 604 Hz = 6.04 x 10^-4; 1,643 W/m2 peak x 6.04 x 10^-4 = 0.99 W/m2 averaged, a tenth of the public limit; continuous, 1,643 W/m2 is 16 times the military and 164 times the public limit.
Basis: W/m2 time-averaged power density at 10 GHz; m of altitude relative to the transmitter; km of distance
Cite this
energyaperture.com/c/clm-1133
CLM-1133, Energy Aperture, as of 2022-01.
Connected records
Other published records linked to this one. A list, not a judgement.
- Also from SRC-270
- CLM-1122About twenty thousand postage-stamp-sized antenna-plus-diode cells, each with an off-the-shelf microwave diode, wired into tiles, then...CLM-1123A five-metre dish and a 100 kW radar-type pulsed tube a kilometre away, bounced partly off the ground on purpose to get more power onto the...CLM-1124One panel the size of a sheet of paper turned about seven-tenths of the microwave power landing on it into DC, and did best at about three...CLM-1125Four square metres of receiver turned 73 per cent of the microwave power arriving at it into 1.65 kW of DC, measured a kilometre from the...CLM-1126They deliberately fried each of the four panels with ever-stronger pulses. A bare panel gave up at 672 watts out; clamping its voltage with...CLM-1127As flown, under two per cent of the microwave power fed to the dish came out of the receiver as electricity, because the beam had to be...CLM-1128A second test used a big radar dish in Massachusetts to light up a strip of LEDs on a tower over a kilometre away, with about a kilowatt...CLM-1129The authors say the 1975 record still stands at twenty times their power, that the custom diodes which set it no longer exist, and that...More on the source page.