Discussion on Spatial and Time Averaging Restrictions Within the Electromagnetic Exposure Safety Framework in the Frequency Range Above 6 GHz for Pulsed and Localized Exposures

Abstract

Both the current and newly proposed safety guidelines for local human exposure to millimeter-wave frequencies aim at restricting the maximum local temperature increase in the skin to prevent tissue damage. In this study, we show that the application of the current and proposed limits for pulsed fields can lead to a temperature increase of 10°C for short pulses and frequencies between 6 and 30 GHz. We also show that the proposed averaging area of 4 cm 2 , that is greatly reduced compared with the current limits, does not prevent high-temperature increases in the case of narrow beams. A realistic Gaussian beam profile with a 1 mm radius can result in a temperature increase about 10 times higher than the 0.4°C increase the same averaged power density would produce for a plane wave. In the case of pulsed narrow beams, the values for the time and spatial-averaged power density allowed by the proposed new guidelines could result in extreme temperature increases. Bioelectromagnetics. 2020;41:164-168.

Transient Thermal Responses of Skin to Pulsed Millimeter Waves

“…More complex models e.g. [6,27] provide more detailed information but also introduce more variables that make the models more difficult to validate with independent data.…”

“…While FCC has no explicit limits on fluence of RF pulses, there is an implicit limit due to the combination of the MPE (maximum permissible exposure) and averaging time, which amounts to 18 kJ/m 2 for both occupational and general public exposures. Some authors have argued that these limits are insufficient to prevent excessive heating from RF pulses from wireless devices operating above 10 GHz [5,6]. Many websites have echoed these concerns, and assert that "short temperature spikes in the skin" can be produced by 5G communications technology, some of which transmits in the mm-wave band as well as at lower RF frequencies.…”

Response to Enders’ Comment on “Discussion on Spatial and Time Averaging Restrictions Within the Electromagnetic Exposure Safety Framework in the Frequency Range Above 6 GHz for Pulsed and Localized Exposures”

“…We wish to thank Professor Achim Enders for his comments on our Letter, "Discussion on Spatial and Time Averaging Restrictions Within the Electromagnetic Exposure Safety Framework in the Frequency Range Above 6 GHz for Pulsed and Localized Exposures" [Neufeld, Samaras, and Kuster, 2020]. We acknowledge that the topic of appropriate and inherently consistent safety guidelines for millimeter wave (mm-W) frequencies is important, and we very much appreciate the continued scientific discussion.…”

Comment on “Discussion on Spatial and Time Averaging Restrictions Within the Electromagnetic Exposure Safety Framework in the Frequency Range Above 6 GHz for Pulsed and Localized Exposures” Bioelectromagnetics, 41:164‐168 by Neufeld, Samaras, and Kuster

“…In recent papers on spatial and time averaging schemes relevant for electromagnetic exposure in the range 6 to 300 GHz, which cumulated in the Letter in Bioelectromagnetics [Neufeld et al, 2020], protection guideline proposals from ICNIRP as well as IEEE have been criticized: “In the case of pulsed narrow beams, the values for the time and spatial‐averaged power density allowed by the proposed new guidelines could result in extreme temperature increases.”…”

“…These three criteria clearly define the frame for a guideline's compromise, which of course must be well‐adjusted to the best of our knowledge. From this point of view, the explicit parameter assumptions of Neufeld et al [2020] have to be analyzed, particularly whether they represent relevant exposure scenarios. The comment will now embed this analysis in a more general discussion on practical situations given by technological constraints and parameters.…”