Neufeld Esra, Kuster Niels
1Foundation for Research on Information Technologies in Society (IT'IS), Zeughausstrasse 43, 8004 Zurich, Switzerland; 2Swiss Federal Institute of Technology (ETH) Zurich, 8092 Zurich, Switzerland.
Health Phys. 2018 Dec;115(6):705-711. doi: 10.1097/HP.0000000000000930.
Extreme broadband wireless devices operating above 10 GHz may transmit data in bursts of a few milliseconds to seconds. Even though the time- and area-averaged power density values remain within the acceptable safety limits for continuous exposure, these bursts may lead to short temperature spikes in the skin of exposed people. In this paper, a novel analytical approach to pulsed heating is developed and applied to assess the peak-to-average temperature ratio as a function of the pulse fraction α (relative to the averaging time [INCREMENT]T; it corresponds to the inverse of the peak-to-average ratio). This has been analyzed for two different perfusion-related thermal time constants (τ1 = 100 s and 500 s) corresponding to plane-wave and localized exposures. To allow for peak temperatures that considerably exceed the 1 K increase, the CEM43 tissue damage model, with an experimental-data-based damage threshold for human skin of 600 min, is used to allow large temperature oscillations that remain below the level at which tissue damage occurs. To stay consistent with the current safety guidelines, safety factors of 10 for occupational exposure and 50 for the general public were applied. The model assumptions and limitations (e.g., employed thermal and tissue damage models, homogeneous skin, consideration of localized exposure by a modified time constant) are discussed in detail. The results demonstrate that the maximum averaging time, based on the assumption of a thermal time constant of 100 s, is 240 s if the maximum local temperature increase for continuous-wave exposure is limited to 1 K and α ≥ 0.1. For a very low peak-to-average ratio of 100 (α ≥ 0.01), it decreases to only 30 s. The results also show that the peak-to-average ratio of 1,000 tolerated by the International Council on Non-Ionizing Radiation Protection guidelines may lead to permanent tissue damage after even short exposures, highlighting the importance of revisiting existing exposure guidelines.
工作在10吉赫兹以上的超宽带无线设备可能会在几毫秒到几秒的突发中传输数据。尽管时间和面积平均功率密度值在连续暴露的可接受安全限值内，但这些突发可能会导致暴露人群皮肤出现短暂的温度峰值。本文开发了一种新的脉冲加热分析方法，并将其应用于评估峰均温度比与脉冲分数α（相对于平均时间增量T；它对应于峰均比的倒数）的函数关系。针对与平面波和局部暴露相对应的两个不同的灌注相关热时间常数（τ1 = 100秒和500秒）进行了分析。为了考虑大幅超过1K升高的峰值温度，使用了CEM43组织损伤模型，其基于实验数据的人体皮肤损伤阈值为600分钟，以允许在低于组织损伤发生水平的情况下出现大的温度振荡。为了与当前安全指南保持一致，职业暴露的安全系数为10，公众暴露的安全系数为50。详细讨论了模型假设和局限性（例如，所采用的热和组织损伤模型、均匀皮肤、通过修改时间常数考虑局部暴露）。结果表明，如果连续波暴露的最大局部温度升高限制为1K且α≥0.1，基于100秒热时间常数的假设，最大平均时间为240秒。对于非常低的峰均比100（α≥0.01），它仅降至30秒。结果还表明，国际非电离辐射防护委员会指南所允许的1000的峰均比即使在短时间暴露后也可能导致永久性组织损伤，突出了重新审视现有暴露指南的重要性。
