## 4 Other Comment  
An extensive body of literature now exists on human exposure to 5G signals using both numerical modeling and onsite measurements [11, 12, 13, 14] as well as modeling studies of thermal responses of tissue to RF-EMF exposure at 5G NR high-band and MMW frequencies. [PERSON] and [PERSON] provide a broad critique of ICNIRP guidelines based on a selective reading of selected references. However, their critique is superficial and misleading in several respects. The authors included a quotation from [15] on the possibility of \"intense surface heating and a steep, rapid rise in temperature\" from pulsed MMWs but did not note that the original authors had made an orders-of-magnitude error in estimating the near-surface heating of tissue from such exposures [16]. This speculation is irrelevant to 5G NR in any event. As another example, [PERSON] and [PERSON] assert that skin modeling studies \"treat the skin as homogeneous dermal tissue\" to justify what they consider limitations in the ICNIRP exposure guidelines. That is not true at all. Thermal modeling studies have used models ranging from simple homogeneous tissue models, to multilayer models of skin and subcutaneous tissues [17], to high-resolution-image-based models of the body [18]. For an extensive review of this literature, see [19]. In their review, [PERSON] et al. [20] concluded that \"...TPD [transmitted power density into skin, the dosimetric quantity used in ICNIRP local exposure guidelines above 6 GHz] provides an excellent estimate of skin temperature elevation through the millimeter-wave band (30-300 GHz) and a reasonable and conservative estimate down to 10 GHz, whereas the SAR [specific absorption rate, in W/kg] is a good metric below 3 GHz\". Many open research issues remain, for example those related to the experimental (as opposed to numerical modeling) assessment of absorbed power in the body from near-field exposures above 6 GHz, which are intended to improve compliance assessment and may possibly lead to refinement of the ICNIRP guidelines for local-body exposures themselves [21]. A more informed and complete review than [PERSON] and [PERSON] provide is needed to help readers understand the current state of knowledge and unresolved questions about these important but complicated issues. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**5G Band** & \begin{tabular}{c} **Uplink** \\ **Frequencies** \\ **(GHz)** \\ \end{tabular} & \begin{tabular}{c} **Downlink** \\ **Frequencies** \\ **(GHz)** \\ \end{tabular} & \begin{tabular}{c} **Channel** \\ **Bandwidths** \\ **(MHz) * \\ \end{tabular} & \
\begin{tabular}{c} **Power** \\ **Penetration Depth L in** \\ **Skin/Muscle, cm (at the** \\ **Center of the Band), cm** \\ \end{tabular} &
\begin{tabular}{c} **\(\Delta\)L in** \\ **Widest Band** \\ **Center of the Band), cm** \\ \end{tabular} \\ \hline N5 & 0.824–0.849 & 0.869–0.894 & 5–25 & 2.1 & 9 mm \\  & & & & (muscle) \\ N66 & 1.710–1.780 & 2.100–2.200 & 5–45 & 1.5 & 0.3 mm \\  & & & & (muscle) \\ N2 & 1.850–1.910 & 1.930–1.990 & 5–40 & 1.4 & 0.2 mm \\ n258 & & 24.25–27.50 & 50–400 & 0.05 (skin) & 0.01 mm \\ \hline \hline \end{tabular}  
* * Uplink: from handset to base station; downlink from base station to handset. Channel bandwidth varies with implementation. Frequency bands as used in the U.S.; a more extensive tabulation can be found at [[https://en.wikipedia.org/wiki/5G_NR_frequency_bands](https://en.wikipedia.org/wiki/5G_NR_frequency_bands)]([https://en.wikipedia.org/wiki/5G_NR_frequency_bands](https://en.wikipedia.org/wiki/5G_NR_frequency_bands)) (accessed on 18 May 2022). The power penetration depth L is the distance at which power density is reduced by a factor of 1/e below that at the surface. For tissue, these values were calculated from data by [PERSON] et al. [10].  
\end{table} 
Table 1: Frequency bands and channel bandwidths used by 5G NR systems. **Author Contributions:** Conceptualization and writing--review and editing--were equally shared by both authors.