Two international guidelines/standards for human protection from electromagnetic fields define the specific absorption rate (SAR) averaged over 10 g of tissue as a metric for protection against localized radio frequency field exposure due to portable devices operating below 3–10 GHz. Temperature elevation is suggested to be a dominant effect for exposure at frequencies higher than 100 kHz. No previous studies have evaluated temperature elevation in the human head for local exposure considering thermoregulation. This study aims to discuss the temperature elevation in a human head model considering vasodilation, to discuss the conservativeness of the current limit. This study computes the temperature elevations in an anatomical human head model exposed to radiation from a dipole antenna and truncated plane waves at 300 MHz–10GHz. The SARs in the human model are first computed using a finite-difference time-domain method. The temperature elevation is calculated by solving the bioheat transfer equation by considering the thermoregulation that simulates the vasodilation. The maximum temperature elevation in the brain appeared around its periphery. At exposures with higher intensity, the temperature elevation became larger and reached around 40 °C at the peak SAR of 100 W/kg, and became lower at higher frequencies. The temperature elevation in the brain at the current limit of 10 W/kg is at most 0.93 °C. The effect of vasodilation became notable for tissue temperature elevations higher than 1–2 °C and for an SAR of 10 W/kg. The temperature at the periphery was below the basal brain temperature (37 °C). The temperature elevation under the current guideline for occupational exposure is within the ranges of brain temperature variability for environmental changes in daily life. The effect of vasodilation is significant, especially at higher frequencies where skin temperature elevation is dominant.

This study analyzed the spread and decay durations of the COVID-19 pandemic in different prefectures of Japan. During the pandemic, affordable healthcare was widely available in Japan and the medical system did not suffer a collapse, making accurate comparisons between prefectures possible. For the 16 prefectures included in this study that had daily maximum confirmed cases exceeding ten, the number of daily confirmed cases follow bell-shape or log-normal distribution in most prefectures. A good correlation was observed between the spread and decay durations. However, some exceptions were observed in areas where travelers returned from foreign countries, which were defined as the origins of infection clusters. Excluding these prefectures, the population density was shown to be a major factor, affecting the spread and decay patterns, with R² = 0.39 (p < 0.05) and 0.42 (p < 0.05), respectively, approximately corresponding to social distancing. The maximum absolute humidity was found to affect the decay duration normalized by the population density (R² > 0.36, p < 0.05). Our findings indicate that the estimated pandemic spread duration, based on the multivariate analysis of maximum absolute humidity, ambient temperature, and population density (adjusted R² = 0.53, p-value < 0.05), could prove useful for intervention planning during potential future pandemics, including a second COVID-19 outbreak.

International guidelines/standards for human protection from electromagnetic fields have been revised recently, especially for frequencies above 6 GHz where new wireless communication systems have been deployed. Above this frequency a new physical quantity ‘absorbed/epithelial power density’ has been adopted as a dose metric. Then, the permissible level of external field strength/power density is derived for practical assessment. In addition, a new physical quantity, fluence or absorbed energy density, is introduced for protection from brief pulses (especially for shorter than 10 s). These limits were explicitly designed to avoid excessive increases in tissue temperature, based on electromagnetic and thermal modeling studies but supported by experimental data where available. This paper reviews the studies on the computational modeling/dosimetry which are related to the revision of the guidelines/standards. The comparisons with experimental data as well as an analytic solution are also been presented. Future research needs and additional comments on the revision will also be mentioned.

An in situ (internal) electric field is used as a dosimetric quantity for human protection from low-frequency electromagnetic fields (lower than 5 MHz) under international safety standard/guidelines. The IEEE standard uses a homogenous elliptical cross section to derive external field strength corresponding to an in situ field strength, while the International Committee on Non-Ionizing Radiation Protection (ICNIRP) guidelines use anatomical models to relate them. In the latter, “the 99th percentile value of the in situ electric field averaged over the cube of its side length of 2 mm” is used to represent the maximum in situ electric field. This metric was introduced to suppress computational artifacts that are inherent when using voxelized anatomical models, in which curved boundaries are discretized with a stair-casing approximation. To suppress the error, a few schemes have been proposed for treating the computational artifacts. In this study, the various schemes to suppress the artifacts are reviewed. Subsequently, a postprocessing method for determining the appropriate maximum in situ field strength is proposed. The performance of the proposed scheme is first verified by comparison with an analytical solution in a multilayered sphere. The method is then applied for different exposure scenarios in anatomically realistic human models where the volume under computation is also considered.

Objective . Cerebellar transcranial direct current stimulation (ctDCS) is a neuromodulation scheme that delivers a small current to the cerebellum. In this work, we computationally investigate the distributions and strength of the stimulation dosage during ctDCS with the aim of determining the targeted cerebellar regions of a group of subjects with different electrode montages. Approach . We used a new inter-individual registration method that permitted the projection of computed electric fields (EFs) from individual realistic head models ( n = 18) to standard cerebellar template for the first time. Main results . Variations of the EF on the cerebellar surface were found to have standard deviations of up to 55% of the mean. The dominant factor that accounted for 62% of the variability of the maximum EFs was the skin–cerebellum distance, whereas the cerebrospinal fluid volume explained 53% of the average EF distribution. Despite the inter-individual variations, a systematic tendency of the EF hotspot emerges beneath the active electrode in group-level analysis. The hotspot can be adjusted by the electrode position so that the most effective stimulation is delivered to a group of subjects. Significance . Targeting specific cerebellar structures with ctDCS is not straightforward, as neuromodulation depends not only on the placement/design of the electrodes configuration but also on inter-individual variability due to anatomical differences. The proposed method permitted generalizing the EFs to a cerebellum atlas. The atlas is useful for studying the mechanisms of ctDCS, planning ctDCS and explaining findings of experimental studies.