ID Number		2611
Study Type		Engineering & Physics
Model		Computational studies in models of human tissue (brain and skin): Peak spatial averaged SAR, temperature, and guideline limits at GHz frequencies (300 MHz-130 GHz).
Details		AUTHORS' ABSTRACT: Morimoto et al. 2016 (IEEE #6421): This study investigates the relationship between the peak temperature elevation and the peak specific absorption rate (SAR) averaged over 10 g of tissue in human head models in the frequency range of 130 GHz. As a wave source, a half-wave dipole antenna resonant at the respective frequencies is located in the proximity of the pinna. The bioheat equation is used to evaluate the temperature elevation by employing the SAR, which is computed by electromagnetic analysis, as a heat source. The computed SAR is postprocessed by calculating the peak spatial-averaged SAR with six averaging algorithms that consider different descriptions provided in international guidelines and standards, e.g. the number of tissues allowed in the averaging volume, different averaging shapes, and the consideration of the pinna. The computational results show that the SAR averaging algorithms excluding the pinna are essential when correlating the peak temperature elevation in the head excluding the pinna. In the averaging scheme considering an arbitrary shape, for better correlation, multiple tissues should be included in the averaging volume rather than a single tissue. For frequencies higher than 34 GHz, the correlation for peak temperature elevation in the head excluding the pinna is modest for the different algorithms. The 95th percentile value of the heating factor as well as the mean and median values derived here would be helpful for estimating the possible temperature elevation in the head. AUTHORS' ABSTRACT: Laakso et al. 2017 (IEEE #6807): Restrictions on human exposure to electromagnetic waves at frequencies higher than 3-10 GHz are defined in terms of the incident power density to prevent excessive temperature rise in superficial tissue. However, international standards and guidelines differ in their definitions of how the power density is interpreted for brief exposures. This study investigated how the temperature rise was affected by exposure duration at frequencies higher than 6 GHz. Far-field exposure of the human face to pulses shorter than 10 s at frequencies from 6 to 100 GHz was modelled using the finite-difference time-domain method. The bioheat transfer equation was used for thermal modelling. We investigated the effects of frequency, polarization, exposure duration, and depth below the skin surface on the temperature rise. The results indicated limitations in the current human exposure guidelines and showed that radiant exposure, i.e. energy absorption per unit area, can be used to limit temperature rise for pulsed exposure. The data are useful for the development of human exposure guidelines at frequencies higher than 6 GHz. AUTHORS' ABSTRACT: Kodera, Hirata et al. 2018 (IEEE #6931): Background: 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 310 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. Methods: 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 MHz10GHz. The SARs in the human model are first computed using a finitedifference time-domain method. The temperature elevation is calculated by solving the bioheat transfer equation by considering the thermoregulation that simulates the vasodilation. Results: 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 12 °C and for an SAR of 10 W/kg. The temperature at the periphery was below the basal brain temperature (37 °C). Conclusions: 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. AUTHORS' ABSTRACT: Hirata et al. 2019 (IEEE #6957): Two international guidelines/standards for human protection from electromagnetic fields are on-going revision. Most attention has been paid to the revisions above 3 or 10 GHz where the new fifth generation wireless communication system will be deployed soon. The frequency of 3 or 10 GHz is the transition frequency at which the metric of the basic restriction (internal physical quantity) is changed from the specific absorption rate to the incident power density. Rationales for the metrics above 3 or 10 GHz were not well established when the current guidelines/standards were published. In this review, we focused on three issues to be considered in the next revision of the exposure guidelines: (i) the averaging area of the incident power density, (ii) the transition frequency at which the metric is changed from the specific absorption rate to the incident power density, and (iii) the exposure averaging time. In addition, some remarks and trends on related product safety will also be reviewed and discussed briefly.
Findings		Not Applicable to Bioeffects
Status		Completed With Publication
Principal Investigator		Nagoya Inst of Tech, Nagoya, Japan
Funding Agency		?????
Country		JAPAN
References		Morimoto, R et al. Phys. Med. Biol., (2016) 61:5406-5425 Laakso, I et al. Phys Med Biol., (2017) 62:6980-6992 Kodera, S et al. Bio Med Eng., (2018) 17:1:- Hirata, A et al. Annals of Telecommunications., (2019) 74:17-24 Rashed, E et al. IEEE Access., (2019) 7:46176-46186 Rashed, EA et al. NeuroImage., (2019) 202:116132- Rashed, EA et al. Physics in Medicine and Biology., (2020) 65:065001-(14 pages) Diao, Y et al. IEEE Access., (2020) 8:154060-154071 Diao, Y et al. Phys Med Biol., (2020) 65:224001- Hirata, A et al. Physics in Medicine & Biology., (2021) 66:08TR01-doi.org/10.1088/1361-6560/abf1b7 Diao, Y et al. IEEE Transactions on Electromagnetic Compatibility., (2021) doi: 10.1109/TEMC.2021.3074658:- Li, K et al. IEEE Access., (2021) 9:115801-115812 Diao, Y et al. IEEE Trans Electromagn Compat. , (2021) 63:1709-1716 Hirata, A et al. IEEE Transactions on Electromagnetic Compatibility., (2021) 63:1619-1630 Li, K et al. IEEE Access. , (2021) 9:151654-151666 De Santis, V et al. IEEE Access., (2022) 10:82236-82245 Taguchi, K et al. IEEE J Electromagn RF Microw Med Biol. , (2022) :(8 pages)-
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