ID Number		741
Study Type		Engineering & Physics
Model		0.6-6 GHz (CW) exposure using vascularized FDTD human models and mapping of SAR distribution and surface heating
Details		FDTD modeling using anatomically-based model of the human eye exposed to 0.6 - 6 GHz MW at 5 mW/cm2 demonstrated a temperature increase of ~ 0.3 degrees C with a variation of +/- 10%. The temperature rise was calculated by the Pennes' bioheat equation. Modeling of the time profile showed that 5 mW/cm2 caused a maximum temperature increase of about 0.5 - 0.6 C in about 30 min. At resonant frequency (1.9 GHz), an SAR of 0.36 W/kg induced a temperature rise of 0.14 C (or 1 W/kg ~ 0.4 C). The maximum temperature increase for the adult eye lens at 900 MHz, 1.5 GHz, and 1.9 GHz at an SAR of 2.0 W/kg was 0.303-0.349 degrees C, and no difference was observed between the adult and children models. The authors report these temperature rises are below the threshold for cataract formation of ~ 3.0 degrees C. Additional FDTD modeling work showed RF exposure from a dipole antenna in the frequency range of 900 MHz to 2.5 GHz (relevant for mobile phone - type exposures) required ~40 W/kg (a 20x factor above current ICNIRP limits) to acheive a 3.5 degree temperature increase in the brain, reported in the literature to be the threshold for physiological damage. Similarly, and exposure of 65 W/kg was required to acheive a 10 degree temperature increase in the rest of the head, also reported as the threshold for significant physiological damage. The paper by Hirata and Shiozawa (2003) calculated maximum temperature increases in the head and brain for the SAR values in the FCC and ICNIRP limits due to handset exposure at five frequencies ranging from 900-2450 MHz. These values were 0.31 and 0.13 C for the FCC limit (l.6 W/kg for 1 g tissue) and 0.60 and 0.25 C for the ICNIRP limit (2 W/kg for 10 g tissue). Further studies using a rabit eye numerical model reported reduced blood flow due to anesthesia also effects the temperature rise due to RF exposure at a given SAR. research looking at exposure to the waist from mobile phones (e.g., attached to a belt) showed good agreement between peak SAR and max temp increases, and temp is mainly influenced by blood flow. In a recent study, the authors report eye temperature increases using improved numerical models of the human eye and compare predicted temperature increases across different studies from Hirata 2007 (0.152-0.175 degrees C/W/kg), Buccella 2007 (0.149-0.160 degrees C/W/kg), Flyckt 2007 (0.089-0.13 degrees C/W/kg), and Wainwright 2007 (0.18-0.19 degrees C/W/kg). AUTHORS' ABSTRACT: Hirata et al. 2012 (IEEE #5650): According to the international guidelines, the whole-body averaged specific absorption rate (WBA-SAR) is used as a metric of basic restriction for radiofrequency whole-body exposure. It is well known that the WBA-SAR largely depends on the frequency of the incident wave for a given incident power density. The frequency at which theWBA-SAR becomes maximal is called the resonance frequency. Our previous study proposed a scheme for estimating the WBA-SAR at this resonance frequency based on an analogy between the power absorption characteristic of human models in free space and that of a dipole antenna. However, a scheme for estimating the WBA-SAR in a grounded human has not been discussed sufficiently, even though the WBA-SAR in a grounded human is larger than that in an ungrounded human. In this study, with the use of the finite-difference time-domain method, the grounded condition is confirmed to be the worst-case exposure for human body models in a standing posture. Then, WBA-SARs in grounded human models are calculated at their respective resonant frequencies. A formula for estimating the WBASAR of a human standing on the ground is proposed based on an analogy with a quarter-wavelength monopole antenna. First, homogenized human body models are shown to provide the conservative WBA-SAR as compared with anatomically based models. Based on the formula proposed here, the WBASARs in grounded human models are approximately 10% larger than those in free space. The variability of the WBA-SAR was shown to be ±30% even for humans of the same age, which is caused by the body shape. AUTHORS' ABSTRACT: Hirata et al. 2014 (IEEE 5677): Temperature elevation in the fetus is of concern for excess heat load, including that from radio-frequency exposure. No previous study succeeded in simulating the temperature difference between the mother and fetus. This study develops a thermal model for a pregnant woman, and then applies it to simulate the temperature variations due to ambient heat exposure and RF exposure. When the pregnant woman model is exposed to ambient temperature of 3545°C, the core temperature elevations in the mother and the fetus are almost identical. Contrarily, the fetal temperature elevation for radio-frequency exposure is higher than that in the mother.
Findings		Effects
Status		Completed With Publication
Principal Investigator		Osaka University, Japan - ahirata@ieee.org
Funding Agency		Private/Instit.
Country		JAPAN
References		Hirata, A et al. Phys Med Biol, (2007) 52:6389-6399 Hirata, A et al. Phys Med Biol, (2007) 52:5013-5023 Hirata, A et al. Bioelectromagnetics., (2007) 28:484-487 Hirata, A et al. IEEE Trans Biomed Eng., (2006) 53:1658-1664 Hirata, A Bioelectromagnetics., (2006) 27:602-612 Hirata, A IEEE Trans. EMC, (2005) 47:68-76 Hirata, A et al. IEEE Trans. Microwave Theory Tech., (2003) 51:1834-1841 Hirata, A et al. IEEE Trans. Electromag. Compatibility, (2003) 45:109-116 Fujimoto, M et al. IEEE Trans EMC, (2002) 44:1-9 Hirata, A et al. IEEE Trans. Electromagnetic Compatibility, (2002) 44:592-594 Hirata, A et al. IEEE Trans. Electromag. Compat., (2000) 42:386-393 Hirata, A et al. IEEE Asis Pacific Microwave Conference, (1999) 2:477-480 Hirata, A et al. Phys. Med. Biol., (2012) 57:8427-8442 Hirata, A et al. Numerical Heat Transfer, Part A: Applications: An International Journal of Computation and Methodology., (2014) 65:1176-1186 Kodera, S et al. International journal of environmental research and public health., (2018) 15:2320-
Comments