Showing papers by "Teruo Onishi published in 2020"

Skin Temperature Elevation for Incident Power Densities From Dipole Arrays at 28 Ghz

Abstract: The relationship between skin temperature elevation and incident power density (IPD) from radio-frequency near-field exposure at 28 GHz for different angles of incidence is evaluated computationally in this study. The averaging scheme of the IPD is crucial for determining the maximum allowable exposure levels of wireless equipment to comply with certain standards/regulations. However, it is still unclear which component of the IPD (i.e., the norm or normal component to the human body) is more related the temperature elevation. In the case of four-element dipole arrays, the distances between the model and the antenna were 15 and 30 mm in transverse-electric- and transverse-magnetic-like polarized waves, respectively, and in the case of eight-element dipole arrays, the distances were 45 mm from the center of the array. From our computational results for four- and eight-element dipole arrays, we confirmed that the normal component of the IPD provides better correlation with the surface skin temperature, regardless of angle of incidence, particularly for smaller angles of incidence (<30°). The enhancement of the ratio of the temperature increase to IPD was observed around the Brewster’s angle, which is mainly attributable to the difference in transmittance at the body surface. This exposure scenario may not occur as the antenna–human distance was too large to consider compliance at the closest distance. In terms of output power, the most restrictive condition for compliance is shown to be normal incidence, suggesting the importance of compliance for such exposure scenarios. Furthermore, the absorbed power density proved to be an appropriate metric to monitor in relation to skin temperature elevation.

Computational Comparison of Power Density Definitions in the Proximity of Antennas for the Assessment of Human Exposure to EMF above 6 GHz

Abstract: This study investigated the definition of power density for local exposure to electromagnetic fields (EMFs) by an antenna positioned near-by a human body at frequencies over 6 GHz. The relationship between the surface temperature elevation and the power densities in various near-field exposure conditions was analyzed. The results show that the applicability of the incident power density limits depends on the many factors, such as frequency, antenna, and antenna to body separation distance. Moreover, the analysis of heating factors of the absorbed power density demonstrated the dependence of locality of exposure. The findings obtained in this study may support the local exposure limits on the spatially-averaged power densities in safety guidelines and standard above 6 GHz.

SAR Dependence on Phantom Dimensions in WPT Exposure Assessment

Abstract: The concept of wireless power transfer (WPT) for distant powering of various electronic devices has received much attention of the research community [1]. Recently, WPT technology has been actively developed for the electric vehicle charge applications [2]. According to the ICNIRP guidelines, the human exposure limits above 100 kHz using the specific absorption rate (SAR) as the assessment criteria are defined [3]. In human safety assessment of inductive coupling WPT systems, phantom of different shapes and dimensions can be used [4]. It is therefore important to consider the effect of phantom size variation on the SAR values obtained in the assessment of WPT systems. This work reports the results of EM simulation of a simple inductive coupling WPT coils operating close to the elliptical phantoms of varying dimensions.