Teruo Onishi

Bio: Teruo Onishi is an academic researcher from NTT DoCoMo. The author has contributed to research in topics: Specific absorption rate & Imaging phantom. The author has an hindex of 13, co-authored 58 publications receiving 538 citations. Previous affiliations of Teruo Onishi include Chiba University & Nippon Telegraph and Telephone.

Comparisons of computed mobile phone induced SAR in the SAM phantom to that in anatomically correct models of the human head

Abstract: The specific absorption rates (SAR) determined computationally in the specific anthropomorphic mannequin (SAM) and anatomically correct models of the human head when exposed to a mobile phone model are compared as part of a study organized by IEEE Standards Coordinating Committee 34, Sub-Committee 2, and Working Group 2, and carried out by an international task force comprising 14 government, academic, and industrial research institutions. The detailed study protocol defined the computational head and mobile phone models. The participants used different finite-difference time-domain software and independently positioned the mobile phone and head models in accordance with the protocol. The results show that when the pinna SAR is calculated separately from the head SAR, SAM produced a higher SAR in the head than the anatomically correct head models. Also the larger (adult) head produced a statistically significant higher peak SAR for both the 1- and 10-g averages than did the smaller (child) head for all conditions of frequency and position.

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.

Characteristics of biological tissue equivalent phantoms applied to UWB communications

Abstract: Previously, the authors studied biological tissue equivalent phantoms able to simulate the electrical constants of the human body in the 3- to 6-GHz band in a single composition ratio. Therefore, in this paper, we examined how to study the antenna characteristics using the phantom when extended to a bandwidth including 900 MHz to 3 GHz and 6 to 10 GHz and performed a quantitative study focusing on the electrical constants of the phantom. The result clearly showed hardly any effect of divergence of the phantom's electrical constants from the target values on the antenna input impedance, radiation efficiency, and radiation directivity. Therefore, in the entire ultra-wideband (UWB), this phantom can be accurately evaluated through antenna characteristic measurements and is clearly effective. Furthermore, differences due to the divergence of the phantom's electrical constants from the target values in the entire UWB bandwidth (3 to 10 GHz) are within ±3% for the average local specific absorption rate (SAR) inside the phantom caused by the electromagnetic wave energy radiated from the antenna. © 2007 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 90(5): 48–55, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.20300

Error Analysis of a Near-Field Reconstruction Technique Based on Plane Wave Spectrum Expansion for Power Density Assessment Above 6 GHz

Abstract: This paper aims to clarify the accuracy of a method for assessing the power density in close proximity to a wireless communication device operating above 6 GHz for the assessment of compliance with radio-frequency exposure guidelines. We focused on a near-field reconstruction technique that estimates the power density in close proximity to a wireless communication device using the results of electric field measurement at a plane several wavelengths away from the device. In this paper, the reconstruction technique was first validated by comparing the results evaluated using this technique with those obtained by computational simulation for the case of a standard horn antenna. Second, the reconstruction errors of the technique were assessed using ten planar array antennas at frequencies from 15 to 100 GHz. Reconstruction errors no larger than 0.35 dB were obtained for the maximum spatially averaged power density at a separation distance of over $0.15\\lambda $ from the antennas using an averaging area of $\\lambda ^{2}$ or larger, where $\\lambda $ denotes the wavelength. Finally, the requirement for electric field measurement was also examined, where the combined error for the compliance assessment of the power density was suggested for an actual testing scenario. These results support the standardization of compliance assessment techniques for wireless communication devices operating above 6 GHz, which are expected to be introduced in the near future.

The Virtual Family—development of surface-based anatomical models of two adults and two children for dosimetric simulations

Abstract: The objective of this study was to develop anatomically correct whole body human models of an adult male (34 years old), an adult female (26 years old) and two children (an 11-year-old girl and a six-year-old boy) for the optimized evaluation of electromagnetic exposure. These four models are referred to as the Virtual Family. They are based on high resolution magnetic resonance (MR) images of healthy volunteers. More than 80 different tissue types were distinguished during the segmentation. To improve the accuracy and the effectiveness of the segmentation, a novel semi-automated tool was used to analyze and segment the data. All tissues and organs were reconstructed as three-dimensional (3D) unstructured triangulated surface objects, yielding high precision images of individual features of the body. This greatly enhances the meshing flexibility and the accuracy with respect to thin tissue layers and small organs in comparison with the traditional voxel-based representation of anatomical models. Conformal computational techniques were also applied. The techniques and tools developed in this study can be used to more effectively develop future models and further improve the accuracy of the models for various applications. For research purposes, the four models are provided for free to the scientific community.

Design, Realization and Measurements of a Miniature Antenna for Implantable Wireless Communication Systems

Abstract: The design procedure, realization and measurements of an implantable radiator for telemetry applications are presented. First, free space analysis allows the choice of the antenna typology with reduced computation time. Subsequently the antenna, inserted in a body phantom, is designed to take into account all the necessary electronic components, power supply and bio-compatible insulation so as to realize a complete implantable device. The conformal design has suitable dimensions for subcutaneous implantation (10 × 32.1 mm). The effect of different body phantoms is discussed. The radiator works in both the Medical Device Radiocommunication Service (MedRadio, 401-406 MHz) and the Industrial, Scientific and Medical (ISM, 2.4-2.5 GHz) bands. Simulated maximum gains attain -28.8 and - 18.5 dBi in the two desired frequency ranges, respectively, when the radiator is implanted subcutaneously in a homogenous cylindrical body phantom (80 × 110 mm) with muscle equivalent dielectric properties. Three antennas are realized and characterized in order to improve simulation calibration, electromagnetic performance, and to validate the repeatability of the manufacturing process. Measurements are also presented and a good correspondence with theoretical predictions is registered.

Analysis of RF exposure in the head tissues of children and adults

Abstract: This paper analyzes the radio frequencies (RF) exposure in the head tissues of children using a cellular handset or RF sources (a dipole and a generic handset) at 900, 1800, 2100 and 2400 MHz. Based on magnetic resonance imaging, child head models have been developed. The maximum specific absorption rate (SAR) over 10 g in the head has been analyzed in seven child and six adult heterogeneous head models. The influence of the variability in the same age class is carried out using models based on a morphing technique. The SAR over 1 g in specific tissues has also been assessed in the different types of child and adult head models. Comparisons are performed but nevertheless need to be confirmed since they have been derived from data sets of limited size. The simulations that have been performed show that the differences between the maximum SAR over 10 g estimated in the head models of the adults and the ones of the children are small compared to the standard deviations. But they indicate that the maximum SAR in 1 g of peripheral brain tissues of the child models aged between 5 and 8 years is about two times higher than in adult models. This difference is not observed for the child models of children above 8 years old: the maximum SAR in 1 g of peripheral brain tissues is about the same as the one in adult models. Such differences can be explained by the lower thicknesses of pinna, skin and skull of the younger child models.

Age-dependent tissue-specific exposure of cell phone users

Abstract: The peak spatial specific absorption rate (SAR) assessed with the standardized specific anthropometric mannequin head phantom has been shown to yield a conservative exposure estimate for both adults and children using mobile phones. There are, however, questions remaining concerning the impact of age-dependent dielectric tissue properties and age-dependent proportions of the skull, face and ear on the global and local absorption, in particular in the brain tissues. In this study, we compare the absorption in various parts of the cortex for different magnetic resonance imaging-based head phantoms of adults and children exposed to different models of mobile phones. The results show that the locally induced fields in children can be significantly higher (>3 dB) in subregions of the brain (cortex, hippocampus and hypothalamus) and the eye due to the closer proximity of the phone to these tissues. The increase is even larger for bone marrow (>10 dB) as a result of its significantly high conductivity. Tissues such as the pineal gland show no increase since their distances to the phone are not a function of age. This study, however, confirms previous findings saying that there are no age-dependent changes of the peak spatial SAR when averaged over the entire head.

Techniques for measuring the microwave dielectric properties of materials

Abstract: This review gives a brief introduction to the principles of microwave measurements of the complex permittivity of materials. The fundamentals of reflection, transmission and resonant methods are summarized and examples of sample cell design and measurement systems are presented for each category. The frequency domain and the fast response time domain methods are discussed in view of their merits and limitations. Accuracy aspects and reference materials for calibration procedures are mentioned briefly. Selected examples of applications indicate the diverse usability spectrum of microwave dielectric measurements in basic research and in the characterization of materials in manufacturing processes as well as monitoring and control routines.