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.

/pdf/the-virtual-family-development-of-surface-based-anatomical-47u5t3e6am.pdf

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

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.

/pdf/design-realization-and-measurements-of-a-miniature-antenna-26zpp391k6.pdf

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

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.

https://iopscience.iop.org/article/10.1088/0031-9155/53/13/019/pdf

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

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.

/pdf/age-dependent-tissue-specific-exposure-of-cell-phone-users-4wsv5f7il2.pdf

Age-dependent tissue-specific exposure of cell phone users

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.

https://iopscience.iop.org/article/10.1088/0026-1394/47/2/S10/pdf

Techniques for measuring the microwave dielectric properties of materials

PROBLEM TO BE SOLVED: To allow an electro-optical probe to be easily handled during measurement, and to reduce deterioration in electric field detection performance. SOLUTION: The electro-optical probe includes an optical element for transmitting light , an electric field detection part including an electro-optical crystal fixed to the tip of the optical element and having a refractive index varied by an electric field, a protective cover accommodating the optical element and the electric field detection part, and a dielectric medium filled in a space between the protective cover and the electric field detection part. Because the electric field detection part is protected by the protective cover, the electro-optical probe is easily handled, and the deterioration in electric field detection sensitivity is suppressed by filling a gap between the protective cover and the electric field detection part with the dielectric medium. COPYRIGHT: (C)2009,JPO&INPIT

Electro-optical probe

This paper presents preliminary research on the compliance assessment of smart surfaces, which are one of the most promising technologies for 5G higher frequency band (NR2) applications. Two different approximate approaches are provided and compared with the reference approach, which is based on full-wave simulation, in terms of assessment accuracy and efficiency to verify their availability and capability quantitatively. Both the two approximate approaches can significantly reduce the assessment time while providing acceptable assessment accuracy.

Incident Power Density Assessment of Smart Surfaces for Exposure Compliance

A surrogate model that “learns” the physics of radio wave propagation is indispensable for the efficient optimization of communication network coverages and comprehensive electromagnetic field (EMF) exposure assessments. The capability of a model to predict reasonable outputs given an input that is beyond the data with which the model is trained, namely, “generalizability,” is a fundamental challenge and a key factor for its practical deployment. In this article, by leveraging the concept of graph neural networks (GNNs), a prediction model for indoor propagation that is “generalized” to not only transmitter (Tx) positions but also new geometries is presented. We demonstrate that a geometry and a Tx antenna can be modeled as a graph with all necessary information being included, and a GNN can acquire the knowledge of propagation physics through “learning” from these graphs. We further show that the model can be generalized to new geometry shapes, beyond the shape (square) for model training. We provide useful information on how to obtain an acceptable accuracy for different scenarios. We also discuss the potential solutions to further improve the model’s capability.

A Generalizable Indoor Propagation Model Based on Graph Neural Networks

The Specific Absorption Rate (SAR) calculations of an anatomical model with respect to regions other than the temporal region have been studied. In those calculations, the Visible Human (VH) model has been mainly used as the anatomically based whole-body realistic human model. We employ two Japanese anatomical models that are realistic high-resolution whole-body voxel models of Japanese adult male and female of average height and weight. In this paper, we show the SAR calculation results pertaining to the VH model and the two anatomical models using the FDTD method when an antenna is located in close proximity to the trunk of the body. In addition, multi-layered flat shape phantoms are introduced to evaluate the effects of tissue thickness and tissue composition. As a result, it is shown that the SAR is affected by a standing wave due to not only fat but also air in the region of the abdomen.

RF dosimetry using Japanese anatomical models

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.

Teruo Onishi

Papers

Electro-optical probe

Incident Power Density Assessment of Smart Surfaces for Exposure Compliance

A Generalizable Indoor Propagation Model Based on Graph Neural Networks

RF dosimetry using Japanese anatomical models

SAR Dependence on Phantom Dimensions in WPT Exposure Assessment