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.

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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.

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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.

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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

A biological tissue equivalent phantom unit to be used by the specific absorption rate measuring system for evaluating absorption of electromagnetic wave energy includes a biological tissue equivalent phantom for absorbing an electromagnetic wave. In addition, two or more electro-optical crystals are arranged at two or more measurement points in the biological tissue equivalent phantom. The electro-optical crystals have a dielectric constant that is approximately equal to that of the biological tissue equivalent phantom. Two or more optical fibers are laid in the biological tissue equivalent phantom for optically connecting each of the electro-optical crystals to an external destination.

Specific absorption rate measuring system, and a method thereof

A specific absorption rate measuring apparatus comprises a probe configured to measure, in a two-dimensional plane, the amplitude and the phase of an electric or magnetic field generated in a phantom of which electrical properties similar to a human body tissues; an electric and/or magnetic field estimation unit configured to estimate a three-dimensional electric field distribution to be produced from a wave source defined by the two-dimensional electric and magnetic fields at a measuring point, based on the measurement results of the probe; and a specific absorption rate estimation unit configured to estimate a three-dimensional distribution of specific absorption rate based on the estimation result of the electric field estimation unit.

Measurement system of specific absorption rate

A disclosed specific absorption rate measurement system according to an embodiment of the present invention measures a specific absorption rate of electromagnetic waves from a radiating source absorbed in a dielectric medium. The system includes a measurement portion that measures a first electric field vector on an observation surface which is a two-dimensional surface in the dielectric medium; an electric field calculation portion that calculates a second electric field vector in a point excluded from the observation surface in accordance with electric field components of the first electric field vector measured on the observation surface, the electric field components being parallel to the observation surface; and a calculation portion that calculates the specific absorption rate from the calculated second electric field vector.

Specific absorption rate measurement system and method

This paper presents a quantitative analysis of the differences between the various definitions of spatially averaged power densities ( $sIPD_{s}$ ) for localized exposure to electromagnetic near-fields at frequencies from 6 to 100 GHz. The spatially averaged modulus of the complex Poynting vector ( $sIPD_{mod}$ ) and spatially averaged norm of the real part of the complex Poynting vector ( $sIPD_{norm}$ ) were compared using numerical approaches, where their relationships with the spatially averaged absorbed power density ( sAPD ) and the local peak temperature elevation on skin tissue were analyzed. Our results demonstrated that outside the typical boundary of the reactive near-field, i.e., $> \lambda $ /( $2\pi$ ), which is used as a rough guide of the applicable condition for reference levels in the RF safety guidelines, but at most 10 mm from the radiation source, the maximum difference between $sIPD_{norm}$ and $sIPD_{mod}$ is smaller than 0.7 dB from 6 to 100 GHz. For the appropriate conditions recommended in the RF safety guidelines, the differences between the ratios of sAPD to $sIPD_{s}$ and those for the plane-wave normal incidence, are at most 1.4 dB and 0.9 dB for $sIPD_{norm}$ and $sIPD_{mod}$ , respectively. Under the same condition, the ratios of the temperature rise to $sIPD_{s}$ for the relatively small antennas (total dimension less than $2\lambda$ ) do not significantly exceed that for the plane-wave normal incidence, which means that the expected maximum temperature rise is lower than the temperature rise that is derived from the operational health effect threshold in terms of the temperature rise divided with the reduction factors employed in the RF safety guidelines. The above results provide suggestive evidence that the effect of the definition of $sIPD_{s}$ on the human exposure characteristics is not significant compared with those of the other factors, i.e., the antenna type (size), frequency, distance from the source, and averaging area.

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Quantitative Comparison of Power Densities Related to Electromagnetic Near-Field Exposures With Safety Guidelines From 6 to 100 GHz

The transmission power is decreased in an appropriate manner, while suppressing the deterioration of the line quality to the minimum. A mobile communication terminal 1 controls the transmission power in response to a request given from a base transceiver station 2 . When an average transmission power Wa that is an average value of the transmission power in a monitoring period Ta is smaller than a threshold value TH, mobile communication terminal 1 continuously controls the transmission power in response to the request given by the base transceiver station 2 . When the average transmission power Wa in the monitoring period Ta is equal to or greater than the threshold value TH, the transmission power is controlled in a transmission power suppressing period Tb that follows the monitoring period Ta so that the average value of the transmission power becomes equal to or smaller than the threshold value in a control period Tc including the monitoring period Ta and the transmission power suppressing period Tb. The average value of the transmission power is thus decreased in the entire control period Tc.

Teruo Onishi

Papers

Specific absorption rate measuring system, and a method thereof

Measurement system of specific absorption rate

Specific absorption rate measurement system and method

Quantitative Comparison of Power Densities Related to Electromagnetic Near-Field Exposures With Safety Guidelines From 6 to 100 GHz

Mobile communication terminal and transmission power control method of the same