A method for measuring the magnetic field strength for human exposure assessment closer than 20cm to wireless power transfer (WPT) systems for information household appliances is investigated based on numerical simulations and measurements at 100kHz and 6.78MHz. Four types of magnetic sources are considered: a simple 1-turn coil and three types of coils simulating actual WPT systems. A magnetic sensor whose cross sectional area is 100cm2 as prescribed in International Electrotechnical Commission 62233 is used. Simulation results show that the magnetic field strength detected by the magnetic sensor is affected by its placement angle. The maximum coefficient of variation (CV) is 27.2% when the magnetic source and the sensor are in contact. The reason for this deviation is attributable to the localization of the magnetic field distribution around the magnetic source. The coupling effect between the magnetic source and the sensor is negligible. Therefore, the sensor placement angle is an essential factor in magnetic field measurements. The CV due to the sensor placement angle is reduced from 21% to 4% if the area of the sensor coil is reduced from 100 to 0.75cm2 at 6.78MHz. However, the sensitivity of the sensor coil is decreased by 42.5dB. If measurement uncertainty that considers the deviation in the magnetic field strength due to the sensor placement angle is large, the measured magnetic field strength should be corrected by the uncertainty. If the magnetic field distribution around the magnetic source is known, conservative exposure assessments can be achieved by placing the magnetic sensor in locations at which the spatial averaged magnetic field strengths perpendicular to the magnetic sensor coils become maximum.

Magnetic resonant coupling between two coils allows effective wireless transfer of power over distances in the range of tens of centimeters to a few meters. The strong resonant magnetic field also extends to the immediate surroundings of the power transfer system. When a user or bystander is exposed to this magnetic field, electric fields are induced in the body. For the purposes of human and product safety, it is necessary to evaluate whether these fields satisfy the human exposure limits specified in international guidelines and standards. This work investigates the effectiveness of the quasistatic approximation for computational modeling human exposure to the magnetic fields of wireless power transfer systems. It is shown that, when valid, this approximation can greatly reduce the computational requirements of the assessment of human exposure. Using the quasistatic modeling approach, we present an example of the assessment of human exposure to the non-uniform magnetic field of a realistic WPT system for wireless charging of an electric vehicle battery, and propose a coupling factor for practical determination of compliance with the international exposure standards.

The purpose of this study is to establish a whole-body averaged specific absorption rate (WB-SAR) estimation method using the power absorbed by humans; a cylindrical-external field scanning technique is used to measure the radiated RF (radio-frequency) power. This technique is adopted with the goal of simplifying the estimation of the exposure dosimetry of humans who have different postures and/or sizes. In this paper, to validate the proposed measurement method, we subject numerical human phantom models and cylindrical scanning conditions to FDTD analysis. We design a radiation system that uses a dielectric lens to achieve plane-wave irradiation of tested human phantoms in order to develop an experimental WB-SAR measurement system for UHF far-field exposure condition. In addition, we use a constructed SAR measurement system to confirm absorbed power estimations of simple geometrical phantoms and so estimate measurement error of the measurement system. Finally, we discuss the measurement results of WB-SARs for male adult and child human phantom models.

To study the biological effects of the ion-current commonly found under ultra-high voltage DC transmission lines, a technique was developed to evaluate the human exposure to the ion-current field. This technique is based on numerical analysis using the boundary element method. The difficulty of handling the space charge in the calculation was overcome by assuming a lumped source ion-current. This technique is applicable to a three-dimensionally complex object such as a human body. In comparison with theoretical values, the accuracy of this technique was evaluated to be satisfactory for our purposes. It was then applied to a human body in an ion-current field. The distribution of the electric field along the body surface was obtained. The general characteristics of the field distribution were essentially the same as in those without space charges. However, it was found that the strength of the field concentration was significantly enhanced by the space charges. Further, the field exposure when a human body was charged by an ion-current was evaluated. As the charged voltage increases, the position of the field concentration moves from a human's head toward his legs. But the shock of micro spark increases. This technique provides a useful tool for the study of biological effects and safety standards of ion-current fields.