Showing papers by "Teruo Onishi published in 2014"

Induced field and SAR in human body model due to wireless power transfer system with induction coupling

Abstract: The present study investigates the SAR (specific absorption rate) and the induced electric field in an anatomically based model for the magnetic field from a wireless power transfer system. The waiting and charging conditions are considered. The transfer frequency considered herein is from 100 kHz and 150 kHz where a magneto-quasi-static approximation is valid. A two-step quasi-static method comprised of the method of moments and the scalar potential finite difference method is then used. First, the method of moments is used to calculate the magnetic field of wireless transfer system without the presence of the human body model. Then, the SAR and the electric field in the model are calculated by solving the scalar potential finite difference method. From computational results, the peak values of the SAR averaged over 10 g of tissue and the induced electric field for the transfer power of 5 W are substantially smaller than 2 W/kg and 18.9 V/m, the basic restrictions for those for general public, prescribed in the international guidelines/standard. The results indicate the induced electric field as a dominant factor when evaluating the compliance of the wireless power transfer system.

An estimation method for vector probes used in determination SAR of multiple-antenna transmission systems

Abstract: This paper presents a fast method to estimate Specific Absorption Rate (SAR) of multiple-antenna transmission systems which employ two or more antennas in a communication. SAR values for arbitrary sets of relative phases of the antennas at a measurement point can be estimated from measured E-field with few known relative phases at the same measurement point. Fundamental concepts and analyzes are presented. Several numerical validations with different antenna configurations have been carried to verify the correctness of the estimation method. It has been highlighted that the proposed estimation method is simple yet provide highly accurate estimated SAR values.

Averaging time required for measuring the specific absorption rate of a MIMO transmitter

Abstract: This paper presents a new method to measure electric field (E-field) for human-body exposure to electromagnetic fields from Multi-Input Multi-Output (MIMO) wireless communication transmitters, and an estimation of averaging time required in the E-field measurement. The proposed method is to measure time-averaged E-field, and the averaging time is the duration required for a measurement system to make averaged E-field converged. The estimation is based on averaging the square of amplitude of received signals or measured E-field strength. Several simulation results with different measurement parameters for MIMO wireless communication transmitters are presented and discussed. It is pointed out that the averaging time in E-field measurements for multi-antenna transmitters is considerably longer than that for single antenna transmitters.

A method in determination of the specific absorption rate of multi-antenna devices

Abstract: This paper presents a simple estimation method to evaluate the Specific Absorption Rate (SAR) of multiple antenna transmitting systems with conventional scalar SAR/E-field probes. For systems with two-element antenna, only three measurements with known relative phase combinations of the antennas are required in order to evaluate SAR for any other relative phase combinations.

Magnetic field measurement near wireless power transfer systems

Abstract: Measurement method of magnetic field near a magnetic source is investigated. Frequencies of the magnetic field are 100 kHz and 6.78 MHz. As a result, even if magnetic sensor is placed nearest to the source, change of current flowing through the source is marginal in this study. When the sensor whose measuring area is 100 cm2 is moved closer to the source, the difference between the actual strength of the magnetic field and that estimated using the sensor increases. At the source-sensor distance of 20 cm, the estimated strengths are 0.9 and 2.2% higher than the actual field strength. On the other hand, the estimated strengths are 10.0 and 10.2% higher at the frequencies of 100 kHz and 6.78 MHz, respectively, at the distance of 0 cm.