For the wireless power transfer (WPT) system in implantable medical devices (IMDs), human tissue is positioned between the transmitting and receiving coils which are different from general WPT systems. Because this space is where the strongest electromagnetic field (EMF) occurs, it is essential to reduce the EMF at the interspace to reduce human exposure to the EMF. In this paper, an out-of-phase coupled WPT system for IMDs is proposed to reduce human exposure to EMF. Considering the EMF exposure and power transfer efficiency (PTE) of the proposed system, a design procedure for determining the phase difference of each capacitor is analyzed and presented. Based on the equivalent circuit model analysis of the proposed system, the EMF and PTE characteristics of the WPT system depending on the design variables are comprehensively analyzed. The proposed system is compared with conventional systems through simulation and measurements. It is verified that the proposed system can reduce the EMF by 41.05% and increase the PTE by 9.62% compared to the conventional system. In addition, through simulation, human exposure to EMFs is assessed considering the exposure environment and electrical properties of human tissues. As a result, the current density, induced electric field, and specific absorption rate were reduced by 44.10%, 38.90%, and 63.82%, respectively.

Numerical Implementation of Representative Mobile Phone Models for Epidemiological Studies Electromagnetic Absorption;Epidemiological Study;Human Head;Mobile Phone; This paper describes an implementation method and the results of numerical mobile phone models representing real phone models that have been released on the Korean market since 2002. The aim is to estimate the electromagnetic absorption in the human brain for case-control studies to investigate health risks related to mobile phone use. Specific absorption rate (SAR) compliance test reports about commercial phone models were collected and classified in terms of elements such as the external body shape, the antenna, and the frequency band. The design criteria of a numerical phone model representing each type of phone group are as follows. The outer dimensions of the phone body are equal to the average dimensions of all commercial models with the same shape. The distance and direction of the maximum SAR from the earpiece and the area above -3 dB of the maximum SAR are fitted to achieve the average obtained by measuring the SAR distributions of the corresponding commercial models in a flat phantom. Spatial peak 1-g SAR values in the cheek and tilt positions against the specific anthropomorphic mannequin phantom agree with average data on all of the same type of commercial models. Second criterion was applied to only a few types of models because not many commercial models were available. The results show that, with the exception of one model, the implemented numerical phone models meet criteria within 30%.

In this study, the radio-frequency (RF) energy exposure of patient assistants was assessed for an open magnetic resonance imaging (MRI) system based on numerical computations of the head and body RF coil. Various poses of the patient assistants were defined to see how poorly they affected the RF energy exposure. For the assessments, the peak spatial-averaged specific absorption rate (SAR) levels were carefully compared with each patient assistant pose based on the finite-difference time domain calculations of RF coil models when the patient was placed in such coils in a 0.3 Tesla open MRI system. Overall, the SAR levels of the patient assistant were much lower than those of the patient. However, significantly increased SAR levels were observed under specific conditions, including a larger loop size of the patient assistants’ arms and a closer distance to the RF coils. A comparably high level of SAR to the patient’s body was also found. More careful investigations are needed to prevent the increase of SAR in patient assistants for open MRI systems at higher field strengths.

If the wireless power transfer system is located to a person; the magnetic fields produce by the wireless power transfer system will vary in the region occupied by the human body. According the Institute of Electrical and Electronic Engineers (IEEE) and International Commission on Non-Ionizing Radiation Protection (ICNIRP), the predicated or the measured values have to be spatially averaged in an area representing the dimension of the human body and compared with the adopted reference level of exposure. Although spatial averaging is better approximation compared to point measurement, the standard of how to perform such an assessment does not exist. This paper describes the method for spatial averaging magnetic field. We analyzed the difference of spatial averaging value (1-and 2-dimensional templates consists of different number of position) and compared it with the standard uncertainty for measurement drift. The proposed methods are given to present the effectiveness of the choice of measurement position

The wide-open side of an open magnetic resonance imaging (MRI) system allows a patient to easily contact the patient assistant during MRI scans. A wide-open-shaped magnet is highly effective when interventional procedures are necessary. Patient assistants can provide comfort by holding a part of the patient’s body. Because current regulations or guidelines are concerned with only patient radio frequency (RF) safety, investigations on the safety of patient assistants exposed to high-magnetic field MRI (up to 1.2 T) are required. In this study, five different poses of patient assistants were numerically simulated at a 1.2 T open MRI system to determine the impact of poses on the RF exposure level. The 10-g averaged specific absorption rate (SAR) levels were analyzed for the poses of each patient assistant wearing gloves. Compared with the patient, up to 29.8% of the patient SAR was observed in the patient assistant. When the patient assistant wore latex gloves, a 63.7% reduction in the 10-g averaged SAR level was observed, which could be a remedy to minimize possible RF hazards. To prevent possible RF hazards during MRI scans, certain clauses regarding the patient assistant’s poses or wearing gloves must be added to the existing MRI screening forms.