Abstract
Accurate dosimetry for a real wireless power transfer system (WPT) using electromagnetic resonance and electromagnetic induction requires an accurate description of the field formed by the system. In particular, the electromagnetic field depends on factors such as the construction of the transmitting and receiving coils, the circuit configuration, the input source of the front end of the transmitting coil, and the input impedance of the rear end of receiving coil. However, both circuit and electromagnetic simulations need to be performed to analyze the entire system, which is a difficult task. In order to overcome this difficulty, a method using an equivalent circuit model is proposed and verified through experiments. Moreover, the worst exposure condition to a magnetic field was examined by considering three variables: the charging mode, the state of charge, and the alignment and misalignment between the transmitting and receiving coils. Accordingly, the strongest magnetic field was created in the constant current mode in the fully charged state with misalignment. For example, the magnetic field strength in the case of 80% state of charge and misalignment was 1.397 times greater than in the case of 20% state of charge and alignment at a point 10 mm from the transmission pad. Finally, the induced electric fields and induced current densities were calculated by using a Japanese adult male whole-body voxel human model, and the results were compared with the values recommended by international guidelines to ascertain their compliance.
Highlights
Many studies have been focused on the application of wireless power transfer system (WPT) technology to various fields [1,2,3,4]
Human exposure and wireless power transfer magnetic field produced by the wireless charging system based on the precise determination of the current flowing under the application of a specific battery voltage and frequency
This study proposed an equivalent circuit model method to represent the source and load conditions for an accurate description of the magnetic field formed around a WPT system
Summary
Many studies have been focused on the application of WPT technology to various fields [1,2,3,4]. This numerical dosimetry can be performed successfully under the condition that the electromagnetic field to which a human body will be exposed is accurately simulated This condition is met only by accurately describing the current flowing in a WPT coil. In [16] and [17], experimental verification and numerical dosimetry were carried out for low-power WPT systems such as mobile phones, which were specified in the Wireless Power Consortium (WPC) standard for the 100-kHz band and in the AirFuel Alliance standard for the 6.78-MHz band These studies lack accurate descriptions of the termination conditions of the load and source. To identify the worst exposure scenario, the SoC, the charging mode (constant current, power, and voltage), and the offset of the transmitting and receiving coils are investigated, which are variables affecting the electromagnetic fields around a WPT system. The currents in the transmitting and receiving coils can be obtained as follows:
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