Capacitive power transfer (CPT) system can be employed for wireless charging of drone applications. However, in the CPT system, cross-coupling capacitance caused by coupling of the two pairs of plates on different sides, which do not form the main capacitance must be considered. Designs that do not properly consider the cross-coupling capacitance can cause decrease in the efficiency of the system. In this article, we propose a separate circular capacitive coupler for the CPT system. To reduce the cross-coupling capacitance in drone applications, the plates on the same side are separated. The circuit model of the coupler is presented; it considers a total of six coupling capacitances. For maximum power transfer efficiency, impedance of the receiver is considered to determine the parameter value of the LC resonance. Through simulation and measurement, we verified that the proposed separated circular coupler can reduce the cross-coupling capacitance. The plate-to-plate power transfer efficiency is maintained at 89.4% with 100-W output power.

Recently, maintenance applications around power lines have been actively studied. These applications usually supply power through magnetic energy harvesting(MEH) to devices around the power line. A major challenge for practical MEH is to overcome magnetic saturation, which can cause degradation of power density under a wide current range in the power line. In this paper, we propose a design methodology to harvest maximized output power by considering the saturation effect. To consider magnetic saturation, the output power model and the saturable magnetizing inductance model based on magnetizing current were comprehensively analyzed. Additionally, the critical point of saturation for the maximum harvested power was analyzed by considering different primary side current conditions. With the proposed design methodology, the accuracy and efficiency of the output model were verified with experimental results compared to the conventional model. To consider the real environment, a 150 kW class of AC resistor load bank was implemented to control the primary current from 0 to 100 A with power frequency of 60 Hz. Experimental results show that the proposed method can harvest an average power of 14.32 W on 70 A power line, which is an increase of 39.8 % compared with the conventional design method.

The paper proposes a method for locating an electric means of transportation such as electric vehicles that adopts dynamic wireless charging system. The method works with magnetic wireless power transfer systems, based on a ferrite core counting approach. The ferrite core counter system operates by counting all the ferrite cores of the source coils used for guiding the magnetic field in a magnetic wireless power transfer system. The proposed ferrite core counter has a position detection accuracy equivalent to the spacing of the ferrite cores. In addition, this paper proposes a ferrite position identification (FPID) messaging unit to correct ferrite core counter errors. FPID blocks which are successively placed under the source coil are recognized by the ferrite core counter, and their passage is reported as a sort of message in the vehicle. This FPID messaging unit provides the ferrite core counter with a system that can correct errors in the number of ferrite cores counted. The effectiveness of the vehicle positioning system with the ferrite core counter and the FPID messaging unit has been demonstrated through simulation and experiments.

This article proposes transmitter coils selection method for maximum power transfer efficiency in the wireless power transfer (WPT) system with multiple transmitter coils and a single receiver coil (MTSR). The proposed method is divided into two main steps. First, transmitter coil selection criteria that can achieve maximum efficiency are derived by analyzing the relative magnitude of the coupling coefficient between each coil. Next, a method for calculating the relative coupling coefficients used for the criteria only with the input current value is presented. This method differs from previous studies in that it can be applied when some transmission coils are deactivated. Therefore, it is possible to select the optimal transmitter coil combination in consideration of the characteristics of the receiver coil using the proposed method without information on the receiver coil. By the proposed transmitter coils selection criteria, the power transfer efficiency has an average of 96.5 $\pm$ 0.5% when the output power is 300 W, even with the position change of the receiver coil. In addition, it is confirmed that the proposed coupling coefficient extraction method has a slight error of 2.5% compared to the measured value by a vector network analyzer.

This article describes a method to reduce electromagnetic interference (EMI) components at odd harmonic frequencies of a wireless power transfer (WPT) system. In a WPT system, a leakage magnetic field is generated, which may adversely affect the human body or other electronic devices. The previous reactive shielding method could reduce the magnetic field, but it has the disadvantage of reducing the power transfer efficiency (PTE). By using frequency split phenomena, the reactive shielding method can reduce the EMI components with increasing PTE. In this article, a reactive shielding method that can reduce the magnetic field while increasing PTE is proposed. Specifically, the method for designing resonant system of transmitting, receiving, and shielding for the WPT system is proposed. In addition, a method for obtaining a coupling coefficient between a shielding coil and a transmitting coil for designing structure in which magnetic field reduction can be maximized is also proposed. The theoretical analysis based on the impedance of each part is strongly correlated with the simulation and measurement result. As a result of the experiment, the PTE is increased by about 2.7%, and EMI components at odd harmonic frequency can be reduced by up to 6.81 dB in a 50 W-WPT system.

In this article, a microrobot capable of creating propulsion force and receiving electrical energy using a wireless power transfer (WPT) system is proposed. As a source of propulsion and rotation for the microrobot, we use the force and torque of magnetic material in a time-variant magnetic field generated by the transmitting coil of the WPT system, with a specifically designed magnetic material which produced even greater force under the same volume. While microrobot propulsion based on the Lorentz force is closely related to the magnitude of the induced current, because the force of the magnetic material in the proposed design is independent of the induced current, it is more practical for miniaturization of the microrobot. Additionally, the proposed model is able to use the LC resonance frequency, and a magnetic material located in the receiving coil introduces a higher coupling coefficient between the transmitting coil and the receiving coil. These characteristics make the proposed microrobot suitable for powering through a WPT system. The feasibility of the proposed model was initially investigated by theoretical analysis and then verified in simulation and an experiment. In the experiment, the fabricated microrobot $4.5\times 2.0\times2.0$ mm ³ in size achieved a power transfer efficiency rate of 4.5% at 103 kHz with a propulsion speed of 7.5 mm/s and rotating motion.