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 paper, we propose a method to reduce the leakage magnetic field from wireless power transfer (WPT) systems with series–series compensation topology by adjusting the phase difference between the transmitter (TX) coil current and the receiver (RX) coil current without additional shielding coils or materials. A WPT system employing the proposed method adjusts the phase difference between the TX coil current and RX coil current by tuning a resonant capacitor of the RX coil. The conditions for minimizing the leakage magnetic field are derived, and the range of the resonant capacitor of RX, considering power transfer efficiency and the leakage magnetic field, is proposed. Through simulations and experiments, it is verified that the proposed method can reduce the leakage magnetic field level without any additional materials. For that reason, the proposed method can be suitable for size-limited, weight-limited or cost-limited WPT systems.

This paper analyzes how over-coupled coils affect odd harmonic current and electromagnetic interference (EMI) in a wireless power transfer (WPT) system, and proposes design considerations for series inductors to solve the EMI problem. When the air gap of the coils of the WPT system decreases below a certain level and the coils are over-coupled, the odd harmonic component of the input impedance of the system decreases and odd harmonic currents increase. The increase in the odd harmonic components current quickly aggravates the EMI issues. To solve the EMI problem of the over-coupled WPT system, additional series inductors were applied to the system, and considerations for designing the series inductors were analyzed. When designing additional series inductors, power transfer efficiency, maximum power transfer, input impedance and odd harmonic components current must be considered. Using simulations and experiments, it was confirmed that the WPT system designed with analyzed considerations maintained relatively high efficiency and reduced EMI issues.

In this paper, we propose a method of wirelessly torque transfer (WTT) and power (WPT) to a drug pump, one of implantable medical devices. By using the magnetic field generated by the WPT system to transfer torque and power to the receiving coil at the same time, applications that previously used power from the battery can be operated without a battery. The proposed method uses a receiving coil with magnetic material as a motor, and can generate torque in a desired direction using the magnetic field from the transmitting coil. The WPT system was analyzed using a topology that generates a constant current for stable torque generation. In addition, a method for detecting the position of the receiving coil without using additional power was proposed. Through simulations and experiments, it was confirmed that WTT and WPT were possible at the same time, and in particular, it was confirmed that WTT was stably possible.

This article analyzes the characteristics of the harmonic components in wireless power transfer (WPT) systems depending on load in the LCC -S topology. In a WPT system, the equivalent load can be changed depending on the charging state. Depending on the equivalent load, the operation of the rectifier can be divided into two modes. The first is continuous conduction mode (CCM), and the second is discontinuous conduction mode (DCM). The harmonic characteristics in CCM and DCM operation were each analyzed. The electromagnetic field (EMF) level is the largest when the output power was the largest. However, the electromagnetic interference (EMI) level is largest when the magnitude of the load was at the boundary between CCM and DCM. In practical WPT systems, a dc–dc converter is used for output voltage regulation, and by using the converter, the equivalent load can be changeable. A design method to suppress the leakage magnetic field is proposed in terms of EMF and EMI. Through simulation and experiment, we verified when EMF and EMI levels have the largest value. Also, the effect of suppressing the leakage magnetic field was verified by changing the value of the equivalent load.

With advancements in the field of electrical engineering, various low-power portable electronic devices have been commercialized. To eliminate and unify different types of cables, inductive wireless power transfer (WPT) technology, which uses magnetic fields to transfer energy, is being applied in numerous applications. Low-power devices typically have small coils and loads, leading to low power transfer efficiency even over short distances. Magnetic materials such as ferrites are used to improve power transfer efficiency (PTE). It is well known that high-permeability ferrites with low magnetic reluctance are ideal for achieving strong magnetic coupling. However, continuous increases in permeability raise the cost and weight of the ferrite, making it necessary to select ferrites with appropriate permeability from a mass-production perspective. This paper models and analyzes the changes in mutual inductance and power transfer efficiency with varying ferrite permeabilities using magnetic circuits, providing guidelines for the selection of suitable ferrites considering efficiency improvements. The proposed method is validated through 3D electromagnetic simulations and experiments, showing a power transfer efficiency difference of up to 0.6% between the experimental and calculated results.