Sunkyu Kong

Coil Design and Shielding Methods for a Magnetic Resonant Wireless Power Transfer System

In this paper, we introduce the basic principles of wireless power transfer using magnetic field resonance and describe techniques for the design of a resonant magnetic coil, the formation of a magnetic field distribution, and electromagnetic field (EMF) noise suppression methods. The experimental results of wireless power transfer systems in consumer electronics applications are discussed in terms of issues related to their efficiency and EMF noise. Furthermore, we present a passive shielding method and a magnetic field cancellation method using a reactive resonant current loop and the utilization of these methods in an online electric vehicle (OLEV) system, in which an OLEV green transportation bus system absorbs wireless power from power cables underneath the road surface with only a minimal battery capacity.

Analytical expressions for maximum transferred power in wireless power transfer systems

In this paper, we present the analytical expressions of the resonant peaks of input impedance and the frequencies of maximum transferred power in the wireless power transfer systems in case of tight magnetic coupling. The analytical expressions predict the frequencies of power source where the maximum power is transferred in both cases of the constant AC voltage source and the constant AC current source. We prove that the resonant frequencies of the input impedance in the wireless power transfer systems coincide with the frequencies at which the transferred power is maximized for the constant AC voltage source and the constant AC current source. The test vehicles of the coupled rectangular coils are simulated with 3D EM solver and fabricated on printed circuit boards. Experimentally, it is verified that the analytical expressions predict the changes in the resonant peaks of input impedance of the wireless power transfer systems, its relationship with frequencies of maximum transferred power and their dependency with the source type in the wireless power transfer systems.

An Investigation of Electromagnetic Radiated Emission and Interference From Multi-Coil Wireless Power Transfer Systems Using Resonant Magnetic Field Coupling

Wireless power transfer (WPT) technology has recently emerged as an innovative and promising technology, and its electromagnetic compatibility (EMC) has become a significant issue. In this study, we investigated the electromagnetic (EM) radiated emission and interference generated by WPT systems using resonant magnetic field coupling, especially in applications with multi-coil configurations. The change in coil resonance associated with multi-coil configurations was analyzed via the impedance profile. We measured the EM radiated emission and analyzed the results with respect to the coil resonance. An analog-to-digital converter chip was designed and fabricated to analyze the effect of electromagnetic interference (EMI). Based on measurement and simulation results, we verified that the EM radiated emission and interference increase at the series or parallel resonance peaks, depending on the source type. In addition, we verified that EMI can be reduced by using ferrite sheet shielding.

Electromagnetic radiated emissions from a repeating-coil wireless power transfer system using a resonant magnetic field coupling

Wireless power transfer technologies have been studied steadily and reached the stage of practical use in recent years. As the commercialized research on the wireless power transfer have been performed, the wireless power transfer system utilizing the repeating-coil have been attempted. Then, the electromagnetic radiated emissions have become an important issue. In this paper, we report the measurement and analysis of the electromagnetic radiated emissions from the repeating-coil wireless power transfer system using a resonant magnetic field. A relationship between the resonance and the transferred power are analyzed with respect to the impedance profile obtained from analytical expressions, simulations and measurements. The results show that the electromagnetic radiated emissions are enhanced at the series resonance peaks of the impedance profile in the repeating-coil wireless power transfer system using a resonant magnetic field coupling in the case of a constant-voltage AC source.

Electromagnetic interference shielding effects in wireless power transfer using magnetic resonance coupling for board-to-board level interconnection

In this paper, we present the analysis of electromagnetic interference (EMI) shielding effects of wireless power transfer (WPT) using magnetic resonance coupling for board-to-board level interconnection. Board-to-board WPT consists of source coil, receiver coil, and load which are manufactured on printed circuit board (PCB). The coil is expressed as a simple equivalent circuit model, of which the components are calculated using the physical dimensions of the coil. It is verified that the results of model estimation in both frequency- and time-domain show a good correlation with simulated and measured results under 1GHz. Voltage transfer ratio (VTR) of board-to-board WPT was achieved to be 0.49. In addition, EMI shielding effects in WPT with materials such as ferrite and metal film is analyzed using verified model. The shielding effects of each film in WPT are compared by observing their magnetic field distribution.

Thin PCB-Type Metamaterials for Improved Efficiency and Reduced EMF Leakage in Wireless Power Transfer Systems

Current wireless power transfer (WPT) technology can only allow power transfer over a limited distance because, as the distance between the transmitter (Tx) and receiver (Rx) coils increases, the power transfer efficiency (PTE) decreases with a steep slope, while the electromagnetic field (EMF) leakage increases. In order to increase the PTE and decrease the EMF leakage simultaneously, we need to develop a method to concentrate the magnetic fields between the Tx and Rx coils. In this paper, we proposed a novel metamaterial structure to realize high efficiency and low EMF leakage. Metamaterials can confine the magnetic fields between the Tx and Rx coils by negative relative permeability. We designed and fabricated a thin metamaterial using a 1.6-mm dual layer printed circuit board (PCB) with a high dielectric constant substrate and a fine pattern to achieve a negative relative permeability with low loss at 6.78 MHz. The thin PCB-type metamaterial has a wide range of applications with low fabrication cost, light weight, and a simple fabrication process. We demonstrated a 44.2% improvement in the PTE and 3.49-dBm reduction in the EMF leakage around the WPT system at 20-cm distance. Furthermore, we first analyzed metamaterials from an EMF point of view using the 3-D magnetic field scanner. Finally, we discussed a combination of metamaterials and ferrites to further improve the PTE and reduce the EMF leakage for long-distance mobile WPT systems.

Structure of handheld resonant magnetic coupling charger (HH-RMCC) for electric vehicle considering electromagnetic field

Inductive charging is a convenient method to transfer electrical power from a source to the batteries without any electrical contact. The problem is that inductive charging technologies may have electromagnetic compatibility (EMC) issues caused by leakage magnetic field. In this paper, an inductive charger design for electric vehicles (EVs) named as Handheld Resonant Magnetic Coupling Charger (HH-RMCC) is proposed. The air gap and thickness of the ferrite core are determined considering the core saturation and leakage magnetic field. The maximum value of the simulated magnetic flux density at the distance of 200 mm away from the charger is 2.28 mG and the simulation result of the power transfer efficiency is approximately 99.5%. The simulation results using 3D Finite Element Analysis (FEA) tool show that HH-RMCC satisfies EMF regulation published by the International Commission on NonIonizing Radiation and Protection (ICNIRP) at the frequency of 20 kHz with high performance.

High-Efficiency PCB- and Package-Level Wireless Power Transfer Interconnection Scheme Using Magnetic Field Resonance Coupling

As technology develops, the number of chips increases while the thickness of mobile products continuously decreases, which leads to the need for high-density packaging techniques with high numbers of power and signal lines. By applying wireless power transfer technology at the printed circuit board (PCB) and package levels, the number of power pins can be greatly reduced to produce more space for signal pins and other components in the system. For the first time, in this paper, we propose and demonstrate a high-efficiency PCB- and package-level wireless power transfer interconnection scheme. We enhance the efficiency by applying magnetic field resonance coupling using a matching capacitor. The proposed scheme can replace a high number of power interconnections with rectangular spiral coils to wirelessly transfer power from the source to the receiver at the PCB and package levels. The equivalent circuit model is suggested with analytic equations, which is then analyzed to optimize the test vehicle design. For the experimental verification of the suggested model, the

Design, implementation and measurement of board-to-board wireless power transfer (WPT) for low voltage applications

Z

Three-phase magnetic field design for low EMI and EMF automated resonant wireless power transfer charger for UAV

-parameter results obtained from the model-based equation and measurement of the designed and fabricated test vehicles are compared at up to 1 GHz. The power transfer efficiency from the source coil to the receiver coil in this scheme is able to reach 85.6%. Finally, we designed and fabricated a CMOS full-bridge rectifier and mounted it on the receiver board to convert the transferred voltage from ac voltage to dc voltage. A measured dc voltage of 2.0 V is sufficient to operate the circuit, which generally consists of 1.5 V devices.