Hongseok Kim

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.

Coil Design and Measurements of Automotive Magnetic Resonant Wireless Charging System for High-Efficiency and Low Magnetic Field Leakage

For wireless charging of electric vehicle (EV) batteries, high-frequency magnetic fields are generated from magnetically coupled coils. The large air-gap between two coils may cause high leakage of magnetic fields and it may also lower the power transfer efficiency (PTE). For the first time, in this paper, we propose a new set of coil design formulas for high-efficiency and low harmonic currents and a new design procedure for low leakage of magnetic fields for high-power wireless power transfer (WPT) system. Based on the proposed design procedure, a pair of magnetically coupled coils with magnetic field shielding for a 1-kW-class golf-cart WPT system is optimized via finite-element simulation and the proposed design formulas. We built a 1-kW-class wireless EV charging system for practical measurements of the PTE, the magnetic field strength around the golf cart, and voltage/current spectrums. The fabricated system has achieved a PTE of 96% at the operating frequency of 20.15 kHz with a 156-mm air gap between the coils. At the same time, the highest magnetic field strength measured around the golf cart is 19.8 mG, which is far below the relevant electromagnetic field safety guidelines (ICNIRP 1998/2010). In addition, the third harmonic component of the measured magnetic field is 39 dB lower than the fundamental component. These practical measurement results prove the effectiveness of the proposed coil design formulas and procedure of a WPT system for high-efficiency and low magnetic field leakage.

Prediction of Ductile Fracture in Cold Forging of Aluminum Alloy

In this paper, the limitation and applicability of the ductile fracture criteria based on a work hypothesis and Cockcroft and Latham were investigated. For this purpose, experimental and numerical investigations for simple upsetting were conducted for aluminum alloys Al1100-O, Al2024-T3, Al6061-T4, and A17075-T4. As a result, the fracture mode of each alloy was observed. The study was extended for pin-shape cold forging of Al1100-O and Al6061-T4 to compare the likeliness of fracturing according to two criteria. Based on experimental data of simple upsetting, the damage factors for the same two criteria were calculated by adopting rigid-viscoplastic finite element analysis. With this approach, the prediction of surface cracking was attempted by comparing the calculated limiting damage factors between simple upsetting and pin-shape forging. It was observed in simple upsetting that Cockcroft and Lathams criterion gave a more reasonable prediction for crack initiation site than work hypothesis, but the limiting damage factors differ depending on the process. In spite of the differences, however, Cockcroft and Lathams criterion might be useful in designing upsetting-like cold forging processes in which the influence of the induced circumferential tensile stress on failure is dominant.

Suppression of leakage magnetic field from a wireless power transfer system using ferrimagnetic material and metallic shielding

This paper describes a method to suppress the leakage magnetic field from a wireless power transfer (WPT) system through the use of a ferrimagnetic material and metallic shielding. To demonstrate the advantages of the coil structure with the ferrimagnetic material and metallic shielding, magnetic field distributions and the electrical performance of three different coil structures are investigated via 3D electromagnetic (EM) field solver and SPICE simulation. Results show that the suggested method considerably reduces the leakage magnetic field in the vicinity of the WPT system without significant loss of electrical performance. The simulation results of the suggested coil structure are experimentally verified with a 100 W-class WPT system for an LED TV.

Expert system for multi-stage cold-forging process design with a re-designing algorithm

Abstract Cold forging has recently become one of the competitive technologies in manufacturing. In order to improve the productivity of cold forging at low production cost, an integrated systems approach is necessary in handling the material preparation and the optimum process design considering the forming machines, tooling, and operation, including quality control. As the first step toward this approach, an expert system for multi-stage cold-forging process design for axi-symmetric geometries with or without a hole in one end has been developed using Prolog language on IBM 486 PC. The system consists of a user interface, a system shell, a material data-base, and a design rule-base. According to the given input data, the system generates the forgeable geometry and the basic process design, depending on the initial billet size and material or the order of upsetting and forward extrusion. In addition, it can provide a flexible process re-design based on either the reduction in the number of forming sequences by combining the possible two processes in sequence, or the reduction of deviation of the distribution and the level of the required forming loads at the last forging step by controlling the forming ratios. The required forming loads and global strain distributions at each step are calculated and displayed on a PC monitor. The designed process sequences can be obtained by AutoCAD or a text file including the dimensions of the drawing. The system developed will be useful in reducing trial-and-error by design engineers in determining the diameter and height of the initial cyclindrical billet from the final product geometry and the intermediate necessary sequences.

An expert system for cold forging process design based on a depth-first search

Abstract Due to the non-deterministic nature of process sequence design for multi-stage cold forging, various process designs are available depending on the initial billet geometry and the order of basic processes such as forward/backward extrusion, upsetting and trimming process. Therefore, various process sequences should be determined and compared to obtain an optimal solution. For this purpose, a depth-first search, a searching technique used in artificial intelligence, has been introduced in developing an expert system for multi-stage cold forging process design. As a result, process designers can select the optimal process sequence from the searched feasible solutions by estimating the values of evaluation functions that are introduced to represent the important design characteristics. In the present investigation, the distributions of the global effective strains in the final product and the forming loads required at each forging stage were selected to be controlled. In general, a more realistic process sequence should be determined by taking into account manufacturing conditions such as the number of forming stages, the forming loads, the shearing diameter of the coil, the open upsetting diameter, and the knock-out lengths of the die and punch. In this paper, a methodology of applying the searching technique for process sequence design is discussed, and the flexibility of the introduced searching technique is evaluated by generating design examples of a shaft part, a wrench and hexagonal bolts of AISI 1045.

Wall Loss Rate of Polydispersed Aerosols

Wall loss rates of polydispersed aerosols in a stirred vessel were studied theoretically and experimentally. A formula for the poly- dispersity factor of the wall loss rate was derived using the moment method of log-normal size distribution and compared with numerical calculations. The representative theory of Crump and Seinfeld (1981) was used as the wall loss rate of monodispersed aerosols in which the Brownian diffusion, the turbulent eddy diffusion, and the gravitational settling are included as wall loss mechanisms. The results of the analysis show that the wall loss rate of a polydispersed aerosol is substantially higher than that based on a monodispersed size distribution model if the particle size distribution can be represented reasonably well by a log-normal function. The existing diagram showing the loss rate as a function only of the particle size was expanded to include the polydispersity effects. Experimental measurements of particle wall loss rate were performed by observing the time-dependent changes in particle number concentration for various stirring intensities in a cylindrical stirred chamber. It was shown that by correcting for the polydispersity effect, the dependence of the wall loss rate on particle size and stirring intensity agreed with the theory of Crump and Seinfeld (1981).

Reduction of electromagnetic field (EMF) of wireless power transfer system using quadruple coil for laptop applications

In this paper, we proposed an effective coil design for electromagnetic field (EMF) noise reduction from the wireless power transfer system by using quadruple coils in transmitter and receiver for laptop computer application. By using quadruple coils for transmitter and receiver, EMF noise was significantly reduced with negligible change in induced voltage. 3D simulations and the field distributions are shown and the pros and cons are of the quadruple coil designs are discussed.

Shielded coil structure suppressing leakage magnetic field from 100W-class wireless power transfer system with higher efficiency

In this paper, the shielded coil structure using the ferrites and the metallic shielding is proposed. It is compared with the unshielded coil structure (i.e. a pair of circular loop coils only) to demonstrate the differences in the magnetic field distributions and system performance. The simulation results using the 3D Finite Element Analysis (FEA) tool show that it can considerably suppress the leakage magnetic field from 100W-class wireless power transfer (WPT) system with the enhanced system performance.

A Three-Phase Wireless-Power-Transfer System for Online Electric Vehicles With Reduction of Leakage Magnetic Fields

Wireless charging of electric vehicles based on wireless power transfer (WPT) has become increasingly popular in recent years. However, a leakage electromagnetic field (EMF) that affects other electronic devices or the human body is inevitably generated from the coils of a WPT system, and requirements regarding the suppression of the leakage EMF are increasing. In this paper, we propose a novel three-phase power line in a WPT system for the reduction of the leakage EMF. The proposed structure employs six power lines to reduce the leakage magnetic flux. This structure is compared with conventional power line structures with respect to induced voltage and magnetic field distribution. We also present analytical solutions of the EMF for the proposed and conventional power line structures. These solutions are then compared with numerical solutions using 3-D finite-element analysis and good agreement is demonstrated. The results of the numerical analysis indicate that the proposed power line can significantly reduce the leakage magnetic field from a WPT system. For verification, the proposed and conventional power lines are implemented and the EMFs are measured. A strong correlation between the numerical and experimental results is exhibited.