Tae-Dong Yeo

Bio: Tae-Dong Yeo is an academic researcher from KAIST. The author has contributed to research in topics: Antenna (radio) & Impedance matching. The author has an hindex of 4, co-authored 19 publications receiving 216 citations.

Design of Maximum Efficiency Tracking Control Scheme for Closed-Loop Wireless Power Charging System Employing Series Resonant Tank

Abstract: This paper presents a maximum efficiency tracking control scheme for a closed-loop wireless power charging (WPC) system for wireless charging of mobile devices. Generally, wireless charging systems need a precise output voltage and current with the highest possible efficiency. In an open-loop system, output voltage and efficiency depend strongly on the coupling coefficient and load condition. Alternatively, a closed-loop WPC system has a constant output voltage against coupling and load variations. Many studies have been carried out regarding closed-loop systems. However, those previous studies have the drawback of efficiency degradation. In this paper, we propose a maximum efficiency tracking control scheme to achieve the highest possible efficiency. Therefore, the proposed WPC system satisfies both the requirements of a constant output voltage and high efficiency. The proposed control scheme determines the current of the transmitter based on the data received by the receiver via Bluetooth. For validation, the proposed WPC system was implemented at 6.78 MHz using loosely coupled series–series resonant coils, and we verified that the proposed system can track the maximum efficiency while maintaining a constant output voltage.

Microwave Power Transfer With Optimal Number of Rectenna Arrays for Midrange Applications

Abstract: In this letter, the microwave power transfer (MPT) system with the optimal number of rectenna arrays for midrange applications is proposed, theoretically analyzed, and verified. A retrodirective power transmitter is designed to overcome the degradation by the near-field effect and enhance the power transfer efficiency. The implemented transmitter is composed of 16 $\times$ 1 patch antennas with a $\lambda /2$ spacing, and each of the antennas has a circuit for simultaneously detecting and shifting the phase, and operates at a frequency of 2.45 GHz. To further improve the power transfer efficiency, the parallel dc combining rectenna array is designed since the conventional RF combining rectenna has several problems in the case of midrange. The fabricated rectenna array consists of 8 $\times$ 1 rectennas with a $\lambda /2$ spacing and a dc power management circuit. In addition, the optimal number of rectenna arrays is proposed, considering the size of the receiver. In the experiments, the optimal number of rectennas is 3 when the transfer distance is 1 m. The achieved power transfer efficiency from three-arrayed rectennas is 4.47%, while the efficiency of 5.01% is achieved from eight-arrayed rectennas. Experimental results from the implemented MPT system show good agreement with the proposed theory.

Dual Resonance Frequency Selective Loop of Near-Field Wireless Charging and Communications Systems for Portable Device

Abstract: In this letter, a frequency selective loop isolator using dual resonance for a mobile wireless charging system is presented. Resonance of the proposed frequency selective loop isolates a transmitting loop from a receiving loop at one frequency whereas it transfers wireless power between them at the second harmonic frequency. Simple arrangement of lumped elements changes operation of the proposed frequency selective loop to a series resonator at 6.78 MHz and a parallel resonator at 13.56 MHz. Experimental results show the difference in the transmission coefficient between with/without the frequency selective loop is approximately 21 dB at 6.78 MHz whereas it is about 2 dB at 13.56 MHz, without degradation of efficiency. Moreover, this approach suggests how to transfer wireless power based on frequency selection.

Fast Fourier-Domain Optimization Using Hybrid L 1− /L ${}_{p}$ -Norm for Autofocus in Airborne SAR Imaging

Abstract: In maneuverable airborne synthetic aperture radar (SAR), high-frequency phase errors (HPEs), which are hard to be compensated by the phase gradient autofocus, often occur causing spurious targets and contrast degradation in SAR imagery. The metric-optimization approaches improve the phase error estimation scalability, including HPEs, but show much lower speed because of the computational burden by the inverse fast Fourier transform (IFFT). Proposed autofocus based on the metric optimization enables the rapid estimation with the scalability including the HPE by eliminating the IFFT. In addition, the metric is adapted to the range compressed data corresponding to the input of the autofocus taking advantage of the convergence speed and the stability in its optimization using a hybrid form of L1− and L p -norm. In the simulation, we focused on the suggestion of the proof of performance generality.

Design of free-positioning wireless power charging system for AAA rechargeable battery

Abstract: This paper presents a free-positioning wireless power charging (WPC) system for AAA Type rechargeable battery. In recent years, misalignment between transmitting coil and receiving coil is very big issue in this area, because efficiency of WPC systems is vulnerable to lateral misalignment and angular misalignment. Unfortunately, the coils could be often misaligned while charging devices, in practical situations. Therefore, this paper proposed the free-positioning WPC system. In order to solve the lateral misalignment, proposed transmitting coil has the uniform magnetic field by changing current distribution. In receiving side, two perpendicular coil having structure of ‘plus’ (+) shape is proposed to solve the angular misalignment. For validation, the proposed wireless power charging system was implemented at 6.78MHz using loosely coupled resonant coils, and we verified that the proposed system is robust to misalignment.

Wireless Power Transfer—An Overview

Abstract: Due to limitations of low power density, high cost, heavy weight, etc., the development and application of battery-powered devices are facing with unprecedented technical challenges. As a novel pattern of energization, the wireless power transfer (WPT) offers a band new way to the energy acquisition for electric-driven devices, thus alleviating the over-dependence on the battery. This paper presents an overview of WPT techniques with emphasis on working mechanisms, technical challenges, metamaterials, and classical applications. Focusing on WPT systems, this paper elaborates on current major research topics and discusses about future development trends. This novel energy transmission mechanism shows significant meanings on the pervasive application of renewable energies in our daily life.

Spotlight Synthetic Aperture Radar Signal Processing Algorithms

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Maximum Efficiency Tracking for Wireless Power Transfer Systems With Dynamic Coupling Coefficient Estimation

Abstract: Maximum efficiency tracking is an important issue for wireless power transfer (WPT) system. Traditional maximum efficiency tracking method normally focuses on load impedance matching with fixed coupling condition. However, WPT system is a loosely coupling system, the coupling coefficient varies due to relative movement between the primary and secondary sides. Unknown to this variation may result in failure of the tracking. In this paper, a novel maximum efficiency tracking method is proposed with integrated dynamic coupling coefficient estimation. This method can take almost all requirements for maximum efficiency tracking into account including adaption for coupling coefficient and load variation, and output controllability. The tracking method is easy to implement because no additional circuitry or measurement is required. Experimental results have verified the correctness of the proposed coupling coefficient estimation method. And the maximum efficiency tracking results show the system can achieve a good performance against coupling coefficient and load variation with the proposed tracking method.

Frequency Selective Surfaces: A Review

Abstract: The intent of this paper is to provide an overview of basic concepts, types, techniques, and experimental studies of the current state-of-the-art Frequency Selective Surfaces (FSSs). FSS is a periodic surface with identical two-dimensional arrays of elements arranged on a dielectric substrate. An incoming plane wave will either be transmitted (passband) or reflected back (stopband), completely or partially, depending on the nature of array element. This occurs when the frequency of electromagnetic (EM) wave matches with the resonant frequency of the FSS elements. Therefore, an FSS is capable of passing or blocking the EM waves of certain range of frequencies in the free space; consequently, identified as spatial filters. Nowadays, FSSs have been studied comprehensively and huge growth is perceived in the field of its designing and implementation for different practical applications at frequency ranges of microwave to optical. In this review article, we illustrate the recent researches on different categories of FSSs based on structure design, array element used, and applications. We also focus on theoretical breakthroughs with fabrication techniques, experimental verifications of design examples as well as prospects and challenges, especially in the microwave regime. We emphasize their significant performance parameters, particularly focusing on how advancement in this field could facilitate innovation in advanced electromagnetics.

Control Design for Optimizing Efficiency in Inductive Power Transfer Systems

Abstract: Inductive power transfer (IPT) converters are resonant converters that attain optimal energy efficiencies for a certain load range. To achieve maximum efficiency, it is common to cascade the IPT converter with front-side and load-side dc/dc converters. The two dc/dc converters are normally controlled cooperatively for the requirements of output regulation and maximum efficiency tracking using a control technique based on perturbation and observation, which is inevitably slow in response. In this paper, a decoupled control technique is developed. The load-side dc/dc converter is solely responsible for output regulation, while the front-side converter is responsible for impedance-matching of the IPT converter by controlling its input-to-output voltage ratio. The controls are linear and therefore fast. DC and small-signal transfer functions are derived for designing the control parameters. The performances of fast regulation and high efficiency of the IPT converter system are verified using a prototype system.