Seung-Tae Khang

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

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.

Wide-coverage array antenna using a dual-beam switching for UHF RFID applications

Based on a dual-beam switching, the wide-coverage array antenna with a 4 × 4 proposed matrix which generates three dual-beams is presented for the ultra high frequency (UHF) radio frequency identification (RFID) applications. The 4 × 4 proposed matrix generates the three dual-beams which can find the approximate location of a tag by covering the wide spatial coverage of 180°. The main beam directions can be controlled by selecting the appropriate input port of the proposed matrix. Due to the compact structure and very low reflection coefficient, the circular polarized square quadrifilar spiral antenna (QSA) array incorporated with the 4×4 proposed matrix has been configured. The fabricated array antenna operates at the 902-928 MHz band and produces three dual-beams at ±12°, ±39°, and ±68°.

Hemispheric coverage multi-beam switched antenna array using a 4-port feeding network for UHF RFID dead zone avoidance

For ultra-high frequency (UHF) radio frequency identification (RFID) dead zone avoidance from the viewpoint of antenna configurations and radiation characteristics, a hemispheric coverage mutli-beam switched square quadrifilar spiral antenna (QSA) array using a 4-port feeding network is presented. The proposed antenna array consists of a 2×2 circular polarized QSA array and a 4-port feeding network for multiple beams. It generates single-, dual-, and quad-beams with a hemispheric coverage by a beam switching, and its maximum beam gains and directions are 7.4 dBic and 65°, respectively. By switching multi-beams with the hemispheric coverage, the proposed 2×2 QSA array with a 4-port feeding network improves the tag identification in the dead-zone read area within the reading range.

Wide-band planar folded loop MIMO antenna with parallel stubs

The proposed antenna consists of two antenna elements with a half elliptic conductor plate, a wedge-shaped feeder, and a shorting pin on a ground. In order to have wider bandwidth, the proposed antenna has parallel stubs. The use of the stubs in the proposed antenna controls radiation loss depending on the height from the ground. To match the proposed antenna, the distance between the conductor plate and the parallel stub is analyzed. In order to find optimized bandwidth for GSM/PCS/UMTS/HSPA/LTE band 8 and 10, changes of return loss depending on parameter change are presented. Proposed planar folded loop MIMO antenna is suitable for stable and reliable MIMO performance for wireless communications.

Dual-Band Half-Elliptic Hoof Antenna With Mathieu Function for a Femto-Cell Network

The design of a half-elliptic hoof antenna for a femto-cell network in a multi-input multioutput system is proposed. The proposed half-elliptic hoof antenna incorporates half-elliptic surfaces, and has multiresonance frequencies in its TM modes. The half-elliptic design of the proposed antenna resonates with two main current paths, and the resonant frequency of each mode can be calculated using the Mathieu function. Moreover, an additional resonator is inserted between the half-elliptic patch and a ground to obtain additional resonance frequency and a wider bandwidth on the high band. The proposed antenna covers the frequency bands from 880 to 960 MHz and from 1710 to 2170 MHz for Global System for Mobile Communications (GSM)/Digital Cellular System (DCS)/Personal Communications Service (PCS)/International Mobile Telecommunications (IMT) with a peak gain of 6.8 dBi. To validate the design of the proposed antenna, the analysis of the antenna using the simulated and measured results is presented and discussed.