DukSoo Kwon

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.

An Eight-Element Compact Low-Profile Planar MIMO Antenna Using LC Resonance with High Isolation

An eight-element compact low-profile multi-input multi-output (MIMO) antenna is proposed for wireless local area network (WLAN) mobile applications. The proposed antenna consists of eight inverted-F antennas with an isolation-enhanced structure. By inserting the isolation-enhanced structure between the antenna elements, the slot and capacitor pair generates additional resonant frequency and decreases mutual coupling between the antenna elements. The overall size of the proposed antenna is only 33 mm× 33 mm, which is integrated into an area of just 0.5 λ× 0.5 λ. The proposed antenna meets 5-GHz WLAN standards with an operation bandwidth of 4.86 - 5.27 GHz and achieves an isolation of approximately 30 dB at 5 GHz. The simulated and measured results for the proposed antenna are presented and compared.

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

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.

EM/light hybrid energy harvesting with directional dipole antenna for IoT sensor

A hybrid electromagnetic (EM) and light energy harvester is proposed for autonomous IoT sensor. The hybrid energy harvester is comprised of dipole rectenna in 915MHz ISM band and flexible photovoltaic film. The photovoltaic film is integrated on metal surface at a certain distance from dipole antenna, which plays a role as a reflector. This integration has little effect on antenna performance and increase of antenna gain. A prototype of IoT sensor with proposed harvester is fabricated. The proposed hybrid energy harvester obtains DC power from both of energy sources which and can be used with IoT sensor.

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.

Polarization modulation RF power transport for sensor network

As the interest in Internet of Things (IoT) has increased, supplying power to sensor nodes and sensor actuator has emerged to a key problem. To solve the issue, an active study of activating sensor nodes by receiving power from a specific power source wirelessly has been on progress. In particular, transmitting and receiving RF power seems to be the prime power transport technique to realize the next generation internet. In order to transmit and receive power efficiently, the polarization direction of both transmit and receive antenna should be the same. Since the receive antenna of the sensor nodes may have a random polarization direction depending on its installation, the transmit antenna should be able to change its polarization for uniform operation of every sensors in a sensor network without any failure. For this need, this paper suggests a modulation technique and a transmit antenna system which can generate 4 types(vertical (90°), horizontal (0°), 45°, 135°) of linear polarization.