Kyoung-Sub Oh

Contactless Energy Transfer Systems Using Antiparallel Resonant Loops

Due to the convenience of using electronic devices, contactless energy transfer (CET) systems have garnered interest in various fields of industry. In this paper, a new design approach that uses antiparallel resonant loops for CET systems is presented. Forward and reverse loops forming an antiparallel resonant structure stabilize the transfer efficiency and therefore prevent it from dramatic distance-related changes, a phenomenon that can occur in CET systems with nonradiative methods (or resonant methods). This paper proposes frequency-insensitive antiparallel resonant loops and the optimal design of these loops for uniform transfer efficiency according to the distance. The proposed technique achieves frequency variation that is one-sixth that of conventional unidirectional loops, thus improving the power efficiency to a maximum of 87%. The improved performance of data transmissions for near-field communication is also verified.

Design of Low-Cost Chipless System Using Printable Chipless Tag With Electromagnetic Code

In this letter, a printable chipless tag with electromagnetic code using split ring resonators is proposed. A 4 b chipless tag that can be applied to paper/plastic-based items such as ID cards, tickets, banknotes and security documents is designed. The chipless tag generates distinct electromagnetic characteristics by various combinations of a split ring resonator. Furthermore, a reader system is proposed to digitize electromagnetic characteristics and convert chipless tag to electromagnetic code.

Switchable Distance-Based Impedance Matching Networks for a Tunable HF System

Distance-based impedance matching networks for a tunable high frequency (HF) system are presented in this paper for the improved performance. The transmitting antenna for a HF system with an operating frequency of 13.56MHz consists of a two-turn loop and three channel impedance matching networks corresponding to the distance of the receiving antenna. Each impedance matching network maximizes the system performance such as uniform power e-ciency and reading range at speciflc distance between a transmitting and a receiving antenna. By controlling the distance-based matching networks, the power e-ciency of the proposed antenna improves by up to 89% compared to the conventional antenna system with the flxed matching (FM) condition for distances, and the reliable reading range according to the impedance matching conditions is also increased. The proposed technique is applicable for near fleld communication (NFC), radio frequency identiflcation (RFID), or wireless power transfer (WPT) devices.

Distance-Insensitive Wireless Power Transfer and Near-Field Communication Using a Current-Controlled Loop With a Loaded Capacitance

Using a current-controlled loop with a loaded capacitance, we experimentally demonstrated distance-insensitive wireless power transfer (WPT) and near-field communication (NFC) without additional tuning network and algorithms. The proposed loop can achieve the uniform mutual inductance within the operating distance by controlling the ratio of the current flowing through the forward and reverse loops according to the loaded capacitance. By reducing the impedance mismatch within the operating distance ranging from 0 to 7 cm, the proposed loop can provide the transfer efficiency over approximately 60% for WPT and a stable channel bandwidth for NFC operating modes. In particular, when the receiving antenna is close proximity to the transmitting antenna, the transfer efficiency of the proposed loop is up to nearly six times higher than that of conventional loop.

Uniform magnetic field distribution of a spatially structured resonant coil for wireless power transfer

A spatially structured resonant coil with uniform magnetic field distribution for wireless power transfer is presented. The characteristics of the proposed resonant coil are verified by the theoretical analysis, simulation results, and experimental measurements. Due to the uniform magnetic field distribution, the overall transfer efficiency between the transmitting and receiving resonant coils can be improved up to 44% compared to the conventional coil regardless of the location of the receiving coil at the transfer distance.

A WIDEBAND PLANAR MONOPOLE ANTENNA ARRAY WITH CIRCULAR POLARIZED AND BAND-NOTCHED CHARACTERISTICS

A wideband circular polarized planar monopole antenna array (PMAA) that employs dual band-notched characteristics is presented in this paper. The proposed antenna array is formed by four pinwheel-shaped folded planar monopole antennas (PMAs) in order to improve the performance of circular polarization and high directivity. Also, it achieves low-proflle, small-sized structure. The attractive characteristics of the proposed PMAA are a wide impedance bandwidth of 87.3% (1GHz to 2.55GHz), the 3dB axial-ratio (AR) bandwidth of 92.3% (1.05GHz to 2.85GHz) excluding dual notch bands, the total bandwidth of 35% (1.8GHz to 2.55GHz), and the maximum gain of 8.24dBic within the total bandwidh. Moreover, in order to generate dual band-notched characteristics in a circular polarized antenna, a folded PMAA with multiple U radiators and inverted W slots is proposed.

Close Proximity Effects of Metallic Environments on the Antiparallel Resonant Coil for Near-Field Powering

This study verifies close proximity effects of metallic environments on the antiparallel resonant coil for near-field powering based on the theoretical analysis and experimental measurements. Compared to the conventional coil with a forward loop, frequency shifting of the antiparallel resonant coil which consists of forward and reverse loops with opposite-direction currents is unchanged regardless of the proximity of metallic plates. Furthermore, highly efficient near-field powering for metallic objects can be achieved with the antiparallel resonant coil because of the added magnetic field caused by the image current of the metallic plates.

Reconfigurable 1

This letter presents a reconfigurable 1 × 4 power divider operated at 2.45 GHz. The proposed circuit has four power transmission states and is designed mathematically to satisfy matching conditions for each state. The experimental results for the transmission losses for each state are 1.2 dB ~ 1.9 dB while the isolations for non-path ports are greater than 25 dB and the reflection coefficients for each power transmission state are less than -20 dB at the target frequency.

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A new balanced Doppler radar front-end architecture with Tx leakage canceller for antenna impedance variation and antenna mutual coupling is proposed. Consisting of two quadrature hybrids, two ring hybrids and 4-port feed antenna system, the proposed balanced structure achieves high transmit/receive (Tx/Rx) isolation stable to antenna impedance variation and antenna mutual coupling. The proposed 4-port feed antenna is configured by dual fed 2 × 1 patch array having 6.97 dBi and 5.65 dBi of measured Tx and Rx peak gain, respectively. In addition, the proposed architecture undergoes no power loss in both transmit and receive paths, and obtains the measured Tx/Rx isolation of more than 45 dB stable at 24 GHz regardless of the load variation. The proposed architecture that can determine the speed as low as 0.5 mm/s (0.078 Hz Doppler shift) is theoretically and experimentally analyzed for high isolation despite of antenna mismatch.

4 Power Divider With Switched Impedance Matching Circuits

This letter presents a simple and innovative method for designing and optimizing two circularly polarized printed quadrifilar antennas (PQAs). The PQAs are operated at UHF RFID (902-908 MHz) and GPS (1575 MHz) and intended for use at a portable terminal. This new antenna system comprises two PQAs concentrically arranged, but electrically isolated. Each PQA comprises four inverted-F monopoles arranged orthogonally and excited with a phase difference of 90°.