Wang-Sang Lee

Multiple band-notched planar monopole antenna for multiband wireless systems

A multiple band-notched planar monopole antenna for multiband wireless systems is presented. The proposed antenna consists of a wideband planar monopole antenna and the multiple U-shape slots, producing band-notched characteristics. In order to generate two band-notched characteristics, we propose that three U-shape slots are required. This technique is suitable for creating ultra-wideband (UWB) antenna with narrow frequency notches or for creating multiband antennas.

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.

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.

Dual-frequency antenna for HF/UHF handheld RFID reader

This paper presents a dual-frequency (HF and UHF) antenna for handheld radio frequency identification (RFID) reader to embrace the benefits offered by both the UHF and HF RFID systems. In the HF (13.56 MHz) band, a spiral-shaped loop antenna is used and placed at the outmost region of the available space. In the UHF (915 MHz) band, a quadrifilar spiral antenna (QSA) is used because it is electrically small and features a low frequency shift by platform size and is placed in the center of the HF antenna. Measurements revealed that the antenna provides a quality factor of 56.5 in the 13.56 MHz and a gain of 2.5 dBic in the 920 MHz band.

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.

A Continuous Power-Controlled Microwave Belt Drier Improving Heating Uniformity

Due to the nonuniform energy distribution in a microwave (MW) cavity, MW-based heating applications remain a substantial barrier. A continuous power-controlled MW conveyor-belt drier using multiple 2.45-GHz MW sources improves heating uniformity. By controlling the input power of MW sources sequentially, the electric field and temperature variations, hot and cold spots in the MW cavity, have been significantly reduced. Experimental results show that the MW heating using the proposed continuous power-controlled method can achieve an improved heating uniformity of approximately 34% compared with a simultaneous multiple input method (conventional mode).