Chi-Jung Kuo

Wireless charging system of mobile handset using metamaterial-based cavity resonator

A metamterial-based cavity resonator using artificial magnetic conductor surfaces is presented and applied to realize a wireless charging system of mobile handset. This wireless charging system demonstrates the advantages of broad bandwidth, small size, long transmitting range, high transferring efficiency and EMI-free feature. The holistic architecture of wireless charging system for a smartphone is established to experimentally validate the usefulness of the metamaterial cavity resonator.

Wireless-Power-Transfer System Using Near-Field Capacitively Coupled Resonators

This brief presents the near-field capacitively coupled wireless charging system consisting of a transmitting dock resonator and a receiving multiband resonator. The transmitting dock resonator comprises a planar strip and a ring-shaped metal plate to deliver power to the multiple folded strips as the receiving 3-D multiband resonator at gigahertz band. The wireless charging system for a mobile handset is established to experimentally validate the application of the compact and high-efficiency capacitively coupled wireless charging system.

A novel wideband circularly polarized dual-fed slot antenna with microstrip feeding network

This study presents the design of novel dual-fed circularly polarized (CP) antenna. This antenna consists of a tapered slot, a backside metal plate and a microstrip-fed delay line phase shifter. Based on the analysis of the radiation mechanism of antenna ground plane, the edge shape is optimized as a half-circle type to enhance the bandwidth of antenna gain and CP purity. The proposed antenna possesses a wideband return loss better than 10 dB in the range of 4.18–7.57 GHz, covering the bandwidth of axial ratio lower than 3 dB from 4.25 to 6.75 GHz. The measured antenna gain is approximately 9–10.5 dBic and the radiation patterns are broadside and consistent within the CP operating bandwidth.

Coupling enhancement between monopole-type resonators using metamaterial cavity

This work presents the strong coupling of monopole-type resonators using a metamaterial cavity with artificial magnetic conductor (AMC) surfaces and metal planes. The AMC surface is constructed by an array of metal patches on a double-layered dielectric substrate backed by a metallic plane, and its reflection phase with respect to the angle and the polarization of obliquely incident plane waves are characterized by the transmission-line model. The measured transmission power is −2 dB when the resonator spacing is 0.4λ. This demonstrates that the power transfer is enhanced significantly by metamaterial cavity compared to the metal cavity and free space.

Broadband and strong coupling metamaterial-based cavity resonator using artificial magnetic surfaces

This study proposes a novel metamaterial-based cavity with a strong coupling effect between the transmitting and receiving devices. It is compact in size and the field distribution is uniform inside the cavity, which is realized by combining four artificial magnetic conductor surfaces at the four sidewalls and two metal palates at the top and bottom walls. The AMC consisting of a periodic array of square patches printed on the metal-backed double-layer dielectric substrate without connecting vias to enhance its operating bandwidth. Two monopole-type antennas are used as the transmitting and receiving terminals to examine the transmission property. The measured insertion loss of the metamaterial-based with different receiving positions are 1.06 dB, 2.26 dB, 2.02 dB, and 0.6 dB for position A, B, C, and D, respectively. The fabrication and measurement of the metamaterial-based cavity are demonstrated to validate its broad bandwidth and compact size.

Wireless powering system with backside metallic plates using electric- and magnetic-coupling mechanisms

This study proposes a novel high-efficiency wireless powering system using the electric- and magnetic-coupling mechanisms to improve the proximity effect of metal plates. The hybrid resonator consisting of the patch and coil is employed in the wireless powering system. A good agreement among the equivalent-circuit model, simulation, and measurement of the proposed wireless powering system is observed by verifying power transmission, impedance matching, resonant frequency, and eddy current distribution. The proposed wireless powering system using the electric- and magnetic-coupling mechanisms with the backside metallic plates increases the power transmission from -14.2 dB to -0.5 dB as compared to the conventional wireless powering system using the magnetic-coupling mechanism.

Printed spiral metamaterial resonators for wireless powering system with proximal metal plates

This study presents the metamaterial-like printed spiral coils (PSCs) for improving the proximity effect of metal plates in wireless power transmission. The proposed four-PSC system is experimentally and theoretically verified by power transmission, impedance matching, resonant frequency, magnetic field distribution, and induced eddy current on metal plate. Results demonstrate that the transmission of the four-PSC system is 9.2 dB higher than the conventional two-PSC system when the backside metal plates are added.

Propagation and Radiation Characteristics of Multilayer Coupled-Line Bandpass Filters Using Conductor-Backed Coplanar Transmission Lines

This paper presents the analytical design formulas for the bandpass filters which are built on the asymmetrically coupled-line conductor-backed coplanar transmission lines (CBCTLs) in multilayer configuration. The full-wave simulation is employed to characterize the far-field patterns of space-wave and surface-wave radiations as well as the frequency-dependent conductor, dielectric, and radiation losses. Good agreement among the results of full-wave simulation, transmission-line model, and measurement justifies the design procedure and validates the analytical design formulas. By properly placing the dielectric materials in multilayer configuration, a bandpass filter for minimizing the radiated power loss and improving the stopband characteristic can be achieved.

Wideband circularly polarized antenna with backside plates

In this study, a novel circularly-polarized microstrip antenna fed by microstrip line to excite wideband and circularly polarized (CP) radiation is proposed. The CP antenna consists of a tapered slot and a delay line phase shifter. The proposed antenna excited wideband return loss better than 10 dB from 4.18 to 7.57 GHz, possessing the 3 dB axial ratio bandwidth from 4.25 to 6.75 GHz, and the measured antenna gain is about 9 to 10.5 dBic with the broadside radiation pattern.

Metamaterial cavity and RF rectifier for wireless powering system

Two critical components for a wireless charging system of mobile handset, i.e. a metamaterial cavity using artificial magnetic conductor surfaces and a RF rectifier with high-power and high-effieency characteristics, are presented. This wireless charging system demonstrates the advantages of broad bandwidth, small size, long transmitting range, high transferring efficiency and EMI-free feature. To overcome the low breakdown voltage limit of silicon-based Schottky diode, the 1-to-4 series dividing transformer is employed to couple the high input RF power into four differential-type bridge diodes. The proposed rectifier is developed to withstand up to 36 dBm of input power before reaching the breakdown limint of Schottky diode, and their corresponding RF-to-DC power conversion efficiency is 58.9 % at the load resistance 10 Ω and operating frequency 920 MHz.