Kittisak Phaebua

Study of a repeater Tx antenna concept of a portable device wireless battery charging system

A Study of a repeater concept of a transmitting antenna (Tx) for wireless battery charging system of a portable devices is reported in this paper. The objective is to extend the charging area by using the repeater coil concept. The repeater coil is located near the Tx active coil in the same plane of Tx active coil without any direct connection from a source. The operating frequency at 6.78MHz is chosen by following the frequency A4WP wireless battery charging system specification. The proposed Tx antenna is designed for extending a charging distance of the portable devices on xy-plane (such as on table) using a repeater coil (called Rp). The charging area of the proposed antenna is larger than a conventional single Tx antenna. The repeater coil is the same size of the single Tx antenna. The single Tx antenna transfers the magnetic energy to the repeater coil. The receiving antenna (small coil) in a mobile phone picks up the magnetic energy from the repeater coil. The suitable separating distance between the single Tx coil and the repeater coil will be investigated. The study is performed by analyzing the power transfer efficiency of the proposed antennas via scattering parameters [S-parameters] and of the two port network representation. The 50 Ohms system impedance is chosen in this study. The optimum impedance matching at the Tx and Rx sides are considered. It is found that the charging area is increased by using the proposed repeater coil antenna.

Area extension of a wireless battery charging system using multiple power repeater coil antennas

Multiple power repeater coil antennas for coverage area extension of a wireless battery charging system are presented in this paper. The low-profile repeater coil is simply constructed using a copper wire and a capacitor. The transmitter resonant coil (Tx), the repeater resonant coils (Rp) and the receiving resonant coil (Rx) are arranged in a planar configuration. Experiment results with two Rp coils are presented to demonstrate the charging range extension. The power transfer efficiency is investigated by the analysis of the scattering parameters of the system as a two-port network with a reference impedance of 50 Ohm. The operating frequency is chosen at 6.78 MHz according to the A4WP wireless battery charging standard. As the power source, a 10 Watt class-E RF generator circuit was used. The load coil which absorbs the energy via magnetic coupling from the Rx resonant coil is connected to a converter circuit which provides 5V constant DC voltage for battery charging of portable devices. The optimum impedance matching is considered for all coupling stages by optimizing the distance between the resonant coils. It is found that the charging area in the horizontal plane can be extended with the proposed multiple Rp coil antennas.

Modified UTD-based UHF RFID tag antenna with two-pronged fork slot for coated metallic cylindrical surface

Abstract This research has proposed a modified uniform geometrical theory of diffraction (UTD) for radiation to investigate the radiation pattern on the coated metallic curved surface. The modified UTD, which accounts for the existence of the impedance surface (coating), is applied to the development of a compact UHF RFID passive tag antenna with a two-pronged fork slot to be mounted on the coated metallic cylindrical drum. In the calculation, the UHF RFID tag was initially represented by electric tangential (Ez-source) and equivalent magnetic tangential to the surface (Mz-source). The results indicated that the Mz-source could achieve a greater communication area, and thus the design of the tag antenna is of equivalent magnetic source. Simulations were then carried out to determine the optimal antenna parameters, and an antenna prototype was fabricated and tested. The simulation and measured results are in agreement. The research findings validate the effectiveness of the modified UTD-based UHF RFID tag for application on the coated metallic curved surface.

Design of a low cost and simple wireless battery charging by using repeater antenna technique

A design of a wireless battery charging (WBC) system for a mobile phone device is reported in this paper. The objective of this design is low cost and low complexity of the electronic circuit and antenna system. The E-class power oscillator is chosen because of low complexity and high power efficiency. The Class-E power amplifier integrated with RC clock crystal oscillator is employed. Transmitting coil antennas consist of a resonator coil and feeding coil. The resonator coil receives an electromagnetic energy from feeding coil without any direct connection from a source. The receiving coil antenna is located inside the body of portable devices. It is also interested to design a repeater antenna to extend the distance of charging system. It is found that by using repeater antenna technique the charging distance can be increased.

Analysis of electromagnetic wave radiation from C-slot RFID tag mounted on impedance curved surface using the UTD solution

The electromagnetic (EM) wave radiation of the C-slot radio frequency identification (RFID) tag located on the impedance surface in this paper is analyzed using the uniform geometrical theory of diffraction (UTD) solution. The UTD radiation solution for the impedance curved surface is employed to predict the EM wave radiation of the RFID tag mounted on the impedance curved product surface. The UTD radiation solution provides the physical insight of the EM field at the observation point and requires less computational time than the other numerical methods. The results show that the UTD radiation solution can accurately predict the radiation pattern of the proposed C-slot RFID tag mounted on the product. The proposed tag antenna can efficiently be applied to the curved surface object, such as the curved metallic product coated with dielectric (layers of paints).