Fang-Yao Kuo

REDUCTION OF PEAK SAR IN HUMAN HEAD FOR HANDSET APPLICATIONS WITH RESISTIVE SHEETS (R-CARDS)

In this paper, reduction of peak speciflc absorption rate (SAR) for handsets with monopole type antenna through R-cards is investigated. While the numerical analysis was performed using flnite integration in time domain (FIT), real measurement has been made to validate the simulation results. Both the simulation and measurement results revealed that a minimum SAR Reduction Factor (SRF) of 60% was achieved. The good agreement between the simulation and measurement results has evidenced the efiectiveness of the proposed approach for SAR reduction in human head for handset applications.

A Novel Dipole Antenna Design With an Over 100% Operational Bandwidth

A novel design of a dipole antenna with ultrawideband characteristics is presented, which uses an additional shorter dipole as a matching element whose imaginary part (or susceptance) of input admittance compensates for that of the principal dipole in the frequency band of operation. Since both dipole elements efficiently radiate energy, the proposed twin-dipole antenna exhibits a higher efficiency compared to a conventional design. The measurement results have revealed that the twin-dipole is able to achieve a bandwidth of 131% (S11 <; -10 dB) from 1.6 GHz up to 7.7 GHz, with good radiation performance and more than 75% radiation efficiency.

Convergence Study of Current Sampling Profiles for Antenna Design in the Presence of Electrically Large and Complex Platforms Using Fit-UTD Hybridization Approach

Designing antennas in the presence of electrically large and complex structures such as cars or aircrafts has become an important issue for next generation communication systems. Based on the principle of equivalence, the hybridization approach integrating FIT- UTD techniques has shown its superiority in terms of its computing e-ciency. In such approach, discrete samplings of continuous electric or magnetic fleld components resulted from low frequency (LF) sub- domain are required to be converted to the excitation current sources for the high frequency (HF) sub-domain. Thus, the overall accuracy of the calculation results will strongly depend on the similarities between the sampled and original fleld distributions with both the magnitude and phase involved. In this paper, convergence study of electric and magnetic current sampling is performed. Impact of the difierent sampling proflles on the overall accuracy is also investigated through numerical examples. Results reveal that convergence of the far-fleld radiation patterns are closely related to the sampling proflles.

Peak SAR reduction in human head for handset applications with resistive sheets (R-cards)

The rapid growth in the use of cellular phones has increased public concerns on the exposure of human head to electromagnetic radiation. The specific absorption rate (SAR) is a defined figure of merit to evaluate the power absorbed by biological tissue. For mobile phone compliance, the SAR value must not exceed the exposure limits [1, 2]. For example, the SAR limit specified in IEEE C95.1:1999 is 1.6 W/kg in a 1g averaging mass while that specified in ICNIRP guidelines is 2 W/kg in a 10g averaging mass [3]. In general, the SAR value is influenced by various parameters such as antenna positions relative to the human body, radiation patterns of the antenna, radiated power, and antenna types. Over the years, lots of attentions have been paid to the analysis of SAR in human head due to the complexity and large scale involved in such kind of problems. Recently research efforts have been devoted to the reduction of peak SAR in human head for handset applications. A ferrite sheet was adopted as protection attachment between the antenna and the head. A reduction over 13% for the spatial peak SAR over 1g averaging was achieved. Experimental study on the effects of attaching conductive materials for SAR reduction was presented. It was concluded that the position of shielding played an important role in the reduction effectiveness. With proper design and arrangement, stop bands at desired cellular frequencies could be obtained to notch out the radiated power. Highly directive antennas were also utilized for SAR reduction.

Aperture-coupled patch array antenna for microwave band RFID handheld reader applications

Radio frequency identification (RFID) is rapidly developing technology which is widely adopted for various data collection applications such as warehouse and retail item management [1]. Currently, several frequency bands have been assigned to RFID applications, such as 125 kHz, 13.56 MHz, 840~960 MHz, 2.45GHz, and 5.8 GHz. The Microwave RFID band 2.45 GHz is allocated around the frequency range from 2.4GHz to 2.4835 GHz. Compared to the UHF RFID systems around 900 MHz, the 2.45 GHz systems have the advantages of compactness, flexibility, and maneuverability for the item management applications. Different from antenna designs for fixed reader, the antenna design in an RFID handheld reader should fulfill several unique requirements, such as high gain, high front-to-back ratio, and asymmetric radiation beamwidth on two orthogonal cut planes.

Convergence analysis of current sampling profiles for antenna design in the presence of electrically large and complex platforms

Designing antennas in the presence of electrically large and complex structures such as cars or aircrafts has become an important issue for next generation communication systems. Based on the principle of equivalence, the hybridization approach which integrates the high frequency (HF) and low frequency (LF) techniques is adopted to perform the design task. In this paper, the convergence analysis of electric and magnetic current sampling is performed. Impact of the different sampling profiles on the overall accuracy and computation effort is also investigated through numerical examples.

Novel ultra wideband antenna featuring over 100% bandwidth

Novel antenna structure consisting of two mutually orthogonal dipole antennas of different frequencies is proposed in this paper. With proper choice of the lengths of the two corresponding dipoles, the antenna was proven to cover a frequency band of operation from 1.6GHz to 7.7GHz, corresponding to 131% bandwidth. Moreover, the measured total efficiency was better than 75% across the band with reasonable gain.

Wave propagation in general bi-isotropic media

Wave propagation in general bi-isotropic (BI) material is presented in this paper. Starting from the general Maxwells equations in vector form, vector decomposition of the fields into directions parallel and perpendicular to the propagation direction leads to the scalarization of Maxwells equations. The defined input-output relations then convert the field quantities into their circuit counterparts. A new equivalent circuit model of a piece of transmission line sections consisting of generators is proposed. Numerical analysis revealed that the bi-isotropy from the material makes mode conversion possible with single BI layer.