Roger Yew-Siow Tay

Dipole configurations with strongly improved radiation efficiency for hand-held transceivers

In this paper the design criteria for antenna structures with improved radiation efficiency while operating in close vicinity to a biological scatterer are investigated. The study is performed using a simple /spl lambda//2 dipole combined with a directive or reflective element. The optimization criteria are the effective radiation efficiency, the spatial peak specific absorption rate (SAR), and the sensitivity of the input resistance to the distance from the scatterer. It is demonstrated that the primary design criterion to improve the radiation efficiency is not directivity but the reduction of the maximum incident magnetic field strength in the exposed skin area of the users head. For the reflectively coupled dipole, all performance parameters are improved by several decibels compared to a standard, /spl lambda//2 dipole, whereas for some other directive structures, the performance is impaired. The study is conducted with the generalized multipole technique (GMT) numerical simulation method, the results of which are validated by measurement methods.

Suitability of FDTD-based TCAD tools RF design of mobile phones

This paper discusses the general suitability and possible limitations of an enhanced finite-difference time-domain (FDTD) simulation environment for straightforward and efficient RF design of complex transmitters. The study was conducted using a current commercially available multi-band mobile phone. Simulations were conducted in free space and with various dielectric loads, whereby different parameters were evaluated such as impedance, efficiency, far-field as well as near-field distributions of e-fields and h-fields, and the specific absorption rate (SAR). The results were compared to measurements. In addition, mechanical-design issues that showed a significant influence on the electromagnetic (EM) field behavior could be predicted by simulations and were experimentally reproduced. The accurate prediction of all essential performance parameters obtained by straightforward simulations suggests that appropriately enhanced software packages are suitable for device design in industrial research and development environments with few limitations, provided flexible graphical user interfaces (GUIs) and graded meshes combined with local grid-refinement schemes are available.

Estimation of the average power density in the vicinity of cellular base-station collinear array antennas

This paper investigates the character of the average power density in the close proximity of base-station antennas, where human exposure to electromagnetic fields radiated from such radiofrequency (RF) sources is the highest. The concept of average power density is used since, in proximity of a large array antenna, the direction of the power flow at a given point is not readily predictable because of the substantially diverging path lengths and direction of propagation of the energy arriving from different array elements. This quantity Is shown to have a marked cylindrical decay near the antennas, which converts to spherical in the far field. On this basis, a set of simple prediction formulas is derived to allow the estimation of the average power density with good precision. The latest IEEE C95.1-1999 Standard for RF safety calls for spatially averaged measurements of incident power density to verify compliance to maximum permissible exposure limits. The advantage of using the concept of average power density and the resulting prediction formulas is that the evaluation of the exposure of humans near cellular base-station antennas becomes extremely simple during surveys when large computerized scanning equipment may not be available.

An efficient RF exposure system with precise whole-body average SAR determination for in vivo animal studies at 900 MHz

A radial electromagnetic cavity has been designed and optimized for the in vivo whole-body exposure of mice to 900-MHz RF fields. Parallel circular plates shorted around the perimeter form the cavity, which is fed at the center in order to excite a cylindrical TEM wave. Plastic housings allow the insertion and equidistant positioning from the exciter of 40 mice, with the electric field parallel to the body axis. The resulting exposure system is highly efficient, featuring more than 80% of the incident power dissipated in the mice. The whole-body average SAR can be determined with remarkable precision by means of straightforward power balance since the RF power leakage from the cavity is extremely low. Fairly uniform exposure of the mice, individually and collectively, has been achieved by means of the symmetric arrangement. This exposure system has been adopted in a replication study on transgenic mice currently being carried out in South Australia, and is being considered for upcoming animal studies in Europe.

Reliable prediction of mobile phone performance for realistic in-use conditions using the FDTD method

The objective of this study was to analyze whether advanced simulation platforms provide the effectiveness, accuracy, reliability, and efficiency to predict impairment of mobile-phone RF performance under various usage patterns. The investigation was based on the mechanical CAD data of a commercial phone with two alternative antennas. Three significant hand positions were modeled and evaluated with the device against the SAM head. The results demonstrated high reliability and suitability for providing decision rationale for the design of complex high-end multi-band mobile phones.

Reliable prediction of mobile phone performance for different daily usage patterns using the FDTD method

The objective of this study was to evaluate whether the performance of mobile phones can be reliably predicted by numerical methods. It has previously been demonstrated [1, 3] that performance can be accurately assessed for standardized testing positions at the head. In this study, the requirements were extended to actual usage patterns such as different positions at the head and especially for different ways of holding the phone with the hand. The latter is of particular importance because fingers placed at certain locations could strongly affect the antenna.

Reliable Prediction of MTE Performance Under Real Usage Conditions Using FDTD

This study discusses the suitability of numerical methods as robust analysis and prediction tools regarding the RF performance of CAD derived mobile telecommunications equipment (MTE) such as mobile phones. The investigation was conducted using one of the latest commercial quad-band mobile phones and in addition included head and different hand models targeting a detailed assessment of in-use situations. In particular, the effect of the users hand position on the antenna performance was given a special focus. In the simulation different parameters were evaluated such as impedance, efficiency, far-field, as well as EM near-field distributions. The results are compared to measurements obtained with the latest tools available. The resulting reliable prediction for various daily usage configurations demonstrate the usability of numerical methods in the early design phase of devices such as complex high-end multi-band mobile phones