A Tilted Subgrid for Two Dimensional FDTD

Although the Finite Difference Time Domain (FDTD) method is well established for addressing a wide variety problems including the characterization of antenna arrays, a long standing challenge is to reduce discretization errors whileavoiding the use of impractically large numbers of cells, particularly when the structure is large and contains regions of fine detail. One solution is to use subgrids. In most published work, Cartesian subgrids are proposed which are in the same orientation as the main grid. However there is considerable benefit to allowing for the subgrid to be tilted. In this work, a method for introducing a tilted subgrid into the 2D FDTD mesh is presented and its effectiveness, accuracy and stability is demonstrated using examples. The method is readily extendable to a full 3D implementation

How children access antiretroviral treatment at Kgapane District Hospital, Limpopo, South Africa

Background: At Kgapane Hospital, Limpopo Province, only 20% of eligible children initiated antiretroviral treatment (ART) in 2007. The aim of this study was to improve the ART programme by assessing how children were accessing ART, and to explore the factors that facilitate or obstruct this access.Method: Mixed methods were used in a descriptive study of human immunodeficiency virus (HIV)-infected children admitted to the hospital over a seven-month period and their caregivers. Children’s subsequent attendance for ART was tracked and caregivers were interviewed about factors influencing access and attendance.Results: Of 132 children initially admitted, 14 (10.6%) subsequently died and 13 (9.8%) relocated. Sixty of the remaining 105 (57.1%) returned within one month to the antiretroviral clinic, three (2.9%) attended later and 42 (40.0%) did not return at all. Quantitative data associated with poor attendance were younger age, higher CD4 count, maternal caregiver, no income and participation in the prevention of mother-to-child transmission program. Qualitative factors included a lack of money for transport, poor social support, and mothers who struggled to accept their diagnosis, had poor understanding of HIV and strong traditional beliefs. Primary care providers delayed HIV testing and referral, displayed poor attitudes, and were insufficient in number. Quantitative factors significantly associated with good attendance were prior knowledge of the child/mother’s HIV status, mother’s ART treatment and referral to the dietician.Conclusion: There are serious deficiencies in the prevention, diagnosis and treatment of HIV in children. Factors were identified to improve health services and these highlight the need for broader strategies aimed at addressing poverty, stigma and education

The analysis of reactively loaded microstrip antennas by finite difference time domain modelling

In recent years, much interest has been shown in the use of printed circuit antennas in mobile satellite and communications terminals at microwave frequencies. Although such antennas have many advantages in weight and profile size over more conventional reflector/horn configurations, they do, however, suffer from an inherently narrow bandwidth. A way of optimizing the bandwidth of such antennas by an electronic tuning technique using a loaded probe mounted within the antenna structure is examined, and the resulting far-field radiation patterns are shown. Simulation results from a 2D finite difference time domain (FDTD) model for a rectangular microstrip antenna loaded with shorting pins are given and compared to results obtained with an actual antenna. It is hoped that this work will result in a design package for the analysis of microstrip patch antenna elements

Fast rigorous impedance matrix calculations in SDM for analysis of open planar structures

Spectral Domain Method (SDM) has been chosen to develop a technique which is accurate, yet retains the interactive design tool capabilities of a simpler method. In this paper several enhancements will be presented to speed up impedance matrix calculation which must be repeated at each spot frequency in SDM. In addition, an adaptive truncation which limits the numerical integration over an infinite surface to the finite computer resources will be introduced. The location vector calculation will also be presented in this contribution to reduce the number of impedance matrix elements to be calculated. Moreover a technique which cannot completely be classified one way or other will be introduced. This enhancement reduces the number of impedance matrix elements in one dimension and hence speeds up overall numerical integration

A new route to fast accurate design tool for open planar circuit analysis

Spectral Domain Method (SDM) is one of the best known techniques for developing full-wave design tool at the operating frequency of interest. However full-wave analysis requires more computer power and takes time to yield results. The aim of this paper is to enhance SDM to make it as fast as the simpler methods. The SDM analysis requires the definition of the unknown current distribution on the metallisation of the circuit. The minimisation of the number of basis functions required is crucial to the efficiency of the technique, therefore, sub-gridding, the inclusion of a priori knowledge of current distribution by using precalculated current basis functions and re-mapping of precalculated basis function are employed in the present implementation

Reply to Justin D’Arms

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43371/1/11098_2005_Article_2319.pd