A Graphical User Interface for a Finite Difference Time Domain Simulation Tool

This paper presents an efficient graphical user interface for the finite difference time domain techniques with emphasis on electromagnetic and antenna applications. The interface is designed for Windows operating systems using combination of programming languages such as Microsoft Visual Basic, Digital Visual Fortran, and the OpenGL 3D graphics API. The interface consists of windows addressing each task in defining the device to be analyzed, the source of the electromagnetic field excitation, the required field parameters to be computed by the finite difference time domain computational engine, and the interactive visualization parameters for the field evolution during the time stepping procedure. One example of simulating a printed antenna is presented. simple to operate, and yet powerful enough to handle complex and composite structures. The development of such an interface is achieved by using a combination of programming languages such as Microsoft Visual Basic, Digital Visual Fortran, and the OpenGL 3D graphics API. The GUI consists of windows addressing each task in defining the device, the source of the electromagnetic field excitation, the required field parameters to be computed by the FDTD computational engine, and the interactive visualization parameters for the field evolution during the time stepping procedure. This FDTD-GUI is being used for the design and analysis of several types of printed antennas for personal wireless communication systems. DE VEL OPMENT INTRODUCTION The finite difference time domain (FDTD) technique [l] is commonly used in the analysis and design of antennas and microwave devices. However, this analysis procedure requires a large number of time iterations leading to a large CPU time. Furthermore, a significant amount of storage allocation for field components, to accurately solve Maxwell’s equations in the time domain, is needed. Thus a huge memory allocation is used for solving practical problems. The solutions to these issues are under continuous investigation for adapting and improving the FDTD technique in order to handle current problems with existing computer resources. However, regardless of these technical limitations in applying the FDTD to practical problems, one major difficulty when using this technique is the description of the geometrical components of the device under test in the computational domain. This task of describing the geometrical details is a very time consuming process, especially if programmed by the designer for every individual case. The optimal solution is to develop an interactive graphical user interface (CUI) that creates and displays device details and transfers geometrical information to the appropriate subroutines of the FDTD computational engine. The purpose of this paper is to address this issue of creating an efficient FDTD-GUI for Windows operating systems. The graphical interface should be 0-7803-63124/00/$10.0002000 EEE. 293 During the development process, the primary goal was to create an efficient interface that could be used quickly without limiting future development to a particular language or platform. Hence, the development ideology was to primarily concentrate on the program logic necessary for an efficient interface for creating FDTD computational domains while minimizing the time needed for addressing specific implementation details. The interface was developed using Microsoft Visual Basic and OpenGL. Choosing to use Visual Basic to create the interface allowed us to focus more on making an efficient, feature-rich interface and less on the details of creating a Windows application. Now that the program logic has been developed, we have the option of developing a subsequent version in C++, or any other language, and focusing more on issues such as optimal memory usage, graphics optimization, and other aspects of application development. Furthermore, this development ideology allows for the creation of a usable interface quickly, and, if required, allows a version for any particular platform (Unix based, Macintosh, etc.) to be easily created at a later date. The computational domain is composed of a geometrical domain, an air buffer, and an absorbing boundary condition region. The geometrical domain contains all of the objects under analysis. The visualization of the geometrical domain requires a flexible yet robust graphics engine. The OpenGL 3D graphics API provides both the flexibility and robustness needed. Furthermore, the OpenGL API is accessible from several languages and a variety of platforms. DEFINING A COMPUTATIONAL DOMAIN The main purpose of the interface is to allow the user to completely define the computational domain for a FDTD analysis. The complete definition of the computational domain is based on defining the following items: Geometrical domain parameters (number of cells, cell dimensions, units, etc.) Geometrical objects (number, composition) Material parameters (permittivity, conductivity, permeability, etc.) Sources for excitation (voltage sources, plane waves, etc.) Computational domain parameters (size of air buffer, perfectly matched layer (PML) region and loss distribution) FDTD run-time parameters (number of time steps, visualization parameters, etc.) Output parameters for FDTD engine (field, voltage, or current sampling; far field data; etc.) An example of constructing a FDTD computational domain containing a new type of meander line antenna, shown in Fig. 1, that was recently designed for personal mobile communication is described in the following section [2,3].