SELTIQ_3DSELTIQ_3DSELTIQ_3D is for Electromagnetic modelling in the resonance region, that is, it deals with structures which have a scale of a few wavelengths. It uses a technique commonly known as `the Method of Moments' to model structures made of conductors and dielectrics. The inclusion of dielectrics is particularly important and makes this a very powerful tool since many antennas and structures include parts of dielectric, for example, printed antennas and polyrods. The method automatically provides currents on the structures from which impedance data, coupling, near and far field patterns can be generated.
SELTIQ_3D is based on the use of EFIE and CFIE formulations (see theory) to provide the solutions, but also contains a graphical user interface with its own mesh generation, mesh checking algorithms and its post-processing facilities.
A few examples are given below to show the range of structures and outputs available. Validation of calculations on structures including dielectrics can also be inspected here.
In 1982 Rao et al reported (1) a significant contribution to the solution of electromagnetic scattering in the resonance region for the time-independent electric field integral equation (EFIE). The paper developed a formulation for perfectly conducting (pec) scatterers using basis functions and a geometry description that were based on surface triangular elements and linear elements (for wires). The importance of the formulation is that it could be applied to geometries of complex shape. In a later paper, Umashankar et al (2), the same geometry description and basis functions were used in the development of the combined field integral equation (CFIE) for lossy-dielectric scatterers. The EFIE and CFIE can be readily extended to incorporate mixed pec and lossy-dielectric/magnetic material (3) and thus have been important contributions to the class of integral equation techniques commonly referred to as the moment-method (MoM).
SELTIQ_3D is a program that has been developed at the University of Wales, Swansea, and is based on the formulations reported in (1), (2) and (3). The program is based on the use of EFIE and CFIE formulations to provide the solutions but also contains a graphical user interface with its own mesh generation, mesh checking algorithms and its post-processing facilities.
The program will run on WINDOWS NT 4.0, WINDOWS 2000 and WINDOWS XP Pro
Figure 1 shows the currents on a corner reflector while Figure 2 shows the response of a corner reflector to an incident plane wave.
 FIGURE 1 Currents on a Corner Reflector |
 FIGURE 2 Response of a Corner Reflector to a Plane Wave |
Figure 3 shows the geometry of a volute antenna (a small section of a two-arm helical antenna) and Figure 4 shows the computed radiation patterns.
 FIGURE 3 Geometry of a Two-arm Volute Antenna |
 FIGURE 4 Radiation Patterns of the Volute of Figure 3 |
The wire-to-pec triangle junction in the EFIE formulation has been the subject of many papers. The established formulation, as summarized by Champagne et al (4), is not at all straightforward to programme within a general-purpose code. Several small junction problems were used to provide initial confidence in the testing of the code. A more significant test came with the application of SeltiQ_3D to a benchmark problem provided by Duffy et al (5).
The problem was that of a wire connected to opposite walls on the inside of a conducting box. In this work the results are compared for the case where there are 2 apertures in the top surface of the box, (Figure 5 ). The rod was excited by a 1 V source and connected to the walls via a 50 ohm load at each end. The results from SeltiQ_3D are shown in Figure 6 where they are compared with the measured results (5). The multiple transitions in the response are associated with the resonances of the box, which are a function of the aperture in the top surface. The good agreement observed would not be possible without a good wire-to-pec triangle model in the EFIE.
 Figure 5 Schematic of the benchmark problem provided by Duffy et al (5) |
 Figure 6 A comparison of the simulated and measured current (5) flowing through the wire at the end that is opposite the excitation. |
REFERENCES
1. Rao, S.M., Wilton, D.R., and Glisson, A.W., 1982, ‘Electromagnetic scattering by surfaces of arbitrary shape’, IEEE Trans. AP-30, 409 - 418.
2. Umashankar, K., Taflove, A. and Rao, S.M., 1986, ‘Electromagnetic scattering by arbitrary shaped 3D homogeneous lossy dielectric objects’, IEEE Trans. AP-34, 758-765.
3. Rao, S.M., Sarkar, T.K., MidyaI, P. and Djordjevic, A.R., 1991, ‘Electromagnetic radiation and scattering from finite conducting and dielectric structures: surface/surface formulation’, IEEE Trans. AP-36, 1034-1038.
4. Champagne, N.J., Johnson, W.A. and Wilton, D.R., 2002, ‘On attaching a wire to a triangulated surface’ AP. Soc. Int. Symposium Digest, 54-7.
5. Duffy, A.P., Benson, T.M. and Christopoulos, C., 1994, ‘Propagation along a wire placed inside a cavity with an aperture: A comparison of measurement and transmissionline modelling (TLM), IEEE Trans. Electromagn. Compat., Vol. 36, no. 2, 144-6.