High-Accuracy Analysis of Surges on a Slanting Conductor and a Cylindrical Conductor by an FDTD Method

A finite-difference time-domain (FDTD) method has become popular in analyzing surge phenomena as well as transient electromagnetic fields because of its high flexibility and straightforwardness. One of the representative limitations of the FDTD method in Cartesian coordinate system is the use of staircase approximation to deal with curved surfaces and slanting thin wires, which are tilted with respect to the coordinate axes. In analyzing a conductor system including curved surfaces, the accuracy may be maintained if the conductor system and its surrounding space are divided into very small cells. It, however, requires long computation time and large memories. The staircase approximation of a slanting wire results in an artificially slowed propagation speed and a lowered resonance frequency. This flaw is inherent in the staircase approximation. In the present paper, surges on a slanting wire and on a cylindrical conductor have been analyzed by the FDTD method with non-rectangular cells, the shapes of which are suitable to fit the curved surface and the slanting conductor. An absorbing boundary condition for the FDTD method using non-rectangular cells has been discussed and the numerical stability has been tested. Also, the accuracy has been investigated in comparison with an analysis based on the method of moments.