Mode structure inside an EMP simulator - an analysis of FDTD simulation

We have performed an analysis of the electromagnetic mode structure inside a bounded-wave EMP simulator, both with and without a test object. This has been done by the application of the singular value decomposition (SVD) method to time-domain data generated by self-consistent, three-dimensional FDTD simulations. This combination of two powerful techniques yields a wealth of information about the internal mode structure, which cannot otherwise be obtained. The TEM mode is dominant throughout the simulator length. The TM/sub 1/ mode dominates over TM/sub 2/, over most of the length. Close to the termination and to the test object, however, the TM/sub 2/ mode becomes stronger. The enhancement near the termination has been explained in terms of the induced current distribution in the resistive sheet and the resulting magnetic field in the vicinity of the termination. The 3-D distribution of instantaneous electric field amplitude near the test object provides a physical picture of this enhancement.