CST MICROSTRIPES has many mechanisms for exciting electromagnetic fields. These include ports, plane-waves, wire and lumped-circuit voltage and current sources, and initial-fields and initial-fluxes (used to define electric or magnetic field conditions at the start of the simulation)
All sources of excitation are low-pass filtered by the 3D-TLM simulator.
Filtering the excitation enables 3D-TLM to sample the time domain output less frequently than at every time step. This reduces the computer memory required for the output, and reduces the size of the time domain output files. The space domain output is also updated less frequently during a simulation. With filtered excitation, space domain output is usually an inexpensive request in terms of computer run time, but it does require internal memory.
The filter frequency chosen by 3D-TLM depends on a number of factors, including the simulation duration, and the mesh grading.
The filter frequency will always be equal to, or above, the maximum model frequency.
3D-TLM can excite plane waves within the whole mesh or over a region of the mesh. By default the plane wave will be excited over the whole mesh and the excitation is applied on the external boundaries. If a smaller region is defined for the plane wave, then only scattered fields will be present outside this region.
The plane wave can propagate in any direction, and have any transverse polarization direction.
A Compact Source can be used as an excitation in CST MICROSTRIPES to provide a computationally efficient equivalent model for a detailed source in a larger model. For example, a detailed printed circuit board (PCB) in a chassis can be replaced with an equivalent compact source for the PCB which eliminates the need for using a fine mesh to capture the geometric detail of the PCB. The compact source occupies the same volume as the PCB and reproduces radiation from the PCB without the need for a detailed geometric description.
The use of a Compact Source requires that the frequency sampled near field radiation on a surface surrounding the source be available (in ESF file format). This data can be obtained from measurements, other specialized analysis tools or from a detailed CST MICROSTRIPES model of the source. Care should be taken to insure that adequate frequency sampling is used in capturing the near field emissions of the source before being used to create a compact model.
Use of a compact source in large models can results in large computational savings of orders of magnitude compared to using a full detailed source model.
If the initial E field has non-zero divergence, this implies the presence of charges. If these charges are not on the surface of a metal, or electric wall, and not in a conducting medium (non-zero sigma), then they will be fixed in space, and result in an electrostatic field.
Because a static field persists for ever, it can dominate a response, and degrade the accuracy of subsequent analysis. Similarly, an initial divergent H field implies the presence of magnetic-monopoles, which will result in a magnetostatic field unless they are on the surface of a magnetic wall.
Because electromagnetic energy travels fast, it is present at any given point for only a short time (unless confined within a loss-less cavity). Thus a localized initial field will produce only a brief transient at any output point. The magnitude of this transient will be of the same order as the initial field (allowing for dispersion). However, when Fourier transformed the brevity of the transient will result in very small absolute values. This is why the values produced by the Fourier program, and shown in the space-domain (single frequency) field plots are so small. In the case of a field in a lossless cavity, the length of the response which is Fourier transformed is determined by the duration of the simulation. Thus in this case, the values produced by the Fourier module, and shown in the space-domain single frequency field plots, will be roughly proportional to the simulation duration.