Supported positions for MTLN `generators`

[lmdiazangulo]

If a voltage generator is located in a non-terminal position, MTLN solver is ignoring it without any warning or error message. The following behavior is proposed:

For wire or unshieldedMultiwire cables:

• current generators:

• Can be located on terminal or interior wire coordinates. If it is an interior coordinate the current source we should think where to locate it: put a current source on both nodes? just in one?
• Generators on interior coordinates need a resistance in parallel: for increasingly large R values the source behaves increasingly as a hard source. R = 0 makes no sense. Generators on interior coordinates represent the following configuration

• voltage generators:

• Can be located only on terminal wire coordinates. An error is reported if it is located in an interior point.

For shieldedMultiwire:

• current generators:

• Current generators can be defined only on terminal coordinates. On interior coordinates the behavior is not well defined. Without additional specifications it is clear which of the following configurations the genrerator should have:

• voltage generators:

• We could support voltage generators also in interior coordinates. In this case, a series resistance is mandatory. The generator represents this configuration

[Alberto-o]

Reviewing the generators, I see that nodalSources are ignored by MTLN. They should be included as well. I think that could be part of this issue.

[lmdiazangulo]

Reviewing the generators, I see that nodalSources are ignored by MTLN. They should be included as well. I think that could be part of this issue.

nodalSource is something different. It is a current density which is located at some point in space. It is not related with wires so it is fine that MTLN ignores it.

[Alberto-o]

@lmdiazangulo please let me know your opinion on this:

About soft and hard generators:

Soft generators

Soft generators are similar to those on the figure. They do not force the value of V/I on the segment, but are an additional contribution

FDTD equations are modified with extra terms:

Hard generators

Hard generators impose a value of V/I where they are defined. A hard current generator would be like this:

Effect encountered

Using a soft current generator in the center segment of transmission line (1 unshielded conductor), current propagates along the line starting from the generator. In semba/fdtd each segment with current generates an electric field which, at the next time step, modifies the current in the segment.

Example: in ngspice, a soft generator with a maximum amplitude of 1A is in the middle segment of a transmission line ended with 50 Ohm on both sides. The current on each resistor is 500 mA.

The same simulation, using the solver, yields the following result:

If the external field of the update equations is removed, the values are 500mV, as in ngspice, where the effect of the field is not existent. Is the modification of the current value due to the "autointeraction" an expected effect?