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Current Source

Hi,

I have a model where I need to use a current source. I created a line, and specified a FEM line port from start point to end point.

image.png.1103b2991fd98e2fa800dd383f10370b.png

Then I applied a current source to this port. Next I validated model, and CEM validated it.

image.png.88bd5b8dc88f6d33862f5f4cbee345f7.png

While solving, FEKO detects following error:

image.png.0c5c1dc3e8f2acb29f1f9534f080d366.png

How to resolve error 4730?
Why didn't CEM validate detect the error?

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JIF

Hello FieldForcer,

Your model seems to be all MoM and you used a FEM source.

How to resolve error 4730?

As the error indicates, the FEM line port and associated current source is only available with FEM. You thus have the option to either embed the line port in a FEM region (I would not recommend this for your model) or use a voltage source to emulate a current source. This is done by simply using a voltage source with a series resistor. Ensure that the resistance is much larger than the model impedance (use 1e6 maybe as a start) and then current injected into the model is I0 = (V0/(Rs + Zin)), but with Rs >> Zin, you have I0 being approximately equal to V0/Rs. Thus you can calculate what V0 you should use to inject the current. But, that assumes that you need to use a current source - is a voltage source not sufficient for you simulations? If you only have once source, you can always scale the values after the simulation in POSTFEKO.

Your current source also seems to be very long and that is not a good idea (not realistic). I would rather model the wires to shorten the current source. I would suggest that the current source be short in terms of a wavelength (maybe lambda/10).

Why didn't CEM validate detect the error?

This is probably just a missing feature / validation test. FEKO tries to test as much as possible in CEM validation, but it is not possible to test everything (not all the information is available). But, in this case, I feel all required info for the test is available and it is simply a 'bug'.

Altair Forum User

Hi JIF,

Thank you very much for replying to my post. Clearly, I can't use a current source because I am using MOM.

1. To simulate a current of 1A, should I put a voltage source of 1e6 with port impedance of 1e6?

image.png.4a31079848c7c96b6647bc272b62059f.png

2. Resistance can be added as a load. There is an option in Source/Load--->Add Load. Here I can specify Real part of Complex impedance to be 1e6 Ohms. Does this add to already specified Port impedance (Ohms) above?

image.png.492a3057ede99b956022bfeb3181cb80.png

Equivalently, I can put up a Resistor value(while Capacitor and Inductor are each zero) in Series/Parallel circuit, and it should do the same trick as Complex impedance above.

Overall which of above is a better method to simulate current source?

The port impedance does not add any resistance, you still need the load. That is a port reference impedance - we have an open issue to rename the text on the dialog.

image.png.88c6e25c666879e9b6acfcd1b970b384.png

3. If wire, where current source is specified, can be solved by FEM, while rest of model is solved by MOM, then 'Error 4730' could be resolved. Can such an approach give solution?