Hi Lisa, You are correct. It won't be possible to link a single multiport simulation with several individual single-port source simulations. However, you can have multiple single-port "exposure" simulations, each linking to a Huygens source file (the one you exported using the Huygens Exporter, for each port). The results can be combined "manually" at post-processing, using the Field Combiner. Note that this algorithm simply does a weighted sum of its inputs, so if you want to compute SAR you have to use it on the E fields, and compute SAR on the combined E field. I can explain in more detail if any of this is unclear, feel free to ask (in that case, please provide a more comprehensive overview of what you are trying to achieve). [image: 1760077688303-2504eb52-f6e1-46b3-b283-41dde348fd7a-image.png]

to get the current density in Python you could use a script like import s4l_v1.document as document try: # add a SimulationExtractor for the simulation call "LF" simulation = document.AllSimulations["LF"] simulation_extractor = simulation.Results() # create an EmSensorExtractor em_sensor_extractor = simulation_extractor["Overall Field"] em_sensor_extractor.FrequencySettings.ExtractedFrequency = u"All" document.AllAlgorithms.Add(em_sensor_extractor) # update the pipeline, make sure current density is extracted em_sensor_extractor.Outputs["J(x,y,z,f0)"].Update() # get data current_density_field = em_sensor_extractor.Outputs["J(x,y,z,f0)"].Data except Exception as exc: import traceback traceback.print_exc()

Dear @lorenero_99, Thank you for contacting us! Please have a read to my recent comment to this post, where I tried to be very detail in explaining how the current flux normalization works and what are the limitations. https://forum.zmt.swiss/topic/733/normalization-for-precise-current-control-via-jupyter/5 For what concerns the impedance, if you use the Ohmic-Current Dominated solver, the Ohmic laws apply and you can extract the resistance (impedance) knowing the applied voltages at the electrodes and the current through them. If you need further explanations, please do not hesitate to contact us immediately! All the best, Antonino

Hi @AntoninoMC, I really appreciate this answer as it helped clear some things up for me. I understand the current extractor much better than I did before and I've realized why I may have been running into some issues. The method of using the analysis as a source also seems to be preferable. I am using the EMLF Electro Quasi-Static model for modelling transcutaneous spinal cord stim, for which precise control of the current is of absolute importance. The multiplier method seems to be the way to go for feeding into the NEURON simulation, as it means I don't have to rerun my EMLF sim. One thing I'm wondering, when I select the analysis/cache as a source, I lose the ability to use the contact impedance model in the NEURON setup. If I use a contact impedance model producer to modulate the resulting EM field from the multiplier, I lose the ability to set pulse parameters, which then seems to prevent NEURON from running a simulation. Do you know if there's a way to use the analysis connection with a multiplier AND a contact impedance model simultaneously for driving a NEURON simulation?

If I understand correctly, you would like to have one simulation with a total current of 2.47mA and another one with 1.98mA. Sim4Life EQS solvers use Dirichlet boundary conditions for the electrodes (fixed voltage) as they solve for electric potential and electrode surfaces are assumed to be equipotential, hence the flux should be able to vary to ensure an equipotential surface. Moreover, when you check “Treat as port” for the LF solvers, you should be able to see in the log that they run 1 simulation per port, by setting this port to 1V and all the rest to 0V. With only 2 electrodes, and assuming you have one anode and one cathode, I would suggest the following: Assign Dirichlet boundary conditions to the electrodes (one setting per electrode, for instance 0.5V and -0.5V). Run the simulation Extract the total current of the simulation (select the "Overall Field" and use the "Current Extractor" from the ribbon). Normalize your fields of interest by the scaling factor: desired current/total current. Visualize the output of your normalized field. I hope this helps!

Hi @Seifeldin_E I assume you’re referring to the second row, where the field is shown on the surface of the spinal cord and peripheral nerves. Here’s the simplest way to achieve this: In the Field Sensor, select Current Density. Add a Masking Filter: Set selection to None (deselect everything). Type Nerve in the search filter and activate all nerve structures. Search for the spinal cord and activate it as well. Add a Surface Viewer — this will extract the surface at the masked regions. How it works: The masking filter replaces all unselected field values with NaN (not-a-number). The surface viewer detects NaN values and extracts the surface surrounding the masked voxels. Alternative method (less robust): Drag a TriangleMesh entity (e.g., Spinal_cord) to the Analysis tab. Select Current Density and the spinal cord mesh (now in Analysis, apply the Model to Grid filter). Add the Interpolation filter. Add a Surface Viewer Be aware: if the field changes abruptly near the surface, this method may interpolate the field on the "wrong" side of the surface. That’s why the masking approach is usually more reliable and easier to use.

The RestoreCamera function has a second argument animate=True. Setting this to False should fix your issue. If you are using s4l_v1.renderer.SaveScreenCapture to save an image of the scene in your script, you might need to give the GUI a chance to refresh during script execution. On Windows, you can do this with win32gui.PumpWaitingMessages() I typically do something like this def refresh_gui() if sys.platform == "win32": import win32gui win32gui.PumpWaitingMessages() for config in all_configurations: # change the model, run a simulation, change camera settings, etc. do_something(config) refresh_gui() s4l_v1.renderer.SaveScreenCapture( width=1024, height=1024, multi_sample=True, transparent_background=True, output_folder="C\temp\screenshots" output_prefix=f"subcase_{config}" )

Hi there, I hope you can help, and that my questions fits within this thread. I have simulated an overall field and I would like to export it to matlab. At first I can live with the UI way i.e. by the import/export menu, but later I'd like to script it too. Now selecting e.g. the E-field and clicking the Imp/Export menu gives me no options but Import. Can anyone show the workflow? And/Or can anyone post a snippet of python code that does the export? Does exporting require a certain license?

Hi, sorry to bother you. Do you happen to know how to calculate the current absorbed by the electrodes and the impedance?

I ran the simulation again. This time it ran completely. Physical results the same but without any errors, i.e. the analysis section could indeed connect ports. So is there a random seed thing and a voxeling issue after all?

Please select the overall field and select the E field, then look under "Field Data Tools". Please "Go to the HTML manual" from "Help" and search for NaN filter. I would recommend using the latest version of Sim4Life v9.0. [image: 1753361215835-bc62f2dd-580a-4b6b-b11d-728454d14416-sim4life_xhh8cgbkwm.png]

Hi, Sorry to bother You. IN ATTACHED VIDEO SHOWS WHAT HAPPENS AFTER CLICKING THE OPTION "CREATE PLOT" AND THE SYSTEM CRASHES. The workstation and memory have been tested, all without errors. Can one of the service engineers help? Kind regards, Thank you, Andrei Andrei Churakov MD,PhD, Associate Professor of the Department of Electronic Engineering and Technology BSUIR E-mail: anchurakov@bsuir.by

This question is quite old. Maybe you found a solution? Otherwise I guess you could use one of these options: you can crop the field, e.g. via the bounding box (or the extent if you have an E-field on a rectilinear grid) you could use the interpolation filter: define your little box grids, and interpolate from the field sensor field to your box grids you could define small field sensors in the simulation setup (not sure it is scalable to hundreds of sensors)

Hi @parsley, Thank you for your feedback and for reporting the issue you experienced. The MATCH tool has already been successfully used/validated by many users and offers several useful features. For example, it allows users to add loading or matching circuits the S-matrix of a simulation and obtain updated scattering parameters without re‑running the full simulation. Have you experienced any problems with this particular workflow? From the information you provided, the issue appears to be related to only the Initial Matching function—the option that generates a matching circuit for a given S-matrix of a simulation at a chosen target frequency. In your case, you reported that it worked with the dipole antenna example but not with your specific antenna model. We would be happy to discuss the details so we can reproduce the problem and resolve it quickly. We will contact you to find out a convenient time to follow up. Thank you again for bringing this to our attention.

[image: 1736961843959-327c9ace-0099-4e59-b102-4a34c31e609c-sim4life_fxfwepw8sg.gif] to extract the inner normal vector to the cortical surface mask the field (set NaN outside GM) using the Mask Filter available under "Field Data Tools" in the top ribbion. add the Grey Matter Surface in the post-pro interpolate the (masked) field to the grey matter surface using the "Interpolator" which is active when the masked field and surface is selected. get the normal component via the NormalFieldEvaluator under the "Field Data Tools"