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Strange results with potential distribution

Posted May 31, 2018, 4:09 p.m. EDT Electromagnetics, Low-Frequency Electromagnetics 1 Reply

Jonas Schulz
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Hi,

I happen to get some weird results while computing a parametric sweep over the distance of two domain point probes from the potential excitation source. With increasing distance from the electrode (pacemaker example), the potential at the point probes increases. Unfortunately I havent been able to retrieve a proper 2D Streamline Plot as well. What I found interesting as well, was that the electric properties of the heart tissue in the comsol pacemaker example, where the properties of an almost perfect conductor.

Thank you very much for your help

Best regards

Jonas

1 Reply Last Post Jun 1, 2018, 8:05 a.m. EDT
Magnus Olsson COMSOL Employee

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Posted: 6 years ago Jun 1, 2018, 8:05 a.m. EDT
Updated: 6 years ago Jun 1, 2018, 8:06 a.m. EDT

Dear Jonas,

The conductivity value seems way too high. Thanks for poiniting it out.

I solved your model and I cannot find anything strange with the proble plots. The device defines what, at some distance away, essentially is the field of a dipole. You have one probe that is closer to the negative (ground) electrode and one that is closer to the positive electrode. When you move these radially away from the electrode body (maintaining each probe's coordinate along the dipole axis), you expect the probe values to approach each other as the total distance to the device increases. As in this model, you have not grounded the outer boundaries, the potential will approach a non zero value far away from the device so the probe starting closest to ground will show increasing potential values. The other one will show decreasing potential values.

You are probably confused as your were expecting the solution approaching zero towards infinity. You can approximate that solution by grounding the outer boundaries. If combining that with the use of infinite elements, the approximation will be even better.

Note that the absolute level for the electric potential is in general of little interest - only potential differences can be measured. If you add inductive effects to your model, even potential difference is meaningless as voltage has to be measured as a line integral of the electric field E (as E is no longer curl free and cannot be represented using the gradient of a scalar potential).

Best regards,

-------------------
Magnus
Dear Jonas, The conductivity value seems way too high. Thanks for poiniting it out. I solved your model and I cannot find anything strange with the proble plots. The device defines what, at some distance away, essentially is the field of a dipole. You have one probe that is closer to the negative (ground) electrode and one that is closer to the positive electrode. When you move these radially away from the electrode body (maintaining each probe's coordinate along the dipole axis), you expect the probe values to approach each other as the total distance to the device increases. As in this model, you have not grounded the outer boundaries, the potential will approach a non zero value far away from the device so the probe starting closest to ground will show increasing potential values. The other one will show decreasing potential values. You are probably confused as your were expecting the solution approaching zero towards infinity. You can approximate that solution by grounding the outer boundaries. If combining that with the use of infinite elements, the approximation will be even better. Note that the absolute level for the electric potential is in general of little interest - only potential differences can be measured. If you add inductive effects to your model, even potential difference is meaningless as voltage has to be measured as a line integral of the electric field E (as E is no longer curl free and cannot be represented using the gradient of a scalar potential). Best regards,

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