Discussion Forum

Hi, I’m trying to simulate a problem that consists of a vertical cylinder conductor, with a certain radius and length, buried into a cylinder material like soil, with conductivity equals to 0.01 S/m, relative permittivity equals to 10 and a unitary relative permeability. I want to inject a current of 1 A or apply a voltage of 1 V into the top of the rod (vertical conductor) and obtain the impedance through a frequency range. This problem has a geometry very similar to a coaxial cable, but the inner conductor is finite (3 m length and 0.00625 m radius). The external conductor has 10 m length and 6 m radius, its bottom and lateral faces are perfect electric conductors (PEC), and the dielectric medium between the inner and outer conductor has those parameters above (sigma = 0.01 S/m, epsilon_r = 10, mur = 1). If I select the electric currents (ec) physics, I can apply a surface terminal with a 1A current at the top of the rod, and a surface ground terminal at the bottom and lateral sides of the outer conductor. I can compute the simulation and obtain the terminal impedance of the port through the frequencies I desire. The main problem is that ec physics doesn’t compute the inductive parcels of the problem, because it only computes sigma and epsilon. Anyone have an idea how to compute the same problem, but considering the sigma, epsilon and mu in the Comsol? I tried other physics like magnetic field without successful. Excite the top face of the soil with a wave guide, like the feed of an antenna, doesn’t result in a very good solution for me since I tried this in another program. I have the objective module and angle impedance for my interest frequency for this problem:

frequency = 1 MHZ -> |Z| = 28.28 ohm, /_Z = 3.20º frequency = 2 MHZ -> |Z| = 28.41 ohm, /_Z = 9.60º frequency = 3 MHZ -> |Z| = 29.75 ohm, /_Z = 15.94º frequency = 4 MHZ -> |Z| = 32.23 ohm, /_Z = 20.83º frequency = 5 MHZ -> |Z| = 35.41 ohm, /_Z = 23.88º frequency = 6 MHZ -> |Z| = 38.92 ohm, /_Z = 25.48º frequency = 7 MHZ -> |Z| = 42.65 ohm, /_Z = 25.59º frequency = 8 MHZ -> |Z| = 46.81 ohm, /_Z = 24.93º frequency = 9 MHZ -> |Z| = 50.74 ohm, /_Z = 22.99º

I uploaded my model (Comsol 4.4) to facilitate to understand my question. The impedance is obtained by the Results, Derived Values, Global Evaluation, terminal impedance (ec.Z11). It seems to me a simple problem, but I just don’t know the way to make this in Comsol. The ec physics looks natural for his problem, with the terminal port, but it doesn’t compute the inductive parcels. So, the results for a few Mhz tends to be a capacitor, which is worng for the problem. Thank you for viewing my question.