Discussion Forum

I created a 2D geometry in COMSOL. In this geometry I have a microchannel with a set of parallel electrodes and media in between them (with its own permittivity and conductivity). 1 Volts is being applied to the bottom electrode (using Terminal under AC/DC electric currents) and the top electrode in the channel is ground.

Considering that in between the electrodes, I want to find the impedance/admittance, If I model the impedance between the plates, I have a resistor in parallel with a capacitor, and therefore =>

I/V = 1/R +jwC (easier to define it this way)

From which, theoretically, the resistor and capacitor are calculated using R=L/sigmaA and C=epsilonA/d

Now based on this, I want to do a sanity check on COMSOL to see that the inverse of the real part of I/V gives me the same Resistor as in theory and the imaginary part of I/V divided by omega(w) also gives me a value for the Capacitor as same as the mathematically calculated capacitor. Yet I am a bit confused on how to define the current in I/V. I have tried defining the current density and surface charge density on the bottom plate, or there is a part in COMSOL that a terminal current is defined automatically, but I won't get the same results as in theory and I know there might be something wrong with the way I am defining the current here. I don't completely understand the definition of displacement current and how it is going to be related in this problem. If I do a line integration (2D) over the bottom electrode does it make sense? and do I have to consider any charges in the top electrode? and I was wondering, how is the current defined in such problems.