How to apply current across electrodes positioned on a microfluidic channel and measure the voltage of the solution in the channel

Hi,

I am new to COMSOL. I am working on a project where i have to design a 7 electrode sensor to measure the conductivity of water.

What i am trying to do

1. I want to apply an ac current (1mA 400mV peak-to-peak) across electrodes 1 and 4
2. i want to keep the voltage at electrode 1 and 7 at the same potential to prevent current leakage.
3. I want to measurre the voltage across electrodes 2 and 3
4. The 7 electrodes are positioned on a microfluidic channel. From the measured voltage,the resistance can be calculated(using ohms law). Then the conductivity can be determined as the inverse of the resistance.

What i have done

I have attempted the simulation by using the "Electric current" and ""creeping flow" physics.I have also used "stationary" and "time dependent " studies.I have simulated the electric potential. Please find attached a screenshot of my simulation of the electrodes with an applied voltage (although i want to apply current).

What i need help with

Please can someone explain how i can apply an ac current to electrodes 1 &4 and measure the voltage across 2&3 in a channel with water?

Thank you for your help.!!