# Electric potential in Comsol

Ma94
Can anyone know please know how can i impose the electrode surface potential to vary lineary and periodically with time as:
E(t)= phimin+v*t for 0<=t<t0
phimax-v*(t-t0) for t0<=t<2*t0
with t0=(phimax-phimin)/v
v=scan rate in V/s

## Answers and Replies

Mentor
What exactly do you have a problem with? Is it the fact that you have different potentials to impose for different time domains? Or do you have problems imposing even a simple time-dependent potential?

It would also help if you indicated what type of study you are doing (what physics and study type you have selected in COMSOL).

Ma94
Thanks for your reply .As you said first i need to implant 2 différent potenials in the surface of an electrode for 2 different time domains .In fact the reference article that i'm using is a little bit difficult ,they said that the potential is a triangle time dependent so i will use time dependent study , for the physics i will use transport of diluted species and another one that i did'nt figure it out.

Mentor
Thanks for your reply .As you said first i need to implant 2 différent potenials in the surface of an electrode for 2 different time domains .
Sorry, but this didn't answer my question. Would you know how to do it with only one time-dependent equation?

I am just trying to gauge the level of the difficulty. Otherwise, my answer might be rather unhelpful.

In any case, to implement piecewise equations, you need to use boolean operators. For instance, to implement
$$\left\{ \begin{array}{cl} 1 & x < 0 \\ x^2 + 1 & x \ge 0 \end{array} \right.$$
you would write
Code:
1 * (x < 0) + (x^2+1) * (x >= 0)
Doing it for periodic functions can be implement using the modulo operator in the boolean expression.