Negative power


Hello, I’m using a diffracting plane wave surrounded by four monitors, inside a small space in the FDTD. On the left and behind the propagation direction I see that the power is negative. I set the simulation time so that no reflection from the FDTD boundaries can reach the monitors from the outside. I don’t understand why the power on the monitors is negative.



A negative value of power is nothing wrong.
I refere you to this piece of information:

I hope this will help you.


Hi @jessica
The direction of propagation determines the the sign of the transmission. Let’s consider that, the power is flowing through the monitor in the negative direction. As a result, the transmission gets negative.


Thank you for your reply.
So summarizing the normal vector of the monitors is always pointing in the up or right direction, that clarifies a lot.