[Meep-discuss] Comparing power from a far field with total power flux

[Karl-Johan Olofsson]

Hello!

I am interesting in comparing the power flux through a far field with the total radiated power from the simulated structure. However, reading the documentation it seems that the scaling of the far fields are not the same as the "close" fields. So is it even possible to look at the ratio of the power flux through a far field and the power flux through the entire structure?

My solution is the following. After the simulation is finished I calculate the Poynting-vector for each point in the far field and then perform a Riemann sum over the area to get the total flux through that far field. Then I compare that to the total power flux out from the stucture with the add.flux and get.flux function. Is this the correct way to go or am I lost? Any guidance would be greatly appreciated.


Karl-Johan

[Ardavan Oskooi]

On 09/19/2018 05:48 AM, Karl-Johan Olofsson wrote:

I am interesting in comparing the power flux through a far field with the
total radiated power from the simulated structure. However, reading the
documentation it seems that the scaling of the far fields are not the same
as the "close" fields. So is it even possible to look at the ratio of the
power flux through a far field and the power flux through the entire
structure?

My solution is the following. After the simulation is finished I calculate
the Poynting-vector for each point in the far field and then perform a
Riemann sum over the area to get the total flux through that far field.
Then I compare that to the total power flux out from the stucture with the
add.flux and get.flux function. Is this the correct way to go or am I lost?
Any guidance would be greatly appreciated.


We have an open PR to compute the Poynting flux of the far fields (
https://github.com/stevengj/meep/pull/27). However, this PR is out of date
and needs to be updated before it can be merged. In the meantime, you can
compute the Poynting flux of the fields yourself in post processing which
is straightforward (remember to do a normalization run first to compute the
incident flux). Note, in case it may be relevant, that similar to the
load_minus_flux routine which is used to compute the reflectance, there is
a load_minus_near2far routine for near2far calculations.

If you are interested in computing the power radiated in a given direction,
consider instead using the mode decomposition feature which is more
efficient for these types of calculations. For a demonstration, see this
tutorial example for planewaves:


https://meep.readthedocs.io/en/latest/Python_Tutorials/Mode_Decomposition/#diffraction-spectrum-of-a-binary-grating