# Radiative power calculaton for plasmonic structure

Hi,

I am working on a problem related to fluorescence enhancement in presence of plasmonic antenna kept at the top of my geometry.
I have used two techniques to calculate radiative power for my structure:

1. Using open transmission box aroung the antenna only (and not the structure).
2. farfield integrate script command to calculate the Poynting vector in the far field and integrate the power over a given solid angle. We then normalize to the original source power.

I am getting different results for Power(radiative) for both these approaches. Which one should I use for my case?
How to calculate sourcepower for a dipole placed inside a dielectric medium for the second method?

Hello @loqm,

To calculate the total power radiated by the dipole the first approach you mentioned should be used. This sounds similar to the method used in this example:

Generally, two methods can be used to determine the power radiated by a dipole: The dipolepower command and a transmission box. From the “Important model settings” section of the example above:

To calculate the power emitted into a given solid angle, the farfield results can be normalized with respect to the integral over the entire sphere to get the fraction of the total power that is emitted into the solid angle. This result can then by multiplied by the total power emitted by the dipole. which can be found using the two methods I mentioned above.

I hope this helps. Let me know if you have any questions.

Hi,
Thank you for your response. But I am still confused. On your page

Two methods have been given to normalize the power integrals. When we calculate the Poynting vector in the far field and integrate the power over a given solid angle, then how do we calculate the sourcepower to normalize the power obatined. Please refer the attached simulation file for your reference. A comment upon the position of “farfield” monitor in geometry would be appreciated.
As in should the monitor used for calculating the integrated power in farfield should be entirely above the structure (at what distance?) or should it be present at the center of the antenna?
antenna.fsp (7.1 MB)

Hello @loqm,

This can be obtained using the sourcepower script command (or dipolepower, if a dipole source is used).

The monitor should be close to the scattering structure, but not inside. The monitors you placed at 10 nm away from the antenna should work for the far field calculation in your simulation.

I have tried to calculate power int the farfiled using both Method 1 and 2 as listed on the page "Integrating power in far field projections.
If I am using sourcepower function in 2nd method then my answer matches with the 1st method but with dipolepower function, 2nd method gives very different result.
I have attached my simulation file above, can you please have a look and comment?