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How to calculate the reflectance and transmittance using scattering wave excitation
Posted 23 juil. 2013, 22:22 UTC−4 RF & Microwave Engineering Version 4.3b 2 Replies
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Recently I am trying to model my 3D periodic structure with COMSOL 4.3b. The periodicity of my sturctuture is 1.5um, but the incident wavelength can be as low as 400nm, so that the diffraction order is very large.
At the beginning, I try to solve it using "plasmonic wire grating" model, since it directly calculates the reflectance and transmittance. However, I found it is a nightmare to including all the diffraction orders at the port BC. Especially you need to varify the correct (m,n) combinations.
Then the comsol support team suggest me to using a scattering wave + PML to avoid the unphysical reflection at the port BC (the model is too big to unload). The field distribution now looks nice, however, I cannot calculate the reflectance or the transmittance in this model. I tried to use the power outflow from the top surface 4*intop1(emw.Poavz*nz)/P0 to calculate the reflectance, but the results >>1 seems to be wrong.
I check on the forum, and I found that I am not the only one who encounter this problem. Therefore, I would like to know if anyone know how to calculate the reflectance and transmittance using scattering wave formulation + PML.
If you need to see the detail of the model, please feel free to email me at sunsong@ihpc.a-star.edu.sg.
Million thanks
Hello Song Sun
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are you still fighting against this problem? I usually model scattering by using the scattering formulation the support suggested you and find it works nicely for calculations of reflectance, transmittance etc..
Maybe one possible problem is that you do not model properly the background field, do you set it into the model analytically? if it is not correct it is likely that you get wrong, unphysical results..
pierfrancesco
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Thank you so much for the reply.
I have solved this problem with a plane-wave excitation approach, which is a two-step method. It works well for the periodical structure. Nevertheless, I am quite interested to know how to calculate it with a scattering formulation approach.
The problem I facing is that I cannot find the correct mathematical expression to calculate the reflectance and transmittance. According to my understanding, the reflectance R = P/P0, where P0 = A*n_media* c_const*epsilon0_const*E0^2 is the input power, A is the area, n_media is the refractive index of the environment, c_const is the speed of light and epsilon0_const is the permitivity of free space, and E0 is the background electrical field in the scattering formulation. However, I cannot find the expression to calculate the reflected power P. I tried several possibilities, but the results are not right.
Therefore, I really appreciate that you can send me an simple example model , which shows me the mathematical expressions to calculate the reflectance and transmittance using scattering formulation.
Wish to hear from you soon.
Best regards
Sun Song