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What is the exact electric field expression when using the PORTs? - Inconsistent values
Posted 2013年1月18日 GMT-5 08:55 Low-Frequency Electromagnetics, RF & Microwave Engineering Version 4.3a 3 Replies
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In the attached 2D model, I use 'Electromagnetic Waves frequency domain' and I would like to study the light propagation inside my structure.
I would like to have a input power flow at port 1 of 100 mW/cm^2, the excitation must be a TE plane wave. My geometry is also periodic, therefore I have imposed the periodic boundary condition and used 2 periodic ports.
As you can see from the model the excitation at port one is Pin = inputPower = 100 [mW/cm^2] * Active_area, where Active_area is the active area of my device (Active_area = width * depth, however depth is just an ideal depth since this is a 2D model).
In order to have a TE polarized wave, I have defined the following 'Electric field amplitude' in port1: E0 = [ 0 0 1]. I don't understand why they call it 'Electric field amplitude', because this field seems to be a 'versor'. No matter what values you put in the z term, if you write E0 = [0 0 1e10] the calculated electric field in my structure would be the same.
SO, DO YOU KNOW WHAT IS THE EXPRESSION OF THE FIELD EXCITED BY PORT1? I cannot find it in the guide.
There is also another issue. I have placed a point probe PowerFlowPoint in the middle of port1. This point probe
probes a ‘powerFlow’ (amplitude of the Poynting vector) of 5.58355 [W/m^2] at the port 1. However at port 1 I have a Port input power of Pin = inputPower = inputPowerFlow*Active_area = 1e-6 W. The power flow corresponding to Pin is inputPower/Active_Area = 100 [mW/cm^2] = 1000 [W/m^2].
HOW WOULD YOU EXPLAIN THIS INCONSISTENCY in the values?
Thanks in advance,
Samuele
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Your result is the same because there is no incident wave in your model.
For TE polarization, equation for the plane incident wave is
E={0, 0, E0*exp(-j*k.r)}
where
k={kx,ky,0} is wavevector and r={x, y, 0} is spatial radius-vector.
Look at the fresnel_equation.mpg from Comsol RF Model Library.
Regards,
Sergei
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Regarding the point probe, you better not use it for calculating power flow. Since power is defined as W per unit area, it's hard to tell what the area of your point probe is ;)
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