I was trying to simulate a dielectric slab with epsilon=4 and Miu=1 and conductivity =0. My objective is simply to get reflected and transmitted spectra following the Fresnel’s equation for normal incidence. The simulation setup is as follows,
solver: Time domain
boundary condition: along x and y open boundary, at zmax open and at zmin open(add space)
port: waveguide port 1 at Zmin (this port is in the background medium, which is normal or air) and waveguide port 2 at Zmax (on the dielectric end)
Simulation range in wavelength: 1.45 to 1.65.
Wave generating at port1 incidents at the dielectric from the normal/ air medium.
post processing: optical; calculate reflectance, transmittance, absorbance.
Result: absorbance is between 0.9 to 0.93 while reflectance and transmittance are very small.
I can‘t understand why absorbance is so high as the conductivity of the dielectric is zero.
please help me.
You haven't said how big your piece of dielectric is.
You have made a mistake - the input port does not see the air background, so you will not get the reflection coefficient you want.
Also, because the port is not infinitely wide, there will be a waveguide mode in which the signal is not at normal incidence - look up waveguide modes, they are composed of at least two waves that do not propagate in the axial direction.
Once in the dielectric, the waveguide mode is not the propagating mode, so there is an impedance mismatch with the waveguide port, which causes a reflection.
I don't get any losses though, just a mismatch.
I agree with Malcolm White Once in the dielectric, the waveguide mode is not the propagating mode, so there is an impedance mismatch with the waveguide port, which causes a reflection.
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