fdtd 3d
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fourier49@yahoo.com.tw
Hi
what kind of photonic crystal are u going to model?
Generally, there are 2 ways two model the defects of the structure
U can either create a geometry file from Matlab that generates a data file and have your fdtd code read from it
or u could simply set-up at the beginning an array containing the dielectric constant values. U can then initialise this array accordingly by placing the appropriate dielcetric constant values.
e.g If u drill your defects in an RT duroid substrate with er=2.3 then the array will be all 2.3 except for where your defects are. At the locations of your defects u insert the correct er (1=air, or smthing else if u fill them). Of course u need to know the exact geometry of ur structure.
Settmar
Don't you think using Er=2.3 is a bit low for a photonic crystal? Even though there exists a bandgap in this material, the bandgap will be very narrow at low frequency and the efficiency can be very poor. There are researchers who use Er=3.5, but they didn't call their structure a photonic crystal but a more appropriate name being the Perforated Structure. This technique is based on the evaluation of the average volume permittivity. However, if you do manage to obtain a usable bandgap with Er=2.3, that is someting I would like to hear more about. The major advantage here is that the material will be cheaper at low permittivity than say Er=10.
Best regards
Sassyboy
Hi, Sassy,
Even εr=3.5 is not enough in some cases. In oder to see the PBG effect, the key issue is not the absolute permittivity but the difference of refractive index (√εr).
1D ---> 2D ---> 3D PBG effect
-------------------------->
need higher refractive index difference
Another reason we choose εr=4, all the manufacture process are available and matured.
Best Regards,
asdfaaa
I cannot agree more on the PBG structure very dependent on the refractive index contrast. You just confirmed this once more.
I find the only barrier from using high dielectric constant material lies only in the COST of it. I recently got a quote for a Roger 6010LM approx. 4 A4 sheets big costing over USD1000. Have you any suggestion of material I could use that a bit cheaper. I am tired of simulations, I like to make the real thing!
Best regards.
Yes, I do agree with you about the high cost of high dielectric constant material, and I also want to say the processing (manufacture) cost is another issue. Using now available process is cheaper than developing new process.
Simulation of Photonic Crystal structure is not a big deal, we can keep playing games with pitch/radius, refractive index ratio. But after simulation, even you can get spectacular results, Can you fabricate the device or NOT? Si is well understood material in semiconductor industry, but the process of PBG in Silicon is still under developing. The fabrication tolerance, your design robustness are the main barrier.
As far as I know, I only got 1 paper demonstrating the PBG device, and that is the only one sucessfully showing the fabricated PBG device. If you want, I can share some interesting simulation to you.
I can not comment anything about those kind of material, if your purpose is pure research, then the price of material is not a big deal, at least you do not need large quantity, if you design purpose is for wide range appliation, for large scale production, then I dont think who can afford such kind of extremly expensive material.
Best Regards,