Hi Filip, Do you think the problem is related to the theory of PML or just a mistake in implementation in MEEP?
I tried in the meanwhile different thickness of the silver layer and in all cases there was something like a resonance that I really do not know where it comes from and I do not know how to get rid of it. I have to run the simulation for a long time so it seems that this reflection effect is inevitable. As you mentioned this phenomenon is observed only at low frequency but I need to let the field decay which means taking into consideration the low frequencies. Best, Ali On Mon, Dec 17, 2012 at 1:47 PM, Filip Dominec <[email protected]>wrote: > Hi, Ali, and all the MEEP users, > first, I believe one should not place any material into the volume > occupied by PML. However, what you report actually seems to be a much > deeper problem in the PML implementation in MEEP. I already wanted to > re-report it. > > In my simulations, I encounter similar weird transverse oscillations > in the vicinity of the PML layer quite often. A typical triggering > simulation is (any non-dispersive) structure in the center of volume, > Bloch-periodicity on the X-Y faces and PMLs on the Z face. An example > is documented e. g. at the bottom of this page: > http://fzu.cz/~dominecf/misc/meep/index.html#pml > > The oscillations have quite a low frequency, probably given by > f=(width/speed_of_light). Their Poynting vector seems to be transverse > to Z axis and they have similar axes of symmetry as the simulated > structure. They seem to build up from low-frequency numerical error, > and then grow exponentially. > > There is always a workaround in making quite a big distance between > the structure and PMLs. However, this substantially increases the > simulated volume. I already started reading some theory on PML in the > Taflove's superbible, but I would be very happy if somebody more > experienced provided their opinion on this instability! > > Filip > > 2012/12/17, Ali Naqavi <[email protected]>: > > Dear MEEP users, > > > > The structure I want to simulate using the meep c++ is so simple: a > > multilayer solar cell with a silver layer at the backside. So the > structure > > looks like this: > > > > PML > > ----------- > > Air > > ----------- > > Silicon > > ------------ > > silver > > ------------ > > PML > > > > > > > > As far as I realized, one should try not to put dispersive materials next > > to PML; otherwise the field might blow up inside PML. Do you know any > > method to get rid of this field blow up? > > > > To resolve the mentioned problem, I put a nondispersive dielectric layer > > under silver so that adjacent to the PML, I do not have silver now but a > > dielectric. Still, there is a non-negligible amount of reflection from > the > > PML. Do you know how to solve this problem? I guess it might be due to > the > > strength of PML but I do not know how to modify it in meep c++. > > > > Best, > > Ali > > > -- Ali Naqavi Institute of Microengineering EPFL | Ecole Polytechnique Fédérale de Lausanne
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