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Light reflectivity and transmitivity of periodic surface structures

May 29, 2015, 9:15 pm
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Hello,
I am trying to simulate the reflectivity and transmitivity of different wavelengths of light on a periodic surface structure.

1) I am using a 2D simulation using the RF module to create a basic cell with two media air and silicon and am trying to repeat it for the entire structure (periodic condition on side walls). I plan to have a electromagnetic wave incident on it (first TE and TM then average it out).

2) I plan to input the refractive index of silicon for different wavelenghts and use this for the simulation over the entire wavelenght range using a parametric sweep. Refractive index is the only material property I have specified.

3) I have used two ports, one for the input of a plane wave (and reflectivity) and one after the silicon side to find the transmitivity.

Is this right approach? I am unable to get reliable results as the values of R and T are fluctuating rapidly (between 0 and 1) over the wavelenght range. Could someone please throw some light on the above problem. I have attached images of the geometry and my results below.

Thank you.
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Mie scattering of core shell dielectric structure

May 31, 2015, 7:45 am
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I am simulating mie scattering from a dielectric core shell structure. I am using the similar principle which has been given in the model file " Scattering by gold nanosphere". But, my solution is shooting to infinity. I have a 3um silica bead (RI 1.46)covered by 500nm coating of RI 2.8. I using a x directed plane wave which is z polarized and solving one quarter of the sphere using PMC for y=0 plane and PEC for z=0 plane. Comsol shows " Inf or NaN found". I could not resolve this issue. Please help me out in this case.
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thickness problem in resonance cavity simulation

June 1, 2015, 7:14 am
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I want to simulate resonance cavity to know resonance frequency and Quality factor of the cavity. I found resonance cavity model in model library. It works well. So I move to the next step. To simulate real cavity I made, I adjust thickness to the simple cylindrical cavity. resonance frequency looks still reasonable, but quality factor looks insane. May the problem come from the Impedance boundary condition. There are conduction wall, so field cannot pass through however in outer boundary of conducting wall, Impedance boundary condition applied one more time. Comsol shows really small energy losses. Or, method for calculate Qfactor was wrong.

Are there any way to simulate resonance cavity which have thickness?
Or other way to solve my problem?
Help me please.. I stuck in this problem longer than 1 month...

here is link of my test file
drive.google.com/open?id=0BwLA...TnpFcmEwUVZrc3M&authuser=0
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A robust model for Perfectly Conducting Sphere

June 2, 2015, 6:58 am
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Hi all,

I'm a Master student which is studying mid-IR, far-IR performance of metal nanoantennas.

Gold, for example, has a relative permittivity which is around -3000 -1000 i in mid-IR

So, a very first step would be to recover the analytical Mie solution of the perfectly conducting sphere. This model is solved in one of the examples, but I find this model very tricky, because if you choose the field in another point -at one of the final steps- you are unable to recover the result. See image.png to see what happens when you choose another point rotated 90º, blue is correct, green is choosing the other point -It's even worse if you rotate 180º -. And that's only one of the problems, for example, the model I want to study lacks of rotational simmetry and so on.

So, when I make a model, either I use Impedance Boundary Conditions (with very negative epsilons), Perfect Electric Conductor or a volume with very negative epsilons, the final solucion always resemble something like scatteringIII.png.

It doesn't go to 1 -as it should- and the peaks and minimum are not as deep. I think that I tried everything but nothing works.

The Sccatering is measured using

emw.relPoavx*nx+emw.relPoavy*ny+emw.relPoavz*nz

around the sphere, on the antenna, little far from the antenna and very far of the antenna.

The las image is meshing.png, using epsilon from -10000 to -10e6 i'm trying to recover Mie Scattering
I thick is good enough, with lambda/5 in the exterior space, 5 layers of PML and 8 nm resolution on the sphere and 15 layers in 2 nm.

Have you recovered perfectly conducting sphere Mie Scattering in a robust way or it is imposible?




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Microstrip Modeling, lumped port problem

June 2, 2015, 7:04 am
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Hello,

I am a new COMSOL user. I am trying to model a grounded 3D microstrip. To study its s11, s12, ... parameters, I need to use ports to excite the microstrip. I used uniform lumped ports at each end of the microstrip. The microstrip is made of copper and i put a transition boundary condition on the face in contact with the dielectric material underneath it. the ground is represented by a perfect electric conductor on the opposed face of the dielectric.
Still, COMSOL doesn't want to do the study as "the uniform lumped port must be between 2 conductive boundaries"
Why ?

Thank you
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Electric field propagation through circular waveguide

June 3, 2015, 6:55 am
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Hi everyone,

I have simulated a straight circular waveguide piece of 19mm diameter for TE01 mode. I have observed that Er and Ez components are zero...Only propagation through Ephi Component along length..What is the reason behind it?
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Normalization in 2d "Mode Analysis"

June 3, 2015, 10:00 am
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Hi!

I'm working on a plasmonic waveguide simulation in Comsol using 2d Mode Analysis to find the supported modes of the structure. I have a quite basic question:

How is the power flowing into the structure defined? For a port in 3d I can define a power, which is (probably) the total power flowing into the structure through the area of the port. For 2d no definition of a excitation boundary condition is needed. I'm just wondering because I need to compare different layouts in absolute field strength and I need to know whether the values have a normalized or somehow arbitrary scale.

Correct me if some of the above assumptions are wrong.

Best,
Julian
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Applying bias electric field in RF module

June 3, 2015, 3:00 pm
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Hello,

I need to apply bias DC field on some material in my simulation.
My simulation is running using Rf module. How can I combine this function in my simulation?
I tried to add manually to the field component through the equation view, but I am not sure its the correct way to do it.

What is the right way?

Thanks,
Elad.
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probleme to start a study with electromagnetic waves, frequency domaines

June 4, 2015, 7:06 am
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When i try ta start a study; i have a error message:"No avaible periodic port. please select a wave vector choose by the user for a Floquet periodicity". But in my study, i don't need to use a periodic condition an d when a other person, a colleague, that's work on his comsol version ( same one 5.0 but not take by the same licence).

Can you help me, please?



PS: pleasure to join your community
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Scattering by nanorods

June 8, 2015, 3:38 am
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Hi,

I am calculating far field pattern of nanorods with near field dipole excitation. Unfortunately, my far field pattern is coming out to be same for both normal dipole and after scattering by the nanorod.
I have one 'physics' node, which calculates the field for dipole source placed in air and I use this field as background for scattering calculations by the nanorod. I have placed far field monitors in both the node ( background and scattering) and I get the same pattern ( no change at all). I have tried with other architectures as well and the result is same. Please let me know, is there any problem with the post processing or in the development of the model etc.


Adarsha
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parametric sweep to trace a particular solution?

June 10, 2015, 6:22 am
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I am trying to trace a particular eigenmode of a structure (e.g. a waveguide) whilst changing some parameter (e.g. wavelength, or the dimensions of the waveguide). I am using "Mode Analysis" study. Parametric sweep can do this, but there is a problem here: the structure generally supports several modes, and sometimes the corresponding eigenvalues (propagation constants) can be densely packed. if I ask Comsol to find just one particular mode, in the parametric sweep Comsol can randomly switch to any other mode. If I ask it to find a certain number of modes, it may trace the desired mode eventually, however the order of output modes can again change randomly. Basically, each time after the parametric sweep I need to check manually profiles of different modes to figure out which is the one I need and try to trace it.

I was wondering if there is a smarter way to do it? If, for instance, I use Livelink for Matlab, at each step of the parametric sweep I can update the trial eigenvalue (i.e. "Search for mode around.." field in the study options). This still does not help, however. Ideally, I need to feed each time not only the eigenvalue, but also the eigenvector from the previous step. I found some study options like "Initial values of variables solved for"... but I am not sure if this is what I need and how to use it properly.

Any advise would be highly appreciated!

PS I am using the "Wave optics" module, for some reason the corresponding tag is missing here. But RF module is similar anyway
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Calculation of radiation rate

June 11, 2015, 10:30 am
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Hi,

I just wanted to calculate the radiation rate ( Purcell enhancement ) from a dipole source placed near a metallic nanoantenna. Could anybody please help me, how to calculate the radiation rate?
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Pulsed Radiofrequency

June 11, 2015, 4:20 pm
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I'm studying pulsed radiofrequency ablations and I've seen a couple of COMSOL tutorials on the subject.

I tried remaking this tutorial and it worked properly.
www.comsol.com/video/video-373

However, the ablation is going through a continuous source and not a pulsed radiofrequency source.
I'm new to COMSOL and I'm wondering how to make a pulsing RF generator?

The frequency would be 500 kHz and the pulse lasts 20 msec. There are two pulses every second. So there would be one 20 msec pulse, 480 msec of nothing applied, another 20 msec pulse, and another 480 msec of nothing applied and the cycle starts over on the next second.

The study I would be doing is testing the change in temperature of the surrounding tissue when heat is transferred from the RF source.


If anyone knows how to simulate this, that'd be great!
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FBAR Temperature effects

June 12, 2015, 10:13 am
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Hi everyone, I am recently working on FBAR simulation and in this I want to include the temperature as a variable and the effects of it on the FBAR. Anyone please tell me..
Thank you
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What will you present at the COMSOL Conference 2015?

June 15, 2015, 1:34 pm
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Hello fellow simulation enthusiasts,

As we are nearing the early abstract submission deadline for the COMSOL Conference 2015 (Boston and Grenoble), the anticipation is building up.

What are you all working on? Are you considering an oral presentation, poster, or both? Will you be ready to submit your abstract by June 19th to save on your registration fee?

Fill us in on your progress by replying to this thread – we want to hear how it's going and help you along the way.

Best regards,
Jennifer

Program Chair, COMSOL Conference 2015 Boston

P.S. Ready to submit your abstract? Visit www.comsol.com/conference2015/call-for-papers
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Port boundary condition: what's relation between "port input power" and "E field amplitude"?

April 14, 2015, 9:28 am
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The port boundary condition is quite useful for exciting the model with an EM wave. However, the description of the port boundary condition's "Port Mode Settings - User Defined" in "RF Module: User's Guide" is quite unclear:

"The mode field can be entered with an arbitrary amplitude and is normalized internally."

Which means, no matter what value I use in the "Port Mode Settings - Input quantity (e.g. Magnetic field) - Magnetic mode field H0", COMSOL will only adopt the direction of the H0 value but normalize its amplitude with other parameters (am I right?). But what's the detail of the normalization?

Fortunately, I found a blog discussing it a little bit:
srdjancomsol.weebly.com/port-boundary-condition-2d.html
srdjancomsol.weebly.com/setting-excitation-in-3d.html
According to the author, for a 3D case, we will have
P=0.5*n*IEI^2*S*cos(θ)/η0
where P is the port input power, |E| is the amplitude of the electric field, S is the area of the port, η0=sqrt(μ0/ε0), and according to my guess, n may be the refractive index, and θ may be the port phase θin.

However, still, the relation between the Pin and E field amplitude is not clear. I realize a very simple 3D example to explore this relation: there is only one block, the top is a port, and 4 walls are perfect electric conductor and perfect magnetic conductor as we know the electric field will be perpendicular to two walls and the magnetic field will be perpendicular to other two walls. By changing the area of the port, I get different |E|, but the problem is, I can't obtain the relation P=0.5*n*IEI^2*S*cos(θ)/η0:

With Pin=1[W], θin=0[rad], H0=(0 1000 0),

width(=depth) [um] Port area [um^2] E [V/m]
0.1 0.01 8.0e6
0.2 0.04 2.0e6
0.3 0.09 1.1e6
0.4 0.16 8.5e5
0.5 0.25 6.7e5
0.6 0.36 5.4e5
0.7 0.49 4.4e5

Can anyone help me? Thank you!
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Setting up plane wave

June 17, 2015, 3:16 pm
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Hi, I am quite new to comsol. My problem is fairly simple. I want to simulate an incident plane wave in 2D using RF module and calculate Fresnel Reflection and Transmission coefficients.
However, I am not sure to setup a plane wave travelling in x-direction. I used exp(-i*k*x) in port settings and chose E-field as input.
I have used a rectangular geometry and setup a port. But I am getting a Gaussian wave rather than a plane wave.
Help would be much appreciated.
Regards
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sweep + Values of variables not solved for

June 5, 2014, 2:30 pm
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I have a model which consists of two studies:
- Study 1 : Stationary with parametric sweep of parameter A
- Study 2 : Eigenmode, with parametric sweep of A, the result of Study 1 is the input for Study 2.

I was amusing that by using "Values of variables not solved for" I would get it work, but when I run a sweep of A I get always the same result for Step 2. I tried setting "Parameter value (A)" to "All" or "Automatic" but it seems that in both cases only the results of the last value of A from Step 1 is considered. If I set "Parameter value (A)" to a specific value and run the simulation for that value it works. My question is how I can access the results from Step 1 in a sweep?
Please advise.

Thanks
Mohsen
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Model convergence issue

June 18, 2015, 3:40 pm
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Hello everyone

I am conducting a time dependent study. My model converges for smaller time scales viz range(10^-12,10^-6,1.1354e-5) . However, when I run the study for a larger range, which is
range(10^-12,10^-4,10^-2), the model does not achieve convergence and gives an error.

If anybody could guide me what the problem might be, I will be obliged.

Thank you
Zaid
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Undefined Variable: comp1.es.Ey

June 20, 2015, 11:27 pm
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Hi,

I am trying to simulate a 2D MZM with two MMI at two sides and waveguide at the middle. It is derived from the MZM example for the wave optics module. We don't have the wave optics module. So I used the RF module to simulate it.

It worked pretty well before I applied non-zero electric potential. Then I observed standing wave like waveform as the first figure shown.

I realized that there will be a lot of radiation at the output MMI which may not be able to be absorbed by the scattering boundary condition as the radiation may not incident normally to the boundary. Therefore, I added a PML in addition to the scattering boundary condition.

After I did that, the simulation gave an error as follow:

Undefined variable.
- Variable: comp1.es.Ey
- Geometry: geom1
- Domain: 1
Failed to evaluate temporary symbolic derivative variable.
- Variable: comp1.emw.epsilonrzz@VDN$y
- Defined as: (((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN)))
Failed to evaluate temporary symbolic derivative variable.
- Variable: comp1.emw.k@VDN$y
- Defined as: (((((((((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN))))*comp1.emw.murzz)+((comp1.emw.muryy*((((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN)))))+(((((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN))))*comp1.emw.murxx)))*0.33333333333333331483)*((((((comp1.emw.epsilonrxx*comp1.emw.murxx)+(comp1.emw.muryy*comp1.emw.epsilonryy))+(comp1.emw.epsilonrzz*comp1.emw.murzz))/3)^(-0.5))*0.5))*comp1.emw.k0)
Failed to evaluate temporary symbolic derivative variable.
- Variable: comp1.pml1.coordy@VDN$y
- Defined as: ((((((((((((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN))))*comp1.emw.murzz)+((comp1.emw.muryy*((((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN)))))+(((((n_clad-(comp1.es.Ey*(((n_clad^3)*0.5)*r13)))*2)*(-((((n_clad^3)*0.5)*r13)*NaN))))*comp1.emw.murxx)))*0.33333333333333331483)*((((((comp1.emw.epsilonrxx*comp1.emw.murxx)+(comp1.emw.muryy*comp1.emw.epsilonryy))+(comp1.emw.epsilonrzz*comp1.emw.murzz))/3)^(-0.5))*0.5))*comp1.emw.k0))*((-((1-i)*(((-6666666.6666666669771)*(((x+3.4694468903532394968e-23)*1.1564822967844132682e-16)-y))*pi)))/(comp1.emw.k^2)))+(((6666666.6666666669771*pi)*(1-i))*(1/comp1.emw.k)))
Failed to evaluate variable.
- Variable: comp1.pml1.invT22
- Defined as: d(comp1.pml1.coordy,y)
Failed to evaluate variable.
- Variable: comp1.pml1.detInvT
- Defined as: (((comp1.pml1.invT22*comp1.pml1.invT11)-(comp1.pml1.invT21*comp1.pml1.invT12))*comp1.pml1.invT33)
Failed to evaluate temporary symbolic derivative variable.
- Variable: comp1.emw.curltestdepEx@VDN${test@4}
- Defined as: ((1/comp1.pml1.detInvT)*(-comp1.pml1.invT21))
Failed to evaluate expression.
- Expression: d((-mu0_const*(-comp1.emw.dHdtx*comp1.emw.curltestdepEx-comp1.emw.dHdty*comp1.emw.curltestdepEy+comp1.emw.iomega*comp1.emw.Jz*comp1.emw.testdepEz)*comp1.pml1.detInvT)*(dvol),{test@4})

It worked until the stationary step (no error comes out), but not any more. Plz help me to figure out the problem and if possible let me know why I have weird waveform as shown in first few figures. Is it really due to the incomplete absorption of the radiated wave by the SBC?

I attached the normE plot of the standing-wave like results and the model file of MZM_SBC and the model with PML added MZM_PML1.

Thank you very much.
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