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You might start with the photonic band gap example in wave optics module. Settings of these two simulations are quite the same.

thanks for your suggestion, but I am using comsol 4.4 and I do not have wave optics module, and I am lost while trying to modify the photonic crystal example.

But I have done some thing like following (2D square Lattice, solid cylinder in solid matrix),but I did not get the z-mode (longitudinal mode), just the transverse mode only:

1. used acoustic-structure interaction, elastic wave (elw) module
2. chose both domain linear elastic material.
3. Floquet periodicity (1,4) and (2,3) boundaries.
4. took the parametric sweep for kx = 0 to pi/a
5. finally got kx vs freq (derived values > global evaluation),

but this kx vs freq gave me just transverse modes only, longitudinal mode missing. I am lost. Please suggest me how to get longitudinal modes.
Also I am having problem with liquid matrix with solid scatterer.

Thank You.

But I have done some thing like following (2D square Lattice, solid cylinder in solid matrix),but I did not get the z-mode (longitudinal mode), just the transverse mode only:

but this kx vs freq gave me just transverse modes only, longitudinal mode missing. I am lost. Please suggest me how to get longitudinal modes.
Also I am having problem with liquid matrix with solid scatterer.

Thank You.

Hi Ukesh,

As far as I know, elastic waves include one longitudinal and one transverse waves while z-mode is referred as another transverse wave. I have problems with simulation of z-mode too. I have tried to ask help from COMSOL technique support. Unfortunately, they said currently it's very difficult to simulate z-mode in COMSOL.

As for the liquid-solid case simulation, I think you may try the Pressure Acoustic module since transverse waves can not propagate in liquid or air while PA module deals with longitudinal wave like sound wave.

Best,

Hi Yangfan,

Thank You very much for your response. I have tried "Pressure acoustic module" for 2D square water matrix and copper cylinder. I chose pressure acoustics for water domain, and then have to choose linear elastic material for copper, COMSOL makes the BC on the boundary between the copper-water as "Sound Hard Boundary". By doing so I got eigenfrequencies but some of the values are "NaN". I plot the band structure but not sure whether it is right or wrong.

Moreover, I have tried "Acoustic-structure Interaction module", Water = pressure acoustic; Copper = linear elastic material; BC on the boundary of the copper-water = Acoustic-structure boundary. Here too, I got some NaN values for eigenfrequencies, I still got the plot.

There is slight difference between above two band structure plots, I think this is due to the different BC used between copper and water matrix. Not sure I am in the right direction or not. Please correct me if I am doing anything wrong.

Thank you,

Ukesh

I uploaded a COMSOL file to the Model Exchange that shows how to set up a phononic band gap eigenfrequency analysis. Here is the link: www.comsol.com/community/exchange/432/.

Nagi Elabbasi
Veryst Engineering