{"id":245180,"date":"2022-12-30T12:31:33","date_gmt":"2022-12-30T12:31:33","guid":{"rendered":"\/forum\/forums\/topic\/inconsistent-differences-between-lumerical-fdtd-and-comsol-fem\/"},"modified":"2022-12-30T12:35:13","modified_gmt":"2022-12-30T12:35:13","slug":"inconsistent-differences-between-lumerical-fdtd-and-comsol-fem","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/inconsistent-differences-between-lumerical-fdtd-and-comsol-fem\/","title":{"rendered":"Inconsistent differences between lumerical fdtd and comsol FEM"},"content":{"rendered":"

Hi ansys support,<\/span><\/p>\n

I want to validate my lumerical FDTD setup by reproducing two similair metasurfaces from two papers. One follows up research on the other so they use the same COMSOL finite element method and the second paper minorly edited this comsol file for the different geometry (which is important later).  <\/span>
I have a normally incident plane wave source in the band of 750-800nm, and a frequency monitor spanning the entire the simulation volume above the SiO2 layer region with 250 sampling points. My goal is to reproduce the surface lattice resonance found in the papers (links below). This resonace is due to the periodicity of the structure which can be tuned with by setting the x and y span of the unitcell roughly equal to the desired resonance wavelength. By looking at the maximum electric field enhancement per wavelength in the volume of the simulation, in the papers referred as maximum field enhancement<\/em>, these resonances can be easiliy indentified by a fano-style peak in the frequency band.<\/span><\/p>\n

The structure of the first metasuface is given below in fig 1 where the pillars are Si and are positioned upon a small layer of SiO2 and a larger layer of gold.<\/span>
I was able to perfectly reproduce the resonance of the first metasurface by using the conformal variant 1 meshing method and stepwise refine the mesh by increasing the number of meshcells per wavelength up to 50. This gave a nice convergence of the <\/em>maximum field enhancement<\/em> of the resonance where it rises towards the value of 140 which was also found in the first paper using comsol FEM.<\/span><\/p>\n

The second metasurface has a slightly different geometry see fig 2 below, but the main difference is that the surrounding medium of the pillars is now water (in immersion). Due to the lower refractive index contrast this resonance is expected to be lower. Setting the background to water and further keeping all but a few geometric settings the same, yielded this time a significant difference in the resonance found in the two methods. In COMSOL an electric field enhancement of approx 90<\/strong> was found, but in lumerical FDTD using conformal variant 1 the simulation yielded a resonance with an electric field enhancement of approx 50<\/strong>. Since the metric in my research is fully dependent on this resonance, because I investigate metasurfaces for SERS, this difference can not be ignored.<\/span><\/p>\n

Different meshing methods such as dielectric volume and yu-mittra 2 can yield higher resonance, but do not exhibit any convergent behavior when increasing meshing as seen for the first metasurface with the conformal variant 1 meshing. I am aware the staircasing of the cylinders could play some factor in this. As the resonances are very strong near the interface of the cylinders and only reside in a relatively small part of the volume of the simulation.<\/span><\/p>\n

I already elimated the use of different material databases and too short simulation time as a possible causes for this difference. What could be a possible reason for this difference?<\/span><\/p>\n

Kind regards,<\/span><\/p>\n

Jeroen Dekker<\/span><\/p>\n

 <\/p>\n

Lattice Resonances and Local Field Enhancement in Array of Dielectric Dimers for Surface Enhanced Raman Spectroscopy | Scientific Reports (nature.com)<\/a><\/span><\/p>\n

Using the near field optical trapping effect of a dielectric metasurface to improve SERS enhancement for virus detection | Scientific Reports (nature.com)<\/a><\/span><\/p>\n

<\/a><\/span><\/p>\n

fig 1. Metasurface 1 two sillicon cylinders in air with small SiO2 spacer and reflective gold layer below.<\/span><\/p>\n

<\/a><\/span><\/p>\n

fig 2 metasurface 2 two sillicon cylinders in water with small SiO2 spacer and reflective gold layer below<\/span><\/p>\n

 <\/p>\n","protected":false},"template":"","class_list":["post-245180","topic","type-topic","status-closed","hentry","topic-tag-metasurface-1"],"aioseo_notices":[],"acf":[],"custom_fields":[{"0":{"_bbp_subscription":["271595","2592"],"_bbp_author_ip":["23.56.168.190"]," _bbp_last_reply_id":["0"]," _bbp_likes_count":["0"],"_btv_view_count":["3798"],"_edit_lock":["1672405636:201582"],"_bbp_topic_status":["unanswered"],"_bbp_status":["publish"],"_bbp_topic_id":["245180"],"_bbp_forum_id":["27833"],"_bbp_engagement":["2592","271595"],"_bbp_voice_count":["2"],"_bbp_reply_count":["4"],"_bbp_last_reply_id":["245517"],"_bbp_last_active_id":["245517"],"_bbp_last_active_time":["2023-01-04 16:05:57"]},"test":"jeroen-dekkertno-nl"}],"_links":{"self":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/245180","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics"}],"about":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/types\/topic"}],"version-history":[{"count":0,"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/topics\/245180\/revisions"}],"wp:attachment":[{"href":"https:\/\/innovationspace.ansys.com\/forum\/wp-json\/wp\/v2\/media?parent=245180"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}