http://gsvit.net/wiki/ 2026-04-30T21:04:42+00:00 http://gsvit.net/wiki/ http://gsvit.net/wiki/lib/tpl/dokuwiki/images/favicon.ico text/html 2025-02-19T10:27:48+00:00 Anonymous (anonymous@undisclosed.example.com) http://gsvit.net/wiki/doku.php?id=fdtd:basic_geometries&rev=1739957268&do=diff Basic geometries Different materials can be placed in the volume where we run the FDTD algorithm. If we review the literature, we can see that it can be nearly everything, unfortunately only small subset of it is now implemented in GSvit. A simplest material is of course vacuum, which means to place nothing in the computational volume. The slightly more complex material is dielectrics or a poor conductor, that can directly go into the Maxwell's equations via its four parameters: electric permi… text/html 2025-02-19T10:27:48+00:00 Anonymous (anonymous@undisclosed.example.com) http://gsvit.net/wiki/doku.php?id=fdtd:boundary_conditions&rev=1739957268&do=diff Boundary conditions If we leave the computational volume as it is, the wave will be reflected from the boundary. In fact, this is similar to a reflection from perfect electric/magnetic conductor that would be located at computational volume faces as the tangential fields are nulled here (also normal components are nulled in this case). In order to simulate free space outside of a computational volume we need to use some special algorithm that will damp the wave leaving computational volume. text/html 2025-02-19T10:27:48+00:00 Anonymous (anonymous@undisclosed.example.com) http://gsvit.net/wiki/doku.php?id=fdtd:broadband&rev=1739957268&do=diff Broadband calculations In many examples the calculation is run for a single wavelength, eg. 633 nm. This is fine if we want to study monochromatic light interaction with some structure. However, in many cases a spectral dependence of some quantity is needed. text/html 2025-02-19T10:27:48+00:00 Anonymous (anonymous@undisclosed.example.com) http://gsvit.net/wiki/doku.php?id=fdtd:computational_domain&rev=1739957268&do=diff Computational domain To calculate electromagnetic field propagation we want to solve Maxwell's equations that link electric and magnetic field components and its time and space evolution. The basic idea being FDTD technique is a succesive update of electric and magnetic field components that are specially placed in the computational volume as shown on the following image: text/html 2025-02-19T10:27:48+00:00 Anonymous (anonymous@undisclosed.example.com) http://gsvit.net/wiki/doku.php?id=fdtd:fdtd_gsvit&rev=1739957268&do=diff FDTD calculations via GSvit As shown on First simulation page, there are three steps in a succesfull calculation. First step is to setup model that we want to use for the calculation. In brief this means to address the following questions: * What should be voxel size and real size of the computational domain? text/html 2025-02-19T10:27:48+00:00 Anonymous (anonymous@undisclosed.example.com) http://gsvit.net/wiki/doku.php?id=fdtd:geometry_modifiers&rev=1739957268&do=diff Geometry modifiers Here we describe a set of functions that can be used to alter the geometry of material objects before the FDTD calculation. Typically they operate on a single material (controlled by index of material in the material file entered via MEDIUM_VECTOR directive) and they shrink or expand it, or add something to it. text/html 2025-02-19T10:27:49+00:00 Anonymous (anonymous@undisclosed.example.com) http://gsvit.net/wiki/doku.php?id=fdtd:materials&rev=1739957269&do=diff Media GSvit is based on use of a regular rectangular mesh, so we use e.g. 200x200x200 rectangular volume elements - voxels on which our problem is defined. Individual voxels in the computational domain can be filled with any material and there is no limitation on this, as discussed e.g. in sections on text/html 2025-02-19T10:27:49+00:00 Anonymous (anonymous@undisclosed.example.com) http://gsvit.net/wiki/doku.php?id=fdtd:near-field_to_far_field&rev=1739957269&do=diff Near field to far field We often need an information about radiation properties in the far field, which for most of the cases is the domain where we are able to measure something. This can be done using a Near Field to Far Field (NFFF) transformation, which uses the values at some set of planes enclosing all the sources and scatterers and calculates the far field time domain or frequency domain results from it for a certain location of far field point. text/html 2025-02-19T10:27:49+00:00 Anonymous (anonymous@undisclosed.example.com) http://gsvit.net/wiki/doku.php?id=fdtd:outputs&rev=1739957269&do=diff Outputs FDTD handles large data arrays and there are numerous possibilities what to show as a result of the calculation. The most straightforward are the instant values of the field amplitudes at some points in the computational domain, or different cross-sections through it. As an opposite example, the most complex (at least from what can be done in GSvit) are the near-field to far-field transform results, that are accumulated from the boundary values during the whole calculation. text/html 2025-02-19T10:27:49+00:00 Anonymous (anonymous@undisclosed.example.com) http://gsvit.net/wiki/doku.php?id=fdtd:sources&rev=1739957269&do=diff Sources To perform a computation we need to setup at least single source of electromagnetic field. The simplest source is a point one, which is physically similar to a small dipole. More rigorous is an electric or magnetic current source which has exactly the same functionality as the electric or magnetic dipole. text/html 2025-02-19T10:27:49+00:00 Anonymous (anonymous@undisclosed.example.com) http://gsvit.net/wiki/doku.php?id=fdtd:tetrahedral_meshes&rev=1739957269&do=diff Tetrahedral meshes To create more complex meshes one can use also tetrahedral mesh, which can be obtained (with one intermediate step) from 3D modeling software, like Blender. Software tools for 3D modeling usually do not provide mesh itself, however they can save some files, e.g. in STL format that can be directly used for mesh generation. Then, a mesh generating software is used, like