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Celia is based on the Yee finite difference time domain (FDTD) method. The FDTD method has achieved unrivalled popularity amongst conventional computational electromagnetic techniques as a result of its ability deal with the complexities of practical electromagnetic engineering problems.
A wealth of background knowledge and methods has been developed over the last two decades on the use and extension of the basic Yee numerical scheme to tackle a wide diversity of applications.
The method itself is a simple core algorithm that is second order accurate in time and space when applied on a rectangular mesh. The primary issue in the flexibility and accuracy of a FDTD solver is the supplementary methods implemented in conjunction with the core solver. These include, for example, specialised material property handling of dispersive or non-linear materials; accurate boundary conditions; a range of antenna feed types; far field evaluation from near field information etc. These methods are necessary to use the Yee solver on practical EM analysis problems.
The aspects of the Celia solver that provide unsurpassed capability in certain applications are the state of the art boundary conditions coupled with the dispersive material capability and antenna transmission line feed types.
For examples of the application of the solver capabilities to practical problems see the Applications page.
The boundary conditions are derived from the Berenger Perfectly Matched Layer (PML) scheme, demonstrably the best currently available. Within Celia this method has been extended to operate in regions of lossy, dispersive dielectrics, such as soils and biological media. This allows the computation of the interaction between antennas and local regions of complex materials, which makes Celia ideally suited to application such as sub-surface radar, dosimetry and bio-EM remote sensing . Details of the implementation can be found in the boundary condition page.
Celia has been equipped with the capability to incorporate dispersive materials within the mesh. At the present time the method implemented is the recursive convolution algorithm of Luebbers. A first order Debye dispersion is currently implemented. A greater range of dispersive material options will be included in future releases.
The Celia solver is equipped with a number of excitation mechanisms. For the computation of antenna response in receive mode or scattering calculations, for example, a Huygens surface construction is provided. This applies a plane wave of arbitrary form within the mesh. The functional form of the wave can be chosen from a number of commonly used analytic forms or provided as a record of time/amplitude samples.
For local excitation within the mesh, or antenna transmit response for example, a number of electric field node excitation types are provided. While similar in principle in the way that they are applied to the mesh, being at an electric field node, they vary in the specific detail of the way the feed signal is computed. Details can be found on the mesh excitation page.
A far field integration capability is included in the solver to enable the calculation of antenna far field response or scatterer far field response.