The finite-difference time-domain (FDTD) method has been widely and effectively used for analysis in many kinds of electromagnetic problems. Generally, the computational space can be divided into many lattices with rectangular; and the length on each of these meshs is equivalent in unitary aspect. In some of those problems, a greatly improved accuracy of the solution can be obtained if a finer discretization is used in specific regions of the computational space. There are limitations of the present form of uniform FDTD. It must increase the computational cost (memory and CPU time). Concerning the impression, we are trying to find more efficient ways of utilizing nonuniform grids. Coarser mesh for uncomplicated structure and finer mesh for complicated structure in nonuniform grids. However, this way can use in part of cutting area only. There are two edges connects the truncation of computational space. A similar scheme has been used with nonuniform FDTD method by a modification to the mesh scheme. The subcell method is a very general approach, capable of analyzing arbitrarily-shaped structures. In local area the mesh change from rectangular to irregular. Subgridding method is dissimilar to the both methods. Furthermore, the anisotropic PML to decrease the electromagnetic wave from nonuniform mesh of the computational space. It have replaced Mur¡¦s first-order absorbing boundary conditions and Berenger¡¦s PML for improving computationally efficient. Finally, compare them with the anisotropic PML in the essay.

Herein a fully parallel, upwind and flux-split Finite-Volume Time-Domain (FVTD) numerical engine for solving Maxwell's Equations on unstructured grids is developed. The required background theory for solving Maxwell's Equations using FVTD is given in sufficient detail, including a description of both the temporal and spatial approximations used. The details of the local-time stepping strategy of Fumeaux et al. is included. A global mesh-truncation scheme using field integration over a Huygens' surface is also presented. The capabilities of the FVTD algorithm are augmented with thin-wire and subcell circuit models that permit very flexible and accurate simulations of circuit-driven wire structures. Numerical and experimental validation shows that the proposed models have a wide-range of applications. Specifically, it appears that the thin-wire and subcell circuit models may be very well suited to the simulation of radio-frequency coils used in magnetic resonance imaging systems. A parallelization scheme for the volumetric field solver, combined with the local-time stepping, global mesh-truncation and subcell models is developed that theoretically provides both linear time- and memory scaling in a distributed parallel environment. Finally, the FVTD code is converted to the frequency domain and the possibility of using different flux-reconstruction schemes to improve the iterative convergence of the Finite-Volume Frequency-Domain algorithm is investigated.

Herein a fully parallel, upwind and flux-split Finite-Volume Time-Domain (FVTD) numerical engine for solving Maxwell's Equations on unstructured grids is developed. The required background theory for solving Maxwell's Equations using FVTD is given in sufficient detail, including a description of both the temporal and spatial approximations used. The details of the local-time stepping strategy of Fumeaux et al. is included. A global mesh-truncation scheme using field integration over a Huygens' surface is also presented. The capabilities of the FVTD algorithm are augmented with thin-wire and subcell circuit models that permit very flexible and accurate simulations of circuit-driven wire structures. Numerical and experimental validation shows that the proposed models have a wide-range of applications. Specifically, it appears that the thin-wire and subcell circuit models may be very well suited to the simulation of radio-frequency coils used in magnetic resonance imaging systems. A parallelization scheme for the volumetric field solver, combined with the local-time stepping, global mesh-truncation and subcell models is developed that theoretically provides both linear time- and memory scaling in a distributed parallel environment. Finally, the FVTD code is converted to the frequency domain and the possibility of using different flux-reconstruction schemes to improve the iterative convergence of the Finite-Volume Frequency-Domain algorithm is investigated.

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The need to accurately measure multi-junction (MJ) tandem solar cells' subcell current-voltage characteristics is increasing due to the vital information they provide about the efficiency, stability, and longevity of the cells. These measurements are rather difficult compared to their counterpart single-layer solar cell measurements. The purpose of this project is to construct an instrument that is able to successfully bias multiple subcells in a tandem solar cell. This would allow accurate measurements of the J-V behaviours of individual subcells within the stack and by extent, allow analysis to optimise future tandem cell technology. The instrument made is a controllable multi-chromatic light-emitting diode array, consisting of six wavelength-different LEDs ranging between ultraviolet and infrared light, which the intensity of is controlled bya slider control Graphical User Interface (GUI). This instrument will bemounted on a laboratory station at the institution of solar cell technology, Ångström laboratory. Although not perfect, the instrumentcan provide sufficient background light for biasing subcells of an MJ solar cell for a wide selection of cell band gaps