The accuracy of improved two dimensional finite difference time domain method (2D FDTD) is verified by comparing with 3D FDTD method and experimental data. The optimized 60° photonic crystal waveguide bend, used in this study as a test case, is composed of InPGaAs/InP material and air holes and TE polarization is considered. The photonic crystal waveguide bend transmission data was measured by End-Fire technique. This computational method can be applied to investigate photonic crystals with irregularly shaped and different materials. Comparison of experimental data with two and three dimensional simulations, it is evident that the improved 2D FDTD simulation shows a very good agreement with 3D FDTD simulation and also with the experimental data of the transmission properties. The efficiency and simplicity of 2D FDTD makes this algorithm promising for simulation of photonic crystals on personal computers of reasonable speed. Since the improved 2D FDTD simulation has a high performance compared to its 3D counterpart and also could easily be run on PCs, the improved 2D FDTD simulation can be considered as a useful tool in studying, designing and improving photonic crystal devices.

The dynamics of fast gas heating in a high power microwave discharge in air, is investigated in the framework of FDTD simulations of the Maxwell equations coupled with the fluid simulations of the plasma. It is shown that, an ultra-fast gas heating of the order of several 100 Kelvins occurs in less than 100 ns. The main role in the heating is played by the electron impact dissociation of 2 O, dissociation via quenching of metastable states of 2 N, as well as, ( ) 1 O D quenching by nitrogen molecules. Among the electronically excited metastable states, ( ) 2 N B, C, a are the most important species. Slow heating of the gas above 1 μ s is attributed to the vibrational relaxation processes of 2 N, among them vibrationaltranslational relaxation of 2 N demonstrates the highest heating rate. The heating rate and thus the gas temperature are significantly increased with increasing of the microwave pulse amplitude, pulse width, and the gas pressure. In all cases, enhanced 2 O dissociation is the main factor behind the enhanced gas heating. The same effects are observed for increasing of the initial gas temperature, and 2 O percentage in a 2 2 N-O mixture.

This paper presents a novel implementation of an electromagnetically coupled patch antenna using air gap filled substrates to achieve the maximum bandwidth. We also propose an efficient modeling technique using the FDTD method which can substantially reduce the simulation cost for modeling the structure. The simulated results have been compared with measurement to show the broadband behavior of the antenna and the accuracy of the proposed modeling technique. The measured results show a 16% of VSWR<2 bandwidth which is considerable considering the inherent bandwidth limitations in microstrip antenna technology.

Top-hat monopole antennas loaded with radially layered dielectric are analyzed using the finite-difference time-domain (FDTD) method. Unlike the mode-matching method (MMM) (which was previously used for analyzing these antennas) the FDTD method enables us to study such structures accurately and easily. Using this method, results can be obtained in a wide frequency band by performing only one time-domain simulation. For the FDTD modeling, the type of medium at each grid point is specified by a code. Also an efficient non-uniform meshing scheme and a novel perfectly matched layer (PML) are presented and used. The excitation signal can be chosen in the form of Gaussian pulse (GP) or sine carrier modulated by Gaussian pulse (SCMGP). These enable us to increase the accuracy of simulation and decrease the required memory and CPU time. Simulation results are presented in the form of graphical figures, which display the spatial variations in amplitude and phase of radiated field. Also, the FDTD computed input impedances of several top-hat monopole antennas are compared with those obtained by measurement. The agreement between computed and measured results is quite well.

Anisotropic media appear regularly in electromagnetic wave engineering. The finite-difference time-domain (FDTD) method is a robust technique to model such media. However, the value of the time step in the FDTD algorithm is bounded by the Courant-Friedrichs-Lewy (CFL) condition. In this paper, a simple analytical approach is developed using the Gershgorin circle theorem to derive a point-wise closed-form relation for the CFL condition in bounded inhomogeneous anisotropic media. The proposed technique includes objects of arbitrary shapes with straight, tilted, or curved interfaces located in a computational space with uniform or adaptive gridding schemes. Both axial and non-axial anisotropies are considered in the analysis. The proposed method is able to investigate the effect of boundaries and interfaces on the stability of the algorithm. It is shown that in the presence of an interface between two anisotropic media, the von-Neumann criterion is not able to predict the stability bound for specific ranges of the permittivity tensor components and unit cell aspect ratios. Exploiting the proposed closed-form formulations, it is possible to tune the CFL time step and avoid the temporal instability by the wise selection of the gridding scheme especially in curved boundaries where subcell modelings such as Yu-Mittra formalism are applicable. Some illustrative examples are provided to verify the method by comparing the results with those of the eigenvalue analysis and time-domain simulations.

In this paper we describe the design and evaluation of Vivaldi elements optimization ‎for operation in the array environment over a wide range of frequency (12-18GHz). ‎The Finite Difference Time Domain (FD TD) is used in design and analysis of finite ‎Vivaldi array and genetic algorithm (GA) for optimization of its radiation pattern. The ‎hybrid method is used to find maximum side lobe level (SLL) over a range of ‎frequency (12-18GHz) by adjustment of the antenna and array parameters. An array ‎SLL improvement of MB was attained by optimization. Here a single Vivaldi antenna ‎and a four-element array are analyzed and compared with measurements. Theoretical ‎and experimental results show good agreement with each other.‎

By applying BOR-FDTD method, fluorescence enhancement by using nano-antennas is investigated. Details of computational method are described including, updating equations, source, detector, absorbing boundary conditions. It is shown that fluorescence enhancement depends on nano-antenna features, ambient environment, the wavelength of incident light and the distance between emitter and nano-antenna. By the precise investigation of the impact of distance on the parameters effective in fluorescence enhancement (Purcell factor, antenna gain, the electric field intensity) we show that by setting the appropriate emitter distance from nano-antenna the highest enhancement can be obtained.