Propagation characteristics of Rayleigh wave under gravity based on FDTD method

The finite difference time domain (FDTD) method has been proposed and used for sound field simulation. To reproduce actual sound wave propagation in sound field simulations, it is necessary to apply the radiation characteristics. With the FDTD method, radiation characteristics can be applied by setting sound pressure in a dense grid arrangement. However, conventional techniques for capturing radiation characteristics use a sparse array of microphones and are considered insufficient for the FDTD simulation. Furthermore, the technique required to apply captured acoustic signals in a dense grid arrangement with the FDTD method has not been considered. In this paper, we propose a novel hardware and software system that captures the radiation characteristics for a dense grid arrangement and applies them to the FDTD method, while controlling the sound wave propagation with the non-propagation region. The proposed system produces the average differences from measured values of sound pressure, propagation time, center frequency, and log-spectral distortion of 1.8 dB, 0.04 ms, 700 Hz, and 3.5 dB, respectively, which is more accurate than the conventional techniques. The result shows that this system is useful for improving the accuracy of sound wave propagation reproduction with the sound field simulation.

In order to study the reflection of electromagnetic wave in Lorentz media, A novel piecewise linear recursive convolution(PLRC) method based on the auxiliary differential equation (ADE) of finite-difference time-domain(FDTD) technique is used to obtain the formulation of 2-D TM wave propagation in lossy Lorentz media.In 1-D case, the reflected coefficients calculated by the PLRC ADE-FDTD method and exact theoretical result are excellent agreement.This expresses that the 2-D formulas of electromagnetic wave propagation in lossy Lorentz media are right.Furthermore, Plane wave reflected by Lorentz media layer is calculated and simulated.Results display that reflected effect is evident.

In this contribution, possibility of using the backward ray tracing (RT) coupled with the finite-difference timedomain (FDTD) method for two-dimensional (2-D) simulations of the wave propagation in urban environments is demonstrated. For increased accuracy of exposure-assessment simulations, the FDTD method is used in small domains including inhomogeneous scatterers, whereas RT is used to simulate the wave propagation between these domains and buildings in urban environment. In this approach, contrary to the forward RT, many rays are generated for each diffracted ray and contributions from each receiver-transmitter path finally provide an excitation for the FDTD domains. A heuristic model of diffraction based on the uniform theory of diffraction has been used in the developed code. For the sake of simplicity, the method is presented in 2-D.

Finite-difference time-domain method for three-dimensional grid of hexagonal prisms

This paper discusses the wavelet-based Finite Difference Time Domain (FDTD) method and high resolution spectral estimation with a specific problem of sound wave propagation through phononic crystals. If the band structures of a phononic crystal are calculated by the traditional FDTD method combined with the fast Fourier transform (FFT), good estimation of the eigenfrequencies can only be ensured by the postprocessing of sufficiently long time series generated by a large number of FDTD iterations. In this paper, a postprocessing method based on the high-resolution spectral estimation via the Yule-Walker method is proposed to overcome the difficulty. Numerical simulation results for two-dimensional phononic crystal show that, the wavelet-based FDTD method improves the efficiency of the time stepping algorithm, and high resolution spectral estimation shows the advantages over the classic FFT-based postprocessing.

Finite-difference time-domain (FDTD) is a versatile modeling technique which employs finite differences as approximations to both spatial and temporal derivatives. It is a numerical analysis technique used for modeling electrodynamics. The FDTD modeling is applied in wide range of applications such as biomedical imaging and biomedical treatment. In investigating the propagation, scattering and radiation of electromagnetic waves, the FDTD is used as a powerful tool. In this paper, we implemented 2D FDTD algorithm in Xilinx ISE platform by using Absorbing Boundary Conditions and Sinusoidal input as an exciting source. We have developed Synthesizable 2D-FDTD algorithm using fixed-point arithmetic. Synthesis and simulation are carried out on Virtex-5 FPGA and Analog Devices -BLACKFIN-533 target devices. It is experimentally found that proposed FPGA realization is 55.55% faster than that of DSP implementation.

The finite difference time domain (FDTD) method is considered a prominent approach in computational electromagnetics for the wave propagation analysis of closed geometries in time domain. However, since this uses a structured mesh, the staircase approximation at the curved boundaries is a computational challenge in FDTD. Recently, meshless methods based on radial point interpolation method (RPIM) on unstructured mesh have gained importance in electromagnetic simulations due to their capability of modeling arbitrary shaped geometries. In the RPIM, the field variable at a node is interpolated by the values at the surrounding nodes which fall in the support domain. After assembly, this results in a banded matrix of size N χ N, where N is the total number of mesh cells. The computational cost of solving this is high for large structures. On the other hand, FDTD is a simple method in which the field variables are directly calculated using update equations. So, the FDTD and Meshless RPIM methods can be combined to model structures with partial curved geometries, with meshless RPIM method at the curved regions and the Cartesian FDTD for the rest of the domain. To validate the method numerically, a WR-229 90 degree waveguide bend is modelled using meshless method at the curved region and FDTD at the straight waveguide regions. Gaussian radial basis functions are used for the interpolation and to generate the shape function matrices in the meshless region. Interface matching conditions for the electric and magnetic fields are matched across the interface boundaries. The external domains are truncated with 2nd order MUR absorbing boundary conditions. The results of the hybrid approach are compared with those from the regular FDTD, with the Meshless approaches and the improvement in the computational cost is reported.

Ultra-wideband (UWB) logging, which uses transient wave rather than the more common harmonic wave, is a potential new technology in electromagnetic logging. Numerical forward modeling performs as a powerful tool for analyzing wave propagation and provides a conceptual framework for interpreting experimental data. The finite-difference time domain (FDTD) method is used for numerical modeling with the absorbing boundaries of UPML. The radiating energy flux density and scattering response excited by a UWB and a WB source in the same model are analyzed comparatively to exhibit the advantages of UWB logging. In the end, a model with a single fracture in it is built up to further demonstrate the utility of UWB logging in field practice.

Time-domain modelling of acoustic wave propagation is computationally expensive, escpecially in applications with large differences in length scales, such as thermoacoustic devices. Thus, there is a need for efficient modelling solutions. One possibility is to combine the established time-domain methods with more efficient methods. The aim of this paper has been to develop a time-domain model combining the equivalent source method (ESM) and the finite-difference time-domain (FDTD) method. The idea was to model the complex acoustic fields using FDTD method and the less complex fields using ESM. These methods were coupled by ensuring continuity of volume velocity and pressure at the boundary between them. Simulations with the combination of the methods were compared to analytical and experimental results, and shown to be accurate and numerically stable for 1-D energy flow, including viscous attenuation. Furthermore, the combination proved significantly quicker than using only the FDTD method. Combining ESM and FDTD has potential as a computationally efficient alternative compared to the latter alone.

Surface impedance concepts are introduced into the finite-difference time-domain (FDTD) method. Lossy conductors are replaced by surface impedance boundary conditions (SIBC), reducing the solution space and producing significant computational savings. Specifically, a SIBC is developed to replace a lossy dielectric half-space. An efficient implementation of this FDTD-SIBC based on the recursive properties of convolution with exponentials is presented. Finally, three problems are studied to illustrate the accuracy of the FDTD-SIBC formulation: a plane wave incident on a lossy dielectric half-space, a line current over a lossy dielectric half-space, and wave propagation in a parallel-plate waveguide with lossy walls.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

SUMMARY Modelling marine controlled-source electromagnetic (CSEM) responses in the fictitious time domain is a novel approach, which facilitates the full exploration of EM diffusive properties in the fictitious wave domain (FWD). Concepts, such as reflections, refractions, diffractions and transmissions, which are used for the analysis of elastic wave propagation can thus be adopted in FWD for interpreting CSEM data. In this paper, we use a high-order finite difference time domain (FDTD) algorithm for modelling marine CSEM responses in both the fictitious time domain and the diffusive frequency domain. A complex frequency shifted perfectly matched layer (CFS–PML) boundary condition is adopted to the FDTD modelling. We demonstrate the performance of the CFS–PML boundary condition and validate the high-order FDTD code in the FWD with the half-space sea water model and in the frequency domain with the 1-D canonical reservoir model. We investigate and analyse the propagation characteristics of electromagnetic fields in the FWD, where we apply wave propagation concepts to interpret marine CSEM data. Similarities between wave and field propagations relevant for marine CSEM data are demonstrated through several 1-D to 3-D numerical examples.

Light wave propagation in liquid crystal displays by the 2-D finite-difference time-domain method

Electromagnetic interference (EMI) is an important issue that needs to be considered for the safe operation of communication-based train control (CBTC) systems in railway environments. In this paper, two EMI scenarios are considered: the EMI of a wireless local area network (WLAN) at subway stations to CBTC systems and the interference of the CBTC system in tunnels to WLAN devices inside the train. To effectively solve those EMI problems, we introduce two hybrid wave propagation modeling techniques, where ray-tracing and finite-difference time-domain (FDTD) methods are hybridized for the first scenario and vector parabolic equation and FDTD methods are hybridized for the second scenario. The two hybrid models combine advantages of each individual method and achieve a better tradeoff between accuracy and efficiency. Based on our analysis, EMI-aware planning such as the optimization of WLAN antenna placement at subway stations can be pursued. The benefits that this approach can produce are demonstrated.

Optoacoustic (OA) imaging is an emerging technology that combines the high optical contrast of tissues with the high spatial resolution of ultrasound. Taking full advantage of OA imaging requires a better understanding of OA wave propagation in light-absorbing media. Current simulation methods are mainly based on simplified conditions such as thermal confinement, negligible viscosity, and homogeneous acoustic properties throughout the image object. In this study a new numerical approach is proposed based on a finite-difference time-domain (FDTD) method to solve the general OA equations, comprising the continuity, Navier-Stokes, and heat-conduction equations. The FDTD code was validated using a benchmark problem that has an approximate analytical solution. OA experiments were also conducted and data were in good agreement with those predicted by the FDTD method. Characteristics of simulated OA waveforms and OA images were discussed. The simulator was also employed to study wavefront distortion in OA breast imaging.

This paper presents the space-time characteristics of time reversed (TR) electromagnetic propagation. Theoretical formulations are deduced from wave equations in multiple-source or multiple-receiver environments. A conclusion that time reversal waveform can faultlessly focus in time and space domains is drawn from the detailed analysis. The finite-difference time-domain (FDTD) method is used to verify the conclusion. Two typical applications are presented to illustrate the advantage and potential of the focusing characteristics in wireless communication.