Near-field Simulations Research Articles

(Al,In)GaN laser diodes in spectral, spatial, and time domain: near-field measurements and basic simulations

The near-field lateral intensity distribution of 405 nm (Al,In)GaN laser diodes is measured in time and wavelength domain. Spectral properties, relaxation oscillations, and filaments are observed. A thermally induced change of the refractive index profile is found to be the driving force behind changes in the dynamic mode configuration. With rate equations those effects can be described in first approximation.

A case study on the influence of THM coupling on the near field safety of a spent fuel repository in sparsely fractured granite

In order to demonstrate the feasibility of geological disposal of spent CANDU fuel in Canada, a safety assessment was performed for a hypothetical repository in the Canadian Shield. The assessment shows that the maximum long term radionuclide release from such repository would meet international criteria for dose rate; however, uncertainties in the assumed evolution of the repository were identified. Such uncertainties could be resolved by the consideration of coupled Thermal-Hydro-Mechanical-Chemical (THMC) processes. In Task A of the DECOVALEX-THMC project, THM models were developed within the framework of the theory of poroelasticity. Such model development was performed in an iterative manner, using experimental data from laboratory and field tests. The models were used to perform near-field simulations of the evolution of the repository in order to address the above-mentioned uncertainties. This paper presents the definition and rationale of task A and the results of the simulations. From a repository safety point of view, the simulations predict that the maximum temperature would be well below the design target of 100°C; however, the stress on the container can marginally exceed the design value of 15 MPa. However, the most important finding from the simulations is that a rock damage zone could form around the emplacement borehole. Such damage zone can extend a few metres from the walls of the emplacement holes, with permeability values that are orders of magnitude higher than the initial values. The damage zone has the potential to increase the radionuclide transport flux from the geosphere; the effect of such an increase should be taken into account in the safety assessment and mitigated if necessary by the provision of sealing systems.

Near-field simulation of acoustic effects in tire tread cavities

We report the results of numerical calculations of acoustic waves that are generated when the tire tread hits the road surface. The tread blocks are modeled by parallelepipeds and their compression and expansion is modeled by the motion of the cavity walls in accordance with a specified law. The acoustic perturbations generated by this process are investigated on the basis of the complete nonlinear Euler equations using the Godunov method. A parametric analysis of the model is carried out.

Evaluation of the angular spectrum approach for simulations of near-field pressures.

The implementation of the angular spectrum approach based on the two-dimensional fast Fourier transform is evaluated for near-field pressure simulations of square ultrasound transducers, where the three-dimensional pressure field is calculated from the normal velocity distribution on the transducer surface. The pressure field is propagated in the spatial frequency domain with the spatial propagator or the spectral propagator. The spatial propagator yields accurate results in the central portion of the computational grid while significant errors are produced near the edge due to the finite extent of the window applied to the spatial propagator. Likewise, the spectral propagator is inherently undersampled in the spatial frequency domain, and this causes high frequency errors in the computed pressure field. This aliasing problem is alleviated with angular restriction. The results show that, in nonattenuating media, the spatial propagator achieves smaller errors than the spectral propagator after the region of interest is truncated to exclude the windowing error. For pressure calculations in attenuating media or with apodized pistons as sources, the spatial and spectral propagator achieve similar accuracies. In all simulations, the angular spectrum calculations with the spatial propagator take more time than calculations with the spectral propagator.

Radiated EMI Recognition and Identification form PCB Configuration Using Neural Network

In this paper the application of neural network (NN) in EMI radiated measurement is proposed to recognize and identify the basic PCB configuration. The emission of electromagnetic (EMI) noise form printed circuit board (PCB) is studied. The different kinds of PCB shape are used for produce electromagnetic field. The fields are measured using near-field probe with termination load and computation using finite element method (FEM). After measurement by near-field probe and simulation by FEM then, is a thinning process. The images acquired from thinning process will be analyzed to calculate number of junction point, end point, cross point, ratio of black and white, position of end point, vertical line and horizontal line, respectively then pass to NN. The trained NN can identify emission pattern successfully. DOI: 10.2529/PIERS060907024549

Simulation of optical near field of a sub‐wavelength gold slit array and its electric quadrupole interaction with 1s excitons in Cu2O

AbstractLaight propagation through a gold film with a periodically structured 50 nm width slit array into Cu2O has been calculated with a FDTD (Finite Difference Time Domain) method with a 5 nm mesh‐grid. Owing to the presence of a guided mode in the slit and a surface plasmon mode at the gold/Cu2O interface, optical near field generation in Cu2O are efficient in the case where the polarization of the incident light is perpendicular to the slit. The efficiency of the electric quadrupole (E2) transition of the 1s ‐exciton in Cu2O, which is modified by the field gradient of the excitation light, is evaluated for the calculated optical near field. Slit period dependences of the near field generation and the E2 transition efficiency are examined for a 50 nm thick array film. The enhancement of the effective E2 transition efficiency in the volume of 50 nm thickness above the film relative to the efficiency by the plane wave excitation is found to reach a factor 28 at the slit period of 110 nm. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Near-field turbulent simulations of rectangular jets using lattice Boltzmann method

We perform large eddy simulation (LES) of the near field of low aspect ratio (AR) rectangular turbulent jets (RTJ) using the lattice Boltzmann method. The computational technique combines a D3Q19 multiple relaxation time (MRT) lattice Boltzmann equation (LBE) with the Smagorinsky model for the subgrid stress. First and foremost, we demonstrate that the MRT-LBE model is more suitable than the widely used single-relaxation-time LBE model for LES of turbulent flows. Then, we proceed to compute four jets with MRT-LBE: AR-1, 1.5, 2, 5; exit velocity u0(m∕s)-60, 39, 60, 23; and Reynolds number Re-184 000, 25 900, 128 000, 14 000. The investigated near-field behavior includes: (1) Decay of mean streamwise velocity (MSV) and inverse MSV; (2) spanwise and lateral profiles of MSV; (3) half-velocity width development and MSV contours; and (4) streamwise turbulence intensity distribution. The simulation results are compared against experimental data. Two unique features of RTJ—the saddle-back MSV spanwise (major axis) profile and axis switching of major axis from spanwise to lateral direction—are investigated. Our simulations show that the jet statistical behavior is more sensitive to inflow velocity and less so to the transverse boundary conditions. Overall, this work demonstrates that the MRT-LBE method is a potentially reliable computational tool for LES of turbulence even at high Reynolds numbers.

Optical near-field simulation of Sb thin film thermal lens and its application in optical recording

Using the finite-difference-time-domain method, the near-field optical distribution and properties of Sb thin film thermal lens are calculated and simulated. The results show as follows. Within the near-field distance to the output plane of thermal lens, the spot size is approximately 100nm, and its intensity is greatly enhanced, which is higher than that of incident light. The spot shape gradually changes from ellipse to round at the distance of more than 12nm to the output plane. The above-simulated results are further demonstrated by the static optical recording experiment.

Photoresponsive polymers for topographic simulation of the optical near-field of a nanometer sized gold tip in a highly focused laser beam

The local perturbation of a diffraction-limited spot by a nanometer sized gold tip in a popular apertureless scanning near-field optical microscopy (ASNOM) configuration is reproduced through topography changes in a photoresponsive polymer. Our method relies on the observation of the photochemical migration of azobenzene molecules grafted to a polymer placed beneath the tip. A local molecular displacement has been shown to be activated by a gold tip as a consequence of the lateral surface charge density present at the edges of the tip's end, resulting from a strong near-field depolarization predicted by theory.

Evaluation of a highly nonlinear microstructured optical fiber by near-field scanning optical microscopy and simulations: nonlinear coefficient and coupling losses

We report on the evaluation of a microstructured optical fiber (MOF) designed for non-linear signal processing applications, i.e., with a very small guided mode (waist ∼1 μm). Calculations predict an intrinsic (assuming propagation in the fundamental mode and zero-loss coupling) non-linear γ coefficient of 40 W-1 km-1 at λ=1.55 μm, but they also predict a basic multimode character. NSOM measurements validate directly the high intrinsic γ value (32±10 W-1 km-1) and also show that with an optimized coupling, the overall losses in efficiency taking into account coupling losses and weak excitation of higher-order modes and leaky modes are only 2.5 dB. This performance is adequate for use in all-optical data processing lines, all the more since it is maintained for relevant propagation lengths and peak power densities.

Interpretation of the failure of the time-independent diffusion equation near a point source

The time-independent diffusion equation (DE) yields inaccurate solutions near sources. To investigate this issue we solve a forward problem of light propagation from a time-independent isotropic point source in an infinite medium of constant refractive index, constant absorption coefficient and constant reduced scattering coefficient using the standard radiative transfer equation (RTE) and three recently reported RTEs. Only one of those equations yields solutions consistent with the results of Monte Carlo simulations in near field, due to its ability to model ray divergence. From that equation we derive a condition for neglecting the divergence of rays emitted by a point source in forward problems that is the same as the reported condition for the accuracy of the time-independent DE. These results strongly suggest that the inaccuracy of the time-independent DE near sources is due to a missing term describing ray divergence, a drawback inherited from the RTE. One of the studied RTEs and the derived equations are free of that drawback.

Near-field optics simulation of a solid immersion lens combining with a conical probe and a highly efficient solid immersion lens-probe system

A solid immersion lens (SIL) combined with near-field probes which are the conic dielectric probe and the local metallic coating on the SIL probe is designed for optical recording by means of a three-dimensional rather than two-dimensional finite difference time domain method to gain more insight in the near-field distribution. Our computation model is realistic to match the real SIL-probe system. The optical properties of near-field distributions between the SIL probe and recording layers are investigated. A promising idea for fabricating a type of the SIL-probe system is proposed. Results of our designation of an optimal SIL-probe system can achieve higher performance (in terms of high throughput and low reflection of the light beam) for optical data storage and microscopy than the conventional metal NSOM probe or SIL used alone.

Simulation of Near Source Two-Dimensional Wave Field and its Application to the Study of Ground Motion Characteristics of the 1999 Chi-Chi, Taiwan Earthquake

Simulation of Near Source Two-Dimensional Wave Field and its Application to the Study of Ground Motion Characteristics of the 1999 Chi-Chi, Taiwan Earthquake

Near-Field Optical Simulation of Super-Resolution Near-Field Structure Disks

We describe the optical properties of readout signals from light-scatting-center super-resolution near-field structure disks by a numerical simulation using a three-dimensional finite-difference time-domain method (FDTD). Since the generation process of the near-field readout signals has a relationship between the direction of the mark train and the polarization direction of incident light, the optical properties of readout near-field signals strongly depended on the incident light polarization. It was found that the land & groove structure, and the scattering center size also influenced the readout signals.

近接場フォトン走査型トンネル顕微鏡シミュレーション

近接場フォトン走査型トンネル顕微鏡シミュレーション

Simulation of near field optical manipulator by boundary element method—aperture‐probe coated with metal

Simulation of near field optical manipulator by boundary element method—aperture‐probe coated with metal

Validation of the finite-difference time-domain method for near-field bioelectromagnetic simulations

Validations of the accuracy of the FDTD method for near-field simulations are critical at this time to assess the accuracy of the FDTD method for the simulation of personal communication devices. Excellent comparisons between the FDTD method and analytical or measured results are shown for a dipole antenna next to a layered half-space, a layered box, and a sphere, and also an infinitesimal dipole near a sphere. © 1997 John Wiley & Sons, Inc. Microwave Opt Technol Lett 16: 341–345, 1997.

Time-domain simulation of the influence of close barriers on sound propagation to the environment

A time-domain numerical model for studying the influence of close barriers on sound levels at a large distance from a source is proposed. It is a combination of a near-field simulation with a near-field to far-field transform based on the Helmholtz–Kirchhoff integral. The near-field simulation is based on a finite-difference time-domain type discretization of a well chosen volume around sources and near objects. The numerical accuracy of the model is studied theoretically and experimentally for a particular sound field. The simulation example is a large power station transformer surrounded by barriers. The evaluation of sound levels in the highly multimodal environment is not trivial. It is performed in small frequency bands around the frequency of the typical pure tones emitted by the source.

Elastic-wave propagation and site amplification in the Salt Lake valley, Utah, from simulated normal faulting earthquakes

AbstractThe two-dimensional seismic response of the Salt Lake valley to near- and far-field earthquakes has been investigated from simulations of vertically incident plane waves and from normal-faulting earthquakes generated on the basin-bounding Wasatch fault. The response to normal faulting earthquakes was simulated using a two-dimensional finite-element method and the plane-wave response was calculated from two-dimensional finite-difference simulations. The plane-wave simulations were then compared with observed site amplifications in the Salt Lake valley, based on seismic recordings from nuclear explosions in southern Nevada, that show 10 times greater amplification within the basin than measured values on hard-rock sites. While previous studies attribute this increased site amplification to the near-surface unconsolidated/consolidated alluvial fill contact, our synthetic seismograms suggest that in the frequency band 0.3 to 1.5 Hz at least one-half the site amplification can be attributed to the impedance contrast between the basin sediments and higher velocity basement rocks. Synthetic seismograms from vertically incident plane-wave sources and buried double-couple sources predict large amplitude Rayleigh-wave propagation from the edges of the basin and, in general, uniform site amplification. In contrast, near-field simulations of basin-bounding, normal-faulting earthquakes predict large-amplitude Rayleigh waves propagating westward from the fault across the basin. Spectra of synthetic accelerograms computed from the normal-faulting earthquakes shows that spectral amplification within the basin is primarily due to source directivity with a maxima near the surface projection of the fault that decays rapidly away from the fault. Importantly, the synthetic modeling of near-field earthquake sources show that near-field directivity effects are important and should be considered in an earthquake hazard assessment of the Salt Lake valley and similar geologic settings along the Wasatch Front.

Techniques for measuring the electromagnetic shielding effectiveness of materials. II. Near-field source simulation

For pt.I see ibid., vol.30, no.3, p.239-50 (1988). Measurements of electromagnetic shielding effectiveness of materials by simulating a near-field source are further discussed. Two specific measurement approaches, the use of a dual TEM cell and the application of an apertured TEM cell in a reverberating chamber, are studied. For each case, the system frequency range, test sample requirements, test field type, dynamic range, measurement time required, and analytical background, are considered, and data taken on a common set of materials are presented.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>