An accurate thin-wire model for 3-D TLM simulations

Accurate modeling of thin wires in large-scale numerical electromagnetic simulations is very time consuming if fine meshing is adopted. Special treatments of such wires to allow their incorporation into relatively coarse meshes have lead to the development of thin-wire nodes for the transmission-line matrix (TLM) method. Previous models require the use of empirical factors. A novel thin-wire node is presented that is derived from rigorous field theory, requires no empirical factors and is shown to be highly effective. Moreover, virtually no computational overhead is incurred in the use of the new wire node.     

An AVM technique for 3-D TLM with symmetric condensed nodes

We demonstrate, for the first time, the feasibility of the adjoint variable method (AVM) in three-dimensional (3-D) time-domain transmission-line modeling (TLM). Using only two 3-D simulations of the original and adjoint problems, the sensitivities of the objective function with respect to all design parameters are estimated. The AVM approach is applied to both perfectly conducting and dielectric discontinuities. Analytical derivatives of the symmetric condensed node (SCN) scattering matrix are utilized in the case of dielectric discontinuities to derive a semi-analytical adjoint system. Our approach is illustrated with waveguide discontinuities.     

Moving boundaries in 2-D and 3-D TLM simulations realized byrecursive formulas

A novel technique for arbitrary boundary positioning in transmission line matrix (TLM) networks is described. This capability removes the restriction that dimensions of TLM models can only be integer multiples of the mesh parameter and allows superior boundary resolution. Since the position of boundaries can be continuously varied even during a simulation, this feature can model moving boundaries for time-domain optimization and phenomena such as the Doppler effect     

Comment on 'Simple method for determining 3-D TLM nodal scattering in nonscalar problems' (and reply)

For the original article see ibid., vol.28, p.2353-4 (1992). The commenters state that they have developed several models for simulating wire structures and are very familiar with the difficulties involved in the resolution of the nonlinear equations system required for obtaining the scattering matrix. It is for this reason that they very much appreciate the procedure proposed by Naylor and Ait-Sadi in the above mentioned. In using this procedure, however, the commenters have found a minor error: two equations which associate incident and reflected voltage pulses at the particular pair of lines under consideration, are only valid when both lines are of the same characteristic impedance. This is demonstrated in an example. In reply the authors concede that there was an error but believe that the operation of the method has been misunderstood. They then discuss certain points in an effort to clarify the situation.<>     

Compositionally graded interface for passivation of HgCdTe photodiodes

A compositionally graded CdTe-Hg_1−xCd_xTe interface was created by deposition of CdTe on p-HgCdTe and subsequent annealing. The compositionally graded layer between CdTe and HgCdTe was formed by an interdiffusion process and was used for passivation. The composition gradient (Δx) in the interfacial region and the width of the graded region were tailored by adopting a suitable annealing procedure. The effect of process conditions on the interfacial profile and photoelectric properties such as lifetime and surface recombination velocity was studied in detail. Surface recombination velocity of the p-HgCdTe could be reduced to the level of 3,000 cm/s at 77 K, which represents very good passivation characteristics. The passivation layer formed by this method can be used for the fabrication of high performance and stable modern infrared detectors. Thus, a passivation process is developed, which is simple, effective, reproducible, and compatible with the HgCdTe device fabrication and packaging processes.     

Using 2-D series TLM for modelling TE modes in dielectric and lossy environments

A method for using the transmission line modelling (TLM) 2-D series node for modelling TE modes in dielectric and lossy media is investigated. This method preserves the standard voltage-electric field analogy in TLM. Good agreement between the series node and other methods is achieved.<>     

Plane wave injection technique to calculate RCS in a 2-D TLM network

A technique for introducing an infinite-appearing plane wave into a two-dimensional transmission line matrix (TLM) network is described. The method has been applied to the calculation of the bistatic RCS for a plane wave normally incident on a conducting square cylinder.<>     

亚波长结构的抗反射特性三维TLM方法模拟

传输线矩阵(Transmission line matrix,以下简称TLM)方法,根据场方程和传输线方程之间的相似性,用等效分布传输线网络模拟给定结构,在时间和空间上进行离散化,是一种强有力的三维时域电磁场数值仿真算法.简要介绍三维扩展型结点TLM方法的模型、激励源和边界条件,并使用该方法对亚波长结构的抗反射特性进行模拟研究,为进一步深入探讨该结构的抗反射特性、进行优化设计提供依据.     

Design of photonic-crystal and wire waveguide interface

The coupling of light between wire-dielectric and photonic-crystal waveguides, characterized by a triangular lattice of air holes, is investigated through a finite-element time domain (FE-TD) approach, in order to optimize the transmission spectrum. The displacement of the inner-hole rows of the photonic-crystal waveguide, on both sides of the interface, has been shown to considerably improve the coupling, resulting in transmission values higher than 90% and 95% over bandwidths of hundreds of nanometers around 1550 nm. The new design approach is successfully proposed for input and output waveguides with width equal to /spl radic/3/spl Lambda/, as well as for larger widths, like 2/spl radic/3/spl Lambda/ and 3/spl radic/3/spl Lambda/, with /spl Lambda/ being the period of the photonic crystal.     

Improved magnetic loss for TLM

A new way of modelling magnetic losses which closely approximates the behaviour of real ferrite materials using the transmission line matrix (TLM) method is described. Numerical results are presented which demonstrate the accuracy possible with this method.<>     

New Scattering Matrix Model for Modeling Ferrite Media Using the TLM Method

This paper aims to extend the transmission line matrix method with a hybrid symmetrical condensed node (HSCN) to model ferrite media in the time domain. To take into account the anisotropy and dispersive properties of ferrite media, equivalent current sources are incorporated into supplementary stubs of the original HSCN. The scattering matrix of the proposed HSCN is provided, and the validity of this approach is demonstrated for both transversely and longitudinally magnetized ferrites. Agreement is achieved between the results of this approach and those of the theoretical and the finite‐difference time‐domain method.     

Electron holographic 3-D nano-analysis of Au/TiO2 catalyst at interface

Three-dimensional (3-D) nanostructures of gold catalysts supported on TiO2 were analysed by electron holography and high-resolution electron microscopy. The contact angle of the gold particle on TiO2 tended to be >90 degrees in the case of gold particles with a size (height) of >4 nm and it tended to be <90 degrees for gold particles with a height of <2 nm. The change in morphology increases the perimeter at the Au/TiO2 interface as the particle size decreases. This change in 3-D structure should be attributed to a change in electronic structure at the interface. It was found that electron holography enabled 3-D analysis at the atomic level and was effective for analysing nanostructured particles.     

Split-step TLM (SS TLM)-a new scheme for accelerating electromagnetic-field simulation

A new unconditionally stable three-dimensional (3-D) transmisson-line (TLM) algorithm is presented. It is stable regardless of the selected time-step. This new algorithm is based on a split-step theory, whose numerical implementation is given in detail. In addition, the theoretical proof of its unconditional stability is provided. This feature provides some potential advantage for time-domain electromagnetic-field computation as the number of iterations can be arbitrarily reduced for a given space sampling. Unfortunately, it is shown that the numerical dispersion of the new scheme increases when the time-step is different from the maximum value of the standard TLM. However, it is shown that some substantial computer cost reduction can be achieved when irregular meshing is used, as compared to classical 3-D TLM schemes. Thus, a new meshing strategy to improve the scheme accuracy is presented and validated through several examples.     

一种用线阵CCD测量物体表面三维轮廓的新方法

提出了一种用线阵CCD对物体三维轮廓进行测量的新方法,通过矩形光栅离焦投影,产生正弦光场,利用线阵CCD对物体进行扫描采样,采用三步相移技术进行相位解调,对物体三维轮廓进行测量,重点分析讨论了用线阵CCD对物体三维轮廓进行测量的原理和特性,并给出了试验简图及实际测量结果。     

3-D vector radix algorithm for the 3-D new Mersenne numbertransform

Three-dimensional convolutions and correlations are used for three-dimensional image-processing applications. Their calculation involves extensive computation, which makes the use of fast transforms very advantageous. As the number of arithmetic operations is very large, the accumulation of rounding or truncation errors arising in the use of the fast Fourier and Hartley transforms tends to increase. Number theoretic transforms are calculated modulo an integer and hence they are not subject to these errors. Previously, a one-dimensional transform called the new Mersenne number transform (NMNT) was introduced and applied successfully to the calculation of 1-D convolutions/correlations. Unlike other Mersenne number transforms, the NMNT can handle long data sequences and has fast algorithms. In the paper, the 1-D definitions are first extended to the 3-D case in detail for use in 3-D image processing applications. The concept and derivation of the 3-D vector radix algorithm is then introduced for the fast calculation of the 3-D NMNT. The proposed algorithm is found to offer substantial savings over the row-column approach in terms of arithmetic operations. Examples are given showing the validity of both transform and algorithm     

Flat Projection for 3-D

The two challenges for three-dimensional (3-D) display are designing the optics for wide fields of view, and delivering pixels at the rates needed to support this. Getting such pixel rates at low cost is merely an extension of the key challenge for two-dimensional (2-D) displays,and the cost advantage of projection in this respect over alternatives increases considerably at the data rates needed for 3-D. Both 2-D and 3-D projection concepts are bulky, so the authors describe how to project images within a flat panel. Flat projection is not only inexpensive: it can generate virtual as well as real images, and allows the screen to take images and input from the viewer as well as vice versa. Real images are created by pointing a projector into a wedge-shaped light guide, and either the projector or the screen can be shuttered in order to time-multiplex a 3-D image on a large screen. Virtual images are created by pointing a projector into a slab embossed with a grating and can deliver the collimated illumination needed if a liquid crystal display is to time-multiplex a 3-D image with the high off-screen resolution provided by holograms.     

3-D Topologies for Networks-on-Chip

Several interesting topologies emerge by incorporating the third dimension in networks-on-chip (NoC). The speed and power consumption of 3D NoC are compared to that of 2D NoC. Physical constraints, such as the maximum number of planes that can be vertically stacked and the asymmetry between the horizontal and vertical communication channels of the network, are included in speed and power consumption models of these novel 3D structures. An analytic model for the zero-load latency of each network that considers the effects of the topology on the performance of a 3D NoC is developed. Tradeoffs between the number of nodes utilized in the third dimension, which reduces the average number of hops traversed by a packet, and the number of physical planes used to integrate the functional blocks of the network, which decreases the length of the communication channel, is evaluated for both the latency and power consumption of a network. A performance improvement of 40% and 36% and a decrease of 62% and 58% in power consumption is demonstrated for 3D NoC as compared to a traditional 2D NoC topology for a network size of N = 128 and N = 256 nodes, respectively.     

TLM方法在电磁散射问题应用中的一种新的平面波照射模型

本文就TLM方法在电磁散射问题中的应用，给出了一种具有辅助平面波源的新的计算模型，该模型具有简化计算过程并且占用较少内存的优点。     

3-D/2-D registration by integrating 2-D information in 3-D

In image-guided therapy, high-quality preoperative images serve for planning and simulation, and intraoperatively as "background", onto which models of surgical instruments or radiation beams are projected. The link between a preoperative image and intraoperative physical space of the patient is established by image-to-patient registration. In this paper, we present a novel 3-D/2-D registration method. First, a 3-D image is reconstructed from a few 2-D X-ray images and next, the preoperative 3-D image is brought into the best possible spatial correspondence with the reconstructed image by optimizing a similarity measure (SM). Because the quality of the reconstructed image is generally low, we introduce a novel SM, which is able to cope with low image quality as well as with different imaging modalities. The novel 3-D/2-D registration method has been evaluated and compared to the gradient-based method (GBM) using standardized evaluation methodology and publicly available 3-D computed tomography (CT), 3-D rotational X-ray (3DRX), and magnetic resonance (MR) and 2-D X-ray images of two spine phantoms, for which gold standard registrations were known. For each of the 3DRX, CT, or MR images and each set of X-ray images, 1600 registrations were performed from starting positions, defined as the mean target registration error (mTRE), randomly generated and uniformly distributed in the interval of 0-20 mm around the gold standard. The capture range was defined as the distance from gold standard for which the final TRE was less than 2 mm in at least 95% of all cases. In terms of success rate, as the function of initial misalignment and capture range the proposed method outperformed the GBM. TREs of the novel method and the GBM were approximately the same. For the registration of 3DRX and CT images to X-ray images as few as 2-3 X-ray views were sufficient to obtain approximately 0.4 mm TREs, 7-9 mm capture range, and 80%-90% of successful registrations. To obtain similar results for MR to X-ray registrations, an image, reconstructed from at least 11 X-ray images was required. Reconstructions from more than 11 images had no effect on the registration results.