Quasi-three-dimensional perturbation technique, includingdielectrics for TWT's

A perturbation technique is described for finding phase velocities and coupling impedances in a traveling wave tube for an arbitrary distribution of dielectric material. A model of the sheath helix is presented. Tape helix results will be presented in a separate paper. In all cases presented, without adjusting the dielectric constant, the calculated perturbed phase velocity provided a better answer than the homogeneous dielectric solution, or Naval Research Laboratories' Small Signal Gain Program. Deviation from theory versus experiment is reported by stating the average sum of the squares difference between theoretical calculations and a second order least squares fit of the measured data. Phase velocities can be calculated for uniform dielectric support rods where the average sum of the squares ⩽1.19×10^-5. For cases with notched dielectric support rods phase velocities can be calculated where the average sum of the squares ⩽1.94×10^-5. For NRL's SSG program the average sum of the squares was ⩽1.01×10^-4 by comparison. For uniform dielectric support rods the perturbation does not significantly alter the basic shape of the predicted dispersion curve. For notched dielectric support rods applying the perturbation does alter and flatten the shape of the predicted dispersion curve in agreement with experiment     

Criteria for positive and negative reflection and refraction for three-dimensional anisotropic geometries

Waves propagating in anisotropic media with a 3D geometry are considered. General mathematical criteria that make it possible to find out if reflection or refraction of waves in such media is positive or negative are formulated.     

Power plane SPICE models and simulated performance for materialsand geometries

A SPICE model for power plane simulation has been developed. It is based on the geometries and materials of the power planes and uses a unit cell composed of RLC elements, transmission line elements or the HSPICE W-element. Simulated resonances in the frequency domain and delays in the time domain are consistent with results calculated from physical dimensions. SPICE model simulations compare well with hardware measurements in both the frequency and time domains. The role of dielectric thickness, dielectric constant and parallel pairs of power planes is demonstrated through simulation. The spreading inductance of power planes is defined, discussed and measured. Power plane performance in terms of impedance, resonances, damping and spreading inductance is optimized by the use of a thin dielectric layer between conductive planes     

Propagation models for short-range wireless channels with predictable path geometries

We consider wireless data services characterized by short distances, no shadowing, low power, and low antenna heights, deployed in places where a high frequency of potential users is expected, e.g., toll booths, parking lots, intersections, etc. Within such a system, we expect to see a well-defined geometry of base-to-user radio paths, as well as a predictable user trajectory, neither of which can be assumed for the wide-area cellular case. This offers the promise of a strong deterministic component of the channel response, in addition to a weaker stochastic component. Here, we combine analysis of the former with measurements and modeling of the latter for three typical outdoor scenarios. Comparisons between predicted and measured behavior show excellent agreement.     

Improved three-dimensional ray tracing technique for microcellularpropagation models

An improved three-dimensional ray tracing technique based in multiple-image and ray launching concepts is presented. The technique yields large improvements in terms of accuracy, computing efficiency and memory requirements compared with the conventional `brute force' ray tracing method     

Creation of three-dimensional patient models for hyperthermiatreatment planning

The finite difference time domain (FDTD) method has been used to simulate hyperthermia treatment using the Sigma-60 applicator of the BSD-2000 Hyperthermia System. In order to use this simulation capability in treatment planning, a detailed anatomical representation of the patient must be created. This paper describes a system developed to create such models from the CT scans of the patients and then display the results of the simulation. About a day and a half is required to create a patient model.     

Calibration of Rent's rule models for three-dimensional integrated circuits

In this paper, we determine the accuracy of Rahman's interconnect prediction model for three-dimensional (3-D) integrated circuits. Utilizing this model, we calculate the wiring requirement for a set of benchmark standard-cell circuits. We then obtain placed and routed wirelength figures for these circuits using 3-D standard-cell placement and global-routing tools we have developed. We find that the Rahman model predicts wirelengths accurately (to within 20% of placement and of routing, on average), and suggest some areas for minor improvement to the model.     

Circuit simulation models for the high electron mobility transistor

A three-terminal model is formulated for the high electron mobility transistor (HEMT) using charge-voltage relationships derived from the Boltzmann transport. Emphasis is placed on modeling the current transport of the two-dimensional electron gas (TEG) and the capacitance of the embedded parasitic MESFET structure. Furthermore, a distributed circuit topology is used to better model high-frequency effects, such as the transit time delay, in both small-signal and large-signal-transient analysis. The HEMT model is implemented in the circuit simulation program HP-SPICE. Both dc and ac simulation results are discussed.     

Circuit models for frequency modulation response of semiconductor lasers

The authors describe a new circuit modelling technique for the directly frequency-modulated CSP semiconductor laser. In particular, this model accounts not only for the carrier density but also the temperature effects. Predictions from this model are compared with other published results of sinusoidal frequency modulation in the range DC-3 GHz and show good agreement.<>     

Quantitative characterization and sorting of three-dimensional geometries: application to left ventricles in vivo

A procedure for automatic sorting of three-dimensional (3-D) shapes is proposed. The procedure is applied to sort into normal and abnormal categories, human left ventricles (LV) using in vivo data from 19 subjects (ten normal and nine abnormal LV's) studied by ultrafast tomography (Cine-CT). The procedure starts by utilizing a vector in a helical coordinate system to describe the spatial geometry of each individual LV cavity. This individual vector is then anatomically aligned and normalized to eliminate effects due to size, yielding a dimensionless vector, denoted as "geometrical cardiogram" (GCG). The GCG characterizes the instantaneous 3-D geometrical information of the individual LV. For the group of healthy subjects, the Karhunen-Loeve Transform (KLT) is then applied to compress the geometric information contained in their individuals' GCG vectors, at end diastole (ED) and end systole (ES), and yield a unique set of basis vectors. The "normal shape domain" is next defined as a truncated set of the KLT basis vectors from which a normal GCG can be reconstructed with a mean squared error (MSE) smaller than a defined threshold. The calculated MSE of any individual GCG reconstructed in this domain is then used as a criterion for sorting the 3-D shapes. Hearts which yield MSE greater than the threshold are considered abnormal. When applied to the study group of 19 subjects a significant difference (p less than 0.0001) between the MSE values obtained for the normal LV's, and those obtained for the abnormal LV's was detected, thus leading to a successful sorting of all the studied LV's. Finally, the KLT is applied to yield a compact representation of the 3-D geometry of any LV (normal or abnormal).     

Reconstruction of vascular networks using three-dimensional models

Reconstructing vasculature in three dimensions is a challenging problem. Early approaches concentrated on coronary vasculature in X-ray images, recent work uses magnetic resonance imagery of cerebral vasculature. In both cases a priori information has been used, and often the way this is represented has proven limiting to the scope of applications supported. For example, a particular representation may be useful only for X-ray images. This paper addresses two issues: (1) representing a collection of vasculature and (2) the reconstruction of individual vasculature from images. The authors' representation learns the variations in branching structures and vessel shapes that occur between individuals. It supports a vascular catalogue containing three-dimensional (3-D) anatomical models. The representation is task independent: here the authors use it to reconstruct vasculature from images. Their algorithm has 4 features to which they draw attention: (1) it is not premised wholly upon X-ray images (though that is the authors' focus here); (2) it produces several feasible solutions rather than one; (3) it can generalize from the catalogue to reconstruct instances not yet learned; (4) it exhibits polynomial time complexity, reasonable memory consumption, and is reliable. Both the authors' representation and reconstruction algorithm are new and useful approaches. In support of these claims, they present results gathered from X-rays of both simulated and real vasculature     

Circuit simulator models for the diode and IGBT with full temperature dependent features

The problems faced in generating analytical models for the insulated gate bipolar transistor (IGBT) and power diode are devising correct equations and determining realistic boundary conditions, especially for two-dimensional (2-D) features, while ensuring convergence of the models. These issues are addressed in this paper in relation to the temperature dependent modeling of NPT IGBTs and diodes. Simulation and experimental results are presented and compared to validate the modeling approach.     

Codes for iterative decoding from partial geometries

This paper develops codes suitable for iterative decoding using the sum-product algorithm. By considering a large class of combinatorial structures, known as partial geometries, we are able to define classes of low-density parity-check (LDPC) codes, which include several previously known families of codes as special cases. The existing range of algebraic LDPC codes is limited, so the new families of codes obtained by generalizing to partial geometries significantly increase the range of choice of available code lengths and rates. We derive bounds on minimum distance, rank, and girth for all the codes from partial geometries, and present constructions and performance results for the classes of partial geometries which have not previously been proposed for use with iterative decoding. We show that these new codes can achieve improved error-correction performance over randomly constructed LDPC codes and, in some cases, achieve this with a significant decrease in decoding complexity.     

A robust method for registration of three-dimensional knee implant models to two-dimensional fluoroscopy images

A method was developed for registering three-dimensional knee implant models to single plane X-ray fluoroscopy images. We use a direct image-to-image similarity measure, taking advantage of the speed of modern computer graphics workstations to quickly render simulated (predicted) images. As a result, the method does not require an accurate segmentation of the implant silhouette in the image (which can be prone to errors). A robust optimization algorithm (simulated annealing) is used that can escape local minima and find the global minimum (true solution). Although we focus on the analysis of total knee arthroplasty (TKA) in this paper, the method can be (and has been) applied to other implanted joints, including, but not limited to, hips, ankles, and temporomandibular joints. Convergence tests on an in vivo image show that the registration method can reliably find poses that are very close to the optimal (i.e., within 0.4 degrees and 0.1 mm), even from starting poses with large initial errors. However, the precision of translation measurement in the Z (out-of-plane) direction is not as good. We also show that the method is robust with respect to image noise and occlusions. However, a small amount of user supervision and intervention is necessary to detect cases when the optimization algorithm falls into a local minimum. Intervention is required less than 5% of the time when the initial starting pose is reasonably close to the correct answer, but up to 50% of the time when the initial starting pose is far away. Finally, extensive evaluations were performed on cadaver images to determine accuracy of relative pose measurement. Comparing against data derived from an optical sensor as a "gold standard," the overall root-mean-square error of the registration method was approximately 1.5 degrees and 0.65 mm (although Z translation error was higher). However, uncertainty in the optical sensor data may account for a large part of the observed error.     

Registration of three-dimensional cardiac catheter models to single-plane fluoroscopic images

Transvenous cardiac procedures require accurate positioning of catheters within the geometrically complex cavities of the heart. Recently, nonfluoroscopic catheter tracking technologies have been developed to quantitate the (degrees-of-freedom) three-dimensional positions of intracardiac catheters. This paper presents a projection-Procrustes method to register an animated three-dimensional (3-D) model of multiple intracardiac catheters with a single-plane fluoroscopic image. Applying the computed transformation to the catheter coordinates enables the animated 3-D model of the catheters to be viewed from the same perspective as the fluoroscopic image. Mathematical simulations show that the computed transformation parameters are sensitive to both the position errors in the 3-D catheter coordinates and to the spatial distribution of the catheter-mounted transducers. Simulations with a realistic geometric model of three catheters with four transducers per catheter showed an angular error of 1.91 degrees +/- 0.27 degree for 3-D catheter position errors of 2.0 mm. An in vitro experiment demonstrated the feasibility of the method using a water tank phantom of three catheters and fluoroscopic images taken over an 80 degrees range. The mean angular error was 0.61 degree +/- 0.48 degree. The results of this study indicate that the projection-Procrustes method is a useful tool for registering 3-D catheter tracking models to single-plane fluoroscopic images.     

Sensitivity analysis of simplified Printed Circuit Board finite element models

Many items of electronic equipment are subjected to harsh vibrations during their lifetime, these vibrations can damage electronic components and potentially risk total device failure. One approach to assess this risk is to compare the predicted vibration response of the Printed Circuit Board against a vibration level that is experimentally determined to produce component failure. Theoretically the vibration response can be determined using a simplified model of the PCB, where the components are modelled using a “smeared” approach; however, the error due to using such a simplified approach has not yet been defined. This paper shows a process to calculate the errors produced by such simplification techniques and derives factors of safety that can be used for all future vibration response models, using these factors ensures that future predictions do not underestimate the real response. Additionally, the errors depends on several other values besides the simplification technique, namely the Printed Circuit Board properties and the component: type, location and density. To account for these factors the process will use a sensitivity analysis approach to consider many possible design cases, this approach involves the creation of a large number of randomly created cases, all with different input values and giving different factors of safety. In this way the statistics of the factor of safety can be built up, giving much greater confidence in the results and insight into the drivers of the modelling error.     

Microwave tomography: an algorithm for cylindrical geometries

The letter presents an efficient algorithm in cylindrical coordinates for microwave diffraction tomography. In comparison with algorithms in cartesian co-ordinates, the mechanical rotation of the object is avoided and higher-quality images are obtained with similar processing time.     

Comparison of various source-gate geometries for power MOSFET's

A simplified model is used to compare the influence of layout geometry on the parasitic drain resistance of a vertical DMOSFET. For each case, optimum dimensions are determined. For every geometry considered at least one-half of the total area is available for current conduction. The hexagon has been favored by some workers but slightly better results can be achieved with rectangles or with circles on hexagonal centers.