Effect of temperature on the absorption loss of chalcogenide glass fibers

The change in the absorption loss of IR-transmitting chalcogenide glass fibers in the temperature range of -90 degrees C /= 6 mum the change in loss was mainly due to multiphonon absorption. The change in loss for tellurium-based glass fibers increased significantly at T = 60 degrees C. The increase in the loss at short wavelengths (lambda /= 9 mum, multiphonon absorption dominated the loss spectrum.     

Z-function convolution in EHV power network electromagnetic transient analysis

Time-convolution in the forms arising in transformation from the frequency-domain to the time-domain has been widely used in the earlier development of electromagnetic transient methods in power systems. Independent work has recently led to new methods based on the z-transform, and the present paper develops methods based on discrete convolution arising from transformation to the time-domain now from the z-plane. The recursive solution sequences to which this leads combines high accuracy with low computing time requirements. Checks and controls in the synthesis of transmission line forward impulse response and surge impedance functions in the z-plane ensure that these are always stable system functions, and that numerical solution procedures which include them have very high inherent stability. The formulations developed are applied to transmission line energization from an equivalent source model, and the electromagnetic transients in short-circuit fault operation. Close comparisons are made between representative solutions from standard time-convolution analysis and from the methods of the present paper.     

Benchmarks of simple, generic, shaped plates for validation oflow-frequency electromagnetic computational codes

The validation of low-frequency measurements and electromagnetic (EM) scattering computations for several simple, generic shapes, such as an equilateral-triangular plate, an equilateral-triangular plate with a concentric equilateral-triangular hole, and diamond- and hexagonal-shaped plates, is discussed. The plates were constructed from a thin aluminium sheet with a thickness of 0.08 cm. EM scattering by the planar plates was measured in the experimental test range (ETR) facility of NASA Langley Research Center. The dimensions of the plates were selected such that, over the frequency range of interest, the dimensions were in the range of λ₀ to 3λ₀. In addition, the triangular plate with a triangular hole was selected to study internal-hole resonances     

Efficient miniature fiber-optic tunable filter based on intracoreBragg grating and electrically resistive coating

An electrically tunable reflection filter based on a platinum-coated single-mode optical fiber that contains an intracore Bragg grating has been demonstrated. The device shows a dc tuning range of 2.15 nm with a corresponding electrical power of 0.54 W. Wavelength modulation (WM) has been observed at frequencies lower than 100 Hz. The wavelength shift depends linearly on the electrical input power. A maximum efficiency of 4.1 nm/W is obtained for dc tuning     

A computationally efficient superresolution image reconstructionalgorithm

Superresolution reconstruction produces a high-resolution image from a set of low-resolution images. Previous iterative methods for superresolution had not adequately addressed the computational and numerical issues for this ill-conditioned and typically underdetermined large scale problem. We propose efficient block circulant preconditioners for solving the Tikhonov-regularized superresolution problem by the conjugate gradient method. We also extend to underdetermined systems the derivation of the generalized cross-validation method for automatic calculation of regularization parameters. The effectiveness of our preconditioners and regularization techniques is demonstrated with superresolution results for a simulated sequence and a forward looking infrared (FLIR) camera image sequence.     

Intelligible Crosstalk Between Two FDM/FM Carriers Accessing Double Cascaded Nonlinear Amplifiers

A method of evaluating double intelligible crosstalk between two frequency division multiplexed frequency modulated (FDM/FM) carriers accessing the same earth station high-power amplifier (HPA) and satellite transponder traveling wave tube amplifier (TWTA) has been developed. The analysis takes into consideration the AM/AM and AM/PM characteristics of the two cascaded memoryless nonlinear amplifiers, and the amplitude and group delay variations of transmission paths preceding the first nonlinear amplifier and of the path between the two nonlinear amplifiers. Results of the double intelligible crosstalk evaluation show the existence of significant distortion cross terms caused by the two cascaded nonlinearities and filters, in addition to individual distortion terms by each nonlinearity. Specific illustrative examples are discussed, and some practical suggestions are given for controlling crosstalk impairment effects in satellite channels with double cascaded nonlinear amplifiers.     

Numerical and experimental analysis of large passivation opening for solder joint reliability improvement of micro SMD packages

In this paper, using a recently developed solder fatigue model for wafer level-chip scale package (WL-CSP), we investigated the improvement on solder joint reliability for a 8-bump micro SMD package by enlarging the passivation layer opening at the solder–die interface. The motivation to enlarge the passivation opening is to reduce the severity of the stress concentration caused by the original design, and also to increase the contact area between the solder bump and aluminum bump pad. It was confirmed in the thermal shock test that with the new design, package fatigue life improved by more than 70%. To numerically predict this improvement represents a unique challenge to the modeling. This is because in order to capture the slightest geometrical difference on the order of a few microns between the two designs, the multiple-layer solder-die interface needs to be modeled using extremely fine mesh, while the overall dimensions of the package and the test board are on the order of millimeters. To bridge this tremendous gap in geometry, a single finite element model that incorporates all necessary geometrical details is deemed computationally prohibitive and impractical. In this paper, we applied a global–local modeling scheme that was also suggested by others [1, 2 and 3]. The global model contains the complete package with much simplified solder–die interface whereas the local model includes only one solder joint, but with detailed solder–die interface. Unlike most global–local models proposed by others, we included time-independent plasticity and temperature-dependent materials in the global model. This greatly improved model correlation accuracy with only moderate increase in run time. Energy-based solder fatigue model was used to correlate the inelastic strain energy with the package fatigue life. In an earlier study [4], we have found that Darveaux’s equations tended to be conservative when applied to the micro SMD, and hence new correlations based on curve-fitting the test data were derived. In this paper, we used the newly derived equation and achieved less than 20% error in N₅₀ life for both designs, which is on par with Darveaux’s equations when used for BGAs. The analysis also revealed two factors that may account for the life improvement. First, a slight decrease in inelastic energy dissipation after enlarging the passivation opening. Second, the shift of the crack initiation location which leads to longer crack growth length for the new design. The second factor was also independently confirmed by the failure analysis.     

Dispersion characteristics of the broadside-coupled coplanarwaveguide

The dispersive properties for the even- and odd-modes of the broadside-coupled coplanar waveguide (CPW) are determined using the spectral domain method. Various numerical results of the even- and odd-mode effective dielectric constants as a function of frequency are presented and discussed. It is found that the structure has a very weak dispersion. This fact is further confirmed through a comparison between the calculated dynamic and quasi-static results of the even- and odd-mode effective dielectric constants. The low dispersion feature signifies the fact that the quasi-static analysis is adequate for designing practical microwave and millimeter-wave circuits employing broadside-coupled CPW     

On the effects of a spacecraft subcarrier unbalanced modulator

This paper presents mathematical models with associated analysis of the deleterious effects which a spacecraft's subcarrier unbalanced modulator has on the performance of a phase-modulated residual carrier communications link. The undesired spectral components produced by the phase and amplitude imbalances in the subcarrier modulator can cause (1) potential interference to the carrier tracking and (2) degradation in the telemetry bit signal-to-noise ratio (SNR). A suitable model for the unbalanced modulator is developed and the threshold levels of undesired components that fall into the carrier tracking loop are determined. The distribution of the carrier phase error caused by the additive White Gaussian noise (AWGN) and undesired component at the residual RF carrier is derived for the limiting cases. Further, this paper analyses the telemetry bit signal-to-noise ratio degradations due to undesirable spectral components as well as the carrier tracking phase error induced by phase and amplitude imbalances. Numerical results which indicate the sensitivity of the carrier tracking loop and the telemetry symbol-error rate (SER) to various parameters of the models are also provided as a tool in the design of the subcarrier balanced modulator.