Solution of arbitrarily dimensional matrix equation in computational electromagnetics by fast lifting wavelet‐like transform

A new wavelet matrix transform (WMT), operated by lifting wavelet‐like transform (LWLT), is applied to the solution of matrix equations in computational electromagnetics. The method can speedup the WMT without allocating auxiliary memory for transform matrices and can be implemented with the absence of the fast Fourier transform. Furthermore, to handle the matrix equation of arbitrarily dimension, a new in‐space preprocessing technique based on LWLT is constructed to eliminate the limitation in matrix dimension. Complexity analysis and numerical simulation show the superiority of the proposed algorithm in saving CPU time. Numerical simulations for scattering analysis of differently shaped objects are considered to validate the effectiveness of the proposed method. In particular, due to its generality, the proposed preprocessing technique can be extended to other engineering areas and therefore can pave a broad way for the application of the WMT. Copyright © 2009 John Wiley & Sons, Ltd.     

Conductive amorphous hydrocarbon film for bio-sensor formed by low temperature neutral beam enhanced chemical vapor deposition

Amorphous hydrocarbon (aCH) material is receiving plenty of attention due to its possible wide application. However, one hurdle facing this application is that high temperature is required to express conductivity of aCH, e.g., post annealing or deposition at high temperature. To form a conductive aCH on a substrate controlled below room temperature, we have developed a neutral beam enhanced chemical vapor deposition (NBECVD) method to control a hydrocarbon molecular structure that has a large conjugated system with delocalized π electrons in film. For material gas, we prepared toluene. As a result, we obtained a highly conductive carbon on a Si substrate with −50 °C using only toluene by optimizing the state of disassociated material gas. From an evaluation of film structure, a polycyclic aromatic hydrocarbon molecular structure was grown and contained in film because NBECVD could avoid irradiating UV to the Si substrate during deposition. Thus, an excited large conjugated chain structure generated by toluene in plasma could be maintained and polymerized on the Si substrate. Furthermore, the conductive aCH film could work as electrode in solution by electrochemical examination. Additionally, we found that nitrogen doped into conductive aCH could increase the working current of an electrode.     

Broadband electromagnetic characterization of carbon foam to metal contact

We investigated how the electrical contact of carbon foam with metallic surface can reduce its shielding properties. The bubble structure of the foam does not ensure a good electrical contact with the metal, and it leads to a significant reduction of the shielding effectiveness. A finite element numerical simulation was carried out by adopting a bubble/pore model of the internal microstructure of the foam, recovered by means of scanning electron microscope images. Experimental tests were carried out by inserting carbon foam samples into a coaxial transmission line. Numerical results agree well with experimental result showing significant performance reduction with respect to an ideal electrical contact.     

Insitu upgradation of biocrude vapor generated from non-edible oil cake's hydrothermal conversion over aluminated mesoporous catalysts

In this work, biocrude vapors generated from hydrothermal conversion of Pongammia pinnata cake using high pressure reactor at 400 °C and 25 kg/cm² were upgraded over three mesoporous catalyst namely SBA-15, KIT-6 and FDU-12. The catalysts were synthesized, aluminated and characterized using X-Ray Diffraction, N₂ adsorption-desorption, SEM techniques. A decrease in the surface area was observed on all three mesoporous catalyst after alumina loading with negligible effect on the pore diameter. Purely siliceous catalysts were found to give negligible effect on the yield of different product phases. Alumina supported SBA-15 (SAR 30) was observed as the suitable catalyst as compared to Al/FDU-12 (SAR 30) and Al/KIT-6 (SAR 30) for maximizing the biocrude yield with low heavy hydrocarbons (46.3 ± 2.2%), polyaromatic hydrocarbons (17.1%) and acidic compounds (9.1%) content. Therefore series of SBA-15 were synthesized by varying silicon to alumina ratio between 20 and 50 for maximizing hydrocarbons with boiling cut fractions between 195 and 317 °C corresponding to gasoline range hydrocarbons. Al/SBA-15(SAR 40) was found to give highest biocrude yield (∼34.8%) with highest selectivity towards gasoline fraction (23.7 ± 1.9%). GC/MS analysis was used to confirm the presence of aliphatic and aromatics. Highest asphaltene content was observed with Al/SBA-15 (SAR 50).     

Fast multi-objective optimization of multi-parameter antenna structures based on improved MOEA/D with surrogate-assisted model

For multi-objective design of multi-parameter antenna structures, optimization efficiency and computational cost are two major concerns. In this paper, an improved multi-objective evolutionary algorithm based on decomposition (MOEA/D) is proposed to improve global optimization capability by diversity detection operation and mixed population update operation. Further, in order to reduce the computational cost, a hybrid optimization strategy integrating a dynamically updatable surrogate-assisted model into the improved MOEA/D is proposed. The numerical results of test functions show that our algorithm outperforms original MOEA/D, modified MOEA/D (M-MOEA/D), and nondominated sorting genetic algorithm II (NGSA-II) in terms of diversity. Experimental validation of Pareto-optimal planar miniaturized multiband antenna designs is also provided, showing excellent convergence and considerable computational savings compared to those previously published approaches.     

ZnO and ZnO1−x based thin film memristors: The effects of oxygen deficiency and thickness in resistive switching behavior

In this study, direct-current reactive sputtered ZnO and ZnO_1−x based thin film (30 nm and 300 nm in thickness) memristor devices were produced and the effects of oxygen vacancies and thickness on the memristive characteristics were investigated. The oxygen deficiency of the ZnO_1−x structure was confirmed by SIMS analyses. The memristive characteristics of both the ZnO and ZnO_1−x devices were determined by time dependent current–voltage (I-V-t) measurements. The distinctive pinched hysteresis I-V loops of memristors were observed in all the fabricated devices. The typical homogeneous interface and filamentary types of memristive behaviors were compared. In addition, conduction mechanisms, on/off ratios and the compliance current were analyzed. The 30 nm ZnO based devices with native oxygen vacancies showed the best on/off ratio. All of the devices exhibited dominant Schottky emissions and weaker Poole-Frenkel conduction mechanisms. Results suggested that the oxygen deficiency was responsible for the Schottky emission mechanism. Moreover, the compliance currents of the devices were related to the decreasing power consumption as the oxygen vacancies increased.     

Gaussian-Hermite moment-based depth estimation from single still image for stereo vision

Depth information of objects plays a significant role in image-based rendering. Traditional depth estimation techniques use different visual cues including the disparity, motion, geometry, and defocus of objects. This paper presents a novel approach of focus cue-based depth estimation for still images using the Gaussian-Hermite moments (GHMs) of local neighboring pixels. The GHMs are chosen due to their superior reconstruction ability and invariance properties to intensity and geometric distortions of objects as compared to other moments. Since depths of local neighboring pixels are significantly correlated, the Laplacian matting is employed to obtain final depth map from the moment-based focus map. Experiments are conducted on images of indoor and outdoor scenes having objects with varying natures of resolution, edge, occlusion, and blur contents. Experimental results reveal that the depth estimated from GHMs can provide anaglyph images with stereo quality better than that provided by existing methods using traditional visual cues.     

Fast total variation deconvolution for blurred image contaminated by Poisson noise

In this paper, we present a fast non-blind deconvolution method for restoring blurred images contaminated by Poisson noise. The problem is formulated by finding the minimizer of the negative logarithmic Poisson log-likelihood combined with the total variation (TV). To attack the challenging task, we adopt the well-known variable splitting and penalty technique to convert the problem into two easier sub-problems: one is a modified TV regularized deconvolution and the other is a simple convex optimization problem. Experimental results show that the proposed method runs very fast and the quality of the restored image is comparable with that of some state of the art methods.     

Failure mechanisms of solder interconnects under current stressing in advanced electronic packages: An update on the effect of alternating current (AC) stressing

The relentless pursuit of miniaturization and integration in electronic industry has put challenges on the reliability of electronic products in aspects of the ever more severe environmental loadings, for example, thermal, electrical, and mechanical stresses. The failure mechanism of solder interconnects under direct current (DC) stressing has been studied and summarized as electromigration (EM), thermomigration (TM), Joule heating, stress-related mechanical degradation. However, the current flow through some paths for example clock buses and signal lines is bidirectional, i.e. alternating current (AC). The damage made in the positive half will be partly healed in the negative half, leading to less EM issues than that in DC stressing. Except for the TM damage, the thermal cycling will also induce thermal-mechanical fatigue issues under AC stressing. Considering these different failure mechanisms between DC and AC stressing, a better understanding of AC stressing will assist in finding out the root cause of failures in practical use. In this review, we discuss the research activities on the effect of AC stressing and their focus on the microstructure evolution of solder or metal interconnects. We firstly explained the discrepancies of reported temperature distribution and analyzed the possible reasons. We then discuss about microstructure evolution of interfacial intermetallic compounds under both DC and AC stressing, as well as the effect of various frequency. Finally, we discuss the failure mechanisms of solder interconnects under AC stressing, especially the unique thermal fatigue. The outlook of AC stressing study has also been discussed.