System integration design in MEMS — A case study of micromachined load cell

One of the critical issues in large scale commercial exploitation of MEMS technology is its system integration. In MEMS, a system design approach requires integration of varied and disparate subsystems with one of a kind interface. The physical scales as well as the magnitude of signals of various subsystems vary widely. Known and proven integration techniques often lead to considerable loss in advantages the tiny MEMS sensors have to offer. Therefore, it becomes imperative to think of the entire system at the outset, at least in terms of the concept design. Such design entails various aspects of the system ranging from selection of material, transduction mechanism, structural configuration, interface electronics, and packaging. One way of handling this problem is the system-in-package approach that uses optimized technology for each function using the concurrent hybrid engineering approach. The main strength of this design approach is the fast time to prototype development. In the present work, we pursue this approach for a MEMS load cell to complete the process of system integration for high capacity load sensing. The system includes; a micromachined sensing gauge, interface electronics and a packaging module representing a system-in-package ready for end characterization. The various subsystems are presented in a modular stacked form using hybrid technologies. The micromachined sensing subsystem works on principles of piezo-resistive sensing and is fabricated using CMOS compatible processes. The structural configuration of the sensing layer is designed to reduce the offset, temperature drift, and residual stress effects of the piezo-resistive sensor. ANSYS simulations are carried out to study the effect of substrate coupling on sensor structure and its sensitivity. The load cell system has built-in electronics for signal conditioning, processing, and communication, taking into consideration the issues associated with resolution of minimum detectable signal. The packaged system represents a compact and low cost solution for high capacity load sensing in the category of compressive type load sensor.     

Selected variants of a Memetic Algorithm for JSP – a comparative study

The article aims to address a research gap concerning the adequate configuration of a Memetic Algorithm adapted to solve the Job-Shop Scheduling Problem. The goal was accomplished by means of conducting a comparative study of 16 variants of a Memetic Algorithm, characterised with different places of hybridisation and local search methods applied. The study involved the solution of eleven instances of JSP and the comparison of the results with the results achieved with an Evolutionary Algorithm lacking the mechanism of hybridisation and selected local search methods. The utilitarian significance of the problem also involved the use of assessment measures intended for both practical applications and research purposes.     

Safety analysis in design—Evaluation of a case study

Safety analysis was applied in the design of a section at a paper mill. The case study involved analysis of layout, transport system, machines, and a number of different activities. The purpose of the analysis was to find measures to decrease occupational accidents. Three years after the installation was finished the occurrence of accidents was investigated. There was a 56% decrease in the number of accidents; the number of working days lost due to accidents was diminished by 75% as compared to 4 years preceding. The results of the safety analysis were also evaluated with respect to the accidents which had occurred. The methods for safety analysis seem to have been efficient in identifying hazards. The general conclusion of the study is that safety analysis can be an effective tool to decrease occupational accident risks.     

Photovoltaic properties of nanocrystalline CdS films deposited by SILAR and CBD techniques—a comparative study

CdS films were fabricated using Successive Ionic Layer Adsorption and Reaction (SILAR) technique from starting solutions having S:Cd ratio 1:1, 3:1, 5:1 and 7:1 and their structural, surface morphological and optical properties were investigated and compared with that of their chemical bath deposited counterparts. The X-ray diffraction profiles showed that the films have cubic crystal structure with preferential orientation along the (111) plane and the intensity of the (111) plane increases for both the techniques as the S:Cd ratio increases. The energy dispersive X-ray analysis revealed that for SILAR deposited films, the S/Cd ratio in the sample increases from 0.8308 (for S:Cd 1:1) to 1.04 (for S:Cd 7:1) as the molar concentration of sulphur in the starting solution increases. But for CBD films, the S/Cd is only ~0.80 for all concentrations of sulphur in the starting solution. The optical band gap increases with the increase in S:Cd ratio in the starting solution in both the techniques.     

Variation in boron doping by planar diffusion – a comparative study of computational hydrodynamics and experimental observations

Abstract

Resistivity maps for Si wafers processed using BN solid sources and hydrogen injection were compared to convective flow patterns predicted computationally. The convective flow patterns were found to mirror the resistivity maps, with low velocity flow domains being associated with high resistivity regions on the wafer and high velocity flow with low resistivity regions. Subtle changes in both the flow patterns and resistivity maps as a function of location within the furnace were consistently reflected in both computed flow domains and measured resistitivies. Finally, axially eccentric placement of the wafer–source stack was found to promote convection between wafer–source pairs by as much as a factor of five.     

Similarity solutions for nonlinear diffusion — a new integration procedure

The nonlinear diffusion equation arises in many important areas of science and technology and most of the known exact solutions turn out to be similarity solutions. For a general similarity solution involving an arbitrary parameter , a new integration procedure is proposed which enables first integrals to be obtained for special values of . The best known exact solutions arise from this analysis when the integration constant is taken to be zero and the procedure provides a natural way of deducing other special exact solutions. A new exact solution is obtained for the power law diffusivity of index —4/3 and new first integrals are deduced for a general equation which includes nonlinear cylindrical and spherical symmetrical diffusion and one-dimensional nonlinear diffusion with an inhomogeneous diffusivity. The procedure has given rise to an extensive number of first-order ordinary differential equations which include a wide variety of differing physical situations and which warrant further study either analytically to determine exact integrals or numerically for particular boundary value problems.     

Unstable crack propagation—a fractographic study using PMMA in liquid environments

Double-torsion tests have been performed in liquid environments on PMMA samples with and without a grease coating to restrict the access of liquid, and over a range of testing speeds. Stable or stick-slip crack propagation could be obtained at will by varying the test conditions. Characteristic fracture markings accompanying unstable crack propagation provide evidence concerning the mechanism of crack arrest.     

Mechanics and mechanisms of fatigue in a WC–Ni hardmetal and a comparative study with respect to WC–Co hardmetals

There is a major interest in replacing cobalt binder in hardmetals (cemented carbides) aiming for materials with similar or even improved properties at a lower price. Nickel is one of the materials most commonly used as a binder alternative to cobalt in these metal-ceramic composites. However, knowledge on mechanical properties and particularly on fatigue behavior of Ni-base cemented carbides is relatively scarce. In this study, the fatigue mechanics and mechanisms of a fine grained WC–Ni grade is assessed. In doing so, fatigue crack growth (FCG) behavior and fatigue limit are determined, and the attained results are compared to corresponding fracture toughness and flexural strength. An analysis of the results within a fatigue mechanics framework permits to validate FCG threshold as the effective fracture toughness under cyclic loading. Experimentally determined data are then used to analyze the fatigue susceptibility of the studied material. It is found that the fatigue sensitivity of the WC–Ni hardmetal investigated is close to that previously reported for Co-base cemented carbides with alike binder mean free path. Additionally, fracture modes under stable and unstable crack growth conditions are inspected. It is evidenced that stable crack growth under cyclic loading within the nickel binder exhibit faceted, crystallographic features. This microscopic failure mode is rationalized on the basis of the comparable sizes of the cyclic plastic zone ahead of the crack tip and the characteristic microstructure length scale where fatigue degradation phenomena take place in hardmetals, i.e. the binder mean free path.     

Process capability analysis—a robustness study

The robustness of two popular process capability ratios, C_p and C_pk, when the random process being observed departs from normality is analysed. The distributions of estimated process capability ratios are derived and used as a basis for validation of large-scale simulation studies in an examination of departures from normality. The simulation studies and analytical results provide a basis for recommended procedures. It is recommended that the impact of process distributions be considered before using popular process capability indexes, due to the lack of robustness when departures from normality are ecountered. As an extension of our findings, we consider the Taguchi loss function as a generalization to process capability analysis regardless of the underlying population distribution.     

A hierarchical approach to analyzing knowledge integration between two fields—a case study on medical informatics and computer science

As a driver in modern science, interdisciplinary research has attracted a lot of attention. Major foci are laid on exploring the relations of multiple involved disciplines as well as the knowledge structure in interdisciplinary field. However, there is still a lack of decomposing the knowledge structure of interdisciplinary field to investigate how knowledge from relevant disciplines is integrated in the field. This study proposes an approach to investigating knowledge integration relationships between two research fields from a perspective of hierarchy. Medical Informatics (MI) and its most relevant field of Computer Science (CS) are chosen in the case study. This study decomposed each keyword network of the two fields into four layers by using the K-core method, then quantified the knowledge integration relationships between different layers of the two fields together. The results present that the MI basic layer shows the strongest knowledge integration with CS, followed by the middle layer, with the detail layer the weakest. And all MI layers have the greatest breadth and strength of knowledge integration with the CS middle layer, followed by the CS marginal layer and detail layer, but with the CS basic layer the weakest. A time series analysis shows that the integration of new CS knowledge into MI is a gradual process without explosive growth and the path of knowledge integration between the two fields were identified. The proposed approach could be applied to deeply understanding the integration of one discipline knowledge by an interdisciplinary field.

     

Problem solving in sintering of tungsten heavy alloy product — a case study

The authors in DMRL are engaged for last three decades in development and production of a repertoire of tungsten heavy alloy products mainly for defence applications where stringent quality control is imperative. An exhaustive knowledge-base has been built over the years with inputs from literature and in-house use R&D. This knowledge-base generally ensures continuous and smooth production of quality products. But, there was a case where this knowledge-base of sintering had been proved to be incapable of ascertaining and solving certain production problem. This particular problem was analysed and solved by Ishikawa technique. Based on the experience, the authors advocate that the knowledge of different statistical and problem solving tools is essential in the field of powder metallurgy.     

The performance of push and pull systems: a simulation and comparative study†

Ideally the just-in-time (pull system) production system holds no buffer inventory so that the production is ‘just in time’. This is achieved only when the stage's operation times are constant and equal; but realistically the variability of operator performance and/or the unequal distribution of task times precludes such an ideal situation. As a result, the production line experiences problems. In this paper we investigate the effects of these variabilities on the performance of push and pull systems and how the manager can decide which production technique to adopt. The implication of the simulation results are reported and openings for future research are identified.     

On coordinate-free measures of efficiency of least squares in a linear model

The efficiency of least squares in the linear model y=Xβ+u,where E(u)=0 and V(u)=Г. is considered. Several measures of efficiency have been defined for assessing the relative performance of least squares and best linear unbiased estimates of β, In this paper .far a consistent discussion, we define a doss of measures called coordinate-free measures of efficiency. Within this new framework almost all previous measures can be expressed.Examples of such measures ere given, and their meanings art examined Some results concerning same measares are also given.     

Benefits of retailer–supplier partnership initiatives under time-varying demand: a comparative analytical study

This paper aims to help supply chain managers to determine the value of retailer–supplier partnership initiatives beyond information sharing (IS) according to their specific business environment under time-varying demand conditions. For this purpose, we use integer linear programming models to quantify the benefits that can be accrued by a retailer, a supplier and system as a whole from shift in inventory ownership and shift in decision-making power with that of IS. The results of a detailed numerical study pertaining to static time horizon reveal that the shift in inventory ownership provides system-wide cost benefits in specific settings. Particularly, when it induces the retailer to order larger quantities and the supplier also prefers such orders due to significantly high setup and shipment costs. We observe that the relative benefits of shift in decision-making power are always higher than the shift in inventory ownership under all the conditions. The value of the shift in decision-making power is greater than IS particularly when the variability of underlying demand is low and time-dependent variation in production cost is high. However, when the shipment cost is negligible and order issuing efficiency of the supplier is low, the cost benefits of shift in decision-making power beyond IS are not significant.     

Retention behavior of ionizable isomers in reversed-phase liquid chromatography: a comparative study of porous graphitic carbon and octadecyl bonded silica

The retention behaviors of 36 positional isomers of ionizable substituted benzene compounds have been compared on two different packing materials: porous graphitic carbon (PGC) and octadecyl bonded silica (ODS) using 35% aqueous acetonitrile as the mobile phase. The effect of the mobile phase pH on the solute retention was studied over a range of pH values from pH 2.0 to 7.0. The retention as a function of pH was modeled using equations based on solute ionization. With PGC, the theoretical equations fitted the observed retention data for each class of solute, indicating that the retention mechanism was uniform over the whole pH range. However, with ODS, only the acidic solutes showed agreement with the theoretical model; for the amine-containing compounds, serious deviations from the theory were observed, suggesting that strongly acidic silanols gave added retention at low mobile phase pH. Overall, PGC demonstrated a higher selectivity toward positional isomers than ODS. This was attributed to the greater steric discriminating ability arising from the flat surface of the PGC compared with the more fluid nature of the ODS bonded phase.     

Same data—different results? Towards a comparative approach to the identification of thematic structures in science

Science studies are persistently challenged by the elusive structures of their subject matter, be it scientific knowledge or the various collectivities of researchers engaged with its production. Bibliometrics has responded by developing a strong and growing structural bibliometrics, which is concerned with delineating fields and identifying thematic structures. In the course of these developments, a concern emerged and is steadily growing. Do the sets of publications, authors or institutions we identify and visualise with our methods indeed represent thematic structures? To what extent are results of topic identification exercises determined by properties of knowledge structures, and to what extent are they determined by the approaches we use? Do we produce more than artefacts? These questions triggered the collective process of comparative topic identification reported in this special issue. The introduction traces the history of bibliometric approaches to topic identification, identifies the major challenges involved in these exercises, and introduces the contributions to the special issue.     

Engineering cartilage tissue interfaces using a natural glycosaminoglycan hydrogel matrix — An in vitro study

Hydrogels are suitable matrices for cartilage tissue engineering on account of their resemblance to native extracellular matrix of articular cartilage and also considering its ease of application, they can be delivered to the defect site in a minimally invasive manner. In this study, we evaluate the suitability of a fast gelling natural biopolymer hydrogel matrix for articular cartilage tissue engineering. A hydrogel based on two natural polymers, chitosan and hyaluronic acid derivative was prepared and physicochemically characterized. Chondrocytes were then encapsulated within the hydrogel and cultured over a period of one month. Cartilage regeneration was assessed by histological, biochemical and gene expression studies. Chondrocytes maintained typical round morphology throughout the course of this investigation, indicating preservation of their phenotype with sufficient production of extracellular matrix and expression of typical chondrogenic markers Collagen type 2 and aggrecan. The results suggest that the natural polymer hydrogel matrix can be used as an efficient matrix for articular cartilage tissue engineering.     

The protective effect of a helmet in three bicycle accidents—A finite element study

There is some controversy regarding the effectiveness of helmets in preventing head injuries among cyclists. Epidemiological, experimental and computer simulation studies have suggested that helmets do indeed have a protective effect, whereas other studies based on epidemiological data have argued that there is no evidence that the helmet protects the brain. The objective of this study was to evaluate the protective effect of a helmet in single bicycle accident reconstructions using detailed finite element simulations.Strain in the brain tissue, which is associated with brain injuries, was reduced by up to 43% for the accident cases studied when a helmet was included. This resulted in a reduction of the risk of concussion of up to 54%. The stress to the skull bone went from fracture level of 80 MPa down to 13–16 MPa when a helmet was included and the skull fracture risk was reduced by up to 98% based on linear acceleration. Even with a 10% increased riding velocity for the helmeted impacts, to take into account possible increased risk taking, the risk of concussion was still reduced by up to 46% when compared with the unhelmeted impacts with original velocity. The results of this study show that the brain injury risk and risk of skull fracture could have been reduced in these three cases if a helmet had been worn.     

ECAP processing and mechanical milling of Mg and Mg–Ti powders: a comparative study

A study was carried out into the possibility of employing ECAP processing in lieu of mechanical milling for the purpose of developing powder-based hydrogen storage alloys. Mg and Mg–Ti powder compacts were encapsulated in a copper block and were subjected to ECAP deformation to an apparent strain of ε = 4. This resulted in the consolidation of the compacts as well as in the refinement of their structures. The values of coherently diffracting volume size were as small as 70–80 nm, quite comparable to those achieved with mechanical milling. It is, therefore, concluded that ECAP processing can be employed successfully for the purpose of structural refinement. As for material synthesis, however, the ECAP is less efficient in expanding the interfacial area. Therefore, it is necessary to impose relatively heavy strains to able to achieve comparable expansion in the interfacial area. It appears that an advantage of ECAP deformation is the development of structures which have improved ability for milling. It is, therefore, recommended that in the processing of hydrogen storage alloys, the powder mixtures may be first processed with ECAP in open atmosphere and then by mechanical milling of a short duration carried out under protective atmosphere.