21 research outputs found

    Ab initio study of elastic properties of orthorhombic cadmium stannate as a substrate for the manufacture of MEMS devices

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    International audienceThe elastic properties of the orthorhombic cadmium stannate (Cd2SnO4) were investigated using density functional theory, applying both energy-strain relationship (which is found in the literature) and stress-strain relationship (which we have developed in this study), both in the generalized gradient approximation and local density approximation (LDA) as implemented in the Quantum Espresso code. The results from both methods were found to be in good agreement with each other. However, the values for the stress-strain calculation were found to be relatively higher than those of the energy-strain and also, were those obtained from the LDA. The study found out that Cd2SnO4 possesses desirable elastic properties that are comparable to those of silicon, the dominant substrate material used in the manufacture of Microelectromechanical Systems. The bulk modulus was found to be nearly twice (more than 1.5 times) that of Si. Moreover, the material was found to be ductile, which when combined with the transparent nature that has been studied earlier and is available in the literature, can form a better substrate for the manufacture of transparent and flexible MEMS such as cardiopulmonary sensors, microbolometers, temperature and pressure sensors

    Structural and Mechanical Properties of NbN Alloyed with Hf, In, and Zr for Orthopedic Applications: A First-Principles Study

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    The search for biocompatible, non-toxic, and wear-resistant materials for orthopedic implant applications is on the rise. Different materials have been investigated for this purpose, some of which have proved successful. However, one challenge that has proven difficult to overcome is the balance between ductility and hardness of these materials. This study employed ab initio calculations to investigate the structural and mechanical properties of niobium nitride (NbN) alloyed with hafnium, indium, and zirconium, with the aim of improving its hardness. The calculations made use of density function theory within the quantum espresso package’s generalized gradient approximation, with Perdew–Burke–Ernzerhof ultrasoft pseudopotentials in all the calculations. It was found that addition of the three metals led to an improvement in both the shear and Young’s moduli of the alloys compared to those of the NbN. However, both the bulk moduli and the Poisson’s ratios reduced with the introduction of the metals. The Young’s moduli of all the samples were found to be higher than that of bone. The Vickers hardness of the alloys were found to be significantly higher than that of NbN, with that of indium being the highest. The alloys are therefore good for wear-resistant artificial bone implants in ceramic acetabulum, and also in prosthetic heads

    Investigation of long acoustic waveguides for the very low frequency characterization of monolayer and stratified air-saturated poroelastic materials

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    International audienceWhen sound propagates in a porous medium, it is attenuated via several energy loss mechanisms which are switched on or o as the excitation frequency varies. The classical way of measuring acoustic energy loss in porous materials uses the Kundt impedance tube. However, due to its short length, measurements are made in the steady state harmonic regimes. Its lower cuto frequency is often limited to a few hundreds of Hertz. Two long acoustic waveguides were assembled from water pipes and mounted to create test-rigs for the low-frequency acoustic characterization of monolayer and stratied air-waveguides were found to be equivalent and provided data down to frequencies of the order of ≈ 12 Hz

    Acoustics of Fractal Porous Material and Fractional Calculus

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    International audienceThis article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC B

    Thermal properties and pressure-dependent elastic constants of cadmium stannate as a substrate for MEMS: An ab initio study

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    International audienceSilicon carbide (SiC) has become a suitable replacement to silicon as a substrate for manufacture of microelectromechanical systems (MEMS) that operate in harsh environmental conditions, owing to its better mechanical properties such as excellent wear resistance. However, just like silicon, SiC is also brittle, a property that limits its application as a substrate for manufacture of flexible MEMS. In this study, we explored the thermal properties as well as the pressure-dependent elastic constants of cadmium stannate (Cd2SnO4) for the first time within the quantum espresso code. The result showed that the elastic constants of SiC are much higher than those of Cd2SnO4. The properties of SiC were found to be more sensitive to the applied pressure compared those of Cd2SnO4, implying that it is less mechanically and thermally stable with the applied pressure compared to Cd2SnO4, and therefore, less appealing compared to Cd2SnO4 for the manufacture of most MEMS

    Investigating the Young's modulus of Cu-Al-Be shape memory alloy using a phase diagram, vibration spectroscopy and ultrasonic waves

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    This work presents a method for determining the effective Young’s modulus (Eeffective) and Poisson ratio of small specimens of a ternary shape memory alloy (SMA), Cu-Al-Be. The alloys were synthesized uniformly and homogeneously using various concentrations of high purity metals and formed into slabs of different geometrical shapes. The phases and fractional quantities of each sub-alloy composing the SMA were determined using SEM/EDS data and the lever rule, and confirmed by matching computed and measured X-ray diffraction peak patterns. The Eeffective was determined using the rule of mixtures, employing elastic moduli obtained from Ab initio (Density functional theory) calculations. To address the challenge of determining Eeffective experimentally for small specimens, high frequency ultrasonic waves and vibration spectroscopy were used. The Eeffective was then used in a 3D finite element model to compute the vibrational spectrum’s resonance peaks, which were found to match those of the experimental vibrational response. The Eeffective was also compared to the pressure wave (P-waves) modulus recovered using non-contact ultrasound waves propagating through the sample’s thickness. Discrepancies mainly occurring for alloys with the ÎČ phase were resolved by determining its anisotropic spatial Young’s modulus. Overall, the presented method provides a comprehensive characterization of the mechanical properties of small alloy specimens

    Thermal properties and pressure-dependent elastic constants of cadmium stannate as a substrate for MEMS: An ab initio study

    No full text
    Silicon carbide (SiC) has become a suitable replacement to silicon as a substrate for manufacture of microelectromechanical systems (MEMS) that operate in harsh environmental conditions, owing to its better mechanical properties such as excellent wear resistance. However, just like silicon, SiC is also brittle, a property that limits its application as a substrate for manufacture of flexible MEMS. In this study, we explored the thermal properties as well as the pressure-dependent elastic constants of cadmium stannate (Cd2SnO4) for the first time within the quantum espresso code. The result showed that the elastic constants of SiC are much higher than those of Cd2SnO4. The properties of SiC were found to be more sensitive to the applied pressure compared those of Cd2SnO4, implying that it is less mechanically and thermally stable with the applied pressure compared to Cd2SnO4, and therefore, less appealing compared to Cd2SnO4 for manufacture of most MEM

    Flow of a Self-Similar Non-Newtonian Fluid Using Fractal Dimensions

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    International audienceIn this paper, the study of the fully developed flow of a self-similar (fractal) power-law fluid is presented. The rheological way of behaving of the fluid is modeled utilizing the Ostwald–de Waele relationship (covering shear-thinning, Newtonian and shear-thickening fluids). A self-similar (fractal) fluid is depicted as a continuum in a noninteger dimensional space. Involving vector calculus for the instance of a noninteger dimensional space, we determine an analytical solution of the Cauchy equation for the instance of a non-Newtonian self-similar fluid flow in a cylindrical pipe. The plot of the velocity profile obtained shows that the rheological behavior of a non-Newtonian power-law fluid is essentially impacted by its self-similar structure. A self-similar shear thinning fluid and a self-similar Newtonian fluid take on a shear-thickening way of behaving, and a self-similar shearthickening fluid becomes more shear thickening. This approach has many useful applications in industry, for the investigation of blood flow and fractal fluid hydrolog
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