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Dumitru J.B.,Polytechnic University of Bucharest | Morega A.,Polytechnic University of Bucharest | Morega M.,Polytechnic University of Bucharest | Pislaru-Danescu L.,ICPE CA
Proceedings of the 2016 International Conference and Exposition on Electrical and Power Engineering, EPE 2016 | Year: 2016

Energy harvesting (EH) is a relatively new area of research seen as a viable and affordable solution for powering up small size, autonomous devices, e.g. wireless sensor arrays. EH devices utilize small-scale parts with low power losses. Key components are the electric power transformers, which convert the voltage/current parameters from the primary, energy harvesting stage to the secondary, storage and delivery levels of the device. Miniaturized constructions, whose implementation may benefit of LIGA fabrication technology, are needed for compact, small size yet power transfer fitted solutions. This paper presents a mathematical model and numerical simulation results for such a miniature, planar, spiral EPT. The study is concerned with the quasi-stationary electromagnetic field and heat transfer analysis of a miniature planar spiral power transformer for EH devices. The paper presents also several key design parameters of the MPST of interest in the DC/DC convertor design. © 2016 IEEE.

Tardei C.,ICPE CA | Mitrea S.,ICPE CA | Craciunescu O.,Institutul National Of Cercetare | Oprita E.I.,Institutul National Of Cercetare | Trusca R.,SC.METAV S.A
Revista Romana de Materiale/ Romanian Journal of Materials | Year: 2012

Intensive research is conducted both in understanding the phenomenon of "repair/healing of the bone" and for the development of techniques, devices and materials for effective applications involved in bone regeneration. This study is aimed at the development of a method to fabricate porous spherical tri-calcium phosphate (β-TCP) granules, which can be impregnated with a drug. Microspheres were prepared by the ionotropic gelation technique using CaCl2 as cross-linking agent. The microstructure and composition of ceramic microsphere were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM). In vitro cell culture tests showed that both ceramic microsphere types were highly biocompatible and favored cell growth during 72 hours of cultivation. Porous tri-calcium phosphate microspheres can be used for bone void filler, but also for drug delivery systems.

Geanta V.,Polytechnic University of Bucharest | Voiculescu I.,Polytechnic University of Bucharest | Stefanoiu R.,Polytechnic University of Bucharest | Savastru D.,Romanian National Institute for Optoelectronics | And 3 more authors.
Optoelectronics and Advanced Materials, Rapid Communications | Year: 2013

The multi-element materials with high entropy, generic called High Entropy Alloys - HEA, contains at least five metal elements, at concentrations between 5 and 35 atomic %. Recent researches in the field has shown that such materials have superior properties compared to traditional alloys (steel, super alloys etc.), and therefore, can be used in the top fields of the industry. High entropy alloys can be designed to have special characteristics such as high hardness combined with toughness and plasticity, which can be influenced by the chemical composition. The paper presents the results regarding the processing and characterization of high entropy multi-element materials from as cast AlCrFeCoNi class, for which were studied the influence of chemical composition on the mechanical and structural properties. It was found that by fast cooling of HEA, the breaking energy values are in the range 60... 72 J, while the microhardness varies in the range of 169... 516 HV0.1, depending on the materials composition.

Carp O.,Institute of Physical Chemistry Ilie Murgulescu | Patron L.,Institute of Physical Chemistry Ilie Murgulescu | Culita D.C.,Institute of Physical Chemistry Ilie Murgulescu | Budrugeac P.,ICPE CA | And 2 more authors.
Journal of Thermal Analysis and Calorimetry | Year: 2010

The thermal stability of two kinds of dextran-coated magnetite (dextran with molecular weight of 40,000 (Dex40) and 70,000 (Dex70)), obtained by dextran adsorption onto the magnetite surface is investigated in comparison with free dextran in air and argon atmosphere. The thermal behavior of the two free dextran types and corresponding coated magnetites is similar, but atmosphere dependent. The magnetite catalyzes the thermal decomposition of dextran, the adsorbed dextran displaying lower initial decomposition temperatures comparative with the free one in both working atmospheres. The dextran adsorbed onto the magnetite surface decomposes in air through a strong sharp exothermic process up to ~450 °C while in argon atmosphere two endothermic stages are identified, one in the temperature range 160-450 °C and the other at 530-800 °C. © 2009 Akadémiai Kiadó, Budapest, Hungary.

Prepelita P.,Romanian National Institute for Lasers, Plasma and Radiation Physics | Medianu R.,Romanian National Institute for Lasers, Plasma and Radiation Physics | Sbarcea B.,ICPE CA | Garoi F.,Romanian National Institute for Lasers, Plasma and Radiation Physics | Filipescu M.,Romanian National Institute for Lasers, Plasma and Radiation Physics
Applied Surface Science | Year: 2010

ZnO thin films with thikness d = 100 nm were deposited onto different substrates such as glass, kapton, and silicon by radio frequency magnetron sputtering. The structural analyses of the films indicate they are polycrystalline and have a wurtzite (hexagonal) structure. The ZnO layer deposited on kapton substrate shows a stronger orientation of the crystallites with (0 0 2) plane parallel to the substrate surface, as compared with the other two samples of ZnO deposited on glass and silicon, respectively. All three layers have nanometer-scale values for roughness, namely 1.7 nm for ZnO/glass, 2.4 nm for ZnO/silicon, and 6.8 nm for ZnO/kapton. The higher value for the ZnO layer deposited on kapton substrate makes this sample suitable for solar cells applications. Transmission spectra of these thin films are strongly influenced by deposition conditions. With our deposition conditions the transparent conducting ZnO layer has a good transmission (78-88%) in VIS and NIR domains. The values of the energy gap calculated from the absorption spectra are 3.23 eV for ZnO sample deposited onto glass substrate and 3.30 eV for the ZnO sample deposited onto kapton polymer foil substrate. The influence of deposition arrangement and oxidation conditions on the structural, morphological, and optical properties of the ZnO films is discussed in the present paper. © 2009 Elsevier B.V. All rights reserved.

Moldovan P.,Polytechnic University of Bucharest | Csaki I.,Polytechnic University of Bucharest | Popescu G.,Polytechnic University of Bucharest | Lucaci M.,ICPE CA | And 2 more authors.
Composites Part B: Engineering | Year: 2015

A metallic matrix composite, with AlSi9Cu3 matrix reinforced with 5% copper coated graphite (GrCu) was processed in semi solid state by centrifugal casting. This technique allows the uniform controlled distribution of the reinforcing material to provide improved tribological properties in certain area. The graphite particles were copper coated for a better embedding in the matrix. The microstructure evolution revealed compounds containing Mn, Si and Mg in the matrix alloy and the final composite and controlled distribution of the copper coated graphite as reinforcing material. The hardness measurement showed 48% improvement towards the matrix alloy and the Young modulus showed 27% improvement. The friction coefficient and wear rate obtained revealed a very good and promising behavior of the composite processed in semi solid state for ball bearings ring application. © 2015 Elsevier Ltd. All rights reserved.

Ciuprina F.,Polytechnic University of Bucharest | Andrei L.,Polytechnic University of Bucharest | Panaitescu D.,ICECHIM | Zaharescu T.,ICPE CA
Proceedings of the 2016 IEEE International Conference on Dielectrics, ICD 2016 | Year: 2016

The influence of the temperature variation and of the sense of this variation, increasing or decreasing, on the dielectric behavior of polypropylene (PP)-SiO2 nanocomposites were studied in this work. The dielectric spectra were recorded in the range 10-2 - 106 Hz in three different modes of temperature variation, between 27 °C and 77 °C. The results show that the relaxation frequency at a given temperature may vary up to four orders of magnitude depending whether that temperature was reached in increasing or decreasing way. Water absorption during temperature variation and chemiluminescence results are discussed in connection with the dielectric behavior. © 2016 IEEE.

Dumitru A.,ICPE CA | Velciu G.,ICPE CA | Marinescu V.,ICPE CA | Sbarcea G.,ICPE CA
Revista Romana de Materiale/ Romanian Journal of Materials | Year: 2012

The elaboration of bulk (1-x)Pb(Mg 1/3Nb 2/3)-xPbTiO 3 by using the columbite method is presented. The main aim of the processing was to avoid the formation of an unwanted pyrochlore phase. Optimized sintering temperatures have been chosen in correlation with the densification evolution. Samples with the PMN/PT ratio of 1.0/0.0, 0.9/0.1 and 0.65/0.35 have been processed; X-Ray diffraction and scanning electronic microscopy investigation are presented. The results showing the formation of pyrochlorefree structure in all the investigated samples at sintering temperatures around 1,100°C.

Prepelita P.,National Institute for Laser, Plasma and Radiation Physics | Craciun V.,National Institute for Laser, Plasma and Radiation Physics | Sbarcea G.,ICPE CA | Garoi F.,National Institute for Laser, Plasma and Radiation Physics
Applied Surface Science | Year: 2014

Transparent thin films of SnO2, ZnO:Al, and ITO were deposited onto glass substrate by vacuum thermal evaporation technique, from 0.5 cm diameter grains (i.e. ITO, ZnO:Al (3%) and SnO2) with 99.99% purity. To improve the quality (i.e. stoichiometry and morphology) of these thin films, they were annealed at 400 °C in air for 2 h. Following this annealing, the samples become suitable to be used as contact electrodes for solar cells. The investigations were performed on samples having a polycrystalline structure, as revealed by X-ray diffraction analysis after annealing process. Moreover, these thin films had a strong orientation with the following planes parallel to the substrate: (1 0 1) for SnO2, (0 0 2) for ZnO:Al and (2 2 2) for ITO film respectively. Atomic force microscopy (AFM) investigations of the ZnO:Al (Rrms = 2.8 nm) and ITO samples (Rrms = 11 nm) show they are homogeneous and a slightly higher roughness (Rrms = 51 nm) for the SnO2 thin film surface. The size and shape of the grains were also observed and investigated by scanning electron microscopy (SEM). All SnO2, ZnO:Al and ITO transparent thin films are uniform and dense.The values obtained for electrical resistivity, transmission and energy bandgap as well as conductivity and transparency properties of these thin films, make them suitable to be used as transparent contact electrodes for solar cells. © 2014 Elsevier B.V. All rights reserved.

Ciuprina F.,Polytechnic University of Bucharest | Andrei L.,Polytechnic University of Bucharest | Tomescu F.M.G.,Polytechnic University of Bucharest | Plesa I.,ICPE CA | Zaharescu T.,ICPE CA
Proceedings of IEEE International Conference on Solid Dielectrics, ICSD | Year: 2013

An electrostatic model to explain and predict the dielectric properties of nanocomposites made of low density polyethylene (LDPE) filled with SiO 2 nanoparticles is presented. In the present approach the modeled nanodielectric is a polymer matrix with uniformly distributed identical spherical nanoparticles embedded, each nanoparticle being surrounded by a three-layer interface. Assuming a possible structure of the interface, an estimation of the dipole types and concentrations is made and then the permittivity and charge distribution inside the interface regions are estimated and used in a numerical model based on the finite element method. The computational domain of the 3D numerical model developed for the LDPE-SiO 2 nanodielectric is reduced to an elementary fraction of the whole geometry (a cube containing eight nanoparticles), by taking into account the existing physical symmetries imposed by appropriate boundary conditions. This model is implemented in the finite element method based software package COMSOL Multiphysics for three filler concentrations: 2, 5 and 10 wt%. The results show a good correlation between the effective permittivity calculated with our model and the experimentally measured permittivity and emphasize the influence of the space charge presence inside nanodielectric on the electric field repartition and on the effective permittivity. A comparison between our results and those obtained with other models is also discussed. © 2013 IEEE.

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