Influence de la précontrainte et de la température sur les propriétés électrique du VHB4910

International audienceLes élastomères diélectriques sont de plus en plus utilisés pour créer des transducteurs dans de nombreux domaines industriels : interface haptique, robotique, biomimétisme, énergie. Dans le domaine de l'énergie, le développement de générateurs électrostatiques souples tient une large place. Toutefois, le courant de fuite diminue l'efficacité et la durée de vie des dispositifs utilisant ces matériaux. Cette étude concerne donc l'influence des facteurs externes (étirement, température) sur les propriétés électriques du polyacrylate VHB4910, un des matériaux largement utilisés pour créer des générateurs. Nous relevons que le courant de fuite augmente avec l'augmentation de l'étirement. Ce comportement peut se combiner avec l'effet de la température

ÉTUDE DES PHÉNOMÈNES HYDRODYNAMIQUESENGENDRÉS DANS LES LIQUIDES DIÉLECTRIQUESPAR UN CHAMP ÉLECTRIQUE TRÈS INTENSE

Insulating liquids represent a weakness in high voltage devices in that their failure to maintain a high applied voltage between component électrodes generally means the breakdown. Much research has gone into attempting to explain the fundamental processes (electronic and hydrodynamic processes) behind this. The clarification of thèse mechanisms, especially the hydrodynamic processes is one of the main tasks of our work, We présent an expérimental study about the évolution of the hydrodynamic phenomena (bubble and shock wave) as a function of injected energy (0,01-lOOnJ), liquid pressure in a large range, from 0.1 to lOMPa, liquid properties, etc. At first, we hâve evidenced the existence of the bubble largely above the critical pressure of the liquids. For the purpose of making the mechanism of cavitation clear the chronology of the events was also discussed. The observed physical phenomena are similar to those obtained by laser induced breakdown in water. The différence is mainly revealed in the dimensions and characteristic times of the phenomena. An analysis of the bubble rebounds and dissipatives processes is also given. Moreover, our expérimental study of the bubble dynamics in viscous liquids allows us to clearly separate two différent hydrodynamic régimes namely inertial and viscous régimes. We hâve shown that viscosity plays an important rôle in putting a lower limit on the size of cavitating bubbles and is the prédominant damping factor for small bubbles. In conséquence, bubble lifetime is much higher than the Rayleigh time and rebounds of the bubble are practically undetectable. Numerical results of the Rayleigh-Plesset model are in good agreement with expérimental observationsLes liquides isolants représentent une faiblesse des dispositifs haute tension, car leur incapacité à maintenir une tension appliquée élevée entre les électrodes des composants signifie généralement une panne. De nombreuses recherches ont été consacrées à expliquer les processus fondamentaux (processus électroniques et hydrodynamiques) à l’origine de ce phénomène. La clarification de ces mécanismes, en particulier des processus hydrodynamiques, est l’une des tâches principales de notre travail. Nous présentons une étude expérimentale sur l’évolution des phénomènes hydrodynamiques (bulle et onde de choc) en fonction de l’énergie injectée (0,01 à 100 nm). ), la pression du liquide dans une large gamme, allant de 0,1 à lOMPa, ses propriétés, etc. Nous avons d’abord mis en évidence l’existence de la bulle bien au-dessus de la pression critique des liquides. Afin de clarifier le mécanisme de cavitation, la chronologie des événements a également été discutée. Les phénomènes physiques observés sont similaires à ceux obtenus par la décomposition en eau induite par laser. La différence est principalement révélée par les dimensions et les moments caractéristiques des phénomènes. Une analyse des processus de rebond de bulle et de dissipation est également présentée. De plus, notre étude expérimentale de la dynamique des bulles dans les liquides visqueux nous permet de séparer clairement deux régimes hydrodynamiques différents, à savoir les régimes inertiel et visqueux. Nous avons montré que la viscosité joue un rôle important en limitant la taille des bulles cavitantes et constitue le facteur d’amortissement prédominant pour les petites bulles. En conséquence, la durée de vie de la bulle est beaucoup plus longue que celle de Rayleigh et les rebonds de la bulle sont pratiquement indétectables. Les résultats numériques du modèle de Rayleigh-Plesset sont en bon accord avec les observations expérimentale

Evaluation of Activation Parameters of Molecular Mobility of Parylene C Using Differential Scanning Calorimetry, Dielectric Spectroscopy, and Thermally Stimulated Depolarization Currents

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Electrical properties of low temperature deposited amorphous barium titanate thin films as dielectrics for integrated capacitors

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Structural, optical and electrical properties of NiMO4 (M=W and Mo)

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Pre-stretch induced leakage current in VHB electroactive polymers

International audienceDielectric elastomers generators (DEGs) constitute promising systems due to their high energy density. This latter isinfluenced by viscoelasticity and the leakage current. An understanding of this leakage current and how it can beinfluenced by the stretch state of material is required to predict or optimize DEGs. In this context, our work consisted instudying the evolution of the leakage current in commercial electroactive polymer (3 M VHB4910) using silver grease aselectrodes. This analysis has been performed in order to evaluate the influence of three different factors: the biaxial prestretch(2 = 4, 9 and 16), the temperature (from 20°C to 80°C) and the high electric field (from 1MVm -1 to 20MVm-1).Main results are (i) the increase in the leakage current at higher pre-stretch due to the increase of the electric field, (ii) apredominant Schottky conduction mechanism (iii) a lower current at room temperature for asymmetric pre-stretchcompared to an equivalent area surface ratio with symmetric pre-stretch, (iv) the point iii fails when the material works attemperatures higher than room temperature. Probable changes in the molecular chains with strain explain these results

Thermally stimulated currents in amorphous barium titanate thin films deposited by RF magnetron sputtering

International audienceThermally stimulated currents (TSCs) are measured in amorphous barium titanate thin films deposited by the rf sputtering technique. The TSC global curve is composed of three overlapping peaks in the 0-200 °C temperature range. At 50 °C, a first TSC peak is observed that can be related to a shallow-trap level. A second peak due to a dipolar polarization process is observed at 95 °C. Finally, a third peak appears at 140 °C that is ascribed to the oxygen vacancy motion and their accumulation at electrodes. The different peaks constituting the global TSC spectrum are separately studied by the fractional polarization technique in order to analyze their fine structures and to determine their activation energies

Effect of Oxygen Addition in the Sputtering Gas on the Dielectric Properties of a-BaTiO3 Films

International audienceAmorphous barium titanate films (a-BTO) were grown by the RF magnetron sputtering technique at low temperature and under various oxygen/argon mixing ratios (OMR). Their dielectric properties (dielectric constant, loss and ac conductivity in the 0.1-105 Hz range), dc leakage currents, and thermally stimulated currents were systematically studied as a function of OMR in the sputtering gas (0 to 20 %). We demonstrate that the presence of oxygen plays a significant role in improving the dielectric properties of a-BTO thin films. The oxygen incorporation successfully suppressed some electrical defects. The bulk conductivity and leakage currents are reduced although a small decrease of dielectric constant has been observed. Films prepared at higher oxygen ratio (20%) have a small leakage current density (3.6 × 10−7 A/m2) and lower tangent loss (2 × 10−3)

Pre-stretch induced leakage current in VHB electroactive polymers

International audienceDielectric elastomers generators (DEGs) constitute promising systems due to their high energy density. This latter isinfluenced by viscoelasticity and the leakage current. An understanding of this leakage current and how it can beinfluenced by the stretch state of material is required to predict or optimize DEGs. In this context, our work consisted instudying the evolution of the leakage current in commercial electroactive polymer (3 M VHB4910) using silver grease aselectrodes. This analysis has been performed in order to evaluate the influence of three different factors: the biaxial prestretch(2 = 4, 9 and 16), the temperature (from 20°C to 80°C) and the high electric field (from 1MVm -1 to 20MVm-1).Main results are (i) the increase in the leakage current at higher pre-stretch due to the increase of the electric field, (ii) apredominant Schottky conduction mechanism (iii) a lower current at room temperature for asymmetric pre-stretchcompared to an equivalent area surface ratio with symmetric pre-stretch, (iv) the point iii fails when the material works attemperatures higher than room temperature. Probable changes in the molecular chains with strain explain these results

The Evaluating of the activation parameters in the transition region of parylene C by thermally stimulated techniques

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