Literatura científica selecionada sobre o tema "Electro-Thermo-Optical characterizations"

In this paper, broadband Spectral Domain Interferometry provides single-shot optical characterization of dispersive thermotropic nematic liquid crystals. The proposed experimental setup enables measuring the chromatic dispersion, the extended Cauchy equation parameters knowing the optical index for one wavelength, and the thermo-optical coefficients to ascribe the dependence of the optical index with the inner temperature. The analysis is applied to the commonly known E 7 mixture and to M L C 2132 , whose chromatic properties are not referenced although the mixture is commercial, demonstrating the latter’s interest for electro-optical or thermo-optical applications of thick nematic liquid crystal cells.

Liquid-crystalline elastomers (LCEs) are the object of many research investigations due to their reversible and controllable shape deformations, and their high potential for use in the field of soft robots and artificial muscles. This review focuses on recent studies about polymer composites based on LCEs and nanomaterials having different chemistry and morphology, with the aim of instilling new physical properties into LCEs. The synthesis, physico-chemical characterization, actuation properties, and applications of LCE-based composites reported in the literature are reviewed. Several cases are discussed: (1) the addition of various carbon nanomaterials to LCEs, from carbon black to carbon nanotubes, to the recent attempts to include graphene layers to enhance the thermo-mechanic properties of LCEs; (2) the use of various types of nanoparticles, such as ferroelectric ceramics, gold nanoparticles, conductive molybdenum-oxide nanowires, and magnetic iron-oxide nanoparticles, to induce electro-actuation, magnetic-actuation, or photo-actuation into the LCE-based composites; (3) the deposition on LCE surfaces of thin layers of conductive materials (i.e., conductive polymers and gold nanolayers) to produce bending actuation by applying on/off voltage cycles or surface-wrinkling phenomena in view of tunable optical applications. Some future perspectives of this field of soft materials conclude the review.

Abstract In this present article, synthesis, characterization, and study of optical parameters through image enhancement methods have been carried out on 4l-hexyloxy-4-cyanobyphenyl (6OCB) pure liquid crystal (LC) and 6OCB with dispersion of 0.5 wt% ZnO nanoparticles. Textural determinations of the synthesized compounds are recorded by using SDTECHS POM connected with a hot stage and camera. differential scanning calorimetry (DSC) is used to measure enthalpy and transition temperature values. The results show that the dispersion of ZnO in 6OCB exhibits nematic phase as same as the pure 6OCB with slightly reduced clearing temperature as expected. Further characterization is carried out by various spectroscopic techniques like X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet visible (UV–Vis) spectroscopy. To evaluate and identify the behavior of optical parameters viz optical transmittance (OT), absorption coefficient (AC), and phase retardation (PR) as a function of temperature, an image processing method has been proposed, i.e. illumination enhancement algorithm (IEA) using MATLAB software. The proposed enhancement algorithm is one of the simplest and efficient algorithms to evaluate the thermo optical parameters for various electro optical applications. The results are compared with the body of the data available.

En 2008, pour la première fois toutes les fonctions d’éclairage avant d’un véhicule sont entièrement à LEDs. Cette source de lumière a ouvert l'âge d'or de l'éclairage automobile par la basse consommation électrique, l’efficacité, la fiabilité, la haute luminosité, la compacité, ainsi que la rentabilité. Ces qualités lui ont permis de gagner la majorité des parts de marché dans l’automobile.La miniaturisation de la LED a permis la pixellisation du faisceau lumineux. Cela améliore davantage la sécurité routière. En effet, éclairer la route sans éblouir les autres usagers est devenu possible avec cette technologie. En outre, le besoin d'éclairage évolue avec l'arrivée de la voiture autonome. C’est alors que les technologies des LEDs pixélisées représentent des perspectives dans le domaine de l’éclairage pour les capteurs, et même dans la communication par la projection des pictogrammes et/ou l’écriture sur la route. Un second axe de recherche sera traité dans cette thèse. Il consiste à étudier les LEDs rouges avec luminophore pour les fonctions de signalisation arrière en automobile.De nouveaux mécanismes de défaillances vont faire surface, dû à ces nouveaux profils de mission et les nouvelles techniques de fabrication des LEDs immatures. Un besoin critique d’une démarche scientifique pour définir et exécuter un plan de tests et des caractérisations électriques, optiques, physiques et thermiques de ces nouvelles technologies.Les objectifs principaux de ces travaux de thèse seront de développer des nouvelles méthodes, des nouveaux bancs de caractérisations Opto-Électro-Thermiques et d’investiguer les modes et les mécanismes de défaillances liés aux processus de fabrication, géométries, matériaux de composition et aux nouveaux profils de mission des systèmes d'éclairage
In 2008, all front lighting functions of a vehicle are based on full LEDs for the first time. This light source opened the golden age of automotive lighting through low power consumption, efficiency, reliability, high brightness, compactness, as well as cost efficiency. These qualities have enabled it to gain the majority of the automotive market share.The miniaturization of the LED made possible the light beam pixelization. This further improves road safety. Indeed, lighting the road without glairing other users has become possible with this technology. In addition, lighting needs are changing with the arrival of the autonomous car. This is when pixelated LED technologies represent prospects in the field of lighting for sensors, and even in communication through the projection of pictograms and / or writing on the road.A second research axis will be dealt with in this thesis. It consists of studying red LEDs with phosphor for automotive rear signaling functions.New failure mechanisms will emerge, due to these new mission profiles and new techniques for manufacturing immature LEDs. A critical need for a scientific approach to define and execute a test plan and electrical, optical, physical and thermal characterizations of these new technologies.The main objectives of this thesis will be to develop new methods, new Opto-Electro-Thermal benchs’ characterizations and to investigate the modes of failure mechanisms related to manufacturing processes, geometries, composition materials and to new lighting systems mission profiles