This study investigates the optical properties of the twisted-nematic liquid-crystals at oblique directions and their applications. A large difference in the phase retardation and the twisted angle of the TN-LC from different viewing directions occurs at the low voltage regime. The proposed viewing angle switching (VAS) panel is developed using this large optically anisotropic behavior of the TN-LC. The proposed VAS panel is only perceived clearly at normal and downward directions in a narrow viewing angle mode to ensure high privacy protection, it highly promising for mobile device applications.

In this study, a liquid-crystal display (LCD) with the capability of switchable viewing-angle is proposed. The contrast ratio of the LCD mainly depends on the transmittance of the bright state and the dark state. By using the improved structure of the pixel electrodes, the viewing angle of the LCD can be switched between the wide viewing-angle mode and the narrow-viewing angle mode. Based on the proposed three-electrode structure, the liquid-crystal orientation of the LCD is controlled to generate different light-leakage conditions at large viewing angles, thus, resulting in the switch of the viewing angle of the LCD. The proposed structure, which has the slim outline and low-cost of the LCD, is a simple way to control the viewing angle of the LCD. Potential applications for the protection of personal privacy are emphasized.

International Telemetering Conference Proceedings / October 23-26, 2000 / Town & Country Hotel and Conference Center, San Diego, California / A thinned array sensor system develops error voltages for steering dish antennas from signals arriving over a broad range of angles, thereby eliminating need for a priori knowledge of signal location.

PDMS has not only the characteristics of good chemical and physical properties,flexible, low surface free energy, and good optically transparent, also has the advantages of low cost, low toxicity and environmental protection. In this study we use PDMS to fabricate liquid crystal device with different micro-confined structures. We had a discussion about liquid crystal in the micro-confined structure through optical textures and measured electro-optical characteristics on our device. Through the experiment we found the liquid crystal device with micro-confined structure had not only the characteristics of wide viewing angle and contrast ratio has been up to standard in normal display. And it also demonstrated the capability in flexible liquid crystal display.

In this study, a liquid crystal display (LCD) is proposed to have a capability of viewing-angle-switching in all directions. In the proposed LCD, a three-electrode structure is used to control the viewing angle of the LCD. By using a bi-direction slit type electrode, fringe fields with two different directions are generated. The fringe fields cause a light leakage of the dark state in all directions. Experimental results reveal that the proposed LCD has viewing angle within 40o in both vertical and horizontal directions when the area ratio of the vertical and horizontal slit is 1:1. Furthermore, contrast ratio (CR) of the proposed LCD increases as cell gap increases. When the angle between polarizer axis and LC is 0, the proposed LCD has the highest CR in the normal direction. The personal privacy is protected based on the proposed LCD due to the all-direction light leakage in the dark state.

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Low power consumption is a critical requirement for all liquid crystal display (LCD) devices. A field sequential color (FSC) LCD was proposed by using red (R), green (G) and blue (B) LEDs and removing the lossy component of color filters which only transmits ~30% of the incoming white light. Without color filters, FSC LCDs exhibit a ~3X higher optical efficiency and 3X higher resolution density as compared to the conventional color filters-based LCDs. However, color breakup (CBU) is a most disturbing defect that degrades the image quality in FSC displays. CBU can be observed in stationary or moving images. It manifests in FSC LCDs when there is a relative speed between the images and observers’ eyes, and the observer will see the color splitting patterns or rainbow effect at the boundary between two different colors. In Chapter 2, we introduce a five-primary display by adding additional yellow(Y) and cyan(C) colors. From the analysis and simulations, five primaries can provide wide color gamut and meanwhile the white brightness is increased, as compared to the three-primary. Based on the five-primary theorem, we propose a method to reduce CBU of FSC LCDs by using RGBYC LEDs instead of RGB LEDs in the second section. Without increasing the sub-frame rate as three-primary LCDs, we can reduce the CBU by utilizing proper color sequence and weighting ratios. In addition, the color gamut achieves 140% NTSC and the white brightness increases by more than 13%, as compared to the three-primary FSC LCDs. Another strategy to suppress CBU is using higher field frequency, such as 540 Hz or even up to 1000 Hz. However, this approach needs liquid crystals with a very fast response time (

Les travaux de cette thèse s’inscrivent dans le cadre du planning de traitements minimalement invasifs des lésions des artères coronaires. Le cardiologue réalise un examen coronarographique, puis dans la continuité, une angioplastie transluminale. L’angiographie rotationnelle à rayons X permet de visualiser sous différentes incidences 2D la lumière des artères coronaires sur plusieurs cycles cardiaques et aussi d’obtenir une reconstruction 3D+T des arbres coronaires. A partir de cette séquence, notre objectif est de déterminer automatiquement une incidence optimale 2D du segment sténosé compatible avec les angles du C-arm afin d’aider le cardiologue lors de l’intervention.Différentes étapes sont considérées pour calculer la position angulaire optimale du C-arm. Afin de suivre la zone de lésion durant le cycle cardiaque, une première méthode est proposée pour mettre en correspondance tous les arbres de la séquence 3D+T. Tout d’abord, un appariement deux à deux des arbres successifs est réalisé afin de construire un arbre d’union. Ces derniers sont ensuite fusionnés afin d’obtenir un arbre mosaïque représentant l’arbre le plus complet de la séquence. L’utilisation de mesures de similarités géométriques et hiérarchiques ainsi que l’insertion de nœuds artificiels permet de prendre en compte les différents mouvements non-rigides des artères coronaires subits au cours du cycle cardiaque et les variations topologiques dû à leurs extractions. Cet appariement nous permet de proposer une deuxième méthode afin d’obtenir une vue angiographique 2D optimale de la zone de lésion tout le long du cycle cardiaque. Cette incidence est proposée spécifiquement pour trois types de région d’intérêt (segment unique, segment multiple ou bifurcation) et est calculée à partir de quatre critères (raccourcissement, chevauchement interne et externe ou angle d’ouverture de bifurcation). Une vue 2D déployée du segment projeté avec le moins de superposition avec les structures vasculaires avoisinantes est obtenue. Nous donnons également la possibilité au cardiologue d’avoir une incidence optimale privilégiant soit le déploiement du stent ou soit le guidage d’outils de la racine de l’arbre à la zone sténosée. Nos différents algorithmes ont été évalués sur une séquence réelle de 10 phases segmentées à partir d’un CT et de 41 séquences simulées. / The thesis work deals with the planning of minimally invasive surgery of coronary artery lesions. The physician performs a coronarography following by a percutaneous transluminal angioplasty. The X-ray rotational angiography permits to visualize the lumen artery under different projection angles in several cardiac cycles. From these 2D projections, a 3D+T reconstruction of coronary arteries can be obtained. Our goal is to determine automatically from this 3D+T sequence, the optimal angiographic viewing angle of the stenotic segment. Several steps are proposed to compute the optimal angular position of the C-arm. Firstly, a mosaic-based tree matching algorithm of the 3D+T sequence is proposed to follow the stenotic lesion in the whole cardiac cycle. A pair-wise inexact tree matching is performed to build a tree union between successive trees. Next, these union trees are merged to obtain the mosaic tree which represents the most complete tree of the sequence. To take into account the non-rigid movement of coronary arteries during the cardiac cycle and their topology variations due to the 3D reconstruction or segmentation, similarity measures based on hierarchical and geometrical features are used. Artificial nodes are also inserted. With this global tree sequence matching, we propose secondly a new method to determine the optimal viewing angle of the stenotic lesion throughout the cardiac cycle. This 2D angiographic view which is proposed for three regions of interest (single segment, multiple segment or bifurcation) is computed from four criteria: the foreshortening, the external and internal overlap and the bifurcation opening angle rates. The optimal view shows the segment in its most extended and unobstructed dimension. This 2D view can be optimal either for the deployment of the stent or for the catheter guidance (from the root to the lesion). Our different algorithms are evaluated on real sequence (CT segmentation) and 41 simulated sequences.