The field-induced cholesteric-nematic phase transition and its dependence on layer thickness, boundary conditions, and temperature

\u3cp\u3eChiral-nematic liquid-crystal layers which have a short pitch, homeotropic boundary conditions, and bistable properties are investigated with respect to the temperature dependence of their field-induced cholesteric-nematic phase transition. Hereto the threshold field needed for the transition is studied as a function of the layer thickness. This is done for various temperatures. The threshold field hardly depends on the layer thickness. Moreover, it sharply rises below -5 °C. Both the value of the threshold field and its temperature dependence can be fully described in terms of liquid-crystal bulk material parameters, the conditions at the homeotropic boundary layer used do not play a role. From the threshold field data the twist elastic constant is determined as a function of temperature. This temperature dependence is compared to the temperature dependence as determined from the square of the long range order parameter calculated from temperature dependent refractive index data. A good correlation is found between both data sets of the twist elastic constant.\u3c/p\u3

Reflective direct-view LCDs using polymer-dispersed liquid crystal (PDLC) and dielectric reflectors

\u3cp\u3eMonochrome and color reflective liquid crystal device (LCD) configurations are described that show promising optical performance (high diffuse reflectance, good contrast, bright colors, no ghosting and a rotationally symmetric and wide viewing angle) and can be combined with active-matrix driving. As with all reflective LCDs, the performance depends on the illumination environment. Since the described display is based on switching between specular and diffuse reflection, the beat optical performance is achieved under illumination conditions with a directional component.\u3c/p\u3

Linearly polarized light-emitting backlight

\u3cp\u3eA new polarized backlight system for liquid-crystal displays (LCDs) is presented in which one linear polarization is preferentially coupled out by anisotropic scattering. The lightguide consists of a polymeric polarization-dependent scattering film adhered to a transparent polymeric substrate. By changing the scattering power of the film, the polarized light outcoupling angles can be influenced and optimized to achieve a maximum outcoupling centered along the normal direction. The other linear polarization is mainly trapped in the lightguide and is shown to be recycled to enhance the overall light and/or energy efficiency. With a proper substrate choice, the achieved local contrast exceeds 14 over a 50-mm range. A collimated light input further enhances the polarized contrast to well over 17.\u3c/p\u3

Efficient and cost-effective polarized-light backlights for LCDs

\u3cp\u3eTo improve the optical efficiency and to reduce the number of optical components of LCD backlighting systems, two types of polarized-light backlights have been made from micro-structured birefringent polymeric layers. One type uses uniaxially oriented PEN and PET foils that have been structured by diamond-tool machining or by hot-embossing, and subsequently laminated onto a flat PMMA light guide. The second type uses a liquid crystalline polymeric layer laminated onto a micro-structured light guide. S-polarized light is preferentially extracted from the light guides. The efficiency has been measured to be 1.6-1.7 times higher than for a conventional backlight. Costs, thickness and complexity are decreased since no micro-prismatic brightness enhancement foils or reflective polarizer foils are needed.\u3c/p\u3

Remote cooling by combining heat pipe and resonator for synthetic jet cooling

This invention relates to thermal management for removing heat generated by a heat source (110). This is done by a combination of a heat conducting member (120), which is thermally connected to the heat source in one end and to a remotely arranged heat sink (130) in the opposite end, and a synthetic jet actuator (140). The synthetic jet actuator is arranged to provide active cooling directly onto the heat source by generating and directing an air flow towards the heat source. The synthetic jet actuator comprises a resonator cavity housing (150) and an oscillating member (160). The oscillator member is arranged at least partly inside said resonator cavity. The combination of the heat conducting member and the synthetic jet actuator provides a highly efficient cooling

Remote cooling by combining heat pipe and resonator for synthetic jet cooling

This invention relates to thermal management for removing heat generated by a heat source (110). This is done by a combination of a heat conducting member (120), which is thermally connected to the heat source in one end and to a remotely arranged heat sink (130) in the opposite end, and a synthetic jet actuator (140). The synthetic jet actuator is arranged to provide active cooling directly onto the heat source by generating and directing an air flow towards the heat source. The synthetic jet actuator comprises a resonator cavity housing (150) and an oscillating member (160). The oscillator member is arranged at least partly inside said resonator cavity. The combination of the heat conducting member and the synthetic jet actuator provides a highly efficient cooling

Polarized back and frontlights for LCDs

\u3cp\u3eNew designs are presented of backlight systems for transmissive and transflective LCD's based on stretched PET films with a well-defined micro-structure, which emit highly collimated or diffuse and linearly polarized light with a high efficiency. Moreover, edge-lit waveguide systems are discussed equipped slanted phase gratings which combine a range of desirable features such as a high transparency in direct view, a direct emission of light at normal angles to the plane of the waveguide and a purely unidirectional out-coupling of light towards the LCD-side. Moreover, these illumination systems emit colored, linearly polarized light which should contribute significantly to the energy efficiency of transmissive, transflective and reflective LCD displays.\u3c/p\u3

Thermoresponsive scattering coating for smart white LEDs

\u3cp\u3eWhite light emitting diode (LED) systems, capable of lowering the color temperature of emitted light on dimming, have been reported in the literature. These systems all use multiple color LEDs and complex control circuitry. Here we present a novel responsive lighting system based on a single white light emitting LED and a thermoresponsive scattering coating. The coated LED automatically emits light of lower correlated color temperature (CCT) when the power is reduced. We also present results on the use of multiple phosphors in the white light LED allowing for the emission of warm white light in the range between 2900 K and 4150 K, and with a chromaticity complying with the ANSI standards (C78.377). This responsive warm white light LED-system with close-to-ideal emission characteristics is highly interesting for the lighting industry.\u3c/p\u3