smart glass ppt

April 2, 2018 | Author: Rakesh Kumar | Category: Liquid Crystal, Refractive Index, Polarization (Waves), Light, Electromagnetic Radiation



A Study on Smart Glass Technology and ApplicationsPresented by  Stanley Varkey  Raja Babu  Rakesh Kumar OUTLINE  WHY Smart Glass Technology  INTRODUCTION to Liquid Crystals  TYPES of Smart Glass Technology  Electrochromic Glass  PDLC  SPD Why Smart Glass Technology?  Use of fixed tint gives no control over transmittance according to changing needs.  Increased energy consumption to offset effects of fixed transmittance. called the director. .LIQUID CRYSTALSInitial step towards Smart Glass Technology The distinguishing characteristic of the liquid crystalline state is the tendency of the molecules (mesogens) to point along a common axis. so that a color will be reflected when the pitch is equal to the corresponding wavelength of light in the visible spectrum. . The Pitch can be controlled by temperature.LC Phases Nematic Phases Chiral nematic Ability to selectively reflect light of wavelengths equal to the pitch length. When an external electric field is applied to the liquid crystal. the dipole molecules tend to orient themselves along the direction of the field.External Control of LC orientation LC have property of birefringence(multiple refractive indices. . light passes through both. the polarized light from the first is extinguished by the second. However.Light and Polarization If two polarizers are set up in series so that their optical axes are parallel. if the axes are set up 90 degrees apart (crossed). . .Effect of Birefringence on Polarisation Light polarized parallel to the director has a different index of refraction than light polarized perpendicular to the director. Use of LC for controlling light emission . Applications Liquid Crystal Displays Liquid Crystal Thermometers Chiral nematic liquid crystals are used. Color reflected is dependent upon temperature. . Temperature Sensitive Panes Tungsten doped VO2 –reflects infrared in response to high ambient temperature .(Thermograms) Tumors have their own heat signatures which can be identified Fault detection on circuit boards Liquid crystal temperature sensors can also be used to find bad connections on a circuit board by detecting the characteristic higher temperature They are used for non destructive mechanical testing of materials under stress.Body Imaging and diagnosis Special liquid crystal devices can be attached to the skin to show a "map" of temperatures. and a voltage drives the ions from the ion storage layer.Electrochromic Glass A power source is wired to the two conducting oxide layers. It is a bistable system. through the ion conducting layer and into the electrochromic layer. Transparent Conducting Oxide-Indium Tin Oxide EC layer-WO3 Electrolyte-Ta2O5 . . best device is 2 months .Specifications Photopic Transmission: ~ Bleached 70% (Transmission State) ~ Colored 28% (Reflection State) Switching Time: ~ 1 second at room temperature ~ 1.5 mW/cm2 Memory: ~ 2 days after switching off.000 cycles w/ 2% loss in contrast Power Requirements: ~ 1.000. Power required only for changing state Tunable transparency Disadvantagess Large size panels not possible – Response time decreases Limited cycle lifetime .Advantages Bistable. particularly at off normal angels. Antidazzle rear view mirrors built on electrochromic oxide films . Can be made flexible-allowing for flexible displays.Applications a) Possible to achieve excellent viewing properties with better contrast. than in the conventional liquid crystal based displays. b) An electrochromic film can be used to produce a mirror with variable reflectance. e. Employed for temperature control under such as for space vehicles. i. Intercalation/denticulation of ions makes this surface infra reflecting/absorbing. .c). Such windows can lead to energy efficiency as well as comfortable indoor climate. the thermal emittance is low/high. Variable transmittance so that a desired amount of visible light and/or solar energy is introduced. d) Crystalline tungsten oxide film at the exposed surface of an electrochromic device. . •In Museums.•The main objective in the ECDs research for architectural that can control . •EC light filters in specialised imaging systems and cameras. the EC glass displays can be used to control the amount of light/radiation falling on the objects under display.depending on the weather. •Cost of cameras can be brought down by using the an EC filter between the scene and image sensor to control exposure. The EC is connected to a photosensitive element which supplied the control bias. the interior temperature and luminosity and therefore the energy consumption of the building. Polymer Dispersed Liquid Crystal Devices constructed from thin polymer films (poly vinyl alcohol)with randomly dispersed liquid crystal droplets in it. . STRUCTURE OF PDLC . . hence scatters.Working Principle Refractive Indices: -Polymer=np -LC = OFF STATE: The LC crystal domains –randomly aligned Light faces varying refractive indices ranging between no and ne . .Working Principle(Contd. The refractive index of the polymer.) ON STATE When Electric Field applied. LC crystals align themselves in the same direction. Light faces no due to LC . Chosen such that it is very close to no Uniform refractive index allows for Minimum refraction. so contrast ratio is higher.Cell gap and density of the droplets.Temperature . 2. the off state become darker . they are proportional to the contrast temperature decreases refractive index seen by the light decreases and the refractive index of the polymer increases. . As a consequence. so it is the scattering.Factors affecting the contrast ratio of PDLC 1. the birefringence( optical property of a material having a refractive index that depends on the polarization and propagation direction of light) becomes larger. Technical Considerations •The birefringence of the liquid crystal Higher the birefringence-Greater opacity in OFF state. Lesser viewing angle in ON state •Thicker film Increased scattering •Liquid Crystal Diameter For optimum scattering of white light the droplet diameter should be 1-2μm. . Specifications Parameter Response Time Power Consumption Visible Light(ON) Visible light (OFF) UV Block(ON) IR Block(ON) Visible angle 2-100ms 3W/m2 80% 40% 98% 40% 140° Value . •Large area screens are easily fabricated . lower power backlit displays are possible. •Blocks UV radiations very well. •Non bi-stable. •Wide viewing angles. Disadvantages •Trade off between ON state viewing angle and OFF state opacity. •Due to higher transmitivitty . . •Lower response time than conventional LC displays. therefore decreased loss of light intensity.Advantages •Do not require polarisers . •Easier fabrication than LC displays. Nano-PDLC potentially suitable for wave front correction devices in adaptive optics (used in astronomy. As privacy windows without sacrificing illumination. large area displays. line-of-sight communications and ophthalmics). Colored displays by introduction of dyes in the LC/binder polymer.Applications Low power. . Use as Spatial Light Modulating Device for holographic data storage. Lightabsorbing microscopic particles are dispersed within the liquid suspension.Suspended Particle Device Suspended Particle Devices(light valves) use liquid suspension which droplets of liquid suspension are distributed. . Working Principle OFF STATE In its unpowered state the particles are randomly oriented and partially block sunlight transmission and view . aligning the particles and raising the transmittance .ON STATE Transparent electrical conductors allow an electric field to be applied to the dispersed particle film. Specifications The suspension includes the light control particle-polyperiodide And the disperse medium-polysiloxane(Silicone oil) In transparent state a small electric current required continuously. Response time depends on viscosity of the suspension medium Transmission range Switching time10-75% 50-200ms . Large panel sizes-Response time not affected. . Disadvantages Electricity is required to keep the window transparent Currently quite costly.Advantages Variable transparency possible. Principle of absorbtion rather than scaterring-better for thermal regulation Faster than electrochomic technology Can be applied to curved surfaces. skylights and interior partitions Can be used for protection against UV raditions. and the glass panel looks opaque. Since particles tend to absorb light. Controlling the amount of heat entering a building-reduced energy consumption in terms of artificial lighting and air conditioners. Architectural windows.Applications Proposed use in optical computing because of fast switching times. window coverings. . Allows for gradient of transmission which can be controlled by the bias voltage. it can provide maximum protection to light-sensitive objects. FUTURE ASPECTS Low power consumption (for portable devices) Fast switching (for hight frame-rate video applications) Polarisation independent (for brighter and more efficient displays) High brightness. contrast and colour resolution .
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