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High Performance Three-Dimensional Display Based on Polymer-Stabilized Blue Phase Liquid Crystal
Title
High Performance Three-Dimensional Display Based on Polymer-Stabilized Blue Phase Liquid Crystal.
Creator
Liu, Yifan, Wu, Shintson, Kik, Pieter, Likamwa, Patrick, Zhai, Lei, University of Central Florida
Abstract / Description
Autostereoscopic 2D/3D (two-dimension/three-dimension) switchable display has been attracting great interest in research and practical applications for several years. Among different autostereoscopic solutions, direction-multiplexed 3D displays based on microlens array or parallax barrier are viewed as the most promising candidates, due to their compatibility with conventional 2D display technologies. These 2D/3D switchable display system designs rely on fast switching display panels and...
Show moreAutostereoscopic 2D/3D (two-dimension/three-dimension) switchable display has been attracting great interest in research and practical applications for several years. Among different autostereoscopic solutions, direction-multiplexed 3D displays based on microlens array or parallax barrier are viewed as the most promising candidates, due to their compatibility with conventional 2D display technologies. These 2D/3D switchable display system designs rely on fast switching display panels and photonics devices, including adaptive focus microlens array and switchable slit array. Polymer-stabilized blue phase liquid crystal (PS-BPLC) material provides a possible solution to meet the aforementioned fast response time requirement. However, present display and photonic devices based on blue phase liquid crystals suffer from several drawbacks, such as low contrast ratio, relatively large hysteresis and short lifetime. In this dissertation, we investigate the material properties of PS-BPLC so as to improve the performance of PS-BPLC devices. Then we propose several PS-BPLC devices for the autostereoscopic 2D/3D switchable display system designs. In the first part we evaluate the optical rotatory power (ORP) of blue phase liquid crystal, which is proven to be the primary reason for causing the low contrast ratio of PS-BPLC display systems. Those material parameters affecting the ORP of PS-BPLC are investigated and an empirical equation is proposed to calculate the polarization rotation angle in a PS-BPLC cell. Then several optical compensation methods are proposed to compensate the impact of ORP and to improve the contrast ratio of a display system. The pros and cons of each solution are discussed accordingly. In the second part, we propose two adaptive focus microlens array structures and a high efficiency switchable slit array based on the PS-BPLC materials. By optimizing the design parameters, these devices can be applied to the 2D/3D switchable display systems. In the last section, we focus on another factor that affects the performance and lifetime of PS-BPLC devices and systems: the UV exposure condition. The impact of UV exposure wavelength, dosage, uniformity, and photo-initiator are investigated. We demonstrate that by optimizing the UV exposure condition, we can reduce the hysteresis of PS-BPLC and improve its long term stability.
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Date Issued
2014
Identifier
CFE0005370, ucf:50466
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005370
DESIGN, FABRICATION AND TESTING OF A SHAPE MEMORY ALLOY BASED CRYOGENIC THERMAL CONDUCTION SWITCH
Title
DESIGN, FABRICATION AND TESTING OF A SHAPE MEMORY ALLOY BASED CRYOGENIC THERMAL CONDUCTION SWITCH.
Creator
Krishnan, Vinu Bala, Vaidyanathan, Raj, University of Central Florida
Abstract / Description
Shape memory alloys (SMAs) can recover large strains (e.g., up to 8%) by undergoing a temperature-induced phase transformation. This strain recovery can occur against large forces, resulting in their use as actuators. The SMA elements in such actuators integrate both sensory and actuation functions. This is possible because SMAs can inherently sense a change in temperature and actuate by undergoing a shape change, associated with the temperature-induced phase transformation. The objective of...
Show moreShape memory alloys (SMAs) can recover large strains (e.g., up to 8%) by undergoing a temperature-induced phase transformation. This strain recovery can occur against large forces, resulting in their use as actuators. The SMA elements in such actuators integrate both sensory and actuation functions. This is possible because SMAs can inherently sense a change in temperature and actuate by undergoing a shape change, associated with the temperature-induced phase transformation. The objective of this work is to develop an SMA based cryogenic thermal conduction switch for operation between dewars of liquid methane and liquid oxygen in a common bulk head arrangement for NASA. The design of the thermal conduction switch is based on a biased, two-way SMA actuator and utilizes a commercially available NiTi alloy as the SMA element to demonstrate the feasibility of this concept. This work describes the design from concept to implementation, addressing methodologies and issues encountered, including: a finite element based thermal analysis, various thermo-mechanical processes carried out on the NiTi SMA elements, and fabrication and testing of a prototype switch. Furthermore, recommendations for improvements and extension to NASA's requirements are presented. Such a switch has potential application in variable thermal sinks to other cryogenic tanks for liquefaction, densification, and zero boil-off systems for advanced spaceport applications. The SMA thermal conduction switch offers the following advantages over the currently used gas gap and liquid gap thermal switches in the cryogenic range: (i) integrates both sensor and actuator elements thereby reducing the overall complexity, (ii) exhibits superior thermal isolation in the open state, and (iii) possesses high heat transfer ratios between the open and closed states. This work was supported by a grant from NASA Kennedy Space Center (NAG10-323) with William U. Notardonato as Technical Officer.
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Date Issued
2004
Identifier
CFE0000038, ucf:46136
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0000038
Three-phase contact line phenomena in droplets on solid and liquid surfaces: electrocapillary, pinning, wetting line velocity effect, and free liquid surface deformation
Title
Three-phase contact line phenomena in droplets on solid and liquid surfaces: electrocapillary, pinning, wetting line velocity effect, and free liquid surface deformation.
Creator
Shabani, Roxana, Cho, Hyoung, Kumar, Ranganathan, Kapat, Jayanta, Chow, Louis, Zhai, Lei, University of Central Florida
Abstract / Description
In this dissertation, physical phenomena relevant to (i) an interface formed between two fluids and a solid phase (wettingline) and (ii) an interface between three fluids (triple contact line) were investigated. In the former case, the wetting line (WL)phenomena, which encompass the wetting line energy (WLE), the wetting line velocity (WLV), and the contact anglehysteresis, were studied using a micropump based on electrowetting on dielectric (EWOD). In the latter case, the air filmlubrication...
Show moreIn this dissertation, physical phenomena relevant to (i) an interface formed between two fluids and a solid phase (wettingline) and (ii) an interface between three fluids (triple contact line) were investigated. In the former case, the wetting line (WL)phenomena, which encompass the wetting line energy (WLE), the wetting line velocity (WLV), and the contact anglehysteresis, were studied using a micropump based on electrowetting on dielectric (EWOD). In the latter case, the air filmlubrication effect and the liquid free surface deformation were taken into account to explain the dual equilibrium states ofwater droplets on liquid free surfaces. A micropump based on droplet/meniscus pressure gradient generated by EWOD was designed and fabricated. By alteringthe contact angle between liquid and solid using an electric field a pressure gradient was induced and a small droplet waspumped into the channel. The flow rate in the channel was found to be constant in spite of the changes in the droplet'sradius. The WL phenomena were studied to unravel the physical concept behind the micropump constant flow rate. Theobservation and measurement reveal that the shrinking input droplet changes its shape in two modes in time sequence: (i)its contact angle decreases, while its wetting area remains constant, and (ii) its WL starts to move while its contact anglechanges. Contact angles were measured for the advancing and receding WLs at different velocities to capture a full pictureof contact angle behavior. The effects of the WLE on the static contact angle and the WLV on the dynamic contact angle inthe pump operation were investigated. Also the effect of EWOD voltage on the magnitude and uniformity of the micropumpflow rate was studied. Dynamic contact angles were used to accurately calculate the pressure gradient between the dropletand the meniscus, and estimate the flow rate. It was shown that neglecting either of these effects not only results in aconsiderable gap between the predicted and the measured flow rates but also in an unphysical instability in the flow rateanalysis. However, when the WLE and WLV effects were fully taken into account, an excellent agreement between thepredicted and the experimental flow rates was obtained.For the study of the TCL between three fluids, aqueous droplets were formed at oil-air interface and two stableconfigurations of (i) non-coalescent droplet and (ii) cap/bead droplet were observed. General solutions for energy and forceanalysis were obtained and were shown to be in good agreement with the experimental observations. Further the energybarrier obtained for transition from configuration (i) to (ii) was correlated to the droplet release height and the probability ofnon-coalescent droplet formation. Droplets formed on the solid surfaces and on the free surface of immiscible liquids have various applications indroplet-based microfluidic devices. This research provides an insight into their formation and manipulation.
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Date Issued
2013
Identifier
CFE0005253, ucf:50598
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0005253
Vertical Field Switching Blue Phase Liquid Crystals for Field Sequential Color Displays
Title
Vertical Field Switching Blue Phase Liquid Crystals for Field Sequential Color Displays.
Creator
Cheng, Hui-Chuan, Wu, Shintson, Likamwa, Patrick, Schoenfeld, Winston, Wu, Xinzhang, University of Central Florida
Abstract / Description
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...
Show moreLow 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 ((<)1 ms). Recently, the polymer-stabilized blue-phase liquid crystal (PS-BPLC) draws great attentions because of improved temperature range which enables the applications for photonic devices and displays. PS-BPLC is a good candidate for FSC LCDs because of its submillisecond gray-to-gray response time, no need for alignment layer, and isotropic dark state. So far, almost all the BPLC devices utilize planar or protruded in-plane switching (IPS) electrode configuration. The structure of planar IPS is relatively simple, but the operating voltage is too high for thin-film transistor (TFT) addressing. Moreover, high voltage causes deformation of polymer network and induces a noticeable hysteresis. Protruded IPS is helpful for lowering the operating voltage, but the manufacturing process becomes more sophisticated. In Chapter 3, we propose a vertical field switching (VFS) mode for blue phase LCDs. The simple structure of VFS cell generates uniform vertical fields on the BPLC materials. From our experimental results, the operation voltage can be reduced to ~10Vrms while eliminating the hysteresis. We also defined a critical field below which hysteresis does not occur. Above critical field, lattice distortion and other irreversible phase transition processes would occur. As a result, the associated response time would be slower. Therefore, VFS mode also shows faster response time than IPS mode. The operating voltage can be further reduced by choosing an optimized cell gap and a larger oblique incident angle in VFS blue phase LCDs.In Chapter 4, we propose several compensation mechanisms to improve the viewing angle of VFS blue-phase LCDs. The compensation principles are analyzed and simulation results evaluated. Because VFS blue-phase LCD processes several advantages over IPS blue-phase LCD and conventional LCDs, it could become a strong contender for next-generation display technology.
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Date Issued
2012
Identifier
CFE0004780, ucf:49772
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0004780