Compensation effect of polyimide thin films on normally white twisted nematic liquid crystal displays

The disadvantages of Normally White Twisted Nematic Liquid Crystal Display (NW-TN-LCD) were discussed. The reason that the negative birefringent polyimide thin films were used to compensate NW-TN-LCD to decrease off-axis leakage, improve contrast ratios and enlarge viewing angles was explained in this paper. A certain polyimide thin film was taken as an example to show compensation effect on NW-TN-LCD.

SYNTHESIS OF A NEW CHIRAL LIQUID-CRYSTAL WITH SCHIFF-BASE GROUP AND INVESTIGATION OF TEMPERATURE-DEPENDING FTIR SPECTRA

A new chiral liquid crystal with Schiff base group has been prepared, The structure of liquid crystal was confirmed by elementary analyses and H-1 NMR. Its phase transition was investigated by polarized optical microscope, DSC and temperature-depending FTIR spectra. The results showed that the chiral Schiff base showed monotropic phases behavior in certain temperature range, the phase sequence is I-N-*-S-B-S-G-K on the cooling sequence.

CHARACTERIZATION OF BLENDS OF POLYPROPYLENE WITH A SEMIRIGID LIQUID-CRYSTAL COPOLYESTER

Blends with a liquid-crystal polymers (LCP) as one component show, in general, very interesting properties. Reduction of shear visocity and improvement of mechanical properties are very remarkable. High melting temperatures and high costs of the LCP limit the use of these blends. A new class of thermotropic LCPs with flexible spaces, with relatively low melting temperatures, can overcome the first problem. In this work, rheological and mechanical properties of blends of polypropylene with low contents of this LCP are presented. Torque during extrusion and viscosity decrease with LCP content. Elastic modulus is remarkably increased when the LCP phase is oriented.

Thermal analysis of LEDS for liquid crystal display's backlighting

This paper investigated the thermal design of the light emitting diode (LED)onto the board and its packaging. The LED was a 6-lead MultiLED with three chips designed for LCD backlighting and other lighting purposes. A 3D finite element model of this LED was built up and thermal analysis was carried out using the multi physics software package PHYSICA. The modeling results were presented as temperature distributions in each LED, and the predicted junction temperature was used for thermal resistance calculation. The results for the board structure indicated that (1) removing the foil attach decreased the thermal resistance, (2) Increasing the copper foil thickness reduced the thermal resistance. package design indicated that the SMT designed LED with integrated slug gave lower thermal resistance. Pb-free solder material gave lower thermal resistance and junction temperature when compared with conductive adhesive

Electrically switchable nonreciprocal transmission of plasmonic nanorods with liquid crystal

The electro-optic response of a cell consisting of a thin layer of liquid crystal deposited onto gold nanorods embedded in thin film alumina with a transparent top electrode has been investigated. For p-polarized light incident from the liquid crystal side, the extinction peak associated with the nanorod longitudinal plasmon resonance is completely suppressed. The peak could be recovered by applying an external electric field parallel to the long axis of the nanorods. No extinction peak suppression is observed when the light was incident from the nanorod side of the cell. The effect is explained by polarization properties of liquid crystal.

Liquid-crystal-based reflectarray antenna with electronically switchable monopulse patterns

A printed rcflectarray antenna, which generates a beam that can be electronically switched from a sum to a difference radiation pattern, is presented. This is achieved by applying a bias voltage of 20 V to one-half of the aperture, which is constructed above a 500 mu m cavity containing liquid crystals. Simulated results are shown to be in good agreement with measurements at X-band.

Liquid crystal tunable mm wave frequency selective surface

A frequency selective surface (FSS) which exploits the dielectric anisotropy of liquid crystals to generate an electronically tunable bandpass filter response at D Band (110-170 GHz) is presented. The device consists of two printed arrays of slot elements which are separated by a 130-mu m thick layer of liquid crystals. A 3% shift in the filter passband occurs when the substrate permittivity is increased by applying a control signal of 10 V. Measured results show that the insertion loss increases from -3.7 dB to -10.4 dB at resonance (134 GHz), thus demonstrating the potential to create a FSS which can be switched between a transmitting and a reflecting structure.

Tunable liquid crystal reflectarray patch element

Numerical and measured results are employed at X-band to demonstrate that the electrical properties ofnematic state liquid crystal can be exploited to produce phase shifters for beam scanning printed reflectarray antennas with a tunable range greater than 180'.