Electrical modeling of liquid crystal displays-LCDs

Abstract

An investigation into the complex dielectric permittivity of nematic liquid crystal () ( NLC on homogeneous or planar, molecular director axis parallel the surface of ) ( the cell and homeotropic molecular director axis perpendicular the surface of the ) cell alignments led to the conception of special equivalent electric circuits representing different dielectric mechanisms that are present in liquid crystal displays ( ) LCDs . In our study, NLC cells with and without polyvinyl alcohol-PVA alignment were subjected to a frequency range of 10 I1 Hz to 10 7 Hz, revealing four distinct mechanisms of dielectric dispersion. In the NLC cells without PVA, the dielectric ( I1 ) dispersion at very low frequencies 10Hzf -1 Hz was attributed to the long ( distance movement of ion carriers trapped in electrodes, to middle frequencies 1 4 )( 4 Hzf -10 Hz finding the NLC static behavior and, at high frequencies 10 Hz 7 ) f )10 Hz dielectric dispersion was attributed mainly to the rotation of NLC molecules around their own axes. While, in the NLC cells with PVA, the dielectric ( ) dispersion at low frequencies 1 Hzf -50 Hz was ascribed to interfacial polarization between NLC and PVA. This study culminated in the development of a single electric circuit that completely models the behavior of LCDs at frequencies of 10 I1 to 10 7 Hz.

The peculiar electrical response of liquid crystal-carbon nanotube systems as seen by impedance spectroscopy

“…reorientation of LC molecules and MWCNTs) and other physical phenomena. Several EECs have been proposed to describe the electrical behavior of LC devices [23][24][25]. A simple EEC has been recently demonstrated [9] to justify the behavior of MWCNT/ LC composites at intermediate frequencies; yet when the Impedance spectroscopy customarily employs sufficiently small voltage signals (100 mV rms ) for the system response to be linear.…”

“…The most common EEC used to describe nematic LC cells [23] is shown in figure 2. To our knowledge, this has only been applied to undoped LC cells; our purpose is to check whether MWCNT-doped cells can be modeled as well, either with the same EEC or modifying some components as a function of the frequency and applied voltage.…”

“…As mentioned above, a comprehensive circuit originally proposed for LC nematic displays (figure 2) has been tested also for doped cells. The study [23] gives an approximation of the EEC components magnitudes for nematic LCs in homogeneous (i.e. planar) alignment.…”

“…Although EECs of different types and configurations of LC cells have been reported [23][24][25], a description of the electrical behavior of CNT-doped LC cells in a wide range of frequencies and voltages has not been performed yet. Once the cell behavior has been mirrored to elementary electrical components (resistors, capacitors, coils, etc), every one standing for a physical effect, the contribution of each cell component-LC, CNTs, external circuitry-to the electrical parameters may be established.…”

Temperature-dependent behavioral model of pixels in active-matrix liquid crystal displays with fringe-field switching mode

“…Conventionally, the electrical and optical behaviors of LC can be solved using Poisson and Euler-Lagrange equations. 7,8 These mathematical methods guarantee accurate results if all the environmental variables are known. 7,8 However, these equations require significant computational time.…”