[Invited Paper] High Precision Measurement of Twist Elastic Constant K22 of Liquid Crystal Materials using Ellipsometry Analysis

A simple method to measure the twist elastic constant of a nematic liquid crystal

We demonstrate a simple method for measuring the twist elastic constant (K22) of a nematic liquid crystal (LC). By adding some chiral dopant to an LC host, the LC directors rotate 180° in a homogeneous cell, which is known as 180° super-twisted nematic (STN) cell. By preparing two such STN cells with different chiral concentrations and measuring their Fréedericksz threshold voltages, we can obt...

degradation of oil impregnated paper insulation under influence of repetitive fast high voltage impulses

در طی سالهای اخیراستفاده ازمنابع انرژی تجدید پذیر در شبکه های مدرن بنا به دلایل زیست محیطی و اقتصادی به طور گسترده استفاده شده است همچون نیروگاههای بادی و خورشیدی .ولتاژتولیدی این نیروگاهها اغلب به فرم dc می باشد وادوات الکترونیک قدرت به عنوان مبدل و پل بین شکل موج dc وac استفاده می شوند.این پروسه باعث ایجاد پالسهایی برروی شکل موج خروجی می شود که می تواند وارد تجهیزات قدرت همچون ترانسفورماتور ی...

Transmissive liquid crystal cell parameters measurement by spectroscopic ellipsometry

A powerful method for liquid crystal ~LC! cell twist angle and retardation measurement is presented. This method is based on the spectroscopic ellipsometry. By varying the polarizer and analyzer angles only, a transmission spectrum containing null transmission at some particular wavelengths can be obtained. Analytical equations derived bases on a polarization analysis of twisted birefringent la...

HIGH TEMPERATURE ELASTIC PROPERTIES OF REFRACTORY MATERIALS

Abstract: A pulse-echo technique, based on ultrasonic "long-bar" mode (LBM) velocity measurements, working up to 1700°C is described. Magnetostrictive transducers and ultrasonic lines used in a 40-85 kHz frequency range are detailed. The conditions of choice of fundamental parameters (frequency, line geometry, sample size) are discussed in relation with the nature and the microstructure of ...

Determination of the liquid-crystal surface elastic constant K24.