Abstract
A method to estimate orientation direction of liquid crystal molecules three-dimensionally under ultrasound excitation was proposed and the relationship between the ultrasound vibration and the molecular orientation was discussed. Our group have reported a technique to control orientation direction of liquid crystal molecules using ultrasound vibration which could be applied to an optical variable-focus liquid crystal lens. The lens consisted of a liquid crystal layer sandwiched by two glass circular discs and a piezoelectric ring. Ultrasound vibration induces change in the refractive index of the lens, enabling the variable-focus function. The three-dimensional orientation direction of the liquid crystal molecules in the lens was predicted from the transmitted light distributions under the crossed Nicol conditions. The liquid crystal molecules were inclined from vertical alignment by the ultrasound vibration, and larger ultrasound vibration gave larger inclination of the molecules. There was a strong correlation between the distributions of ultrasound vibration and the liquid crystal molecular orientation; the molecular orientation was changed remarkably between the antinodal and nodal parts of the ultrasound flexural vibration on the glass plate and the molecules aligned towards the antinode.
Highlights
Camera modules are inserted into electronic devices such as smartphones that are widely used in everyday life
Our research group developed a method to control the molecular orientation of these liquid crystals by applying optical device technology and devices based on use of the acoustic radiation force which have been cultivated to date[27,28]
We fabricated a liquid crystal lens using this technique without using indium tin oxide (ITO) electrodes and a variable-focus function was produced in this ultrasound liquid crystal lens by varying the sound pressure acting on the liquid crystal layer[29]
Summary
Camera modules are inserted into electronic devices such as smartphones that are widely used in everyday life. As an optical liquid crystal device application, Sato and colleagues developed a variable focus liquid crystal lens using the birefringence of a nematic liquid crystal[12,13,14,15,16] These liquid crystal lenses require complex indium tin oxide (ITO) electrode patterns to control the molecular orientations of their liquid crystals[17], the lenses have a structure that does not require any mechanical moving parts, enabling device downsizing and providing high robustness for use in camera modules in electronic (a) Glass plate (b) (t = 0.7) PZT (t = 1). We have evaluated both the two-dimensional orientation direction of the liquid crystal molecules and the three-dimensional orientation of these molecules, and the relationship between orientation direction and ultrasound vibration in a liquid crystal lens under ultrasound excitation has been clarified
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