Dual-Frequency Cholesteric Liquid Crystal Privacy Window
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Solution Overview
Problem
Conventional cholesteric liquid crystal (CLC) light modulation elements require high switching voltages and have slow transition times between states, making them inefficient for fast and energy-efficient bistable operations, especially in reverse mode applications.
Innovation Solution
A dual-frequency cholesteric liquid crystal medium with specific chiral compounds and polymer particles is used, allowing for low electric field switching between transparent and opaque states by exploiting frequency-dependent dielectric anisotropy, eliminating the need for homogeneous polyimide coatings and reducing voltage requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional cholesteric liquid crystal media are used, then the light modulation element can achieve bistable switching between transparent and opaque states, but high switching voltages are required and transition times are slow
Solution Approach 1:
The patent changes the dielectric anisotropy parameter of the liquid crystal medium by using dual-frequency liquid crystal molecules that exhibit positive dielectric anisotropy at low frequencies and negative dielectric anisotropy at high frequencies. This parameter change enables the medium to respond differently to low-frequency and high-frequency electric fields, allowing fast switching at low voltages while maintaining bistability.
Solution Approach 2:
The patent employs periodic electric fields with different frequencies to control the liquid crystal medium. By applying low-frequency electric fields during the isotropic phase and high-frequency electric fields during the nematic phase, the system achieves rapid transitions between states. The periodic frequency switching enables fast response times without requiring high continuous voltages.
2Reliability
If conventional cholesteric liquid crystal media are used, then bistable switching is achieved, but transition times between states are slow
Solution Approach 1:
The patent exploits the frequency-dependent dielectric anisotropy parameter of dual-frequency liquid crystal molecules to achieve fast switching. By changing the frequency parameter of the applied electric field, the system can rapidly transition between transparent and opaque states. The high-frequency response of the liquid crystal molecules at the isotropic phase enables extremely fast transition times.
Solution Approach 2:
The patent uses periodic electric field application with frequency modulation to accelerate transitions. During phase transitions, high-frequency electric fields are applied to induce rapid molecular reorientation. This periodic frequency switching mechanism reduces transition times significantly compared to conventional DC or low-frequency AC field applications.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables fast, energy-efficient, and bistable switching between states with minimal hysteresis, improving the operational efficiency and stability of CLC light modulation elements.
Implementation Method 1
Cholesteric liquid crystals exhibit selective reflection of circular-polarised light, with the direction of rotation of the light vector corresponding to the direction of rotation of the cholesteric helix.
Implementation Method 2
The reflection wavelength λ is given by the pitch p of the cholesteric helix and the mean birefringence n of the cholesteric liquid crystal
Implementation Method 3
The commonest display devices are based on the Schadt-Helfrich effect and contain a liquid-crystal medium having a twisted nematic structure, such as, for example, TN ('twisted nematic') cells having twist angles of typically 90°
Implementation Method 4
The nematic-isotropic phase transition temperature, T NI, of the liquid-crystalline host phase is at least 80 °C
Data Source
AI summary
The present invention relates to a light modulation element comprising a pair of opposing transparent substrates, which are provided with an electrode structure provided on the inner surface of each substrate and a cholesteric liquid crystalline medium comprising one or more particles. The invention further relates to the use of a light modulation element as described above and below in optical or electro optical components or devices. The invention further relates to an optical or electro-optical component or device, comprising a light modulation element as described above and below.