Research on multiple application methods of liquid crystal
Liquid crystal optical devices use the electro-optical effects of liquid crystal, such as guest-host effect, TN mode, and STN mode, to enable them to function as shutters or optical switches, such as switching the transmission of light, blocking, and controlling the intensity of transmitted light. The disadvantage of this type of shutter is that it cannot completely block the incident light, and the response speed is generally slow. Methods of increasing shutter speed include dual-frequency driving method, voltage modulation method, three-electrode method, and high-speed switching effect of ferroelectric liquid crystal. Examples of its application are welding masks, shutters for stereo televisions, LCD printers, etc.
The principle of liquid crystal shutters can also be used for optical apertures that change the light transmission area and dimming devices that can adjust the amount of light transmission. For example, a combination of pen-section electrodes with concentric semicircles printed on both the upper and lower substrates to properly apply voltage to the concentric circles forms an optical aperture. Typical examples of dimming devices are polymer droplet scattering liquid crystal displays (PDLC), which can be used as electronically controlled electronic curtains and screens. In addition, there are liquid crystal glasses used by car drivers to prevent glare at night.
If the two conductive glasses that make up the liquid crystal cell are not parallel, but are inclined to each other to make a sharp shape (or bend the conductive glass into a curved surface) to control the direction of the polarization of the incident light, the liquid crystal cell can be regarded as having two polarization angle The prism used. Applying voltage to it can make the refractive index of the corresponding extraordinary light continuously change to the refractive index of ordinary light. The voltage controls the orientation of the liquid crystal molecules in the cell, changes the refractive index, and adjusts the focal length accordingly. According to this principle, a liquid crystal lens with variable focal length can be made. Has developed a voltage-transmitted light intensity characteristic lens, a zoom micro lens.
Using the anisotropy of liquid crystal refractive index and the total reflection principle of the liquid crystal interface, as well as the principle of polarization plane rotation caused by the polarization beam splitter and the TN liquid crystal cell, an optical switch can be made. A symmetric or asymmetric structure electrode is provided in the nematic liquid crystal cell to establish an electric field distribution, and the refractive index distribution generated by the reorientation of the liquid crystal molecules is used to turn the light to make a beam polarizer. However, this kind of device has certain difficulty in transmission characteristics and response speed due to the thickening of the liquid crystal layer to a certain extent.
The liquid crystal light valve can be used as a spatial modulator for making holograms. It is a display device that uses light addressing to enlarge and project the image formed by the liquid crystal layer onto the screen. In addition to the liquid crystal light valve, the spatial modulator of liquid crystal can also use a matrix structure, electronically controlled birefringence, or a cholesteric-nematic phase transition effect to make a hologram.
In addition, the liquid crystal spatial modulator can also be made into optical logic for logic or image processing, and can also be made into optical memory for writing and erasing of information.
The arrangement of liquid crystal molecules of a liquid crystal sensor is easily affected by external heat, electric field, magnetic field, pressure, etc. Therefore, once external stimuli are received, the optical and other characteristics of the liquid crystal change accordingly. Using this property, various liquid crystal sensors can be fabricated.
Common temperature sensors. When the product of the pitch of the liquid crystal and the refractive index is in the range of visible light, it will show a specific color, and the pitch of most cholesteric liquid crystals changes with temperature. According to this principle, a temperature sensor can be produced. The sensor can be made of two glass sheets with liquid crystal to make a liquid crystal cell, which can be used as a temperature probe, or it can be directly coated with cholesteric liquid crystal on the surface to be measured; it can also be made of certain liquid crystal into microcapsules, and then added with adhesive Ink, and then coated or printed on a black opaque substrate (film). At present, this type of temperature sensor can be used for non-destructive testing of electronic parts and mechanical parts, measurement of the temperature distribution on the surface of the human body, early breast cancer and subcutaneous masses.
In addition, there are electric field sensors, voltage sensors, ultrasonic sensors, infrared sensors and so on.
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