Research on various application paths of liquid crystal

Research on various application paths of liquid crystal

Liquid crystal optical devices
By using the electro-optical effect of liquid crystal, such as the guest-host effect, TN mode, and STN mode, it can have the function of a shutter or optical switch, such as switching the transmission of light, blocking, and controlling the intensity of transmitted light. The disadvantage of this shutter is that it cannot completely block the incident light, and generally has a slow response speed. Methods for increasing the shutter speed include dual-frequency drive method, voltage modulation method, three-electrode method, and ferroelectric liquid crystal high-speed switching effect. Examples of its application include welding masks, shutters for stereoscopic televisions, and liquid crystal printers.

The principle of liquid crystal shutter can also be used to change the optical aperture of the light transmission area and the dimming device that can adjust the light transmission amount. For example, the upper and lower substrates are printed with concentric semicircular pen segment electrodes. The voltage acts on the concentric circles to form an optical aperture. A typical example of a dimming device is a polymer droplet scattering liquid crystal display (PDLC), which can be used as an electrically controlled electronic curtain and screen. In addition, there are also liquid crystal glasses used by car drivers to protect against strong light when driving at night.

If the two pieces of conductive glass that make up the liquid crystal box are not parallel, but tilted to each other to form a wedge shape (or the conductive glass is bent into a curved surface), the polarization direction of the incident light can be controlled, and the liquid crystal box can be used as a prism with two polarization angles. Applying voltage to it can continuously change the refractive index of the corresponding extraordinary light to the refractive index of ordinary light. By controlling the orientation of the liquid crystal molecules in the box by voltage, the refractive index is changed, and the focal length is adjusted accordingly. Based on this principle, a liquid crystal lens with variable focal length can be made. The developed voltage-transmitted light intensity characteristic lens and variable focus micro lens have been developed.

Optical switches can be made by using the principles of liquid crystal refractive index anisotropy and total reflection at the liquid crystal interface, as well as the principle of polarization plane rotation caused by polarization beam splitters and TN liquid crystal boxes. In a nematic liquid crystal box, electrodes with symmetrical or asymmetrical structures are set up to establish an electric field distribution, and the light is redirected by using the refractive index distribution generated by the reorientation of liquid crystal molecules, so that a beam polarizer can be made. However, this device has certain difficulties in transmission characteristics and response speed because the liquid crystal layer must be thickened to a certain extent.

Liquid crystal light valves can be used as spatial modulators for making holograms. They are display devices that use light addressing to enlarge and project the image formed by the liquid crystal layer onto the screen. In addition to using liquid crystal light valves, liquid crystal spatial modulators can also use matrix structures, electrically controlled birefringence, or cholesteric-nematic phase change effects to make holograms.

In addition, the liquid crystal spatial modulator can also be made into optical logic for logic or image processing, or it can be made into optical memory for writing and erasing information.

Liquid crystal sensor
The arrangement of liquid crystal molecules is easily affected by external heat, electric field, magnetic field, pressure, etc. Therefore, once it is stimulated by external stimuli, the optical and other properties of liquid crystal will change accordingly. Using this property, various liquid crystal sensors can be made.

Common ones include temperature sensors. When the product of the pitch and refractive index of the liquid crystal is within the visible light range, a specific color will be presented, and the pitch of most cholesteric liquid crystals changes with temperature. Based on this principle, a temperature sensor can be made. The sensor can be made of a liquid crystal box with two glass sheets sandwiching liquid crystal as a temperature probe, or it can be directly coated on the measured surface with cholesteric liquid crystal; it can also be made of a certain liquid crystal into a microcapsule, and then add an adhesive to make ink, and then coat or print it on a black opaque substrate (film). Now this type of temperature sensor can be used for non-destructive testing of electronic parts and mechanical parts, measurement of body temperature distribution on the human body surface, early diagnosis of breast cancer and subcutaneous masses, etc.

In addition, there are electric field sensors, voltage sensors, ultrasonic sensors, infrared sensors, etc.