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>> Acoustic-field-based Ultrasonic LCDs Get Rid of ITO Constraints 2nd,May,2018
The global rare earth market is now almost monopolized by China, coupled with rising prices and limited supply, prompting Japanese researchers to actively look for alternative ways to control liquid crystal displays (LCDs). A team consisting of researchers from Tokyo Tech, Doshisha University and Precision and Intelligence Laboratory used a sound field-based directional ultrasonic wave to control the liquid crystals. Instead of using rare indium tin oxide (ITO) to make electric field control LCD pixels.
In the most recent issue of Applied Physics Letters, researchers published a paper entitled "Control of liquid crystal molecular orientation using ultrasound vibration." The article emphasizes that the pixel can be controlled by switching the electric field to the sound field without moving the components and without using the rare earth metal, indium.
"We have proposed a technique that uses ultrasonics to control the nematic liquid crystal orientation and explore the optical properties of these directional samples," the researchers pointed out in the article. "We made ultrasound liquid crystal cells about 5 to 25 microns thick, And 2 ultrasonic transducers for lead zirconate titanate."
Acoustic-field-based Ultrasonic LCDs Get Rid of ITO Constraints
The researchers showed through the ultrasound liquid crystal cell prototype that the sound field is as easy to control as the electric field or magnetic field.
(Source: Tokyo Tech & Doshisha University)
Ultrasonic transducers utilize the "flexural vibration mode" of the liquid crystal cell. Since the acoustic radiation forces the liquid crystal layer to change the orientation of the molecules, the characteristics of the light transmission ability are changed. The researchers adjusted the frequency and voltage of the ultrasound drive to change the spatial distribution of the liquid crystal molecules and thereby control the intensity distribution of the emitted light. The use of this mechanism consists in changing the thickness of the liquid crystal by ultrasound.
"To this end, we propose a technique that uses ultrasonic vibration to control the orientation of liquid crystal molecules," the researchers pointed out. "Using sound fields instead of electric or magnetic fields eliminates the need for ITO electrodes."
In fact, liquid crystals are a state between a liquid and a solid, composed of extended anisotropy (having different properties in the x, y, and/or z planes, respectively). The liquid crystal is usually controlled by an electric field or a magnetic field, and the coupling is made at each pixel unit position. The most common type uses an ITO film to sputter on top of the glass plate that confines the liquid crystal, but this method is not only expensive and time consuming, but also the light source is attenuated because the light source must be transmitted through the ITO.
Ultrasound, on the other hand, does not detract from optical transmission and can be controlled by simply focusing lens distortion in a manner similar to a human eye lens. According to the researchers, the result is that sound waves can be adjusted to a resonant mode, allowing the glass substrate to change the molecular orientation of the restricted liquid crystal and its light transmission intensity.
Acoustic-field-based Ultrasonic LCDs Get Rid of ITO Constraints
By adjusting the prototype's 5 micron thickness (black) to 10 micron (red) and 25 micron (blue), the optical transmission intensity distribution of the liquid crystal layer can be acoustically adjusted
(Source: Tokyo Tech & Doshisha University)
Ultrasonic liquid crystal cell coated with polyphthalamide oriented film over 2 glass plate interlayers (120 and 50-by-5-by-0.7) exterior, between 2 glass plates and with 5, 10 or 25 micron epoxy edge Droplets serve as spacers. Ultrasonic piezoelectric zirconate titanate (PZT) transducers were used to polarize the thickness from the opposite edge of the liquid crystal sandwich between the glass plates. The PZT transducer produces a continuous sinusoidal standing wave across the glass, resulting in the oscillation of the orientable liquid crystal.
The researchers found that there are many different resonant frequencies that can affect acoustically-activated LCDs, most of which are between 59 and 189 kHz; the acoustic signal directly affects the thickness of the liquid crystal layer, resulting in flexible vibration and optical transmission of the substrate. Change. The researchers said that through the ultrasonic deflection vibration of the glass substrate, it is possible to control the orientation of the nematic liquid crystal molecules so as to precisely control the thickness of the liquid crystal and the intensity of light transmission.
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