Although the transparent display has a good appearance, it is still a short time to enter life
Our reporter Jiao Yang
During the National Day holiday just past, Shenzhen Metro Line 10 once again became a check-in point for Internet celebrities.
This subway line not only leads to various tourist attractions, it is also the first cloud computing rail transit route in China. What is even more surprising is that the windows of this subway line use transparent OLED displays.
The reporter learned that as long as you touch these transparent smart windows, you can watch videos, read news, and learn all kinds of real-time information, such as train operation information, location-based service information (LBS), rail transit transfer information, and real-time flight information , Road traffic congestion information, weather forecast information, emergency service information, etc.
Transparent sub-pixels are the key to the "naked makeup" of the display
This touch-operated smart car window was designed and developed by the technical team of CRRC Qingdao Sifang Vehicle Research Institute Co., Ltd. (hereinafter referred to as CRRC Sifang Institute).
Li Peiyuan, an R&D engineer at CRRC Sifang Institute, told a reporter from Science and Technology Daily: "The transparent OLED window system is actually a combination of the transparent OLED display and the traditional subway windows."
How does the transparent OLED display achieve high-definition color display?
First of all, all OLED screens have "self-luminous" characteristics, which means that each red, green or blue sub-pixel on the OLED screen will emit light by itself, without relying on additional backlight sources, which can save traditional The common liquid crystal layer, backlight layer and other modules in LCD screens achieve higher color contrast and are lighter and thinner in form.
But for transparent OLED displays, the real difficulty is to make these millions of pixels "sufficiently transparent". For this reason, panel manufacturers have introduced the concept of "transparent pixels".
According to a technology previously announced by LG, a well-known manufacturer of OLED screens, the transparent OLED screen is based on the original four pixels of red, green, blue and white, adding a new “transparent sub-pixel”.
This kind of pixel does not emit light, nor does it participate in image display, but it itself is made of highly transparent materials.
In order to further improve transparency, LG compresses each square pixel into a rectangular pixel that is only half of the original size, occupying half of the original area, and the other half of the area on the side of each pixel is vacated, allowing light to pass through, thereby achieving more High light transmittance.
Simply put, a transparent OLED display is actually "half responsible for display and half responsible for transparency."
When countless such pixels are evenly distributed on the panel, the screen will naturally obtain a certain transparent effect, but at the same time it can also take into account the display of color images.
The reporter learned that the transparent OLED window system of Shenzhen Metro Line 10 uses a 55-inch transparent OLED display screen, which is provided by LG's LG Display Company.
"This 55-inch transparent OLED touch screen uses projected capacitive (P-Cap) thin film technology to provide a sensitive touch experience, and at the same time has higher transparency than traditional transparent LCD screens." LG public information introduction, LG The transparent OLED touch screen is made of toughened, anti-reflective, and anti-drop glass, and the thinnest point is only 7 mm.
Users can install it in different structures and spaces according to the physical environment and desired effects, and support horizontal and vertical display modes.
"The design team of CRRC Sifang has innovatively adopted ultra-thin fully-laminated technology and highly integrated solutions to make transparent OLED displays have the advantages of wide viewing angles, full colors, and high light transmittance." Li Peiyuan said, smart car windows are extremely small In the pixel space, the circuits and micro-illuminators are precisely arranged and designed to make the OLED display transparent, while also presenting a 1080P (1920×1080) full HD color screen.
The combination of touch and display relies on ultra-thin full-fit technology
So, how does this smart screen perfectly integrate with the car window?
"On the basis of the hollow glass of the car window, the technical team embedded the transparent OLED display screen and the touch operation layer in the middle of the car window through the ultra-thin full lamination technology." Li Peiyuan said, the highly integrated solution adopted by CRRC Sifang, It realizes the arrangement of all supporting boards and wires on the car windows, so that it is easy to install and maintain while ensuring high reliability.
"Each transparent OLED display is equipped with a control system equipped with a 4G module and a network card to provide 4G Internet access. The transparent OLED window has a capacitive touch function that can interact with passengers." Li Peiyuan said.
The reporter learned that the capacitive touch screen is made of transparent metal oxide as a coating, which is bonded to a single-layer glass surface.
It is not like a resistive touch screen. Any touch will form a signal. A capacitive touch screen needs to be directly touched with a finger. The capacitance of the finger can absorb the current in each corner of the touch screen, and the current flowing through these four electrodes is proportional to the distance from the finger to the four corners. To get the touch point.
So, how does the transparent OLED display adapt to the vibration and impact of the rail transit industry, and how does it meet the electromagnetic compatibility requirements?
Li Peiyuan explained that the electromagnetic environment is poor during train operation, and the large 55-inch touch screen is susceptible to external interference.
When choosing the main window control system, after many comparisons and selections, the R&D staff finally chose the Advantech RISC/ARM 3.5-inch single-board computer RSB-4680 because of its characteristics of stable operation in complex environments.
According to the data, the RISC/ARM 3.5-inch single board computer RSB-4680, with its high-performance operation, industrial-grade vibration-resistant wide-temperature strict design standards, stability and reliability, can be perfectly qualified for high-vibration applications in various rail transit applications such as subways. Harsh environment.
At the same time, it provides abundant expansion resources such as Mini-PCIe, M.2, etc., which can expand Wi-Fi, Bluetooth and cellular data modules.
"In order to better iteratively upgrade products and enter the 5G Internet of Things era, the transparent OLED display also reserves a 5G interface for future 5G TV live broadcasts." Li Peiyuan said that at present, in order to ensure the clarity and smoothness of the car window system, every For the windows of the car, the technicians of CRRC Sifang Institute monitor the electromagnetic environment on the spot, and set different touch parameters in a targeted manner to achieve the best touch effect.
Transparent OLED display is not yet suitable for personalized applications
What scenes are the transparent OLED display suitable for? Can it be used for the windows of family cars and other commonly used electronic products?
It is understood that the size of the window glass of the subway is relatively large and the surface is relatively flat, while the window glass of the family car has a small area and a certain curvature, which has a certain impact on the display effect of the transparent OLED screen.
In addition to the objective factors of the screen itself, its display effect is also affected by environmental factors.
Since the screen is transparent, the background environment will also be displayed through the screen during the display process, which will affect the look and feel.
In a strong light environment, the contrast effect is poor.
In addition, the windows of a family car have to go up and down several times, and repeated wear and tear can easily damage the screen structure. At the same time, the screen also needs to take into account the functions of waterproof, sun protection, and wind resistance, which puts a new test on the manufacturing process.
The reporter learned that as early as 2010, Samsung launched a concept laptop equipped with a transparent OLED screen. Users can run the Windows system normally on the translucent screen and directly perform touch operations.
In mid-August this year, Xiaomi also launched a "transparent TV" that can broadcast video content normally like a traditional TV.
According to industry insiders, the “transparent” display screens now have preliminary mass production capabilities, but there is still a big gap between the actual effect and the existing display screens.
Because the most important step for an OLED display to become transparent is to increase the spacing between pixels and increase the overall light transmittance of the screen by adding transparent non-luminous parts.
However, increasing the pixel pitch will also bring about a problem, which is the reduction of resolution.
The current 55-inch transparent OLED display has a resolution of up to 1080P. According to the standard RGB PPI (number of pixels per inch) calculation formula, the PPI of the transparent OLED display is only about 40, while the current mainstream smartphones The screen PPI is usually above 300, and a few 2K resolution mobile phones can reach PPI above 500.
If the pixel density is too low, it will cause the screen to appear more "grainy", and the pixels can even be vaguely seen when viewed at close range.
In addition to the fineness of the picture, the brightness and color performance of the picture are also shortcomings of transparent OLED electronic products.
Due to the addition of the transparent non-luminous part, the brightness of the screen will be impaired.
Li Peiyuan told reporters that as a relatively novel display solution, the future business expansion of transparent OLED displays will face two main problems. One is that transparent displays are expensive to manufacture, which is not conducive to promotion, and the other is limited by basic technology. Development, for each transparent OLED display screen of different sizes, it is necessary to carry out a matching application system design.
But Li Peiyuan also believes that with the development of technology and the further expansion of the application market, after the development cost is reduced, the customized transparent display window will be used in more scenarios, such as subway platforms and commercial exhibition halls.