Thin, flexible, efficient electronic displays
Technology Update: Electrophoretic technology helps designers of electronic devices to think outside the rectangle for a thin, flexible, energy-efficient user interface.
When selecting an electronic display, designers traditionally looked at factors like contrast, brightness, response time, viewing angle, lifetime, and mechanical and electrical specifications. Are there other factors that need to be considered?
Until recently those designing devices or systems with electronic displays considered something flat and rectangular, usually made of glass, with certain optical characteristics. Replacements meant removing a liquid crystal display (LCD), light emitting diode, or other display technology.
Electrophoretic technology displays can be unique shapes and sizes and use plastic substrates instead of glass on nonflat surfaces to convey information. Applications include replacing paper- and cardboard-based signs (paper displays) with electronic displays.
Ruggedness is a key advantage, although the form and feel of a flexible display is very appealing in some applications like an eNotepad or eNewspaper. There is no glass to shatter or rigid surface, and mechanical stresses are better tolerated, such as for smart cards or other applications that flex in users’ hands or in a wallet or pocket.
Shape: Electrophoretic technology displays can be any shape and fit product design. Examples include point-of-purchase signs, handheld devices like automobile key fobs, wristwatches, and remote control units. The first Ana-Digi wristwatch from Art Technology integrates analog “hands” within the display, a round electrophoretic display with a hole in the middle.
Size, weight: Electrophoretic displays can be used for small key fobs or large indoor or outdoor signs; thinness and low weight suit both ends of the spectrum. Mass-produced 650-micron-thin displays are used in USB memory drives, shelf labels, smart cards, and other products. In handheld applications, such as personal digital assistant (PDA), eBooks, and global positioning system (GPS) devices, the weight of the display and the components required to support the display is critical. Electrophoretic displays are reflective and do not require a backlight, or inverter to drive a backlight, consuming less power and reducing battery size.
Surface: Some automotive applications have displays that jut out of an automobile dashboard. Handheld electronic devices have an aesthetically pleasing curved design. Electrophoretic displays are intrinsically flexible and have been deployed in the field for years using flexible substrates, in low information content displays or segmented/icon type displays. Without rigid glass, backplane image displays could fit into clothing, bags, or a variety of curved surfaces making them smart surfaces!
Replacing paper: The most coveted application for plasma, LCD, and organic light emitting diode (OLED) technologies is the television set. The Holy Grail for display technologies like electrophoretic is to replace paper in printed documents. Applications include eBooks like the Sony Reader, Amazon Kindle, and Barnes & Noble Nook; eNewspapers; e-Textbooks and eManuscripts; Signboards; ePamphlets; eMaps; eReligious books; eMusic—the list is huge. But printed paper in some form or the other has been around for hundreds of years, is easy on the eyes, is robust, is sunlight readable, consumes no power, is available in different sizes, is portable, and is inexpensive on a per-copy basis.
Electronic Paper Display Technologies – Table Comparison
Electrophoretic: In E Ink Pearl electrophoretic imaging film, capsules are formed into a paste and coated onto a flexible plastic substrate in an efficient roll-to-roll process; tightly packed capsules, less than 50 microns diameter on average, give the appearance of paper. Other technologies include electrochromic, MEMS (microelectric mechanical systems) and cholesteric liquid crystal display. Courtesy: E Ink, Control Engineering
Over the years, attempts have been made to replace paper with electronic display technologies. Paper still is winning. Some minimum requirements for an electronic display to replace printed paper include: appearance, lower cost of ownership, robustness, varied sizes, thin, low weight, long use between charges, sunlight readability, and easy access to content.
Electrophoretic display technology provides:
- Robustness: Electrophoretic displays allow designers to envision products that can take the everyday rough-and-tumble experienced by pulp-based books and newspapers. These displays won’t easily dent; there is no polarizer to scratch or glass to shatter. Designers do not have to “cushion” the display like you would with a glass-based display. This allows for better designs to sustain bump and vibration and withstand drop tests easily. More than 20 million flexible displays have been shipped in low-resolution displays like the kind used in wristwatches, smart cards, and shelf labels.
- Appearance: Electrophoretic displays can look like paper with very high resolutions to render a smooth image with gray tones that mimic the book or newspaper reading experience. They are reflective and do not cause eyestrain commonly associated with backlight LCDs that are used in computer monitors and laptops. This allows the user to read a book for hours without experiencing the level of fatigue associated with other display technologies.
- Power consumption: Electrophoretic displays are reflective so they don’t have a backlight to contend with, saving power. Secondly, they are image persistent. Once an image is formed on the display, it requires no power to maintain the same image. The image can be retained for months if desired. This feature allows applications like an eBook or eNewspaper, which can run for days on one battery charge. Various portable electronics have less-efficient displays.
- Sunlight readability: Books, magazines, and newspapers are often read outdoors, which is impossible with an ordinary laptop. Devices using electrophoretic displays are sunlight readable, requiring no shade. Most manufacturers of electronic books use this technology.
Electrophoretic displays take charge
Electrophoretic displays are based on the principle of electrophoresis, which explains the motion of charged particles in a fluid under the influence of an electric field. The principal component of an E Ink electrophoretic display is a microcapsule, and there are millions of them in each display. Each microcapsule contains a mixture of positively charged black particles and negatively charged white particles suspended in a fluid.
With tens of millions of electrophoretic displays deployed in the field, designers can think outside the electronic design rectangle.
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