Appliance Design - November 2007 - (Page 29)

DISPLAYS & INDICATORS Using different color displays in an application can serve as a way to easily convey different types of information, as in this hypothetical example, where different colors represent different time zones. sion force is more than 1,000 times greater than the gravitational force, making the oil stable in all directions. When a voltage difference is applied across the hydrophobic insulator, an electrostatic element is introduced into the stack, which causes the water to move toward the insulator and push the oil aside. The balance of electrostatic forces and surface tension determines the degree to which the water moves the oil aside. In this fashion, the optical properties of the stack can be continuously tuned between the colored OFF state and the white ON state, provided the pixel is small enough for the human eye to average its parts. The images below the illustration show a typical oil retraction obtained for a group of pixels measuring 160 sq. microns. The oil retraction is sufficient to display about 80 percent of the pixel area as white space. Part of the electrode has been omitted in the upper right corner of each pixel to control oil motion. This ensures that all the oil moves to the same corner in each pixel, improving pixel homogeneity and display uniformity. Performance The electrowetting reflective display delivers a number of attractive performance features. According to Liquavista, the displays offer superior brightness than other reflective technologies across a wide viewing angle. When the full-color versions become available, they will be much brighter than LCD counterparts because the electrowetting displays won’t require the polarizers that significantly reduce the light from LCDs. The company says that the contrast ratio of an electrowetting display is also advantageous, approaching that of paper. Resolution is currently about 160 dpi, with further improvements expected. As resolution increases, so will pixel switching speed. Currently, about 5 milliseconds (on/off ), the speed will improve, making the displays suitable for displaying video. The multi-layer structure of the fullcolor version of the electrowetting display will also deliver a broader color gamut than other technologies, providing superior color rendering, according to Liquavista. Another key advantage of the electrowetting approach is significantly reduced power consumption, because its high reflectivity maximizes use of ambient light, cutting the need for power-hungry backlighting. LCDs rely heavily on the backlighting, which can consume a large percentage of the power budget, depending on the application. a. b. c. d. Fig. 1. Electrowetting display principle. The optical stack (from bottom) consist of a reflective electrode, hydrophobic insulator, layer of colored oil, and a layer of water, all sandwiched between either glass or polymer substrates. In equilibrium, the colored oil forms a continuous film layer between the water and the insulator, as seen at left in (a) and (c). In this state, the pixel shows the color of the oil. When a voltage difference is applied across the insulator, the water moves toward the insulator and pushes the colored oil aside, as shown at right in (b) and (d). When the colored oil is displaced, it exposes the underlying reflecting surface. The pixel now shows the color of the reflector. www.applianceDESIGN.com applianceDESIGN November 2007 29 http://www.appliancedesign.com

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Appliance Design - November 2007 Contents Editorial Shipments/Forecasts News Watch Today’s LEDs are Brighter and More Colorful than Previous Versions, Allowing Designers More Opportunities to Improve and Differentiate Their Products. When Converting from CCFL to LED Backlights in LCD Panels, New Driving Methods are Needed. Electrowetting Technology Allows Displays to be Designed in an Extensive Range of Colors. Noise Problems are Not Always Easy to Find or Fix, but Acoustic Labs Can Help Designers Ferret Out the “Good” Noise from the “Bad.” A New Sanitization Protocol for Clothes Washers Combines the Best of Three Well-Established Provisions to Ensure Efficiency, Quality and Safety. Stricter EMC Requirements Raise the Bar for Appliances with Electronic Controls and Require Testing to New Levels. Despite Added Cost and Complexity, Gas-Modulating Systems have Migrated from Large-Scale Boiler Applications to Smaller Residential and Commercial Furnaces and Appliances. A New Treatment Technology Hardens the Surface of Light Alloys such as Aluminum and Magnesium and Expands Their Potential Applications. DesignMart Advertiser’s Index Association Report: AHAM

Appliance Design - November 2007

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