Display Daily

An Electronic Billboard Based on Electrowetting Technology

by: Arthur Berman

Public Displays - It seems that electronic billboards are well on their way to becoming ubiquitous.  At this time, most of these giant colorful displays use LEDs to produce an image.  One problem with such billboards is that, being emissive, the LEDs needs to be extremely bright to be seen in daylight.  As a result, such billboards can consume a great deal of energy, perhaps as much used by thirty typical homes.  Power hunger at this level is considered undesirable to the extent that some cities, such as Houston, have capped or totally banned electronic billboards.  To address this issue, Miortech (Eindhoven, The Netherlands) is developing a passive electronic display technology that produces a color image based on electrowetting.

Miortech, was spun off in 2006 from a company called Liquavista, an early pioneer in electrowetting technology.  The initial interests of Miortech were electronically dimmable mirrors for automotive applications.  Miortech then went on to establish a subsidiary called Etulipa with the goal of implementing electrowetting technology in displays and digital signage.

The incentive for this business decision was explained by Miortech Chief Executive Officer Hans Feil: “We found that advertisers and billboard owners are extremely keen to enable a technology that allows for instantaneous creative updates and the ability to respond in real-time to current events and market conditions.”

In an electrowetting device, first developed by Philips Research, two immiscible liquids are contained between a transparent upper substrate and hydrophobic (water repelling) lower substrate on which there is also a reflective electrode.  One liquid is typically a clear (or colored) polar liquid and the other a dark (or contrasting colored) oil.

When no voltage is applied across the device, surface tension prevents the polar liquid from wetting the hydrophobic surface.  This leaves the hydrophobic surface covered by the dark oil.  In this configuration the device is non-reflective and dark.  The application of a voltage greatly increases the wettability of the hydrophobic surface.  Within about 10 ms of the application of a voltage, the polar liquid pushes away the oil exposing the reflective substrate.  In this configuration, the device is reflective. That is, in a well lit ambient, the device is now bright.

Summarizing the company’s current status, Feil stated: “We can now demonstrate full color reflective displays with the same approach as in digital printing: the so-called CMY-technology.”

A video illustrating the operation of a demonstration display system can be seen below.

Electrowetting creates an image by modulating ambient light, hence it consumes much less power than an equivalent sized LED-based billboard.  An associated environmental benefit might be reduced light pollution.

The company reports that the next step towards commercialization will be to build a prototype electrowetting electronic billboard for demonstration to media owners.

I will close this article with a brief historical note.  During the mid-1980s there was a Raychem subsidiary company called Taliq with a business plan that (at least from the 50,000 foot level) seems similar to that of Etulipa.  Taliq developed reflective PDLC based electronic billboards.  After struggling mightily for many years, Taliq ultimately failed mainly because their reflective CMY display was unable to produce the vibrant, eye catching colors of a LED display.  In addition, passive displays must be lit at night.  Available front lighting was found to be insufficient and compromised the power savings advantage.  In the Taliq case, a suitable back lighting configuration was never achieved.  To succeed, Etulpia will need to successfully address these same issues. -Arthur Berman