Beamsplitter Coating Enables Virtual Display in Automobiles

Brent D. Johnson

The modern automobile control console has evolved from "dummy lights" to an integrated series of high-tech displays. A new example of such an advanced display is the in-dash navigation system in the 2004 DaimlerChrysler Pacifica, which enables the driver to program a course on the console and follow graphical instructions that appear on a virtual display.

The DaimlerChrysler Pacifica features a high-tech in-dash navigation system that uses a beamsplitter coating to create a virtual display over the instrument cluster.

Creating such a system required engineering skill and specialized optical materials. Specifically, combining LED pointers with a virtual overlay to create the display was a development issue.

"We wanted to create a virtual display with good readability but transparent enough to let the gauges be seen," explained Martha Shea of Denso International America Inc. in Southfield, Mich. In the Pacifica's system, the navigation information is projected from above onto an acrylic screen. This enables simultaneous viewing of the LED gauges and pointers in the instrument cluster and of the navigation map, and it does so without overilluminating the console.

To accomplish this, the system employs a beamsplitter coating from Evaporated Metal Films Corp. of Ithaca, N.Y., that was originally designed for telecommunications applications. The coating combines dielectric materials and a polymer that are dip-coated to the substrate at low temperature in a vacuum. The coating reflects approximately 20 to 30 percent of visible light and transmits the rest to the display, where it is superimposed as a reflection on the screen.

Alternative coatings were considered, such as those made only of dielectric materials, but they require deposition at temperatures too high to be compatible with the substrate material in the display. The beamsplitter material is compatible with the substrate and exhibits good optical performance and durability.

In addition, the coating tolerates exposure to direct sunlight, and it does not wash out because the top dielectric coating provides specular reflection with low diffuse reflection.