Advanced Technologies for Smart Windows.

Micromirror Arrays for Smart Windows

Open State-Daylight (C) University of Kassel
Open State-Daylight
Closed State-Reflection (C) University of Kassel
Closed State-Reflection

1 The idea behind

Daylighting in general should be preferred above electric lighting. It is free and characterized as a high illuminance with full-spectrum light which gives a perfect color rendering, variable angles of the light incidence, as well as a big variation in intensity and colors, which gives a positive effect on human well-being. Daylight can also offer a favorable thermal energy inside the buildings. However, daylight can also produce uncomfortable solar glare and very high luminance reflections e.g. on display screens, both of which interfere with good vision.

This problem can be met by a flexible system, which can fit the requirements of daylight illumination, glare protection and heat regulation all at the same time. In order to overcome these problems, millions of micromirrors can be implemented in the interspace of conventional insulation glasses, providing efficient transmission control and significantly improved daylight distribution. Such micromirrors have a size of less than 0,1mm², which means about 12 mirror elements / mm² or 12.000.000 mirrors / m².

2 Advantages

Miniaturizing lamella blinds down to micromirrors has some very obvious advantages: Beneath segmentability and the “uncut” outlook, they are protected between the window panes against wind, weather and dirt. Furthermore the miniaturization is beneficial as well to considerably improve the mechanical stability of such devices. The electric field between the mirrors and the electrode upon the pane will make the mirror switch. This makes those mirrors maintenance free for their whole lifetime.

3 Results

In principle, fabrication of micromirrors summarized in three steps: deposition of thin-film layers, micropatterning to define the mirror shape and release of the mirror using a self assembling step, in which the mirrors will stand up in a nearly 90⁰ out-of plane position making use of the intrinsic stress of the deposited layers.

4 Contact

Prof. Dr. Hartmut Hillmer
University of Kassel