Different concepts for active windows for dynamic light regulation and vibrant climatization support in buildings are compared, followed by a MEMS concept using millions of micromirrors inside insulation or vacuum glazing to guide and control light by electrostatic mirror actuation. The concept enables energy saving, tailored personalized lighting, security, and smart personalized environments in buildings. The window transmission is controlled continuously, showing the eye a variable-tone pane. The amount, direction, and degree of steering of the guided light are tailored to winter, summer, and variable daytime requirements, protecting rooms and persons inside from sun-light while providing tailored natural daylight illumination. The concept is based on reflection, in contrast to existing concepts based on absorption. These micromirror arrays have been designed, fabricated, and characterized. Experimental results on electrostatic actuation voltages, extrapolated lifetime, power consumption, and heat impact regulation are presented.
Energy saving potentials of micromirror arrays in active windows for smart personal environments (SPE) are studied. Such systems enable large area daylight guiding in buildings by application of electrostatically actuated micromirror arrays inside the noble gas or vacuum spacer between the panes of insulation glazings. The working principle in winter and summer scenarii is described. An alternative fabrication process for micromirror arrays, called transfer printing, is presented. For the first time we succeeded in fabricating micromirror arrays applying this novel transfer print.
IntroductionAdvances in micro-electromechanical system (MEMS) technology lead to increasingly more powerful MEMS-based sensors and actuators. It is accompanied by a reduction in size and average cost of these devices. The broad availability of low-cost sensors and actuators allows the creation of new network systems operating in the background and improving daily life without being noticed by the user. Such systems work autonomously based on data collected by sensors, programs or learned rules, and change the environment by actuators. These systems are referred to as smart systems [1,2]. By tailoring the system performance to individual preferences or medical needs, these systems can be personalized.
We present a method to fabricate planar metal layers to be used as micromachined mirrors. Released mirrors of pure metal involve severe stress and reveal specific challenges to obtain planar mirror structures. Introducing sub-structures generating corrugated patterns, the metal mirror layers can be mechanically stabilized and undesired mirror bending can be reduced. For our investigations we used different arrangements of line structures on our metal mirrors, such as a group of straight or curved lines oriented differently. Comparing all the implemented different designs, planar micromirrors were achieved via sub-structures with a combination of straight lines arranged orthogonally to a single line. These planar micromirrors allow steering of the incident light by reflection and adjustment of the window transmittance. The presented low-cost method is suitable for large area fabrication of micromirror arrays, but also can be customized for other applications, where planar free-standing metal layers are required.
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