Smart Glass Design Saves Power

A design from researchers at the University of Kassel aims to decrease energy consumption for lighting and temperature technologies. The smart system uses micro-optical-electro-mechanical (MOEM) micromirror arrays to regulate and steer sunlight. The system is unaffected by wind, window cleaning, and weather conditions due to a noble gas such as argon or krypton filling the space between the windowpanes.

“Our smart glazing is based on millions of micromirrors, invisible to the bare eye, and reflects incoming sunlight according to user actions, sun positions, daytime, and seasons, providing a personalized light steering inside the building,” said Hartmut Hillmer, professor in the electrical engineering and computer science departments.

State-of-the-art glazings are optimized for the climates of certain seasons (summer or winter), omitting variables such as current light conditions and temperatures. The system developed by the researchers automatically reacts to local climate, daylight, season, temperature, and motion sensing via an electronic control mechanism that receives input from sensors to direct and position the mirrors.

SEM micrograph of vertically standing, flat micromirror array with an inset of the magnified area. Courtesy of Hillmer et al.

The system’s MEMS micromirror arrays are integrated inside insulation glazing, with their direction operated by voltage between respective electrons. Motion sensors in the room detect the number, position, and movement of users in the room, which sends signals to the mirror systems to respond accordingly.

During the summer, if the room is empty, the smart glazing will close itself to light by switching the micromirrors vertically, reflecting solar radiation outside to keep the room cool. When someone enters the room, the system will open the upper mirrors to reflect sunlight onto a limited area of the ceiling overhead. The lower part of the window remains closed, continuing to reflect solar radiation outside.

Artistic representation of how the system responds to seasonal changes and motion inputs. Courtesy of Hillmer et al.

Conversely, in the winter when the room is empty, the mirrors open and reflect the solar radiation onto a central wall that acts as a radiation heater. When a person enters the room, the system reflects the light toward the ceiling to reduce glare and continue to utilize the solar radiation for heat.

Tests of the system showed a significantly higher actuation speed in the submicrosecond range, 40× lower power consumption than electrochromic or liquid crystal concepts. The researchers performed rapid aging tests of the micromirror structure. The tests were designed to simulate extreme weather events and impacts, long-term use, extreme temperatures, and sudden changes in temperature. The system survived all tests with no failures or damages. The tests on long-term use subjected the system to harsh conditions throughout and indicated an expected lifetime well beyond 40 years.

The research was published in Journal of Optical Microsystems (www.doi.org/10.1117/1.JOM.1.1.014502).