Optical MEMS Micromirrors Could Be a Driving Force in “Smart Glass”

April 09, 2021 by Jake Hertz

New research proposes a smart glass technology that could save energy in buildings by up to 35%.

Between residential and commercial infrastructures, buildings accounted for 40% of the total U.S. energy consumption in 2019. Of this 40%, the majority of the energy is spent on heating and cooling the building.

In an effort to conserve this energy, smart glass—glass with light transmission properties that can be dynamically changed—has become a hot research topic in recent years. While the technology is nowhere near perfect, recent research from the University of Kassel shows how micro-opto-electromechanical system (MOEMS) mirror arrays may open doors for smart glass technology.


What Is Smart Glass? 

Smart glass refers to glass, often for windows, that can change its light transmission properties based on its environment. For example, on a winter day, smart glass allows more light to enter a room to naturally heat it. On a summer day, the glass may allow less light to filter through, keeping the room cool.

Working principle of how smart glass works

Working principle of how smart glass works. Image used courtesy of Gauzy

There are currently many techniques used to accomplish this feat. Techniques are either active (requiring electrical stimulation) or passive. Among active techniques, polymer dispersed liquid crystal (PDLC) glass, suspended particle device (SPD) glass, and electrochromic (EC) glass, are the most popular. 

PDLC or SPD solutions, for example, often consist of a conductive film on the glass, which is coated between two sheets of transparent material. The presence of an electrical signal will align the film’s particles to either increase or decrease the transparency of the material.


MOEMS Micromirrors 

Another technique commonly investigated is micro-opto-electromechanical (MOEMS) mirrors, also known as optical MEMS. 

Optical MEMS is a technology that uses microscopic, electronically-controlled mechanical devices to redirect light. Built on a semiconductor substrate, the technology uses control circuitry to produce currents that generate magnetic forces to manipulate the mechanical part as desired. 


Tilting-mirrors optical MEMS

In tilting-mirrors optical MEMS, either current passes through a circuit on the substrate or a charge accumulates on the substrate. Image (modified) used courtesy of Laser Focus World

MEMS techniques offer many positive attributes: they’re small and low cost while offering fast control speeds and high precision in light steering compared to other methods. For this reason, optical MEMS has found a home in many applications—LiDAR being one of the most popular. 


Micromirror Arrays Sandwiched in Window Panes

In a paper published in the Journal of Optical Microsystems, researchers from the University of Kassel have unveiled their findings on a new form of smart glass that leverages millions MOEMS invisible to the naked eye.

The micromirror array is placed in between window panes, where the orientation of the mirrors is controlled by the voltage between respective electrodes. The system also relies on motion sensors in the room to detect the number and position of people in the room, steering light accordingly. 


Example use cases of the MOEMS smart glass

Example use cases of the MOEMS smart glass. Image (modified) used courtesy of Hillmer et al.

Researchers claim this technique yields high actuation speeds (<1ms), 40 times lower power consumption than PDLC displays, and overall energy savings of 35% for buildings in daylight. The researchers also claim that their technique allows for a 30% reduction in a building's CO2 production. 


The Future of Smart Glass

Many companies are becoming more environmentally conscious by analyzing energy consumption habits at the source. Where buildings seem to be one of the largest contributors to overall energy consumption along with CO2 emissions, smart glass—and the MOEMS technology underlying it—may be a more common fixture in future facilities.