Smart Window Retains State Without Power
BGU researchers developed a hybrid smart window that retains transparency settings without continuous power and passively regulates heat
Researchers at Ben-Gurion University of the Negev have developed a smart window that can switch from transparent to opaque at the touch of a button and retain its selected state for months without a continuous power supply. The secret lies in tiny molecular “nanosprings” that provide unprecedented stability.
The patented technology was published in the journal Nanoscale Advances and presented at an SPIE conference.
Smart windows can change their level of transparency to regulate the amount of sunlight and heat entering a building. They are considered among the most promising technologies for green construction and reduced energy consumption. However, most existing solutions have a significant limitation: they require a constant power supply to remain transparent or opaque. Many also fail to control the heat passing through the window, substantially reducing their energy efficiency.
At BGU’s Liquid Crystal Devices and Nanophotonics Laboratory, Prof. Ibrahim Abdulhalim and doctoral student Nivin Hussein of the Department of Electro-Optics and Photonics Engineering have developed a distinctive engineering solution: a smart-window device containing liquid crystals arranged in a unique nanoscale helical structure.
The device requires only a brief electrical signal to switch between transparent and opaque states. Once the desired state is selected, it remains stable even after the electrical current is completely disconnected.
The study’s principal innovation lies in the material’s molecular structure. The researchers compressed the liquid crystals’ natural helical structure to an exceptionally short pitch of approximately 100 nanometers, about one-tenth of the length previously used in similar systems.
Under these conditions, the molecules do not disassemble. Instead, they reorganize into rigid nanosprings consisting of only five to ten turns. These tiny coils respond with high precision to changes in electrical frequency and voltage.
For example, a low frequency of 20 hertz causes the helical structure to disperse into microscopic regions that scatter light, making the window opaque. A high frequency of one kilohertz aligns the nanosprings perpendicular to the surface, returning the window to a fully transparent state.
The hybrid window combines this advanced liquid-crystal layer with a nanostructured layer of vanadium dioxide (VO₂), a smart material capable of regulating the transfer of heat from solar radiation.
The VO₂ layer blocks excess heat during the summer while allowing infrared solar energy to enter during the winter. This can reduce the energy required to heat and cool buildings.
By combining privacy control, light management, and passive thermal regulation, the technology creates a new platform for highly energy-efficient smart windows intended for the next generation of sustainable buildings.
In extended laboratory tests, the device demonstrated impressive durability. The selected state remained unchanged for 96 consecutive hours and retained almost complete stability after both 30 and 90 days. This represents a dramatic improvement over previous technologies, which deteriorated within a few hours.
“The ability to combine long-term optical memory without electricity with passive thermal regulation opens a new direction in the field of smart windows,” said Prof. Abdulhalim. “We believe this technology could contribute to the development of more energy-efficient buildings and improve control over light, privacy, and thermal comfort in residential, automotive, and working environments.”
Prof. Ibrahim Abdulhalim | Photo: Courtesy
In addition to its potential use in energy-saving smart windows for buildings and vehicles, the new mechanism could support other technological applications.
Its rapid response time of a fraction of a second, high optical contrast, and ability to retain visual information without electricity make the technology suitable for rewritable displays, advanced electronic paper, and energy-efficient information signs.
The technology has been patented through BGN Technologies, BGU’s technology commercialization company.
“As the commercialization company of Ben-Gurion University, we seek technologies that not only represent scientific breakthroughs but also have the potential to reach the market and create meaningful change,” said Ran Melamed, Vice President of Business Development for Engineering and Exact Sciences at BGN Technologies. “In this case, we see broad potential for collaborations that could benefit from both the unique technology and the way it is implemented.”
The research, grant number 223-11-061, was supported by the Ministry of Energy, Water and Infrastructure.
