International. A nano-thin window covering can more than double the thermal protection for residential and commercial windows.
This technology is now on its way to commercialization, thanks in part to $5 million in federal funding from Sustainable Development Technology Canada announced in late February.
It's one aspect of the perfect window that is the goal of ECE professor Nazir Kherani and his collaborators at startup 3E Nano Inc.
"Windows are the weakest energy link in any building," said Kherani, who co-founded 3E Nano in 2015. "Think of the heat that escapes in the winter months and the heat that enters the cool, ventilated space during the summer months."
"A window's resistance to heat flow is measured by the R-value, which is the ability to prevent heat from entering or escaping from a building. Currently, 3E Nano windows in prototype, as well as in pre-alpha R8 implementation rate and above. This compares markedly to an average window, whose R-value is in a range of R1 from single-pane to R3, a dual panel," Kherani continued.
In its simplest configuration, the 3E Nano coating comprises a nanothin metallic film sandwiched between two sapphire-like nanothin films. This three-layer dielectric-metal-dielectric cell is opaque to certain wavelengths of light, but not to others.
As a result, the cladding can control the flow of light in and out of the building in three parts of the solar spectrum, visible, near-frequency infrared and mid-frequency infrared. Both near-infrared light, which accounts for nearly half of the sun's total energy, and average infrared light can be reflected.
It prevents heat from the sun from penetrating inside, but also prevents heat from the room inside the building (i.e. medium infrared radiation) from escaping through the windows, achieving low emissivity. At the same time, visible natural light is allowed to enter through the window into the interior, which reduces the need for artificial interior lighting.
Kherani believes 3E Nano coating is about to become a core product.
"The combination of earth-abundant aluminum and nitrogen results in a sapphire-like coating material in its optical and structural properties," Kherani said.
"The stability and multifunctional character of the sapphire-like structure is suitable for high-volume, low-cost manufacturing," he added.
In essence, the coating is a one-dimensional structure that is nanothin but tough. It is applied by cathodic deposition, a process that throws argon atoms at an aluminum target in a vacuum system, striking the aluminum atoms like billiard balls on a lightweight polymer substrate.
After nitrogen gas is added, the resulting chemical reaction forms a colorless, sapphire-like film only tens of nanometers thick (about one-thousandth the thickness of a strand of hair).
This properly combined with a nano-thin silver layer results in a robust coating that can be adjusted for optical and electrical properties.
Kherani and his team envision other aspects of the perfect window as integrated functionalities ranging from metamaterial structuring to dynamic systems that maintain ideal temperatures and natural lighting within buildings.
"In the lab, we have created a metamaterial that retains solar control and low-emission properties but has high transparency in the gigahertz range critical for communication, inspired by nature with nearly invisible hexagonal honeycomb patterns," Kherani said.
