Engineers at the University of Toronto have taken inspiration from the squid to develop a prototype for “liquid windows” that can change the wavelength, intensity, and distribution of light emitted through them, thereby reducing energy costs by substantial amounts.
In a new paper published in the Proceedings of the National Academy of Sciences, they described their discoveries. “Buildings use a ton of energy to heat, cool, and illuminate the spaces inside them,” said co-author Raphael Kay. Kay likes to think of buildings as living organisms that have “skin,” which includes an outer layer of exterior façades and windows.
This system has blinds that can open and close in a crude way to ease the load on lighting and heating and cooling systems; electrochromic windows that change their opacity when a voltage is applied are a more sophisticated option.
To collect inspiration, they looked to nature. Last year, Toronto engineers built a system with optofluidic cells based on marine arthropods such as krill, crabs, and tilapia, which can disperse and collect pigment granules in their skin to change their color and shading. A pink flower of color is emitted by injecting a bit of water with a pigment or dye through a tube connected to the cell’s center. Squid skin is transparent and has an outer layer of pigment cells called chromatophores that control light absorption.
Each chromatophore is attached to muscle fibers that line the skin’s surface, which in turn are attached to a nerve fiber. It’s a simple matter to stimulate these nerves with electrical pulses, which cause the muscles to contract. Because the muscles are pulling in different directions, the cell expands along with the pigmented areas, changing the color. When the cell shrinks, the pigmented areas follow suit.
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A second layer of iridophores is embedded beneath the chromatophores, and unlike the chromatophores, the iridophores are an example of structural color, similar to the crystals in butterfly wings, with the exception that squid iridophores are dynamic rather than static.
The squid’s ability to change color at the speed of light is inspiring; DIY YouTubers the Backyard Brains even posted a photo of a longfin inshore squid’s skin changing colors in 2012, in sync with Cypress Hill’s “Insane in the Brain.” The electric signals of the music themselves induced the color changes.
The structure of squid skin, which may provide the key to designing dynamic, tunable facades, was identified by Kay and his colleagues. “Sunlight contains visible light that affects lighting in the building, but it also contains invisible wavelengths, such as infrared light, which we think of as heat,” Kay said.
By adding custom pigments or particles to the fluid, wavelengths of light can be filtered, as can the direction in which light is scattered. These sheets can be combined into stacks, with each stack performing a different optical function such as filtering the wavelength, tuning how light is scattered indoors, and controlling intensity, all using small digital pumps.
Using a simple and low-cost approach, Kay says, it could be possible to design “liquid-state, dynamic building facades” with tunable optical properties to save energy on heating, cooling, and lighting.
A single layer controlling the transmission of near-infrared light could reduce energy costs by 25 percent while adding a second layer controlling the transmission of visible light could reduce energy costs by 50 percent.
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Ben Hatton, a co-author of the book, said, “The concept of a building that can learn, that can adjust this dynamic array on its own to take into account seasonal and daily changes in solar conditions, is very exciting for us.”
It will take some effort, but if you consider that all of this can be done with simple, non-toxic, low-cost materials, it’s a challenge that can be solved. The energy that buildings consume is enormous around the world. It is more than what we spend on manufacturing or transport.