GLOBAL CHALLENGES

Smarter Windows Dim with Harvested Energy

R. Colin Johnson | Date: 02-25-11 | Comments

Smarter windows of the future will harvest ambient radio frequency (RF) energy, then use it to automatically dim as they track the sun's path across the sky each day.

Today, people need to manually close and open blinds to cover the windows when the sun's glare is overbearing, then open them again to admit ambient light when the sun begins to set. Smarter windows, however, would harvest ambient radio frequency (RF) energy to provide the power to auto-dim windows as they track the sun across the sky.

Windows make employees happy and can save on lighting bills, but without blinds being drawn in sync with the sun, they can cause eye-straining glare, inflate air conditioning bills in the summer, and let heat escape in the winter. Wouldn't it be cool--or maybe "hot" is the right word--to harvest ambient RF energy then use it with smart algorithms that auto-dim windows?

Energy-harvesting smart windows use an RF device developed by Holst Centre and IMEC to switch Philips'e-Skin between open (top) and closed (bottom) states. (Source: Philips Research)

Philips Research has been working to realize this dream of "smart windows" with the Holst Centre for Wireless Autonomous Sensor Technologies and Flexible Electronics and the Interuniversity MicroElectronics Center (IMEC). Philips contributed its e-Skin to the project, for which the Holst Centre developed an RF energy harvester to power the window's smart auto-dimming function.

Philips e-Skin can change colors in response to electrical signals that release inks stored in reservoirs around its edges, allowing nearly any color to be spread across its surface. Philips designed e-Skin to not only dim windows, but to change the color of any surface to which it is applied. For instance, e-Skin could be applied to a smartphone cover, which could then change color to match the clothing or mood of its user.

For the smart-window demonstration, Philips used the electrical energy harvested from the ambient microwave signals that permeate any place where you can get a signal for your cell phone. In fact, the Holst Centre's RF energy harvester was able to generate enough electricity to power the e-Skin from the emissions of a single cell phone.

Philips e-Skin uses reservoirs of ink around its edges to change color from yellow (top) to magenta (bottom), which could be combined on two layers to make red. (Source: Philips)

The resulting energy-autonomous smart windows can change to different colors depending on whether they are trying to reflect or absorb sunlight. In the demonstration, an e-Skin panel just 75 millimeters (3-inches) square could be switched from opaque to clear by harvesting the RF energy from a nearby cell phone. However, the researcher further claimed that a window 250 times larger could be dimmed with the same amount of harvested energy, and that the large antenna needed could be constructed from flexible foils built into walls.