Preterm infants appear to mature better if they are shielded from most wavelengths of visible light, from violet to orange. But it has been a challenge to develop a controllable light filter for preterm incubators that can switch between blocking out all light--for sleeping--and all but red light to allows medical staff and parents to check up on the kids when they're awake.
Now, in a paper accepted for publication in Applied Physics Letters, a journal of the American Institute of Physics, researchers describe a proof-of-concept mirror that switches between reflective and red-transparent states when a small voltage is applied.
The research team had previously identified a magnesium-iridium reflective thin film that transforms into a red-transparent state when it incorporates protons. Providing those protons in a way that is practical for preterm incubators, however, was the challenge. The typical method--using dilute hydrogen gas--is unacceptable in a hospital setting. So the team created a stack of thin films that includes both an ion storage layer and the magnesium-iridium layer: a voltage drives protons from the ion storage layer to the magnesium-iridium layer, transforming it into its red-transparent state. Reversing the voltage transforms it back into a reflective mirror.
The researchers report that the device still allows some undesirable light wavelengths through, but a force of just 5 V changes the device's state in as little as 10 seconds. The researchers are now looking at other materials to improve color filtering and switching speed.
- Kazuki Tajima, Mika Shimoike, Heng Li, Masumi Inagaki, Hitomi Izumi, Misaki Akiyama, Yukiko Matsushima, Hidenobu Ohta. Controllable light filters using an all-solid-state switchable mirror with a Mg-Ir thin film for preterm infant incubators. Applied Physics Letters, 2013; 102 (16): 161913 DOI: 10.1063/1.4801848
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