As concern grows about the potential for powerful lasers to disable satellite sensors, engineers continue to develop protective solutions. As part of research for the US Defense Advanced Research Projects Agency and the Army Research Office, engineers at the University of Florida have designed an "artificial eyelid" that would essentially let a satellite blink to protect its eyes. The device's surface is covered with thousands of tiny apertures, versions of which are 10 µm to 1 mm wide, made by MCNC of Research Triangle Park, N.C. When the device detects the flash of light from a laser, for example, the shutters close, changing the surface from transparent to opaque. A stress gradient between polyimide and gold thin films holds the shutters in a "normally open" position, explained Paul H. Holloway, a professor of materials science and engineering. Electrostatic attraction causes the shutters to close as quickly as 0.1 ms. Besides protecting sensors, the device could be built into helmet visors for pilots, shielding their eyes from laser attacks. The 0.1-ms response time is fast enough that a pilot would not perceive it. But to protect the eye, response times must improve to about 1 ns, Holloway said. "One ten-thousandth of a second is fast enough to protect many sensors, but not the eye from a large pulsed laser." To improve the speed, the designers are working to combine the shutter with nonlinear optical materials, he said. By varying the open duty cycle, the device could function as sunglasses, Holloway noted. However, with current technology, the artificial eyelid would likely fall outside the price range of consumer applications.