Electronic Design

Tiny Grates Reveal Super-Small Motion

Motion detectors just got 1000 times better, thanks to researchers' efforts at Sandia National Laboratories and a little-known optical property. Light diffracted from very small gratings that move very small lateral distances undergoes a relatively large, and therefore easily measurable, change in reflection. This prompted Sandia's researchers to develop a device that reflects a bright light from a very small moving object, detecting motion with 1000 times more sensitivity than other motion sensors.

The device lays a tiny comb-like structure over another such structure, forming a grating. A space of 300 nm lies between the top and bottom combs and 600 to 900 nm between comb teeth. The bottom comb is locked in place, and horizontal springs secure the top comb. Any motion, no matter how tiny, sends the top comb skittering over the bottom comb, laterally deforming the grating. This disturbance changes the amplitude of light in the visible to near-infrared range, which is diffracted by a tiny laser beam shining on the apparatus. The device measures this change to detect and calculate the motion.

In effect, the device acts like an accelerometer. Researchers say it's about the size of those inexpensive microelectromechanical devices that open air bags in automobiles. Possible applications for the device include earthquake studies, skid and traction control in automobiles, and internal navigation systems in airplanes. Sandia sees a time frame of three to five years before the devices are available for use.

For details, go to www.sandia.gov.

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