Fish ear spawns sensor

March 8, 2007
U.S. Navy ships tow arrays of hydrophones thousands of feet long to locate enemy submarines by sound.

A new type of sensor incorporating optical fibers detects the direction from which underwater sounds come. The design could help the U.S. Navy locate enemy submarines.

But determining the direction from which sounds come can be tricky, especially for low-amplitude sounds because they can get lost in background noise. A new type of sensor from researchers at the Georgia Institute of Technology could give better directional information and cut line length by a factor of five.

Inspiration for the design came, appropriately enough, from fish ears. Fish ears contain thousands of tiny hairs cells that move in response to sound waves passing through them. The arrangement gives fish a keen sense of directional hearing that helps thwart attackers.

The sensor contains two small plates attached by a hinge. One plate mounts rigidly while the other is free to move. The movable plate is of a composite with the same density as water so it shifts in the sound field and follows the water motion. An optical fiber glues to the surface of the plates. Motion of the movable plate modifies a light signal sent through the optical fiber, which a photodetector analyzes. A modified version of the sensor could detect acoustic shear, boosting directional sensitivity. Researchers recently tested a prototype sensor in the university's 160,000-gallon acoustic tank. Next step: field tests.

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