Navy studies cicadas to develop better sonar

This summer, billions of 17-year Brood II cicadas will swarm the East Coast and bring the distinctive, loud noise they make to attract mates.

The U.S. Navy has been studying cicadas for several years hoping to develop a device that would mimic its ability to make noise so loud for their small size. Such a device could be used for remote sensing underwater, ship-to-ship communications and rescue operations.

Active sonar systems emit sound and then listen for the waves that bounce back, but currently require large equipment unsuitable for small ships or unmanned craft. Passive sonar systems just listen for the noise other objects make. These are much more compact, but they are unable to emit any sound.

Derke Hughes, a researcher at the Naval Undersea Warfare Center, has been working on the unfunded project in his free time with other volunteers. They have found a ribbed membrane on the torso that vibrates when the cicadas deform their bodies.

The cicadas have a rapidly buckling rib that repeatedly impacts their corrugated exoskeleton, called a tymbal. This process is much like a hammer striking a gong.

The cicadas use thick sets of muscles along the torso that allow the chest to cave in so far the ribs buckle inward, then snap back to their original shape, and they are able to repeat this process 300 to 400 times per minute.

The team has yet to work out an accurate model describing how the sound is made during the physical process. “We’re still working on that,” Hughes said in a press release. The Naval researchers are presenting their findings at the 21st International Congress on Acoustics this week.