When it comes to sonar, bats certainly have us beat. So, engineers are joining them instead.
Horseshoe bats have particularly powerful echolocation abilities and use sound to fly through incredibly dense forests without bumping into anything.
Engineers at Virginia Tech have been observing the movements of their ears and noses in the hopes of achieving bat-quality sonar that could one day guide drones. They presented their new sonar system prototype, which bears movable batlike ears and nose parts, at the 169th Meeting of the Acoustical Society of America on May 20.
"Bats outperform even state-of-the-art man-made sonar," mechanical engineer Rolf Mueller said in an interview. "Our hypothesis is that these dynamics are an important factor in that, so if we reproduce that we hope we can go beyond what engineers can currently do and get close to what bats can do."
Reproducing bat behavior with a machine requires detailed observation, so Mueller and his team kept bats in the lab and used high-speed cameras to record their motions. When the bats use their own natural sonar system, echolocation, they produce sound with their vocal cords much the way humans do. However, instead of letting the sound come out of their mouths, they emit the sound from their specially adapted noses.
"Around the nostrils they have a little 'megaphone' and the walls of that megaphone are in motion when the bats make the sound," says Mueller. The baffle shapes of the nasal megaphones around the nostrils are called "noseleaves."
As the walls of these nasal megaphones deform, they alter the sounds that the bats emit. Similarly, horseshoe bats also can shift the shape of their ears at the extremely fast rate of within one-tenth of a second, allowing them to filter incoming sounds according to their needs.
These dynamic parts allow the bats to control the sound not only as it goes out but also as it comes in, making their sonar system more efficient. By mimicking these moving parts, the researchers hope to create a more compact and efficient robotic sonar system that employs just two receiving channels — the ears — and one emitting channel — the nose.
"An obvious application are systems that need to move around natural environments like drones," Mueller says.
A modern naval sonar array, which could be comprised of hundreds of receiving channels and measure several meters across, would not be a practical addition to a such a small aircraft, but this new robotic sonar system is approximately bat-sized. It will be some time before you see any bat-eared drones flying overhead, however.
"We've gotten to the point where we can reproduce the motions that we observed in bats," says Mueller, but "right now it's still a desktop system."
A paper that he presented at the 168th ASA meeting may be found here.
