While just about everyone knows that bats locate prey in the dark using echolocation, one thing that many people may not realize is the fact that horseshoe bats are particularly good at it. With this in mind, engineers at Virginia Tech are now developing a sonar system that emulates the system used by those bats. Once perfected, it could be a much more compact and efficient alternative to traditional manmade sonar arrays.
Bats in general hunt by emitting ultrasound squeaks from their mouths. When those sound waves strike an object, they're reflected back to the bat and detected by its ears. By analyzing the nature of those reflections, along with the amount of time that they take to come back to the bat, the animals are able to seek out prey and avoid flying into obstacles.
Horseshoe bats are unique, in that they emit the squeaks from their noses. Within their noses are folds of tissue known as noseleaves, which they can move in order to change the characteristics of those squeaks – one particular squeak variation, for instance, is particularly well-suited to detecting the tiny frequency shifts caused by the fluttering wings of insects such as moths.
The bats are likewise able to change the shape of their ears, allowing them to filter the incoming sound depending on the task at hand. Both the noseleaf and ear adjustments occur within just a tenth of a second.
A team led by Prof. Rolf Mueller set about replicating this setup by first studying a colony of 30 horseshoe bats, analyzing their nose and ear movements using high-speed video, ultrasonic microphone arrays, and laser Doppler vibrometry. They then created computer models, and have now built a prototype (seen above). The device is made from flexible rubber, is about 2.5 times the size of an actual horseshoe bat, and uses four motors to move its "ears" and "nose" almost as quickly as the real bats do.
It is reportedly the first sonar system to feature both a dynamic emitter (the nose) and dynamic receivers (the two ears). By contrast, modern naval sonar systems can have several hundred receiving elements within receivers that measure several meters across, and still aren't capable of gathering as much detail as is managed by the bats.
Mueller now plans on mounting the prototype on a drone, to see if it can compensate for flight motion by adjusting the frequency of its outgoing sonar pulses – just like real horseshoe bats already do.