New Bat-based Sonar System

A moving sonar system, based on the echolocation system of horseshoe bats, has been built by US researchers.

The new system could revolutionise man-made sonar systems, which are currently stationary, reducing their size and complexity, and increasing performance.

Biological sonar, known as echolocation, is used by all bats to help them hunt, navigate and fly in the dark. By emitting a really loud noise and listening to the returning echoes, they can visualise the world around them to locate and identify prey and avoid obstacles.

Most bats project sound using their mouths, but horseshoe bats use another unique method.

"These bats project sound through their noses, which are like horseshoe shaped megaphones," explains Virginia Tech study author Rolf Mueller. "The structure is in motion, so the walls of the megaphone twitch, move and adjust to change the sound."

The bats' ears are also dynamic, changing shape to help them receive and decipher the echoes. "They have about 20 muscles which can contract and change the ear shape in one tenth of a second - that's three times as fast as a human can blink."

The team first created a computer model using data collected by tracking and recording the movement of the bats' ears and noses. After looking at the structure and key movements, they then built a robotic model with these same features and all the degrees of freedom of the bat. The prototype was presented at the Acoustical Society of America meeting in Pittsburgh, Pennsylvania last week.

This prototype is a first step towards refining our current sonar systems. Naval sonar, for example, uses up to a thousand emitter and receiver elements contained in a housing 7 or 8 metres in diameter. Yet the horseshoe bat's incredible systems, and the prototype, are tiny in comparison and have only 3 elements: one megaphone nose emitter and two ear receivers.

Although the current model cannot function as naval sonar just yet, the hope is that by imitating the bat's dynamic approach we could eventually create new structures one tenth of the current diameter with one hundredth of the elements!

The researchers also want to understand just how the bats manage to navigate such difficult surroundings, and how we can apply this to our systems.

"The [naval] technology we currently have really breaks down in cluttered environments with lots of objects, but the horseshoe bats live in forests and are really good at dealing with that," says Mueller, "One cave we study has an entrance with a 45-degree wooded mountain slope below - the bats come flying out over that and straight into dense trees at about 10 metres per second with no problems."

As well as collecting more information from real bats, they are going mount the bat-sonar on a small drone and monitor that whilst it flies it around different environments too.