Holy sonar technology, Batman!

College Park, MD (June 22, 2004)--What can the Navy and NASA learn by taking a close look at a bat's ear? Maybe the secrets to new shapes for antennas. European researchers have created detailed 3-D maps of the shapes and crevices of bat ears created by millions of years of evolution to help bats find their way.

Bats shriek, then their specialized ear shapes listen to how the sounds bounce back, much as humans watch how light bounces back from all over the room. Rolf Mueller at the Maersk Institute of the University of Southern Denmark mapped the ways different bat ear shapes interact with the range of sounds a bat can hear, and presented his work at last month's meeting of the Acoustical Society of America.

Bat ears have an incredible range of design. Furrowed at the edges, tall and curved banana-wise, rounded, pointy – there are about 1,000 species of bats and not much less different ear shapes.

In their approach, the researchers performed CT scans of bat ears to obtain highly detailed images and 3-D shapes, which are then rendered on a computer. Next they modeled the interaction between each ear shape and ultrasound waves from the bat's surroundings.

One of the features Mueller thinks would be useful to sonar technologists is the tragus, a spike shape in front of the outer ear opening. You can find your own tragus by putting your finger in your ear, palm toward your face. Your fingertip is touching your tragus.

The tragus is a new feature in antenna design that the researchers hope will allow them to listen to echo sound from two directions simultaneously. Mueller plays with the shapes of the bat ears and the position of the tragus by altering the 3-D shape representation and then observing how the changes in shape affects the interaction between ear surface and sound.

Ordinary sonar antennas are disk shaped and smooth -- efficient in catching incoming sound waves from straight ahead. These antennas can find an echo in a space shaped like a blimp, or an elongated football with a fanned tail. The detection volume of the bat ear shape is more like a rose; it probes space with an intricate arrangement of petals listening at different frequencies and in different directions.

These biologically based ultrasound-sensitivity maps gave rise to several ear-shaped designs for antennas. Mueller's project is heading toward commercialization of these designs – right now, he is in the process of making the ear antennas able to wiggle up and down, turn inward and outward to catch sounds just as bat ears do.

Mueller's project is part of a European Union project, called CIRCE, to understand how the body and brain process sensory information by constructing a bionic bat head, just centimeters across, like a real bat head. Testing the bat-inspired devices in realistic biosonar scenarios helps learn more about how bats perceive the world.

More information

How Bats' Ears Probe Space: Look Around While You Whistle

A technical explanation

More about the EU's project

Rolf Mueller
University of Southern Denmark
+45-6550-3655

Martha J. Heil
American Institute of Physics
301-209-3088