Understanding how the geometry of a bat’s ear and nose creates functional sonar patterns

Bat sonar is fairly simple in concept — the bat emits a sound through its nose leaves, which bounces off of objects and returns to their ears some time later, indicating the distance to the object. To determine which direction the distance measure comes from, the bats actually emit a range of frequencies. Their ears and noses shape the sound so that different frequencies are emitted with different strengths in different directions. For example, the high frequencies might be focused in a lobe directly in front of the bat, while the lower frequencies "sweep" the ground underneath them.

Different bat species have very different lifestyles, and consequently, very different sonar patterns. These differences are due to the shape of the nose-leaves and ears. Understanding exactly how that shape influences the sonar pattern is the long-term goal of this project. Our approach is to combine a mix of shape features , shape correspondence, and shape “texture” identification to control and manipulate the geometry and determine how it affects the beam patterns.

One thing that makes this project fascinating is there is no clear link between geometry and sonar pattern - very simple ears can create complex sonar patterns, and vice-versa. Complicating this is the fact that even measuring and comparing sonar patterns is a shape-comparison problem in and of itself. Sonar is a 4D function - in each direction for each frequency, measure the strength of that frequency.

Beyond shape analysis, we are also experimenting with building a physical analog to bat sonar for robot applications - basically replacing the laser scanner with a 3D printed nose and ears.

Funded in part by NSF grant DBI 1053171.

Collaborators

• Rolf Mueller (Mechanical Engineering, Virginia Tech)
• Washington Mio (Mathematics, University of Florida)
• Charless Fowlkes (Computer Science, UC Irvine).

Papers