Performing Boolean Surgery to Unlock Biosonar's Secrets

Over the last approximately 60 million years of evolutionary history, bats have developed highly optimized biosonar systems in which they broadcast ultrasound at various frequencies and then detect the echoes to sense their surroundings.

At last month's meeting of the Acoustical Society of America in New York, researchers (Rolf Mueller, University of Southern Denmark, +45-6550-3655, rolfm@mip.sdu.dk) presented the first high-resolution, three-dimensional maps to depict spatial regions in which the ears are sensitive to low- mid-, and high-frequency ultrasound. These biologically based ultrasound-sensitivity maps vary considerably over the studied sample of bat species and are likely to vary even more over the approximately 1000 species which exist in total. They may help inspire much better designs for artificial antennas of any type, from the acoustic ones in ship sonar systems and medical devices to the electromagnetic antennas in cell phones.

In their approach the researchers perform CT scans of bat ears to obtain highly detailed images and 3D shapes which are then rendered on a computer. Next they model the interaction between each ear shape and ultrasound waves from the bat's surroundings. The researchers can understand how the anatomical features of an ear shape bring about the spatial sensitivity patterns by performing painless "Boolean surgery," in which they can modify an ear's shape on a computer (often by removing some features and--as part of their future plans--mixing features from different species) and see how the modifications change the ear's detection of ultrasound. (Paper 4aAB6 at meeting; also see lay-language paper.)