Bat noses inspire robotic sonar

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Scans reveal secrets of how sound is sprayed from a bat nose.
Rolf Müller, a computational physicist at Shandong University in Jinan, China, has combed the caves of Southeast Asia to find out. “We are looking at different species to understand their physical tricks,” says Müller, who models the way that bat noses act like antenna, and how their ears work as dishes to collect sound.
The work matters not just to biophysicists who want to understand how animals evolve complex systems, but also to roboticists trying to find new ways of navigating in situations in which light sensors don’t work so well, including at night or underwater.
Few biophysical studies of bat noses have been done. One researcher bent back a bat’s noseleaf — the complex structure surrounding its nostrils — to see what would happen; another scientist smeared the delicate structures with petroleum jelly. Both procedures messed up the bats’ navigation.
To get a better picture of what’s going on in a bat nose, Müller took X-ray scans of the face of a Rufous horseshoe bat (Rhinolophus rouxii ), compiling scans to build a three-dimensional computer model of the nose cavities. He then shot sound waves of differing frequencies through the modelled nose to see where they resonated, and how they were emitted from the noseleaf.
Sonar emitted from a bat noseleaf: red highlights the possible sound sources.Rolf Mueller
High frequency sounds, Müller found, resonated in a structure in the middle-back of the nose called the sella, and were emitted from the noseleaf as a narrowly focused beam. Low-frequency sounds resonated in a cavity called the lancet, at the top of the noseleaf. Furrows in the lancet created four secondary sound sources, so that sonar was emitted from a total of six sources, rather than just the two nostril holes. “It widens the beam — you have a wider array and you can splash the sound around better,” says Müller. The study was published in Physical Review E 1. (...)

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