by Richard Conniff/Scientific American
One big problem with putting autonomous drones to work delivering packages—or flying search-and-rescue missions—is that the sky is complicated and unpredictable. Trees, utility wires and spiraling footballs can turn up almost anywhere in the flight path. A new strategy for dodging these obstacles could come from an unexpected source: the way bats wiggle their ears.
The idea first occurred to Rolf Mueller, a Virginia Tech mechanical engineering professor, a few years ago while looking at bat photographs. He noticed that the ears of some species often looked blurry, because the animals were continually making rapid ear movements. But why?
Mueller studies bat behaviors, including their adaptations to the Doppler effect or Doppler shift. Both terms refer to the way sound waves from a fast-moving object such as a train or an ambulance get compressed—and therefore higher in pitch—as the object approaches a listener. Then the sound waves lengthen out again and become lower in pitch as the vehicle moves away. Even when the train or ambulance is out of sight, a person can tell roughly where it is at any moment from these changes in sound. Bats use the Doppler shift to locate objects in much the same way, but far more precisely.
Scientists have known since the 1930s that insect-hunting bats produce bursts of sound as they bob and weave through the night. They use the reflected sound waves to identify obstacles and target prey, an ability called echolocation or biosonar. Research in the 1960s showed that bats also interpret Doppler shifts, in sounds bounced off of flying insects, to zero in on a meal with high precision—even while maneuvering at breakneck speed through Read the rest of this entry »