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  Research: bats' "noseleaves" focus their sonar   



    BEIJING, Nov. 29 (Xinhuanet) -- Scientists at Shandong University in Jinan, China have solved a "100-year-old riddle" about the wrinkles and grooves around 300 bat species' noses that could lead to improved sonar and radio technology.

    Bats are famous for their ability to "see" in the dark by listening to the echoes of their ultrasonic calls. This is known as echolocation, or "biosonar." Researchers said the wrinkles and grooves -- known as "noseleaves" -- help the bats navigate and locate prey in the dark by focusing their sonar.

    While most bats emit sonar from their mouths, roughly 300 species fire it from their noses.

    Scientists have long speculated these noseleaves might help shape bat sonar, but nobody knew for certain, explained biologist turned computational physicist Rolf M┨ller at Shandong University.

    He and his doctoral student Qiao Zhuang have now discovered precisely how one kind of bat facial feature improves biosonar, solving "a 100-year-old riddle," M┨ller told LiveScience.

    The noseleaves essentially help the bats make the most of the ultrasound they emit, M┨ller explained.

    "For the bat, sound energy is like money to us -- we usually only have a limited amount of it and we must make a choice on how to distribute it," he said.

    The furrows the researchers investigated help shape how the lower frequency sound "illuminates" the environment, while the other frequencies remain untouched and thus able to scan the world in different ways.

The researchers employed X-ray scans to generate three-dimensional computer models of the noseleaves of the rufous horseshoe bat, native to southern Asia. M┨ller and Zhuang then simulated how ultrasound pulses the bats emit interact with the noseleaves.

    The bats send ultrasonic pulses that start at about 60 kilohertz in frequency, quickly rise to a constant frequency of roughly 80 kilohertz, and then fall back to 60 kilohertz at the end. Computer simulations revealed horizontal furrows along the top of the noseleaves behaved as cavities that resonate strongly with certain frequencies of sound, just as blowing into "a set of clarinets," can produce deep, resonant tones, M┨ller said.

    As a result, the grooves cause the different frequencies of sound to focus different ways. The lower frequency 60-kilohertz sound gets spread vertically, while the 80-kilohertz frequency continues to be focused ahead.

    The complexity the noseleaves add to the bat ultrasound beams could help "in performing difficult sonar tasks like navigating in complex environments such as dense forests or doing several things at once, such as looking for prey and avoiding obstacles," M┨ller speculated.

    Facial grooves and flaps are even found on bats without noseleaves. Their findings suggested "all facial structures seen in bats are now candidates for acoustic 'beam-shaping devices,'" M┨ller said.

    Likewise, "the outer ears of most bats also have intriguing shape features," M┨ller said. "These features could act in similar ways as the noseleaves."

    The goal of this research is to not only better understand how bat echolocation works, but to apply the principles to improving antenna technology, for use in sonar, scanners and wireless communication, M┨ller said.

    M┨ller and Zhuang reported their findings in the Nov. 24 issue of the journal Physical Review Letters.






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