This photo shows a bat with the landmarks on the ear and a high-speed video camera pointed at it in the laboratory of Rolf Mueller, Virginia Tech associate professor of mechanical engineering. Image: Virginia Tech |
“Certain
bats can deform the shapes of their ears in a way that changes the
animal’s ultrasonic hearing pattern. Within just one tenth of a second,
these bats are able to change their outer ear shapes from one extreme
configuration to another,” said Rolf Müller, associate professor of
mechanical engineering at Virginia Tech.
Müller and his students wrote a paper on their work that is appearing this week in Physical Review Letters,
a prestigious peer-reviewed journal of the American Physical Society.
The students are: Li Gao of Shandong, China, a Ph.D. student with
Müller, and Sreenath Balakrishnan of Thrissur, Kerala, India, a master’s
candidate with Virginia Tech’s Department of Mechanical Engineering, as
well as Weikai He and Zhen Yan, of the School of Physics at Shandong
University.
Müller
explained the significance of their work, saying, “In about 100
milliseconds, this type of bat can alter his ear shape significantly in
ways that would suit different acoustic sensing tasks.”
By
comparison, “a human blink of an eye takes two to three times as long.
As a result of these shape changes, the shape of the animals’ spatial
hearing sensitivity also undergoes a qualitative change,” Müller added.
Bats
are flying mammals most well known for their abilities to navigate and
pursue their prey in complete darkness. By emitting ultrasonic pulses
and listing to the returning echoes, the animals are able to obtain
detailed information on their surroundings. Horseshoe bats, in
particular, can use their sonar systems to maneuver swiftly through
dense vegetation and identify insect prey under difficult conditions.
Acting
as biosonar receiving antennas, the ears of bats perform a critical
function in bringing about these ultrasonic sensing capabilities.
Using
a combination of methods that included high-speed stereo vision and
high-resolution tomography, the researchers from Virginia Tech and
Shandong University have been able to reconstruct the three-dimensional
geometries of the outer ears from live horseshoe bats as they deform in
these short time intervals.
Using
computer analysis of the deforming shapes, the researchers found that
the ultrasonic hearing spotlights associated with the different ear
configurations could suit different hearing tasks performed by the
animals. Hence, the ear deformation in horseshoe bats could be a
substrate for adapting the spatial hearing of the animals on a very
short time scale.
The
research piggybacks earlier work led by Müller and reported this spring
in the Institute of Physics’ journal Bioinspiration and Biometrics.
That study provided key insights into the various shapes of bat ears
among the different species, and illustrated how the differences could
affect how their navigation systems worked.
The
National Natural Science Foundation of China, Shandong University, the
Shandong Taishan Fund, and the China Scholarship Council supported the
most recent work.
This photo shows a sequence of deforming ears on the bat, taken in the laboratory of Rolf Mueller, Virginia Tech associate professor of mechanical engineering. Image: Virginia Tech |
The
collaboration between Shandong University and Virginia Tech started
with Müller’s opening of a new international laboratory based at the
Chinese facility in 2010. The new laboratory focuses on bio-inspired
research. In the past, the lab was used by an interdisciplinary group of
researchers from the University of Utah, North Carolina State
University, and University of California Los Angeles to conduct
experiments on the extraordinary capabilities of bats to generate
high-powered ultrasonic pulses.
Müller’s aspiration in teaching is to bridge the gap between disciplines, especially between biology and engineering.
Müller’s
research is focused on the understanding of how the most capable
biological sensory systems can achieve their best performances. His
recent achievements include: providing the first physical explanation
for the role of a prominent flap seen in mammalian ears in 2004;
discovery of a novel helical scan in the ear directivity of a bat in
2006; discovery of frequency-selective beam-forming by virtue of
resonances in noseleaf furrows of a bat, an entirely new bioacoustic
paradigm in 2006; establishing the first immediate and quantitative
characterization of the spatial information created by a mammal’s outer
ear in 2007; and now uncovering the acoustic effect of non-rigid ear
deformations in bats.
Ear Deformations Give Bats a Physical Mechanism for Fast Adaptation of Ultrasonic Beam Patterns
