Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Bats have an ambulance in their ears

05.06.2019

Anybody who has been passed by an ambulance at high speed has experienced a physical effect called the Doppler shift: As the ambulance moves toward the listener, its motion compresses the siren's sound waves and raises the sound pitch. As the ambulance moves away from the listener, the sound waves get dilated and the pitch is lowered. A listener wearing a blindfold could use this Doppler shift pattern to track the motion of the ambulance.

In a paper published by the Proceedings of the National Academy of Science, the authors, Rolf Mueller, professor of mechanical engineering in the College of Engineering, and his doctoral student, Xiaoyan Yin, demonstrate that the ears of bats come with a "built-in ambulance" that creates the same physical effect.


This research has led to the design of a bat-inspired robotic sonar head, shown here being attached to a drone, with a movable 'noseleaf' and "ears."

Credit: Virginia Tech

Yin and Mueller think the study of ear-generated Doppler shifts in bat biosonar could give rise to new sensory principles that could enable small, yet powerful sensors. An example of this type of sensor would be for drones that can operate in dense foliage or autonomous underwater vehicles navigating near complex underwater structures.

"The animals move their ears fast enough so that sound waves that impinge on the ears are transformed by the motion of the ear surfaces and shifted to higher or lower frequencies," said Mueller.

"In fact, the bat species studied (horseshoe bats and Old World Roundleaf bats) can move their ears so fast that Doppler shifts of around 350 Hz can be created. This is about seven times larger than the smallest Doppler shift the animals haven been shown to be able to detect."

Video: https://www.youtube.com/watch?time_continue=1&v=S7fHCk7EePg

Doppler shifts have long been known to play an important role in the biosonar system of bats such as the species studied by Mueller and Yin. The bats have the enviable ability to hunt in very dense vegetation, but to accomplish this, they have to solve the problem of how to distinguish a moth, their preferred prey, from hundreds of leaves that surround it.

"The solution these two types of bats have come up with has been to tune in on the Doppler shifts that are produced by the wing beat motion of their prey," Mueller explained. "These 'good Doppler shifts' serve as a unique identifying feature that sets prey apart from static distractors, such as leaves in foliage."

Researchers became aware early on that the bats' own flight motion also produces Doppler shifts that would interfere with the perception of the prey-induced Doppler shifts. In the late 1960s a solution to this conundrum was discovered when it was found that horseshoe bats decrease their emission frequency by an amount that is carefully controlled to exactly eliminate any of the "bad Doppler shifts" caused by the bats' flight velocity.

"Since these groundbreaking discoveries, the general belief in the scientific community has been that the role of Doppler shifts in the biosonar systems of these animals has been completely understood," said Mueller. "Doppler shifts due to prey motions are 'good Doppler shifts' that the animals' entire hearing system is optimized to detect, whereas Doppler shifts due to the bats' own flight motion are 'bad Doppler shifts' that the animals eliminate through feedback control of their emission."

While Mueller and Yin found speculation in the literature of the early 1960s that bats may be producing Doppler shifts with their own ear motions, the idea was never followed up with experimental work.

The work conducted by Mueller and Yin has measured the motion of the ear surfaces carefully using stereo-vision based on high-speed video cameras, and the authors were able to predict how fast surfaces move in different portions of the ear. They also estimated the angle between the directions of the ear motions and the direction the bat has its biosonar pointed in and found that motion speeds and directions were aligned to maximize the Doppler shifts produced.

To show that Doppler-shifted signals entered the ear canal of the biomimetic pinna and would be accessible to bats, the researchers built a flexible silicone replicate of a bat ear that could be made to execute fast motions by pulling on an attached string.

The final piece in the research has been to find possible uses for the ear-generated Doppler shifts.

"We were able to show that the Doppler shifts produce distinct patterns over time and frequency that can be used to indicate the direction of a target," said Mueller. "In the context of these bat species' biosonar systems, they typically concentrate and emit most of their ultrasonic energy in a narrow frequency band. However, for telling the direction of a target, it is usually convenient to look at how multiple frequencies are transmitted by the ear and the 'spectral color' that results. The Doppler shift patterns produced by the ear motions could give these bat species the option to concentrate their energy in a narrow frequency band yet be also able to tell target direction."

Media Contact

Lindsey Haugh
jangus@vt.edu
540-231-2476

 @vtnews

http://www.vtnews.vt.edu 

Lindsey Haugh | EurekAlert!
Further information:
https://vtnews.vt.edu/articles/2019/06/me-dopplershift.html
http://dx.doi.org/10.1073/pnas.1901120116

More articles from Life Sciences:

nachricht If Machines Could Smell ...
19.07.2019 | Fraunhofer-Institut für Produktionstechnik und Automatisierung IPA

nachricht Algae-killing viruses spur nutrient recycling in oceans
18.07.2019 | Rutgers University

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Better thermal conductivity by adjusting the arrangement of atoms

Adjusting the thermal conductivity of materials is one of the challenges nanoscience is currently facing. Together with colleagues from the Netherlands and Spain, researchers from the University of Basel have shown that the atomic vibrations that determine heat generation in nanowires can be controlled through the arrangement of atoms alone. The scientists will publish the results shortly in the journal Nano Letters.

In the electronics and computer industry, components are becoming ever smaller and more powerful. However, there are problems with the heat generation. It is...

Im Focus: First-ever visualizations of electrical gating effects on electronic structure

Scientists have visualised the electronic structure in a microelectronic device for the first time, opening up opportunities for finely-tuned high performance electronic devices.

Physicists from the University of Warwick and the University of Washington have developed a technique to measure the energy and momentum of electrons in...

Im Focus: Megakaryocytes act as „bouncers“ restraining cell migration in the bone marrow

Scientists at the University Würzburg and University Hospital of Würzburg found that megakaryocytes act as “bouncers” and thus modulate bone marrow niche properties and cell migration dynamics. The study was published in July in the Journal “Haematologica”.

Hematopoiesis is the process of forming blood cells, which occurs predominantly in the bone marrow. The bone marrow produces all types of blood cells: red...

Im Focus: Artificial neural network resolves puzzles from condensed matter physics: Which is the perfect quantum theory?

For some phenomena in quantum many-body physics several competing theories exist. But which of them describes a quantum phenomenon best? A team of researchers from the Technical University of Munich (TUM) and Harvard University in the United States has now successfully deployed artificial neural networks for image analysis of quantum systems.

Is that a dog or a cat? Such a classification is a prime example of machine learning: artificial neural networks can be trained to analyze images by looking...

Im Focus: Extremely hard yet metallically conductive: Bayreuth researchers develop novel material with high-tech prospects

An international research group led by scientists from the University of Bayreuth has produced a previously unknown material: Rhenium nitride pernitride. Thanks to combining properties that were previously considered incompatible, it looks set to become highly attractive for technological applications. Indeed, it is a super-hard metallic conductor that can withstand extremely high pressures like a diamond. A process now developed in Bayreuth opens up the possibility of producing rhenium nitride pernitride and other technologically interesting materials in sufficiently large quantity for their properties characterisation. The new findings are presented in "Nature Communications".

The possibility of finding a compound that was metallically conductive, super-hard, and ultra-incompressible was long considered unlikely in science. It was...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

2nd International Conference on UV LED Technologies & Applications – ICULTA 2020 | Call for Abstracts

24.06.2019 | Event News

SEMANTiCS 2019 brings together industry leaders and data scientists in Karlsruhe

29.04.2019 | Event News

Revered mathematicians and computer scientists converge with 200 young researchers in Heidelberg!

17.04.2019 | Event News

 
Latest News

Heat flow through single molecules detected

19.07.2019 | Physics and Astronomy

Heat transport through single molecules

19.07.2019 | Physics and Astronomy

Welcome Committee for Comets

19.07.2019 | Earth Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>