Bats lend an ear to sonar engineering

May 10, 2011

Researchers have mapped out the diversity of bat ears in a hope to inspire the design of new intuitive methods of manipulating waves with physical shapes, such as SONAR and RADAR.

Published today, Tuesday, 10 May, in IOP Publishing's journal Bioinspiration & Biomimetics, the study provides key insights into the variability of the shapes of bat ears that exists between different species, and shows how this variability may affect the functionality of one of the most impressive navigational systems in nature.

Bats are one of a few animal groups that demonstrate biosonar—the ability to generate and emit ultrasonic pulses and gauge the reflections to obtain detailed information on their surroundings.

Bats use biosonar as a way of navigating and hunting for food, however researchers have seen its potential to inspire new ways of engineering where manipulating outgoing or incoming with structures is a principal component.

Lead author Professor Rolf Müller, of Virginia Tech, said: "Using physical shapes to manipulate an outgoing or a received wave has application in many areas of engineering. Besides the obvious analogues of SONAR and , such principles could also find application in biomedical ultrasound, non-destructive testing, wireless communications, and sensory systems for autonomous robots and nodes in sensor networks."

The ear of a bat plays a crucial role in the overall sensing system by acting as a baffle to diffract the incoming waves therefore determining the ear's pattern of sensitivity to direction and frequency.

The researchers, working in a joint research laboratory of Shandong University and Virginia Tech, created 3D computer models of 100 bat pinnae—the visible part of the ear that resides outside of the head—from 59 different species, and transformed the models into cylindrical representations.

The representations were statistically analysed using principal component analysis—a method that has previously been applied to analyse human faces, palms, and ears —and were shown to vary in the opening angle of the pinna, breaks of symmetry between the right and left sides, and changes in width at both the top and bottom.

The researchers also demonstrated how this variability can affect the properties of beamforming—the process by which the incoming signal is diffracted by the shape of the pinna to create a "beampattern" through which the bat sees it environment.

The variability occurs as a result of the evolution of bats whose habitats range from environments with virtually no structures, to those with simple structures (calm water surfaces), to habitats with very complicated structures (dense forests).

The researchers found, for example, that a group of bats that hunts for prey in dense vegetation with trains of long, closely-spaced objects are separated from other bats by the widths of their pinna openings, demonstrating how biodiversity can provide a useful insight into how a general principal can be customised to fit different needs.

Professor Müller continued, "In order for this to happen, the ears of must be studied further. An example would be to expand the sample to include more diversity and find more specific relationships between pinna shape and beamforming across different species. Small local shape features that are hard to capture by the present analysis can also have a big impact on the function."

Explore further: Researchers use 3D printers to create custom medical implants

More information: A method for characterizing the biodiversity in bat pinnae as a basis for engineering analysis, Jianguo Ma and Rolf Müller 2011. Bioinspir. Biomim. 6 026008 doi:10.1088/1748-3182/6/2/026008

Abstract
A quantitative analysis of the interspecific variability between beamforming baffle shapes in the biosonar system of bats is presented. The data set analyzed consisted of 100 outer ear (pinna) shapes from at least 59 species. A vector-space representation suitable for principal component analysis (PCA) was constructed by virtue of a transform of the pinna surfaces into cylindrical coordinates. The central axis of the cylindrical transform was found by minimizing a potential function. The shapes were aligned by means of their respective axes and their center of gravity. The average pinna of the sample was a symmetrical, obliquely truncated horn. The first seven eigenvalues accounted already for two-thirds of the variability around the mean, which indicates that most of the biodiversity in the bat pinna can be understood in a more low-dimensional space. The first three principal components show that most of the variability of the bat pinna sample is in terms of opening angle, left–right asymmetry, and selective changes in width at the top or the bottom of the pinna. The beampattern effects of these individual components have been characterized. These insights could be used to design bioinspired beamforming devices from the diversity in biosonar.

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kevinrtrs
1 / 5 (6) May 10, 2011
This sonar navigation ability of bats is a major stumbling block for evolutionary ideas. The bat could not have continued it's existence without the sonar so there's no way that sonar could have developed in step-wise fashion. It's an all-or-nothing situation. Either you eat or you starve to death.
PaulieMac
5 / 5 (2) May 10, 2011
Your constant protestations of irreducible complexity are boring - which is bad enough. But, so much worse, they are dishonest, as your arguments are soundly refuted *every* *single* *time*.

A small flighted predator, born with a mutation that very slightly increases its ability to hear, say, the buzz of small insect prey would obviously have some small statistical survival advantage.

A high pitched call - easily distinguishable - to attract mates...

It could all flow out from those two. A high pitched call and a statistical advantage from better hearing. Two characteristics that would allow a flighted predator to adapt - over time - to hunting in the dark, and allow exploitation of a new niche: the cave.

Conjecture on my part, to be sure. Reasonable conjecture born of one or two minutes thinking about this specific subject.

Reasoned thought - you should try it some time. It doesn't actually hurt, much.
antialias
5 / 5 (3) May 10, 2011
Paulie:

I think the problem simply stems from his inability to understand that an organism does not need to be perfect at what it does - it just needs to be better than everyone else (e.g plants are only 3% efficient at converting sunlight into energy. But that is enough of an advantage for them to survive)

Early on in the development of life that hurdle was fairly low. Whenever a new niche is opened up (e.g. like hunting in the dark) that hurdle is also very low.

As with the eye: Very, very poor eyesight is still superior to no eyesight at all... And you can get very poor eyesight with a very simple structure (e.g. that used by some bacteria to distinguish light from dark). Each minute improvement (through lucky mutation) means the resulting organism will be superior to the 'standard model'.
Ethelred
5 / 5 (2) May 10, 2011
Usually Kevin ignores the articles that are so clearly against him. This was a really stupid post even by Kevin's low standards.

He just plain ignored the fact that fruit bats use sonar even though they have rather poor sonar. They do have color vision and other indications of having CHANGED KIND from primates to bats. So kevin pretends they don't exist. Just like he ignores flying squirrels the most blatant transition species that exists at the moment.

Perhaps if Kevin was to get his eyes checked he could have those many blind spots fixed.

Ethelred
CSharpner
5 / 5 (1) May 10, 2011
The bat could not have continued it's existence without the sonar

Why would you say this? They can't eat fruit? They can't catch prey like any other animal?

Why do you put zero effort into considering traits emerging over generations? PaulieMac gave you excellent examples just above, as I and many others have explained the SIMPLE process of evolution to you countless times, then you ignore it all and post junk like this.

I know you know the simple evolutionary process because, I, myself, have explained it to you multiple times as have many others here. In the context of what you know we know you know (heh) about evolution, please explain your comment above.

Then, explain how we can see objects BILLIONS of light years away if the universe is only 6000 years old.
Skeptic_Heretic
5 / 5 (1) May 12, 2011
This sonar navigation ability of bats is a major stumbling block for evolutionary ideas. The bat could not have continued it's existence without the sonar so there's no way that sonar could have developed in step-wise fashion.
Except for the fact that sonar was developed in a step-wise solution not just in nature, but also in English and US sonographics labs during WW2.

Moron.