Sonar is an important sensory modality for engineers as well as in nature. In engineering, sonar is the dominating modality for underwater sensing. In biology, it is likely to have been a central factor behind the unprecedented evolutionary success of bats, a highly diverse group that accounts for over 20% of all mammal species. However, it remains unclear to what extent engineered and biosonar follow similar design and operational principles. In the current work, the key sonar design characteristic of beamwidth is examined in technical and biosonar. To this end, beamwidth data has been obtained for 23 engineered sonar systems and from numerical beampattern predictions for 151 emission and reception elements (noseleaves and pinnae) from bat biosonar. Beamwidth data from these sources is compared to the beamwidth of a planar ellipsoidal transducer as a reference. The results show that engineered and biological both obey the basic physical limit on beamwidth as a function of the ratio of aperture size and wavelength. However, beyond that, the beamwidth data revealed very different behaviors between the engineered and the biological sonar systems. Whereas the beamwidths of the technical sonar systems were very close to the planar transducer limit, the biological samples showed a very wide scatter away from this limit. This scatter was as large – if not wider – than what was seen in a small reference data set obtained with random aluminum cones. A possible interpretation of these differences in the variability could be that whereas sonar engineers try to minimize beamwidth subject to constraints on device size, the evolutionary optimization of bat biosonar beampatterns has been directed at other factors that have left beamwidth as a byproduct. Alternatively, the biosonar systems may require beamwidth values that are larger than the physical limit and differ between species and their sensory ecological niches. / Master of Science / Sonar is an important method of sensing for engineers in undersea environments, but it is also used by several species of animals for for everyday use. The most prominent species that uses sonar, or echolocation, are bats, one of the most diverse groups of mammals. The study of bat biosonar systems serves as a counterpoint to many of the concepts in technical sonar. In technical sonar, arrays are made to be larger in size, with more elements, and operate at higher frequencies in order to decrease their beamwidth which increases their resolution. Unlike technical sonars bats must rely on smaller sized systems that they can carry around and they operate in air which has worse qualities for propagating sound waves. Even with these disadvantages, bats are able to operate in complex environments, such as dense vegetation, with ease. This work compared 151 emission and reception elements of bat biosonar systems with 23 engineered sonars to find that the biosonar had very different behavior from the engineered sonars. The engineered sonars, as well as a set of experimental baffles, closely followed the curve for the beamwidth limit of planar transducers but the biosonar samples had a large scatter from the curve. These results could be interpreted to show that while the engineered sonars attempt to minimize the beamwidth in order to maximize the resolution, the biosonar did not place much importance on having low beamwidths and high resolutions during its evolution. Alternatively, the results could indicate that it is preferable for biosonar to have larger beamwidths, a contrast to standard sonar design.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/79902 |
| Date | 31 October 2017 |
| Creators | Todd, Bryan Donald |
| Contributors | Mechanical Engineering, Mueller, Rolf, Ben-Tzvi, Pinhas, Leonessa, Alexander |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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