Abstract
Bottlenose dolphins project broadband echolocation signals for detecting and locating prey and predators, and for spatial orientation. There are many unknowns concerning the specifics of biosonar signal production and propagation in the head of dolphins and this manuscript represents an effort to address this topic. A two-dimensional finite element model was constructed using high resolution CT scan data. The model simulated the acoustic processes in the vertical plane of the biosonar signal emitted from the phonic lips and propagated into the water through the animal's head. The acoustic field on the animal's forehead and the farfield transmission beam pattern of the echolocating dolphin were determined. The simulation results and prior acoustic measurements were qualitatively extremely consistent. The role of the main structures on the sound propagation pathway such as the air sacs, melon, and connective tissue was investigated. Furthermore, an investigation of the driving force at the phonic lips for dolphins that emit broadband echolocation signals and porpoises that emit narrowband echolocation signals suggested that the driving force is different for the two types of biosonar. Finally, the results provide a visual understanding of the sound transmission in dolphin's biosonar.
Highlights
Institute, National University of Singapore, 12A Kent Ridge Road, Singapore 119222, Singapore.and sizes across species, the acoustic path in the odontocete’s head is mainly influenced by three different structures: the air sacs and spaces; the bony structures which include the cranium, maxilla, and mandible; and the soft tissues which include the melon, connective tissue, musculature, blubber, etc
A 2D finite element model was constructed based on a high-resolution computer tomography (CT) scan and was used to simulate the process of a short-duration, broadband impulsive sound emitted from the right phonic lips into the water after propagating through the complex anatomic structures in a bottlenose dolphin’s head in the vertical plane
The detailed sound propagation process was calculated and the time history of the click wavefront traveling through the forehead at five different moments was captured and compared
Summary
National University of Singapore, 12A Kent Ridge Road, Singapore 119222, Singapore.and sizes across species, the acoustic path in the odontocete’s head is mainly influenced by three different structures: the air sacs and spaces; the bony structures (skull structures) which include the cranium, maxilla, and mandible; and the soft tissues which include the melon, connective tissue, musculature, blubber, etc. Traditional experimental methods have been performed, the underlying mechanism of how the internal structures function in the processes is still understood only in a very general fashion. In order to investigate the specific details of how these structures function and further increase our understanding of the mechanics of biosonar sound production and propagation, numerical modeling techniques have been applied to simulate the biosonar systems of odontocetes (Aroyan et al, 1992; Aroyan et al, 2001; Krysl et al, 2006; Cranford et al, 2014; Wei et al, 2014; Wei et al, 2016; Song et al, 2016; Wei et al, 2017; Wei et al, 2018).
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