Simulation of ultrasound beam formation of baiji (Lipotes vexillifer) with a finite element model

Abstract

The baiji (Lipotes vexillifer) of the Yangtze River possesses a sophisticated biosonar system. In this study, a finite element approach was used to numerically investigate the propagation of acoustic waves through the head of the Yangtze River dolphin, which possesses an inhomogeneous and complex structure. The acoustic intensity distribution predicted from models with and without the melon and/or skull showed that the emitted sound beam was narrow and formed a highly directed acoustic beam, and the skull and melon significantly enhanced the directional characteristics of the emitted sound. Finally, for a short duration impulsive source, the emitted sound pressure distributions were also simulated at different propagation times. The results provide useful information for better understanding the operation of the biosonar system in this rare and perhaps extinct animal.

Biosonar signal propagation in the harbor porpoise's (Phocoena phocoena) head: The role of various structures in the formation of the vertical beam

“…Previous studies have used numerical models and experimental measurements to display that the internal structures in the dolphin's head such as the air sacs, melon and skull contribute to the formation of biosonar beam (Aroyan et al, 1992;Houser et al, 2004;Au et al, 2010;Cranford et al, 2014;Finneran et al, 2014;Wei et al, 2014;Song et al, 2016;Wei et al, 2016). Aroyan et al (1992) suggested that the air sacs and skull were the dominant factors in shaping the beam and the melon might be capable of mild focusing in the formation of the short-beaked common dolphin's biosonar beam.…”

“…An accurate model requires high accuracy image reconstruction technology such as the computed tomography (CT) scan because the anatomical features in the animal's head are extremely complex. The numerical modeling has been used for investigating sound production, transmission and reception on different species of odontocetes, including short-beaked common dolphin (Delphinus delphis) (Aroyan et al, 1992;Aroyan, 2001), Cuvier's beaked whale (Ziphius cavirostris) (Cranford, 2000), humpback whales (Megaptera novaeangliae) (Adam et al, 2013), bottlenose dolphin (Tursiops truncatus) (Cranford et al, 2014), baiji (Lipotes vexillifer) (Wei et al, 2014;Wei et al, 2016). However, the physiological mechanism of the biosonar beam formation in an echolocating harbor porpoise's head is still not well understood.…”

Acoustic beam control in biomimetic projector via velocity gradient

“…14 Previous studies on the dolphin biosonar had shown that the melon as an adipose tissue possesses gradient sound speed property, and it plays an important role in the beam control. [15][16][17][18][19] It was suggested that the biosonar beam may be modulated by the melon to accommodate dynamic spatial relationships with the prey and complex acoustic surroundings. 20 In order to optimize such devices, more detailed and quantified studies are urgently needed to clarify the physical mechanism of beam directivity manipulation by the GRIN material at the subwavelength scale.…”

Finite element simulation of broadband biosonar signal propagation in the near- and far-field of an echolocating Atlantic bottlenose dolphin (Tursiops truncatus)

“…There is a general consensus on the roles of the skull and air sacs from the results of prior numerical simulation research and experimental measurements (Aroyan et al, 1992;Houser et al, 2004;Au et al, 2010;Finneran et al, 2014;Cranford et al, 2014;Wei et al, 2014;Song et al, 2016;Wei et al, 2016;Wei et al, 2017;Wei et al, 2018). Although there are differences in the geometry of the air sacs and rostrum across species, these structures act as acoustic reflectors because of impedance mismatch between them and the surrounding soft tissues directing the waves forward to form a radiating beam.…”

“…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). There is a general consensus on the roles of the skull and air sacs from the results of prior numerical simulation research and experimental measurements (Aroyan et al, 1992;Houser et al, 2004;Au et al, 2010;Finneran et al, 2014;Cranford et al, 2014;Wei et al, 2014;Song et al, 2016;Wei et al, 2016;Wei et al, 2017;Wei et al, 2018).…”