Decoding the Extreme Physics of Ultrasound Generation in the Bat Larynx

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Ultrasonic call emissions with frequencies ranging up to 40-times those produced by human vocal cords; sound intensities that exceed that of a jet engine; subglottic pressures that would shred the human larynx to pieces; the highest tissue velocities found anywhere in nature; exquisite control of intensity and tone that would be the envy of any soprano; and call rates that are double that of the fastest machine gun. These are the capabilities that make the larynx of an echolocating bat one of the most extreme acoustic "instruments" in nature. This project will develop and employ a suite of scientific tools to gain a comprehensive understanding of the extreme physics that underlies the generation of ultrasound in the bat larynx. In addition to extending our understanding of a mammal that perceives the world in a way that is fundamentally distinct from most other mammals, particularly humans, the current research will explore a rich, coupled multiphysics problem that lies at the very edge of current scientific capabilities. Beyond the scientific advancement of elucidating the physics of ultrasound generation in bats, the broader impacts of the project span the fields of computational physics, bioinspired ultrasonic technologies, assistive technologies, vocal dysfunction, animal behavior and cyber-enabled science. The coupled aerodynamics, tissue mechanics and bioacoustics computational models developed here have a wide variety of applications in biophysics and engineering. The undergraduate and graduate trainees working on this project will become part of a new generation of scientists and engineers who can apply computation, experimental methods, and data-enabled science across disciplines to solve the most complex problems.The intellectual merits of the research span the areas of acoustics, biomechanics, aerodynamics, computational physics, nonlinear dynamics, data-enabled science and organismal biology. The science in this project is driven primarily by a first-of-its-kind, image-based, coupled aero-tissue-acoustic computational model of bat laryngeal function. In addition, sophisticated experimental tools, such as nano-indentation, micro-Computed Tomography and scanning electron microscopy for model parameterization, will be employed. Novel ex-vivo experiments to support the development and testing of these models will also be conducted. The specific objectives of the projects are (1) conduct ex-vivo analysis of vocal fold dynamics and acoustics in a vocalizing excised bat larynx; (2) conduct 3D imaging and biomechanical testing of a bat larynx for model development; (3) develop and validate a coupled aero-tissue-acoustics computational model for simulation and analysis of ultrasonic vocalization in the bat larynx; and finally (4) decode the physics of ultrasound generation using the validated aero-tissue-acoustic model. The topic of the current project has inherent appeal to high-school and university students, and the group will leverage this for a broad outreach to the wider community. This project is jointly funded by the Physics of Living Systems Program in the Division of Physics and the Physiological Mechanisms and Biomechanics Program of the Division of Integrative Organismal Systems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.