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Date of Award
Campus Access Dissertation
Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)
Administrative Home Department
Department of Mechanical Engineering-Engineering Mechanics
Andrew R. Barnard
Committee Member 1
Christopher N. Plummer
Committee Member 2
Troy M. Bouman
Carbon nanotube (CNT) thin film speakers produce sound with the thermoacoustic effect. Compared to traditional loudspeakers that use a moving coil with a magnet motor, these speakers heat and cool their surface at acoustic frequencies to generate sound pressure waves. The principal of thermoacoustics was discovered more than 100 years ago, however a material that heats and cools fast enough was not available until the CNT films were introduced.
The main goal of this dissertation was to understand how material properties of the CNT speakers vary across the CNT film and how to model it. This effort has three main objectives with emphasis on understanding CNT speakers’ behavior and obtaining their material properties to use in multi-physics modeling.
i) Using Near Field Acoustic Holography (NAH) to obtain the acoustic properties at the CNT film during operation
ii) Investigation of material properties impact on the CNT speaker’s performance, specifically surface variations in material properties
iii) Using experimentally validated material properties to obtain a fully coupled multi-physics simulation model
Using NAH method, it is shown for the first time that the particle velocity at the surface of an open-air, double-sided CNT speaker is nominally zero, as predicted by theoretical lumped element models. However, the sound pressure levels, and the temperature distribution are not uniform on the source surface, contrary to common lumped parameter model assumptions. To obtain the material properties on the CNT film and understand it better, CNT surface temperature and acoustic measurements were gathered for different sizes of CNT speaker. The material properties are then used to validate a fully coupled multi-physics (Electrical-Thermal-Acoustical) FEA model with experimental SPL measurements for each speaker. It is shown that the simulation results agree with measurements within 3dB. Better understanding the physical acoustic properties of these speakers and having a fully coupled model will drive future design improvements.
Asgarisabet, Mahsa, "MATERIAL CHARACTERIZATION AND MULTIPHYSICS MODELING OF CARBON NANOTUBE THERMOACOUSTIC LOUDSPEAKERS", Campus Access Dissertation, Michigan Technological University, 2023.