Modeling of matching layers for acoustic channel coupling

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Chien, Raymond
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Electronic thesis
Mechanical engineering
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Acoustic communication systems have been in development for the past twenty years, where an acoustic-electric channel is formed using piezoelectric elements to communicate across barriers by using acoustic pressure waves. The power efficiency of such a system is governed by the material differences and thicknesses of the layers between the piezoelectric elements among other factors. In ultrasound systems, gels are applied to surfaces for increased efficiency by providing an intermediary layer such that the differences in acoustic impedance between layers is less abrupt compared to simply having an air barrier which would cause even more losses. Other methods that have been used include quarter wave matching, and other forms of horn design, where thickness in materials are modified; in this type of matching, thicknesses are designed such that wave reflections can benefit the nature of the system for a desired bandwidth or power transmission coefficient.
This thesis is a study and comparison of the different ways to model acoustic electric channels for impedance matching and bandwidth design using COMSOL Multiphysics software and an implementation of the KLM model in MATLAB. In addition the basic theory and design of these models are discussed.
The modeling of an acoustic-electric channel brings many challenges due to the piezoelectric and acoustic elements of the problem. The KLM model proposed by Krimholtz et al 1970 is used to model such channels by using an analogy to circuit network theory. In the KLM model the individual layers are modeled as ''circuit components'' which can be impedance matched for a desired performance. The KLM model is commonly implemented in MATLAB, and can provide a model for the behavior of the system, but it does not include multidimensional effects such as directivity and beam steering of acoustic waves. A more powerful and accurate method of modeling is achieved by using finite element methods in tools such as COMSOL Multiphysics. A 2-D multiphysics model can be created in such a software to model the effects of the piezoelectric element and the transmission of acoustic pressure waves through solid media, which can then be compared to models such as the KLM. The advantages between the methods are clear, the KLM model provides a quick-to-run design tool, while the finite element methods are more computationally intensive, but can provide a more accurate result pertaining to the physics. From this study, we find that both methods give the same waveform, but with differences in magnitude.
In the transmission of electric signals, data and/or power, wireless communications are limited when met with metallic barriers due to the effects of Faraday shielding.
May 2020
School of Engineering
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Rensselaer Polytechnic Institute, Troy, NY
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