Date of Award

3-30-2022

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Systems Engineering

First Advisor

Andrew Wright

Abstract

Acoustic localization of robots in indoor environments suffer from inevitable reverberation, for which, the use of unidirectional microphones as sensory receptors is preferred. While unidirectional microphones remain prohibitively expensive for ubiquitous usage, externally applying a custom structure around an inexpensive omnidirectional microphone can also grant it desired directionality. The structure can be fabricated via single or multimaterial 3D printing, and its effectiveness can be determined via its Sound Transmission Loss (STL). As an alternative to increasing thickness of a 3D printed single material structure, this research proposes the use of 3D printed multimaterial structures to achieve increased STL. The following steps are undertaken in this investigation. A custom STL testing facility (small-sized reverberation chamber) is developed to measure the random incidence STL of 3D printed specimens. The chamber is validated against two reference specimens (Gypsum Board and Acrylic Sheet) experimentally. The STL characteristics of single material 3D printed structures (ABS, PLA, at 50%, 100% infills) are evaluated experimentally. Snell’s law and the universal wave equation are adapted to engineer the design of the multimaterial structure (host material of one thermoplastic material and embedded obstacles of another), which offers increased STL over a single material structure at a targeted frequency. Then, the STL characteristics of multimaterial structures (ABS+TPU, PLA+TPU, at 50%, 100% infills) are evaluated experimentally and compared with the single material structures. The effect of increasing the spacing between the embedded obstacles on STL is examined. Finally, the influence on the directionality of an inexpensive omnidirectional electret microphone is experimentally compared in the presence of the 3D printed single and multimaterial structures. It is discovered that, without (approximately) doubling the thickness, the multimaterial 3D printed structure offers an STL improvement of up to 5.47 dB over the single material 3D printed structure at the targeted frequency in a reverberant environment. This increased attenuation at the targeted frequency can minimize the reverberation captured by the omnidirectional microphone from a certain direction. Thereby, the design of cost-effective and thinner unidirectional microphones – useful in the space constrained robot localization application – can be facilitated.

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