Experimental analysis of near-field acoustic scattering by rigid spheroidal objects

An experimental analysis of near-field acoustic scattering by rigid spheroidal objects was conducted. For this purpose, a 2.844 x 1.424 x 1.220 m anechoic chamber was designed and built, and five spheroidal objects were fabricated out of a starch powder held together by a cellulose binder (ρ = 1039 ± 1% kg/m3 at 20°C). The objects created are a sphere, a 2:1 prolate spheroid, a 2:1 oblate spheroid, a 5:1 prolate spheroid, and a 5:1 oblate spheroid, all having a major-axis length of about 12.9 cm. A Selenium ST300 super-tweeter was selected as the sound source in the acoustic scattering experiments, and a Brüel & Kjær 3.175 mm (1/8 in) condenser microphone was used to scan the scattered sound in front and behind the five objects. The resultant acoustic pressure and relative phase angle profiles were compared to the theoretical predictions. It was found that the complexity of the acoustic pressure and relative phase angle profiles increased with the incidence cross-sectional area of the spheroid, i.e., the larger the incidence area the more features the profiles exhibit. The experimental and theoretical relative phase angle profiles, presented in this dissertation, are considered one of the main features that make this study unique and original. The relative phase angle profiles provide valuable information that can be used with that from the acoustic pressure scans to gain a better understanding of the acoustic scattering field around rigid spheroidal objects. The remarkable agreement seen between experiment and theory has raised the level of confidence in the computer code, developed to solve the problem of acoustic scattering by rigid spheroidal objects, and the experimental method followed. One of the main outcomes of this dissertation is the development of an economically feasible and accurate experimental method that can be used to study the near-field acoustic scattering by rigid objects. In addition, the experimental setup can be easily modified to conduct research in closely related topics, such as far-field acoustic scattering by rigid objects, and near-field acoustic scattering by compressible objects