The research objective of this Faculty Early Career Development (CAREER) project is to characterize the behavior of reflected sound energy from architectural surfaces, and in particular to quantify the effect of fractal geometries on surface scattering. Fractal surfaces can have self-similar irregularities at multiple scales, and since scattering is dependent on the relationship between wavelength and surface irregularity size, fractals can cause scattering across a broad frequency range. Broad-band scattering is necessary in spaces where reflection mitigation and uniform sound energy distribution are required across the audible frequency spectrum. The research approach will begin with the generation of virtual and physical fractal surfaces produced by varying several stochastic fractal generation parameters. The scattering behavior of these surfaces will be determined through numerical simulation using Boundary Element Method numerical modeling, and experimental measurement using free-field and reverberant-field methodologies. This prediction-measurement scheme will be used to establish a correlation between fractal geometry generation parameters and broad-band scattering effectiveness of the surfaces. Recently developed and standardized scattering quantifiers will be evaluated, leading to modifications or the development of a new quantifier. The research will culminate in a statistical model that will be used to produce an algorithm for predicting scattering output from input fractal parameters
The proposed research will add significantly to the knowledge base of acoustic scattering by producing an architectural acoustics related numerical prediction data for fractal surfaces that scatter in more than one plane. The research will also produce published experimental data of either single-plane or multi-plane fractal surface scattering. If successful, this characterization of fractal effects on scattering and quantification modifications will significantly impact work in several fields, including the testing and design of scattering surfaces, computational modeling of sound fields, and scattering quantification. Extensions of this work could also advance acoustic scattering research in underwater acoustics and acoustical oceanography. Potential benefits to society will include optimized acoustic scattering surface design with specific applications for increased control of acoustic behavior in critical listening environments such as classrooms and performing arts auditoria, and more effective highway noise barriers. Also, student participation will be broadened through increased involvement of women, ethnic minorities, and other under-represented groups in the sciences, addressing pipeline and retention concerns in the science and engineering workforce.
