FINITE ELEMENT SIMULATION OF SOUND WAVE PROPAGATION INTO THE HUMAN HEAD

Carnegie-Mellon University, Pittsburgh PA

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The Air Force Office of Scientific Research (AFOSR) is interested in finding the pathways through which sound energy travels into the human head. Due to the high sound levels encountered on the flight deck of air craft carriers, it is possible to suffer hearing loss even when wearing ear plugs and ear muffs. This is due to sound reaching the cochlea through conducting pathways other than air. The goal of this research is to find these pathways so that devices may be developed to reduce the acoustic energy traveling through them. In order to verify these paths it is necessary to obtain the pressure throughout the head. Since we are interested in learning the pathways to the ear in situations with high levels of sound, a simulation must be performed. The head is a complex scatterer with multiple layers and complex geometries so a closed form solution doesn't exist. The discrete-time finite element method allows for simulation of complex geometries with multiple layers, and is therefore ideal for approximating sound scattering from the human head. A method that can be used to approximate the propagation of energy is acoustic ray tracing. Ray tracing uses the pressure data computed from the finite element code to propagate a grid of rays through the geometry that should roughly correspond to the ray paths predicted by geometrical acoustics when geometrical acoustics are appropriate. One can then approximate the energy in a volume by the density of rays going through a cross-section in the direction of propagation. In this way, one can determine the dominant energy pathways by locating the paths with a high density of rays passing through it.