Numerical Investigation of Impulse Noise Propagation Into the Human Head.

Recent data from heavy weapon training environments suggest that protecting the Warfighter from impulse noise exceeding 140 dB may require mitigating alternative paths of noise propagation into the head, rather than focusing solely on the air conduction through the ear canal. We have developed finite element (FE) models of the human head and ear to simulate the biomechanical response of the ear subjected to impulse noise. We have used MRI images, detailed geometric representations, and published material models to generate the model. The head-ear FE model incorporated major ear structural components with the U.S. Naval Research Laboratory (NRL) high-fidelity head model. The loading conditions derived from notional weapons firing and/or explosive incidents were used to characterize the biomechanical effects in the ear. The simulation results showed the sound transmission differences between bone conduction and air conduction pathways. The computationally predicted pressure responses in the brain and the inner ear were validated with experimental data. Using the local ear model, we analyzed the dynamic behavior of inner ear when subjected to skull vibration stimulated by the impulse noise, and established the relationship between the impulse noise and the basilar membrane response. This work provides a novel attempt to separate multiple transmission modes of blast impulse noise, such as air conduction (through ear canal) and bone conduction, into the inner ear and examine their effects on the responses of sensitive inner ear organs.