A life-sized model of the human cochlea: Design, analysis, fabrication, and measurements

The cochlea is the auditory portion of the inner ear that provides the transduction of sound pressure into neural excitation and thus is a key component of the hearing process. The cochlea acts like a spectrum analyzer, however there are details in the processing which are still not understood. In particular, there is evidence of an active process which enhances the displacement and place response of the basilar membrane in response to sound. Linear and non-linear models have been proposed, but there is yet to be a mathematical model with physically realizeable parameters to explain adequately the behavior. Physical models have long been sought to aid in the identification of complex functions and to study the effect of important anatomical features of the inner ear.; In this work, a life-sized passive cochlea model was developed using a combination of micro- and macro-fabrication techniques. The coiled cochlea is approximated as a straight box model with a partition separating two fluid channels. The partition has an elastic portion representing the basilar membrane that is linearly tapered in width from 100 mum to 500 mum. Approximately 9000 discrete fibers are micromachined from aluminum deposited onto a polyimide thin film. A magnet-coil system excites the fluid channel to represent the stapes.; Three samples were evaluated using a laser vibrometer. The physical model demonstrates a traveling wave that peaks at a characteristic place. The stiffness properties of the model are evaluated using low frequency pressure and velocity measurement data.; Asymptotic expansion procedures offer simple, efficient, and reasonably accurate approximate solutions in contrast to FEM or other large scale modeling methods. Calculations using a phase integral asymptotic approximation confirm the general character of the responses measured and improvements in correlation result from using the measured stiffness data in the analytical model.