Cochlear -based transducers: Modeling and design.

Three mathematical models are introduced in this thesis for modeling the coupled fluid structure systems, especially the cochlear-based transducers. A full three dimensional FEM model is developed with the use of the 27-noded mixed fluid element coupled with 9-noded structure element. The fluid displacements and pressure are chosen as solution variables and the pressure degrees of freedom are condensed out in the element level. A modified pressure boundary condition is also derived to approximately account for the viscous effect in the boundary layer under several legitimate assumptions to avoid overly intricate formulations. The viscous boundary condition is applied on previously inviscid 2.Sd FEM framework. A model WKB method, was developed with the ability to consider more than one wave mode in the direction of wave propagation. It is proved capable of producing an accurate solution for the fluid structure interaction problems with the structure modeled as a locally reacting impedance, a membrane or a plate. Three cochlear-based transducers were designed in order to mimic the functioning of the passive and active cochlea, mechanically or electronically. A single-channel trapped fluid transducer, with the inspiration drawn from the low-pass filtering behavior of the passive cochlea, was designed and optimized using nondimensional formulas derived from a boundary integral method. The transducer achieves a sensitivity of -200dB re 1V/muPa in a 10kHz frequency range. A radio frequency channelizing filter is developed at 20-90MHz with 20 output channels. The filter topology is derived from an electrical-mechanical analogy of the passive cochlea and can be scaled to any frequency. A preliminary design of active cochlear-based MEMS transducer is also presented in the thesis. The piezoelectric sensing is shown to have better sensitivity with a unique sensing structure. A series of the cantilever beams are connected to the center of the membrane and piezoelectric material is deposited on the beam surface for sensing as well as actuation if necessary. The preliminary design shows 15dB increase in the sensitivity compared to the passive transducer with an improved filtering.Ph.D.Applied SciencesMechanical engineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126897/2/3287481.pd