Cochlear Properties and Micromachined Hair-like Shear Sensors.
Orthotropic material properties of the gerbil basilar membrane are determined using a
geometrically nonlinear finite element composite orthotropic plate model. This model
extracts material properties based on point stiffness and space constant reported from
two sets of experimental data. Two boundary conditions are investigated. The material
properties are quantified at different lo... read morecations along the length of basilar membrane
for both boundary conditions. The orthotropy of gerbil basilar membrane varies along the
length of the gerbil basilar membrane from a maximum of 65 close to the base to a
minimum of 10 in the upper middle turn. A sixteen fold scaled-up guinea pig cochlea
model is designed and fabricated. The physical model geometry and fluid properties were
chosen in a way to satisfy scaling law which is derived from dimensionless analysis with
Buckingham Pi theorem to ensure the motion of the enlarged cochlear model resembles that
of the guinea pig cochlea. The frequency responses of the cochlear basilar membrane were
recorded and compared with a mathematical model based on WKB method. The test results
show the experiment characteristic frequencies are about 100-300Hz different from those
computed using WKB and the magnitudes of the ratio of cochlear membrane to drive
velocity are about 15-25dB lower than those calculated from WKB method. The phases for
WKB and experimental results are very close. A novel hair-like sensor using capacitive
sensing scheme for direct shear measurement is designed, fabricated and tested. The
capacitive sensor base is fabricated using PolyMUMPsTM foundry process and hair posts
sitting on the sensor base are post fabricated at Tufts cleanroom facility. The sensors
were successfully fabricated, released and packaged. The sensors are tested in a flow
cell with laminar air flow at different flow rates using both LCR meter and a commercial
differential capacitance measurement sensor MS3110. The test results are compared with
benchmark sensors which have no hair posts. LCR meter tests showed a bulged sensor
membrane under flow due to flow pressure. Differential capacitance measurements using
MS3110, which eliminate pressure effect on sensor, showed higher sensitivities for the
hair sensors than sensors without hairs. The measured single hair sensor sensitivity is
, about half of the predicted sensitivity . The RMS resolution of the sensors in a 1Hz
band for 32 sensors in parallel is 5.1Pa and the RMS resolution is 0.33Pa with 120
seconds of averaging.
Thesis (Ph.D.)--Tufts University, 2012.
Submitted to the Dept. of Mechanical Engineering.
Advisor: Robert White.
Committee: Jason Rife, Barry Trimmer, David Mountain, and Judith Gallman.
Keyword: Mechanical engineering.read less