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A Numerical Elastic Model for Deforming Bat Pinnae
In bats, the directivity patterns for reception are shaped by the surface geometry of the
pinnae. Since many bat species are capable of large ear deformations, these beampatterns
can be time-variant. To investigate this time-variance using numerical methods, a digital
model that is capable of representing the pinna geometry during the entire deformation cycle
has been developed.
Due to large deformations and occlusions, some of the surfaces relevant to sound diffraction
may not be visible and the geometry of the entire pinna has to be computed from limited
data. This has been achieved by combining a complete digital model of the pinna in one
position with time-variant sparse sets of three dimensional landmark data. The landmark
positions were estimated using stereo vision methods. A finite element model based on
elasticity was constructed from CT scans of the pinna post mortem. This elastic model
was deformed to provide a good fit to the positions of the landmarks and retain values of
smoothness and surface energy comparable to life. This model was able to handle ratios
of data to degrees of freedom around 1:5000 and still effect life-like deformations with an
acceptable goodness of fit.