Eigenanalysis Of The Biodiversity In Bat Pinna Shapes

More than 900 species of bat across the world exhibit large pinna diversity in response to their living environments. Global echo-locating task for sonar system requires sensing ability in common while various habitations specialized each species for most surviving advantage.In this research, numerical analysis method is implemented to quantify the similarity and diversity of pinnae shapes in order to find out features of them. Principal Component Analysis is implemented to investigate the eigenears from 100 pinnae. Cylindrical radii of the discrete pixels on the inner and outer surfaces are used to represent the shape of each pinna. Eigenvectors and eigenvalues of the cylindrical radii maps of both surfaces reveal the feature of all these pinnae and the importance in the dataset. Coefficients of the pinnae in eigenear coordinates indicate the shape feature of the pinnae, which means the closer two pinnae locate to each other, the more they share in common. A certain coefficient of the eigenear results in some deformation on the ear, and correspondingly results in the deformation of the beamforming.The pinnae distribution in eigenear coordinates shows that pinnae are well classified by its class, bats from same class sharing a limited region. Pinnae from bats of different beam also differ clearly in eigenspace. In order to explore the acoustic properties of the resulting eigenvectors ("eigenears"), the center of the eigenear coordinate system is positioned at the average pinna which is similar to an obliquely truncated cone and has a simple beam pattern dominated by a single, upward-pointing main lobe. The first eigenear is similar in shape to the average ear. Subtracting or adding the first eigenear results in a wider or narrower cone. In the vicinity of the average ear, this operation will likewise result in a wider of narrower main lobe. The second eigenear has a symmetry-breaking effect horizontally on both the pinna shape and its beam pattern. The third eigenear has a symmetry-breaking effect vertically on the pinna shape and the beam pattern. A combination of these eigenears would lead to a specific beamforming. Thus the eigenears may serve as basic components to design specific biosonar.