Study On The Acoustic Role Of The Noseleaf In A Egyptian Slit-faced Bat,Nycteris Thebaica

All the bats of Microchiroptera and fruit bats in Megachiroptera through ultrasonic to identify objects, detect the surrounding environment, prey and avoid predators. Most of these bats emit ultrasonic through oral, around300bat species are known to emit their ultrasonic biosonar pulses through the nostrils, around bats nostrils has many intricate and elaborate parts, ie. noseleaves. Some prior experimental evidence indicates that these "noseleaves" have an effect on the shape of the animals’radiation patterns and acoustic field. Here, the noseleaf of Egyptian slit-faced bat is composed of three distinctive parts("pit","upper leaf" and "lower leaf"), upper leaf and lower leaf together constitute the "anterior leaf". In this paper, three distinctive parts of noseleaf of Egyptian slit-faced bat are studied to predict the effect of these parts in radiation partern, the role of turned outward of anterior leaf as well as studied. The research content mainly includes the following three aspects:(1) To build3D-digital structure of noseleafThe bat noseleaf specimens are resected from the bat body. First, we should scanning noseleaf by means of a Micro X-ray computer tomography. We obtain a group shadow image by scanner, thus, stacking of tomographic cross-sections are derived by a three-dimensional cone beam reconstruction method. Cross-section images are pre-filtered using an isotropic Gaussian smoothing kernel and then thresholded to classify pixels as representing either air or noseleaf tissue. In order to reconstruct three-dimensional digital noseleaf conveniently, the cross-section images should have only two gray value. By means of computer related to images processing, we can get the3D digital structure of noseleaf of Egyptian slit-faced bat.(2) The calculation of the sound fieldWe add the sound source in nostril at proper position and definite of a cuboids region surrounding the noseleaf for near field calculation region. Thus, meshing the calculation region by means of finite-difference time-domain (FDTD) method and set a perfectly matched layer (PML) at boundary of calculation region. We can get the acoustic near field value using FDTD by computer simulation. But for the acoustic far field radiation pattern, we can use Kirchhoff integral method to obtain. (3) Analysis of the resultsThe far field radiation pattern directivity correlation coefficient and directivity index is showed by analysis of the radiation pattern. Then, analysis the data and draw conclusions.According to the results, we draw the following conclusions:(1) In the acoustic near field the pit mainly has an effect on rising magnitudes in the vicinity of the pit. For the upper leaf, it mainly slightly affects the amplitudes in and in the front of the pit; it can adjust the width of sidelobe in this region. The lower leaf seems to overall regulate the amplitude in near filed and focus the acoustical far field especially the mainlobe.(2) The anterior leaf turned outward a certain angle to expand the far-field beam width and reduce the sidelobe, thus, improve the direction of beam.(3) The results show that the components (pit, upper leaf and lower leaf) of noseleaf of Egyptian slit-faced bat have an important function in acoustic near field and far field radiation pattern. These acoustic functions play an important role in biosonar system, from the point of view of the sonar system, the components of noseleaf in acoustic field of clear division of labor and develop their potentials. This collaboration make bats can be better in daily behavior in complex environment.