中文摘要：

大足鼠耳蝠在导航和探测空间物体方位和距离的回声定位过程中,通过嘴巴发出超声波,并不断改变嘴巴张角的大小.利用微型X射线断层扫描仪得到大足鼠耳蝠的头部断层图像,对图像进行高斯滤波和二值化处理,利用三维重构技术获得原始头部结构的三维数字模型,通过数字形变方法得到不同嘴巴张角的头部模型,最后利用数值方法对各个数字结构进行声场计算,得到近场声压幅度分布图和远场辐射波瓣图.研究结果表明：大足鼠耳蝠可以通过改变嘴巴张开的角度来调整发射声场的方向性.在一定的张开角度下,辐射声波的频率越高,辐射波束的方向性就越强,而在一定的频率下,辐射波束的方向性随着嘴巴张开角度的增加而增加.大足鼠耳蝠通过调节嘴巴开合的角度改变辐射波瓣图,以提高其在飞行和捕食过程中的定位能力.

英文摘要：

Rickett＇s big-footed bat,Myotis ricketti can emit ultrasonic through the mouth to navigate and detect special objects in the process of echolocation,meanwhile,it changes various sizes of mouth opening angle constantly in a reasonable range.The purpose of this work is to study the effect of different mouth opening angle on emission sound field.Firstly,a series of cross-section images of Rickett＇s big-footed bat head was obtained by scanning its head using X-ray microcomputer tomography（micro-CT）.However,masses of glitches and noises of images caused a thorny problem that these cross-section images were not to be used to build three-dimensional digital model directly.In order to eliminate plenty of glitches and noises,cross-section images were processed by an isotropic Gaussian smoothing filter and binarization processing.After modified initial cross-section images,an original three-dimensional digitalmodel of head sample was constructed by using a three-dimension cone-beam volumetric reconstruction method,and other digital models with different mouth opening angel were structured by digital deformation within a reasonable range based on primary angel.These kinds of three-dimensional digital representations were composed of cube voxels,and different digital models required to be manually handled by reducing or increasing the number of cube voxels in the position of the mouth.Next,finite-difference time-domain method and Kirchhoff integral were used as numerical methods to calculate the acoustic field which including near-field and far-field.Finally,acoustic near-field pressure magnitude and radiation pattern were presented as results to reveal the relationship between mouth opening angle and emission sound field.The study shows that Rickett＇s big-footed bat can control and adjust the directivity of radiation sound field by changing the size of mouth opening angle.Given an opening angle,the higher the frequency of the radiation sound wave is,the stronger the directivity of radiation beam is.At a given freq