两种菊头蝠超声发射特性与鼻叶形态的相关性

The correlation between ultrasonic emission characteristic and noseleaf shape in two types of horseshoe bat

采用有限元方法对两种菊头蝠超声发射特性与鼻叶形态的相关性进行了数值研究.首先对两种菊头蝠鼻叶样品进行CT扫描,获得鼻叶的原始数字投影图像.利用三维锥形光束重建算法得到鼻叶的横断面图像,图像处理使鼻叶可清晰分辨边界,然后利用三维数字图像处理技术获得蝙蝠鼻叶的三维数字图像模型.采用有限元方法模拟了两种鼻叶结构的近场声压分布,从近场外推得到了远场方向敏感性函数,来分析在方位角、仰角的指向性.最后,测量鼻叶超声波束在仰角方向上的宽度,得到两种鼻叶的超声发射特性,通过与两种鼻叶鞍状叶长度做对比,得到了两种菊头蝠的超声发射特性与其鼻叶鞍状叶长度的相关性.结果表明,鞍状叶在超声发射过程中对于控制仰角指向性有重要的作用,同时鞍状叶长度与超声频率有明显的负相关性.

Finite element method is adopted for the numerical study of the correlation between ultrasonic emission characteristic and noseleaf shape of two types of horseshoe bat.With evolution and natural selection,most bats have developed an ultrasonic echolocation system with high performance,called biosonar,The signal sender is surrounded by complicated wrinkle noseleaf whose position and structure are considered to change the direction of ultrasonic pulse.Experimental studies have suggested noseleaf really has complicated acoustic function.In this paper,the noseleaf samples of Bourret’s horseshoe bat and Rufous horseshoe bat are chosen to simulated.The first step is to acquire original biological data.In experiment,high-resolution X-ray micro CT machine is adopted to scan samples of noseleaf of two horseshoe bats to get original digital shadow images.Then the cross-section view of the noseleaves are reconstructed with the method of cone beam reconstruction.These images with 256 gray level are then processed through Gaussian filter and boolean process,and images with clear definition of air and biological tissue could be got. With three-dimensional digital image processing technique,three-dimensional digital image attributes of two horseshoe bat noseleaf are acquired.The near-field sound pressure distribution of the two noseleaves structure is simulated with finite element method,and the far-field sensitivity function is extrapolated based on Kirchhoff integral theorem from near field,to analyze the directivity at azimuth and elevation angles.Finally,the width of noseleaf ultrasonic beam in the direction of elevation angle is measured to get the ultrasonic emission characteristics of the two types of noseleaves.Thus,the correlation between the ultrasonic emission characteristics and the length of noseleaf sella of the two types of bats are gotten through contrast between the length of their noseleaf sella.The result indicates sella plays a significant role in controlling the directivity at elevation angle in the process of emitting ultrasound,and there is obvious negative correlation between the length of sella and ultrasonic frequency.