不同种类蝙蝠外耳本征声场波束的计算和功能分析

Eigen computation and function analysis of ear's beampattern from various specis Bats' s

现在使用的智能天线主要通过对阵列天线相位的调制进而调节声场波束,而不同种类蝙蝠仅通过两个外耳对声音反射,就对声场波束形成起到重要作用,所以研究不同种类蝙蝠外耳对接收回波调节作用的声学共性对智能天线改进具有重要作用.共选取30只蝙蝠外耳,利用有限元声场模拟得到蝙蝠声场波束,并对声场波束的指向进行归一化和球面小波压缩,初步利用主成分分析法应用到不同种类蝙蝠的特征分析中,通过主成分分析方法得到蝙蝠本征波束以及平均声纳波束,并对本征波束进行了叠加分析,只考虑了最大本征值和第二本征值对应的第一和第二本征向量,并分析了其作用,分析表明:1)第一本征向量的叠加明显调整了主瓣的宽度,而第二本征向量的叠加则使主瓣在方位角和仰角方向的宽度交替变化;2)在本征空间中,距离远近表示声场波束相似程度,本征波束的分析对区分不同属的蝙蝠具有一定作用.

The man-made intelligent antenna can be used to manipulate sound field beampattern by modulating the phase of antenna array.At the same time,some biological system possess the same ability.One of the very typical example is echo-locating bats.Different species of bats can realize the same function using certain structures of their outer ears.Therefore,studying the common features of those bats can generate profound influence on the improvement of intelligent antenna.The current research involves calculating the acoustic beampattern of 30 ears from different bat species at their specific frequencies utilizing the finite element method.To perform the calculation,several procedures are followed in this study.First,rotate all the beampatterns into one direction.Then,beampatterns arecompressed using spherical wavelet.The compressed beampatterns are analyzed through principal component analysis.Two eigen beampatterns that contain most of the information are selected for analysis.The results show that the greater the weight of first eigen beampattern has,the more convergence the main lobe shows.The physical explanation for this phenomena is that the mainlobe carries most of the acoustic energy and is used by bats to target the prey.Additionally,when the second eigen beampattern has more weight,more side-lobes appears.The physical insight to this results is that the appearance of the side lode optimizes the energy distribution in the outgoing acoustics beam and helps bats to avoid obstacles when preying.In summary,it can be concluded that：1）the first eigenvector can adjust the width of the mainlobe,and the second eigenvector can change the mainlobe position both in azimuth and in elevation;2）in the eigen space,the distance between beams of two bats represents the degree of similarity of the sonar beampattern.Hence,the analysis of the eigen-beam in this study can be used to distinguish different genera of bats.