生物声呐系统信号调制机制之探索及实验研究

Rapid development of communications has required better performance of antenna.Concepts such as biomimetic antenna，smart antenna and arry antenna have been put forward for improvement in antenna performance. However, these antennas are still far away from practical application due to the incomplete understanding of an appropriate working principle for excellent and satisfactory antenna. It is of great importance to get the idea how the antenna can be made capable of efficient and accurate work for designing and improving new antennas..Bats are a group of mammals most noted for the use of sophisticated active and passive biosonar systems.Horseshoe bats use a biosonar system. Specifically, they emit ultrasonic pulses through the nostrils and listen to the returning echoes with their ears. Noseleaves are a common anatomical feature in horseshoe bats. The noseleaves of horseshoe bats are elaborate structures consisting of three parts: a smooth baffle (“horseshoe”) which fills approximately the bottom three-quarters of a circle around the nostrils, a forward-pointing central spike (“sella”) which is adjacent to the upper rim of the nostrils, and a pointed flap (“lancet”) which is located above the sella. It has been observed that horseshoe bats continuously vibrate the horseshoe part of their noseleaves and often change the shape of their pinnae during echolocation process. However, previous study of the roles noseleaves and pinnae play in bat biosonar system has been done under the hypothesis they are static. The mechanism and significance of the dynamic behavior of noseleaves and pinnae have not been systematically studied. .In our proposed work, we will select a species of horseshoe bat (Rhinolophus Ferrumequinum) to carry out the dynamic functional characterazation of noseleaves and pinnae. The temporal relationship between pulses and echoes with noseleaf vibration and pinna deformation will be investigated. The results will help us understand the underlying physics of noseleaf vibration. How the right and left pinnae deform and coordinate with each other to detect the echoes will also be revealed. The consequences of our research will be potentially applicable in designing biomimetic anntenna like artifical bat head.

信息时代的到来，对天线的性能提出了更高要求。研制高灵敏度、低功耗的天线已成为当前通讯技术领域的研究热点，为此，人们提出了智能天线、仿生天线等概念。蝙蝠声呐系统是仿生天线研究中最常被模仿的范例。与通讯系统类似地，蝙蝠可能通过振动鼻叶和外耳来对其发射和接收的超声波实现某种调制和解调，但此前学术界对此关注较少，只是对静态的鼻叶或外耳模型进行声场数值计算，并且此类计算迄今为止还缺乏相关实验验证。针对此现状，本项目以菊头蝠为研究对象，拟借助高速相机、超声测量仪、激光测振仪等设备，实时观测、记录菊头蝠鼻叶运动与超声发射、双耳形变与超声接收在时间上的关系，建立量化的声场模型来揭示蝙蝠声呐系统动态工作机理，并利用三维打印机制作出蝙蝠头部模型，利用超声探测仪在多点式测量，实测得到空间不同位置的声压值，并与计算所得的声场进行比较，验证计算方法的合理性与否。本项目的研究结果对于仿生天线的设计具有重要的指导意义。

在长期的自然演化过程中，蝙蝠发射（即鼻孔及周围鼻叶）和接收（即耳朵）超声波的器官，形成了复杂的外形结构。以往的研究工作表明，这些生物结构决定了蝙蝠声呐波束的形成，并且可以影响声场的近、远场分布特性，有助于提高蝙蝠声呐系统的指向性和灵敏度。 .在本项目中，我们研究了蝙蝠鼻叶对超声波发射场分布的调制作用，以及蝙蝠外耳对超声波接收场分布的调制规律。我们选择了两类不同属蝙蝠（菊头蝠和普氏蹄蝠）研究其不同的鼻叶结构，发现菊头蝠的马蹄叶和普氏蹄蝠的前叶都展现出与超声波脉冲发射脉冲同步的运动行为特性。鼻叶的运动呈现出双相的速度脉冲图样，起先是朝着远离头的方向运动，运动速度较小但时间较长，然后再做反向运动，运动速度较大而时间较短。每一个运动周期接受，鼻叶都回到初始位置，然后再继续下一个运动周期。在运动过程中，鼻叶会产生形变，进而影响发射声场的强度分布。另外，我们观察到普氏蹄蝠面部另一特征结构与其年龄相关的显著变化，建模计算出了声场强度的空间分布。.蝙蝠的外耳接收环境反射的回声超声波。我们研究了回声脉冲抵达蝙蝠头部与蝙蝠双耳形变在时间上的相关性，发现在回声抵达时，蝙蝠外耳正在形变过程中，也就是说，蝙蝠的外耳正在进行非刚性运动。并且，蝙蝠的双耳可相互配合，调节其朝向和形貌，优化声场接收的灵敏度。除此以外，我们还研究了蝙蝠外耳皮瓣对频率驱动扫描的影响，发现皮瓣本身是一个相对较小的结构，不能对声波产生显著的影响。然而，皮瓣可以将原来的半开腔分为两个半开放腔，引起皮瓣两侧的共振，导致远场频率驱动的副瓣扫描。.本项目的研究成果，有助于进一步深入认识生物声呐系统工作原理，对智能天线等设备的设计和研制具有重要的指导作用。