低频声波的定向辐射

实现低频声波在空间中的定向传播，是一个迫切需要解决的关键科学问题。为实现低频声波的定向传播，要考虑影响声波指向性的因素：声源辐射面积、辐射面结构和所辐射声波的频率。而影响声波传播的因素有：(1)媒质的性质，例如声阻抗、声衰减；(2)边界条件，不同的边界会产生声波不同的传播模式，例如点源在不同边界附近的辐射表现(点声源在声学硬边界表现为单级子的指向性，即全指向性；点声源在声学软边界为偶极子的指向性，呈现为八字型，具有一定的指向性)；(3)结构的控制，例如通过米氏共振结构来控制低频声波的传播。文章简要介绍了影响声波传播的因素和控制声波传播的方法，并主要从边界条件和结构控制两方面来说明如何实现低频声波的定向辐射。

Directional radiation of low-frequency acoustic waves

How to realize the directional propagation of low frequency acoustic waves in space is an important scientific issue. The factors that affect the directivity are:the area of the radiation source, the structure of its surface, and the acoustic frequency. The factors that influence wave propagation are: (1) Properties of the transmission medium such as acoustic impedance and attenuation;(2) Boundary conditions, different boundaries will produce different propagation modes, for example, ata rigid boundarya point source will behave as a monopole and radiatein all directions,whereas at a soft boundaryit behaves like a dipole, emitting with splay type. (3) Structural control,for example, by means of a Mie resonance structure. This paper presents a brief introduction to the factors that influence the propagation of sound waves and their methods of control, with emphasis on how to realize the directional radiation of low frequency acoustic waves through control of the boundary conditions and structure.