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.