Acoustic Deflector Based On Gradient-index Media

In recent years, more and more attentions have been paid to acoustic artificial structures. And the gradient index (GRIN) media have been attracting increasing attention due to their unique performance. By controlling the parameters of GRIN media, various optical phenomena can be realized, such as bending and convergence. However, acoustic wave is another classical wave whose wave equation is similar with that of electromagnetic counterpart. The concept of acoustic GRIN lens can be proposed according to the theoretical principle of optical GRIN lens. It has been extensively proven that acoustic GRIN media can be realized by selecting the structural parameters of sonic crystals in the direction transverse to the acoustic propagation or employing acoustic metamaterials formed by coiling up space. Thus, acoustic GRIN systems will have the potential to control the acoustic waves, which would have more implications for acoustic devices.In this letter, the study is about the design, construction and characteristics of a circular structure that works as an omnidirectional acoustic deflector of airborne sound, which is able to guide the waves at any refraction angle. This article is divided into the following five sections.In the first chapter, the background and the development of the phononic crystal, acoustic metamaterial and the acoustic gradient index (GRIN) metamaterial are reviewed.In the second chapter, Eaton lens and a retroreflector approximation is introduced.Here derive a more accessible form of the refractive index for any refraction angle with some accuracy using the retroreflector approximation.In the third chapter, a method for retrieving effective properties of locally resonant acoustic metamaterials is showed here. According to this method, a "cell" structure is proposed, of which the effective refractive index can be controlled by the radii of rigid circles. Deflection behavior of GRIN media and our structure is proved using FEM simulations. It can be found that the structure performed as well as GRIN in terms of acoustic deflection. Without loss of generality, this kind of structures is able to deflect acoustic waves by any angles using this method.In the fourth chapter a retroreflector made of resin is placed between two waveguide plates, and pressure field can be measured. The acoustic retroreflector is proved experimentally.In the fifth chapter the main conclusion of this article and prospects for future work are presented.