Tunable Pipe-type Acoustic Metamaterials Based On Piezoelectric Composite Side-branches

By using artificially designed and constructed subwavelength unit structures arranged according to certain rules,the whole structure presents the properties that natural materials do not possess,so as to achieve the purpose of controlling the sound field.This kind of subwavelength structure is called as acoustic metamaterials.Based on the principle of the generalized Snell's law,acoustic metamaterials can control the wavefront of sound waves to obtain different sound fields.Therefore,acoustic metamaterials are widely used in various fields.However,once the traditional acoustic metamaterials are made,their functions are fixed and cannot be changed in real time,which brings a lot of inconvenience to the application of metamaterials in practical engineering field.Therefore,some researchers have designed and manufactured active control materials,and realized real-time control of sound fields by means of the variable structure,the external active circuit and the external magnetic field.However,the ability to tune the performance of acoustic metamaterials without structural modifications or complex active control circuits is still a remarkable challenge.Therefore,we design a method of replacing traditional side-branch with the piezoelectric side-branch pipe that consists of the piezoelectric composite sheets.On this basis,we design a tunable pipe-type acoustic metamaterial.Merely by adjusting the external capacitances of the piezoelectric composite sheets,we can accurately switch the functions between the extraordinary transmission,the acoustic focusing,the acoustics deflection focusing and the formation of various sound fields for the same incident wave.Our work provides a promising potential in active controls and integration designs of acoustic metamaterials and devices.This paper mainly includes the following contents:The first chapter is the introduction,which mainly introduces the background and development of acoustic metamaterials,and emphasizes on the active control of acoustic metamaterials.According to the different regulation parameters,the classification is made and some examples are introduced.In addition,we introduce the related theories of acoustic metamaterials,including the acoustic wave equation,the equivalent medium theory,the electromechanical-acoustic analogy and the generalized Snell's law.In the second chapter,we design a piezoelectric side-branch structure composed of piezoelectric composite sheets to replace the traditional side-branch structure.The acoustic properties of the piezoelectric side-branch structure are studied by the theoretical derivation,finite element numerical simulation and experimental methods,and its control function is also proved.In the third chapter,we design tunable pipe-type acoustic metamaterials based on piezoelectric composite side-branches.By adjusting the external capacitance connected to the PCS,we can accurately switch the functions for the same incident wave.The forth chapter is the summary and the prospect of the future work.