Acoustic Wave Manipulation Based On Phononic Crystal

In this paper,we mainly focus on the application of phononic crystals in the field of acoustic wave manipulation.As a functional material with periodic structure,phononic crystals are composed of two or more materials arranged in a periodic sequence.They have a characteristic that inhibits the passage of acoustic waves in a fixed frequency range.Some phononic crystal structures of certain permutations also have the characteristic of changing the direction of acoustic waves in a fixed frequency range.Therefore,phononic crystals have great application value in the field of acoustic wave control.In this paper,we firstly introduce the basic concepts of phononic crystals,which include the structural periodicity,elastic wave properties and the bandgap characteristics of phononic crystals.These work forms a foundation of the following studies.The transfer matrix method,the plane wave expansion method and the finite element method are used to calculate the bandgaps for three different types of phononic crystals.The application range of these three bandgap computing methods is obtained by comparison.The results of bandgap calculation can be applied to the following design procedure of the phononic crystal structure.Then,a phononic crystal acoustic stealth structure with gradient refractive index is designed,which realizes the absorption of acoustic waves in different frequencies and from different directions.Numerical simulations are performed for stealth effect in acoustic waves.The results show that the good acoustic stealth is achived by the designed structure in a large frequency range.Finally,a phononic crystal structure of ultrasonic wave diffuser is desinged,which has the ability to spread the ultrasonic wave of a single direction to a uniform launch in all directions.Simulation of this effect is carried out in ultrasonic waves.The results show that the designed structure has the function of uniform diffusion of ultrasonic waves in fixed frequency.