Research On Acoustic Manipulations Based On Phase Controlled Metamaterials

As a kind of classical mechanical waves,acoustic waves can be applied to many key fields,such as architectural acoustics,electroacoustics and medical ultrasound.Therefore,the research on acoustic manipulations is of great significance.Based on phase modulation,we can manipulate the acoustic propagation path and design acoustic functional devices by using the units of phase controlled metamaterials,realizing various exotic acoustic effects,such as anomalous refraction and reflection,acoustic focusing,Bessel beam,self-bending beam and so on.Compared with the traditional mechanisms,acoustic manipulations based on phase controlled metamaterials have the advantages of high flexibility,broad bandwidth and easy integration,which has more extensive application prospects.In this paper,based on the phase controlled metamaterials,a variety of novel acoustic functional devices has been designed and realized rich acoustic manipulations.In addition to the first chapter and the sixth chapter,which are the introduction and the summary and prospect,respectively,the main research contents are divided into the following four parts(1)Basic theories and methods of acoustic metamaterials;(2)Broadband acoustic focusing lenses based on phase controlled metamaterials;(3)Enhanced directional acoustic emission lens based on anisotropic metamaterials;(4)Acoustic manipulations based on three-dimensional generalized Snell's law.The details are shown as follows:In second chapter,we introduce the basic theories and methods of acoustic metamaterials.It includes the generalized Snell's law,calculation method of reciprocal vector of sonic crystal and equivalent parameter inversion method of acoustic metamaterials,which offers the theoretical basis for designing units of phase controlled metamaterials and realizing rich acoustic manipulations.In third chapter,we realize two types of broadband acoustic focusing lenses based on units of phase controlled metamaterial composed of different numbers of same cavity structures.The phase delays of units could cover a whole 2? range byusing only six cavity structures.Based on phase modulation,we realize acoustic focusing lenses with different focal lengths both numerically and experimentally by arranging the units of phase controlled metamaterial into hyperbolic phase distribution.The working bandwidth could reach about 2.1 kHz.In addition,acoustic Airy beam with self-bending property can be obtained by using Airy beam phase distribution.Based on two symmetric acoustic Airy beams,we realize the acoustic focusing lens with strong ability of round obstacles and high self-healing property.In fourth chapter,we realize enhanced directional acoustic emission lens based on anisotropic metamaterial consisting of an array of units constructed by a square cavity and two symmetric straight channels.The anisotropic property of acoustic transmission in the metamaterial exists in the range of 8430–9460 Hz,which arises from different effective impedances of the unit in the orthogonal directions.By placing a cylindrical source at the center of the metamaterial,we realize the enhanced directional acoustic emission with an unchanged wavefront.More interestingly,we also realize the enhanced directional acoustic emission for two cylindrical sources in the anisotropic metamaterial.In fifth chapter,we theoretically derive and demonstrate three-dimensional generalized Snell's law based on reflected acoustic metasurfaces.Auasi-three-dimensional acoustic metasurfaces with a deep sub-wavelength thickness of ?/10 are constructed with 16 phased unit cells composed of a straight pipe and two ring-like Helmholtz resonators.Based on the three-dimensional generalized Snell's law,we design quasi-three-dimensional acoustic metasurfaces with different phase distributions and realize many reflected acoustic field manipulations in three-dimensional space,including anomalous reflections,point focusing,line focusing in two perpendicular directions,non-diffracting Bessel beam and self-bending beam.