Manipulation Of Acoustic Field Through Artificial Structures

In recent twenty years,acoustic artificially structures have received extensive attention from scientific community.By manually designing specific structures,they can generate properties that are not found in nature and can effectively manipulating sound waves.Acoustic artificial structure mainly include phononic crystal,acoustic metamaterials and acoustic metasurfaces.The study of artificial structure has brought novel physics properties,such as negative refractive affect,but also can more effective control of the sound field,such as imaging and cloaking.In recent years,the study of topological phononic crystal has injected fresh blood into the acoustic artificial structure and brought more application prospects.In order to promote the further development of artificial structure,we must constantly introduce new ideas and perspectives to create better application values.Artificial structure in this thesis,we studied some interesting physical and novel features,including Weyl physical in low dimensional phononic crystal system,the super resolution focusing of spherical wave in three dimensional reverberation field,the reshape of three-dimensional acoustic reverberation field by active tunable metasurface and the induced asymmetric interactions between two parallel coupling plates.The main works are listed as follows:1.The Weyl physical in one-dimensional phononic crystalWeyl is the double linear degeneracy point in three dimension momentum space.In a one-dimensional layered phononic system stacked with water and glass,Weyl points are synthesized by introducing two structural parameters to construct a virtual three-dimensional momentum space.The linear degeneracy Weyl points were successfully measured experimentally by ultrasonic transmission method.The existence of Weyl point makes the presence of vortex-like reflection phase structure in parameter space,and the center of the vortex is located at the Weyl point.According to the bulk-boundary-correspondence interpretation of our synthetic Weyl systems,the vortex-like reflection phase ensures the existence of phononic crystal interface state and fermi-like arc.Experimentally,we have successfully measured the vortex structure of the reflected phase and the interface state distribution is in good agreement with the simulation results.In addition,according to the characteristics of the interface state,we designed a structure that can stimulate the strong collimation beam.2.The Weyl physical in two-dimensional phononic crystalThe phononic crystal systems with two-dimensional graphene structure have Dirac degenerate points.In this system,we introduce a new parameter-the rotation angle of scatter-to construct a three dimension system which has Weyl points.For a phononic crystal with a specific rotation,which in fact is a two dimension system,has no topology protected interface state.However,from a three-dimensional perspective,the interface state distribution around the Weyl points in the projection plane is gapless and topology protected.Meanwhile,the topology protected Fermi arc is also present.In addition,in the three dimensional phononic crystal systems,the distribution of interface states projected along different directions is different,so we discussed the interface states distribution when projected parallel along ?? and ?M direction,which further verify the chiral of Weyl points.3.The super resolution focusing of three-dimensional spherical waveA pyramidal membrane resonator unit with perfect absorption properties was designed,and then 12 identical units were assembled into a nearly spherical dodecahedron.The time-reversal technique was used to excite the focused spherical wave in the laboratory,and the absorption performance of the designed near-spherical acoustic metamaterial was measured by analyzing the time-domain signal of the focused spherical wave.The three-dimensional step scanner is used to measure the focusing spot of spherical wave with/or without absorber.In experiment,we successfully obtained the super-resolution focusing that breaks the diffraction limit.In addition,the absorber can effectively identify two focusing spots with a distance of 0.4?.4.The reshape of three-dimensional acoustic reverberation field by active tunable metasurfaceWe designed a metasurface that can actively adjust the sound field.The metasurface unit is a cleverly designed membrane resonance unit,on which a magnet disk and a plastic ring are attached to adjust the intrinsic mode and realize the interaction with a miniature electromagnet supported by a bracket at a distance of 2.5 mm from the membrane.Changing the polarity of the electromagnet can change the direction of the force between the electromagnet and the disk,and thus change the shape of the membrane,that is,change the resonance frequency of the membrane.The phase of transmission wave at the frequency between the two resonant frequency at the two modes can have a difference of nearly 180 degrees.In experiment,we have designed 360 resonance units to realize the "strong field area" and "silent area" successfully.5.The induced asymmetric interactions between two parallel coupling platesAcoustic radiation forces can be induced when objects are stimulated by external acoustic waves.Meanwhile,the interaction between objects can be induced.We designed a parallel coupled plate system in which the vibration modes are completely different when excited by acoustic waves with opposite directions.The interaction force can be four orders of magnitude higher than the force acting on the entire system and 100 times greater than the force acting from the opposite direction when the acoustic wave stimulated from the side of thinner plate.