Designing Of Functional Sound Field By Artificial Structures

Over the past few decades,manipulation of sound wave propagation and field distribution by artificial structures has received considerable attention as the alternative to traditional acoustic manipulation methods.Such as the achievement of acoustic focusing using the phase control,the realization of the acoustic stealth with acoustic metamaterials,and the transport of topological edge state protected by topological symmetry,and so on.The practical applications of sound control by artificial structures have been promoted due to the rapid development of artificial structure.For example,particle trapping,rotating,and self-assembly,cell rotating and sorting using phononic plate,and ultrasonic focusing and imaging assisted by artificial structure lens.Because of the flexibility of the design of artificial structure,the complex sound field which is difficult to realize by single-array ultrasonic transducer can be obtained by using artificial structure.In addition,the acoustic radiation force manipulation is carried out by using the acoustic field controlled by artificial structure,which provides a new control method for the realization of particle transmission and self-assembly.In this issue,we firstly investigate the special sound field designed by artificial structure,and then to analyze the acoustic radiation force,and the realization of particle delivery in the induced acoustic field.Secondly,we investigate sound focusing with one-point focus or multi-point focus by designing artificial structure lens.Finally,we investigate the Fresnel lens focus ultrasonic waves,and then achieved photoacoustic imaging of object by using the focused sound field and laser pulse.1.Acoustically driven particle delivery assisted by a graded grating plateAccording to the abnormal transmission properties of the grating structure plate,a one-dimensional periodic grating structure phononic crystal plate is designed.By analyzing the resonant frequency of the phononic crystal plates with different grating height,it is found that the grating height is different and the corresponding resonant frequency is different.Therefore,a one-dimensional phononic crystal plate with graded height grating is designed and prepared,which can change the distribution position of local acoustic pressure field on the grating structure plate by adjusting the frequency.The acoustic radiation force exert on the particle in the acoustic pressure field is further utilized to realize the round-trip movement of the single particle on the surface of the grating structure plate.2.Analysis of self-collimation acoustic pressure field by phononic crystal and the acoustic radiation force exert on the internal particleBased on the self-collimation propagation of acoustic wave in phonon crystal with flat dispersion surface,a phononic crystal with a dispersion curve of square or rectangle is designed to obtain the acoustic pressure field of self-collimation propagation mode inside the phononic crystal.The acoustic radiation force of the particle placed inside the phononic crystal is further analyzed,and it is found that the acoustic pressure field scattered by the particle will restore its self-collimation propagation mode inside the phononic crystal,and the forward thrust can be applied continuously to the particle,so that the particle has the trend of long-range movement in the direction of the sound source.It provides a way of thinking for the long-range transport of particles in phononic crystals.3.Ultrasonic multifunctional focusing using sandwiched composite acoustic lensAn acoustic lens composed of sandwiched composite ring arrays is designed and prepared.The acoustic lens is composed of two materials: resin and silicone rubber,the sound velocity of water is adjacent to the longitudinal velocity of the two materials,and the sound velocity of water is between the sound velocity of the two materials,so the acoustic impedance mismatch of the composite structure made by the two materials is very low in water.Sound wave transmittance is high.Further through the analysis,it is found that the phase is directly related to the thickness of the two materials,and the phase shift from 0 to 2? can be achieved by changing the thickness ratio of the two materials under the condition that the overall thickness is constant.Based on these principles,the axial single point and double point with high transmittance,as well as the multi-point focus acoustic lens are designed and prepared.4.Construction of ultrasonic waves focusing in a wide frequency band and realizing object photoacoustic imagingBased on the principle of Fresnel zone plate,the acoustic wave focusing underwater with high frequency is obtained.By analyzing the focusing effect of the acoustic lens of the Fresnel zone,it is found that the focal length of the acoustic lens is linearly related to the working frequency,the focal length tends to increase linearly with the increase of frequency,and the full width at half maximum(FWHM)of the focal spot along the longitudinal direction increases gradually,while the FWHM along the transversal direction remains almost unchanged.The photoacoustic imaging of the object is realized by combining the acoustic lens focusing sound field with the pulsed laser.