Research On High-frequency Acoustic Field Control And Application

At present,acoustic field control has been widely used in many fields such as biomedicine,industrial non-destructive testing,underwater communication,and geological survey.Basic research is the general organ that involves technical problems in the process of theoretical practice.However,for a long time,the research on acoustic field control is limited by the physical properties of sound waves,the inherent acoustic properties of natural materials and other external conditions,and it is difficult to solve the scientific problem of high-frequency wave manipulation and efficient application.Based on theory,simulation and experiments,this paper deeply explores the typical characteristics of high-frequency underwater acoustic field,and proposes a variety of new active and passive realization methods for high-frequency underwater acoustic field control.According to different types of acoustic wave functions,the methods of wave manipulation are proposed and the experiment verify the ability of ultrasonic applications.The proposed methods in this paper will enable new capabilities in beam-steering and diversified wave functionalities,improve accuracy and transmission efficiency,and drive new applications of ultrasound.The specific research contents can be summarized into the following four parts:Chapter 1: The geometric acoustic lens for high-frequency acoustic field control and application.The work in this chapter proposes two methods of high-frequency wave manipulation based on the principle of geometric acoustics.First,a new concept of "acoustic projector" is firstly proposed for the dynamic acoustic focusing effect using acoustic mirror.Based on the principle of sound wave reflection and interference,the focused beam;generated the piezoelectric material;can be arbitrarily adjusted within a 60° sector range,and the focal length change rate can reach 109% by adjusting the angle of the two acoustic mirrors.the application of ultrasound imaging can be realized by recording and processing the echo signals received by the piezoelectric material under different scanning angles.Second,a liquid lens is designed using the acoustic refraction method to achieve high-quality actively acoustic focusing,and the design parameters of the liquid lens are optimized by artificial intelligence methods.The lateral and longitudinal resolutions of the acoustic focusing beam are 1 mm and 17 mm using hydrophone test,respectively.Finally,the B-mode ultrasound imaging of tungsten wire and pig eyeballs demonstrates that this liquid lens has good ultrasound application ability.Chapter 2: Acoustic metamaterials for high-frequency acoustic field control and application.In this chapter,phononic crystals and auto-focusing metamaterials are proposed for highfrequency wave manipulation and application.Firstly,we proposed a gradient phononic crystal for acoustic focusing at 1 MHz by calculating the equivalent refractive index and designing the cellular structure.The focal length of the focused beam is 39 mm,and the lateral and longitudinal beam resolutions are 2.7 mm and 2.8 mm,respectively.Secondly,the auto-focusing metasurface using the Airy focusing distribution function is demonstrated to produce the sharp focusing ultrasonic field.Two kinds of self-focusing metasurface structures with different designing acoustic field distributions are constructed by artificial intelligence methods.The two different focused acoustic field characteristics are verified by experiments,and it is clear that the self-focusing metamaterial can achieve acoustic beam focusing and have ability to adjust focusing effect through different designing parameter.Chapter 3: Active piezoelectric metamaterial for high-frequency acoustic field control and application.The work in this chapter demonstrates three piezoelectric metamaterials for steering acoustic wave functions based on piezoelectric forward and reverse polarization.One is a checkerboard piezoelectric metamaterial that can control the directivity of the acoustic beam.Through theoretical calculation,simulation simulation and experimental test,it is found that the piezoelectric metamaterial can work in the frequency range of 1 MHz-2 MHz,which shows ultra-broadband achromatic properties.The second is a disc-type piezoelectric metamaterial for acoustic beam focusing.The positive and negative polarization regions of the piezoelectric material are designed according to the Airy function distribution,and an ultrasonic transducer based on this piezoelectric material show excellent performance of great focusing feature.At an operating frequency of 2 MHz,the measured focal length is 16.9 mm,and the lateral resolution of the acoustic beam can reach 0.63λ.The third is a disctype piezoelectric metamaterial for sharp acoustic vortex focusing.The electrode pattern of this piezoelectric metamaterial is design based on the Fresnel-spiral diffraction grating,and the vortex piezoelectric metamaterial was packaged into a transducer for acoustic pressure measurement.Experiments show that the phase of the ultrasonic wave generated by the device has a vortex distribution of 0-2π at 1 MHz frequency,and focusing at 20.1 mm.Finally,the non-contact manipulation of 100 μm microspheres and B,C mode ultrasound imaging of the object underwater are achieved by the transducer based on the focusing piezoelectric metamaterial.Moreover,the results of sub-wavelength imaging show this piezoelectric metamaterial has an imaging lateral resolution of 0.4λ.Chapter 4: Piezoelectric metasurface for high-frequency acoustic field control and application.This chapter proposes the piezoelectric metasurface based on the binary modulation of the amplitude at the sound source plane by designing the electrode pattern.The different acoustic wave functions are achieved by means of piezoelectric metasurfaces at three frequencies of 30 MHz,50 MHz and 100 MHz,respectively.First,the piezoelectric metasurface for generating 30 MHz focused and vortex acoustic beams was fabricated by the focusing distribution of Airy functions and the principle of Fresnel spirals.The acoustic vortex field can be focused with a phase distribution characteristic of 0-2π at the focal point.Secondly,a high-frequency ultrasonic transducer is fabricated using the above-mentioned 30 MHz piezoelectric metasurface,and applied in acoustic tweezers experiments including:(1)quantitatively simulated the acoustic radiation force on the particles and cells,(2)the translation and rotation operations on the particles,(3)precise contactless manipulation of single and multiple cells,including grasping,moving,and enrichment.Finally,the working frequency of piezoelectric metasurfaces for acoustic beam focusing is further increased to 50 MHz and 100 MHz.The experimental results show the lateral resolution of two focused piezoelectric metasurfaces are 40 μm and 26 μm,and the ultrasonic application of the piezoelectric metasurfaces are further demonstrated by selective manipulation of 15 μm diameter polystyrene microspheres and high-resolution B-mode ultrasound imaging of zebrafish eye structure.