Artificial-structure-based Acoustic Field Engineering And Biological Applications

Acoustics,as an applied and highly permeable discipline,has attracted extensive attentions from many researchers in academia.Modulating the sound field to meet the requirement of various application scenarios is an important part of acoustics.As one of the carriers of energy and information,the study of acoustic wave propagation is of great importance to the development of related disciplines.In this dissertation,I will focus on the meta-structure-assisted transmission properties of acoustic waves in different media and systematically investigate the artificially modulated sound fields.In addition,various functional sound fields at different scales are generated and further applied to different biological effects based on the constructed sound field patterns.Details of the research contents are listed as follows:(1)Based on the acoustic caustic theory in two-dimensional space,the geometrical relationship between acoustic wave propagation trajectories in the air and the phase of the array elements was investigated.A flexible soft substrate that can be continuously deformed at large angles was designed and realized.An equal-phase excitation plane was constructed by an embedded piezoelectric unit array,realizing the transmission of a large-angle bending beam.This active modulation method is capable of satisfying the arbitrary switching of multiple large-angle non-diffraction self-accelerated sound beams in the air.It was found that the flexible piezoelectric transducer could generate a wide range of large-angle bending acoustic beams under broadband frequency excitation.This large-angle bending sound transmission around possible obstacles in the air can meet the demand for versatile applications.(2)Inspired by biomimetic functional artificial structures,an erasable chemical modification reagent of nano-silica particles was prepared.By providing a selective superhydrophobic surface decoration on a planar ultrathin substrate,starkly contrasted acoustic impedance boundaries were created,which resulted in the complete reflection of sound waves in water with a wide frequency range as well as large-angle incidences.Furthermore,structural ultrasound beams with different functions were constructed via patterning the near-zero/one sound transmission regions.In addition,the broadband focus responses of the ultrathin meta-skin lenses were verified in several frequency bands and the acoustic radiation force enhancement induced by focused ultrasound was comprehensively studied.Based on the multifunctional ultrasonic tool,the radiation pressure of the acoustic field was studied under different input parameters.Based on the constructed weakly focused ultrasonic field,the behavioral responses of induced Caenorhabditis elegans(C.elegans)were explored.The differences between the thermal and mechanical mechanisms of ultrasound-based biological behavior control in this system were further discussed.(3)Based on the anisotropy parameters of a piezoelectric crystal,the surface acoustic wave was well modulated in the microscale fluid environment.The anisotropic phase velocity distribution of the lithium niobate piezoelectric crystal was calculated with the finite element simulation,and the holographic distribution of the interdigital transducer was designed.The propagated Rayleigh surface wave was focused by the holographic interdigital transducer with a very narrow focal spot,based on which we developed a functional device with enhanced energy at the pre-designed focal spot.The parameters such as phase velocity,deflection angles,and anisotropy parameters of the piezoelectric crystal(lithium niobate)were experimentally studied.Nonetheless,a microfluidic bio-chip based on the PDMS microscale channels was constructed for efficiently aligning and sorting the particles of different sizes.In this part,the influences of the anisotropic parameters and other physical properties of piezoelectric crystal on the high-precision surface acoustic wave field were carefully considered,providing an important method and showing application prospects for the design of the microfluidic device with small voxels.