Research On Acoustic Superdiffractive Lenses Based On Helmholtz Resonators

As one of the essential properties of waves,diffraction has significant application in high resolution imaging,medical ultrasound diagnosis and treatment.Manipulating the acoustic waves beyond the diffraction limit offers an alternative application potential in high-resolution imaging and medical ultrasound diagnosis and treatment.As one of the frontier directions in the field of acoustic research,acoustic metamaterials can effectively regulate wave transmission.Therefore,it has a wide range of application potential to freely manipulate the sound field by reasonably designing subwavelength artificial structure.It is expected to get the super-resolution effect that breaks the diffraction limit,which has a wide application potential in acoustic super-resolution imaging and medical ultrasound therapy.First of all,this thesis introduces the regulation principle of the acoustic meta-lens on the sound field.The model of the unit structure that constitutes the acoustic lens is analyzed,and the regulation method of the sound field by the unit structure is studied.The possibility of using that the unit structure is an annular sub subwavelength structure composed of a Helmholtz resonant cavity and a Fabry-Perot resonant straight tube is studied.The phase control method of the Helmholtz resonant cavity and the Fabry-Perot resonant straight tube is studied,and the influence of the internal parameter adjustment of the unit structure on the sound field phase is simulated and analyzed by the finite element software COMSOL Multiphysics.Finally,based on the Helmholtz and FabryPérot hybrid structure,a two-dimensional acoustic lens array is designed to form a circular two-dimensional structure acoustic super-diffractive meta-lens.The numerical simulation and experimental measurement results prove that the designed acoustic metalens generated super-diffraction focusing phenomenon in a two-dimensional plane.The designed acoustic meta-lens directly manipulates the incident plane acoustic waves,and it formed a focal spot size that breaks through the diffraction limit in the focus.The full width at half maximum of the focal spot is 0.428 wavelengths.At the same time,the different phase delays generated by the designed acoustic meta-lens forms an acoustic needle phenomenon with the focusing depth of about five wavelengths in the two-dimensional plane.The full width at half maximum of the spot is 0.467 wavelengths,and the focal spot size breaks the diffraction limit..Meanwhile,the acoustic needle phenomenon breaking the diffraction limit can be proved through numerical simulation and experimental measurement.The proposed method can greatly promote the application and development of acoustic superfocusing technology in acoustic imaging,particle manipulation and other fields,and it has significant application in high resolution imaging,medical ultrasound diagnosis and treatment.