Study On The Improvement Method Of Super Lens Imaging Based On Nearfield Acoustics

Near field acoustics has been developed on the basis of the rapid development ofoptics in recent years.It has been widely used in many fields such as security,anticounterfeiting,military reconnaissance,medical inspection,underwater exploration and s o on.It has attracted people's attention.This paper studies nearfield acoustic holography t hat bases on Fourie-transformation,and analyzes the causes of errors in the near-field acousti c holography imaging,and make full use of perfect imaging properties of acoustic metamat erial lenses to readuce error.This study has directive significance to improve the resolution of the near-field acoustic holography,and identify accurately and locate sound source.This paper starts with the theory of sound radiation,and solves the Helmholtz equa tion respectively for the steady small amplitude acoustic wave field in ideal fluid med ium,in plane,cylindrical and spherical coordinate systems.This paper studies detailedl y the arithmetic in different coordinates systems and analysis the reasons of errors.Ther e are causes of error:(1)The window effect of the discrete distribution of the sound pressure se nsor on the holographic surface.(2)There are some winding error because of the measure d signal and the "illusion" surrounding the aperture(3)The evanescent wave with the detail i nformation of the sound source only exists in the near field,but the position of the holograph ic surface is far away from the sound source,and the sound source is lost.The imaging of sub wavelength acoustic metamaterial lens is studied in the third cha pter.The evanescent wave is amplified by the negative refraction of photonic crystal,so the e vanescent wave began to decay after passing through the super lens.Inspired by this,this p aper put forward innovative ideas.The sub wavelength acoustic probe is placed in the n ear field of sound source,and the source information is firstly converged at one point,then acquired and reconstructed by acoustic sensor in focus.The method can not only reduce the error caused by discrete acquisition,but also reconstruct the evanescent wave in the near field.The collected sound source information is intact and the imagin g effect is good.In this paper,the acoustic super lens is modeled by using COMSOL software,and the imaging effect of point source through lens is simulated.The image point pressure is very close to the point pressure,and the imaging effect is good,These benefits provide strong theoretical evidence for the above ideas.