基于近场声学的超透镜成像改进方法研究

发布时间：2018-01-16 08:20

本文关键词：基于近场声学的超透镜成像改进方法研究　出处：《中北大学》2017年硕士论文　论文类型：学位论文

【摘要】：近场声学是近年来在光学飞速发展的基础上发展起来的,该技术在保密防伪、军事侦察、医用检查、水下探测、等各个方面获得了广泛的应用,引起人们的关注。近场声全息技术作为全息技术的一种,是光全息基础上发展起来的,本文对基于空间Fourie变换的近场声全息进行了研究,分析了近场声全息在成像中产生误差的原因,并充分利用声学超材料透镜的完美成像性质有针对性的对此进行改进,对提高近场声全息的分辨率,准确识别和定位声源具有指导意义。本文从声波辐射理论入手,对理想流体介质中稳态小振幅声波场分别在平面、柱面以及球面坐标系下的Helmholtz方程求解,详细研究了基于空间Fourie变换的近场声全息在不同坐标系下的算法实现以及误差产生原因。产生误差原因有:(1)全息面上的声压传感器的离散分布带来的“窗效应”;(2)实测信号和分布在孔径周围无限多个“虚像”造成卷绕误差;(3)携带声源细节信息的倏逝波只存在于近场中,而全息面布置位置离声源较远,丢失声源细节信息。通过第三章对亚波长声学超材料透镜的成像研究,因负折射声子晶体对携带声源细节信息的倏逝波具有放大作用,所以倏逝波在通过超透镜后才开始衰减,受此启发,本文提出创新思想,即设计亚波长声学探头置于声源近场中,将声源信息先汇聚于一点,再在聚焦点用声传感器采集并重建。该方法不仅减小了因离散采集带来的误差,同时也将近场中的倏逝波一并重建,采集到的声源信息完整,成像效果效果良好。文中运用运用COMSOL软件对声学超透镜进行了建模,并模拟仿真了点源通过透镜的成像效果,像点声压值与物点声压值非常相近,成像效果良好,为上文创新思想提供有力的理论证据。
[Abstract]:Near-field acoustics has been developed in recent years on the basis of the rapid development of optics. The technology has been widely used in security, military reconnaissance, medical inspection, underwater detection, and so on. As a kind of holography technology, the near-field acoustic holography is developed on the basis of optical holography. In this paper, the near-field acoustic holography based on spatial Fourie transform is studied. The causes of errors in near-field acoustic holography are analyzed and the resolution of near-field acoustic holography is improved by making full use of the perfect imaging properties of acoustic metamaterial lens to improve the resolution of near-field acoustic holography. It is significant to identify and locate the sound source accurately. This paper starts with the theory of sound wave radiation, and the steady state small amplitude acoustic wave field in the ideal fluid medium is respectively in the plane. The Helmholtz equations in cylindrical and spherical coordinates are solved. The algorithm realization of near-field acoustic holography based on spatial Fourie transform in different coordinate systems and the cause of error are studied in detail. The "window effect" caused by the discrete distribution of the acoustic pressure sensor on the holographic surface; (2) the winding error caused by the measured signals and the infinite "virtual images" distributed around the aperture; 3) the evanescent wave with detail information of sound source only exists in the near field, but the position of the holographic plane is far away from the sound source, and the detail information of the sound source is lost. In chapter 3, the imaging of subwavelength acoustic metamaterial lens is studied. Because the negative refraction phonon crystal can amplify the evanescent wave which carries the detail information of the sound source, the evanescent wave only begins to decay after passing through the superlens. The sub-wavelength acoustic probe is designed to be placed in the near field of the sound source, the sound source information is gathered at a point first, and then the acoustic sensor is used to collect and reconstruct the sound source information in the focus. This method not only reduces the error caused by discrete acquisition. At the same time, the evanescent wave in the near field is reconstructed together, the sound source information collected is complete, and the imaging effect is good. In this paper, we use COMSOL software to model the acoustic superlens. The imaging effect of point source passing through lens is simulated. The image point sound pressure value is very close to the object point sound pressure value, and the imaging effect is good, which provides strong theoretical evidence for the above innovative ideas.
【学位授予单位】：中北大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O429

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