柱面型声透镜设计及验证

介绍了声透镜波束形成的基本原理和分析方法,分析了柱面型声透镜的设计方法。用ZEMAX光学软件设计并用ABS塑料制作了一个组合声透镜,在水池中完成其多个参数的测量。在频率500kHz和20°的视场范围内该声透镜的角度分辨率为l°。实验结果表明,该声透镜系统的波束宽度、旁瓣高度和视场范围均达到了设计要求．并很好的验证了柱面型声透镜的聚焦性能。     

聚焦波束形成声图法误差分析

聚集波束形成声图测量方法可以实现近场目标的被动定位．利用该方法接收数据或进行数据处理的过程中必定会有各种误差产生,本文从聚焦峰尺度、阵元偏差、波长等方面对聚焦波束形成声图测量方法的影响进行了分析,经仿真研究与实验数据分析可以得出聚焦波束形成声图法受距离与波长的影响较大,但对于阵元的位置要求不高,利用该方法可以实现近程目标的高精度定位。     

基于近场波束形成法的声发射源定位研究

引入近场波束形成法处理声发射信号,研究在小区域布置少量传感器来实现声发射源定位的新方法.首先,利用板波理论进行声发射信号传播特性研究,对比了板中声发射信号与空气中声波传播的差异性,分析了波束形成法应用于声发射源定位的问题.并在板上进行断铅实验,验证了近场波束形成法进行声发射源定位的有效性.最后,在旋转机械碰摩模拟实验台上进行了碰摩实验,利用波束形成法进行碰摩声发射源定位,所提出的方法能有效地定位旋转机械初始碰摩位置.所得结果可为声发射源定位提供一种新途径.     

声呐用圆柱声透镜实验研究

本文是声呐用圆柱声透镜的实验研究总结。概述了圆柱液体声透镜的聚焦能力和指向特性。实验表明,所用透镜能形成较好指向性,旁瓣小于-15dB。     

声透镜聚焦声场的有限元仿真

采用有限元软件对物理模型进行仿真,得到声透镜辐射聚焦声场的焦距,并与实测结果进行比较,显示两者吻合较好。     

基于多波束系统的水下目标近程回波亮点声图像

模拟多波束系统,仿真得到了水下目标的二维回波亮点声图像。先采用小分置角双基地目标回波特性计算的近场板块元方法,计算得到水下目标的传递函数。再根据多波束系统的理论,建立了水下目标回波亮点二维声图像的基本框架,实现了水下目标回波亮点二维声图像仿真。最后得到了水下目标不同方位角情况下近程二维回波亮点的声图像。     

超声透镜声场的数值计算

0引言平面换能器与声透镜结合可以形成有效的聚焦系统。声透镜聚焦换能器在超声显微镜、超声无损检测和成像声纳等方面有着广泛的应用。声透镜一般由曲面和平面共轴排列,由于声透镜材料声速往往大于传播介质声速,因此凹面镜会形成聚焦效果,如何准确计算透镜所形成的声场是声学透镜设计的重要基础。本文依据射线传播理论、混合传播理论和波动传播理论归纳出三种数值计算方法,分别进行声场计算,并与实测结果进行比较。     

凸形弧线旋转曲面声透镜研究

通过对凸形弧线旋转曲面声透镜在不同面形参数下的声场的数值计算,研究了透镜面形参数与其声场分布特特间的关系,证实透镜面形参数对声场分布有明显影响,根据在声场中尽可能长的距离范围内,获得声束宽度较小,旁瓣水平适中的声束的要求,提出了透镜的优化面形参数,结果得到实验验证。     

带凹槽平板型声透镜聚焦性能的理论分析与数值模拟

基于相位补偿和惠更斯-菲涅尔原理,利用理论分析和数值模拟的方法,研究了一种带凹槽的平板型声透镜,讨论了凹槽个数、声透镜材料等参数对声透镜聚焦性能的影响。结果表明:优化后的菲涅尔声透镜聚声效率理论上可达40%,放大倍数约为7倍,是一种较为高效、成本低廉的新型声透镜。     

多途条件下聚焦波束近程定位

讨论了直线阵通过聚焦波束形成技术对近程点目标的高精度定位问题并通过仿真验证,对多途的影响及海面起伏的影响也作了初步分析。通过波束引导减少了扫描的运算量,并且通过虚阵、时间反转镜和乘积声图的方法提高了聚焦点"亮度"和声图质量。仿真结果表明,虚阵和时间反转镜技术可以较好地抑制多途干涉,使用乘积声图可以使观察到的信号变得更清晰。在信噪比为0dB时可以很好地检测到目标。     

Planar-structure microscope-lens for simultaneous acoustic and optical imaging

A new type of combined acoustic and optical microscope lens with a planar structure is proposed. It can meet the demand for simultaneously obtaining both an acoustic image and its optical counterpart. The lens is composed by uniting a Fresnel-zone-type acoustic lens developed by the authors with a rod-type gradient-index optical lens (SELFOC). An acoustic beam is converged to a focal point in water by an acoustic planar lens that is composed of annular grooves formed on the end of the SELFOC rod. An optical beam, emitted by a He-Ne laser source and guided into the rod, converges due to the gradient of the refractive index and focuses on a spot in water. By designing the length of the rod properly, the focal spot of the optical beam is set to coincide with that of an acoustic beam. The design and fabrication of the lens are described, and results of some preliminary experiments for simultaneous observation of acoustic and optical images of the same portion of a specimen are shown.     

环状光束通过球差透镜的聚焦特性

利用偏心高斯光束相干叠加的方法,建立了柱坐标系下环状光束的新模型.从广义衍射积分理论出发,经过大量数值计算分析,详细研究了环状光束通过球差透镜的聚焦特性,定量分析了环状光束的阶数L,M、偏心高斯光束的束腰宽度w0以及球差系数C4对聚焦光场实际焦点(轴上最大光强)位置以及轴上最大光强的影响.研究结果表明,本文提出的模型可统-描述基模高斯光束和环状光束.在透镜焦距和入射光束波长一定的情况下,环状光束通过球差透镜的聚焦特性不仅与透镜的球差系数C4有关,而且还与环状光束的阶数L,M以及偏心高斯光束的束腰宽度w0有关.     

Optical analysis of time-averaged multiscale Bessel beams generated by a tunable acoustic gradient index of refraction lens

Current methods for generating Bessel beams are limited to fixed beam sizes or, in the case of conventional adaptive optics, relatively long switching times between beam shapes. We analyze the multiscale Bessel beams created using an alternative rapidly switchable device: a tunable acoustic gradient index (TAG) lens. The shape of the beams and their nondiffracting, self-healing characteristics are studied experimentally and explained theoretically using both geometric and Fourier optics. By adjusting the electrical driving signal, we can tune the ring spacings, the size of the central spot, and the working distance of the lens. The results presented here will enable researchers to employ dynamic Bessel beams generated by TAG lenses.     

Graded-index fiber lens proposed for ultrasmall probes used in biomedical imaging

The quality and parameters of probing optical beams are extremely important in biomedical imaging systems both for image quality and light coupling efficiency considerations. For example, the shape, size, focal position, and focal range of such beams could have a great impact on the lateral resolution, penetration depth, and signal-to-noise ratio of the image in optical coherence tomography. We present a beam profile characterization of different variations of graded-index (GRIN) fiber lenses, which were recently proposed for biomedical imaging probes. Those GRIN lens modules are made of a single mode fiber and a GRIN fiber lens with or without a fiber spacer between them. We discuss theoretical analysis methods, fabrication techniques, and measured performance compared with theory.     

Numerical calculation of the sound field focused by acoustic lens with an arbitrary axisymmetric sound speed distribution

The expressions that describe the sound field focused by an acoustic lens with different sound speed distribution (SSD) in lens are given. Numerical calculation results are presented, in which the axial and lateral sound pressure distributions and the -3 dB sound beam profile along the focused field are given out for three types of the acoustic focused lens with revolving-arc curved outer surface and four types' axisymmetric SSD. It is shown that, when sound beam is focused by a lens with SSD, the best focal point moves away from the lens and achieves a large focal region compared with the no-SSD case. The maximum axial focused intensity at the best focal point is smaller than that of the no-SSD case, but the focused beam width at the best focal point is larger than that of the no-SSD case. The larger the coefficient of the SSD, the larger the focused beam width and the larger focal region, but the divergent angle is almost the same.     

Mean focal length of an aberrated lens

We outline an approach for the calculation of the mean focal length of an aberrated lens and provide closed-form solutions that show that the focal length of the lens is dependent on the presence of defocus, x-astigmatism, and spherical aberration. The results are applicable to Gaussian beams in the presence of arbitrary-sized apertures. The theoretical results are confirmed experimentally, showing excellent agreement. As the final results are in algebraic form, the theory may readily be applied in the laboratory if the aberration coefficients of the lens are known.     

Focal shift and focal switch of partially coherent flat-topped beams passing through an alignment and misalignment lens system with aperture

The focal shift and focal switch of partially coherent flat-topped (PCFT) beams passing through a lens system with an aperture are studied in detail. We have shown that a focal shift is also present for beams propagating through an aligned optical system and the amount of the focal shift depends not only on the radius aperture of the focusing system, but also on the spatial coherence and order of the flat-topped beam of the incident partially coherent light. A new phenomenon called ‘focal switch’ occurs for misaligned optical systems, i.e. the focal shift experiences a sudden transition as the aligned optical system becomes misaligned, and the influence of the spatial coherence, order of flat-topped beam and aperture size reduction, on the focal switch is investigated in detail. Finally, the necessary conditions for the focal switch to take place are investigated.     

平顶多高斯光束通过球差透镜的聚焦特性

利用广义惠更斯-菲涅耳衍射积分公式,研究了平顶多高斯光束通过球差透镜的聚焦特性。推导出轴上光强分布的表达式,并对轴上光强进行大量的数值计算及分析。研究结果表明,当平顶多高斯光束的阶数N一定时,透镜的球差将在很大程度上影响光束的聚焦特性;当透镜的球差一定时,N值的改变将影响轴上最佳聚焦点的位置;当无球差时,轴上最佳聚焦点并不在几何焦点处,轴上最佳聚焦点位置随着N值增加向几何焦点靠近,例如当阶数N由0增大为1时,则归一化最佳聚焦点由0.91增大到0.98。