基于光声信号的高铁钢轨表面缺陷检测方法

针对传统的基于超声信号的高铁钢轨无损检测方法对于表面微裂纹检测效果不佳的问题,提出了一种基于光声信号的高铁钢轨表面缺陷检测方法.首先,使用有限元及K-wave方法建立了钢轨模型并获得了模拟光声信号;然后利用时间反演的方法对钢轨表面的光声图像进行了重建,并研究了不同传感器中心频率对成像结果的影响;最后设计实验采集了钢轨表面的光声信号并进行了处理和分析.实验结果表明,基于光声信号的高铁钢轨表面缺陷检测方法对于表面微裂纹有很好的检测效果,该方法在钢轨探伤领域有较大的可行性及发展潜力.     

声光栅正弦结构光投射器的光学系统设计

针对一种新型的声光波干涉测量技术,对声光栅正弦结构光投射器的三维测量工作原理进行了系统的分析,讨论了影响投射器光学系统结构的因素和影响接收屏上的光照度的因素,并进行了光学系统设计。在优化设计过程中,采用了限制光线最大入射角的方法,达到控制投射系统的球差和保证接收屏上照明均匀的要求。所设计的声光栅正弦光投射器具有很好的成像质量。应用该系统对在500mm处的石膏像上投射干涉条纹,可以得到能量比较均匀、变形量很小的干涉条纹图,利用该条纹图和相关的算法可以对具有复杂几何形状的物体进行有效的三维测量。     

基于声学扫描振镜的超声/光声双模态成像技术

超声/光声双模态成像技术因其同时兼具超声的高分辨率结构成像和光声的高对比度功能成像优势,极大地推动了光声成像技术的临床应用推广.传统超声/光声双模态成像技术多基于超声成像所用阵列探头同时收集光声信号,系统结构紧凑且无需图像配准,操作便捷.但该类设备使用阵列探头和多通道数据采集,使得其成本较高;且成像结果易受通道一致性差异影响.本文提出了一种基于声学扫描振镜的超声/光声双模态成像技术,该技术采用单个超声换能器结合一维声学扫描振镜进行快速声束扫描,实现超声/光声双模态成像,是一种小型化、低成本的双模态快速成像技术.本文开展了系列仿体和活体成像研究,实验结果表明:系统有效成像范围为15.6 mm,超声和光声成像B扫描速度分别为1.0 s^–1和0.1 s^–1 (光声成像速度主要受制于脉冲激光器重复频率).基于本文所提技术研究,有助于进一步推动超声/光声双模态成像技术的临床转化和普及;也为基于超声信号检测的多模态成像技术提供了一种低成本、小型化和快速声信号检测的参考方案.     

基于维纳滤波反卷积的光声成像

为了提高光声成像(PAT)的对比度和分辨率,需对组织样品的光声(PA)信号进行基于探头脉冲响应的滤波反卷积以恢复其频谱特性.对宽带光声信号而言,由于带通滤波的截止频率由人为确定,噪声不能得到有效抑制,很难获得稳定的反卷积结果.针对此问题,提出了基于维纳滤波反卷积的光声成像方法,利用点光声源获得超声探头的脉冲响应.利用维纳滤波抑制反卷积过程中噪声的影响,滤波器参数由离散小波变换(DWT)动态估计,样品光声图像由时域后向投影算法重建.数值模拟与成像实验均表明该方法有效地抑制了噪声对反卷积的影响,提高了光声成像的对比度和分辨率.     

奥氏体不锈钢窄间隙焊缝侧壁未熔合相控阵超声检测*

针对核电站主管道奥氏体不锈钢窄间隙焊缝侧壁未熔合超声检测困难的问题,该文开展基于电子背散射衍射技术的相控阵超声检测研究,并结合全聚焦方法和相位相干成像方法抑制结构噪声。利用电子背散射衍射技术建立壁厚69.5 mm,且同时包含母材和焊缝的奥氏体不锈钢窄间隙焊缝模型。沿焊缝熔合线设置深度26.5 mm、高度3.0 mm的侧壁未熔合,经过仿真优化确定了中心频率2.25 MHz、32阵元以及45°纵波楔块的相控阵超声检测参数。仿真和实验检测结果显示,侧壁未熔合检测信噪比相差不超过0.6 dB,验证了所建模型的有效性。在此基础上,利用全聚焦方法和相位相干成像方法削弱结构噪声,检测信噪比较相控阵扇扫描图像分别提升2.3 dB和4.7 dB,且侧壁未熔合深度与高度定量误差均不超过6.7%。     

有限方位扫描的光声断层成像分辨率研究

通过有限元仿真实验,定量地研究了有限方位扫描对反投影光声断层成像分辨率的影响,并且给出了有限方位扫描角与分辨率之间关系的经验公式.本文的研究结果对光声成像扫描轨迹设计、成像效果评估等具有参考价值. 关键词： 光声成像 有限方位扫描 分辨率 断层成像     

基于光声成像的生物组织微结构定征研究进展

光声成像是一种新兴的复合型生物医学成像技术,它既具有光学成像丰富的光学对比度,又具有声学成像成像深度深、深层组织空间分辨率高的优点.作为一种非侵入式的成像技术,光声成像逐渐显现出极大的生物医学应用潜力.该文首先介绍了光声成像的物理机制,以及光声显微镜和光声计算机断层成像这两种典型的光声成像技术;然后讨论了从光声射频信号...     

奥氏体不锈钢焊缝中的声学仿真模型与全聚焦成像检测

声波在奥氏体不锈钢焊缝中传播时声束弯曲,为超声成像带来了困难。基于Ogilvy焊缝模型,建立了奥氏体不锈钢焊缝非均匀各向异性声场仿真模型,采用Dijkstra路径搜索算法对各向异性条件下的声传播路径和声传播时间进行了数值模拟和分析。在此基础上,采用Verasonics超声相控阵成像系统,进行了奥氏体不锈钢焊缝的全聚焦成像实验,采集全矩阵回波数据,并结合理论模型计算的声传播路径和相应的传播时间,进行了成像结果修正。结果表明,与均匀介质模型的全聚焦成像结果相比,基于该文模型的焊缝全聚焦成像检测结果具有更高的缺陷定位精度和分辨率,验证了该方法的可行性,为奥氏体不锈钢焊缝成像检测提供了新的思路。     

声速不均匀介质的光声成像重建算法

为提高声速不均匀介质的光声成像精度,提出一种基于反卷积的光声成像重建算法.本算法不需预先知道介质的声速分布.先通过探测到的光声信号构造出一个新函数,并用不同位置探测到的光声信号间的相关性来估计空间两点间的声波传播时间,以补偿声速的不均匀性.然后基于反卷积方法由该函数解出待测组织内的电磁波吸收分布.仿真研究结果表明,当介质声速差异在10%以内时,重建图像能正确反映待测目标的大小、位置和电磁波吸收系数,算法具有良好的抗噪性能.由于生物软组织内的声速差异一般小于10%,因此本算法是一种有效的光声成像重建算法.     

用于超声悬浮场可视化的光学全息相位倍增方法研究

基于二次曝光全息干涉测量原理,采用四倍相位倍增光路对声悬浮声压场分布进行了可视化研究.拍摄了给定模式的超声悬浮场在不同超声换能器激励电流时的光学全息图并进行光学再现,由再现光波的全息干涉条纹图样得到了反映声压场分布的光波波前相位变化,并进行了对比分析.结果表明,与无相位倍增光路相比,采用四倍相位倍增光路可使同一声压场的全息干涉条纹数目大大增加,测量灵敏度明显提高,为进一步研究声悬浮场声压分布提供了一种有效方法.     

Fusion of conventional ultrasound imaging and acousto-optic sensing by use of a standard pulsed-ultrasound scanner

Acousto-optic sensing (AOS) is a dual-wave sensing technique based on the ultrasound modulation of diffuse light in a turbid medium. We experimentally demonstrate the feasibility of combining AOS and conventional ultrasound imaging by use of a commercially available pulsed-ultrasound scanner coupled with a photorefractive crystal-based optical interferometry system. Optically absorbing targets embedded in highly diffusive phantoms (mus'= 10 cm(-1)) are imaged through a thickness of 27 mm with millimeter resolution. The acousto-optic images are intrinsically coregistered with the ultrasound images.     

基于自衍射效应的自参考光谱干涉方法的研究

研究一种基于非线性透明光学介质中的自衍射和自参考光谱干涉的新方法来进行飞秒激光脉冲测量. 实验中, 基于此新方法设计一种简单装置, 对800 nm 中心波长, 约40 fs 近无啁啾飞秒激光脉冲进行测量, 并与自参考光谱相干电场重建法测量结果进行比较, 得到了一致的结果. 此新方法与相应的装置结构简单, 可以对深紫外到中红外光谱范围的飞秒脉冲进行测量. 关键词： 飞秒激光脉冲 自参考光谱干涉 自衍射 脉冲测量     

Detection of ultrasound-modulated photons in diffuse media using the photorefractive effect

Ultrasound-modulated optical tomography is a dual-wave sensing technique in which diffusive light in a turbid medium interacts with an imposed acoustic field. A phase-modulated photon field emanates from the interaction region and carries with it information about the optomechanical properties of the medium. We present a technique for detection of ultrasound-induced optical phase modulation using an adaptive, photorefractive-crystal-based interferometry system. Experimental results are presented demonstrating detection of ultrasound-modulated signals in highly scattering media by use of pulsed ultrasound insonation.     

Monitoring stress changes in a concrete bridge with coda wave interferometry

Coda wave interferometry is a recent analysis method now widely used in seismology. It uses the increased sensitivity of multiply scattered elastic waves with long travel-times for monitoring weak changes in a medium. While its application for structural monitoring has been shown to work under laboratory conditions, the usability on a real structure with known material changes had yet to be proven. This article presents experiments on a concrete bridge during construction. The results show that small velocity perturbations induced by a changing stress state in the structure can be determined even under adverse conditions. Theoretical estimations based on the stress calculations by the structural engineers are in good agreement with the measured velocity variations.     

Implementation of the Laser Diffraction Technique for Acoustic Cavitation Bubble Investigations

Knowledge of the acoustic cavitation cloud would be useful for improving ultrasound reactor design. Among the characterisation techniques, few are adapted to bubble investigations in an intense ultrasound field. Some problems raised by these measurements result from interactions between the acoustic pressure wave and the measuring light wave. This paper reports the implementation of the laser diffraction technique to determine the size and volume concentration of bubbles generated by a dipping horn operating at 20 kHz. Measurements were performed with a Malvern 2600 instrument. The size distribution, deduced from the diffraction pattern scattered by the bubble cloud crossed by a laser beam, is disturbed by the acoustic pressure wave involving deviation of a light beam at low diffusion angles (acousto‐optic effect). A bubble size correction procedure based on the subtraction of the light energy due to the ultrasound wave is described. The size measurements, and thus the correction procedure, were validated by a second laser technique based on a different measuring principle: phase Doppler interferometry. The measurement reliability was further confirmed by an original application of laser diffraction based on measurements performed just after sonication. These three methods lead to a mean bubble size (Sauter mean diameter) of about 10 μm at a high ultrasound power input. Concerning the void fraction, only measurements achieved after sonication and by laser diffraction predict a correct estimation of this parameter.     

Femtosecond holographic interferometry for studies of semiconductor ablation using vanadium dioxide film

A recording medium based on the phenomenon of phase transition from semiconductor to metal is applied to holography in the femtosecond time domain. The results of holographic interferometry studies of semiconductor ablation are presented.     

Dual-modal photoacoustic/CT imaging system

Photoacoustic(PA) tomography(PAT) breaks the barrier for high-resolution optical imaging in a strong lightscattering medium, having a great potential for both clinical implementation and small animal studies. However,many organs and tissues lack enough PA contrast or even hinder the propagation of PA waves. Therefore, it is challenging to interpret pure PAT images, especially three-dimensional(3 D) PA images for deep tissues, without enough structural information. To overcome this limitation, in this study, we integrated PAT with X-ray computed tomography(CT) in a standalone system. PAT provides optical contrast and CT gives anatomical information. We performed agar, tissue phantom, and animal studies, and the results demonstrated that PAT/CT imaging systems can provide accurate spatial registration of important complementary contrasts.     

光声成像技术的最新进展

光声成像技术是生物医学领域中新兴的无损检测技术,具有对比度高、分辨率好、穿透能力强等优点.本文介绍了光声成像技术近年来的进展状况,主要涉及成像探测方式的改进、成像速度的加快、成像分辨率的提高以及图像重构算法的发展等.以该项技术在现代临床诊断中的应用为例,描述了其在生物医学领域中应用范围的拓宽.最后,总结了该项技术现存的...     

Use of speckle interferometry and modal assurance criterion for identification of component modes

One of the problems encountered in performing modal analysis is the identification of different modes occurring at close natural frequencies. This paper proposes to face such a problem by an original application of the modal assurance criterion (MAC) that is typically used to verify the reliability of numerical structural models by evaluating the correspondence between numerical and experimental mode shapes. To properly apply the MAC, experimental mode shapes must be retrieved acquiring data at a high number of experimental points suitably distributed on the surface of the structure. Using usual modal analysis techniques based on pointwise transducers, difficulties can be encountered to retrieve mode shapes with the required spatial resolution. In order to overcome such difficulties, Speckle interferometry techniques can be used. This paperproposes a procedure based on the application of a highly reliable MAC evaluated by time average Speckle interferometry for recognising the modes contributing to the stationary vibration patterns. The results obtained from the modal analysis of a thin square plate have shown that the proposed procedure is capable of pointing out the component modes.     

U-shaped optical fiber sensor based on multiple total internal reflections in heterodyne interferometry

In this paper, an optical fiber sensor based on multiple total internal reflections (MTIRs) in heterodyne interferometry is proposed. With the optical fiber sensor the phase shift difference due to the multiple total internal reflections effect between the p- and s-polarizations is measured by using heterodyne interferometry. Substituting the phase shift difference into Fresnel's equations, the refractive index for the tested medium can be calculated. The resolution of the sensor can reach 1.6×10^?6 refractive index unit (RIU). The optical fiber sensor could be valuable for chemical, biological and biochemical sensing. It has some merits, such as, high resolution and stability, high sensitivity, high resolution and real-time measurement.