Real-time photodisplacement microscope for high-sensitivity simultaneous surface and subsurface inspection

We have developed a new photodisplacement microscope system for practical use that achieves high-sensitivity simultaneous real-time imaging of surface and subsurface structures from a single space-frequency multiplexed interferogram. In this system a linear region of photothermal displacement is excited on the sample surface for subsurface imaging by a line-focused intensity-modulated laser beam. Surface information such as reflectivity and topography along with the displacement is detected with a charge-coupled device sensor-based parallel heterodyne interferometer. Surface and subsurface information components are space-frequency multiplexed into the sensor signal as orthogonal functions based on a frequency-optimized undersampling scheme, allowing each to be discretely reproduced by using a real-time Fourier analysis technique. Preliminary experiments demonstrate that this system is effective, simultaneously imaging reflectivity, topography, and photodisplacement for the detection of subsurface lattice defects in silicon, at a remarkable speed of only 0.26 s/256x256 pixel area. This new microscope is promising for nondestructive hybrid surface and subsurface inspection and other applications.     

Circuit for detecting defects in insulating coatings

The block diagram of a microcomputer-based instrument for inspection of insulation coatings in buried pipelines is described. Mathematical expressions for the design of its component parts are derived.Translated from Izmeritel'naya Tekhnika, No. 11, pp. 49–51, November, 1994.     

An optical technique for detecting defects in thin plates and diaphragms

A non-destructive test is proposed for thin plates and diaphragm elements that consists of recording the images of a coarse grating reflected by the plates or elements when they are laterally loaded. A defective region is indicated by an obvious distortion of the lines constituting the grating image.     

Improving instrument reliability by detecting latent component defects

A method of observing latent defects is proposed in the form of electrical parameters of components exceeding permissible bounds. Translated from Izmeritel'naya Tekhnika, No. 3, pp. 24–26, March, 1996.     

Three-dimensional reconstruction of subsurface defects using finite-difference modeling on pulsed thermography

We develop a technique to analyze pulsed thermography videos in order to detect and reconstruct subsurface defects in homogeneous and layered objects. The technique is based on the analysis of the thermal response of an object to a heat pulse. This thermal response is compared to the predictions of a finite-difference model that is systematically and progressively adjusted to minimize a cost function. With this minimization process, we obtain a depth and a thickness function that allow us to determine the three-dimensional shape, size, depth, thickness, and location of internal defects. The detected defects are reliably reconstructed with graphics of easy interpretation.     

NDTE using pulse thermography: Numerical modeling of composite subsurface defects

The ability to predict subsurface defect information in composite materials through a non-invasive, efficient inspection protocol is fast becoming a vital research area. In numerically modeling the thermographic process associated with an infrared (IR) technique we can afford inspectors the ability to predict subsurface defect information associated with a specific material configuration. The research involved in this study looks specifically at the finite element modeling (FEM) of delaminations in a composite flat plate setup. To date the modeling of delaminations has been restricted to only two dimensional (2D) numerical representations and associated primarily with rear faced detection. The results of this research, however, clearly show that the rear faced detection technique has limitations in defect depth prediction and the 2D approximation associated with this technique ignores a paramount effect in the form of lateral thermal diffusion. It is also made clear that the representation of experimental flat plate models with flat bottomed holes, under pulse phase thermographic inspection, in simulating delaminations is misguided.     

Extended bidirectional reflectance distribution function for polarized light scattering from subsurface defects under a smooth surface

By introducing the scattering probability of a subsurface defect (SSD) and statistical distribution functions of SSD radius, refractive index, and position, we derive an extended bidirectional reflectance distribution function (BRDF) from the Jones scattering matrix. This function is applicable to the calculation for comparison with measurement of polarized light-scattering resulting from a SSD. A numerical calculation of the extended BRDF for the case of p-polarized incident light was performed by means of the Monte Carlo method. Our numerical results indicate that the extended BRDF strongly depends on the light incidence angle, the light scattering angle, and the out-of-plane azimuth angle. We observe a 180 degrees symmetry with respect to the azimuth angle. We further investigate the influence of the SSD density, the substrate refractive index, and the statistical distributions of the SSD radius and refractive index on the extended BRDF. For transparent substrates, we also find the dependence of the extended BRDF on the SSD positions.     

A method based on small amplitude homogenization for detecting defects using elastic waves

This work is concerned with the resolution of inverse problems for the detection of defects inside a medium using the propagation of elastic waves, under the assumption of small contrast on the value of the stiffness between the matrix material and that of the defect. This is the so-called small amplitude, small contrast or small aspect ratio assumption. Following the framework developed for optimal design problems, we consider a formal second order asymptotic expansion with respect to the aspect ratio, which allows us to simplify the inverse problem considering it as an optimization problem. According to this and through solving the wave equation in the time domain, we can develop a gradient type algorithm that reduces, in the time interval being considered, the difference between the boundary values obtained from a problem with certain defect distribution that is numerically solved and those values obtained from an assumption on the distribution of the defect. An adaptive procedure is presented for locating the wave source in order to improve the results.     

一种扬声器异常音的时域特征检测方法

扬声器的异常音故障常见于生产过程中,通常可由有经验的听音员凭人耳听音检测出来。与人耳听测异常音的机理类似,一种在时域检测异常音的方法被提出。通过对声响应信号进行经验模态分解得到本征模态函数,再根据本征模态函数与激励信号的瞬时频率差对各模态去混淆处理,可得到包含异常振动信息的模态函数,据此可判断是否存在异常音。算法验证分为仿真和实验两部分。仿真验证中分析了模拟的合格扬声器与故障扬声器的声响应,结果表明算法对于摩擦和碰触导致的异常音是灵敏的。实验验证中检测了20只扬声器,测量得到的故障频率与用高阶谐波失真法得到的结果一致。且对于不同异常音故障,可在经验模态函数的局部特征中观察到不同的时域特征。     

Time dependent temperature fields and stress interactions with subsurface or surface breaking defects

A fundamental solution is developed which has a jump in temperature 2T ₀ H(t–t ₀) on a semi-infinite cut (a transient thermal dislocation) together with continuous traction and displacement fields. This solution is used together with fundamental elastic dislocation solutions to study the interaction of time dependent temperature fields with subsurface or surface breaking cracks. Potential applications of this analysis to the problem of the influence of surface temperatures on delamination theories of wear and the photodisplacement and photothermal imaging methods are discussed.     

Evaluation study of the effectiveness of the integrated genetic-algorithm-based strategy for the tomographic subsurface detection of defects

An assessment is presented of the integrated genetic-algorithm strategy based on a numerically computed Green's function for subsurface inverse scattering problems arising in nondestructive evaluation/testing industrial applications. To show the effectiveness and current limitations of such a microwave technique in dealing with various scenarios characterized by lossless and lossy host media as well as in noisy environments, several numerical experiments are considered. The results obtained confirm the effectiveness of the approach in fully exploiting the available a priori information through a suitable scattering model, which allows a nonnegligible enhancement of the reconstruction accuracy as well as a reduction of the overall computational burden with respect to standard imaging approaches.     

High-resolution photothermal microscope: a sensitive tool for the detection of isolated absorbing defects in optical coatings

The photothermal deflection technique allows us to highlight the presence of inhomogeneities of absorption in optical components. This nondestructive tool is of great interest to the study of the role of contaminants, inclusions, and impurities in the laser-induced damage process. We show that the detection of nanometer-sized isolated absorbing defects requires the development of an adapted photothermal setup with high detectivity and high spatial resolution. Thus it is essential to improve the resolving power up to its theoretical limit.     

Rapid subsurface detection of nanoscale defects in live microprocessors by functional infrared emission spectral microscopy

We demonstrate the rapid and nondestructive detection of subsurface nanometer-size defects in 90 nm technology live microprocessors with a new technique called functional infrared emission spectral microscopy. Broken, leaky, and good transistors with similar photoemission images are identified from each other by their different emission spectra that are calculated as linear combinations of weighted basis spectra. The basis spectra are derived from a spectral library by principal component analysis. Leaky transistors do not exhibit apparent morphological damage and are undetectable by optical or scanning probe microscopy alone. The emission signals from two or more transistors combined incoherently, and defect detection is primarily limited by the signal-to-noise ratio of the detected spectrum and not by the separation distance of neighboring transistors.     

The use of X-radiography and computer software for detecting defects during the manufacture of steel-belt tyres

This paper describes an algorithm which can be incorporated into a real-time X-ray system to detect defects characteristics of steel belt tyres. The algoritm is based on the Fourier transform, which permits, by power spectrum analysis, the detection of deviations in the steel cord pattern from the normal structure. The algorithm can be used as a real-time method during the preliminary stage of rubber sheet production, or for inspection of the final product.     

基于短时傅里叶变换的异常音检测方法

提出一种基于短时傅里叶变换的扬声器异常音检测方法,该方法首先对由扫频信号激励的扬声器声响应信号进行短时傅里叶变换,然后根据扬声器异常音信号的特点将所获得的时频图分割为若干区域,并提取各个区域内的时频图所对应的矩阵,最后通过计算被测扬声器声响应信号所对应区域内的矩阵与黄金样品所对应的矩阵之间的距离来判断该扬声器是否存在异常音。还简要介绍了基于该方法实现的扬声器异常音在线检测仪,实验室及企业生产线初步检验结果表明,该方法简单有效,可用于部分种类扬声器的异常音在线检测。     

低温扫描隧道显微镜(LT-STM)的调试技术

本文介绍了低温扫描隧道显微镜(LT-STM)的结构特点,该设备由真空系统、低温系统、扫描和数据采集系统、电源控制系统、控制计算机等组成,该实验设备具有高性能、高精度的特点,对实验人员的实验技能要求很高.我们结合它的使用对其调试方法进行了分析、探讨和总结,其实验结果证明了这种调试方法的正确性和可行性,为今后调试同类实验设备提供了可靠的经验.     

Three-dimensional observation of defects in nitrogen-doped 6H-SiC crystals using a laser scanning confocal microscope

Different defective structures of nitrogen-doped 6H-SiC single crystals were examined using a combination of laser scanning confocal microscopy (LSCM), scanning electron microscope (SEM) and KOH–K₂CO₃ etching. The form, depth and size of the defects in etched silicon carbide (SiC) crystals were observed by LSCM. Using these 3D LSCM images, defective structures varying in the growth direction were observed from a side view for the first time. To study the size, depth and form of defect etch pits in detail, we observed the defect etch pits configuration in some volumes through taking 3D LSCM pictures. Information on defects obtained using this approach will be very helpful for investigation of MP and SD formation mechanism in conducting SiC substrates, as well as the observation of polytype stability in nitrogen-doped SiC crystals.     

A step towards development of aid for visually challenged

The work done towards developing a visual aid to help visually challenged people is described in this paper. An ultrasonic device is used for measuring the distance to a nearby object and SIFT algorithm based approach is used for object recognition from the captured image. Features of the recognized object as well as the distance to the object are converted to voice output which is available to the visually challenged person for navigation. The system developed and results obtained are described and suggestions are given for further work to be done to develop a better and more compact visual aid.