New techniques of local damage detection in machinery based on stochastic modelling using adaptive Schur filter

Vibration signal analysis is one of the most effective techniques of monitoring machinery and detecting local damage in their parts, e.g. bearings and gearboxes. However, such detection is sometimes difficult, especially in heavy industrial machines, because of a small proportion of damage-induced components in relation to the remaining components of registered signals. Therefore, more effective signal processing algorithms are being looked for. Moreover, local damage (cracking, pitting, spalling, breakage, etc.) in bearings and gearboxes generates broad-spectrum impulse signals, while the other type can be effectively modelled as a sum of narrowband signals. In this article, techniques based on Schur adaptive filter are proposed for local damage detection. In such an approach, the analysed signal is modelled by means of autoregressive process and the filter is described by so-called reflection coefficients. Schur algorithm is an effective algorithm with very good numerical properties and it is capable of tracking rapid changes in second order statistics of the analysed signal. Thus, the method is well-suited to analysing non-stationary signals and it is potentially interesting for use in bearing and gearbox monitoring.Reflection coefficients describing the signal model, defined with the use of Schur algorithm, may be applied in a variety of ways, giving a chance of employing different solutions in different conditions. In the first proposed solution, detection is based on the weighted sum of derivatives of reflection coefficients, while in the other one – on new signal obtained as power in frequency bands calculated from a parametric spectrogram, whose starting point are reflection coefficients. All these operations are aimed at enhancing changes that occur in the signal at the moments when damage-induced impulses appear. The article also presents guidelines for methods of determining parameter values in the employed analyses. The proposed solutions have been applied for analysing signals coming from a two-stage gearbox of a large machine driving a mining belt conveyor and the obtained results were analysed. They prove the effectiveness of the proposed techniques. It is worth emphasizing that these techniques can be easily adapted for monitoring machinery in varying operating conditions.     

Acoustic-based damage detection method

Most of the structural health monitoring (SHM) methods is either based on vibration-based and contact acoustic emission (AE) techniques. Both vibration-based and acoustic emission techniques require attaching transducers to structure. In many applications, such as those involving hot structural materials for thermal protection purposes or in rotating machines, non-contact measurements would be preferred because the operating environment is prohibitive leading to potential damage in contact sensors or their attachments. In this paper, a new non-contact, acoustic-based damage detection method is proposed and tested with an objective that the proposed method is able to detect the location and extend of damage accurately. The proposed acoustic-based damage detection method is a direct method. In this proposed method, changes in vibro-acoustics flexibility matrices of the damage and health structure are used to predict the location and extend of damage in the structure. A case study involving actual measured date for the case of a fixed–fixed plate structure is used to evaluate the effectiveness of the proposed method. The results have shown that the proposed acoustic-based damage detection method can be used to detect the location and extend of the damage accurately.     

Nonlinear acoustic techniques for landmine detection

Measurements of the top surface vibration of a buried (inert) VS 2.2 anti-tank plastic landmine reveal significant resonances in the frequency range between 80 and 650 Hz. Resonances from measurements of the normal component of the acoustically induced soil surface particle velocity (due to sufficient acoustic-to-seismic coupling) have been used in detection schemes. Since the interface between the top plate and the soil responds nonlinearly to pressure fluctuations, characteristics of landmines, the soil, and the interface are rich in nonlinear physics and allow for a method of buried landmine detection not previously exploited. Tuning curve experiments (revealing "softening" and a back-bone curve linear in particle velocity amplitude versus frequency) help characterize the nonlinear resonant behavior of the soil-landmine oscillator. The results appear to exhibit the characteristics of nonlinear mesoscopic elastic behavior, which is explored. When two primary waves f1 and f2 drive the soil over the mine near resonance, a rich spectrum of nonlinearly generated tones is measured with a geophone on the surface over the buried landmine in agreement with Donskoy [SPIE Proc. 3392, 221-217 (1998); 3710, 239-246 (1999)]. In profiling, particular nonlinear tonals can improve the contrast ratio compared to using either primary tone in the spectrum.     

基于不同作用体制的激光引信探测技术

随着激光技术的飞速发展,半导体激光传感器已被广泛应用于近炸引信领域。对目前广泛使用的激光近炸引信体制中的几何截断定距、距离选通定距、脉冲鉴相定距以及伪随机编码定距的原理、特点进行了分析,指出了每种体制的局限性,为应用在具体背景下的激光近炸探测体制的选择提供了一定的参考价值。     

安全检测技术中的物理学原理

安检技术对爆炸事件的预测预警起着至关重要的作用,而物理学原理在安全检测技术领域中有非常重要的应用.本文主要介绍了X射线检测技术、太赫兹光谱技术、红外线光谱技术、拉曼光谱和表面增强拉曼光谱技术、离子迁移谱技术等几种常用或最新的安全检测技术中的物理学原理,并期待物理学在安检技术领域做出新的贡献.     

Quantum dots investigated with charge detection techniques

The detection of the quantum dot charge state using a quantum point contact charge detector has opened a new exciting route for the investigation of quantum dot devices in recent years. In particular, time-resolved charge detection allowed the precise measurement of quantum dot shot noise at sub-femtoampere current levels, and the full counting statistics of the current. The technique can be applied to different material systems and holds promise for future application in quantum dot based quantum information processing implementations. We review recent experiments employing this charge detection technique, including the self-interference of individual electrons and back-action phenomena.     

Fatigue damage detection using a speckle-contrast technique

An optical setup based on speckle-contrast measurement is proposed as an alternative to analyze fatigue damage on surfaces of metal samples. Based on the dispersion of the light, generated by a laser beam reflected by the surface, roughness and fatigue damage are analyzed after a specially designed fatigue test of metallic samples. The experimental results are obtained from an aluminum alloy type A319 modified with strontium with nodular silicon precipitates that was subjected to a fatigue procedure based in the norm ASTM E647.     

Combined X-ray-electron imaging techniques: Limitations on lateral resolution

Capabilities of the imaging techniques, in which X-rays are converted to electrons and then the emitted electrons are registered by means of an electron microscope, are analyzed, the focus being on the factors limiting lateral resolution at the stage of electron emission. Bearing in mind the tendency to use harder synchrotron X-rays for some combined X-ray-electron microscopy methods, calculations were made for two significantly different X-ray energies: E = 1.828 keV (K-edge of Si) and E = 11.923 keV (L₃-edge of Au). By using Monte Carlo simulations of the electron trajectories beneath the surface of the sample we show that the radius of the spot from which photoelectrons are emitted could be as small as 1 nm. However, when proper account is taken of an entire electron cascade associated with the re-building of electron shells after photoelectron emission, spots more than one order of magnitude larger result, limiting the best lateral resolution to 20–30 nm.     

On the performance of correlation-based packet detection techniques

This work studies the performance of packet detection techniques in wireless systems where nodes transmit in a sporadic and asynchronous manner. Modeling a transmitter as a M/D/1 queue and focusing on a correlation-based approach, we derive exact expressions for the detection probability and false alarm rate at the receiver under AWGN conditions for any packet generation rate. Very tight approximations are also provided, and the performance of the correlator is compared to that of a likelihood-ratio-test solution. A significant aspect that has been frequently overlooked in literature is the necessity of addressing false alarms that may be caused by the data portion of sent messages. This factor has emerged in this work as a key consideration.     

Study of bubble damage detectors for neutron detection

Bubble damage detectors have been prepared by using polyacrylamide as detector solid and freon as detector liquid. Tests show that the prepared detectors are sensitive to fast neutrons and have proportionality between bubble number and neutron fluence within a certain range of neutron fluence. Therefore, it can be used as a fast neutron detector and a dosimeter. Our experiments also show that the sensitivity of the detector increases with temperature.     

Fabry-Perot干涉技术及其在疲劳损坏检测中的应用

从激光超声的特点出发,分析目前主要的超声检测技术,重点研究Fabry-Perot干涉仪的原理和工程应用。共焦Fabry-Perot干涉仪具有只对固体表面的振动速度灵敏、有较大的入射孔径、集光能力强等优点,克服了其它干涉检测技术对工作环境的严格要求,广泛应用于工业生产中。为检测碳钢的疲劳破坏,设计了一个激光超声检测系统,分析不同超声频率和加载不同循环压力造成的疲劳损坏情况。     

卫星太阳能电池阵破损自动检测系统的研究

介绍了国内首次研制的卫星太阳能电池阵破损自动检测系统的检测原理、系统结构与设计及现场试用结果。系统采用专用照明系统,电池阵列经光学系统清晰成像至CCD传感器上,经信号放大、A/D转换后输入计算机管理和控制系统。图像传感探头自动扫描整块电池板,并由距离传感器控制,始终保持采集图像清晰。利用特有的系统控制和检测软件,处理每幅电池图像信息,检测结果通过列表形式给出损伤电池的位置、破损类型、破损度等参数。现场试验结果表明:该系统的检出率达98.5%以上,检测速度为每分钟20片电池,达到了快速、高精度、自动化检测太阳能电池阵的使用要求。     

卫星太阳能电池阵破损自动检测系统的研究

介绍了国内首次研制的卫星太阳能电池阵破损自动检测系统的检测原理、系统结构与设计及现场试用结果。系统采用专用照明系统,电池阵列经光学系统清晰成像至CCD传感器上,经信号放大、A/D转换后输入计算机管理和控制系统。图像传感探头自动扫描整块电池板,并由距离传感器控制,始终保持采集图像清晰。利用特有的系统控制和检测软件,处理每幅电池图像信息,检测结果通过列表形式给出损伤电池的位置、破损类型、破损度等参数。现场试验结果表明:该系统的检出率达98.5%以上,检测速度为每分钟20片电池,达到了快速、高精度、自动化检测太阳能电池阵的使用要求。     

Sensitivity analysis of an auto-correlation-function-based damage index and its application in structural damage detection

Structural damage detection using time domain vibration responses has advantages such as simplicity in calculation and no requirement of a finite element model, which attracts more and more researchers in recent years. In present paper, a new approach to detect the damage based on the auto correlation function is proposed. The maximum values of the auto correlation function of the vibration response signals from different measurement points are formulated as a vector called Auto Correlation Function at Maximum Point Value Vector, AMV for short. The relative change of the normalized AMV before and after damage is used as the damage index to locate the damage. Sensitivity analysis of the normalized AMV with respect to the local stiffness shows that the normalized AMV has a sharp change around the local stiffness change location, which means the normalized AMV is a good indicator to detect the damage even when the damage is very small. Stiffness reduction detection of a 12-story frame structure is provided to illustrate the validity, effectiveness and the anti-noise ability of the proposed method. Comparison of the normalized AMV and the other correlation-function-based damage detection method shows the normalized AMV has a better detectability.     

Statistical techniques for target detection in polarization diversity images

We address the problem of target detection in active polarimetric images. This technique, which has the appealing feature of revealing contrasts that do not appear in conventional intensity images, provides several images of the same scene. However, because of the presence of nonhomogeneity in the reflected intensity, it is preferable to perform target detection on the orthogonal-state contrast image, which is a measure of the degree of polarization of the reflected light when the coherency matrix is diagonal. We show that one can determine a simple nonlinear transformation of this orthogonal-state contrast image that leads to additive noise, and we then propose a simple and efficient technique for detecting targets in these images.     

向长波方向发展的光子数分辨探测技术

研究了光子数分辨探测器技术发展的物理基础,技术现状和发展趋势.重点分析了目前能达到单光子分辨的发展中的三种探测技术：越界超导传感技术（superconducting transition-edge sensor）,电荷积分单光子探测技术(charge integration photon detection)和雪崩光电二极管单光子分布探测技术(delayed single photon probability mapping based on avalanche photodiode),讨论了探测器的光子数分辨能力及其噪音来源.     

向长波方向发展的光子数分辨探测技术

研究了光子数分辨探测器技术发展的物理基础，技术现状和发展趋势．重点分析了目前能达到单光子分辨的发展中的三种探测技术：越界超导传感技术（superconducting transition-edge sensor），电荷积分单光子探测技术（charge integration photon detection）和雪崩光电二极管单光子分布探测技术（delayed single photon probability mapping based on avalanche photodiode），讨论了探测器的光子数分辨能力及其噪音来源．     

Signal detection techniques for scattering-type scanning near-field optical microscopy

Scattering-type scanning near-field optical microscopy (s-SNOM) has been playing more and more important roles in investigating electromagnetic properties of various materials and structures on the nanoscale. In this technique, a sharp tip is employed as the near-field antenna to measure the sample's properties with a high spatial resolution. As the scattered near-field signal from the tip is extremely weak and contaminated by strong background noise, the effective detection, and subsequent extraction of the near-field information from the detected signals is the key issue for s-SNOM. In this review, we give a systematic explanation of the underlying mechanisms of s-SNOM, and summarize and interpret major signal detection techniques involved, including experimental setups, theories for signal analysis and processing, and exposition of advantages and disadvantages of such techniques. By this, we hope to provide a practical guide and a go-to source of detailed information for those interested in and/or working on s-SNOM.     

Large amplitude vibrations and damage detection of rectangular plates

In this work, geometrically nonlinear vibrations of fully clamped rectangular plates are used to study the sensitivity of some nonlinear vibration response parameters to the presence of damage. The geometrically nonlinear version of the Mindlin plate theory is used to model the plate behaviour. Damage is represented as a stiffness reduction in a small area of the plate. The plate is subjected to harmonic loading with a frequency of excitation close to the first natural frequency leading to large amplitude vibrations. The plate vibration response is obtained by a pseudo-load mode superposition method. The main results are focussed on establishing the influence of damage on the vibration response of the plate and the change in the time-history diagrams and the Poincaré maps caused by the damage. Finally, a criterion and a damage index for detecting the presence and the location of the damage is proposed. The criterion is based on analysing the points in the Poincaré sections of the damaged and healthy plate. Numerical results for large amplitude vibrations of damaged and healthy rectangular and square plates are presented and the proposed damage index for the considered cases is calculated. The criterion demonstrates quite good abilities to detect and localize damage.     

Acoustic detection of invisible damage in aircraft composite panels

The wing and body panels of modern commercial and military aircraft often consist of a three-layer structure in which two thin skins of fibre-reinforced composite or of aluminium are held apart by a much thicker core consisting of a honeycomb structure made from either folded paper-like material impregnated with aramid resin or from thin, folded aluminium sheet. A major maintenance inspection problem arises from the fact that impact by a heavy soft object has the potential to deflect the skin and damage the core, after which the skin can return to its original shape so that the defect is nearly invisible. This paper gives details of an acoustic inspection system that can reveal such damage and provide information on its nature and size using a hand-held “pitch-catch” device that can be scanned over the suspected area to produce a visual display on a computer screen. The whole system operates in the frequency range 10-30 kHz and embedded programs provide optimal examination procedures.