Finite-Element Analysis for Remote Field Eddy Current Responses from Near- and Farside Cracks

Results of three-dimensional finite-element analysis investigations of remote field eddy current (RFEC) signal responses from internal and external stress corrosion cracking (SCC) in steel pipes are presented. The fine shallow SCC cracks were simulated by double axial slits located on the near- and farside pipe surfaces under simulated RFEC excitation. Although it is normally a characteristic of RFEC testing that responses to interior or exterior defects are approximately equal, there is a considerable difference between the farside and nearside responses from very fine defects such as SCC cracks.     

Finite element modelling and physics of remote field eddy currentresponses for axially aligned cracks

A simplified physical model for two-dimensional (2-D) finite element analysis of axially aligned crack responses for the remote field eddy current (RFEC) technique is proposed. Two formulations are applied to model the problems. Reasonable agreement between calculated results and some preliminary experimental results is achieved. A hypothesis, based on the physical model, is presented. It explains the RFEC signals from axially aligned cracks and makes some predictions of possible features for future verification     

Multi-Helical Path Exploitation in Sparsity-Based Guided-Wave Imaging of Defects in Pipes

In this paper, a defect localization scheme for cylindrical pipes is presented which relies on guided-wave scattering by defects. The proposed scheme is predicated on the use of a sparse array of ultrasonic transducers and the sparse nature of defects on the pipe surface. Two circular rings of transducers, functioning as transmitters and receivers, are used to encompass the region to be inspected. Multiple helical paths exist for waves to travel from the transmitters to the receivers, after being scattered by the defects. Model based dictionary matrices are constructed for each path, relating the signals arriving at the receivers to the locations of potential defects. The resulting linear signal model is inverted by group sparse reconstruction to localize defects present in the pipe. Experimental validations of the proposed multi-helical path exploitation approach are provided for defects on an aluminum pipe.     

Longitudinal AC interactions with axial slits in steel pipes

The Remote Field Eddy Current (RFEC) nondestructive inspection technique uses low frequency AC and through wall transmission to inspect pipes and tubes from the inside. In steel pipes, it has generally greater sensitivity to circumferential rather than axial slits because the perturbation of magnetic fields orthogonal to slits dominates. Circumferential AC magnetic fields, generated by passing AC axially along a steel pipe from an external supply, have therefore been tested in order to give greater sensitivity to axially aligned cracks characteristic of stress corrosion cracking in pipe-lines. Anomalous source missing magnetization defect models suggest that, as slit widths are reduced, the importance of magnetic interactions is reduced until eddy current interactions predominate. This suggests that, for very fine axial cracks, true RFEC geometry, which gives circumferential eddy currents, will give stronger signals than circumferential AC magnetic fields.Research supported by Natural Sciences and Engineering Research Council of Canada, Pipetronix Ltd., and Gas Research Institute.     

Remote Field Eddy Current Control Using Rotating Magnetic Field Transducer: Application to Pressure Tubes Examination

The remote field eddy current (RFEC) technique is used to investigate the possibility of detecting the discontinuities practiced on pressure tubes samples from nuclear reactors, pressurized heavy water reactors (PHWR) type. In this article, we propose to develop the RFEC using the technique of rotating magnetic field (RMF). A method for calculating the field generated by the eddy current transducer with RMF using propagator matrix was developed. The experimental measurements are realized for artificial discontinuities practiced in pressure tubes samples.     

Transient Eddy Current NDE System Based on Fluxgate Sensor for the Detection of Defects in Multilayered Conducting Material

This paper describes a novel transient eddy current non destructive evaluation (NDE) system for the detection of defects in a multilayered conducting material by using fluxgate magnetometer as a sensor. In conventional eddy current NDE, the depth of defect detection is restricted due to the excitation frequency and its associated skin depth. Similarly, in conventional pulsed eddy current testing the time derivative of the secondary magnetic field, which decays much faster than the magnetic field itself, is measured by the induction coil. However, in this work we use fluxgate magnetometer which measures magnetic field directly and double “D” differential excitation coil in order to enhance the depth of investigation. In addition to this, the other instruments such as transmitter, transmitter controller and data acquisition system used for this work are the same one used for TEM based geophysical applications. The system has been used for the detection of an artificially engineered defect in an aluminum plate at a depth of 2 mm as well as 20 mm below the surface.     

Comparison of conventional,through-wall and remote field eddy current techniques

A through-wall eddy current system produces similar signals for defects of equal size, independent of the location of the defects in the sample being tested. The remote field eddy current technique is also reported to generate similar signals for equal defects, independent of the location of the defects in the wall of the tube which is being inspected. A theoretical study of an ideal conventional through-wall eddy current system is presented, and the results are compared with the results of a remote field eddy current system. It is shown that while the remote field system does not always obey the one-dimensional skin effect equation, it detects external material loss with nearly equal sensitivity to internal material loss. Experimental results are presented which show that the complex plane displays of similar ID and OD defects are similar in shape, size and orientation.     

Use of magnetically-saturated regions in remote field eddy current tools

The remote field eddy current (RFEC) technique is of potential interest for inspecting pipelines for stress corrosion cracking. Magnetic saturation techniques would allow higher operating frequencies and scanning speeds to be used. The use of selectively-saturated regions (windows) near the exciter and detector offers additional advantages. Finite element, analytic, and experimental measurements are presented in this paper. They show that, while saturation techniques are helpful, the effects are less than initially estimated from simple skin depth approximations.     

基于涡流成像的碳纤维增强树脂基复合材料细观结构可视化

对碳纤维增强树脂基复合材料（CFRP）的细观结构成像方法进行了研究,利用涡流成像技术实现了CFRP层合板中纤维方向及纤维缺失、褶皱和空隙过大等缺陷的可视化。首先通过有限元仿真和电路理论分析了CFRP板中涡流的生成机制和分布特性,阐述了基于涡流法的CFRP细观结构成像机制。然后介绍了用于扫描成像的高频涡流检测（HF-ECT）实验系统并确定了涡流探头的形式及其参数。最后利用涡流成像技术分别对单层板、正交层合板和四方向斜交层合板进行了检测,绘制了涡流检测（ECT）信号的三维伪彩图并得到了清晰的纤维纹路分布。通过引入滤波去噪技术和二维快速傅里叶变换（2D-FFT）对图像进行进一步处理,提高了图像分辨率并完成了不同方向上纤维纹路的分离,从而实现对层合板每单向层中缺陷的精确定位。     

飞机多层金属板隐藏缺陷远场涡流探头设计及试验研究

由于飞机多层金属板结构厚度大、复杂等特性,现有检测方法无法发现原位内部缺陷,对于多层板金属缺陷的检测一直都是航空无损检测的难题。远场涡流检测技术因打破趋肤效应的限制,涡流能量可穿透较厚的被测试件,对金属板结构中隐藏缺陷的检测具有潜在优势。该文针对飞机多层金属板隐藏裂纹的原位检测,建立多层金属板构件隐藏裂纹平面远场涡流检测有限元仿真模型,研究不同角度、不同深度裂纹检测幅值、相位的变化规律。为验证该仿真模型的正确性,开展远场涡流检测多层金属板的试验。试验结果表明:设计开发的远场涡流探头可检测埋深13 mm的裂纹缺陷,当裂纹倾斜角度为0°时,检测灵敏度最高,当裂纹倾斜角度为90°时,检测灵敏度最低,与仿真结果保持一致,且能够对缺陷进行精准定位,可为飞机多层金属板构件隐藏裂纹的定量检测提供依据。     

Markov chain Monte Carlo posterior density approximation for a groove-dimensioning purpose

The purpose of this paper is to present a new approach for measurand uncertainty characterization. The Markov chain Monte Carlo (MCMC) is applied to measurand probability density function (pdf) estimation, which is considered as an inverse problem. The measurement characterization is driven by the pdf estimation in a nonlinear Gaussian framework with unknown variance and with limited observed data. These techniques are applied to a realistic measurand problem of groove dimensioning using remote field eddy current (RFEC) inspection. The application of resampling methods such as bootstrap and the perfect sampling for convergence diagnostics purposes gives large improvements in the accuracy of the MCMC estimates.     

Extension of an absolute vector error correction technique to wideband, high-frequency measurements

The authors have previously demonstrated how a transmitter (Tx), a reciprocal transmitter/receiver (Tx/Rx) signal path and two unidirectional receiver (Rx) paths can be used together with short, open and load standards for the absolute vector error correction (AVEC) of a Tx/Rx module. Once calibrated, this Tx/Rx module can then provide accurate vector measurements of the signals that are flowing into and/or out of the test port. In order to simplify the analysis, the AVEC technique was applied to a simplified baseband circuit that did not include frequency conversion mixers in a previous paper. Now, in this paper the authors first show how the AVEC technique can be extended to the vector calibration of high-frequency receivers that involve frequency conversion mixers. The authors then show how to calibrate a system that allows for wideband absolute phase relationship measurements of periodic modulated signals, provided that the same local oscillator is employed for the two down-conversion receivers, and different radio frequencies and intermediate frequencies are employed in these receivers. This novel AVEC technique is one of the key concepts in the design of a wideband absolute vector signal measurement system, which overcomes the limitations of traditional measurement instruments by combining the features of vector signal analysers, spectrum analysers and vector network analysers.     

金属材料缺陷的电磁超声/涡流复合检测技术研究

电磁超声检测和涡流检测因其非接触、检测速度快、对试件表面要求低等优点而被广泛应用于金属材料的缺陷检测中,但电磁超声检测存在近表面的检测盲区,涡流检测对内部深层缺陷灵敏度不高。基于电磁超声和涡流的复合检测方法,设计了能同时满足电磁超声检测和涡流检测的复合式探头,建立了电磁超声和涡流复合检测有限元模型,并对金属试件中不同类型的缺陷进行了检测实验。仿真和实验结果表明,该复合探头不仅能快速检测表面裂纹,而且可激发出具有明显指向性的纵波,一定程度上削弱了波形转换产生的干扰波,可实现对内部缺陷的准确定位、识别,为电磁超声和涡流复合式检测技术在板材的复杂缺陷检测中的应用提供了基础。     

Geometrically anisotropic probes: an improved eddy current technique

Geometrically anisotropic eddy current probes are a type of separate function probes especially fit to the detection of defects showing a preferential direction. This kind of flaw induces a coupling between the transmitter and the receiver by guiding eddy currents from the one to the other. On the other hand, this coupling will be almost non-existent in the presence of defects or spurious effects not displaying this geometrical particularity. Basic studies on an elementary two-coil set-up allow the acknowledgment of the intrinsic qualities of such probes: good signal-to-noise ratio, influence field practically constant on the whole defect length, ability to detect bridged defects, insensitivity to lift off. These results can be improved by achieving multicoils probes adapted to different kinds of problems. An application to continuous casting slabs testing yields very interesting results in the detection of cracks, while getting rid of the effect of oscillation marks with no need of any signal processing. These achievements are promising for the improvement of eddy current testing, in terms of detection sensitivity as well as of rapidity to obtain information.     

Pulsed Eddy Current Testing of Carbon Steel Pipes’ Wall-thinning Through Insulation and Cladding

Pulsed eddy current testing of wall-thinning through cladding and insulation was studied from both theoretical and experimental aspects. The analytical solution was derived for a simplified four-layered structure and was used to conduct simulations to ascertain the feasibility of this method. A pulsed eddy current testing probe consisting of a circular excitation coil and an AMR-sensor-embedded differential detector was fabricated to measure the time-varying magnetic field signals on the axisymmetric excitation coil??s axis. The measurement system was able to measure magnetic field down to a few hundred micro-Gausses in an unshielded environment. Simulation and test results showed that over a certain time after turning off the excitation current the magnetic field signal??s decay behavior is almost merely relevant to the pipe??s wall thickness. Future development of a carbon steel pipe??s wall-thinning can be evaluated by using decay coefficients estimated from previously obtained test data.     

Transmitter pre-filtering for the downlink of a time-division-duplex/direct sequencecode division multiple access system over time-varying multipath fading channels

In this paper, we investigate an optimised transmitter pre-filtering technique for downlink time-division-duplex (TDD) code division multiple access (CDMA) communications, which employs the conventional matched filter (MF) detector at the mobile receivers. The proposed pre-filtering technique eliminates the multiple-access interference and intersymbol interference (MAI/ISI) effects by applying a very simple transmission scheme that combines a signal transformation with a cyclic prefix strategy under a power constraint condition. Two constrained pre-filtering transformations are suggested depending on the information required at the mobile unit. An open-loop transmitter pre-filtering is first formulated; however, this solution does not consider the properties of the noise at the mobile receiver. A second solution is then presented via a closed-loop transmitter pre-filtering that includes an optimum gain for a given transmit and noise power. Some associated issues such as system efficiency, computational complexity and channel estimation errors are also addressed. Simulation results show that the proposed transmitter pre-filtering scheme can be used to increase the system performance and capacity. In addition, its performance is compared with another similar transmit pre-processing scheme in order to evaluate the performance improvement by the proposed algorithm.     

钻柱信道内双声接收器的回波抑制方法分析

在随钻测井中地面噪声与周期性信道结构形成的下行回波导致传输性能降低,为此,结合钻柱信道的噪声分析,利用上、下行信道的瞬态脉冲响应,构建回波噪声抑制模型,提出了双声接收器的检测方式。在钻柱激励端分别施加单位正弦脉冲信号和PSK调制数据,在接收端耦合下行的高斯噪声,应用钻柱内一维低频纵波传输的有限差分算法,在单接收器和双接收器模式下时域和频域仿真分析了钻柱内声信号的传输特性,验证了双声接收器检测方式的有效性。该方法可实现井下回波噪声的抑制,从而改善信噪比,提高传输速率,为钻柱声遥测系统优化设计提供方法基础。     

Independent Component Analysis–Based Feature Extraction Technique for Defect Classification Applied for Pulsed Eddy Current NDE

With the development of nondestructive detection, the emerging testing techniques provide new challenges to signal analysis and interpretation approach applied to the inspection evaluation. Some researchers have developed the methods that focus on feature analysis of detected signals. This article presents a new feature analysis by the Independent Component Analysis (ICA) approach to evaluate the defects tested by the pulsed eddy current (PEC) technique. ICA is a high-order statistics technique used to separate multi-unknown sources, which has been successfully applied to facial image identification and separation of the components of 1D signal. In this article, the ICA approach is utilized to project the response signals of various defects into the independent components (ICs) feature subspace by signal representation model. Dependent on the selected ICs, each defect is represented by different projected coefficients, which are proposed to discriminate and classify the defects that belong to three categories. The improved ICA model is proposed to improve the classification of two similar categories of single defects: metal loss and subsurface defects. The evaluation using the series of experimental data has validated the classification of single defects and the defects with lift-off effect by our ICA approach. The comparison with Principal component analysis (PCA)–based approach further verified the better performance of the ICA-based model.     

A Methodology for the Evaluation of a GPS Receiver Performance in Telematics Applications

This paper presents a methodology to evaluate the position availability of automotive grade global positioning system (GPS) receivers intended for Telematics applications utilizing a multichannel GPS satellite signal simulator in a controlled laboratory environment. Initially, field testing of two distinct GPS receivers was conducted in an urban canyon environment and a foliage environment to assess each receiver's position availability performance. Test scenarios were then developed on a multichannel GPS satellite signal simulator in order to create controlled and repeatable stimuli to the GPS receivers. The scenarios take into account the actual satellite constellations at the same day, time, and locations of the field data collections. Furthermore, the number of visible satellites and power levels was adjusted in order to stimulate the hardware tracking sensitivity, hardware acquisition sensitivity, dynamic range, and navigation filter design, all of which impact position availability for GPS receivers. Quantitative results demonstrated good correlation between the results obtained using the developed test scenarios and the results from the field testing. The proposed methodology will result in reducing validation cost and time to market for automotive Telematics products     

钢管漏磁在线检测技术的研究

介绍了钢管漏磁检测的基本原理，对钢管在线漏磁检测系统进行总体设计。分析了漏磁场理论模型和讨论了影响缺陷漏磁信号的一些因素及补偿方法，针对该系统的特点设计了高速数据采集板，借助Windows系统平台，在所研制硬件的基础上，采用多线编程和虚拟设备驱动技术编制了数据采集、分析、状态显示、实时控制等面向对象、多功能模块化的软件，详细叙述了漏磁信号数据分析的方法和过程。这种系统具有检测速度快、数据吞吐量大、效率高、钢管缺陷分辨率高等特点。