Showing papers by "Gui Yun Tian published in 2008"

Feature extraction and selection for defect classification of pulsed eddy current NDT

Abstract: Pulsed eddy current (PEC) is a new emerging nondestructive testing (NDT) technique using a broadband pulse excitation with rich frequency information and has wide application potentials. This technique mainly uses feature points and response signal shapes for defect detection and characterization, including peak point, frequency analysis, and statistical methods such as principal component analysis (PCA). This paper introduces the application of Hilbert transform to extract a new descending feature point and use the point as a cutoff point of sampling data for detection and feature estimation. The response signal is then divided by the conventional rising, peak, and the new descending points. Some shape features of the rising part and descending part are extracted. The characters of shape features are also discussed and compared. Various feature selection and integrations are proposed for defect classification. Experimental studies, including blind tests, show the validation of the new features and combination of selected features in defect classification. The robustness of the features and further work are also discussed.

Fast analytical modelling for pulsed eddy current evaluation

Abstract: Numerical simulations of electromagnetic non-destructive evaluation (ENDE) can be time-consuming in comparison to analytical methods which provide fast closed-form solutions to the ENDE problems. In this paper, the Truncated Region Eigenfunction Expansion (TREE) modelling is extended to solve problems of pulsed eddy current (PEC) evaluation from the traditional multifrequency eddy current. The Fourier transform is employed to make the TREE feasible for solutions to PEC problems in both time and frequency domains. Moreover, because PEC employs magnetic field sensors/arrays to quantify magnetic field, the magnetic field signals from solid-state magnetic field sensors have been simulated using the extended TREE. It has been found that the predicted signals using the extended TREE has good agreement with the experimental results. Consequently, the established model can not only offer an effective solution in terms of faster simulation time and higher computational accuracy, but also be used for PEC evaluation in industry and in the inverse process for exploring the structural and electrical information of stratified conductive specimens during real-time monitoring.

Accurate sound source localization in a reverberant environment using multiple acoustic sensors

Abstract: This paper introduces a new method for the estimation of sound source distance and direction using at least three microphone sensors in indoor environments. Unlike the other methods that normally use approximations in obtaining the time difference between sensors, this method exploits the existed geometrical relationships of the sensors to form an exact solution to estimating the source position. To overcome reverberation, an enhancing pre-process has been used for different sound sources with different spectra, e.g., single frequency, multiple frequencies and different noise shapes. Source direction and distances are estimated from time of sound wave travel and distances of acoustic sensors. Using the method described in this paper a level of 1° accuracy is obtained. Several experimental tests have been undertaken that verify the results. Conclusions and future work are also described.

Data fusion for defect characterisation using a dual probe system

Abstract: We present recent work on a dual probe system containing electromagnetic acoustic transducers (EMATs) generating and detecting surface ultrasonic waves, and a pulsed eddy current (PEC) probe This system is able to detect and size surface and near-surface defects in electrically conducting samples by looking at changes in the detected signal for each probe By combining the information from each probe using a weighted logic function for data fusion, it is possible to both classify and size defects, with increased reliability By combining the data in this way one obtains information about the defects which is not available when using either probe in isolation Typical results on steel and aluminium samples are presented, along with information about the data fusion function The dual probe and data fusion routine has been demonstrated to work at manual-scanning speeds, with higher speeds possible following some simple improvements to the system

A microwave measurement system for metallic object detection using swept-frequency radar

Abstract: Guns and knives have become a significant threat to public safety. Recently, a variety of techniques based on Electromagnetics (EM) have been used for their detection. For example, walk-through metal detection has been used in airports; X-ray and THz detection systems have been used for luggage screening. Different EM frequencies for metallic object detection have demonstrated different merits. This paper reports on a 1-14 GHz swept-frequency radar system for metallic object detection using reflection configuration. The swept frequency response and resonant frequency behaviour of a number of metallic objects, in terms of position, object shape, rotation and multiple objects have been tested and analysed. The system working from 1 to 14 GHz has been set up to implement sensing of metal items at a standoff distance of more than 1 meter. Through a series of experimental investigations, it can be found that the optical depths derived from the Fourier Transform of the power spectrum profile is in close relation with the relative location of the metallic object. The cross correlation between coherencepolarisation and cross-polarisation RF returns can be used to distinguish different objects. Therefore the optical depth and the cross correlation can be used as useful features for metallic object detection and characterisation in this portion of the microwave frequency spectrum.

New Techniques for the Quantification of Defects Through Pulsed Magnetic Flux Leakage

Abstract: Although the probability of defect detection using magnetic flux leakage (MFL) inspection is sufficient for most applications for which it is used; inspection of ferromagnetic pipeline, wire rope, etc., accurate defect characterisation is problem atic. The use of pulsed excitation in conjunction with MFL provides an opportunity for the extra c ion of depth information from the MFL signal using analysis of the transient section of t he induced signal. This paper explores the use of pulsed magnetic flux leakage (PMFL) for the dete ction and quantification of defects in rolled steel water pipeline. For the newly developed PMFL system described in this paper, the time-frequency analysis employed in previous work is exte nded to look at shape features such as skewness. The paper concludes that PMFL can provide enhanced def ct characterisation capabilities for flux leakage based inspection systems an d could form the foundation of a fully automated defect characterisation system for pipeline ins pection.

Simulation of magnetic field distribution of excitation coil for EM flow meter and its validation using magnetic camera

Abstract: Distribution of magnetic flux density in electromagnetic (EM) flow meter is significantly important for obtaining accurate flow rate. Analysis of Helmholtz coils used to generate homogeneous magnetic flux density in the cross section of flow pipe of electromagnetic (EM) flow meter is presented in this paper. In this work a simulation model with the EM module of finite element analysis software, COMSOL, is built and experimental testing of the distribution of magnetic flux density is applied to verify its uniformity. A 2D magnetic camera system with 64 Hall sensors is prototyped. The magnetic field data are picked up by the National Instruments PCI 6255 data acquisition card.The results from the simulation and measurements are presented and compared in the paper. The study helps to design the electrode sensor arrays of EM flow meter. In addition to this, the distribution data of magnetic flux density are useful for the improvement of accurate flow rate measurement of EM flow meter.

Metal magnetic memory testing technique for stress measurement

Abstract: Stress concentration is the main reason to cause fati gue failure and damage. However the early damage, especially the hidden that with no-continua nce in it is very difficult to be taken effective evaluation. Metal magnetic memory (MMM) testing technique is a new technique in the field of non-destructive testing, which is effective for the diagnosis before ferromagnetic parts failure. MMM testing principle was presented, and MMM diagnostics instrument (EMS-2003) was used to test the specimens. The relationship between torsion and the vertical component of surface magnetic intensity-Hp(y) was also analyzed. Hp(y) gradient as well as dots where Hp(y) changes its polarity was used to diagnose the s tress concentration zones. Conclusions were derived based on the experiment result s, and its trend was highlighted.

Sensors and sensing systems

Abstract: Sensors are very important for measurement science and technology. They serve as a vital component in new measurement techniques and instrumentation systems. Key qualities of a good sensor system are high resolution, high reliability, low cost, appropriate output for a given input (good sensitivity), rapid response time, small random error in results, and small systematic error. Linearity is also useful, but with the advent of lookup tables and software, it is not as important as it used to be. In the last several years, considerable effort around the world has been devoted to a wide range of sensors from nanoscale sensors to sensor networks. Collectively, these vast and multidisciplinary efforts are developing important technological roadmaps to futuristic sensors with new modalities, significantly enhanced effectiveness and integrated functionality (data processing, computation, decision making and communications). When properly organized, they will have important relevance to life science and security applications, e.g. the sensing and monitoring of chemical, biological, radiological and explosive threats. A special feature in this issue takes a snapshot of some recent developments that were first presented at an international conference, the 2007 IEEE International Conference on Networking, Sensing and Control (ICNSC). The conference discussed recent developments, from which a few papers have since been brought together in this special feature. Gas sensing for environmental monitoring remains a topical subject, and two papers deal with this issue. One is concerned with the exploitation of nanostructured Au-doped cobalt oxyhydroxide-based carbon monoxide sensors for fire detection at its earlier stages (Zhuiykov and Dowling), whilst another examines the role of oxygen in high temperature hydrogen sulfide detection using MISiC sensors (Weng et al). Again for environmental monitoring, another paper deals with accurate sound source localization in a reverberant environment using multiple acoustic sensors (Atmoko et al). Not only is gaseous monitoring important, there are particular difficulties when it comes to the continuous monitoring of solids by non-destructive evaluation techniques. Examples of potential solutions for specialist applications are sensors for the detection and measurement of thin dielectric layers using reflection of frequency-scanned millimetre electromagnetic waves (Bowring et al), and an electrostatic sensor for velocity measurements of pneumatically conveyed solid particles (Xu et al). For potential medical applications, position measurement of internal organs is an on-going challenge. Tracking of internal organ motion with a six degree-of-freedom MEMS sensor is discussed by Bandala and Joyce. We hope that these papers provide an insight into exciting developments that continue to take place in the field of sensors and control.