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1345 KiB

Open AccessArticle

Information Theory Filters for Wavelet Packet Coefficient Selection with Application to Corrosion Type Identification from Acoustic Emission Signals

by Gert Van Dijck and Marc M. Van Hulle

Sensors 2011, 11(6), 5695-5715; https://doi.org/10.3390/s110605695 - 27 May 2011

Cited by 8 | Viewed by 9169

Abstract

The damage caused by corrosion in chemical process installations can lead to unexpected plant shutdowns and the leakage of potentially toxic chemicals into the environment. When subjected to corrosion, structural changes in the material occur, leading to energy releases as acoustic waves. This [...] Read more.

The damage caused by corrosion in chemical process installations can lead to unexpected plant shutdowns and the leakage of potentially toxic chemicals into the environment. When subjected to corrosion, structural changes in the material occur, leading to energy releases as acoustic waves. This acoustic activity can in turn be used for corrosion monitoring, and even for predicting the type of corrosion. Here we apply wavelet packet decomposition to extract features from acoustic emission signals. We then use the extracted wavelet packet coefficients for distinguishing between the most important types of corrosion processes in the chemical process industry: uniform corrosion, pitting and stress corrosion cracking. The local discriminant basis selection algorithm can be considered as a standard for the selection of the most discriminative wavelet coefficients. However, it does not take the statistical dependencies between wavelet coefficients into account. We show that, when these dependencies are ignored, a lower accuracy is obtained in predicting the corrosion type. We compare several mutual information filters to take these dependencies into account in order to arrive at a more accurate prediction. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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Processing stages for making predictions of the corrosion type. A steel probe (2) is inserted in a bypass (1) of the chemical process plant and is therefore exposed to the same environmental conditions as the installation. Acoustic events are captured by means of a broadband sensor (3). Subsequently AE signals are amplified and filtered (4). In order to obtain a fair validation of the system, the acquired signals are split into a training (5) and testing set (6). Features are extracted from the training signals by means of a Wavelet Packet Decomposition (7). A classifier (8) is trained based on the selected wavelet coefficients of the training set. Testing signals are projected onto the selected basis functions. Subsequently, the wavelet coefficients of the testing signals are used to test the overall performance of the system. Full article ">
Example signals of different corrosion types. The example of the absence of corrosion in (a) was captured from stainless steel in CaCl2 40 weight% at 85 °C environment. The example of the absence of corrosion in (b) was captured from carbon steel NaOH 20 weight% + NaCl 3 weight% at 80 °C environment. The examples in (c) and (d) are from continuous emissions during uniform corrosion of carbon steel in H3PO4 10 weight% at environment temperature. The signals in (e) and (f) are burst emission pitting signals captured from stainless steel in brackish water + FeCl3 1 weight% at 45 °C environment. In (g) a SCC burst emission signal was captured from stainless steel in CaCl2 40 weight% at 85 °C environment; (h) SCC burst emission signal was captured from carbon steel Ca(NO3)2 60 weight% at 105 °C environment. Full article ">
Templates (wavelet packets) corresponding to the 12-tap Coiflet filter. Full article ">
Library of wavelet packet functions. Different subspaces are represented by Wij. Index ‘i’ is the scale index, index ‘j’ is the frequency index. The depth ‘I’ of this tree is equal to 4. Every subtree within this tree, where each node has either 0 or 2 children, is called an admissible tree. Two admissible trees are emphasized, one shaded in grey and one marked with diagonals. Full article ">
Evolution of the accuracy of the k-nearest neighbor classifier (k = 3) as a function of the number of wavelet coefficients selected with the LDB algorithm and the mutual information filter algorithms. The horizontal line indicates the accuracy when all 1,024 samples are used (no FSS). Full article ">
Evolution of the accuracy of the decision tree J48 classifier as a function of the number of wavelet coefficients selected with the LDB algorithm and the mutual information filter algorithms. The horizontal line indicates the accuracy when all 1,024 samples are used. Full article ">
Evolution of the accuracy of the Gaussian mixture model as a function of the number of wavelet coefficients selected with the LDB algorithm and the mutual information filter algorithms. The horizontal line indicates the accuracy when the 1,024 samples were sub-sampled with a factor 15 to avoid numerical problems in the estimation of the parameters of the model. This subsampling was performed by taking the first time sample and then every 15th sample. Full article ">
Evolution of the accuracy of naïve Bayes classifier as a function of the number of wavelet coefficients selected with the LDB algorithm and the mutual information filter algorithms. The horizontal line indicates the accuracy when all 1,024 samples are used. Full article ">
Scatter plots of the first 3 coefficients that were selected most often by the local discriminant basis algorithm (LDB) as a triplet in the 10 training sets of the 10 fold cross-validation. These are the coefficients γ0,0,77, γ0,0,78 and γ0,0,79 in subspace W00. These scatter plots illustrate that the first three selected coefficients are highly redundant. Full article ">

413 KiB

Open AccessArticle

Measuring Oscillating Walking Paths with a LIDAR

by Mercè Teixidó, Tomàs Pallejà, Marcel Tresanchez, Miquel Nogués and Jordi Palacín

Sensors 2011, 11(5), 5071-5086; https://doi.org/10.3390/s110505071 - 6 May 2011

Cited by 17 | Viewed by 9829

Abstract

This work describes the analysis of different walking paths registered using a Light Detection And Ranging (LIDAR) laser range sensor in order to measure oscillating trajectories during unsupervised walking. The estimate of the gait and trajectory parameters were obtained with a terrestrial LIDAR [...] Read more.

This work describes the analysis of different walking paths registered using a Light Detection And Ranging (LIDAR) laser range sensor in order to measure oscillating trajectories during unsupervised walking. The estimate of the gait and trajectory parameters were obtained with a terrestrial LIDAR placed 100 mm above the ground with the scanning plane parallel to the floor to measure the trajectory of the legs without attaching any markers or modifying the floor. Three different large walking experiments were performed to test the proposed measurement system with straight and oscillating trajectories. The main advantages of the proposed system are the possibility to measure several steps and obtain average gait parameters and the minimum infrastructure required. This measurement system enables the development of new ambulatory applications based on the analysis of the gait and the trajectory during a walk. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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985 KiB

Open AccessArticle

Delaunay Triangulation as a New Coverage Measurement Method in Wireless Sensor Network

by Hassan Chizari, Majid Hosseini, Timothy Poston, Shukor Abd Razak and Abdul Hanan Abdullah

Sensors 2011, 11(3), 3163-3176; https://doi.org/10.3390/s110303163 - 15 Mar 2011

Cited by 36 | Viewed by 11873

Abstract

Sensing and communication coverage are among the most important trade-offs in Wireless Sensor Network (WSN) design. A minimum bound of sensing coverage is vital in scheduling, target tracking and redeployment phases, as well as providing communication coverage. Some methods measure the coverage as [...] Read more.

Sensing and communication coverage are among the most important trade-offs in Wireless Sensor Network (WSN) design. A minimum bound of sensing coverage is vital in scheduling, target tracking and redeployment phases, as well as providing communication coverage. Some methods measure the coverage as a percentage value, but detailed information has been missing. Two scenarios with equal coverage percentage may not have the same Quality of Coverage (QoC). In this paper, we propose a new coverage measurement method using Delaunay Triangulation (DT). This can provide the value for all coverage measurement tools. Moreover, it categorizes sensors as ‘fat’, ‘healthy’ or ‘thin’ to show the dense, optimal and scattered areas. It can also yield the largest empty area of sensors in the field. Simulation results show that the proposed DT method can achieve accurate coverage information, and provides many tools to compare QoC between different scenarios. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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768 KiB

Open AccessArticle

Virtual Surface Characteristics of a Tactile Display Using Magneto-Rheological Fluids

by Chul-Hee Lee and Min-Gyu Jang

Sensors 2011, 11(3), 2845-2856; https://doi.org/10.3390/s110302845 - 2 Mar 2011

Cited by 35 | Viewed by 9615

Abstract

Virtual surface characteristics of tactile displays are investigated to characterize the feeling of human touch for a haptic interface application. In order to represent the tactile feeling, a prototype tactile display incorporating Magneto-Rheological (MR) fluid has been developed. Tactile display devices simulate the [...] Read more.

Virtual surface characteristics of tactile displays are investigated to characterize the feeling of human touch for a haptic interface application. In order to represent the tactile feeling, a prototype tactile display incorporating Magneto-Rheological (MR) fluid has been developed. Tactile display devices simulate the finger’s skin to feel the sensations of contact such as compliance, friction, and topography of the surface. Thus, the tactile display can provide information on the surface of an organic tissue to the surgeon in virtual reality. In order to investigate the compliance feeling of a human finger’s touch, normal force responses of a tactile display under various magnetic fields have been assessed. Also, shearing friction force responses of the tactile display are investigated to simulate the action of finger dragging on the surface. Moreover, different matrix arrays of magnetic poles are applied to form the virtual surface topography. From the results, different tactile feelings are observed according to the applied magnetic field strength as well as the arrays of magnetic poles combinations. This research presents a smart tactile display technology for virtual surfaces. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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Graphical abstract

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MR Fluid: (a) Liquid Phase. (b) Solid Phase. Full article ">
Microscopic surface response: (a) 45 G case. (b) 120 G case. Full article ">
Monitoring device with dual strain gages and sensor tip. Full article ">
Photograph of experimental apparatus for MR haptic display. Full article ">
Procedure of experiments: (a) scan direction. (b) experiment I. (c) experiment II. (d) experiment III. Full article ">
Normal force response of experiment I. Full article ">
Magneto-static simulation result. Full article ">
Shearing force responses in experiment I: (a) single magnet (0.552T). (b) double magnets (0.604T). Full article ">
Normal force response of experiment II (Single magnet). Full article ">

5076 KiB

Open AccessArticle

Characterisation of the LMS200 Laser Beam under the Influence of Blockage Surfaces. Influence on 3D Scanning of Tree Orchards

by Ricardo Sanz-Cortiella, Jordi Llorens-Calveras, Joan R. Rosell-Polo, Eduard Gregorio-Lopez and Jordi Palacin-Roca

Sensors 2011, 11(3), 2751-2772; https://doi.org/10.3390/s110302751 - 2 Mar 2011

Cited by 41 | Viewed by 11301

Abstract

The geometric characterisation of tree orchards is a high-precision activity comprising the accurate measurement and knowledge of the geometry and structure of the trees. Different types of sensors can be used to perform this characterisation. In this work a terrestrial LIDAR sensor (SICK [...] Read more.

The geometric characterisation of tree orchards is a high-precision activity comprising the accurate measurement and knowledge of the geometry and structure of the trees. Different types of sensors can be used to perform this characterisation. In this work a terrestrial LIDAR sensor (SICK LMS200) whose emission source was a 905-nm pulsed laser diode was used. Given the known dimensions of the laser beam cross-section (with diameters ranging from 12 mm at the point of emission to 47.2 mm at a distance of 8 m), and the known dimensions of the elements that make up the crops under study (flowers, leaves, fruits, branches, trunks), it was anticipated that, for much of the time, the laser beam would only partially hit a foreground target/object, with the consequent problem of mixed pixels or edge effects. Understanding what happens in such situations was the principal objective of this work. With this in mind, a series of tests were set up to determine the geometry of the emitted beam and to determine the response of the sensor to different beam blockage scenarios. The main conclusions that were drawn from the results obtained were: (i) in a partial beam blockage scenario, the distance value given by the sensor depends more on the blocked radiant power than on the blocked surface area; (ii) there is an area that influences the measurements obtained that is dependent on the percentage of blockage and which ranges from 1.5 to 2.5 m with respect to the foreground target/object. If the laser beam impacts on a second target/object located within this range, this will affect the measurement given by the sensor. To interpret the information obtained from the point clouds provided by the LIDAR sensors, such as the volume occupied and the enclosing area, it is necessary to know the resolution and the process for obtaining this mesh of points and also to be aware of the problem associated with mixed pixels. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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Graphical abstract

779 KiB

Open AccessArticle

Non Destructive Defect Detection by Spectral Density Analysis

by Ondrej Krejcar and Robert Frischer

Sensors 2011, 11(3), 2334-2346; https://doi.org/10.3390/s110302334 - 24 Feb 2011

Cited by 37 | Viewed by 10239

Abstract

The potential nondestructive diagnostics of solid objects is discussed in this article. The whole process is accomplished by consecutive steps involving software analysis of the vibration power spectrum (eventually acoustic emissions) created during the normal operation of the diagnosed device or under unexpected [...] Read more.

The potential nondestructive diagnostics of solid objects is discussed in this article. The whole process is accomplished by consecutive steps involving software analysis of the vibration power spectrum (eventually acoustic emissions) created during the normal operation of the diagnosed device or under unexpected situations. Another option is to create an artificial pulse, which can help us to determine the actual state of the diagnosed device. The main idea of this method is based on the analysis of the current power spectrum density of the received signal and its postprocessing in the Matlab environment with a following sample comparison in the Statistica software environment. The last step, which is comparison of samples, is the most important, because it is possible to determine the status of the examined object at a given time. Nowadays samples are compared only visually, but this method can’t produce good results. Further the presented filter can choose relevant data from a huge group of data, which originate from applying FFT (Fast Fourier Transform). On the other hand, using this approach they can be subjected to analysis with the assistance of a neural network. If correct and high-quality starting data are provided to the initial network, we are able to analyze other samples and state in which condition a certain object is. The success rate of this approximation, based on our testing of the solution, is now 85.7%. With further improvement of the filter, it could be even greater. Finally it is possible to detect defective conditions or upcoming limiting states of examined objects/materials by using only one device which contains HW and SW parts. This kind of detection can provide significant financial savings in certain cases (such as continuous casting of iron where it could save hundreds of thousands of USD). Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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1604 KiB

Open AccessArticle

Ultrasonic and LIDAR Sensors for Electronic Canopy Characterization in Vineyards: Advances to Improve Pesticide Application Methods

by Jordi Llorens, Emilio Gil, Jordi Llop and Alexandre Escolà

Sensors 2011, 11(2), 2177-2194; https://doi.org/10.3390/s110202177 - 15 Feb 2011

Cited by 191 | Viewed by 18986

Abstract

Canopy characterization is a key factor to improve pesticide application methods in tree crops and vineyards. Development of quick, easy and efficient methods to determine the fundamental parameters used to characterize canopy structure is thus an important need. In this research the use [...] Read more.

Canopy characterization is a key factor to improve pesticide application methods in tree crops and vineyards. Development of quick, easy and efficient methods to determine the fundamental parameters used to characterize canopy structure is thus an important need. In this research the use of ultrasonic and LIDAR sensors have been compared with the traditional manual and destructive canopy measurement procedure. For both methods the values of key parameters such as crop height, crop width, crop volume or leaf area have been compared. Obtained results indicate that an ultrasonic sensor is an appropriate tool to determine the average canopy characteristics, while a LIDAR sensor provides more accuracy and detailed information about the canopy. Good correlations have been obtained between crop volume (C_VU) values measured with ultrasonic sensors and leaf area index, LAI (R²= 0.51). A good correlation has also been obtained between the canopy volume measured with ultrasonic and LIDAR sensors (R²= 0.52). Laser measurements of crop height (C_HL) allow one to accurately predict the canopy volume. The proposed new technologies seems very appropriate as complementary tools to improve the efficiency of pesticide applications, although further improvements are still needed. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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Graphical abstract

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Sprayer equipped with ultrasonic sensors and LIDAR (left). The system includes a control unit with compact field point and computer to data processing (right). Full article ">
Scheme of electronic connections between all the elements installed in the prototype. Full article ">
Functioning principle of ultrasonic sensors. Distance to the external layout of the crop (left) can be transformed into crop volume (right). Full article ">
Functioning principle of the LIDAR sensor. The laser beams obtain for each crop slice a variable number of identified points according the distance to the sensor and angle from the horizontal. Full article ">
From impact points measured on the crop canopy (left) the average distance to the crop axis is calculated (middle) as crop width. Crop area is also determined for every individual height (right) from the Cartesian coordinates of every single point. Full article ">
Simulated crop profile (top) obtained with laser sensor. Differences between max and min height on a single crop slice are used to measure canopy height. LWA is calculated according crop height variation along the row and compared with manual measurements (bottom). Full article ">
Relation between laser impact obtained with LIDAR and LAI (left). On the right correlation between canopy height calculated with LIDAR and canopy volume manually measured. Full article ">
Correlation curves between measured leaf area index (LAI) and percent of zero values obtained with the two sensors (left). On the right side correlation between LAI and crop volume estimated with ultrasonic sensors and LIDAR. Full article ">
Correlation curves between measured leaf area index (LAI) and percent of zero values obtained with the two sensors (left). On the right side correlation between LAI and crop volume estimated with ultrasonic sensors and LIDAR. Full article ">

403 KiB

Open AccessArticle

Measurement of Blood Pressure Using an Arterial Pulsimeter Equipped with a Hall Device

by Sang-Suk Lee, Dong-Hyun Nam, You-Sik Hong, Woo-Beom Lee, Il-Ho Son, Keun-Ho Kim and Jong-Gu Choi

Sensors 2011, 11(2), 1784-1793; https://doi.org/10.3390/s110201784 - 31 Jan 2011

Cited by 35 | Viewed by 17002

Abstract

To measure precise blood pressure (BP) and pulse rate without using a cuff, we have developed an arterial pulsimeter consisting of a small, portable apparatus incorporating a Hall device. Regression analysis of the pulse wave measured during testing of the arterial pulsimeter was [...] Read more.

To measure precise blood pressure (BP) and pulse rate without using a cuff, we have developed an arterial pulsimeter consisting of a small, portable apparatus incorporating a Hall device. Regression analysis of the pulse wave measured during testing of the arterial pulsimeter was conducted using two equations of the BP algorithm. The estimated values of BP obtained by the cuffless arterial pulsimeter over 5 s were compared with values obtained using electronic or liquid mercury BP meters. The standard deviation between the estimated values and the measured values for systolic and diastolic BP were 8.3 and 4.9, respectively, which are close to the range of values of the BP International Standard. Detailed analysis of the pulse wave measured by the cuffless radial artery pulsimeter by detecting changes in the magnetic field can be used to develop a new diagnostic algorithm for BP, which can be applied to new medical apparatus such as the radial artery pulsimeter. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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Diagram showing the basic structure of the wrist wearable radial arterial pulsimeter. Schematic cross-section of one form of the pulse-sensing and skin-contacting components of the arterial pulsimeter using multiple Hall devices and permanent magnets, respectively. The pressure chamber between the skin-contacting and pulse-sensing components is filled with air. Full article ">
(a) PCB pulse-sensing component mounted with a multiple 5 × 9 = 45 array of Hall devices corresponding to the permanent magnets underneath. (b) A graph of output voltage versus magnetic field for the commercial, A3515-and A3516-type Hall device showing high sensitivity of 1.2 mV/Oe and linearity in the magnetic field and temperature range from −5 Oe to +5 Oe and from −40 °C, to +150 °C, respectively. Full article ">
Typical pulse waveform of 1 point obtained by the compositional analysis of pulse signal of the clinical product testing of the pulsimeter using Hall device. Example of measuring time (seconds) versus temporally typical signal of 1 point pulse obtained from the analysis of an arbitrary pulse signal of 1 position of a small permanent magnet. Full article ">
(a) Typical real features of a pulse wave and a first pulse wave combined to provide the main pulse and the reflective pulse. (b) Regression analysis equation for the estimated algorithm of blood pressure needs the following 6 major correlative factors; (1) the period of the pulse wave, (2) the time of the systolic period, (3) the reflective time, (4) the notch time, (5) the ratio of area (systolic period area/diastolic period area), and (6) the increasing pressure index (reflective wave peak/systolic wave peak). Full article ">
Photographs of the arterial pulsimeter with Hall device in clinical tests. Here the weight and power consumption of the wrist wearable, radial arterial pulsimeter are 80 g and 1.65 W, respectively. The product testing of the proposed arterial pulsimeter and the measuring feature, which are a wristwatch or bracelet, transfer the increased pressure to the skin-contacting part intact when the pressure of the constant pressure chamber is increased. Full article ">

1242 KiB

Open AccessArticle

The Effect of Tensile Hysteresis and Contact Resistance on the Performance of Strain-Resistant Elastic-Conductive Webbing

by Tien-Wei Shyr, Jing-Wen Shie and Yan-Er Jhuang

Sensors 2011, 11(2), 1693-1705; https://doi.org/10.3390/s110201693 - 28 Jan 2011

Cited by 30 | Viewed by 10216

Abstract

To use e-textiles as a strain-resistance sensor they need to be both elastic and conductive. Three kinds of elastic-conductive webbings, including flat, tubular, and belt webbings, made of Lycra fiber and carbon coated polyamide fiber, were used in this study. The strain-resistance properties [...] Read more.

To use e-textiles as a strain-resistance sensor they need to be both elastic and conductive. Three kinds of elastic-conductive webbings, including flat, tubular, and belt webbings, made of Lycra fiber and carbon coated polyamide fiber, were used in this study. The strain-resistance properties of the webbings were evaluated in stretch-recovery tests and measured within 30% strain. It was found that tensile hysteresis and contact resistance significantly influence the tensile elasticity and the resistance sensitivity of the webbings. The results showed that the webbing structure definitely contributes to the tensile hysteresis and contact resistance. The smaller the friction is among the yarns in the belt webbing, the smaller the tensile hysteresis loss. However the close proximity of the conductive yarns in flat and tubular webbings results in a lower contact resistance. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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918 KiB

Open AccessArticle

Fiber Bragg Gratings, IT Techniques and Strain Gauge Validation for Strain Calculation on Aged Metal Specimens

by Ander Montero, Idurre Saez de Ocariz, Ion Lopez, Pablo Venegas, Javier Gomez and Joseba Zubia

Sensors 2011, 11(1), 1088-1104; https://doi.org/10.3390/s110101088 - 19 Jan 2011

Cited by 11 | Viewed by 13209

Abstract

This paper studies the feasibility of calculating strains in aged F114 steel specimens with Fiber Bragg Grating (FBG) sensors and infrared thermography (IT) techniques. Two specimens have been conditioned under extreme temperature and relative humidity conditions making comparative tests of stress before and [...] Read more.

This paper studies the feasibility of calculating strains in aged F114 steel specimens with Fiber Bragg Grating (FBG) sensors and infrared thermography (IT) techniques. Two specimens have been conditioned under extreme temperature and relative humidity conditions making comparative tests of stress before and after aging using different adhesives. Moreover, a comparison has been made with IT techniques and conventional methods for calculating stresses in F114 steel. Implementation of Structural Health Monitoring techniques on real aircraft during their life cycle requires a study of the behaviour of FBG sensors and their wiring under real conditions, before using them for a long time. To simulate aging, specimens were stored in a climate chamber at 70 °C and 90% RH for 60 days. This study is framed within the Structural Health Monitoring (SHM) and Non Destructuve Evaluation (NDE) research lines, integrated into the avionics area maintained by the Aeronautical Technologies Centre (CTA) and the University of the Basque Country (UPV/EHU). Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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1249 KiB

Open AccessArticle

A Laser-Based Vision System for Weld Quality Inspection

by Wei Huang and Radovan Kovacevic

Sensors 2011, 11(1), 506-521; https://doi.org/10.3390/s110100506 - 6 Jan 2011

Cited by 117 | Viewed by 18473

Abstract

Welding is a very complex process in which the final weld quality can be affected by many process parameters. In order to inspect the weld quality and detect the presence of various weld defects, different methods and systems are studied and developed. In [...] Read more.

Welding is a very complex process in which the final weld quality can be affected by many process parameters. In order to inspect the weld quality and detect the presence of various weld defects, different methods and systems are studied and developed. In this paper, a laser-based vision system is developed for non-destructive weld quality inspection. The vision sensor is designed based on the principle of laser triangulation. By processing the images acquired from the vision sensor, the geometrical features of the weld can be obtained. Through the visual analysis of the acquired 3D profiles of the weld, the presences as well as the positions and sizes of the weld defects can be accurately identified and therefore, the non-destructive weld quality inspection can be achieved. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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Graphical abstract

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Design principle of the laser-based vision sensor: (a) schematic of the sensor and (b) design of sensor parameters based on laser triangulation. Full article ">
Fabricated laser-based vision sensor mounted on a multi-axis motion system. Full article ">
Human-machine interface of the laser-based vision system. Full article ">
Calibration of vision system: (a) setup for the system calibration; (b) detected corner points of the reference coupon in the pixel space; (c) detected corner points of the reference coupon in the coordinate space. Full article ">
Calibration results of the laser-based vision system: (a) measurement of the stand-off distance before calibration; (b) measurement of the width before calibration; (c) measurement of the thickness before calibration; (d) measurement of the width after calibration; (e) measurement of the thickness after calibration. Full article ">
Results of weld quality inspection for laser-arc hybrid welding: (a) weld as the inspection target; (b) 3D-view of the inspected weld; (c) top-view of the inspected weld; (d) side-view of the inspected weld. Full article ">
Results of weld quality inspection for laser welding: (a) weld as the inspection target; (b) detail of the weld; (c) top-view of the inspected weld; (d) detailed top-view of the inspected weld; (e) detailed side-view of the inspected weld. Full article ">
Geometrical evaluation of the inspected weld: (a) longitudinal profile of the weld; (b) traversal profile of the weld at point 1; (c) traversal profile of the weld at point 2; (d) traversal profile of the weld at point 3; (e) traversal profile of the weld at point 4. Full article ">

2807 KiB

Open AccessArticle

Position-Controlled Data Acquisition Embedded System for Magnetic NDE of Bridge Stay Cables

by Rocio Maldonado-Lopez and Rouven Christen

Sensors 2011, 11(1), 162-179; https://doi.org/10.3390/s110100162 - 24 Dec 2010

Cited by 3 | Viewed by 11071

Abstract

This work presents a custom-tailored sensing and data acquisition embedded system, designed to be integrated in a new magnetic NDE inspection device under development at Empa, a device intended for routine testing of large diameter bridge stay cables. The data acquisition (DAQ) system [...] Read more.

This work presents a custom-tailored sensing and data acquisition embedded system, designed to be integrated in a new magnetic NDE inspection device under development at Empa, a device intended for routine testing of large diameter bridge stay cables. The data acquisition (DAQ) system fulfills the speed and resolution requirements of the application and is able to continuously capture and store up to 2 GB of data at a sampling rate of 27 kS/s, with 12-bit resolution. This paper describes the DAQ system in detail, including both hardware and software implementation, as well as the key design challenges nd the techniques employed to meet the specifications. Experimental results showing the performance of the system are also presented. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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2328 KiB

Open AccessArticle

Sub-Frequency Interval Approach in Electromechanical Impedance Technique for Concrete Structure Health Monitoring

by Yaowen Yang and Bahador Sabet Divsholi

Sensors 2010, 10(12), 11644-11661; https://doi.org/10.3390/s101211644 - 21 Dec 2010

Cited by 70 | Viewed by 10528

Abstract

The electromechanical (EM) impedance technique using piezoelectric lead zirconate titanate (PZT) transducers for structural health monitoring (SHM) has attracted considerable attention in various engineering fields. In the conventional EM impedance technique, the EM admittance of a PZT transducer is used as a damage [...] Read more.

The electromechanical (EM) impedance technique using piezoelectric lead zirconate titanate (PZT) transducers for structural health monitoring (SHM) has attracted considerable attention in various engineering fields. In the conventional EM impedance technique, the EM admittance of a PZT transducer is used as a damage indicator. Statistical analysis methods such as root mean square deviation (RMSD) have been employed to associate the damage level with the changes in the EM admittance signatures, but it is difficult to determine the location of damage using such methods. This paper proposes a new approach by dividing the large frequency (30–400 kHz) range into sub-frequency intervals and calculating their respective RMSD values. The RMSD of the sub-frequency intervals (RMSD-S) will be used to study the severity and location of damage. An experiment is carried out on a real size concrete structure subjected to artificial damage. It is observed that damage close to the PZT changes the high frequency range RMSD-S significantly, while the damage far away from the PZT changes the RMSD-S in the low frequency range significantly. The relationship between the frequency range and the PZT sensing region is also presented. Finally, a damage identification scheme is proposed to estimate the location and severity of damage in concrete structures. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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1622 KiB

Open AccessArticle

Feasibility of Fiber Bragg Grating and Long-Period Fiber Grating Sensors under Different Environmental Conditions

by Jian-Neng Wang and Jaw-Luen Tang

Sensors 2010, 10(11), 10105-10127; https://doi.org/10.3390/s101110105 - 10 Nov 2010

Cited by 48 | Viewed by 13752

Abstract

This paper presents the feasibility of utilizing fiber Bragg grating (FBG) and long-period fiber grating (LPFG) sensors for nondestructive evaluation (NDE) of infrastructures using Portland cement concretes and asphalt mixtures for temperature, strain, and liquid-level monitoring. The use of hybrid FBG and LPFG [...] Read more.

This paper presents the feasibility of utilizing fiber Bragg grating (FBG) and long-period fiber grating (LPFG) sensors for nondestructive evaluation (NDE) of infrastructures using Portland cement concretes and asphalt mixtures for temperature, strain, and liquid-level monitoring. The use of hybrid FBG and LPFG sensors is aimed at utilizing the advantages of two kinds of fiber grating to implement NDE for monitoring strains or displacements, temperatures, and water-levels of infrastructures such as bridges, pavements, or reservoirs for under different environmental conditions. Temperature fluctuation and stability tests were examined using FBG and LPFG sensors bonded on the surface of asphalt and concrete specimens. Random walk coefficient (RWC) and bias stability (BS) were used for the first time to indicate the stability performance of fiber grating sensors. The random walk coefficients of temperature variations between FBG (or LPFG) sensor and a thermocouple were found in the range of −0.7499 °C/ to −1.3548 °C/. In addition, the bias stability for temperature variations, during the fluctuation and stability tests with FBG (or LPFG) sensors were within the range of 0.01 °C/h with a 15–18 h time cluster to 0.09 °C/h with a 3–4 h time cluster. This shows that the performance of FBG or LPFG sensors is comparable with that of conventional high-resolution thermocouple sensors under rugged conditions. The strain measurement for infrastructure materials was conducted using a packaged FBG sensor bonded on the surface of an asphalt specimen under indirect tensile loading conditions. A finite element modeling (FEM) was applied to compare experimental results of indirect tensile FBG strain measurements. For a comparative analysis between experiment and simulation, the FEM numerical results agreed with those from FBG strain measurements. The results of the liquid-level sensing tests show the LPFG-based sensor could discriminate five stationary liquid-levels and exhibits at least 1,050-mm liquid-level measurement capacity. Thus, the hybrid FBG and LPFG sensors reported here could benefit the NDE development and applications for infrastructure health monitoring such as strain, temperature and liquid-level measurements. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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783 KiB

Open AccessArticle

Measuring Relative-Story Displacement and Local Inclination Angle Using Multiple Position-Sensitive Detectors

by Iwao Matsuya, Ryuta Katamura, Maya Sato, Miroku Iba, Hideaki Kondo, Kiyoshi Kanekawa, Motoichi Takahashi, Tomohiko Hatada, Yoshihiro Nitta, Takashi Tanii, Shuichi Shoji, Akira Nishitani and Iwao Ohdomari

Sensors 2010, 10(11), 9687-9697; https://doi.org/10.3390/s101109687 - 1 Nov 2010

Cited by 29 | Viewed by 11056

Abstract

We propose a novel sensor system for monitoring the structural health of a building. The system optically measures the relative-story displacement during earthquakes for detecting any deformations of building elements. The sensor unit is composed of three position sensitive detectors (PSDs) and lenses [...] Read more.

We propose a novel sensor system for monitoring the structural health of a building. The system optically measures the relative-story displacement during earthquakes for detecting any deformations of building elements. The sensor unit is composed of three position sensitive detectors (PSDs) and lenses capable of measuring the relative-story displacement precisely, even if the PSD unit was inclined in response to the seismic vibration. For verification, laboratory tests were carried out using an Xθ-stage and a shaking table. The static experiment verified that the sensor could measure the local inclination angle as well as the lateral displacement. The dynamic experiment revealed that the accuracy of the sensor was 150 µm in the relative-displacement measurement and 100 µrad in the inclination angle measurement. These results indicate that the proposed sensor system has sufficient accuracy for the measurement of relative-story displacement in response to the seismic vibration. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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Schematic diagram of the relative-story displacement sensor. (a)Arrangement of three LEDs and three PSD units (Birds eye view); (b) Photographs of the LED array; and (c) the PSD unit. Full article ">
Cross-section view of the relative-story displacement sensor. (a) XZ-plane view and (b) YZ-plane view. Full article ">
Displacement of the light spot which comes from the LED and is focused on the PSD surface by the lens in response to the torsional motion of the upper layer. The schematic shows the XY-plane. The original point for the torsional motion is located at the center of the PSD1. If the upper layer was counterclockwise rotated with the angle ψ, the light spot on the PSD3 displaces by l0·ψin X-direction, and the light spot on the PSD2 displaces by l0·ψin negative Y-direction. Full article ">
Experimental setup for measuring the relative-story displacement and the inclination angle using two PSD units. (a) Front perspective view; and (b) XZ-plane view. Full article ">
Output voltages from the PSD units according to (a) the lateral displacement δx and (b) the inclination angle θy in the static experiments. Full article ">
The results of the dynamic experiments using the shaking table and the θ-stage. (a) The output voltages from PSDs; (b) the calculated displacement δx; and (c) the calculated angle θy. Full article ">

327 KiB

Open AccessArticle

A Sensor Network Data Compression Algorithm Based on Suboptimal Clustering and Virtual Landmark Routing Within Clusters

by Peng Jiang and Shengqiang Li

Sensors 2010, 10(10), 9084-9101; https://doi.org/10.3390/s101009084 - 11 Oct 2010

Cited by 4 | Viewed by 9377

Abstract

A kind of data compression algorithm for sensor networks based on suboptimal clustering and virtual landmark routing within clusters is proposed in this paper. Firstly, temporal redundancy existing in data obtained by the same node in sequential instants can be eliminated. Then sensor [...] Read more.

A kind of data compression algorithm for sensor networks based on suboptimal clustering and virtual landmark routing within clusters is proposed in this paper. Firstly, temporal redundancy existing in data obtained by the same node in sequential instants can be eliminated. Then sensor networks nodes will be clustered. Virtual node landmarks in clusters can be established based on cluster heads. Routing in clusters can be realized by combining a greedy algorithm and a flooding algorithm. Thirdly, a global structure tree based on cluster heads will be established. During the course of data transmissions from nodes to cluster heads and from cluster heads to sink, the spatial redundancy existing in the data will be eliminated. Only part of the raw data needs to be transmitted from nodes to sink, and all raw data can be recovered in the sink based on a compression code and part of the raw data. Consequently, node energy can be saved, largely because transmission of redundant data can be avoided. As a result the overall performance of the sensor network can obviously be improved. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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Non-Destructive Techniques Based on Eddy Current Testing

by Javier García-Martín, Jaime Gómez-Gil and Ernesto Vázquez-Sánchez

Sensors 2011, 11(3), 2525-2565; https://doi.org/10.3390/s110302525 - 28 Feb 2011

Cited by 909 | Viewed by 68249

Abstract

Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any [...] Read more.

Non-destructive techniques are used widely in the metal industry in order to control the quality of materials. Eddy current testing is one of the most extensively used non-destructive techniques for inspecting electrically conductive materials at very high speeds that does not require any contact between the test piece and the sensor. This paper includes an overview of the fundamentals and main variables of eddy current testing. It also describes the state-of-the-art sensors and modern techniques such as multi-frequency and pulsed systems. Recent advances in complex models towards solving crack-sensor interaction, developments in instrumentation due to advances in electronic devices, and the evolution of data processing suggest that eddy current testing systems will be increasingly used in the future. Full article

(This article belongs to the Special Issue Advanced Sensing Technology for Nondestructive Evaluation)

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