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Ground-penetrating radar (GPR) has become one of the key technologies in subsurface sensing and, in general, in nondestructive testing (NDT), since it is able to detect both metallic and nonmetallic targets. GPR has proven its ability to work in electromagnetic frequency range for subsoil investigations, and it is a risk-reduction strategy for surveying underground various targets and their identification and detection. This paper presents the results of a case study which exceeds the laboratory level being realized in the field in a real case where the scanning conditions are much more difficult using GPR signals for detecting and assessing underground drainage metallic pipes which cross an area with large buildings parallel to the riverbed. The two urban drainage pipes are detected based on GPR imaging. This provides an approximation of their location and depth which are convenient to find from the reconstructed profiles of both simulated and practical GPR signals. The processing of data recorded with GPR tools requires appropriate software for this type of measurement to detect between different reflections at multiple interfaces located at different depths below the surface. In addition to the radargrams recorded and processed with the software corresponding to a GPR device, the paper contains significant results obtained using techniques and algorithms of the processing and post-processing of the signals (background removal and migration) that gave us the opportunity to estimate the location, depth, and profile of pipes, placed into a concrete duct bank, under a structure with different layers, including pavement, with good accuracy.

Wind turbine blades (WTB) are one of the most damageable components of a wind turbine system and due to their importance must be tested during the fabrication and before installing. WTB are produced from composite materials with polymeric matrices, most of the stages of producing are manufacturing and can result in different types of defects. Therefore, non-destructive testing (NDT) techniques that provide surface and internal information of the blade are required. In this paper, ultrasonic testing using noncontact transducers for the control of composites type Glass Fiber Reinforced Plastics (GFRP) with orthophthalic polyester resins matrix is presented in order to prove its capabilities for such applications. The mechanical properties determined by above mentioned method are confirmed by destructive tests using Dynamic Mechanical Analysis.

This paper presents two methods for electromagnetic nondestructive evaluation (eNDE) of composite materials reinforced with carbon woven fibers using a sensor with orthogonal coils and a sensor with metamaterials lens. The samples were impacted with low energy in order to study delamination influence. The electromagnetic behavior of composite was simulated by finite-difference time-domain (FDTD) software, showing a very good concordance with eNDE tests.

The paper investigates the formation of evanescent waves in metallic strip gratings on the Ag/ZnO/SiO 2 /Si structure with silver strips when TEz incident wave in the radiofrequency range was used. The Ag/ZnO/SiO 2 /Si structure was fabricated by vacuum thermal evaporation technique and Scanning Electron Microscopy was used to evidenceits high quality structure with parallel silver strips of same width and thickness. Simulation of the evanescent wave formation at the edge of Ag strips, with thicknesses in the range of micrometers, was performed, before performing the test in the subwavelength regime by the mean of a new transducer improved with metamaterials lens. The generation in slits, in air, of the electric evanescent mode, when metallic strip grating was excited with a TEz polarized wave at a frequency of 474 MHz, was successfully demonstrated.

Metallic strip gratings (MSG) have different applications, ranging from printed circuits to filters in microwave domains. When they are under the influence of an electromagnetic field, evanescent and/or abnormal modes appear in the region between the traces, their utilization leading to the development of new electromagnetic nondestructive evaluation methods. This paper studies the behavior of MSGs in the sub-subwavelength regime when they are excited with TE(z) or TM(z) polarized plane waves and the slits are filled with different dielectrics. The appearance of propagating, evanescent and abnormal modes is emphasized using an electromagnetic sensor with metamaterials lens realized with two conical Swiss rolls, which allows the extraction of the information carried by the guided evanescent waves. The evanescent waves, manipulated by the electromagnetic sensor with metamaterial lenses, improve the electromagnetic images so that a better spatial resolution is obtained, exceeding the limit imposed by diffraction. Their theoretical and experimental confirmation opens the perspective for development of new types of sensors working in radio and microwave frequencies.

Metallic strip gratings have a range of applications, from printed circuits boards to filters in microwave domains. These applications impose a rigorous and rapid quality control. This paper proposes the obtaining of electromagnetic images of metallic strip gratings using evanescent waves that are formed in slits. For their detection, two procedures can be use, namely, the diffraction of evanescent waves on circular apertures and respectively, the propagation through metamaterials, conical Swiss rolls type. In this case, the spatial resolution is better than λ/1000. The use of metamaterial, conical Swiss rolls type, allows the obtaining of a resolution in the range of λ/2000, the electromagnetic image being improved.

This paper proposes the study and implementation of metamaterials in electromagnetic non-destructive examination; these materials can serve as electromagnetic flux concentrators in the radio frequency range. Thus, the use of new types of metamaterials, namely conical Swiss roll, is proposed. Here, we present a method of extracting the necessary parameters (effective magnetic permeability and the frequency) from the data obtained by measuring network parameters. Due to the fact that conical Swiss rolls can serve as radio frequency flux concentrators, they can be used in the fabrication of electromagnetic lenses, being designed on the basis of Fourier optic principles. As a direct application, carbon fibre reinforced plastic (CFRP) plates with and without delaminations, created by impacts with low energy, were examined by means of electromagnetic transducers with a metamaterial lens. The characteristics of a carbon fibre woven structure become visible and the delaminations are clearly emphasised.

This paper presents a model for evaluation of effective thermal conductivity for the composites with carbon nanotubes (CNT) having log-normal function of distribution of CNT, with direct effect over depolarization factor. The CNT are considered having cylindrical shape with L/d ratio very high. The model parameters are calculated in function of the data from literature. The influence of volume fraction of reinforced materials, of the aspect ratio of the particles included and of the ratio of the two thermal conductivities is presented.

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.

International audience; The current stage of non-destructive evaluation techniques imposes the development of new electromagnetic methods that are based on high spatial resolution and increased sensitivity. Printed circuit boards, integrated circuit boards, composite materials with polymeric matrix containing conductive fibers, as well as some types of biosensors are devices of interest in using such evaluation methods. In order to achieve high performance, the work frequencies must be either radiofrequencies or microwaves. At these frequencies, at the dielectric/conductor interface, plasmon polaritons can appear, propagating between conductive regions as evanescent waves. Detection of these waves, containing required information, can be done using sensors with metamaterial lenses. We propose in this paper the enhancement of the spatial resolution using electromagnetic methods, which can be accomplished in this case using evanescent waves that appear in the current study in slits of materials such as the spaces between carbon fibers in Carbon Fibers Reinforced Plastics or in materials of interest in the nondestructive evaluation field with industrial applications, where microscopic cracks are present. We propose herein a unique design of the metamaterials for use in nondestructive evaluation based on Conical Swiss Rolls configurations, which assure the robust concentration/focusing of the incident electromagnetic waves (practically impossible to be focused using classical materials), as well as the robust manipulation of evanescent waves. Applying this testing method, spatial resolution of approximately λ/2000 can be achieved. This testing method can be successfully applied in a variety of applications of paramount importance such as defect/damage detection in materials used in a variety of industrial applications, such as automotive and aviation technologies. © 2015.

This article presents a novel send-receive type of inner-eddy-current transducer. A rotating magnetic field created by three rectangular coils, fed by a triphased alternating-current system, was used for emission. The reception part is made from a circumferential array of coils, consecutively interrogated by measurement equipment. The source that creates the rotating magnetic field is described. The field created by this in free space is presented, and the forward problem using the volume integral method and dyadic Green's function for cylindrical layered media is solved. The experimental measurements are in good agreement with the predictions of the model.

This article presents the electronic equipment and experimental results obtained with an eddy-current transducer with a rotating magnetic field, at the control of Zr2.5%Nb pressure tube samples. Different types of artificial discontinuities with diverse shapes, positions, and severities were examined. In all the cases, the signal-to-noise ratio obtained was higher than 3. This fact recommends that the transducer and measurement system should be used in the examination of pressure tubes from pressurized heavy water reactor (PHWR) nuclear power plants.

International audience; This paper proposes the study and implementation of a sensor with a metamaterial (MM) lens in electromagnetic nondestructive evaluation (eNDE). Thus, the use of a new type of MM, named Conical Swiss Rolls (CSR) has been proposed. These structures can serve as electromagnetic flux concentrators in the radiofrequency range. As a direct application, plates of composite materials with carbon fibers woven as reinforcement and polyphenylene sulphide as matrix with delaminations due to low energy impacts were examined. The evaluation method is based on the appearance of evanescent modes in the space between carbon fibers when the sample is excited with a transversal magnetic along z axis (TMz) polarized electromagnetic field. The MM lens allows the transmission and intensification of evanescent waves. The characteristics of carbon fibers woven structure became visible and delaminations are clearly emphasized. The flaws can be localized with spatial resolution better than λ/2000. © 2015, by the authors; licensee MDPI, Basel, Switzerland.

The most common defects in turbine blades may be faulty microscopic and mesoscopic appeared in matrix, no detected by classical nondestructive testing (i.e. using phased array sensors), broken fibers can also appear and develop under moderated loads, or cracks and delaminations due to low energy impacts, etc. The paper propose to present the results obtained from testing of glass fiber reinforced plastic used in the construction of the wind turbine blades as well as the monitoring of the entire scalable blade using wireless sensors placed on critical location on blade. In order to monitories the strain/stress during the tests, the determination of the location and the nature of defects have been simulated using FEM.

Using glass fabric reinforced composites for structure of wind turbine blades requires high mechanical strengths especially to cyclic stresses. Studies have shown that approximately 50% of composite material failure occurs because of fatigue. Composites behavior to cyclic stresses involves three stages regarding to stiffness variation: the first stage is characterized by the accelerated decline of stiffness with micro-cracks, the second stage - a slight decrease of stiffness characterized by the occurrence of delamination and third stage characterized by higher decreases of resistance and occurrence of fracture thereof. The aim of the paper is to analyzed the behavior of composites reinforced with glass fibers fabric type RT500 and polyester resin subjected to tensile cyclic loading with pulsating quasi-static regime with asymmetry coefficient R = 0. The samples were tested with the universal tensile machine LS100 Lloyd Instruments Plus, with a load capacity of 100 kN. The load was applied with different speeds of 1 mm/min, 10 mm/min and 20 mm/min. After tests, it was observed that the greatest permanent strains were recorded in the first load cycles when the total energy storage by material was lost due to internal friction. With increasing number of cycles, the glass/polyester composites ability to store energy of deformation decreases, the flow phenomenon characterized by large displacements to smaller loading forces appearing.

The improvement of electromagnetic image quality of microscopic discontinuities in conductive pieces, damages of CFRP composites as well as metallic strip gratings from flexible printed circuits can be made using evanescent modes generated in slits, in spaces between carbon fibers and respectively in cracks. In order to generate the evanescent modes, plane electromagnetic waves, TMz polarized are used as excitation. The manipulation of the evanescent modes is made by means of metamaterials lens, conical Swiss roll type. The sensor allows the electromagnetic nondestructive evaluation of metallic strip grating, emphasizing the interruption of strips, CFRP delaminations due to impact with low energy as well as micrometric open at surface cracks in metallic pieces.

This work is dedicated to the calculation of the electromagnetic field created by an arbitrary current source in the proximity of a cylinder consisting of a certain number of concentric layers made of materials with various electrical conductivities and magnetic permeabilities, using the method of the transfer matrix. The general results obtained are then particularized for the case of an eddy current transducer with a rotating magnetic field, having its reception part of a special construction. The inversion method used to determine the thickness of the protective coatings on a conductive cylinder is presented.

The present work approaches the problem of determining, by analytical solutions, the electromagnetic field created by an arbitrary distribution of alternating currents placed outside an infinitely long non-magnetic conductive cylinder. Making use of the dyadic Green function method, the electromagnetic field outside the cylinder is expressed as the sum of the field in free space and the field created by the currents induced in the conductive cylinder. The general results we obtained are particularized for the analytical solutions describing the operation of an eddy current transducer with rotating magnetic field for the case of a conductive cylinder non-coaxial with the current source.

The most important part of wind turbine is the blade that must be tested during the fabrication and during the functioning when can be damaged by moisture absorption, fatigue, wind gusts or lightning strikes. The novelty of the paper is represented by the employing of wireless sensors embedded in a scalable wind turbine blade made from Glass Fiber Reinforced Plastics together with Fiber Bragg Gratings in order to effectuate structural health monitoring in static conditions. The sensors are placed on critical location on blade determined by FEM simulation and a comparison between the complementary methods is done.

This paper presents two methods, non-contact low frequency ultrasound method and fiber Bragg gratings, and their application to nondestructive testing of glass fiber reinforced composites used in wind turbine blades. Theoretical models are used and experimental results are in good concordance with destructive testing results.

The control of wind turbine's components is very rigorous, while the tower and gearbox have more possibility for revision and repairing, the rotor blades, once they are deteriorated, the defects can rapidly propagate, producing failure, and the damages can affect large regions around the wind turbine. This paper presents the test results, performed on glass fiber reinforced plastics (GFRP) suitable to construction of wind turbine blades (WTB). The Young modulus, shear modulus, Poisson's ratio, ultimate stress have been determined using tensile and shear tests. Using Dynamical Mechanical Analysis (DMA), the activation energy for transitions that appear in polyester matrix as well as the complex elastic modulus can be determined, function of temperature.

The paper analyses the elasto-plastic behavior of ten samples of E355 steel pipe of the same inner diameter, but with wall thickness ranging between 1.100 and 2.500 mm and length about 100 mm. The samples were subjected to variable internal pressure which was increased from 0 to 600-800 bar (up to the breaking of the pipe), being used the hydraulic oil, type HM46. The outer diameter of the tested pipes was measured successive for each increase of pressure with 100 bars, thus being determined the flow curve of the pipe material characterized by the elasto-plastic behavior and a tenacious failure. It was found that thin pipes, with the ratio between the inner and outer diameter less than 1.1, shows a different flow curve compare to pipes with thick walls, having the ratio between the inner and outer diameter greater than 1.1, the deformations being about two times higher. The rheological models of each type of pipes were identified.

This paper presents a method for estimating the reliability of eddy-current nondestructive inspection by using the rotating magnetic field method. The results of the inspection are considered as memory-less stochastic processes, with the possibility of representation in a bi-dimensional space: ‘good product’ and ‘bad product’. The general formulae are calculated by using the master equation for the time behaviour of the probabilities, the numerical data used for results estimation being obtained by means of an automatic eddy current installation with rotating magnetic field. The samples used had 20 μm, 40 μm and 98 μm deep artificial faults, and the control speed ranged between 0.05 and 1 m s−1.

This work proposes the utilization of the phase information from the response signal of an eddy current transducer with orthogonal coils in order to get an enlarged image of carbon fibers from a graphite-epoxy composite type [−45 2 0 ,+45 2 0 ] S and [−45 2 0 ,0 2 0 +45 2 0 ] S consisting of 24 fiber layers. A 2D Fourier transform was then applied to the phase signal, which is propagated backward by means of an operator that represents the solution of a Helmholtz equation. The image can be focused on a fiber layer choosing an adequate phase multiplication constant. With the view to obtain a clear-cut fiber contour, a Canning optimal regularizing algorithm was used. By choosing another phase multiplication constant the image can be focused on another fiber layer.

This work presents a new type of eddy-current sensor used in non-destructive evaluation, being able to detect with equal sensitivity both long and short flaws, in any orientation. The proposed sensor is of send–receive encircling type, using for the control operation a rotating magnetic field.

The work presents a method for the quantitative evaluation of the shape and severity of discontinuities by processing the signal delivered by the sensor with orthogonal coils. Unlike other sensors used by now to this end, the sensor we propose presents the advantage of a more exact localization of the discontinuity and an increased resolution.

The automatic systems for eddy current non-destructive control permit rendering evident superficial discontinuities in the electroconductive products. Their response is influenced by numerous factors and therefore it is quite difficult to quantitatively estimate the shape and severity of the detected discontinuity, based on the sensor's response. This work presents an artificial intelligence system based on fuzzy logic, dedicated to the quantitative evaluation of the severity of material discontinuities existing on wires, which dramatically reduces noise influence and enables to determine the discontinuity depth as a function of prescribed quality classes.

Prosthetic heart valves of the Bjork-Shiley Convexo-Concave (BSCC) type have long been used extensively in implants; however, there have been reports of cases where one component of the valves failed, leading to the demise of the patient. This paper presents a new method for noninvasive electromagnetic evaluation for this type of valve, using an eddy current transducer with orthogonal coils. In vitro experiments have shown that discontinuities of outlet strut with depths equal or larger than 0.4mm can be detected with a probability of detection (POD) of 86.4%, and in the case of discontinuities with depth equal or larger than 0.6mm with POD of 97%.Copyright © 2008 by ASME

This paper presents complementary methods used in nondestructive evaluation (NDE) of composite materials reinforced with carbon woven fibers as two electromagnetic methods using sensor with orthogonal coils and sensor with metamaterials lens as well as ultrasound phased array method and Fiber Bragg gratings embedded instead of a carbon fiber for better health monitoring. The samples were impacted with low energy in order to study delamination influence. The electromagnetic behavior of composite was simulated by finite- difference time-domain (FDTD) software, showing a very good concordance with electromagnetic nondestructive evaluation tests.

For the control of fuel channels of PHWR CANDU type, a novel type of rotating magnetic field eddy current transducer was developed, as well as the afferent electronic equipment. So, the position and the tilt of garter springs using neuro‐fuzzy network could be determined, and the presence of the discontinuities on external and internal surface of the tubes can be emphasized. A numerical code for the solving of the forward problem was developed.

To evaluate fatigue state of austenitic and ferromagnetic steels a sensors array was developed. The studied samples had different degree of fatigue damage until the state of fatigue cracks. The resolution of sensors array was improved using maximum likelihood procedure. To determine the weight vector, the forward problem was solved, using dyadic Green’s functions for layered media.

This paper present the results obtained at examination of steam generator tubes samples made from Incoloy 800, using eddy current transducer with rotating magnetic field. The emission part creates a magnetic rotating field which induces eddy currents in the walls of tubes, the reception being made with an array of sensors. The method presents the advantages of a complete inspection of tube's surface at one passing. To increase the precision of discontinuity localisation, a super resolution algorithm is used. The results are comparables with those obtained at the inspection with rotating probe, being obtained a good correlation, the speed of control being superior in the case of transducer with rotating magnetic field.

In this paper we have studied the electromagnetic field scattering on ideal surface breaking and subsurface cracks, solving the forward and inverse problems of diffraction. The aim of this paper is to present the possibility of the evaluation of position and severity of long and thin cracks in electrically conductive materials. This procedure presents the advantage of reduced calculation time and power, reported for the classical inversion method. The simulated data are compared with experimental data, being in good correlation.

For the inspection the pressure tubes from PHWRs nuclear power plant an eddy current transducer with rotating magnetic field were improved. This paper presents this transducer and the equipment used. To detect the garter springs position, a neuro-fuzzy system trained with artificial data obtained from an analytical model using dyadic Green's function and afferent numerical code is used. Here, the results of pressure tubes sample inspection, emphasising position, localisation and shapes of slots are presented.

This paper proposes the use of a new type of eddy current transducer – the inner eddy current transducer with rotating magnetic field. This transducer has the capability to detect the discontinuities of pressure tubes and also the presence and concentration of Zirconium hydrides. This method is very promising for the determination and characterisation of blisters and delayed hydride cracking. By inversion of data, it is possible to estimate the depth and equivalent diameter of blisters.

This work is dedicated to the theoretical modelling of the eddy current transducer with orthogonal coils destined to control flat metallic surfaces. The exact solutions of the Maxwell equations for the assembly transducer-conductive half-space are obtained by modelling the current source by a Dirac distribution and using the dyadic Green functions of the problem. Theoretical solutions are presented describing the transducer operation in the presence of a discontinuity in the conductive medium.

Monitoring large structures is gaining a lot of interest, diagnosis and prognosis methods, as well as sensors based on different physical principles being developed. The monitoring is in tight connection with the nondestructive examination. This paper presents a new type of passive wireless sensors for monitoring of strain-stress having a special type of metamaterial as sensitive element, namely a split ring resonator. In order to increase the sensitivity and the tuning on a desired interrogation frequency, self-assembled layer-by-layer single wall carbon nanotubes/graphene method is used. In the same time, radio-frequency identification (RFID) tag, an essential element for wireless sensors, can be realized using split ring resonators.Copyright © 2014 by ASME

This work is dedicated to the theoretical and experimental study of a new type of eddy current transducer developed to measure the thickness of the metallic protective coating on ferromagnetic steel wires. The transducer is of send-receive type. The emission part generates a rotating magnetic field while the reception part consists of a number of coils surrounding the wire. The transducer is connected to an eddy current control installation with rotating magnetic field of multiplied input stages.

This work presents the analytical solutions describing the operation of a rotating magnetic field transducer used in the eddy current defectoscopy for detecting the long flaws situated parallelly to the inspected piece generatrix. The method uses the expanding of the real transducer's three-phase system into an infinite sequence of axial and longitudinal currents whose intensity is given by a Fourier expansion, estimating the electromotive voltage induced in the transducer. By solving the equation of diffusion for the three media and considering the boundary conditions, the vector magnetic potential is determined for each medium. This work also presents the most important theoretical parameters of the transducer, as well as the experimental graphs obtained for cases of the transducer's applications.

In this paper we present a numerical simulation of an eddy current transducer with orthogonal coils. The investigation develops a 3D numerical analysis based on the magnetic scalar and vector potentials. In order to test the accuracy of our numerical analysis we used both the standard finite element method and the hierarchical finite element method of high order. It is found that the image from the transducer when it passes over a discontinuity is in excellent agreement with 3D theoretical predictions. This numerical modelling approach is very useful in analyzing and optimizing transducers with orthogonal coils.

This work presents two methods for nondestructive evaluation of the severity of material discontinuities in nonmagnetic conductive plates by eddy currents generated by a transducer with orthogonal coils. The first method deals with long rectilinear discontinuities located beneath the surface under test and having a negligible width. It is based on the geometrical theory of diffraction of electromagnetic waves generated by the transducer. The conditions under which a real transducer satisfies the diffraction model hypotheses are specified. In this case, the experimental results are in good agreement with the theoretical ones. The second method concerns small volumetric discontinuities whose shape and size are evaluated by an eddy-current holographic procedure. When the discontinuity size is comparable with that of the transducer, this permits reconstruction of the shape and determination of the depth of the discontinuity beneath the surface under test.