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![Primary and secondary magnetic field. Eddy current on the test piece (adapted from [14]).](profile/Javier-Garcia-Martin/publication/51873231/figure/fig1/AS:213129528123392@1427825447821/Primary-and-secondary-magnetic-field-Eddy-current-on-the-test-piece-adapted-from-14.png)
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![B-H curve in high nickel steel (adapted from [26]).](profile/Javier-Garcia-Martin/publication/51873231/figure/fig10/AS:213129532317697@1427825448030/B-H-curve-in-high-nickel-steel-adapted-from-26_Q320.jpg)
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 in...
Contexts in source publication
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... an alternating energized coil of impedance approaches an electrically conductive non-ferromagnetic material, the primary alternating magnetic field penetrates the material and generates continuous and circular eddy currents. The induced currents flowing within the test piece generate a secondary magnetic field that tends to oppose the primary magnetic field, as shown in Figure 1. This opposing magnetic field, coming from the conductive material, has a weakening effect on the primary magnetic field. ...Context 2
... hundred or two hundred are typical values of relative permeability. Figure 10 shows two magnetization curves of unannealed and annealed steel and plots the relation between B and H fields [26]. The relationship between H and B is not linear and presents hysteresis in ferromagnetic materials. ...Context 3
... first part of the curve has the greater slope, and the second part has the smaller slope [27]. Saturation state is reached when the increase of H causes very little increase in B, as Figure 10 indicates. ...Context 4
... following subsection explains this phenomenon. Figure 10. B-H curve in high nickel steel (adapted from [26]). ...Context 5
... the normalized impedance plane of Figure 11, the lift-off curves start at the air point , when there is no test piece. In this case, air point is instead of as discussed in the previous section because a different transformation in the Y-axis has been used as shown in Equation (17). ...Context 6
... Figure 11 plots lift-off lines in steps of 0.1 mm. The impedance values are plotted using triangles. ...Context 7
... some cases, when measuring the thickness of non-conductive coatings over metal, lift-off is employed as a useful property. Figure 11 demonstrates that when the test piece is closely adjacent to the coil probe, the triangle separation is larger than when the test piece is further away. This means that the resolution to measure non-conductive coatings is greater for thin coatings [33]. ...Context 8
... means that the resolution to measure non-conductive coatings is greater for thin coatings [33]. Figure 11. Lift-off in steps of 0.1 mm (triangle) and tilt in steps of 10 (round) for a normalized impedance plane (adapted from [33]). ...Context 9
... presented an analytical model of wobble in heat exchanger tube inspection with bobbin coils [34]. Figure 12 illustrates the offset position of the tube inside the bobbin coils. Wobble simulation: a bobbin coil in an offset position to a tube (adapted from [34]). ...Context 10
... technique can be applied to the measurement of metal thickness beneath non- conductive coatings and to the measurement of microstructure and strain/stress, where the output is highly sensitive to the lift-off effect. They proposed an approach using two reference signals calculated in two stages as Figure 13 shows. Figure 13. ...Context 11
... proposed an approach using two reference signals calculated in two stages as Figure 13 shows. Figure 13. Diagram block using normalization to reduce lift-off effect (adapted from [31]). ...Context 12
... is the reciprocal of conductivity . As an example, Figure 14 illustrates the electromagnetic field penetration inside aluminum at two different frequencies (200 Hz and 10 kHz) [38]. Typical values of standard penetration depth for pure aluminum are 5.99 mm at 200 Hz and 0.847 mm at 10 KHz. . ...Context 13
... authors such as Guang et al. presented a system for the inspection of aircraft structures [43]. The system generated pulse excitation that energized a planar multi-line coil of Figure 15(a). The transient field was detected via a giant magnetoresistive GMR field sensor placed on the line of symmetry at the center of the source coil. ...Context 14
... the absence of discontinuities, the normal component of the magnetic field was zero at the center of the source coil. When the uniform distribution of the induced currents was distorted by a rivet and/or crack as sketched qualitatively in Figure 15(b) the zero field on the line of symmetry was destroyed and a nonzero transient signal of the normal component was measured by the GMR sensor. [43]). ...Context 15
... researchers such as Abidin et al. studied the influence of duty cycle in pulses testing rivet joints [53]. Figure 16 [53]). (b) Spectrum distribution under different pulse widths (adapted from [53]). ...Context 16
... most widely-used probes encircle the test piece in eddy current testing. These probes are commonly used to test bars or tubes either externally or internally and are shown in Figures 17(a,c). ...Context 17
... coils are sensitive to parallel discontinuities to the axis of the tube or bar as eddy currents describe radial circumferences in an opposing sense of currents around the energized coil current, as shown in Figure 17(b). Internal encircling coil probes permit internal testing of tubes. ...Context 18
... encircling probes usually test heat exchanger tubing at power plants at a constant rate of speed. Figure 17(c) shows an internal coil probe for ferromagnetic inspection [58]. [58]). ...Context 19
... types of sensors are used in flat surface inspection. The eddy currents on the test piece are circumferences parallel to the surface as Figure 18(a) illustrates. When a penetrating crack occurs on the surface, current flow is strongly altered and the crack can be detected. ...Context 20
... probes can also automatically detect longitudinal cracks in tubes or bars using a rotating system. The eddy current probe rotates at a high speed around the test material, which is moved longitudinally, and scans its surface helically as Figure 18(b) illustrates [60]. ...Context 21
... compensate for this disadvantage, absolute mode probes are incorporated along with differential ones to detect the presence or absence of weld seams and long cracks. Figure 19(a) shows a horseshoe-shaped coil, which is useful in the detection of laminar flaws. The authors Placko et al. used this type of probe to inspect graphite composite materials [12]. ...Context 22
... authors Placko et al. used this type of probe to inspect graphite composite materials [12]. The magnetic flux penetrates parallel to the surface, and the eddy currents encircle the magnetic flux lines in the test piece as Figure 19 (a) shows. Laminar flaws alter eddy current flow significantly, which explains their high sensitivity to them. ...Context 23
... authors have tested spiral coils in eddy current testing. Ditchburn et al., for instance, presented the detection of long cracks in steel using the probe shown in Figure 19(b) [39]. Eddy currents describe circumferences on the test piece surface. ...Context 24
... authors asserted that spiral coils offered attractive features in terms of sensitivity. Arrays of coils create electromagnetic eyes used in eddy current testing as Figure 19(c) illustrates. Coil matrices permit 2D image extraction and the use of image processing techniques. ...Context 25
... simplest absolute probes consist of a single coil that generates eddy currents and senses changes from the eddy current field as Figure 21(a) shows. Absolute probes provide an absolute voltage signal as Figure 21(b) illustrates. ...Context 26
... simplest absolute probes consist of a single coil that generates eddy currents and senses changes from the eddy current field as Figure 21(a) shows. Absolute probes provide an absolute voltage signal as Figure 21(b) illustrates. The disadvantage of these coil probes is their high sensitivity to temperature variations. ...Similar publications
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Citations
... The need to detect defects in aviation components is critical, aiming to preclude catastrophic failures and ensure the optimal performance of aircraft systems. In light of this, the demand for advanced non-destructive testing (NDT) techniques is constantly increasing, and specific materials and objects require their ongoing development [1][2][3]. ...
... , (2) where T ECP , T ECA represent the total inspection time of the test object using a single-element eddy current transducer (ECP) and ECA, respectively. To account for the scanning trajectory of the test object with a single-element ECP and ECA, let's assume that the width of the test object (or the inspected area of the test object) coincides with the width of the array [10]. ...
Eddy current array (ECA) technology is increasingly being used in the aerospace industry for non-destructive testing of aircraft components. This study evaluates the performance of ECA in detecting defects in aircraft components, focusing on its effectiveness, reliability, and sensitivity. The study evaluates the effectiveness of ECA technology in eddy current defectoscopy by introducing a dimensionless efficiency coefficient, then seeks to validate this coefficient through experimental testing of aircraft component materials with artificially induced defects of various sizes, types, and orientations to simulate real-world scenarios. ECA’s sensitivity in detecting small and subsurface defects is analyzed, along with precise defect sizing and positional information. Reliability and repeatability are investigated through repeated measurements. Furthermore, the article analyses the impact of various factors on the performance of ECA, including surface conditions, probe configurations, and inspection parameters. Comparative analysis is performed to assess the advantages and limitations of ECA in comparison to other conventional inspection methods. The findings of this study will contribute to a better understanding of the capabilities and limitations of ECA in detecting aircraft component defects. The results will aid in optimizing inspection strategies, enhancing the reliability of defect detection, and improving the overall maintenance practices in the aerospace industry.
... ECT relies on the interaction between a primary magnetic field and the test material, inducing eddy currents within the object. These currents can reveal discontinuities such as cracks, corrosion, and material degradation, which are detected by monitoring changes in coil impedance or measuring the induced magnetic field [1]. ECT offers a high level of sensitivity for identifying materials and assessing microstructural states [2]. ...
... In eddy current testing, the impedance parameterŻ 0 for each coil is a complex number, defined as in Equation (1), which represents the ratio of the voltage to the current (V 0 /I 0 ) under a single-frequency harmonic excitation f [1]: ...
... Figure 1 illustrates the phenomenon where an induced current is generated in the conductor due to the changing magnetic flux density when an alternating current is passed through the primary coil, as defined by Faraday's law of electromagnetic induction in Equation (4). The electromotive force (ε) is directly proportional to the rate of change in the magnetic flux density over time, represented by Φ B [1]. When the excitation coil is brought close to the test object, the object induces circular currents (eddy currents) under the influence of an alternating magnetic field. ...
The electromagnetic eddy current non-destructive testing system enables the non-destructive analysis of surface defect information on tested materials. Based on the principles of eddy current detection, this paper presents a digital eddy current detection method using high-speed sampling based on STM32. A differential eddy current coil is used as the detection probe, and the combination of a differential bridge and a differential amplifier circuit helps to reduce common-mode noise interference. The detection signal is collected via an STM32-based acquisition circuit and transmitted to the host computer through Ethernet for digital demodulation processing. The host computer performs operations such as smoothing averaging, sinusoidal fitting, and outlier removal to extract the amplitude and phase of the detection signal. The system also visually displays the condition of the tested object’s surface in real time through graphical visualization. Testing showed that this system can operate at frequencies up to 8.84 MHz and clearly identify defects as narrow as 1 mm on the surface of the tested steel plate.
... Moreover, magnetic imaging finds significant application in nondestructive testing, a method that enables the detection of surface cracks or internal defects in materials without inflicting damage [12]. Common electromagnetic techniques in this realm include eddy current testing [13,14], magnetic particle inspection, and magnetic flux leakage detection [15][16][17]. Specifically for ferromagnetic materials, nondestructive evaluation employing magnetic flux leakage detection is advantageous. ...
The precise mapping of magnetic fields emitted by various objects holds critical importance in the fabrication of industrial products. To meet this requirement, this study introduces an advanced magnetic detection device boasting high spatial resolution. The device’s sensor, an array comprising 256 unpackaged gallium arsenide (GaAs) Hall elements arranged in a 16 × 16 matrix, spans an effective area of 19.2 mm × 19.2 mm. The design maintains a 1.2 mm separation between adjacent elements. For enhanced resolution, the probe scans the sample via a motorized rail system capable of executing specialized movement patterns. A support structure incorporated into the probe minimizes the measurement distance to below 0.5 mm, thereby amplifying the magnetic signal and mitigating errors from nonparallel probe–sample alignment. The accompanying interactive software utilizes cubic spline interpolation to transform magnetic readings into detailed two- and three-dimensional magnetic field distribution maps, signifying field strength and polarity through variations in color intensity and amplitude sign. The device’s efficacy in accurately mapping surface magnetic field distributions of magnetic and magnetized materials was corroborated through tests on three distinct samples: a neodymium–iron–boron magnet, the circular magnetic array from a smartphone, and a magnetized 430 steel plate. These tests, focused on imaging quality and magnetic field characterization, underscore the device’s proficiency in nondestructive magnetic field analysis.
... Eddy current testing is another non-destructive evaluation method based on Faraday's law of electromagnetic induction. It involves oscillating electrical currents induced in a conductive medium by an alternating magnetic field [107,110]. The Several other non-destructive techniques are employed for the detection of defects in AM parts. ...
... Eddy current testing is another non-destructive evaluation method based on Faraday's law of electromagnetic induction. It involves oscillating electrical currents induced in a conductive medium by an alternating magnetic field [107,110]. The presence of material defects disrupts the flow of eddy currents, generating a secondary magnetic field that opposes the main field. ...
Over the past decade, significant research has focused on detecting abnormalities in metal laser powder bed fusion (L-PBF) additive manufacturing. Effective online monitoring systems are crucial for enhancing process stability, repeatability, and the quality of final components. Therefore, the development of in situ detection mechanisms has become essential for metal L-PBF systems, making efficient closed-loop control strategies to adjust process parameters in real time vital. This paper presents an overview of current in situ monitoring systems used in metal L-PBF, complemented by ex situ characterizations. It discusses in situ techniques employed in L-PBF and evaluates the applicability of commercial systems. The review covers optical, thermal, acoustic, and X-ray in situ methods, along with destructive and non-destructive ex situ methods like optical, Archimedes, and X-ray characterization techniques. Each technique is analyzed based on the sensor used for defect detection and the type or size of defects. Optical in situ monitoring primarily identifies large defects from powder bed abnormalities, while thermal methods detect defects as small as 100 µm and keyholes. Thermal in situ detection techniques are notable for their applicability to commercial devices and efficacy in detecting subsurface defects. Computed tomography scanning excels in locating porosity in 3D space with high accuracy. This study also explores the advantages of multi-sensor in situ techniques, such as combining optical and thermal sensors, and concludes by addressing current research needs and potential applications of multi-sensor systems.
... DDY current (EC) nondestructive testing [1] is recognized as an efficient and powerful noncontact method in analyzing the integrity of materials. The extensively used EC probes are typically built using induction coils [2], for which the sensitivity is proportional to the excitation frequency and inversely correlated with the coil size. ...
This work presents a flaw detection system consisting of an array of eddy-current (EC) probes based on giant-magnetoresistance (GMR) sensors for mapping the defects on a metal sheet. Before measurement, a spatially dependent calibration process was done to compensate for the inter-channel inconsistency in output offsets and responsivity. The calibrated 8-channel probe array exhibits high sensitivity in revealing tiny features of defects with superior spatial resolution. The proposed system allows for the visualization of the geometric characteristics of the surface defects with an inter-spacing of more than 2 mm. The suggested approach has great potential in the nondestructive testing of metallic sheets for the characterization of minor and intricately shaped flaws.
... Eddy current (EC) testing (ECT), which is one of the common non-destructive testing (NDT) methods, is widely used to detect defects on the surface or subsurface of metal materials [1,2]. This method not only plays a key role in the inspection of defects but can also obtain information about their structure and state. ...
A flexible or planar eddy current probe with a differential structure can suppress the lift-off noise during the inspection of defects. However, the extent of the lift-off effect on differential probes, including different coil structures, varies. In this study, two planar eddy current probes with differential pickup structures and the same size, Koch and circular probes, were used to compare lift-off effects. The eddy current distributions of the probes perturbed by 0° and 90° cracks were obtained by finite element analysis. The analysis results show that the 90° crack can impede the eddy current induced by the Koch probe even further at relatively low lift-off distance. The peak-to-peak values of the signal output from the two probes were compared at different lift-off distances using finite element analysis and experimental methods. In addition, the effects of different frequencies on the lift-off were studied experimentally. The results show that the signal peak-to-peak value of the Koch probe for the inspection of cracks in 90° orientation is larger than that of the circular probe when the lift-off distance is smaller than 1.2 mm. In addition, the influence of the lift-off distance on the peak-to-peak signal value of the two probes was studied via normalization. This indicates that the influence becomes more evident with an increase in excitation frequency. This research discloses the lift-off effect of differential planar eddy current probes with different coil shapes and proves the detection merit of the Koch probe for 90° cracks at low lift-off distances.
... Highly sensitive magnetometers [1] have a diverse range of applications that span from geophysics and exploration [2], to non-destructive magnetic materials testing [3][4][5], archaeology and palaeomagnetism [6], environmental monitoring [7], navigation and positioning [8], space exploration [9], biology, neuroscience [10][11][12], and fundamental physics research [10,13]. Over the past few decades, advances in quantum science spurred the development of various types of magnetometers with very different operating principles: from electron spin resonance magnetometers such as SQUIDS to optically pumped magnetometers (OPMs) with NV centers in diamond or thermal atoms. ...
We realise an intrinsic optically pumped magnetic gradiometer based on non-linear magneto-optical rotation. We show that our sensor can reach a gradiometric sensitivity of 18 fT cm−1Hz−1 and can reject common mode homogeneous magnetic field noise with up to 30 dB attenuation. We demonstrate that our magnetic field gradiometer is sufficiently sensitive and resilient to be employed in biomagnetic applications. In particular, we are able to record the auditory evoked response of the human brain, and to perform real-time magnetocardiography in the presence of external magnetic field disturbances. Our gradiometer provides complementary capabilities in human biomagnetic sensing to optically pumped magnetometers, and opens new avenues in the detection of human biomagnetism.
... Ultrasonic testing capability to detect small defects with high sensitivity makes it particularly suited for critical applications, such as detecting internal flaws in metal plates. Eddy current testing is commonly employed in industries offering high sensitivity for surface and near-surface defects [10][11][12][13]. Nevertheless, its limited penetration depth restricts its effectiveness in detecting deep-seated defects. ...
This paper presents a nondestructive method for accurately identifying internal flaws in metal plates, which is crucial for ensuring structural integrity in safety-critical applications. The technique relies on analyzing laser-induced ultrasound (LIU) longitudinal wave time-of-flight, as demonstrated through a theoretical five-layer model. Experimental validation was conducted using a piezo-sensor in contact with a slab containing millimetric artificial cavities immersed in air, resulting in a discrepancy of 5.05%. In contrast, experiments performed in a water medium exhibited a lower discrepancy of 2.5%. (Discrepancy refers to differences between measurements obtained through an experimental time-of-flight analysis and caliper measurements.) The results obtained in water-based experiments affirm the accuracy of the proposed model. B-scan measurements and the five-layer model were utilized to generate 2D reconstructed images, enabling precise localization and sizing of cavities and kissing bonds between plates, finding an average size of kissing bond of 30 µm. In conclusion, the proposed five-layer model, based on a longitudinal wave time-of-flight analysis, provides a straightforward framework for an easy cavity and kissing bond measurements in metal plates.
... The induced eddy currents generate a secondary magnetic field opposing the primary one, triggering a change in coil impedance, which is measured by the ECT instrument. The inspection depth in the sample is defined as the standard penetration depth [30], which is calculated according to where f, , = 0 r denote the excitation frequency, the electrical conductivity and the magnetic permeability of the material, respectively, and where r is the relative magnetic permeability and 0 = 1.256 ⋅ 10 6 H∕m is the magnetic permeability in vacuum [27]. According to Eq. (2), the penetration depth of the eddy currents can be adjusted by setting a suitable excitation frequency f. ...
Powder bed fusion of metals (PBF-LB/M) is currently the most widely adopted additive manufacturing technology for the fabrication of metal parts. However, the inconsistent quality of PBF-LB/M-manufactured parts and high costs for part certification are impeding wider industrial adoption. In-situ monitoring technologies are expected to enable process control in order to ensure consistent quality, and to replace some of the post-process inspection steps, therefore, reducing part certification costs. Eddy current testing (ECT) is a standardized nondestructive testing technique, which can be used as an in-situ monitoring technology to measure the part quality during the PBF-LB/M build cycle. However, the process-induced complex temperature fields in PBF-LB/M parts during the build cycle are among the most relevant disturbances due to the temperature dependence of the electrical conductivity. This study investigates the process-induced temperature influence on in-situ monitoring of relative density using ECT. Parts made from AlSi10Mg were manufactured on a PBF-LB/M machine and the build cycle was monitored using ECT and an infrared camera, which was used to extract the part surface temperature right before the ECT measurement. The results demonstrate that the temperature increase of the parts during the build cycle decreases the electrical conductivity independently of the relative part density, which was measured via micro-computed tomography. Therefore, a temperature compensation method was proposed and applied demonstrating that a layer-to-layer difference of 0.15 % relative density can be detected via ECT. Consequently, it has been demonstrated that ECT is an effective in-situ monitoring technology for PBF-LB/M, even in the presence of temperature disparities within parts.
... Authors such as Peng et al. [12] have used differential coils to detect surface cracks in aluminum plates by measuring the variations in the inductive and resistive components of the coil. However, the sensitivity of coils is much lower than the sensitivity of the current magnetic sensors, so EC-NDE techniques that use these magnetic sensors are more reliable than the classical techniques [13,14]. Giant magnetic resistance (GMR) sensors are the most popular magnetic sensors used to develop EC-NDE systems [13,15,16]. ...
... However, the sensitivity of coils is much lower than the sensitivity of the current magnetic sensors, so EC-NDE techniques that use these magnetic sensors are more reliable than the classical techniques [13,14]. Giant magnetic resistance (GMR) sensors are the most popular magnetic sensors used to develop EC-NDE systems [13,15,16]. The magnetic fields induced by eddy currents can also be used in medical applications. ...
Eddy currents are an electromagnetic phenomenon that represent an inexhaustible source of inspiration for technological innovations in the 21st century. Throughout history, these currents have been a subject of research and technological development in multiple fields. This article delves into the fascinating world of eddy currents, revealing their physical foundations and highlighting their impact on a wide range of applications, ranging from non-destructive evaluation of materials to levitation phenomena, as well as their influence on fields as diverse as medicine, the automotive industry, and aerospace. The nature of eddy currents has stimulated the imaginations of scientists and engineers, driving the creation of revolutionary technologies that are transforming our society. As we progress through this article, we will cover the main aspects of eddy currents, their practical applications, and challenges for future works.
