Eddy Current Array Research Articles

Online Quality Control of Powder Bed Fusion with High-Resolution Eddy Current Testing Inductive Sensor Arrays

Online Quality Control of Powder Bed Fusion with High-Resolution Eddy Current Testing Inductive Sensor Arrays

Eddy Current Array for Defect Detection in Finely Grooved Structure Using MSTSA Network.

In this paper, we focus on eddy current array (ECA) technology for defect detection in finely grooved structures of spinning cylinders, which are significantly affected by surface texture interference, lift-off distance, and mechanical dither. Unlike a single eddy current coil, an ECA, which arranges multiple eddy current coils in a specific configuration, offers not only higher accuracy and efficiency for defect detection but also the inherent properties of space and time for signal acquisition. To efficiently detect defects in finely grooved structures, we introduce a spatiotemporal self-attention mechanism to ECA testing, enabling the detection of defects of various sizes. We propose a Multi-scale SpatioTemporal Self-Attention Network for defect detection, called MSTSA-Net. In our framework, Temporal Attention (TA) and Spatial Attention (SA) blocks are incorporated to capture the spatiotemporal features of defects. Depth-wise and point-wise convolutions are utilized to compute channel weights and spatial weights for self-attention, respectively. Multi-scale features of space and time are extracted separately in a pyramid manner and then fused to regress the bounding boxes and confidence levels of defects. Experimental results show that the proposed method significantly outperforms not only traditional image processing methods but also state-of-the-art models, such as YOLOv3-SPP and Faster R-CNN, with fewer parameters and lower FLOPs in terms of Recall and F1 score.

Eddy Current Sensor Array for Electromagnetic Sensing and Crack Reconstruction with High Lift-Off in Railway Tracks.

A reliable and efficient rail track defect detection system is essential for maintaining rail track integrity and avoiding safety hazards and financial losses. Eddy current (EC) testing is a non-destructive technique that can be employed for this purpose. The trade-off between spatial resolution and lift-off should be carefully considered in practical applications to distinguish closely spaced cracks such as those caused by rolling contact fatigue (RCF). A multi-channel eddy current sensor array has been developed to detect defects on rails. Based on the sensor scanning data, defect reconstruction along the rails is achieved using an inverse algorithm that includes both direct and iterative approaches. In experimental evaluations, the EC system with the developed sensor is used to measure defects on a standard test piece of rail with a probe lift-off of 4-6 mm. The reconstruction results clearly reveal cracks at various depths and spacings on the test piece.

Evaluation of Eddy Current Array Performance in Detecting Aircraft Component Defects

ABSTRACT 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.

An improved multi-frequency eddy current array sensor for detecting micro-defects of welding seam in metal plates

This study proposes an improved multi-frequency eddy current array sensor for the accurate detection of micro-defects (under-welding, over-welding, partial welding breakage, and minute penetration holes) of welding seam in metal plates. The primary goal is to further reduce the external and internal noise of the induced coil by optimizing the composition structure of the eddy current probe, thereby improving its sensitivity and signal-to-noise ratio in micro-defect detection. In response to the issue of external noise, this research introduces a gradient differential coil model, which can compensate for initial errors based on a geometrically balanced structure. By establishing a 3D simulation model and a physical mechanical structure, the suppression effect of this structure on excitation magnetic field and external environmental interference is verified. Furthermore, for the internal noise, a mathematical model of the direct stranded litz wire is established. Theoretical calculations and experimental validation confirm that the litz wire exhibits lower eddy current loss and higher Q value compared to traditional copper conductors, thus mitigating internal noise and improving signal-to-noise ratio. On this basis, the excitation mode of the eddy current coil probe array is set to a multi-frequency excitation method based on a center frequency, greatly reducing the electromagnetic interference between channels. Experimental results demonstrate that the improved eddy current sensor can effectively recognize as low as Φ1 mm weld penetration defect at a lift-off value of 0.5 mm, achieving a remarkably high signal-to-noise ratio of approximately 17.7 dB.

High resolution magnetic field imaging probe with two rows of TMR sensors for small defects inspection

It is still a challenging problem to detect small defects for eddy current array probes, which requires the probes to possess excellent sensitivity, as well as high spatial resolution. This paper presents a novel high-resolution magnetic field imaging probe with two rows of tunneling magnetoresistance (TMR) array sensors. The bare die sensors are integrated on a printed circuit board by golden wire bonding technology. The two rows of sensors are placed staggered with each other. The data of the two arrays are merged into a matrix, in which way the image pixel pitch is increased to 0.25 mm. The probe employs a differential scheme to suppress the noise, so as to detect the weak signal of small defects. To highlight the weak defect indications, feature extraction and segmentation algorithms are developed. The experimental results confirm that the proposed method can inspect a small defect with dimensions 1 mm (length) × 0.1 mm (width) × 0.1 mm (depth) on a stainless-steel sample.

Eddy current array developments for remote deployment on the ITER project

The inspection of welds and components for nuclear applications can be more challenging due to extreme levels of radiation and temperature. A development project in collaboration with the UK Atomic Energy Authority (UKAEA) is being conducted to develop non-destructive testing (NDT) procedures for inspecting the remotely welded joints within the ITER facility. Initially, a feasibility study has been carried out to identify the most suitable non-destructive technique. Eddy current array (ECA), phased array ultrasonics and guided wave electromagnetic acoustic transducers (EMATs) were considered as candidate solutions and, following the feasibility study, ECA was selected to be taken forward for further development. Subsequently, dedicated high- and low-frequency array probes have been developed and tested to detect and size surface and buried defects employing encoder and calibration curves. The research has been extended to characterise defects such as tungsten inclusions using the phase angle. To avoid damage to the electronics in extreme environments, the ECA probe coils were separated from the excitation and data acquisition unit with 60 m coaxial coils to achieve a high signal-to-noise ratio. The results revealed that the ECA technique can successfully be deployed remotely for the detection and sizing of defects down to 3 mm in extreme environments.

Space–Time Pulsed Eddy Current Array for NDT of Wellbore Casings Based on MIMO Technique

Space–Time Pulsed Eddy Current Array for NDT of Wellbore Casings Based on MIMO Technique

Classification of non-magnetic metals based on eddy current array sensors

ABSTRACT With the promotion of the circular economy, there has been a growing focus on recycling scrap metal. Eddy current detection offers a new direction for the classification of non-magnetic metals. However, most existing research employs double-coil eddy current sensors, and there is a need to improve the detection range and accuracy. Aiming at the above problems, this paper proposes a classification of non-magnetic metals based on eddy current array sensors, which uses sensors to obtain the mutual inductance trajectory of the metal as it passes through each receiving coil, and uses the phase value of its amplitude peak point for the classification of the metal. The paper discusses the impact of different running trajectories and lift-off heights on the classification accuracy. The experimental findings indicate that compared to the dual-coil sensor, the effective detection range increases by over five times. Moreover, the classification accuracy within the detection range reaches 98.4%.

Standard development for Eddy Current Arrays in lieu of Magnetic Particle Testing

The technology of Eddy Current Arrays has advanced considerably in recent years. In several trials, superior performance compared to magnetic particle testing was shown. In response, ASME has published new articles on Eddy Current Array (ECA) testing in the 2019 edition of the BPV, and IIW has started a working group to develop ISO standards for the use of eddy current array testing in lieu of magnetic particle testing. Significant interest has been indicated by stake holders, including manufacturers, end-users and regulators. In the paper, the work performed in the IIW working group will be presented. This includes a literature survey on the relative performance of eddy current array testing and magnetic particle testing. In particular, the performance in terms of probability of detection and characterization will be explored. The technical background of performance differences with conventional eddy current testing, magnetic particle testing and dye penetrant testing will be evaluated. Conclusions are drawn on the most important properties to be treated in a new ISO standard in the ISO 17635 framework. The scope of the IIW working group includes a general standard, a weld testing standard and acceptance criteria. Finally, the issues discussed in standard development will be presented and the resulting formulations explained. Comparisons will be made between the ASME and IIW/ISO resolutions.

How to Reach 100% Inspection Coverage of Aeroengine Fan Blades with a High Probability of Detection

In aviation, quality is paramount to determine an aircraft’s airworthiness and keep personnel and passengers safe. Non-destructive testing (NDT) methods are largely used throughout an aircraft’s lifetime, including raw material selection, manufacturing, assembly, and in-service maintenance. As a key component of aircraft, engines are governed under strictly scheduled maintenance programs where they are dismantled and thoroughly inspected. Part of this global inspection concerns the individual verification of fan blades to assess the absence of flaws, such as surface cracks. Due to the complex geometry of fan blades, established methods such as penetrant testing (PT) and magnetic particle inspection (MPI) have been successfully used in past decades to detect surface-breaking flaws in fan blades. However, these techniques are complex to deploy and do not permit results traceability. As an alternative, eddy current (EC) technologies proved to be a good candidate to discriminate flaws as small as 1 mm long. Combining both conventional and eddy current array technology provides valuable information on the integrity of the component. Powered with the development of dedicated signal processing methods, the proposed solution helped to increase signal-tonoise ratio, avoiding any false calls. Once this was achieved, a careful study of the probe’s deployment and compliance with the various changes of geometries—from the blade’s surface to its edges and root, helped ensure optimal crack detection. Finally, recent advances in robotics enabled an automated inspection strategy to perform 100% coverage with high reproducibility and repeatability. This greatly improved the probability of detection of sub-millimeter surface-breaking cracks. This paper describes the study performed to assess the capability of eddy current solutions (conventional and advanced) to replace traditional methods of inspecting titanium fan blades. It also shows how dedicated signal processing enables increased probability of detection. The proposed approach to provide full coverage of the complex geometry and the associated developments are detailed. Finally, the paper presents an integration of the complete inspection technique in an automated system.

Comparison of different reinforcement methods on crack monitoring characteristics of eddy current array sensor

PurposeThis paper aims to study the influence of different reinforcement methods on crack monitoring characteristics of eddy current array sensors, and the sensors with two different reinforcement methods, SUS304 reinforcement and permalloy reinforcement, are proposed.Design/methodology/approachFirst, the finite element model of the sensor is established to analyze the influence of the reinforcement plate’s electromagnetic parameters on the crack identification sensitivity. Then, the crack monitoring accuracy test of sensors with two reinforcement methods is carried out. Finally, the fatigue crack monitoring experiments with bolt tightening torques of 45 and 63 N · m are carried out, respectively.FindingsIn this study, it is found that the crack identification sensitivity of the sensor can be improved by increasing the relative permeability of the reinforcement plate. The crack monitoring accuracy of the sensors with two different reinforcement methods is about 1 mm. And the crack identification sensitivity of the sensor reinforced by permalloy reinforcement plate is significantly higher than that of the sensor reinforced by SUS304 reinforcement plate.Originality/valueThe sensor reinforced by reinforcement plate can work normally under the squeezing action of the bolt, and the crack monitoring sensitivity of the sensor can be significantly improved by using the reinforcement plate with high relative permeability.

An Applied Study on Eddy Current Array Testing Technology for Transportable Pressure Vessels

To solve the problems with the penetrant testing of transportable pressure vessels (“TPVs”), such as failure to detect near-surface defects, low testing efficiency, and damage of penetrating agents to testers’ health and the high-purity media in the TPVs, an experimental study on the eddy current array (“ECA”) testing technology is carried out, and the result is compared with the results of the dye penetrant testing and fluorescent penetrant testing. According to the experiment result, the ECA testing technology is characterized by moderate requirements for the status of the surface to be tested, fast testing, environmental-friendliness, electronic data storage, testing imaging, and accurate testing results. These advantages enable the ECA testing technology to be a green and environmental-friendly nondestructive testing technology that will promote future development and have exciting prospects in TPV testing.

3D surface crack characterization by eddy current array image and a fast algorithm search

Abstract Nowadays, 3D eddy current nondestructive characterization of crack and corrosion defects while using ECA remains an industrial challenge because the obtained image permits to determine only the 2D defect shape. Consequently, this article is devoted to determine directly the crack length and width by eddy current images through sensor array. Afterwards, we extract the maximal impedance amplitude to estimate the crack depth while using the deterministic algorithm that we have recently developed. In fact, the obtained results have demonstrated the effectiveness and the reliability of the proposed method.

Towards Enhanced Eddy Current Testing Array Probes Scalability for Powder Bed Fusion Layer-Wise Imaging

This work presents a new eddy current testing array probe and readout electronics that target the layer-wise quality control in powder bed fusion metal additive manufacturing. The proposed design approach brings important benefits to the sensors' number scalability, exploring alternative sensor elements and minimalist signal generation and demodulation. Small-sized, commercially available surface-mounted technology coils were evaluated as an alternative to usually employed magneto-resistive sensors, demonstrating low cost, design flexibility, and easy integration with the readout electronics. Strategies to minimize the readout electronics were proposed, considering the specific characteristics of the sensors' signals. An adjustable single phase coherent demodulation scheme is proposed as an alternative to traditional in-phase and quadrature demodulation provided that the signals under measurement showed minimal phase variations. A simplified amplification and demodulation frontend using discrete components was employed together with offset removal, vector amplification, and digitalization implemented within the microcontrollers' advanced mixed signal peripherals. An array probe with 16 sensor coils and a 5 mm pitch was materialized together with non-multiplexed digital readout electronics, allowing for a sensor frequency of up to 1.5 MHz and digitalization with 12 bits resolution, as well as a 10 kHz sampling rate.

Gap Measurement of Double-Layer Metal Tube Based on Analytical Solution of Eddy Current Array Under Transmit-Receive Mode

Gap Measurement of Double-Layer Metal Tube Based on Analytical Solution of Eddy Current Array Under Transmit-Receive Mode

A New 2D Displacement Measurement Method Based on an Eddy Current Sensor and Absolute Encoding

A new method of two-dimensional (2D) plane displacement measurement based on an eddy current sensor is proposed in this paper. A series of grooves with different widths and depths are graved on the linear displacement table to form 2D absolute coding using the idea of pseudorandom coding. The eddy current sensor array is arranged above the groove to identify the coding. An artificial neural network is used to establish a measurement model which is the mapping relationship between the output of the eddy current sensor array and the 2D displacement of the workbench. A feasibility experiment showed that in the range of 20 × 20 mm, the root mean square error of measurement in the X- and Y-directions are 83 and 73 μm, respectively. The new method integrates eddy current sensor and artificial neural network modeling to realize 2D displacement measurement, which provides a new solution for displacement and angle measurement.

A quantitative crack monitoring method based on crack disturbed voltage

PurposeThe flexible eddy current array sensor has the characteristics of lightweight and flexibility, which has a great application prospect in the field of fatigue crack monitoring. But the exciting layout and feature signal extraction have a great influence on the crack monitoring characteristics of the sensor. This paper aims to propose a method using crack disturbed voltage as sensitivity to characterize crack propagation.Design/methodology/approachFlexible eddy current array sensors with reverse and codirectional exciting layout are proposed, and the advantages and disadvantages of three characterization methods based on the change of trans-impedance amplitude, the change of the trans-impedance’s real and imaginary part and the crack disturbed voltage are compared and analyzed by finite element simulation. Finally, the fatigue crack monitoring experiment is carried out.FindingsThe crack disturbed voltage and the change of trans-impedance’s imaginary part can effectively characterize the crack propagation for sensors with different exciting layouts. The codirectional exciting layout sensor has better crack identification sensitivity than the reverse exciting layout sensor, especially the induction coil 2. When the distance between the exciting coil and the induction coil is 0.1, 0.2 and 0.3 mm, it is increased by 372.09%, 295.24% and 231.43%, respectively.Originality/valueCrack disturbed voltage can effectively characterize the crack propagation for sensors with two different exciting layouts.

Influence of the defect characteristic in aluminum alloy 7075 in non-destructive electromagnetic testing

The paper presents the results obtained from aluminum alloy 7075 T6 using eddy current testing method (ECT). This method is based on eddy current 3x3 sensor array, commanded through PC by a data acquisition system, allowing several different delay and amplitude technique at transmission and reception. The response of each sensor is stored, ensuring details for reconstructions and imaging procedures. Based on software CIVA simulation and experiment, defect characterization is obtained using the information received by each sensor of the array and establishing the position of the flaw upon the reacting sensor from array. The signal is post processed using super resolution algorithm to enhance signal to noise ratio, thus both surface and under surface flaws shall be identified, (thin or volumetric) or having different tilting reported to the surface and correlation between theoretical and experimental results.

Novel Eddy Current Array Sensor Delivery Tool for Automated Nondestructive Examination of Spent Fuel Pool Liner

Abstract Inspection of a spent fuel pool (SFP) liner of a nuclear power plant is important to validate the integrity of this component to perform its intended function (e.g., confirm that there are not any defects in the pool liner). Eddy current array (ECA) testing offers a reliable and sensitive nondestructive examination (NDE) technique to inspect SFP liners but requires a delivery system to transport the ECA sensor to these hard-to-reach and harsh environment locations. This work presents an ECA sensor delivery tool design for use with inspection of an SFP. The design for a payload delivery tool proof-of-concept model is proposed that can transport an ECA sensor with positional feedback. The tool allows the sensor to traverse the wall of a nuclear SFP liner, with both horizontal and vertical motion capabilities to support positioning and inspection. The tool provides both manual and automatic operating modes with variable speeds. Computational-based simulations and analysis validate that the performance requirements for the ECA sensor delivery tool are satisfied to support inspection of an SFP liner upper region.