Table 5.
Summary of previous studies on application of GMR sensor in eddy current testing.
| Author | Reseach Area | Signal Analysis Tool/Software Simulation | Observations |
|---|---|---|---|
| [103] | Defect classification in aluminium plate test pieces | Neural Network Processing | Probe optimization and defect classification using limited defect features. |
| [95] | To increase the accuracy of the GMR sensor by numerically compensating the hysteresis effect | Finite Impulse Response | Strongly reduced the hysteresis and optimized the probe design by increasing the speed of inspection |
| [104] | Optimize the eddy current testing probe for subsurface tiny crack defect inspection | Maxwell design simulation | The system is able to detect tiny defect cracks of up to 3 mm under the surface. Experimental results prove the main source of noise is the current excitation frequency. |
| [97] | Developed an eddy current testing probe based on an array of GMR sensors for pipe inspection | Fast Fourier Transformation | The array of GMR sensors is able to detect various types of defect. The signal output of the array sensor can be used to classify and define the properties of different defects. |
| [105] | Designed and construct an automatic eddy current system for inspection of an artificial straight defect in an aluminium plate. | Neural network/multilayer perceptron/competitive neural network/finite element simulation | Implementation of the neural network classification technique increases the accuracy of defect classification |
| [106] | Designed and developed an eddy current testing probe using a rotating exciting magnetic field for detection of radial cracks around a fastener | Finite element model simulation | The eddy current testing probe current shift exciting magnetic field is 90° in phase. The simulation and experimental results show the system is able to detect all orientations of a defect under the fastener |
| [107] | Developed an ECT system to classify multiple classes of defect thickness in conductive plates. | Support vector machine—SVM | The system successfully classified the thickness defect with an error lower than 1.52%. |
| [99] | Investigated the defect properties based on the phase signal of a GMR sensor | Finite element method (FEM) program | The experimental results proved the phase signal output of the GMR sensor provides more defect information. |
| [108] | Developed an ECT probe for surface defect inspection. | - | The probe was able to detect and measure an artificial defect with a dimension of 0.15 mm width and 0.2 mm depth. |
| [100] | Investigated the efficiency of defect detection using a differential pick-up coil and GMR sensor | - | Both sensors were able to detect defects with thicknesses of more than 1 mm. The GMR sensor detects the defect when the sensing direction crosses the edge defect while the pick-up coil needs the whole magnetic field to cross the defect to detect it. |
| [109] | Designed a 2-D magnetic field camera system to measure the properties of the magnetic field around inner and outer defects in a piping system | - | The system is able to sense the magnetic field in the radial and axial direction. |
| [110] | Proposed a method for deep subsurface defect inspection. | Finite Element Method (FEM) | Experimental and simulation show the system is able to detect deep subsurface defects |
| [111] | Investigated defect signals of an artificial rectangular straight defect in aluminium plates. | - | The experiments showed the direction of the defect is easy to detect if the defect is crossing the magnetic field. |
| [101] | Designed an ECT system based on a GMR sensor and a Field Programmable Gate Array (FPGA) as controller | Fourier Transform analysis | The system able to display the defect signals in amplitude and phase mode. A signal demodulation function has been realized for defect characteristic analysis. |
| [96] | Developed a low-cost ECT system with an automatic calibration system to reduce the uncertainty of GMR sensor measurement. | Static (DC) and dynamic (AC) analysis | The system is capable of inspecting defects using DC and AC exciting magnetic fields with a high percentage of accuracy |
| [112] | Developed an ECT system based on a GMR sensor for surface defect inspection | Polynomial regression | The system scans the defect in the direction of the sensor sensitive scanning area for accurate measurement. |
| [58] | Designed and optimized an ECT probe based on two planar excitation coils and a rectangular magnetic field biasing architecture | LabVIEW/sum squared difference (SSD) and normalized cross correlation (NCC) | Improved the inspection capabilities of the ECT probe with fast scanning time |
| [102] | Developed an ECT probe with radial magnetization | - | The 50° angle axis sensitivity of the GMR sensor to the defect orientation reduces by 28% the average value of the VD parameter |
| [113] | Investigated the performance of magnetic detection in an ECT probe for non-destructive inspection. | Numerical simulations | The results show a GMR sensor is better compared to the coil detector in term of sensitivity and dimensions. |
| [114] | Designed and modeled a magnetic field based on guide magnetic slopes | Finite element method (FEM) | The experimental results show the GMR sensor is sensitive only to the z-component of the magnetic field. |
| [94] | Implementation of an ECT to measure the thickness of metallic plates | - | The experiments show a frequency of 250 Hz is the optimum excitation coil frequency for maximum depth magnetic field penetration in the metal plate |
| [115] | Developed an ECT inspection systems using a GMR sensor | - | The system has the ability to inspect subsurface cracks at frequencies lower than 3.3 kHz |
| [74] | Investigated the optimal arrangement of a GMR sensor for optimum defect inspection. | Analytical model | The analysis shows the length and height of the GMR sensor influence signal strength loss by up to 10% a in 250 µm defect baseline |
| [116] | Investigated the characteristics of the current around an artificial crack for defect geometry identification | Fast Fourier transform/Tikhonov regularization algorithm | Characteristics of the current show a significant pattern with different geometry of cracks. |
| [98] | Proposed a novel invariance analysis for ECT signals in deep subsurface defects under fastener heads | Finite Element (FE) | Presented a reliable ECT inspection technique for different sizes and geometries of cracks under fastener heads. |
| [117] | Proposed an ECT system for inspection of hidden corrosion defects. | FEM | The inspection results show high accuracy with mean errors of less than 2% |
| [118] | Developed a PEC–GMR system for ECT non-destructive testing | Principal component analysis and the k-means algorithm | The system is capable of detecting cracks with a size of 1 mm located up to 10 mm subsurface |
| [119] | Developed an ECT–NDT system based on (GMR) sensors for circuit board (PCB) inspection | COMSOL Multiphysics | The system is capable of detecting and characterizing the type of defect track narrowing, circular holes and track dilatation. |
| [120] | Developed a general procedure for ECT defect sizing and classification in multilayered structures | Partial least squares (PLS)/kernel partial least squares (KPLS) | The KPLS regression method gives a better prediction performance compared to the PLS regression method |
| [121] | Proposed a novel ECT technique based on the induced velocity of eddy currents | Numerical model | The proposed method increases the sensitivity and the depth defect detection of the system. |
| [122] | Investigated the optimum asymmetrical coil-GMR configuration for surface defect inspection | - | The experimental results demonstrated that the intermediate peak does not have any influence on DV value with the depth of defects |
| [123] | Analyzed the sensitivity of GMR sensors and GMI sensors in detecting the magnetic field | Finite Element/Moments analysis | The experimental and modeling results show the GMR and GMI sensors are able to detect the changes of orientation of a magnetic field excited by using AC and DC current sources |
| [54] | Investigate the effect of lift-off in metallic plate thickness measurement | Linear Transformer Model/experimental | The lift-off, material conductivity and the plate thickness have a significant influence on the measurement of metallic plate thickness |
| [124] | Developed an ECT system based on a GMR sensor array for outer steel rope track defect inspection. | Finite element model | The experimental results reveal that the ECT system is able to detect both of LF and LMA type defects in the rope track. |
| [55] | Proposed a novel design of a rotating magnetic field ECT for SG tubes. | Finite Element modeling | The simulation and experimental results show that the probe is sensitive to defects in ferromagnetic and non-ferromagnetic tubes. |
| [125] | Investigated the performance of the PEC technique in material thickness measurement | Experimental | The method was verified experimentally to be suitable for material thickness measurement since the PEC method has deep magnetic penetration. |
| [126] | Enhanced the sensitivity of the ECT-GMR system using analysis of two signal GMR sensors | (3-D) Finite Element Mesh | Simulation results show that the proposed method improved significantly the sensitivity of the system in detection of multilayer subsurface defects |
| [127] | Developed an ECT-GMR system for inspection of defects under fasteners in airframe structures | Time domain and frequency domain features | Experimental results demonstrate the feasibility of the proposed approach for the detection of simulated cracks (less than 1 mm length) that are buried 4 mm deep in the second layer |