TY - JOUR A1 - Reimund, Verena A1 - Blome, Mark A1 - Pelkner, Matthias A1 - Kreutzbruck, Marc T1 - Fast defect parameter estimation based on magnetic flux leakage measurements with GMR sensors N2 - We present a fast inverse scheme that is capable of simultaneously estimating the parameters depth, opening and length for rectangular 3D geometries of surface-breaking defects. The parameter estimation is realized by an iterative least-squares minimization using the trust-region reflective algorithm. A semi-analytic magnetic dipole model that allows the sensor characteristics to be incorporated is used for predicting the stray magnetic fields. Giant magneto-resistance (GMR) measurements were carried out on a test specimen that includes a series of artificial defects. For the estimation of the defect depths relative errors between 0.6% and 15.9% have been obtained. Due to its very low computational costs, the inverse scheme can suitably be employed in automated production environments. KW - Magnetic flux leakage KW - GMR sensor KW - Nonlinear least-squares optimization PY - 2011 U6 - https://doi.org/10.3233/JAE-2011-1391 SN - 1383-5416 SN - 0925-2096 VL - 37 IS - 2-3 SP - 199 EP - 205 PB - IOS Press CY - Amsterdam, The Netherlands AN - OPUS4-24637 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Pelkner, Matthias A1 - Neubauer, Andreas A1 - Blome, Mark A1 - Reimund, Verena A1 - Thomas, Hans-Martin A1 - Kreutzbruck, Marc ED - Chady, T. ED - Gratkowski, S. ED - Takagi, T. ED - Udpa, S.S. T1 - Flux leakage measurements for defect characterization using NDT adapted GMR sensors N2 - High-precision magnetic field sensors are of increasing interest in non destructive testing (NDT). In particular GMR-sensors (giant magneto resistance) are qualified because of their high sensitivity, high signal-to-noise ratio and high spatial resolution. We performed magnetic flux leakage measurements of artificial cracks with a GMR-gradiometer and a 3-axes GMR-magnetometer. Cracks of a depth of 44 μm still could be detected with a sufficient high signal-to-noise ratio. A semi-analytic magnetic dipole model was used for swiftly predicting magnetic stray fields. The reliable reconstruction based on measurements of artificial rectangular-shaped defects is demonstrated. KW - GMR KW - NDT KW - Magnetic flux leakage KW - Reconstruction PY - 2011 SN - 978-1-60750-749-9 SN - 1383-7281 N1 - Serientitel: Studies in applied electromagnetics and mechanics – Series title: Studies in applied electromagnetics and mechanics VL - 35 SP - 217 EP - 224 PB - IOS Press CY - Amsterdam, The Netherlands AN - OPUS4-25374 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pelkner, Matthias A1 - Neubauer, Andreas A1 - Reimund, Verena A1 - Kreutzbruck, Marc T1 - Routes for GMR-sensor design in non-destructive testing N2 - GMR sensors are widely used in many industrial segments such as information technology, automotive, automation and production, and safety applications. Each area requires an adaption of the sensor arrangement in terms of size adaption and alignment with respect to the field source involved. This paper deals with an analysis of geometric sensor parameters and the arrangement of GMR sensors providing a design roadmap for non-destructive testing (NDT) applications. For this purpose we use an analytical model simulating the magnetic flux leakage (MFL) distribution of surface breaking defects and investigate the flux leakage signal as a function of various sensor parameters. Our calculations show both the influence of sensor length and height and that when detecting the magnetic flux leakage of µm sized defects a gradiometer base line of 250 µm leads to a signal strength loss of less than 10% in comparison with a magnetometer response. To validate the simulation results we finally performed measurements with a GMR magnetometer sensor on a test plate with artificial µm-range cracks. The differences between simulation and measurement are below 6%. We report on the routes for a GMR gradiometer design as a basis for the fabrication of NDT-adapted sensor arrays. The results are also helpful for the use of GMR in other application when it comes to measure positions, lengths, angles or electrical currents. KW - Giant magneto resistance KW - Non-destructive testing KW - Magnetic flux leakage KW - Sensor array PY - 2012 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-271325 SN - 1424-8220 VL - 12 IS - 9 SP - 12169 EP - 12183 PB - MDPI CY - Basel AN - OPUS4-27132 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pelkner, Matthias A1 - Neubauer, Andreas A1 - Reimund, Verena A1 - Kreutzbruck, Marc ED - Thompson, D. O. ED - Chimenti, D. E. T1 - Local magnetization unit for GMR array based magnetic flux leakage inspection N2 - GMR sensors are increasingly used for magnetic surface inspection due to their high sensitivity and high spatial resolution. In case of simple planar or cylindrical shaped components, the GMR-based inspection procedure can be automated easily. We present GMR measurements of real fatigue cracks. In addition, we present a probe design using a local magnetization unit and commercially available GMR sensors. The design was carried out by means of finite-element method (FEM) simulations. Using the local probe we measured bearings containing artificial reference cracks of different depths and orientations. Cracks with a depth of 40 µm could be resolved with a signal-to-noise ratio better than 6. A further reduction of the measuring time can be obtained using a sensor array. For this purpose we present a study of the optimized size of the sensing GMR-layers for a NDE-adapted sensor array. The geometric sensor parameters were investigated through simulations of the magnetic flux leakage of surface cracks using an analytic model. T2 - 38th Annual Review of Progress in Quantitative Nondestructive Evaluation CY - Burlington, VT, USA DA - 2011-07-17 KW - GMR KW - Magnetic flux leakage KW - NDE KW - Sensor array PY - 2012 SN - 978-0-7354-1013-8 U6 - https://doi.org/10.1063/1.4716332 SN - 0743-0760 SN - 0094-243X N1 - Serientitel: AIP conference proceedings – Series title: AIP conference proceedings IS - 1430 SP - 1005 EP - 1012 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-26107 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pelkner, Matthias A1 - Reimund, Verena A1 - Erthner, Thomas A1 - Kreutzbruck, Marc T1 - Size adapted GMR arrays for the automated inspection of surface breaking cracks in roller bearings N2 - Their small size together with a remarkable field sensitivity are the most prominent features of present-day GMR sensors paving the way for various applications in automated non-destructive testing (NDT). This work presents a prototype for fast and automated magnetic testing of roller bearings. A local magnetization unit excites the magnetic field inside the bearing. As a result of a design study and the following wafer fabrication the probe was equipped with NDT-adapted GMR sensor arrays in which 48 elements measures the field response. The detection of artificial and 40 µm deep defects could be resolved with a SNR better than 20 dB. In addition, we report of first results of a POD (Probability of Detection) analysis using GMR sensors to investigate bearings with EDM (electronic discharge machining) notches having depths down to 10 µm. Finally, we estimate successfully the depth of a 57 µm notch from the measured data. KW - Giant magneto resistance KW - Non-destructive testing KW - Magnetic flux leakage KW - Sensor array PY - 2014 U6 - https://doi.org/10.3233/JAE-141866 SN - 1383-5416 SN - 0925-2096 VL - 45 IS - 1-4 SP - 473 EP - 479 PB - IOS Press CY - Amsterdam, The Netherlands AN - OPUS4-31278 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pelkner, Matthias A1 - Reimund, Verena A1 - Erthner, Thomas A1 - Panke, Nicolai A1 - Kreutzbruck, Marc ED - Chimenti, D.E. ED - Bond, L.J. ED - Thompson, D.O. T1 - Automated inspection of surface breaking cracks using GMR sensor arrays N2 - We present a prototype for automated magnetic stray field testing of ferromagnetic roller bearings. For this purpose NDE-adapted GMR sensor arrays (giant magneto resistance) are used for the detection of surface breaking cracks. The sensors are miniaturized down to the lower µm-regime to achieve adequate spatial resolution. In doing so, sensor arrays with up to 48 elements are used to inspect the bearing surface within a few seconds only. In contrast to magnetic particle inspection (MPI), where the global magnetization requires a further inspection step and succeeding demagnetization, the presented prototype only locally magnetize the surface area in the vicinity of the GMR Sensors. For the local magnetization, the applied sub-surface magnetic field was simulated and proofed for detecting flaws with a depth of a few 10 µm. By multiplexing the sensor array with an adapted read out electronics we quasi simultaneously detect the normal field component of about 100µm above the surface. The detection of artificial notches with a depth of 40 µm and more could be resolved with a SNR better than 20 dB. The presented testing facility is fast and provides a step towards automated testing of safety relevant steel components. T2 - 40th Annual review of progress in quantitative nondestructive evaluation CY - Baltimore, Maryland, USA DA - 2013-07-21 KW - GMR KW - Magnetic flux leakage KW - Sensor array KW - Non-destructive testing PY - 2014 SN - 978-0-7354-1212-5 SN - 978-0-7354-1211-8 U6 - https://doi.org/10.1063/1.4864984 SN - 0094-243X N1 - Serientitel: AIP conference proceedings – Series title: AIP conference proceedings VL - 1581 33B SP - 1393 EP - 1399 PB - AIP Publishing AN - OPUS4-31280 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pelkner, Matthias A1 - Pohl, Rainer A1 - Erthner, Thomas A1 - Kreutzbruck, Marc A1 - Commandeur, C. T1 - Detection of hidden defects in thin steel plates using GMR sensor arrays N2 - At BAM, the Federal Institute for Materials Research and Testing, a group of scientists develops NDT-applications based on GMR sensor technology. In particular, the knowledge gained in the field of automated testing systems based on the magnetic flux leakage (MFL) were combined with GMR sensors to achieve high resolution testing of ferromagnetic materials. In cooperation with Europe's second largest steel producer, Tata Steel Europe, BAM is working on solutions for the detection of small inhomogeneities in thin steel plates. The objective is to incorporate an automated testing facility in a production line. Before setting up an automated testing system, a feasibility study was carried out in order to verify the ability of GMR-MFL-testing and eddy current testing (ET) for the detection of hidden defects in thin steel plates. For this purpose, Tata Steel Europe fabricated in a first step test samples of 0.2 mm thick steel plates in which defects of different depth (5 – 60 µm) were introduced. Only in case of GMR-MFL-testing, we were able to detect parts of the hidden defects trustworthily with a SNR better than 10 dB. The lift off between sensor and surface was 250 ìm. On this basis, we investigated different testing scenarios including velocity tests and different lift offs. The achieved results for this special testing problem were presented leading to a practical example for GMR-based testing and paving the way to an automated testing system in a production line. T2 - ECNDT 2014 - 11th European conference on non-destructive testing CY - Prague, Czech Republic DA - 2014-10-06 KW - Magnetic flux leakage KW - GMR KW - Hidden defects PY - 2014 UR - http://www.ndt.net/events/ECNDT2014/app/content/Paper/286_Pelkner.pdf SN - 978-80-214-5018-9 SP - 1 EP - 7(?) AN - OPUS4-32234 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pelkner, Matthias A1 - Erthner, Thomas A1 - Reimund, Verena A1 - Kreutzbruck, Marc A1 - Sergeeva-Chollet, N. T1 - MR-based eddy current probe design for hidden defects N2 - We present a simulation study which pursues the objective to find probe geometries for a MR-based eddy current (EC) probe (MR magneto resistance, e.g., GMR giant magneto resistance, TMR tunnel magneto resistance). MR sensor technology exhibits two significant advantages compared with conventional coil systems. First, MR sensors are relatively frequency-independent within common EC-frequency ranges which enable us to operate them in hidden defects testing problems. Secondly, MR technology is well suited for miniaturization helping us to design small elements in the order of below 100 µm. In this paper simulation and experimental results obtained with the probes for low frequency application, i.e. for hidden defects detection are discussed. Our simulations are based on two different approaches for a better validation, a commercial finite element method software (Opera, Vectorfields) and the semi-analytical software CIVA. We investigated both coil arrangement in order to excite sufficient high eddy currents inside the test samples and position of MR-elements at the array chip. In doing so the MR sensors were positioned that they are not exposed to excitation fields. In addition, different coil geometries, in particular coil length, e.g. Ι = 20 mm, were analyzed in order to generate a consistent eddy current distribution beneath an array of up to 32 MR-elements. To prove obtained probe principles we built GMR-EC-probes. The first test measurements are in good agreement with the simulations performed by BAM and CEA. On basis of our findings the IMAGIC consortium developed new MR-EC-probes using integrated ASIC technology. T2 - ECNDT 2014 - 11th European conference on non-destructive testing CY - Prague, Czech Republic DA - 2014-10-06 KW - Magneto resistance (MR) KW - Eddy current (EC) KW - Simulation KW - GMR KW - Magnetic flux leakage KW - Hidden defects PY - 2014 UR - http://www.ndt.net/events/ECNDT2014/app/content/Paper/409_Pelkner.pdf SN - 978-80-214-5018-9 SP - 1 EP - 8(?) AN - OPUS4-32231 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CHAP A1 - Pelkner, Matthias A1 - Kreutzbruck, Marc ED - Fermon, C. ED - Van de Voorde, M. H. T1 - Spin Electronics for Non Destructive Testing N2 - Electromagnetic methods are widely used in Non-destructive Testing industries (NDT). In order to meet the requirements, safety-relevant products and structures have to be tested reliably during production or within subsequent maintenance cycles. For this purpose industrial users call for adapted testing methods which allow the detection of relevant defects such as cracks and pore in ferromagnetic or conductive materials. Automated testing systems and the application of sensor arrays are of great interest in order to enhance inspection quality and to decrease testing time and costs. Magneto resistance (MR) sensors like giant magneto resistance (GMR) or tunnel magneto resistance sensor (TMR) have proofed their suitability in many NDT-applications due to their extraordinary properties which combine high field sensitivity, a high spatial resolution and low costs. Due to their small size these sensors can be useful – in addition to the pure detection task – for a more detailed defect characterization and defect reconstruction providing defect size, orientation and geometry. This chapter gives a brief introduction of electromagnetic testing methods, i.e., magnetic particle inspection (MPI) and eddy current testing (ET), followed by two different approaches for which MR sensor arrays were successfully adapted. KW - Magneto resistance KW - GMR KW - TMR KW - Non-destructive testing KW - Magnetic flux leakage KW - Eddy current PY - 2017 SN - 978-3-527-33985-3 SP - 81 EP - 102 PB - Wiley-VCH Verlag GmbH & Co. KGaA CY - Weinheim AN - OPUS4-41463 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -