In this paper, we propose a new approach to solve the magnetostatic inverse problem. The goal of the work is, from measurements of the magnetic field in the air, to rebuild a model for the magnetization of a ferromagnetic shell structure. It's then possible to calculate the field where sensors cannot be placed. This problem is usually ill posed or rank-deficient, it's then necessary to use mathematical regularizations. These techniques are based upon the injection of knowledge about the mathematical behavior of the solution. We preferred to add physical information. This solution allows us to get a faithful solution and to reduce significantly the number of sensors. Moreover, our method has been tested on a mock-up with real measurements and led to very promising results.

In this paper, we present the first proof of concept confirming the possibility to record magnetoencephalographic (MEG) signals with Optically Pumped Magnetometers (OPMs) based on the parametric resonance of 4He atoms. The main advantage of this kind of OPM is the possibility to provide a tri-axis vector measurement of the magnetic field at room-temperature (the 4He vapor is neither cooled nor heated). The sensor achieves a sensitivity of 210 fT/√Hz in the bandwidth [2 Hz - 300 Hz]. MEG simulation studies with a brain phantom were cross-validated with real MEG measurements on a healthy subject. For both studies, MEG signal was recorded consecutively with OPMs and Superconducting Quantum Interference Devices (SQUIDs) used as reference sensors. For healthy subject MEG recordings, three MEG proofs of concept were carried out: auditory and visual evoked fields (AEF, VEF), and spontaneous activity. M100 peaks have been detected on evoked responses recorded by both OPMs and SQUIDs with no significant difference in latency. Concerning spontaneous activity, an attenuation of the signal power between 8-12 Hz (alpha band) related to eyes opening has been observed with OPM similarly to SQUID. All these results confirm that the room temperature vector 4He OPMs can record MEG signals and provide reliable information on brain activity.

Abstract-This paper presents an original approach for determining the unknown magnetization of a ferromagnetic shell. Magnetic measurements using sensors close from the device under test are used to rebuild distributions located on the shell. These distributions are representative of the magnetization and tangential moments or charges can be used. This identification problem is a particular case of an inverse problem and is generally ill posed. Instead of using classical mathematical tools to solve such a problem, we preferred to change it in a better posed one by adding our physical knowledge of the problem. All our results have been validated on a mockup with real measurements.

In this paper, we present a proof of concept study which demonstrates for the first time the possibility to record magnetocardiography (MCG) signals with 4 He vector optically-pumped magnetometers (OPM) operated in a gradiometer mode. Resulting from a compromise between sensitivity, size and operability in a clinical environment, the developed magnetometers are based on the parametric resonance of helium in zero magnetic field. Sensors are operated at room-temperature and provide a tri-axis vector measurement of the magnetic field. Measured sensitivity is around 210 fT/√Hz in the bandwidth [2 Hz; 300 Hz]. MCG signals from a phantom and two healthy subjects are successfully recorded. Human MCG data obtained with the OPMs are compared to reference electrocardiogram (ECG) recordings: similar heart rates, shapes of the main patterns of the cardiac cycle (P/T waves, QRS complex) and QRS widths are obtained with both techniques.

Abstract-This paper deals with the modeling of thin steel shells placed in a static magnetic field. The variable used is the scalar reduced potential. In front of the diversity of the formulations encountered, it proposes a methodological approach of different methods and compares them, in term of speed and easiness of computation.Index Terms-Boundary integral method, finite elements method, magnetostatic, thin shell.

Our goal is to identify sheet steel magnetization with near field measurements. Indeed, direct calculation of the whole magnetization is impossible because the remanent part of the magnetization is nondeterminist. Consequently, our strategy is to obtain a magnetostatic formulation able to compute magnetic field as close as possible to the sheet and which is adapted to solve an inverse problem. In this paper, a scalar potential integral formulation is introduced and compared to a magnetization formulation. We are especially interested in the magnetic anomaly created by ferromagnetic ships.Index Terms-Inverse problem, magnetization identification, scalar magnetic potential, thin magnetic sheet.

Luc Rouveyre, et al.. Fault detection for polymer electrolyte membrane fuel cell stack by external magnetic field. Electrochimica Acta, Elsevier, 2019, 313, pp. Abstract:An original non-invasive approach of fuel cell diagnosis is proposed in order to locate different kinds of faults in PEMFC stacks from magnetic field measurements. The method is based on the solving of an inverse linear problem linking the magnetic field signature outside of the fuel cell to the current density distribution inside.The searched solution is a linear combination of conservative current distribution obtained by a set of electrokinetic problems solved by a finite face element method. As the problem is ill-posed, the solution is stabilized using a truncated singular value decomposition. In this work, 30 sensors are used to perform the 2 magnetic tomography of a PEMFC stack consisting of 100 cells with a large active area of 220 cm 2 . External magnetic measurement makes possible to identify 2D or 3D changes of current density distribution induced either by a cell flooding or membrane drying as well as by material degradation in a PEMFC stack.

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