Optimization Design on a High-performance Magnetic Shielding Barrel for Atomic Magnetometer Measurement Application

The ultra-high-precision measurement of the atomic magnetometer is largely restricted by the size of its working magnetic field. In order to reduce the residual magnetic field as much as possible, this article carried out the research on the methods to improve the shielding performance. Firstly, the axial shielding factor that limits the shielding performance of the magnetic shielding barrel was derived with various parameters including the radius, length, thickness, number of layers, distance between adjacent layers, etc. of the magnetic shielding barrel. Secondly, simulation was carried out to verify the correctness of the formula. Simulation shows that the shielding performance of the magnetic shielding barrel decreases with the size of magnetic shielding barrel increase. Besides, with the increase of the distance between two adjacent spacing layers, the shielding performance first increases rapidly and then gradually decreases, indicating that the optimal distance between adjacent layers is 9mm. Especially, the performance of the magnetic shielding barrel improves significantly as the layer thickness and number of layers increase. Experimental results show that the internal remanence of the three-layer magnetic shielding barrel is less than 1nT, and the available axial length of homogeneity range is greater than 200mm.

Evolution of the Stress-Induced Residual Magnetic Field of X70 Pipeline Steel With Multiple Corrosion Defects

The aim of this research is to investigate the correlation between the residual magnetic field (RMF) and multiple corrosion defects in ferromagnetic steels. Specimens of X70 pipeline steel were machined into standard bars with a single corrosion defect, double corrosion defects and triple corrosion defects, respectively. Tensile tests were carried out to detect the RMF signals on the surface of these specimens. The variations of abnormal magnetic changes of the RMF signals with the external loads were investigated and the results showed that the tangential component and the normal component of the RMF signals of three defect patterns presented different shapes. It was found that the RMF signals were capable of capturing the location and the number of defects in pipeline steels. The peak values of the tangential component and the slopes of the normal component were not influenced by the defects number. This research will promote the investigation on the corrosion defect cluster of ferromagnetic steels based on the metal magnetic memory (MMM) technique.

Analysis of the Possibility of Plastic Deformation Characterisation in X2CrNi18-9 Steel Using Measurements of Electromagnetic Parameters

An analysis was conducted on the possibility of making an assessment of the degree of plastic deformation ε in X2CrNi18-9 steel by measuring three electromagnetic diagnostic signals: the Barkhausen noise features, the impedance components in in-series LCR circuits, and the residual magnetic field components. The impact of ε on a series of different extracted features of diagnostic signals was investigated. The occurrence of two regions of sensitivity was found for all the features of the analysed signals. The two regions were separated by the following critical deformation value: ε ~ 10% for the components of the residual magnetic field and ε ~ 15% for the normalised components of impedance. As for the Barkhausen noise signal, the values were as follows: ε ~ 20% for the mean value, ε ~ 20% for the peak value of the signal envelope, and ε ~ 5% for the total number of the signal events. Metallographic tests were performed, which revealed essential changes in the microstructure of the tested material for the established critical values. The martensite transformation occurring during the plastic deformation process of X2CrNi18-9 austenitic steel process generated a magnetic phase. This magnetic phase was strong enough to relate the strain state to the values of diagnostic signals. The changes in the material electromagnetic properties due to martensitic transformation (γ → α’) began much earlier than indicated by the metallographic testing results.

Quantitative Stress Evaluation and Defect Identification in Ferromagnetic Steels Based on Residual Magnetic Field Measurements

In this paper, the correlation between the residual magnetic field (RMF) and the applied load is investigated. Tensile tests were carried out to measure RMF signals on the surface of 30CrNiMo8 steel specimens with three types of machined defect shapes. Results show that the RMF curves of the three different defective specimens demonstrate similar overall evolution patterns during the loading process, while the magnetic signals exhibit noticeable differences in the defect area. It suggests that the profiles of the stress-induced RMF curves are strongly dependent on the defect’s shape, notch width, and load level. An improved method is proposed to extract some quantitative characteristic parameters from the magnetic signals. The characteristic parameters that reflect the fluctuation degree are in quadratic polynomial relation with the applied load, which can be potentially used to evaluate the applied load acting on a ferromagnetic material with a macro defect. The characteristic parameters that reflect the acting range seem to be independent of the applied load, and the normal ones are capable of capturing the defect’s location and shape. This paper presents a supplement for quantitative defect identification for discontinuities in ferromagnetic steels by RMF measurements.

Detection of Early Stage of Fatigue Changes in Non-Alloy Steel Using Residual Magnetic Field Method

In this work, the fatigue of P265GH steel acc. to EN 10216-2 has been evaluated by measuring a residual magnetic field (RMF). During experiment the notched-specimen has been loaded with a servo-hydraulic uniaxial MTS test machine and a special magnetic sensor was applied. The measurement distribution of the residual magnetic field was performed in two axes. In the first stage of experiment the specimen was gradually loaded with quasi-static force in range of 0 to 16 kN (~ 0.7 Rm). The increase of strength of residual magnetic field was observed only from 0 to 8 kN, whereas in range 8 to 16 kN this effect was not noticed. In the second stage the controlled tensile fatigue test was performed (R = 0, Fmax = 16 kN). Up to 21k load cycles no changes to residual magnetic field were noticed. At 31k cycles the significant increase of amplitude of strength of residual magnetic field change was observed but visual inspection does not show any visible crack, while at 35k cycles crack was visible. It means that applied methodology allow to find the initiation of crack. The performed observation on SEM showed ductile fatigue of fracture.

Evaluation of Fatigue Damage in 304 Stainless Steel by Measuring Residual Magnetic Field

To demonstrate the feasibility of the passive magnetic NDT method for damage assessment of 304 austenitic stainless steel, the residual magnetic field change of the 304 stainless steel specimens under fatigue loads was investigated. The measurement was carried out using a fluxgate sensor and the magnetic characteristics were extracted for analysis of fatigue state. Then, the XRD test was carried out to investigate the mechanism of magnetic field changes and verify the reliability of the proposed method. The results show that the variation of the maximum gradient is consistent with the process of fatigue crack growth, which indicates that the fatigue damage can be estimated by residual magnetic field measuring. In future stage, how to distinguish the magnetic field changes derived from martensite transformation or stress magnetization effect will be investigated.

Effect of intratumoral implantation of barium hexaferrite, magnetite, hematite, aluminium oxide and silica on the dynamics of Erlich tumor growth and survival value of tumor-carrying mice

Introduction. We have earlier shown antitumoral effect of barium hexaferrite implant BHF for models of two intratumoral transplantable solid tumor of mice LIO-1 and Erlich (2 sm3 tumors). In the mentioned work on the model of a rather big sized solid Erlich tumor (3 sm3) we have studied a comparative antitumoral effect after the implantation of BHF particles with a residual magnetic field of 150 mGsm referring to particles of iron oxides with residual magnetic field that was nearing to the zerohematite (Fe2O3) and magne tite (Fe3O4), and as well as for the control aluminium oxide (Al2O3) and silica (nSiO2 ∙ mH2O). Material and methods. Trials have been conducted with 70 white mice female mice with a mass of 2324 g. Malignant epithelial tumor of Erlich was intramuscularly transplanted into the right hind extremity. When tumors reached a size of 3 sm3, mice were divided into 6 groups whom BHF, magnetite, hematite, aluminium oxide, silica or physiologic saline were implanted, correspondingly. Results. As a result of the conducted studies it was found that BHF being implanted into a big-sized tumor (3 sm3) has a mild antitumoral effect for all the studies periods. Particles of iron oxides magnetite and hematite with a magnetic field nearing the zero did not possess the antitumor effect. By the end of experiment (29 days) in all groups including a control group, death of mice at 20 to 50 percent have been seen, and tumors were significantly necrotized, whereas in a group with implantation of silica into the tumor 100 percent of mice have survived and tumors itself did not have necrosis and had even pink colouring.

Effective Suppression of Residual Magnetic Interference in a Conductive Shielded Room for Ultra-Low Field Nuclear Magnetic Resonance

Residual magnetic interference induced by applied magnetic field pulses inside a conductive shielded room (SR) has been a common issue in ultra-low-field (ULF) nuclear magnetic resonance (NMR). The rapid cutoff of the applied pre-polarizing field (Bp) induces eddy currents in the walls of the SR, which produces a decaying residual magnetic interference that may cause severe image distortions and signal loss. In this study, a pair of cancellation coils (CC) and control electronics were designed for the suppression of the residual magnetic interference in a SR. Simulations show that this method was effective in suppressing the residual magnetic field (Br) after removal of the pre-polarizing magnetic field. Then, a small-scale SR was designed and the effectiveness of this cancellation scheme was experimentally verified. The test results showed a good agreement with the simulation, which indicated that the cancellation scheme was capable of reducing Br field to a much lower level. The scheme proposed in this study provides a solution for suppressing the residual magnetic field in the ULF NMR system. After decoupling the eddy–current field, the effect of the suppression may be further improved by optimization of the cancellation coil in further work.