Magnetic Signal Research Articles

A novel anomaly detection method for magnetic flux leakage signals via a feature-based unsupervised detection network

High-precision anomaly detection, as the key technology of magnetic flux leakage (MFL) signal detection, is a challenging task. It is difficult to detect anomalies in MFL signals due to the variety of anomalies and the characteristics of the anomalies are easily submerged in the variation of the natural signals. To address the above issues, a feature-based unsupervised detection network (FUDet) is designed, which accomplishes the unsupervised anomaly detection task through feature discrimination and feature reconstruction. Firstly, a bidirectional discrimination module is proposed, which can input normal and anomaly feature distributions to mine the characteristics of samples, so as to enhance the ability of the model to recognize anomaly signals. Secondly, a dynamic noise generation module is designed to generate different feature distributions for each input that are consistent with the characteristics of MFL signals. This module creates an adversarial effect with the discriminator, allowing it to identify more subtle feature differences through training. Finally, a reconstruction classification module is designed to naturally reconstruct the non-normal features and normal features into normal signals, which can be used to detect anomalies by comparing the difference between the input signals and the reconstructed signals. Experimentally, the method is proved to outperform the P-AUROC of the state-of-the-art method by 3.1% under MFL signals and achieves outstanding results in MFL signal anomaly detection.

Voids and cracks detection in bulk superconductors through magnetic field and displacement signals

Voids and cracks detection in bulk superconductors through magnetic field and displacement signals

High Stability Hydrogel Magnetic Relaxation Switch Sensor Driven by pH for the Sensitive Detection of Cd2.

The traditional magnetic relaxation switching (MRS) sensors have excellent sensitivity, but their stability is poor because the magnetic relaxation signal is easily affected by the external magnetic field or environmental oxidation. In this study, a highly stable hydrogel bead-based MRS (Gel-MRS) sensor was established for the accurate and sensitive detection of Cd2+ in rice. A pH-responsive hydrogel bead was applied as a core element for the target stimulus and transverse relaxation signal transduction. The stability experiments showed that the transverse relaxation time (T2) change of the Gel-MRS sensor was one-seventh that of traditional magnetic nanoparticles under an external magnetic field and less than a fifth that of Fe2+/Fe3+ conversion in air. The excellent stability was due to the fact that T2 of the Gel-MRS sensor came from the swelling system mediated by pH rather than the traditional aggregation/dispersion or Fe2+/Fe3+ conversion of magnetic nanoparticles. In addition, the target Cd2+ could exclusively trigger a pH response of the hydrogel beads, altering the T2, thus resulting in excellent relaxation properties (R2 = 56.89) and pH responsiveness of the Gel-MRS sensor. The swelling process of the hydrogel beads followed quasi-second-order dynamics. The Gel-MRS sensor demonstrated a remarkable limit of detection as low as 0.009 ng/mL for Cd2+, with a linear range of 0.01-5 ng/mL. The excellent stability and sensitivity made the Gel-MRS sensor have great application potential in food and environmental detection.

Harnessing the Heart's Magnetic Field for Advanced Diagnostic Techniques.

Heart diseases remain one of the leading causes of morbidity and mortality worldwide, necessitating innovative diagnostic methods for early detection and intervention. An electrocardiogram (ECG) is a well-known technique for the preliminary diagnosis of heart conditions. However, it can not be used for continuous monitoring due to skin irritation. It is well known that every body organ generates a magnetic field, and the heart generates peak amplitudes of about 10 to 100 pT (measured at a distance of about 3 cm above the chest). This poses challenges to capturing such signals. This paper reviews the different techniques used to capture the heart's magnetic signals along with their limitations. In addition, this paper provides a comprehensive review of the different approaches that use the heart-generated magnetic field to diagnose several heart diseases. This research reveals two aspects. First, as a noninvasive tool, the use of the heart's magnetic field signal can lead to more sensitive advanced heart disease diagnosis tools, especially when continuous monitoring is possible and affordable. Second, its current use is limited due to the lack of accurate, affordable, and portable sensing technology.

Steady-state magnon entanglement and backaction-evading of a weak magnetic signal via two-tone modulated cavity electromagnonics

Cavity electromagnonics explore the coupling between microwave cavity fields and magnons in micromagnets. This field has emerged as a promising platform for probing fundamental aspects of quantum mechanics and advancing quantum technologies. This paper investigates a scheme involving two-tone frequency modulation to engineer simultaneous magnon-photon two-mode squeezing and beam-splitter-like interactions. We demonstrate that this scheme enables the direct generation of macroscopic magnonic squeezed and entangled states. Moreover, it facilitates ultra-sensitive magnon-based magnetic field sensing through quantum non-demolition (QND) interactions between magnons and photons. The present scheme provides promising opportunities for generating macroscopic nonclassical quantum states in solid magnetic materials and developing spintronics-related quantum devices.

Proximity coupling induced two dimensional magnetic order in EuO-based synthetic ferrimagnets

Proximity effects allow for the adjustment of magnetic properties in a physically elegant way. If two thin ferromagnetic (FM) films are brought into contact, electronic coupling alters their magnetic exchange interaction at their interface. For a low-TC\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_C$$\\end{document} rare-earth FM coupled to a 3d transition metal FM, even room temperature magnetism is within reach. In addition, magnetic proximity coupling is particularly promising for increasing the magnetic order of metastable materials such as europium monoxide (EuO) beyond their bulk TC\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_C$$\\end{document}, since neither the stoichiometry nor the insulating properties are modified. We investigate the magnetic proximity effect at Fe/EuO and Co/EuO interfaces using hard X-ray photoelectron spectroscopy. By exciting the FM layers with circularly polarized light, magnetic dichroism is observed in angular dependence on the photoemission geometry. In this way, the depth-dependence of the magnetic signal is determined element-specifically for the EuO and 3d FM parts of the bilayers. In connection with atomistic spin dynamics simulations, the thickness of the EuO layer is found to be crucial, indicating that the observed antiferromagnetic proximity coupling is a short-ranged and genuine interface phenomenon. This fact turns the bilayer into a strong synthetic ferrimagnet. The increase in magnetic order in EuO occurs in a finite spatial range and is therefore particularly strong in the 2D limit—a counterintuitive but very useful phenomenon for spin-based device applications.

Trimodal Multiplexed Lateral Flow Test Strips Assisted with a Portable Microfluidic Centrifugation Device.

During the COVID-19 pandemic, the use of lateral flow assays (LFAs) expanded significantly, offering testing beyond traditional health care. Their appeal lies in the ease of use, affordability, and quick results. However, LFAs often have lower sensitivity and specificity compared with ELISA and PCR tests. Efforts to improve LFAs have increased detection times and complexity, limiting their use in large-scale point-of-care settings. To address this, we propose a novel approach using probes that generate multiple signals to enhance the sensitivity and selectivity. This concept also allows multiplexed LFAs to detect multiple analytes concurrently. We developed a trimodal probe that integrates fluorescence, color, and magnetism into a single nanohybrid. The strong plasmonic absorption and high fluorescence of Au nanoparticles and polymer dots enable qualitative and semiquantitative diagnosis, while the magnetic signal facilitates accurate quantitative measurements. As proof-of-concept targets, we selected CYFRA 21-1 and CA15-3, biomarkers for lung and breast cancer, respectively. This trimodal LFA demonstrated a remarkable detection limit of 0.26 ng/mL for CYFRA 21-1 and 2.8 U/mL for CA15-3. To the best of our knowledge, this is the first platform of a trimodal LFA with multiplexing ability. The platform's accuracy and reliability were validated using clinical serum samples, showing excellent consistency with electrochemiluminescence immunoassay results. This universal concept can be applied to other targets, paving the way for the next-generation LFAs.

Magnetic enhancement in paleosols with hydroclimatic and vegetation cover variabilities (Holocene vs. late MIS 3) in the central Korean Peninsula

Magnetic susceptibility enhancement (kE) is useful for reconstructing terrestrial paleohydroclimate variabilities. However, kE and its driving process(es) in the Korean Peninsula remain uninvestigated. Therefore, this study investigated two kEs of similar magnitudes, dated MIS 1 (Holocene) and late MIS 3 (~ 29–36 ka), from a paleosol sequence in the upland of paleo-fluvial terrace in the central Korean Peninsula. We observed increased ferri- and antiferro-magnetic mineral components,including ultrafine particles, and stronger chlorite weathering for the two kEs, suggesting pedogenic component predominance. The Fe-bearing (phyllo)silicate weathering mechanism proposed for the Chinese Loess Plateau sequences can explain the pedogenesis-induced kEs for the studied site. Superparamagnetic-domain (SPD) to pseudo-single-domain sized particles of pedogenic magnetite are likely major contributors to kEs. Moreover, we recognized the younger kE interval as more SPD contribution but less in total ferrimagnetic contribution, and more antiferromagnetic contribution than the older ones. The magnetic differences between the periods can result from vegetation cover impact and surrounding hydroclimate conditions, consistent with the recent suggestion for part of the southeast Chinese sites with relatively more rainfall. Consequently, our study provides a baseline for improving the relationship between mineral magnetic signals and local/regional hydroclimatic and environmental variabilities.

Insights into the magnetic signature in VS2 nanosheets for spintronics applications: an experimental and ab initio approach

Insights into the magnetic signature in VS2 nanosheets for spintronics applications: an experimental and ab initio approach

A 85Rb transverse modulation magnetometer in the geophysical range based on atomic alignment states

Abstract We have constructed a transverse modulated magnetometer based on spin alignment in a paraffin-coated 85 Rb cell operated in a geophysical magnetic field of 47.1 µT. When an orthogonal driving magnetic field ( x ^ axis) is resonant on the Larmor frequency ( z ^ axis), we have proposed a new method to zero the static residual magnetic fields in the transverse plane and achieved a sensitivity of 1.8 pT Hz − 1 with bandwidth of 200 Hz. The repump light ( F g = 2 → F e = 2 ) redistributes the populations in the ground state, rendering the state | F g = 2 ⟩ dark. This effect significantly amplifies the optical rotation signals nearly fourfold. The numerical solution of the Liouville equation is in good agreement with the experimental results. By using perturbation treatment and employing appropriate approximations, the derived analytical expressions for optical rotation are deduced to succinctly elucidate the dynamics of atomic alignment under parametric modulation. These outcomes could be extended for the advancement of an alignment magnetometer that has been designed to detect a weak magnetic signal in the geophysical range.

Structural Distortions and Short‐Range Magnetism in a Honeycomb Iridate Cu3ZnIr2O6

Layered honeycomb iridates receive significant attention in the materials chemistry and physics fields due to the relevance of their crystal structures to the Kitaev model of a quantum spin liquid (QSL). In quest of liquid‐like magnetic ground state signatures, first‐generation alkali metal iridates A2IrO3 ≡ A3[AIr2]O6 (A = Li, Na) and second‐generation iridates T3[AIr2]O6 (T = Cu, Ag, H) are developed. T3[AIr2]O6 is synthesized from A3[AIr2]O6 via metathesis reactions replacing alkali ions located between honeycomb layers. Herein, the next level of chemical and structural complexity is introduced by synthesizing the honeycomb iridate, Cu3ZnIr2O6, in which alkali ions between and within the honeycomb layers are both selectively exchanged with two different transition metals. Analysis of powder X‐Ray diffraction data reveals corrugation of the honeycomb layers in Cu3ZnIr2O6 that hinders complete magnetic frustration and results in a spin glass behavior observed from magnetization and specific heat data. Thus, Cu3ZnIr2O6 represents yet another model, which broadens understanding of intricate relationships between intralayer distortions and magnetism of prospective Kitaev QSL compounds.

Photocatalytic degradation of the remazol red ultra RGB dye using SrFe12O19-Fe3O4 magnetic oxides dispersed in silica: Effect of reduction temperature

Dyes are the most frequently discarded industrial wastes in aquatic ecosystems, among which Remazol Red ultra RGB stands out. In this context, magnetic iron-based catalyst dispersed in silica were prepared by Pechini route as an alternative for the photodegradation of Remazol Red Ultra RGB. The XRD and Mössbauer spectroscopy results indicated the formation of a magnetic material that, after reduction treatment with H2, forms a magnetite phase combined with Sr hexaferrite dispersed in amorphous silica. The TPR-H2 profiles indicated the reduction of Fe3+ to Fe2+ within the considered temperature range, the amount of Fe2+ increased with rising temperature. The SEM images showed sponge-like morphology for the samples. The EDS spectra and mapping confirmed a high uniformity in the distribution of active iron species in the silica. The magnetic measurements showed a lower magnetic signal for the sample reduced at 600 °C, due to the lower magnetic moment of Fe2+ formed after the reduction. The diffuse reflectance spectra showed a main absorption region between 500 and 200 nm and the estimated band-gap values were of 1.4 and 1.9 eV for the reduced sample and the fresh oxide, respectively. The surface charge was obtained via zeta potential, demonstrating good stability under pH changes and reaching a negative potential in the pH range from 2 to 6. The photocatalytic tests showed that the samples with higher content of Fe2+ demonstrated a greater photocatalytic degradation of the Remazol Red Ultra RGB dye, reaching 100 % degradation in 1 h for the solid reduced at 600 °C. A plausible mechanism for the photodegradation of Remazol Red Ultra RGB was proposed, considering the different elementary steps involving the participation of iron sites and the formation of oxidant radicals.

Magnetic symmetries of terbium tetraboride (TbB4) revealed by resonant x-ray Bragg diffraction

A recent experimental study of TbB4 at a low temperature using resonant x-ray Bragg diffraction implies a magnetic symmetry not found in any other rare-earth tetraboride. The evidence for this assertion is a change in the intensity of a TbB4 Bragg spot on reversing the handedness (chirality) of the primary x-ray beam [R. Misawa, K. Arakawa, T. Yoshioka, H. Ueda, F. Iga, K. Tamasaku, Y. Tanaka, and T. Kimura, ]. It reveals a magnetic chiral signature in TbB4 that is forbidden in phases of rare-earth tetraborides known to date, as the previous magnetic symmetries are parity-time (PT) symmetric with anti-inversion present in the magnetic crystal class. Misawa appeal to a PT-symmetric diffraction pattern to interpret their interesting diffraction patterns. In addition to the use of symmetry that does not permit a chiral signature, calculated patterns impose cylindrical symmetry on Tb sites with no justification. We review magnetic symmetries for TbB4 consistent with a published neutron powder diffraction pattern and susceptibility measurements. On the basis of this information, noncollinear antiferromagnetic order exists below a temperature ≈44 K with no ferromagnetic component. Our symmetry-informed patterns encapsulate Tb electronic degrees of freedom in terms of multipoles consistent with established sum rules for dichroic signals. The investigated symmetry templates are noncentrosymmetric, noncollinear antiferromagnetic constructions with propagation vector k=(0,0,0). An inferred chiral signature for a parity-even absorption event has an interesting composition. There is the anticipated product of Tb axial dipoles and chargelike quadrupoles (from Templeton-Templeton scattering). Beyond this contribution, though, symmetry allows a product of dipoles in the chiral signature. A predicted change in the intensity of a Bragg spot with rotation of the crystal about the reflection vector (an azimuthal angle scan) can be tested in future experiments. Likewise contributions to Bragg diffraction patterns from Tb anapoles and higher-order Dirac multipoles. Published by the American Physical Society 2024

Self-Supervised Marine Noise Learning with Sparse Autoencoder Network for Generative Target Magnetic Anomaly Detection

As an effective physical field feature to perceive ferromagnetic targets, magnetic anomaly is widely used in covert marine surveillance tasks. However, its practical usability is affected by the complex marine magnetic noise interference, making robust magnetic anomaly detection (MAD) quite a challenging task. Recently, learning-based detectors have been widely studied for the discrimination of magnetic anomaly signal and achieve superior performance than traditional rule-based detectors. Nevertheless, learning-based detectors require abundant data for model parameter training, which are difficult to access in practical marine applications. In practice, target magnetic anomaly data are usually expensive to acquire, while rich marine magnetic noise data are readily available. Thus, there is an urgent need to develop effective models to learn discriminative features from the abundant marine magnetic noise data for newly appearing target anomaly detection. Motivated by this, in this paper we formulate MAD as a single-edge detection problem and develop a self-supervised marine noise learning approach for target anomaly classification. Specifically, a sparse autoencoder network is designed to model the marine noise and restore basis geomagnetic field from the collected noisy magnetic data. Subsequently, reconstruction error of the network is used as a statistical decision criterion to discriminate target magnetic anomaly from cluttered noise. Finally, we verify the effectiveness of the proposed approach on real sea trial data and compare it with seven state-of-the-art MAD methods on four numerical indexes. Experimental results indicate that it achieves a detection accuracy of 93.61% and has a running time of 21.06 s on the test dataset, showing superior MAD performance over its counterparts.

Obtaining frequency-time diagram from perturbation signal-time diagram

Abstract In the field of nuclear fusion energy development, magnetic confinement tokamak reactors, which use strong magnetic fields to confine high-temperature plasmas, are crucial for sustainable and clean fusion energy. Disruption caused by plasma instability can terminate the fusion reaction and even cause irreparable damage to the equipment. Therefore, a thorough understanding of the underlying physical mechanisms is essential for predicting and preventing plasma disruption. The recently proposed analytical theory of plasma disruption may predict and prevent plasma disruption, but its validation requires the frequency-time signals. The Heavy Ion Beam Probe (HIBP) can provide such signals, however, because its scarcity in the world, particularly in China, it is necessary to develop more suitable methods. Here we show a new approach that employs Fast Fourier Transform (FFT) on magnetic perturbation signals to obtain frequency-time diagrams. We successfully applied this algorithm to acquire the frequency-time diagram of the J-TEXT-1054560 discharge. This new method offers an effective tool for validating the plasma disruption theory, overcoming the limitations of traditional techniques and providing a crucial methodological basis for understanding and predicting plasma disruption. This new analytical approach will accelerate the advancement of fusion technology.

About Jordan and Einstein Frames: A Study in Inflationary Magnetogenesis

In this paper, we make a detailed side-by-side comparison between Jordan and Einstein frames in the context of cosmic magnetogenesis. We have computed the evolution of the vector potential in each frame along with some observables such as the spectral index and the magnetic field amplitude. We found that contrary to the Einstein frame, the electric and magnetic energy densities in the Jordan Frame do not depend on any parameter associated with the scalar field. Furthermore, in the Einstein frame, and assuming scale invariance for the magnetic field, most of the total energy density contribution comes from the electric and magnetic densities. Finally, we show the ratio between magnetic field signals in both frames printed in the CMB.

High-resolution magnetic resonance imaging features of time-of-flight magnetic resonance angiography signal loss and its relevance to ischemic stroke.

Focal signal loss of intracranial artery stenosis is commonly observed on three-dimensional time-of-flight magnetic resonance angiography (3D-TOF-MRA). We aimed to investigate the underlying pathophysiology of vessel signal loss observed on 3D-TOF-MRA and its relevance to recent ischemic stroke. High-resolution magnetic resonance imaging (HR-MRI) was performed in 401 patients with unilateral or bilateral moderate-to-severe stenosis (50-99%) of the middle cerebral artery (MCA) on TOF-MRA. The patients were classified according to the presence or absence of focal signal loss in the M1 segment of the MCA. The wall features between the vessels with and without signal loss were compared, and their relationship with recent ischemic stroke was analyzed. A total of 414 stenotic lesions caused by atherosclerotic plaque were detected, including 231 with signal loss on TOF-MRA and 183 without. The signal loss group, compared to the group without signal loss, showed a higher degree of stenosis (P<0.001), grade 2 enhanced plaques (82.3% vs. 28.4%; P<0.001), and concentric pattern (63.2% vs. 34.4%; P<0.001). Multivariate analysis suggested grade 2 enhanced plaques and concentric pattern were independently associated with signal loss. Patients in the signal loss group were more likely to have had a recent ischemic stroke (62.4% vs. 40.4%; P<0.001). In addition to the degree of stenosis, the vulnerability and morphology of plaques on HR-MRI may influence signals on 3D-TOF-MRA. The presence of signal loss on 3D-TOF-MRA is associated with recent ischemic stroke.

Quaternary ammonium chitosan-based active packaging films incorporated with dialdehyde guar gum-proanthocyanidins conjugates: Characterization and application in the edible coating of pork

In this study, antioxidant and antibacterial proanthocyanidins (PA) were covalently conjugated with dialdehyde guar gum (DGG) to produce DGG-PA conjugates. Then DGG-PA conjugates were incorporated into quaternary ammonium chitosan (QAC)-based matrix to create QAC/DGG-PA films. The structure, physicochemical properties, and antioxidant and antibacterial effects of DGG-PA conjugates and QAC/DGG-PA films were analyzed. The active packaging potentials of QAC/DGG-PA film-forming solutions in the edible coating of pork loins were evaluated. Results showed DGG-PA conjugates had unique UV absorption peak (280 nm), infrared bands (1610 and 1521 cm−1) and proton nuclear magnetic resonance signals (6.82 ppm) of PA groups. DGG-PA conjugates showed amorphous state with sheet-like and fibrous morphology. DGG-PA conjugates had good biocompatibility and antioxidant and antibacterial effects. After adding DGG-PA conjugates, the surface of QAC-based films became smooth and the crystallographic nature of the films declined. DGG-PA conjugates elevated the light/water vapor/oxygen barrier performances, mechanical properties, and antioxidant and antibacterial effects of QAC-based films. QAC/DGG-PA edible coatings effectively prolonged the shelf life of pork loins from 4 days to 6−10 days. Results verified QAC/DGG-PA films and their film-forming solutions had good application potentials in active packaging.

Design of High Gain and High Sensitivity Extremely-Low Frequency Magnetic Signal Receiving System

Design of High Gain and High Sensitivity Extremely-Low Frequency Magnetic Signal Receiving System

Asteroseismic signatures of core magnetism and rotation in hundreds of low-luminosity red giants

ABSTRACT Red giant stars host solar-like oscillations which have mixed character, being sensitive to conditions both in the outer convection zone and deep within the interior. The properties of these modes are sensitive to both core rotation and magnetic fields. While asteroseismic studies of the former have been done on a large scale, studies of the latter are currently limited to tens of stars. We aim to produce the first large catalogue of both magnetic and rotational perturbations. We jointly constrain these parameters by devising an automated method for fitting the power spectra directly. We successfully apply the method to 302 low-luminosity red giants. We find a clear bimodality in core rotation rate. The primary peak is at $\delta \nu _{\mathrm{rot}}$ = 0.32 $\mu$Hz, and the secondary at $\delta \nu _{\mathrm{rot}}$ = 0.47 $\mu$Hz. Combining our results with literature values, we find that the percentage of stars rotating much more rapidly than the population average increases with evolutionary state. We measure magnetic splittings of 2$\sigma$ significance in 23 stars. While the most extreme magnetic splitting values appear in stars with masses $\gt $1.1 M$_{\odot }$, implying they formerly hosted a convective core, a small but statistically significant magnetic splitting is measured at lower masses. Asymmetry between the frequencies of a rotationally split multiplet has previously been used to diagnose the presence of a magnetic perturbation. We find that of the stars with a significant detection of magnetic perturbation, 43 per cent do not show strong asymmetry. We find no strong evidence of correlation between the rotation and magnetic parameters.