Field Magnetic Imaging Research Articles

Indoor Mapping of Magnetic Fields Using UAV Equipped with Fluxgate Magnetometer.

Unmanned aerial vehicles (UAVs) are used nowadays in a wide range of applications, including monitoring, mapping, or surveying tasks, involving magnetic field mapping, mainly for geological and geophysical purposes. However, thanks to the integration of ultrasound-aided navigation used for indoor UAV flight planning and development in sensorics, the acquired magnetic field images can be further used, for example, to enhance indoor UAV navigation based on the physical quantities of the image or for the identification of risk areas in manufacturing or industrial halls, where workers can be exposed to high values of electromagnetic fields. The knowledge of the spatial distribution of magnetic fields can also provide valuable information from the perspective of the technical cleanliness. This paper presents results achieved with the original fluxgate magnetometer developed and specially modified for integration on the UAV. Since the magnetometer had a wider frequency range of measurement, up to 250 Hz, the DC (Direct Current) magnetic field and low frequency industrial components could be evaluated. From the obtained data, 3D magnetic field images using spline interpolation algorithms written in the Python programming language were created. The visualization of the measured magnetic field in the 3D plots offer an innovative view of the spatial distribution of the magnetic field in the area of interest.

Magnetic imaging and statistical analysis of the metamagnetic phase transition of FeRh with electron spins in diamond

Magnetic imaging based on nitrogen-vacancy (NV) centers in diamond has emerged as a powerful tool for probing magnetic phenomena in fields ranging from biology to physics. A key strength of NV sensing is its local-probe nature, enabling high-resolution spatial images of magnetic stray fields emanating from a sample. However, this local character can also form a drawback for analyzing the global properties of a system, such as a phase transition temperature. Here, we address this challenge by using statistical analyses of magnetic-field maps to characterize the first-order temperature-driven metamagnetic phase transition from the antiferromagnetic to the ferromagnetic state in FeRh. After imaging the phase transition and identifying the regimes of nucleation, growth, and coalescence of ferromagnetic domains, we statistically characterize the spatial magnetic-field maps to extract the transition temperature and thermal hysteresis width. By analyzing the spatial correlations of the maps in relation to the magnetocrystalline anisotropy and external magnetic field, we detect a reorientation of domain walls across the phase transition. The employed statistical approach can be extended to the study of other magnetic phenomena with NV magnetometry or other sensing techniques.

Wide-Field Dynamic Magnetic Microscopy Using Double-Double Quantum Driving of a Diamond Defect Ensemble

Wide-field magnetometry can be realized by imaging the optically-detected magnetic resonance of diamond nitrogen vacancy (NV) center ensembles. However, NV ensemble inhomogeneities significantly limit the magnetic-field sensitivity of these measurements. We demonstrate a double-double quantum (DDQ) driving technique to facilitate wide-field magnetic imaging of dynamic magnetic fields at a micron scale. DDQ imaging employs four-tone radio frequency pulses to suppress inhomogeneity-induced variations of the NV resonant response. As a proof-of-principle, we use the DDQ technique to image the dc magnetic field produced by individual magnetic-nanoparticles tethered by single DNA molecules to a diamond sensor surface. This demonstrates the efficacy of the diamond NV ensemble system in high-frame-rate magnetic microscopy, as well as single-molecule biophysics applications.

Magnetic field imaging in a laboratory plasma

In laboratory plasmas, arrays of probes have typically been used to measure the evolution of the magnetic field topology. Here, we present initial image-based measurements of the magnetic topology in a low-temperature plasma using a purely optical diagnostic. Laser induced fluorescence measurements of neutral velocity distribution functions are made using a fast camera, imaging the Zeeman splitting of σ-peaks in neutral argon. The separation of σ-peaks provides spatially resolved magnetic field magnitude measurements with a detection threshold on the order of 10 G.

Characterization of microscopic ferromagnetic defects in thin films using magnetic microscope based on Nitrogen-Vacancy centres

In this work we present results acquired by applying magnetic field imaging technique based on Nitrogen-Vacancy centres in diamond crystal for characterization of magnetic thin films defects. We used the constructed wide-field magnetic microscope for measurements of two kinds of magnetic defects in thin films. One family of defects under study was a result of non-optimal thin film growth conditions. The magnetic field maps of several regions of the thin films created under very similar conditions to previously published research revealed microscopic impurity islands of ferromagnetic defects, that potentially could disturb the magnetic properties of the surface. The second part of the measurements was dedicated to defects created post deposition - mechanical defects introduced in ferromagnetic thin films. In both cases, the measurements identify the magnetic field amplitude and distribution of the magnetic defects. In addition, the magnetic field maps were correlated with the corresponding optical images. As this method has great potential for quality control of different stages of magnetic thin film manufacturing process and it can rival other widely used measurement techniques, we also propose solutions for the optimization of the device in the perspective of high throughput.

Large Faraday Rotation in Optical-Quality Phthalocyanine and Porphyrin Thin Films.

The magneto-optical phenomenon known as Faraday rotation involves the rotation of plane-polarized light as it passes through an optical medium in the presence of an external magnetic field oriented parallel to the direction of light propagation. Faraday rotators find applications in optical isolators and magnetic-field imaging technologies. In recent years, organic thin films comprised of polymeric and small-molecule chromophores have demonstrated Verdet constants, which measure the magnitude of rotation at a given magnetic field strength and material thickness, that exceed those found in conventional inorganic crystals. We report herein the thin-film magnetic circular birefringence (MCB) spectra and maximum Verdet constants of several commercially available and newly synthesized phthalocyanine and porphyrin derivatives. Five of these species achieved maximum Verdet constant magnitudes greater than 105 deg T-1 m-1 at wavelengths between 530 and 800 nm. Notably, a newly reported zinc(II) phthalocyanine derivative (ZnPc-OT) reached a Verdet constant of -33 × 104 deg T-1 m-1 at 800 nm, which is among the largest reported for an organic material, especially for an optical-quality thin film. The MCB spectra are consistent with resonance-enhanced Faraday rotation in the region of the Q-band electronic transition common to porphyrin and phthalocyanine derivatives, and the Faraday A-term describes the electronic origin of the magneto-optical activity. Overall, we demonstrate that phthalocyanines and porphyrins are a class of rationally designed magneto-optical materials suitable for applications demanding large Verdet constants and high optical quality.

Non-destructive visualization of short circuits in lithium-ion batteries by a magnetic field imaging system

To develop a high-density and long-life lithium-ion battery, a technology is needed that allows non-destructive visualization of the spatial distribution of deteriorated parts after cycle test. In the present study, we measured the distribution of the magnetic field leaking from the lithium-ion battery during its operation. Based on the measurement results, we evaluated the spatial distribution of electric current density that corresponds to the reaction rate of the active material and the ion diffusion rate in the electrolyte solution inside a battery using the electric current reconstruction process. With respect to the changes in the internal state of the lithium-ion battery associated with cycle deterioration, we successfully visualized the part where the electrical conductivity has changed that is the deteriorated part causing the battery capacity to decrease inside the lithium-ion battery.

Analysis of current density in the electrode and electrolyte of lithium‐ion cells for ageing estimation applications

Lithium-ion battery is the commonly used energy storage technology in electric vehicles (EVs) because of its inexpensive manufacturing cost and high energy capacity. For optimal utilization of its capacity and lifetime, reliable state of health (SoH) monitoring solutions have to be included in the battery management system (BMS). SoH of a cell is affected by several reasons such as internal degradation or external damages that need to be estimated. This article analyses the current density in electrode and electrolyte of an EV lithium-ion cell using a simulation assisted method that leads to improvement in SoH estimation accuracy. The experimental results are analysed through the fusion of the magnetic field images captured by quantum fluxgate magnetometers, installed on the surface of the cell, together with the real-time simulation of the multi-physics model of the cell. The magnetic field sensors measure the magnetic field intensity with an accuracy of ±2 mT. The real-time simulation input data is updated from the measurements of both the magnetic field sensors and the battery cycler. The multi-physics model of the cell is developed in COMSOL modelling software, and real-time data fusion process is implemented on dSPACE Microlabbox real-time simulator. Results confirm that the proposed monitoring solution provides useful insight that can be employed in ageing estimation of EV batteries.

A multi-magneto-inductive sensor array system for real-time magnetic field imaging of ferromagnetic targets.

In this Note, we develop a real-time magnetic field imaging system by employing a multi-magneto-inductive (MI) sensor array. The sensor array consists of 3 × 3 tri-axial MI sensors, which we constructed by using three sensor coils. Outputs from several rows of sensors are routed to a master-controller responsible for data pre-processing and data reconstruction. The data are streamed to a host computer via a universal serial bus interface, and the image can be generated and displayed at a rate of several frames per second. The magnetic field imaging is implemented on a knowledge of the MI sensors' response, magnetic field perturbations, and the nature of the ferromagnetic object respecting permeability and conductivity. The performance of the system has been further evaluated by extensive numerical modeling of magnetic field distribution patterns with partial differential equation solution. The proposed magnetic field imaging system can be employed in many potential applications, for instance, medicine, security screening, quality assurance, and other areas of nondestructive evaluation, designs associated with magnetic fields, teaching, and research.

High-Resolution Environmental Magnetism Using the Quantum Diamond Microscope (QDM): Application to a Tropical Speleothem

Quantum diamond microscope (QDM) magnetic field imaging is a recently developed technique capable of mapping magnetic field sources in geologic samples at 1 micrometer resolution. Applying QDM imaging to speleothems can provide high‐resolution time series of detrital input into the cave environment, which, in turn, can yield useful paleoenvironmental information. Here we map the magnetic field over a speleothem from midwest Brazil over a 174 year timespan with annual to sub-annual resolution and perform backfield remanence acquisition experiments to quantify changes in the magnetic grain population through time. We find that magnetic particles occur in highly enriched layers of 10–100 µm thickness that sample the same detrital source population. Combined with petrographic observations and electron microprobe mapping of Mg and Ca, we conclude that detrital enrichment in our sample is caused by drier conditions leading to slow or halted speleothem growth. This interpretation is compatible with oxygen isotopic data and implies that speleothem magnetism can be used to infer the past occurrence of drought and potentially quantify their duration. Future high-resolution magnetic imaging of speleothems may provide additional insight into the mechanism of detrital enrichment and establish their role as a proxy for local moisture and infiltration.

Evaluation of the Quality of Solder Joints within Silicon Solar Modules Using Magnetic Field Imaging

Solar cells and modules are already a mature technology in mass production. It is critical to optimize and to systematically monitor their performance. The introduction of automated soldering processes and the increasing usage of novel contacting schemes can cause harmful defects, e.g., missing and defective contacts, and, thus, affect the electrical performance of solar modules after production or in field usages. Herein, magnetic field imaging (MFI) is utilized to do a non‐destructive, quantitative analysis of the modules to investigate the quality of the soldering contacts. In detail, the cross connector, interconnector, and rear‐side pads are investigated. The typical in‐field observed defects are presented. For the first time, the quality of rear‐side pads under operation is studied in detail. It is shown that 1) directly after production, the current conduction takes place not only via the rear pads but also via the press‐on contact between the bare aluminum and the rear‐side ribbons; 2) an off‐centered ribbon on the pad leads to abnormal current distribution; and 3) single rear‐side pad breaks as a function of thermal cycles due to thermo‐mechanical stress.

Electrical Detection of Magnetic Circular Dichroism: Application to Magnetic Microscopy in Ultrathin Ferromagnetic Films

Imaging the magnetic configuration of thin-films has been a long-standing area of research. Since a few years, the emergence of two-dimensional ferromagnetic materials calls for innovation in the field of magnetic imaging. As the magnetic moments are extremely small, standard techniques like SQUID, torque magnetometry, magnetic force microscopy and Kerr effect microscopy are challenging and often lead to the detection of parasitic magnetic contributions or spurious effects. In this work, we report a new magnetic microscopy technique based on the combination of magnetic circular dichroism and Seebeck effect in semiconductor/ferromagnet bilayers. We implement this method with perpendicularly magnetized (Co/Pt) multilayers sputtered on Ge (111). We further show that the electrical detection of MCD is more sensitive than the Kerr magnetometry, especially in the ultra-thin film regime, which makes it particularly promising for the study of emergent two-dimensional ferromagnetic materials.

3D magnetically controlled spatiotemporal probing and actuation of collagen networks from a single cell perspective.

Cells continuously sense and react to mechanical cues from their surrounding matrix, which consists of a fibrous network of biopolymers that influences their fate and behavior. Several powerful methods employing magnetic control have been developed to assess the micromechanical properties within extracellular matrix (ECM) models hosting cells. However, many of these are limited to in-plane sensing and actuation, which does not allow the matrix to be probed within its full 3D context. Moreover, little attention has been given to factors specific to the model ECM systems that can profoundly influence the cells contained there. Here we present methods to spatiotemporally probe and manipulate extracellular matrix networks at the scale relevant to cells using magnetic microprobes (μRods). Our techniques leverage 3D magnetic field generation, physical modeling, and image analysis to examine and apply mechanical stimuli to fibrous collagen matrices. We determined shear moduli ranging between hundreds of Pa to tens of kPa and modeled the effects of proximity to rigid surfaces and local fiber densification. We analyzed the spatial extent and dynamics of matrix deformation produced in response to magnetic torques on the order of 10 pNm, deflecting fibers over an area spanning tens of micrometers. Finally, we demonstrate 3D actuation and pose extraction of fluorescently labelled μRods.

Detection and Imaging of Magnetic Field in the Low-Frequency Regime Using a Ferromagnetic Thin Film Coated With a Thermo-Fluorescent Layer

A novel and original method of low-frequency magnetic field imaging is presented, that uses a magnetic thin film coated with fluorescent dye. Due to high permeability and consequent hysteresis losses, the film is heated by the field. As the fluorescence of the coated material is temperature-dependent, magnetic field mapping can be obtained in a short time and on a large surface by recording images with an S-CMOS camera. This principle had been previously presented in the microwave regime, for both electric and magnetic fields imaging; here, we propose first results in the low-frequency regime (kilohertz frequency range).

Characterization of a preclinical PET insert in a 7 tesla MRI scanner: beyond NEMA testing

This study evaluates the performance of the Bruker positron emission tomograph (PET) insert combined with a BioSpec 70/30 USR magnetic resonance imaging (MRI) scanner using the manufacturer acceptance protocol and the NEMA NU 4–2008 for small animal PET. The PET insert is made of 3 rings of 8 monolithic LYSO crystals (50 × 50 × 10 mm3) coupled to silicon photomultipliers (SiPM) arrays, conferring an axial and transaxial FOV of 15 cm and 8 cm. The MRI performance was evaluated with and without the insert for the following radiofrequency noise, magnetic field homogeneity and image quality. For the PET performance, we extended the NEMA protocol featuring system sensitivity, count rates, spatial resolution and image quality to homogeneity and accuracy for quantification using several MRI sequences (RARE, FLASH, EPI and UTE). The PET insert does not show any adverse effect on the MRI performances. The MR field homogeneity is well preserved (Diameter Spherical Volume, for 20 mm of 1.98 ± 4.78 without and −0.96 ± 5.16 Hz with the PET insert). The PET insert has no major effect on the radiofrequency field. The signal-to-noise ratio measurements also do not show major differences. Image ghosting is well within the manufacturer specifications (<2.5%) and no RF noise is visible. Maximum sensitivity of the PET insert is 11.0% at the center of the FOV even with simultaneous acquisition of EPI and RARE. PET MLEM resolution is 0.87 mm (FWHM) at 5 mm off-center of the FOV and 0.97 mm at 25 mm radial offset. The peaks for true/noise equivalent count rates are 410/240 and 628/486 kcps for the rat and mouse phantoms, and are reached at 30.34/22.85 and 27.94/22.58 MBq. PET image quality is minimally altered by the different MRI sequences. The Bruker PET insert shows no adverse effect on the MRI performance and demonstrated a high sensitivity, sub-millimeter resolution and good image quality even during simultaneous MRI acquisition.

Parabolic Diamond Scanning Probes for Single-Spin Magnetic Field Imaging

Enhancing the measurement signal from solid state quantum sensors such as the nitrogen-vacancy (NV) center in diamond is an important problem for sensing and imaging of condensed matter systems. Here we engineer diamond scanning probes with a truncated parabolic profile that optimizes the photonic signal from single embedded NV centers, forming a high-sensitivity probe for nanoscale magnetic field imaging. We develop a scalable fabrication procedure based on dry etching with a flowable oxide mask to reliably produce a controlled tip curvature. The resulting parabolic tip shape yields a median saturation count rate of 2.1 $\pm$ 0.2 MHz, the highest reported for single NVs in scanning probes to date. Furthermore, the structures operate across the full NV photoluminescence spectrum, emitting into a numerical aperture of 0.46 and the end-facet of the truncated tip, located near the focus of the parabola, allows for small NV-sample spacings and nanoscale imaging. We demonstrate the excellent properties of these diamond scanning probes by imaging ferromagnetic stripes with a spatial resolution better than 50 nm. Our results mark a 5-fold improvement in measurement signal over the state-of-the art in scanning-probe based NV sensors.

Detection of Opposite Magnetic Polarity in a Light Bridge: Its Emergence and Cancellation in Association with LB Fan-shaped Jets

Abstract Light bridges (LBs) are relatively bright structures that divide sunspot umbrae into two or more parts. Chromospheric LBs are known to be associated with various activities including fan-shaped jet-like ejections and brightenings. Although magnetic reconnection is frequently suggested to be responsible for such activities, not many studies present firm evidence to support the scenario. We carry out magnetic field measurements and imaging spectroscopy of an LB where fan-shaped jet-like ejections occur with co-spatial brightenings at their footpoints. We study LB fine structure and magnetic field changes using TiO images, Near-InfraRed Imaging Spectropolarimeter, and Hα data taken by the 1.6 m Goode Solar Telescope. We detect magnetic flux emergence in the LB that is of opposite polarity to that of the sunspot. The new magnetic flux cancels with the pre-existing flux at a rate of 5.6 × 1018 Mx hr−1. Both the recurrent jet-like ejections and their base brightenings are initiated at the vicinity of the magnetic flux cancellation, and show apparent horizontal extension along the LB at a projected speed of up to km s−1 to form a fan-shaped appearance. Based on these observations, we suggest that the fan-shaped ejections may have resulted from slipping reconnection between the new flux emerging in the LB and the ambient sunspot field.

Magnetic field imaging and light induced capacitance alteration for failure analysis of Cu-TSV interconnects

This paper discusses Cu-filled Through Silicon Via (TSV) failure analysis cases where known FA methods were used in an alternative way. Results are shown using magnetic field imaging (MFI) on a cross-sectioned chip to detect a leakage current path, and MFI and Light Induced Capacitance Alteration (LICA) to detect opens in TSV daisy chains.

Off-axis electron holography of Néel-type skyrmions in multilayers of heavy metals and ferromagnets

Magnetic skyrmions are complex swirling spin structures that are of interest for applications in energy-efficient memories and logic technologies. Multilayers of heavy metals and ferromagnets have been shown to host magnetic skyrmions at room temperature. Lorentz transmission electron microscopy is often used to study magnetic domain structures in multilayer samples using mainly Fresnel defocus imaging. Here, off-axis electron holography is used to obtain in-focus electron optical phase images of Néel-type domains and skyrmions in an Ir/Fe/Co/Pt multilayer sample. The preparation of the sample, reconstruction of the holograms and influence of sample tilt angle on the signal-to-noise ratio in the phase images are discussed. A good agreement is found between images of individual skyrmions that are stabilized using an external magnetic field and simulated images based on theoretical models of Néel-type skyrmions.

An experimental study on characterizing damage and fracture of a rock-like material based on three-dimensional magnetic field imaging

PurposeThe results showed that the use of a magnetic marker could relatively accurately reflect the fracture pattern inside the rock-like material (RLM).Design/methodology/approachThis study investigated the internal structure and fracture pattern of a fractured RLM. Magnetized iron oxide powder, which was used as a magnetic marker, was mixed with water and glue to form a magnetic slurry, which was subsequently injected into a fractured RLM. After the magnetic slurry completely filled the cracks inside the RLM and became cemented, the distribution and magnitude of the magnetic field inside the RLM were determined using a three-dimensional (3D) magnetic field imaging system.FindingsA model for determining the magnetic field strength was developed using MATLAB.Originality/valueThis model of 3D magnetic will further be used as a finite element tool to simulate and image cracks inside the rock.