Magnetic Disturbances Research Articles

Anisotropic magnetoresistive sensors for control of additive manufacturing machines

Abstract Magnetic sensors are employed for dimensional measurements by detection of sensor motion relative to a small magnet. This is widely used everywhere in industrial automation, car industry and in many home appliances. The use of magnetic sensors in machines for additive manufacturing improves control and long term reliability by non contact position measurements. Magnetic sensors with linearized characteristic based on the anisotropic magnetoresistance (AMR) effect can replace mechanical switches, while specialized AMR angle sensors are preferred for the measurement of rotational motions. Both are easy to use and can be integrated with help of 3D printed holders at low cost. In this work, appropriate sensors are selected, integrated and discussed regarding magnetic disturbance signals apparent in low-cost 3D printers.

FFC NMR Relaxometer with Magnetic Flux Density Control

This paper describes an innovative solution for the power supply of a fast field cycling (FFC) nuclear magnetic resonance (NMR) spectrometer considering its low power consumption, portability and low cost. In FFC cores, the magnetic flux density must be controlled in order to perform magnetic flux density cycles with short transients, while maintaining the magnetic flux density levels with high accuracy and homogeneity. Typical solutions in the FFC NMR literature use current control to get the required magnetic flux density cycles, which correspond to an indirect magnetic flux density control. The main feature of this new relaxometer is the direct control of the magnetic flux density instead of the magnet current, in contrast with other equipment available in the market. This feature is a great progress because it improves the performance. With this solution it is possible to compensate magnetic field disturbances and parasitic magnetic fields guaranteeing, among other possibilities, a field control below the earth magnetic field. Experimental results validating the developed solution and illustrating the real operation of this type of equipment are shown.

Design of a stiffness variable flexible coupling using magnetorheological elastomer for torsional vibration reduction

In this study, the design of an magnetorheological elastomer flexible coupling whose torsional stiffness can be controlled by an embedded magnetic field generator is proposed. It is designed to minimize the torsional vibration transmission between shafts adaptively to the dynamic disturbance. The coupling insert is composed of magnetorheological elastomer which is a smart material whose stiffness can be controlled by an external magnetic field. This article also proposes a compact magnetic field generator which can be fitted inside the coupling hubs, to control the torsional stiffness of the magnetorheological elastomer. The finite element method was used to design and estimate the dynamic stiffness variation of the magnetorheological elastomer coupling due to the applied magnetic field and disturbance frequency. Also, torsional vibration experiments were conducted to validate the performance of the proposed magnetorheological elastomer coupling. Results showed that it can adaptively tune in a range of frequencies between 16.8 and 23.5 Hz and has 95.7% stiffness variation under magnetic field of 150mT. The proposed system is expected to achieve a higher MRE effect with a softer base matrix.

The online estimation of the joint angle based on the gravity acceleration using the accelerometer and gyroscope in the wireless networks

This study aims at the online estimation of the hip and knee angle in the sagittal plane for the motion surveillance only using the tri-axis accelerometers and gyroscopes of IMU, without considering the magnetic disturbance. The proposed method utilizes the projection of gravity acceleration on each sensor coordinate system to estimate the joint angle which rotating around the horizontal axis and approximately horizontal axis. With the third row of the rotation matrix independent of the yaw angle, the proposed method first calculates the projection of the gravity acceleration on each IMU sensor coordinate system only using accelerometer and gyroscope. And then, the rotation matrix between two adjacent coordinate systems is directly calculated. After evaluating the body to sensor rotation matrix, the rotation matrix between two adjacent body segments can be calculated, ultimately. Two types of experiments are adopted in the paper. The results show that the proposed method obtains the outstanding performance with the RMSE lower than 0.8 deg in the horizontal rotation experiment. In the limb joint experiment, the RMSE of the hip joint is lower than 3.12 deg, while the RMSE of the knee joint is lower than 3.83 deg for all predefined locomotion modes. The characteristic of our approach is that it can be run online without any parameter adjustment and additional time latency while ensuring estimation accuracy.

Interfacial Ferromagnetic Coupling and Positive Spontaneous Exchange Bias in SrFeO3-x/La0.7Sr0.3MnO3 Bilayers.

Negative exchange bias is usually discovered in ferromagnetic (FM)/antiferromagnetic (AFM) heterostructures after a field-cooling (FC) process. Relatively, positive exchange bias (PEB) is a rarely observed phenomenon. So far, almost all of the models for PEB whether undergoing FC or zero-field-cooling (ZFC) treatment have been explained by an interaction of strong AFM coupling at the interface. In this work, by selecting a special material of SrFeO3-x as the AFM layer, coupled with FM-La0.7Sr0.3MnO3 (LSMO), we obtain a novel PEB effect of the bilayer after ZFC measurement, of which the shift directions are unfixable and dependent on the initial magnetization direction. Based on a transient magnetic field to control the remanence (Mr) direction of LSMO at room temperature and then cooling below the TN of SrFeO3-x without any magnetic field disturbance, the shift direction can be locked only toward the transient magnetic field. Combined with experimental results and first-principles calculations, we propose that the above phenomena are explained as the field-induced AFM phase of SrFeO3-x transforming into the FM phase at an FM coupling bilayer interface. Thus, our finding may provide a new approach to realize and tune the zero-field-cooling PEB with FM coupling heterostructures.

UKF Magnetometer-Free Sensor Fusion for Pelvis Pose Estimation During Treadmill Walking.

Inertial measurement units are an efficient tool to estimate the orientation of a rigid body with respect to a global or navigation frame. Thanks to their relatively small scale, these devices are often employed in clinical environments in form of wearable devices. A direct consequence of this large use of inertial sensors has been the development of many sensor fusion techniques for pose estimation in many practical applications. In this paper we study the feasibility of a nonlinear "Unscented" variant of the well-known Kalman Filter for gyroscope/accelerometer sensor fusion in pelvis pose estimation during treadmill walking. In addition, orientation estimation has been obtained without IMU magnetometer data, in order to propose a method suitable also for environments where magnetic disturbances could arise. Pelvis heading (yaw), bank (roll) and attitude (pitch) angles have been evaluated both using the proposed filter and a gold standard optometric system. The root mean square errors obtained using the proposed sensor fusion with respect to the gold standard are below 1 degree for each axis, showing also a significant high correlation (> 0.90). Findings of this study highlight the suitability of a magnetometer-free UKF approach for pose estimation of pelvis during human walking on treadmill, providing information useful also for further estimation of center of mass displacement in the same experimental conditions.

A Parallel Attitude-Heading Kalman Filter Without State-Augmentation of Model-Based Disturbance Components

This paper proposes an inertial and magnetic sensing-based parallel orientation Kalman filter (KF), which is composed of two separate KFs: one for attitude estimation with an external acceleration model as presented in author's previous work and the other for heading estimation with a magnetic disturbance model. The novelty of the proposed attitude-heading KF, compared to other model-based KFs, is that the disturbance models are implemented by inserting them into the measurement equations without state-augmentation. In this case, there is no increase in the matrix size of the corresponding KF structure, which is advantageous as the computational cost is approximately halved when compared with the state-augmentation type approaches. The proposed KF has been experimentally verified in magnetically disturbed conditions. The proposed method has advantages over the KF with state-augmentation in the calculation efficiency and ease of use.

Use of Magnetic Circuits for Toroidal GMI Current Sensors

In this paper, the approach of using magnetic circuits in giant magneto-impedance (GMI) current sensors is introduced for the first time in order to reduce the impact of magnetic disturbances on the sensor response. The studied current sensor had a toroidal structure. The GMI sensitive element circled the conductor carrying the measured current. The way to use a magnetic circuit in this configuration was established, and the rules of design and implementation were defined and validated by the simulation and by the measurements. The theoretical idea was to place the sensitive element on the surface of a magnetic circuit. However, in practical conditions, both simulation and measurement have demonstrated that a magnetic circuit must be placed at each side of the sensitive element, if the idea is to prevent from the effect of the different types of magnetic disturbances.

Features of the HF Signal Propagation on Oblique Sounding Paths During Solar and Magnetic Activity in September 2017

We present the results of studying the influence of solar and magnetic activity in September 2017 on the HF signal characteristics on subauroral and midlatitude paths. A connection between the ionospheric effects caused by the magnetic storm and the magnetic disturbance intensity is established. It is shown that the formation of a strong sporadic Es layer in the auroral ionosphere during a magnetic storm makes it possible to use the propagation mode with reflection from Es in the interests of HF communication to neutralize the effects of the negative phase of the storm and absorption growth when unfavorable conditions for the F-mode propagation with reflection from the upper ionosphere occur.

Diffusive versus Free-streaming Cosmic-Ray Transport in Molecular Clouds

Abstract Understanding the cosmic-ray (CR) ionization rate is crucial in order to simulate the dynamics of molecular clouds, and interpret the chemical species observed in these objects. Calculating the CR ionization rate requires both accurate knowledge of the spectrum of MeV to GeV protons at the edge of the cloud as well as a model for the propagation of CRs into molecular clouds. Some models for the propagation of CRs in molecular clouds assume them to stream freely along magnetic field lines, while in others they propagate diffusively due to resonant scattering off of magnetic disturbances excited by MHD turbulence present in the medium. We discuss the conditions under which CR diffusion can operate in a molecular cloud, calculate the local CR spectrum and ionization rate in both a free-streaming and diffusive propagation model, and highlight the different results from the two models. We also apply these two models to the propagation through the ISM to obtain the proton spectrum seen by Voyager 1, and show that such a spectrum favors a diffusive propagation model.

Anti-aging effects of long-term space missions, estimated by heart rate variability

Reports that aging slows down in space prompted this investigation of anti-aging effects in humans by analyzing astronauts’ heart rate variability (HRV). Ambulatory 48-hour electrocardiograms from 7 astronauts (42.1 ± 6.8 years; 6 men) 20.6 ± 2.7 days (ISS01) and 138.6 ± 21.8 days (ISS02) after launch were divided into 24-hour spans of relative lower or higher magnetic disturbance, based on geomagnetic measures in Tromso, Norway. Magnetic disturbances were significantly higher on disturbed than on quiet days (ISS01: 72.01 ± 33.82 versus 33.96 ± 17.90 nT, P = 0.0307; ISS02: 71.06 ± 51.52 versus 32.53 ± 27.27 nT, P = 0.0308). SDNNIDX was increased on disturbed days (by 5.5% during ISS01, P = 0.0110), as were other HRV indices during ISS02 (SDANN, 12.5%, P = 0.0243; Triangular Index, 8.4%, P = 0.0469; and TF-component, 17.2%, P = 0.0054), suggesting the action of an anti-aging or longevity effect. The effect on TF was stronger during light (12:00–17:00) than during darkness (0:00–05:00) (P = 0.0268). The brain default mode network (DMN) was activated, gauged by increases in the LF-band (9.7%, P = 0.0730) and MF1-band (9.9%, P = 0.0281). Magnetic changes in the magnetosphere can affect and enhance HRV indices in space, involving an anti-aging or longevity effect, probably in association with the brain DMN, in a light-dependent manner and/or with help from the circadian clock.

Analytic Expressions for Radial Diffusion.

I briefly review, compare and contrast two theoretical works that have significantly influenced radial diffusion research thus far, namely, the works of Fälthammar (1965, https://doi.org/10.1029/JZ070i011p02503) and the works of Fei et al. (2006, https://doi.org/10.1029/2005JA011211). Leveraging Fälthammar's model for magnetic field disturbances, I demonstrate that Fei et al's formulas are incorrect: they underestimate radial diffusion by a factor two in the presence of magnetic field disturbances. This underestimation comes from the erroneous assumption that radial displacements driven by magnetic field disturbances are statistically independent from radial displacements driven by induced electric fields while in fact both displacements are proportional to each other. Fei et al.'s approach is similar to Fälthammar's approach in that they both analyze radial diffusion by pieces, depending on the nature of the driver. Yet, the Fokker-Planck equation requires only one radial diffusion coefficient to characterize statistically a trapped radiation belt population cross drift shell motion. Thus, it is worth questioning the practice that consists of defining the coefficient as a sum of independent contributions. In addition, both theoretical models rely on the assumption that the background magnetic field is primarily dipolar, leading to flawed estimates. To overcome these limitations and to improve radial diffusion quantification, I use a general formulation for the variation of the third adiabatic invariant (1) to describe how to compute a radial diffusion coefficient in the most general way and (2) to highlight the assumptions that need to be questioned.

Data Mining Reveals the Dynamics of Auroral Substorms

An analysis of 5 decades of satellite data has pieced together the most comprehensive picture yet of substorms, the magnetic disturbances that cause surges of aurora.

A New Calibration Method for Triaxial Fluxgate Magnetometer Based on Magnetic Shielding Room

The triaxial fluxgate magnetometers (TFMs) are widely used in space exploration, positioning and navigation, geological exploration, etc. As a high-precision vector magnetometer, the measurement accuracy will directly determine the accuracy of the obtained magnetic field data. The TFM has three kinds of own errors in measurement: zero offset error, proportional coefficient error, and nonorthogonal error. These three kinds of errors will cause the TFM to deviate from the actual magnetic field value, and the fluxgate magnetometer needs to be calibrated. At present, the accuracy of the calibration method adopted by the fluxgate magnetometer depends on the stability of the natural environment magnetic field and the triaxial turntable (there is an uncontrollable residual magnetic interference), which limits the further improvement of the calibration accuracy. And due to the wide application of electromagnetic equipment, the natural electromagnetic environment is further damaged, and the calibration accuracy is subject to deterioration. In this paper, a magnetic shielding room (MSR) is used to provide a near-zero magnetic environment, and a triaxial uniform magnetic field coil (TUMC) is installed inside the MSR to construct a controllable arbitrary vector direction magnetic field, which solves the magnetic field disturbance problem of the original method. The TUMC and TFM error models were built and the MSR magnetic ambient noise model was added. The emphasis is on the degree of distortion of the magnetic field generated by the MSR as a ferromagnetic boundary condition and the influence of the deviation of the center point of TUMC on the calibration accuracy. Then, based on the above error model and magnetic environmental conditions, the calibration accuracy of the calibration magnetic field distribution is analyzed. Finally, the calibration experiment of the TFM is carried out by using the existing MSR, which proves the feasibility and effectiveness of the calibration method, and the method can greatly improve the calibration efficiency.

Adaptive Anti-Disturbance Method for Magnetometer and INS Integration in a Road Vehicle

The integration of magnetometers and Inertial Navigation Systems (INS) is widely used in low-cost navigation systems. However, even if the system has been calibrated, random magnetic disturbances still appear in practical applications, which lead to large heading errors. To solve this problem, an adaptive anti-disturbance method to overcome random magnetic disturbance is proposed. First, disturbances are classified and analysed in detail based on actual road vehicle driving data. Then an Adaptive Robust Extend Kalman Filter (AREKF) is designed to resist sudden disturbances. However, an AREKF may accumulate errors slowly when a long-term disturbance exists. Considering this situation, this paper proposes that AREKF is used to maintain accuracy in the early stages, at the same time as the magnetometer is quickly calibrated with a Kalman filter. Then, the new magnetometer parameters are put into the AREKF to suppress long-term disturbances. Finally, cascading these two modules, not only the sudden disturbance can be overcome, but the situation of long-term disturbances can be suppressed. The results of simulation and an actual driving test show that the proposed method can effectively overcome random magnetic disturbances in both the short and long term.

Feasibility of quantifying the physical exposure of materials handlers in the workplace with magnetic and inertial measurement units

Handling tasks can expose workers to risk factors. The objective was to describe the feasibility of using magnetic and inertial measurement units (MIMUs) to quantify the physical exposure of materials handlers in the workplace. Full-body kinematics were obtained with MIMUs on 10 handlers gathering products ordered by retailers with a pallet truck. An observer classified the visual difference (VD) of segment orientation between a MIMUs avatar and video recordings in three categories (none, minor and major) for each product transfer. The feet, arms, shoulders and head were considered similar for ≥97% of observations. The trunk segment obtained the most differences with 9% of minor VD and 5% of major VD, which were related to the duration of the magnetic disturbances of the MIMUs. Estimating parameters of the physical exposure of handlers in the workplace is feasible with kinematics and an order list, but visual verification remains important for scientific rigour.Practitioner Summary: The feasibility of measuring physical exposure with magnetic and inertial measurement units was evaluated on materials handlers in the workplace. Visual observation of the postures indicated that most of the data is considered acceptable. Magnetic disturbances can increase the measurement error, so data must be verified to ensure validity.

Response of the magnetosphere–ionosphere system to sudden changes in solar wind dynamic pressure

The geomagnetic sudden commencement (SC) is a plasma and magnetic field disturbance in the magnetosphere–ionosphere region, which appears as a response of this system to a sudden change in the solar wind dynamic pressures associated with shock and tangential discontinuity of solar wind. As this mechanism seems to be simple, the SC has been widely investigated based on observations in the region from the surface of the Earth to the magnetosphere. A schematic model of the SC was presented by Araki (Solar wind sources of magnetospheric ultra-low-frequency waves. American Geophysical Union, Washington, DC, pp 183–200, 1994), who compiled many observational results and theories related to this phenomenon. Recent advances in supercomputing allow us to present new numerical results including three-dimensional global current systems of the SC which cannot be obtained only by direct observations and theoretical analysis. The simulation study not only confirms the results of a previous model on the initial response of the magnetosphere–ionosphere system to solar wind changes (the preliminary impulse) but also presents new findings on dynamical processes in the magnetosphere–ionosphere system in the period following the initial response (the main impulse). Furthermore, the simulation study reveals the SC sequence in the context of break and recovery of the steady magnetosphere–ionosphere convection system. The transient flow vortex in the flank magnetosphere in the main impulse phase plays an essential role in recovering the convection system. This report describes the SC process from the viewpoint of the state transition of the magnetosphere–ionosphere compound system Tanaka (Space Sci Rev 133:1, https://doi.org/10.1007/s11214-007-9168-4, 2007).

Introduction to the physics of solar eruptions and their space weather impact.

The physical processes, which drive powerful solar eruptions, play an important role in our understanding of the Sun-Earth connection. In this Special Issue, we firstly discuss how magnetic fields emerge from the solar interior to the solar surface, to build up active regions, which commonly host large-scale coronal disturbances, such as coronal mass ejections (CMEs). Then, we discuss the physical processes associated with the driving and triggering of these eruptions, the propagation of the large-scale magnetic disturbances through interplanetary space and the interaction of CMEs with Earth's magnetic field. The acceleration mechanisms for the solar energetic particles related to explosive phenomena (e.g. flares and/or CMEs) in the solar corona are also discussed. The main aim of this Issue, therefore, is to encapsulate the present state-of-the-art in research related to the genesis of solar eruptions and their space-weather implications. This article is part of the theme issue 'Solar eruptions and their space weather impact'.

Arterial Blood Oxygen Saturation and Its Dynamics Due to the Environmental Electromagnetic Conditions

Background. As widely known, the geomagnetic field intensity does change abruptly during global magnetic disturbances specified as magnetic storms. Those are due to the changing solar activity influencing solar wind parameters and the state of the magnetosphere. This chain of physical processes with their origin in the Sun is described as the space weather. To understand the space weather effects in the environment is most important since those are related to the biosphere as well. Namely, the low-frequency geomagnetic field dy­namics, linked with space weather conditions, seems to be a quite probable factor influencing both the pathological and functional state of a human being and biological objects, in general, during magnetic storms. Objective. In this study, the dynamics of an oxygen saturation parameter in human arterial blood is analyzed with regard to extreme space weather when magnetic storms occur. Methods. Experimental setup for measuring changes of the relative concentration of oxyhemoglobin in arterial blood (saturation of arterial blood with oxygen), is a pulse oximeter-spectrophotometer. Measurements were carried out using pulse-oximetry sensor covering the first phalanx of a finger, and laser radiation was directed to the side of the second phalanx. The He-Ne laser with a wavelength of 632 nm was used as a source of electromagnetic radiation. Observational values of the geomagnetic field with a high-time resolution (1-sec) are obtained from the midlatitude Hurbanovo Geomagnetic Observatory (Slovak Republic). Deviations/oscillation ranges regarding the average value were calculated at all frequencies, and low pass filter was applied from the Seewave-1.7.6 package (F-filter) for frequencies of 0.1, 0.5, 0.01, 0.05, 0.001, and 0.0001 Hz. The data on magnetic storms for 2015 were derived from the file of Kyoto Geomagnetic Center which indicated the dates and the amplitudes of magnetic storms on the Earth. Results. The following variables were analyzed: the average arterial oxygen saturation at the patient’s rest, peak-to-peak value of saturation, changes in the average oxygen saturation under laser radiation. A group of 33 persons was daily monitored from March 30, 2015, to May 25, 2015. In the presence of Earth's magnetic field disturbances, the average value of arterial oxygen saturation at the state of rest in 29 persons out of 33 was 93.9 ± 0.9%, peak-to-peak value of oxygen was 1.25 ± 0.24%, and the change in the average arterial oxygen saturation under laser radiation made up 2.34 ± 0.41%. In 4 persons under study the peak-to-peak value of saturation at rest did not differ from the case of the undisturbed geomagnetic field. Conclusions. The results of this study of some blood parameters, namely the oxygen saturation (and oxygenetion) value of the arterial blood and its dynamics due to exposed laser radiation in case of both the undisturbed and disturbed GMF, can be summarized as follows: the decrease of the blood oxygenation in case of the disturbed GMF (magnetic storm conditions) is quite apparent although more detailed statistical investigations along with biophysical explanations are needed; the presence of some experimentees in the observed group who have constant sweep of arterial blood oxygen saturation is, in our opinion, an aspect to explain the different frequency of tick attacks on various people although strict medical and epidemiological investigations are needed; the dynamics of the decrease of oxygen saturation in the arterial blood of human beings exposed to laser radiation, in persons with sensitivity to radiation, may be an indicator of the degree of influence of perturbations of the geomagnetic field.

How To Manage Geomagnetic-Field Disturbances in the Northern Auroral Zone To Improve the Accuracy of Magnetic Measurement-While-Drilling Directional Surveys

Summary The auroral zone is the region surrounding the geomagnetic North and South Poles, and it is where the largest and most frequent disturbances in the Earth's magnetic field are experienced. Because geomagnetic disturbances affect the accuracy of magnetic measurement-while-drilling (MWD) directional data, surveying wells in the auroral zone is challenging. Development of industry practices to enable accurate surveying and safe operations in these areas is important. The objective of this study was to investigate how magnetic disturbances in the auroral zone influence the geomagnetic-field parameters of declination, dip angle, and total magnetic-field intensity. This investigation analyzed the statistical properties of data from 20 land-based magnetic observatories and variometer stations in Scandinavia, Greenland, and Alaska—all located in the auroral zone. The results were used to estimate magnetic-field-disturbance covariations as a function of distance and direction. Additionally, methods to reduce azimuth uncertainty using data from distant monitoring stations were studied. Uncritical use of data obtained from monitoring stations can result in uncertain azimuth measurements. In cases where data from more than one nearby monitoring station are available, the challenge is often to identify which stations are providing the most-accurate corrections. Important criteria for the selection of monitoring stations are not limited to directions and distances, but also include the location of the ionospheric current relative to the rig location. Procedures and methods for predicting the location of ionospheric currents were tested. The data sets analyzed in this study contain measured deviations from the quiet mean for periods with low, moderate, and high geomagnetic activity. Station pairs with mutual distances ranging from 150 to 850 km were considered. The general trends of the magnetic data from station pairs located along the east/west direction are more correlated than in the north/south direction, and the differences in magnetic fluctuations between station pairs are lower in the east/west direction than in the north/south direction. This holds true for all distances, directions, and disturbance levels.