Change Of Magnetic Flux Research Articles

Magnetocaloric cooling of a thermally-isolated microstructure

A solid-state micro magnetic refrigerator (SSMMR) has some advantages to cool microdevices because of its high efficiency and simple structure. In this study, we demonstrated the actual cooling of a thermally-isolated microstructure, which is a main component of the SSMMR, by the magnetocaloric effect. The thermal isolation structure is composed of parylene high-aspect-ratio beams for both high thermal isolation and high stiffness. A magnetic field switch was designed and fabricated to control the magnetic flux density from 0 T to about 1 T. Under this magnetic flux density change, the maximum temperature change of 1.0 °C was confirmed.

ABRUPT CHANGES OF THE PHOTOSPHERIC MAGNETIC FIELD IN ACTIVE REGIONS AND THE IMPULSIVE PHASE OF SOLAR FLARES

We compared time profiles of changes of the unsigned photospheric magnetic flux in active regions with those of their associated soft X-ray (SXR) bursts for a sample of 75 ≥ M5 flares well observed by Global Oscillation Network Group longitudinal magnetographs. Sixty-six of these events had stepwise changes in the spatially integrated unsigned flux during the SXR flares. In superposed epoch plots for these 66 events, there is a sharp increase in the unsigned magnetic flux coincident with the onset of the flare impulsive phase while the end of the stepwise change corresponds to the time of peak SXR emission. We substantiated this result with a histogram-based comparison of the timing of flux steps (onset, midpoint of step, and end) for representative points in the flaring regions with their associated SXR event time markers (flare onset, onset of impulsive phase, time of peak logarithmic derivative, maximum). On an individual event basis, the principal part of the stepwise magnetic flux change occurred during the main rise phase of the SXR burst (impulsive phase onset to SXR peak) for ~60% of the 66 cases. We find a close timing agreement between magnetic flux steps and >100 keV emission for the three largest hard X-ray (>100 keV) bursts in our sample. These results identify the abrupt changes in photospheric magnetic fields as an impulsive phase phenomenon and indicate that the coronal magnetic field changes that drive flares are rapidly transmitted to the photosphere.

Dynamics of Coronal Bright Points as Seen by Sun Watcher Using Active Pixel System Detector and Image Processing (SWAP), Atmospheric Imaging Assembly (AIA), and Helioseismic and Magnetic Imager (HMI)

The Sun Watcher using Active Pixel system detector and Image Processing (SWAP) onboard the PRoject for OnBoard Autonomy-2 (PROBA2) spacecraft provides images of the solar corona in EUV channel centered at 174 Å. These data, together with the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO), are used to study the dynamics of coronal bright points. The evolution of the magnetic polarities and associated changes in morphology are studied using magnetograms and multi-wavelength imaging. The morphology of the bright points seen in low-resolution SWAP images and high-resolution AIA images show different structures, whereas the intensity variations with time show similar trends in both SWAP 174 Å and AIA 171 Å channels. We observe that bright points are seen in EUV channels corresponding to a magnetic flux of the order of 1018 Mx. We find that there exists a good correlation between total emission from the bright point in several UV–EUV channels and total unsigned photospheric magnetic flux above certain thresholds. The bright points also show periodic brightenings, and we have attempted to find the oscillation periods in bright points and their connection to magnetic-flux changes. The observed periods are generally long (10 – 25 minutes) and there is an indication that the intensity oscillations may be generated by repeated magnetic reconnection.

Finite-Element and Analytical Calculations of No-Load Core Losses in Energy-Saving Induction Motors

This paper presents a no-load core loss analysis of a three-phase energy-saving small-size induction motor supplied by a sinusoidal voltage. In the field-circuit approach, the distribution and changes of magnetic flux density in the motor are computed using a time-stepping finite-element method. The discrete Fourier transform is used to analyze the magnetic flux density waveforms in each element of the motor model. The rotational aspect of the field is included by introducing a correction to the losses generated by the first harmonic of magnetic flux density. The core losses in each element are evaluated using a loss curve measured on a toroidal core at different frequencies. Finally, an approximate analytical formulation is derived for rapid field computation. The results are compared with measurements.

Can Law of Conservation of Energy Be Broken?

The law of conservation of energy is an empirical law of physics. It states that the total amount of energy in an isolated system remains constant over time. And it is impossible to break. However, three of evidence presented in this paper cannot be explained by the Law of conservation of energy. Why is the magnetic potential energy gone when the magnet is antimatter annihilated? Why can the steady direct current (DC) be produced when coils are cutting magnetic lines without any obstruction? Why can’t the induced current hinder the change of temperature and magnetic flux? All of these just suggest that the total amount of energy in an isolated system is not conserved over time—the law of conservation of energy can be broken.

Effect of the plate surface characteristics and gap height on yield stresses of a magnetorheological fluid

Effects of the plate material, surface roughness and measuring gap height on static and dynamic yield stresses of a magnetorheological (MR) fluid were investigated with a commercial plate–plate magnetorheometer. Magnetic and non-magnetic plates with smooth (Ra ∼ 0.3 μm) and rough (Ra ∼ 10 μm) surface finishes were used. It was shown by Hall probe measurements and finite element simulations that the use of magnetic plates or higher gap heights increases the level of magnetic flux density and changes the shape of the radial flux density profile. The yield stress increase caused by these factors was determined and subtracted from the measured values in order to examine only the effect of the wall characteristics or the gap height. Roughening of the surfaces offered a significant increase in the yield stresses for non-magnetic plates. With magnetic plates the yield stresses were higher to start with, but roughening did not increase them further. A significant part of the difference in measured stresses between rough non-magnetic and magnetic plates was caused by changes in magnetic flux density rather than by better contact of the particles to the plate surfaces. In a similar manner, an increase in gap height from 0.25 to 1.00 mm can lead to over 20% increase in measured stresses due to changes in the flux density profile. When these changes were compensated the dynamic yield stresses generally remained independent of the gap height, even in the cases where it was obvious that the wall slip was present. This suggests that with MR fluids the wall slip cannot be reliably detected by comparison of flow curves measured at different gap heights.

Reconstruction of total solar irradiance 1974–2009

Context: The study of variations in total solar irradiance (TSI) is important for understanding how the Sun affects the Earth's climate. Aims: Full-disk continuum images and magnetograms are now available for three full solar cycles. We investigate how modelled TSI compares with direct observations by building a consistent modelled TSI dataset. The model, based only on changes in the photospheric magnetic flux can then be tested on rotational, cyclical and secular timescales. Methods: We use Kitt Peak and SoHO/MDI continuum images and magnetograms in the SATIRE-S model to reconstruct TSI over cycles 21-23. To maximise independence from TSI composites, SORCE/TIM TSI data are used to fix the one free parameter of the model. We compare and combine the separate data sources for the model to estimate an uncertainty on the reconstruction and prevent any additional free parameters entering the model. Results: The reconstruction supports the PMOD composite as being the best historical record of TSI observations, although on timescales of the solar rotation the IRMB composite provides somewhat better agreement. Further to this, the model is able to account for 92% of TSI variations from 1978 to 2009 in the PMOD composite and over 96% during cycle 23. The reconstruction also displays an inter-cycle, secular decline of 0.20 (+0.12 / -0.09) Wm-2 between cycle 23 minima, in agreement with the PMOD composite. Conclusions: SATIRE-S is able to recreate TSI observations on all timescales of a day and longer over 31 years from 1978. This is strong evidence that changes in photospheric magnetic flux alone are responsible for almost all solar irradiance variations over the last three solar cycles.

GENERIC MODEL FOR MAGNETIC EXPLOSIONS APPLIED TO SOLAR FLARES

An accepted model for magnetospheric substorms is proposed as the basis for a generic model for magnetic explosions, and is applied to solar flares. The model involves widely separated energy-release and particle-acceleration regions, with energy transported Alfv\'enically between them. On a global scale, these regions are coupled by a large-scale current that is set up during the explosion by redirection of pre-existing current associated with the stored magnetic energy. The explosion-related current is driven by an electromotive force (EMF) due to the changing magnetic flux enclosed by this current. The current path and the EMF are identified for an idealized quadrupolar model for a flare.

A bending-mode galfenol electric power harvester

Iron–gallium alloys (galfenol) are promising transducer materials that combine high magnetostriction, desirable mechanical properties, high permeability, and a wide operational temperature range. In this study, we present results from a proof-of-concept prototype energy harvester that produces an output voltage proportional to the load-induced bending of the galfenol element caused by a base acceleration of the device. The device consists of a polycrystalline galfenol strip bonded to an aluminum cantilever beam, which has an effective length of 35.81 mm. Two brass pieces, each containing a permanent magnet, are used to mass load each end of the beam and to provide a magnetic bias field through the galfenol strip. The voltage induced in an induction coil closely wound around the cantilever beam captures the time rate of change of magnetic flux within the galfenol strip as the beam vibrates. The first bending-mode resonant frequency of the device was 223 Hz. The power generated from the prototype when subjected to a 1g acceleration at 222 Hz was 2.2 mW (root mean square), which corresponded to an efficiency of more than 60% for the electrical power output per unit mechanical power input to the harvester.

J044105 磁歪材料を用いた振動物体からのエネルギーハーベスト

Up to the present, by using the Terfenol-D (Tb-Dy-Fe alloy from ONR/USA) giant magnetostrictive alloys containing rare earth elements, there was an example of measuring power generation due to vibration of the impact force and compression force of the uniaxial direction. Terfenol-D has been limited field of application because it is brittle but high cost. In this study, we investigated the characteristics of the vibration generator when two magnetostrictive alloys of magnetostrictive FeCo-and FeGa, in that way, the inverse magnetostrictive effect of magnetostrictive material is used, and the beam is vibrated and paste the magnetostrictive material plate to the cantilever. A leakage flux is generated by the inverse magnetostrictive effect distortion due to vibration, so that the induced currents generated by the change in magnetic flux of time were compared for each material. So, in addition, we also measured and compared the amount of magnetostriction and magnetization characteristics. As a result, important finding that applied stress and the amount of magnetostriction are strongly related with the output voltage of the magnetostrictive vibration generator.

Spin-motive force due to a gyrating magnetic vortex

A change of magnetic flux through a circuit induces an electromotive force. By analogy, a recently predicted force that results from the motion of non-uniform spin structures has been termed the spin-motive force. Although recent experiments seem to confirm its presence, a direct signature of the spin-motive force has remained elusive. Here we report the observation of a real-time spin-motive force produced by the gyration of a magnetic vortex core. We find a good agreement between the experimental results, theory and micromagnetic simulations, which taken as a whole provide strong evidence in favour of a spin-motive force.

Investigation of Vibration Mitigation of Flexibly Support Rigid Rotors Equipped with Controlled Elements

Abstract The subject of investigations presented in this article is achieving the optimum attenuation of lateral vibration of rotors by means of two design variants of constraint elements: semiactive magnetorheological squeeze film dampers and actively controlled hydrodynamic bearings. The damping effect of magnetorheological dampers is controlled by the change of magnetic flux generated in electric coils and of the hydrodynamic bearings by the change of magnitude of the proportional gain of a feedback controller exciting movement of the bearing housings. In the developed mathematical models the rotor is considered as absolutely rigid and the controllable constraint elements are represented by force couplings. The rotor turns at constant angular speed, is loaded by its weight and in addition it is excited by a centrifugal force caused by the disc unbalance. In both design cases its lateral vibration is governed by a nonlinear equation of motion. The pressure distribution in the lubricating film in the magnetorheological squeeze film damper is described by a Reynolds equation modified for Bingham fluid whose yield shear stress depends on magnetic induction. The hydraulic forces acting in the hydrodynamic bearings are determined for the case of π-film cavitation and position of the bearing housings is adjusted by actuators activated by a proportional feedback controller. The aim of the analysis is to deal with approaches leading to minimizing amplitude of the rotor steady state vibration and magnitude of the force transmitted into the rotor casing and to compare efficiency of both design variants. The performed computer simulations show that the arrangement with the magnetorheological squeeze film damper gives better results in reducing magnitude of the transmitted force than those when the rotor is supported by hydrodynamic bearings with actively controlled position of the bearing housings.

Solar Irradiance Models and Measurements: A Comparison in the 220–240 nm wavelength band

Solar irradiance models that assume solar irradiance variations to be due to changes in the solar surface magnetic flux have been successfully used to reconstruct total solar irradiance on rotational as well as cyclical and secular time scales. Modelling spectral solar irradiance is not yet as advanced, and also suffers from a lack of comparison data, in particular on solar cycle time scales. Here, we compare solar irradiance in the 220–240 nm band as modelled with SATIRE-S and measured by different instruments on the UARS and SORCE satellites. We find good agreement between the model and measurements on rotational time scales. The long-term trends, however, show significant differences. Both SORCE instruments, in particular, show a much steeper gradient over the decaying part of cycle 23 than the modelled irradiance or that measured by UARS/SUSIM.

Vorticity of Subsurface Flows of Emerging and Decaying Active Regions

We study the temporal variation of the vorticity of subsurface flows of 828 active regions and 977 quiet regions. The vorticity of these flows is derived from measured subsurface velocities. The horizontal flows are determined by analyzing high-resolution Global Oscillation Network Group Doppler data with ring-diagram analysis covering a range of depths from the surface to about 16 Mm. The vertical velocity component is derived from the divergence of the measured horizontal flows using mass conservation. We determine the change in unsigned magnetic flux density during the disk passage of each active region using Michelson Doppler Imager (MDI) magnetograms binned to the ring-diagram grid with centers spaced by 7.5° ranging ± 52.5° in latitude and central meridian distance with an effective diameter of 15° after apodization. We then sort the data by their flux change from decaying to emerging flux and divide the data into five subsets of equal size. We find that the vorticity of subsurface flows increases during flux emergence and decreases when active regions decay. For flux emergence, the absolute values of the zonal and meridional vorticity components show the most coherent variation with activity, while for flux decrease the strongest signature is in the absolute values of the meridional and vertical vorticity components. The temporal variation of the enstrophy (residual vorticity squared) is thus a good indicator for either flux increase or decrease. There are some indications that the increase in vorticity during flux emergence happens about a day later at depths below about 8 Mm compared to layers shallower than about 4 Mm. This timing difference might imply that the vorticity signal analyzed here is caused by the interaction between magnetic flux and turbulent flows near the solar surface. There are also hints that the vorticity decrease during flux decay begins about a day earlier at layers deeper than about 8 Mm compared to shallower ones. However, the timing difference between the change at different depths is comparable to the time step of the analysis.

Study of EPS Hall-Effect Torque Sensor Technology

In an electric power steering (EPS) system, it is important to make a precise and reliable measurement of the torque on the steering wheel. A non-contact torque sensor has been developed for EPS system. The sensor is based on a magnetic principle that the magnetic flux path is changed with the torsion of a torsion bar which is placed in the steering shaft. The change of magnetic flux density in the working airgap is detected by a standard Hall-effect IC. The sensor has broad prospects for its good performance, simple structure and low cost. This paper introduces the torque sensor’s working principle, analyzes the magnetic circuit by 3D simulation, and concludes its key technologies and development trends.

The Effect of Magnetic Flux Change on Blood Flow and Vascular Aging in the Peripheral Vascular System under Magnetic Stimulus

The Effect of Magnetic Flux Change on Blood Flow and Vascular Aging in the Peripheral Vascular System under Magnetic Stimulus

The Influence of Stress Ratio on Changes in Magnetic Flux Density around Fatigue Crack Tips of Carbon Tool Steel

Fatigue failure of steel occurs when cracks form in a component and continue to grow to a size large enough to cause fracture. In order to understand the strength of a steel component, it is important to locate these cracks. We developed a scanning Hall probe microscope (SHPM), equipped with GaAs film sensors to observe fatigue cracks at room temperature in air while they were growing. In our previous works [1,2], the correlation between crack growth and magnetic field in high carbon tool steels (JIS SKS93 and JIS SUJ2) were determined. We also reported the sensitivity of the SHPM equipped with a three-dimensional line-probe that was developed to decrease the sensor gaps. By using the line-probe sensor we succeeded to measure the magnetic flux density distributions in very close proximity to the specimen’s surface. However, in order to further understand the relation between magnetic flux density and crack growth, other materials, microstructures and fatigue test conditions should be evaluated. In the present work, we focus on the effect of stress ratios on the changes of the magnetic flux density in annealed carbon tool steel.

Experimental method for determining the total demagnetizing factor of thin amorphous ribbons

The basis of the method is the influence of the demagnetizing field on the maximum rate of magnetic flux change of the amorphous ribbon. The method allows to determine the demagnetizing factor of thin amorphous ribbons in a wide range of its values. With the proposed method the frequency dependence of the demagnetizing factor of amorphous ribbon with a helical magnetic anisotropy was found out.

Magnetic field changes associated with three successive M-class solar flares on 2002 July 26

With an extensive analysis, we study the temporal evolution of magnetic flux during three successive M-class flares in two adjacent active regions: NOAA 10039 and 10044. The primary data are full disk longitudinal magnetograms observed by SOHO/MDI. All three flares are observed to be accompanied by magnetic flux changes. The changes occurred immediately or within 1 ∼ 10 minutes after the starting time of the flares, indicating that the changes are obvious consequences of the solar flares. Although changes in many points are intrinsic in magnetic flux, for some sites, it is caused by a rapid expansion motion of magnetic flux. For the second flare, the associated change is more gradual compared with the ‘step-function’ reported in literature. Furthermore, we use the data observed by the Imaging Vector Magnetograph (IVM) at Mees Solar Observatory to check possible line profile changes during the flares. The results from the IVM data confirm the flux changes obtained from the MDI data. A series of line profiles were obtained from the IVM's observations and analyzed for flux change sites. We find that the fluctuations in the width, depth and central wavelength of the lines are less than 5.0% even at the flare's core. No line profile change is observed during or after the flare. We conclude that the magnetic field changes associated with the three solar flares are not caused by flare emission.

ESTIMATION OF THE RECONNECTION ELECTRIC FIELD IN THE 2003 OCTOBER 29 X10 FLARE

The electric field in the reconnecting current sheet of the 2003 October 29 X10 flare is estimated to be a few kV m–1 in this study, based on the rate of change in the photospheric magnetic flux in the newly brightened areas of Transition Region and Coronal Explorer (TRACE) UV ribbons. For comparison, the motion speed of Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) hard X-ray (HXR) footpoints and the photospheric magnetic field strength are also used for the electric field calculation. This X10 flare event is selected due to its distinct two-phase HXR kernel motion, two arcade systems with different magnetic shear, and the high cadence and complete coverage of the TRACE 1600 A Michelson Doppler Imager (MDI) magnetogram and RHESSI HXR observations. We pay particular attention to the electric field characteristics in different flare phases, as well as the temporal correlation with the HXR emission and its power-law spectral index and the photospheric magnetic field strength. We found that in the early impulsive phase, the reconnection electric field peaks just before the HXR emission peaks and the energy spectrum hardens. The result is consistent with the scenario that more particles are accelerated to higher energies by larger reconnection electric fields and then precipitate into the lower chromosphere to produce stronger HXR emissions. Such a particle acceleration mechanism plays its most significant role in the impulsive phase of this flare. In addition, our results provide evidence that the highly sheared magnetic field lines are mapped to the magnetic reconnection diffusion region to produce a large reconnection electric field.