Change Of Magnetic Flux Research Articles

Research on Dynamic Magnetic Flux Measurement Under DC-Biased Magnetization by the Type-c Transducer

This paper proposes a novel real-time measurement method of the dynamic magnetic flux in magnetically controlled devices based on the type-c transducer. The principle of the device is using an auxiliary core with an auxiliary winding to inject a high-frequency signal. Because the auxiliary core shares a partial magnetic path with the main iron core, the output current in the auxiliary winding will change synchronously when the dc-bias magnetic flux changes, and then reflect the real-time operating state of the main flux in the main core. The theoretical analysis indicates the sensitivity of the transducer is heavily affected by the auxiliary core’s length, width, and permeability. The Magnet software is used in this research to build the model of the proposed transducer and to select the optimal size and design of the transducer. At last, to verify the design, a cosimulation with the Magnet and Simulink software is used to measure the output waveform of the transducer under dc-bias condition in the main core. The simulation results coincide with the theoretical results that prove the validity of the methods.

High strain-rate magnetoelasticity in Galfenol

This paper presents the experimental measurements of a highly magnetoelastic material (Galfenol) under impact loading. A Split-Hopkinson Pressure Bar was used to generate compressive stress up to 275 MPa at strain rates of either 20/s or 33/s while measuring the stress-strain response and change in magnetic flux density due to magnetoelastic coupling. The average Young's modulus (44.85 GPa) was invariant to strain rate, with instantaneous stiffness ranging from 25 to 55 GPa. A lumped parameters model simulated the measured pickup coil voltages in response to an applied stress pulse. Fitting the model to the experimental data provided the average piezomagnetic coefficient and relative permeability as functions of field strength. The model suggests magnetoelastic coupling is primarily insensitive to strain rates as high as 33/s. Additionally, the lumped parameters model was used to investigate magnetoelastic transducers as potential pulsed power sources. Results show that Galfenol can generate large quantities of instantaneous power (80 MW/m3), comparable to explosively driven ferromagnetic pulse generators (500 MW/m3). However, this process is much more efficient and can be cyclically carried out in the linear elastic range of the material, in stark contrast with explosively driven pulsed power generators.

Electromagnetic Energy Harvester With Flexible Coils and Magnetic Spring for 1–10 Hz Resonance

This paper presents an energy harvester with microfabricated flexible coils (rolled and aligned to a magnet array for maximum magnetic flux change) and magnetic spring to generate electrical power from human body motion. The magnet array is suspended by a magnetic spring for a resonant frequency of several hertz. An analytical model of vibration-driven energy harvester with magnetic spring through magnet and coil arrays is developed to explore the power generation with various magnet ranges and vibration amplitudes. Experimental results show that the electromagnetic energy harvester with six 7-turn microfabricated coils (occupying 3.8 cc and weighing 8.5 gram) generates an induced electromotive force (EMF) of $\mathrm{V}_{\mathrm {rms}} =6.7$ mV with 0.53- $\mu $ W power output (into 21- $\Omega $ load) from 0.27-g acceleration at 8 Hz (corresponding to 1.05-mm vibration amplitude). Its larger-scale version with sixteen 200-turn wire-wound coils (occupying 26 cc and weighing 98 gram) generates an EMF of $\mathrm{V}_{\mathrm {rms}} =1.3$ V with 4.3-mW power output (into 100- $\Omega $ load) from 0.5-g acceleration at 5.5 Hz (corresponding to 4.1-mm vibration amplitude). When the larger-scale version of the energy harvester is placed in a backpack of a human walking at various speeds, the power output is increased as the walking speed is increased from 0.45 m/s (slow walking) to 2.68 m/s (slow running), and reaches 14.8 mW at 2.68 m/s. [2014-0323]

Local magnetic behavior across the first order phase transition in [formula omitted] magneto caloric compound

We visualize, with a magneto optical imaging technique with indicator film, the local magnetic response of the compound La(Fe0.9Co0.015Si0.085)13 during its first order magneto structural transition. The technique allowed us by comparing the stray fields of the main magneto caloric phase and of secondary phases present in the sample to obtain the magnetic behavior of each phase above and below the Curie temperature with respect to the surrounds. Computing the change in the total magnetic flux, when the sample crosses the Curie point, both in cooling and heating, we are able to correlate the average thermal hysteresis of the transition with the local magnetic properties at single sites and analyze the influence of defects on the transition dynamics.

Multilayer Scanning Coil Detector for Improved Detection of Surface Pathogen Contamination

This paper presents an investigation into improved pathogen detection on food and food contact surfaces using a multilayer scanning coil detector combined with wireless magnetoelastic (ME) biosensors. In contrast to our previous studies of surface pathogen detection where a single-layer planar coil was employed, a more sensitive detector with a multi-layer coil design was investigated in this work. The two-fold roles of the coil detector are: (1) the application of an alternating magnetic field for the excitation of the ME sensor’s vibration and (2) detection of the resultant magnetic flux changes induced by the vibrating sensor. Surface pathogen detection can then be realized when the sensor comes into contact and binds specifically with the pathogen of interest, causing the sensor’s resonant frequency to decrease. For surfaces with large roughness and curvatures (e.g., leafy greens and cantaloupes), a long stand-off distance (distance between the sensor and detector) may be required. Hence, enhancement in the excitation power and sensitivity of coil detector with a multilayer design is a key to improving the system’s detection capabilities. Furthermore, smaller ME biosensors with higher mass sensitivity can also be measured with this sensitive multilayer coil detector. Several design parameters, including the number of layers, width, height, and spacing of coil turns, were studied. Coils were fabricated using standard microelectronic fabrication techniques (photolithograpy, electroplating, etching and sputtering) and tested.Both theoretical calculations and experimental data showed that the above coil geometric parameters have a significant impact on the signal amplitude and stand-off distance. Finally, with the newly fabricated multilayer coil detector, simultaneous measurement of multiple biosensors on spinach leaf surfaces was demonstrated. This multilayer scanning coil detector therefore facilitates the detection of pathogens on food and food contact surfaces.

P10. Magnetic vestibular stimulation (MVS) influences fMRI resting-state fluctuations. The modulation of the default-mode network as an exemplary case

Introduction Dizziness in the presence of strong magnetic fields has been noticed ever since the first magnetic resonance experiments at high field strengths (>1 Tesla) have been conducted. It was suggested that this was due to the changing magnetic flux in the inner ear induced by the gross subject-motion within the magnetic field and that the motionless presence in the static magnetic field could not affect subjects significantly ( Schenck, 1992 ). Recently however, Roberts et al. (2011) showed that healthy subjects at rest who are kept in total darkness and exposed to the static magnetic field of an MR tomograph developed a persistent nystagmus, while patients with bilateral peripheral vestibular failure did not. Furthermore, the nystagmus’ slow phase velocity was modulated systematically depending on the subject’s head orientation relative to the field. The authors argued that the ionic fluids in the inner ear, which are constantly flowing as cells maintain resting activity, will be diverted by a (magnetic) Lorentz-force and this creates a pressure onto the cupula “the rotatory motion sensor” in the inner ear, thus leading to a nystagmus akin to a constant (accelerating) rotatory stimulation. This model was further supported by a simulation study ( Antunes et al., 2012 ) and a recent study of patients with unilateral labyrinthine disorders ( Ward et al., 2014 ). It was speculated that this magnetic vestibular stimulation (MVS) effect might influence fMRI results, because a nystagmus is indicative for a vestibular imbalance. Methods The aim of the current study was to investigate if this MVS effect does indeed modulate the fluctuations of the BOLD signal in areas related to the vestibular system. Here we treat the case of MVS influencing resting-state networks, presenting results from resting-state experiments conducted at two different field strengths (1.5 Tesla & 3 Tesla) and focus in particular on the influence of MVS on the default mode network. Results Those subparts of the default mode network that were significantly modulated between field strengths were also commonly associated with vestibular functions. Furthermore, the signal-scaling behavior of these subparts was different from the other parts of the default mode network that were not significantly modulated. In fact, the signal-scaling behavior was in agreement with a modulation due to MVS as expected from a Lorentz-model perspective (i.e. linear increase) while the other parts that were not significantly modulated by the MVS effect showed a scaling behavior that was expected simply from considering fMRI signal-scaling behavior due to increased field strength (i.e. approximately square root increase, e.g. see ( Duyn, 2012 )). Conclusion The MVS effect significantly affected BOLD signal modulation. Those parts which were more closely connected to the vestibular peripheral sense-organs did modulate in accordance with the Lorentz-model prediction and those subparts which modulated less, but still modulated significantly above the expected increase due to field-strength related signal-increase, were further removed in terms of connectivity from the vestibular peripheral sense-organs and therefore were modulated less strongly by MVS.

DYNAMICS OF ON-DISK PLUMES AS OBSERVED WITH THE INTERFACE REGION IMAGING SPECTROGRAPH, THE ATMOSPHERIC IMAGING ASSEMBLY, AND THE HELIOSEISMIC AND MAGNETIC IMAGER

We examine the role of small-scale transients in the formation and evolution of solar coronal plumes. We study the dynamics of plume footpoints seen in the vicinity of a coronal hole using the Atmospheric Imaging Assembly (AIA) images, the Helioseismic and Magnetic Imager magnetogram on board the Solar Dynamics Observatory and spectroscopic data from the Interface Region Imaging Spectrograph (IRIS). Quasi-periodic brightenings are observed in the base of the plumes and are associated with magnetic flux changes. With the high spectral and spatial resolution of IRIS, we identify the sources of these oscillations and try to understand what role the transients at the footpoints can play in sustaining the coronal plumes. IRIS sit-and-stare observations provide a unique opportunity to study the evolution of footpoints of the plumes. We notice enhanced line width and intensity, and large deviation from the average Doppler shift in the line profiles at specific instances, which indicate the presence of flows at the footpoints of plumes. We propose that outflows (jet-like features) as a result of small-scale reconnections affect the line profiles. These jet-like features may also be responsible for the generation of propagating disturbances (PDs) within the plumes, which are observed to be propagating to larger distances as recorded from multiple AIA channels. These PDs can be explained in terms of slow magnetoacoustic waves.

The global build-up to intrinsic edge localized mode bursts seen in divertor full flux loops in JET

A global signature of the build-up to an intrinsic edge localized mode (ELM) is found in the temporal analytic phase of signals measured in full flux azimuthal loops in the divertor region of JET. Toroidally integrating, full flux loop signals provide a global measurement proportional to the voltage induced by changes in poloidal magnetic flux; they are electromagnetically induced by the dynamics of spatially integrated current density. We perform direct time-domain analysis of the high time-resolution full flux loop signals VLD2 and VLD3. We analyze plasmas where a steady H-mode is sustained over several seconds during which all the observed ELMs are intrinsic; there is no deliberate intent to pace the ELMing process by external means. ELM occurrence times are determined from the Be II emission at the divertor. We previously [Chapman et al., Phys. Plasmas 21, 062302 (2014); Chapman et al., in 41st EPS Conference on Plasma Physics, Europhysics Conference Abstracts (European Physical Society, 2014), Vol. 38F, ISBN 2-914771-90-8] found that the occurrence times of intrinsic ELMs correlate with specific temporal analytic phases of the VLD2 and VLD3 signals. Here, we investigate how the VLD2 and VLD3 temporal analytic phases vary with time in advance of the ELM occurrence time. We identify a build-up to the ELM in which the VLD2 and VLD3 signals progressively align to the temporal analytic phase at which ELMs preferentially occur, on a ∼2−5ms timescale. At the same time, the VLD2 and VLD3 signals become temporally phase synchronized with each other, consistent with the emergence of coherent global dynamics in the integrated current density. In a plasma that remains close to a global magnetic equilibrium, this can reflect bulk displacement or motion of the plasma. This build-up signature to an intrinsic ELM can be extracted from a time interval of data that does not extend beyond the ELM occurrence time, so that these full flux loop signals could assist in ELM prediction or mitigation.

QUASI-PERIODIC OSCILLATION OF A CORONAL BRIGHT POINT

Coronal bright points (BPs) are small-scale luminous features seen in the solar corona. Quasi-periodic brightenings are frequently observed in the BPs and are generally linked with underlying magnetic flux changes. We study the dynamics of a BP seen in the coronal hole using the Atmospheric Imaging Assembly images, the Helioseismic and Magnetic Imager magnetogram on board the Solar Dynamics Observatory, and spectroscopic data from the newly launched Interface Region Imaging Spectrograph (IRIS). The detailed analysis shows that the BP evolves throughout our observing period along with changes in underlying photospheric magnetic flux and shows periodic brightenings in different EUV and far-UV images. With the highest possible spectral and spatial resolution of IRIS, we attempted to identify the sources of these oscillations. IRIS sit-and-stare observation provided a unique opportunity to study the time evolution of one footpoint of the BP as the slit position crossed it. We noticed enhanced line profile asymmetry, enhanced line width, intensity enhancements, and large deviation from the average Doppler shift in the line profiles at specific instances, which indicate the presence of sudden flows along the line-of-sight direction. We propose that transition region explosive events originating from small-scale reconnections and the reconnection outflows are affecting the line profiles. The correlation between all these parameters is consistent with the repetitive reconnection scenario and could explain the quasi-periodic nature of the brightening.

Analysis of a High-Tc Superconducting Power Converting System

This paper presents the analysis of a high-Tc superconducting (HTS) power converting system, as well as its operational characteristics. The converting system can be used to charge and discharge a magnet made of series-connected pancake coils. The HTS converting system consists of two heaters, a primary copper winding, a secondary HTS winding, a series-connected HTS pancake coil, an iron core and a conventional copper load. In the experiments, the charging and discharging periods were 7.5 and 2 s, respectively. A partial region of the superconducting tape in a secondary HTS winding is switched to a normal region by a buried heating coil. To measure the converting-current with respect to the magnet flux changes, a hall sensor was installed at the center of the pancake coil. In this experiment, the charging-current and discharging-energy reached about 51.7 A and 36.8 J, respectively. The experimental results have been compared with theoretical predictions by using the finite difference method.

Micromachined Energy-Harvester Stack With Enhanced Electromagnetic Induction Through Vertical Integration of Magnets

This paper presents a stacked microfabricated power generator that vertically integrates multiple magnets on silicon wafers in a batch process to enhance electromagnetic induction multiple times. The power output is increased by increasing the magnetic flux change for each power-generator unit in the stack, in addition to the increase due to increased number of units. A stack consisting of two arrays of four power-generator units is fabricated and characterized. Wax-bonded Nd-Fe-B powders are embedded in the silicon wafer and magnetized as an integrated micromagnet, which serves as a proof mass suspended by a parylene diaphragm. Dual-layer coils are isolated by a parylene layer, connected via a hole and fabricated with electroplating copper on the same wafer. Experimental results show an improvement by about a factor of four on the power output from the same coils when two power-generator arrays are stacked vertically. In particular, an array of four microfabricated power generators occupying a volume of 51 × 11 × 0.4 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> in the stack produces an induced electromotive force of 1.02 mV with 0.55 nW power output when it is vibrated at 400 Hz with vibration amplitude of 10 μm.

Controlling the magnetic susceptibility in an artificial elliptical quantum ring by magnetic flux and external Rashba effect

Magnetic susceptibility is investigated in a man-made elliptical quantum ring in the presence of Rashba spin-orbit interactions and the magnetic flux. It is shown that magnetic susceptibility as a function of magnetic flux changes between negative and positive signs periodically. The periodicity of the Aharonov-Bohm oscillations depends on the geometry of the region where magnetic field is applied, the eccentricity, and number of sites in each chain ring (the elliptical ring is composed of chain rings). The magnetic susceptibility sign can be reversed by tuning the Rashba spin-orbit strength as well. Both the magnetic susceptibility strength and sign can be controlled via external spin-orbit interactions, which can be exploited in spintronics and nanoelectronics.

Free vibration of wavy single-walled fluid-conveying carbon nanotubes in multi-physics fields

Fluid-conveying carbon nanotubes (CNTs) have attracted much attention and they are used in nano-electromechanical systems (NEMS). In this study, we investigate the free vibration of embedded single-walled fluid-conveying carbon nanotubes in magnetic and temperature fields. The CNTs are modeled as wavy Timoshenko beams. Based on the nonlocal beam theory, the governing equations of motion are derived using Hamilton’s principle. These equations are solved using the Galerkin approach, thereby obtaining a set of ordinary differential equations from the partial differential equations of motion. Numerical examples are analyzed to determine the differences between the proposed model and some previously reported models, as well as the effects of the nonlocal parameter, the fluid velocity and density, the temperature and magnetic field flux change, and the surrounding elastic medium on the dynamic behavior of wavy CNTs. The numerical results validate the proposed analytical model, thereby allowing us to conclude that this method may facilitate the application of fluid-conveying CNTs as NEMS devices.

Influence of the closing rotor slots on the additional losses in the induction motor

Purpose – The purpose of this paper is to present the distribution of the magnetic field and additional losses analysis of the induction motors (IM) with opened and closed rotor slots. Design/methodology/approach – 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 additional losses in each element are evaluated at different frequencies. Findings – An approximate analytical formulation is derived for rapid losses computation confirmed by the results of field-circuit method. For high-voltage motors due to the size ratios of the core and relatively deep stator and rotor slots major role in causing loss of higher harmonics play a fundamental slot harmonics. Higher harmonics order bigger than 100 cause only small part of total higher harmonics core losses. Closed rotor slots construction influenced significantly on no-load losses mainly due to reduction of losses at slot upper part. For nominal load condition that influence is not so strong according to the saturation of slot tips by rotor leakage flux. Nevertheless, core losses at load are several times higher as at no-load. Research limitations/implications – In future research authors will take into account motors feed from PWM inverter, working in the frequency range up to 400 Hz. Practical implications – The results of investigation will be used in more detailed design of IMs especially for motors with closed rotor slots. Originality/value – The methods presented in the paper was not used before. Also results of additional losses in the motor core calculation, especially according motors with closed slots at no load and load conditions are new.

A guided wave sensor based on the inverse magnetostrictive effect for distinguishing symmetric from asymmetric features in pipes.

The magnetostrictive guided wave sensor with a single induced winding cannot distinguish axially symmetric from non-axially symmetric features in a pipe, because it is impossible for the sensor to detect the non-axially symmetric mode waves. When we study the effect of the change of the magnetic field in the air zone for receiving the longitudinal guided wave mode, we find that the change of the magnetic flux in the air zone is almost equivalent to the change of the flux in the pipe wall, but in opposite directions. Based on this phenomenon, we present a sensor that can detect the flexural-mode waves in pipes based on the inverse magnetostrictive effect. The sensor is composed of several coils that are arranged evenly on the outside of pipes. The coils induce a change in magnetic flux in the air to detect the flexural-mode waves. The waves can be determined by adding a phase delay to the induced signals. The symmetric and asymmetric features of a pipe can be distinguished using the sensor. A prototype sensor that can detect F(1,3) and F(2,3) mode waves is presented. The function of the sensor is verified by experiments.

PHYSIC BASIS OF ELECTROMAGNETIC INDUCTION LOW

The statement on the macro level of EMF dependence on change in magnetic flux in time wrong reflects the physical phenomenon of electromagnetic induction low by Faraday, because EMF can be inducted if the magnetic flux of the circuit does not change. Changing magnetic flux of the circuit when the electromotive force arises is only a result of crossing the magnetic field lines by conductor and is an exception, which applies only to certain classes of electric machines.

On a Technique to Relate EMF &amp;amp; Rate of Change of Magnetic Flux

Faradays law of Induction is the principle of generating electricity in Hydro, Thermal, Wind and Nuclear power stations. In this paper we present a method to study the relationship between induced electromagnetic force (EMF) and the rate of change of Magnetic field and hence to verify this principle. This method involves the rotation of a magnet fixed to a rotor at different angular speeds and to find the EMF induced in the copper coil kept close to the rotor. The data collected is plotted in MATLAB. The results show that Induced EMF is directly proportional to the rate change of Magnetic flux with a correlation coefficient of 0.98.

On a Technique to Relate EMF &amp;amp; Rate of Change of Magnetic Flux

Faradays law of Induction is the principle of generating electricity in Hydro, Thermal, Wind and Nuclear power stations. In this paper we present a method to study the relationship between induced electromagnetic force (EMF) and the rate of change of Magnetic field and hence to verify this principle. This method involves the rotation of a magnet fixed to a rotor at different angular speeds and to find the EMF induced in the copper coil kept close to the rotor. The data collected is plotted in MATLAB. The results show that Induced EMF is directly proportional to the rate change of Magnetic flux with a correlation coefficient of 0.98.

Construction, Measurement, Shimming, and Performance of the NIST-4 Magnet System

The magnet system is one of the key elements of a watt balance. For the new watt balance currently under construction at the National Institute of Standards and Technology, a permanent magnet system was chosen. We describe the detailed construction of the magnet system, first measurements of the field profile, and shimming techniques that were used to achieve a flat field profile. The relative change of the radial magnetic flux density is less than $10^{-4}$ over a range of 5 cm. We further characterize the most important aspects of the magnet and give order of magnitude estimates for several systematic effects that originate from the magnet system.

The solar cycle dependence of the weak internetwork flux

Abstract We examine data from the Hinode Observing Program 79 (the “HOP 79” irradiance program) as observed using the Hinode Solar Optical Telescope Spectro-Polarimeter for systematic changes in the weakest observable magnetic flux during the period 2008–2013. At moderate latitudes we find no evidence for systematic changes as a function of time and solar latitude in either the unsigned line-of-sight flux or in the measures of the transverse flux. However, in the polar regions, changes are apparent in the measure of signed magnetic flux corresponding to reversal of the polarity of the poles, changes that persist even for the weakest observed flux. Also evident in measures of the weakest signed flux are preferences for positive (negative) polarity at mid-north (mid-south) latitudes (20°–60°). Center-limb variations in various measures of the weak flux appear to be independent of the solar cycle. The results are consistent with the operation of a small-scale solar dynamo operating within and just below the solar photosphere, but the measures of the weakest signed flux still contain small signatures of the global solar cycle.