Dimensional Magnetic Field Research Articles

Changes in the Magnetic Fields of Star-Shaped JIS-SKS93 Plates Embedded in Clear Acrylic Cold Mounting Resin under Tensile Stress

Fatigue failure of machine components occurs when cracks form in the stress concentration area and propagate under continued loading during component work. In order to understand the relation between the phenomena of stress concentration and crack propagation, non-destructive evaluation methods using in-situ measurements in the stress concentration areas are necessary. In the present work, a scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor was developed and the three dimensional magnetic fields were observed at room temperature in air. The effect of stress on the changes in the magnetic field in steel components is reported. A steel specimen (JIS SKS93) embedded in acrylic resin were strained at different loads and the magnetic field before and after straining were observed. The obtained magnetic images clearly corresponded with the shape of the steel plate. It was possible to measure the changes in the magnetic field of the steel sample after straining under tensile loading, by neutralizing the initial magnetic field of the specimens prior to testing.

Changes in the Magnetic Fields of Star-Shaped JIS-SKS93 Plates Embedded in Clear Acrylic Cold Mounting Resin under Tensile Stress

Fatigue failure of machine components occurs when cracks form in the stress concentration area and propagate under continued loading during component work. In order to understand the relation between the phenomena of stress concentration and crack propagation, non-destructive evaluation methods using in-situ measurements in the stress concentration areas are necessary. In the present work, a scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor was developed and the three dimensional magnetic fields were observed at room temperature in air. The effect of stress on the changes in the magnetic field in steel components is reported. A steel specimen (JIS SKS93) embedded in acrylic resin were strained at different loads and the magnetic field before and after straining were observed. The obtained magnetic images clearly corresponded with the shape of the steel plate. It was possible to measure the changes in the magnetic field of the steel sample after straining under tensile loading, by neutralizing the initial magnetic field of the specimens prior to testing.

On Ohmic heating in the Earth’s core II: Poloidal magnetic fields obeying Taylor’s constraint

The extremely small Ekman and magnetic Rossby numbers in the Earth’s core make the magnetostrophic limit an attractive approximation to the core’s dynamics. This limit leads to the need for the internal magnetic field to satisfy Taylor’s constraint, associated with the vanishing of the azimuthal component of Lorentz torques averaged over every cylinder coaxial with the rotation axis. A special class of three dimensional poloidal interior magnetic fields is chosen that satisfies Taylor’s constraint identically on every cylinder in a spherical shell exterior to an inner core. This class of fields, which we call small-circle conservative, demonstrates existence of interior fields satisfying Taylor’s constraint, regardless of the morphology of the field on the core surface. These poloidal fields are used to examine the Ohmic dissipation present in the Earth’s core. To address the question of dissipation, we demand that the 3-D core fields agree with recent observations of the core field structure on the core–mantle boundary. We use these poloidal fields to show that the true lower bound on core dissipation must necessarily lie below a value that we calculate. For 2004 we find that this lower bound must lie below 10 10 W, and when nutation constraints are also considered the bound must lie below 2 × 10 10 W. These numbers are small compared to suggested values of the order of a few TeraWatts. A more restrictive bound may be forthcoming when the time-dependency of the field is considered, using a variational data assimilation technique.

Magnetic Microscopic Evaluation of Early-Stage Fatigue in WMZ (Weld Metal Zone) of Low Carbon Steel Plates (JIS, SS400)

Cyclic stresses around welding joint-part affect the strength of mechanical components. In order to understand the fatigue phenomena caused by the cyclic stresses, non-destructive methods that can be related to number of stress cycles are necessary. In the present work, we used a newly developed scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor and observed three dimensional magnetic fields of the specimen before and after four point fatigue testing at room temperature in air. Low carbon steel plates (JIS, SS400) were used in the experiments. It was found that the intensity of the magnet field in a direction perpendicular to the specimen surface was strongly affected by the fatigue testing. This result means that we can evaluate the fatigue in welding-joint area using quantitative magnetic field measurements. Furthermore, it was discovered that the key factor to evaluate the fatigue is the range between “S” and “N” (“peak-to-bottom” values) of the magnetic fields.

Localization of Partial Magnetization around Artificial Slits in Square Bars of Medium Carbon Low Alloy Steel JIS S45C

Fatigue failure of steel occurs when cracks form and grow in the material’s stress concentration area. In order to understand the relation between stress concentration and crack propagation phenomena, non-destructive evaluation methods that can be related to in-situ measurements around the stress concentration area are necessary. In the present work, we developed a scanning Hall probe microscope (SHPM) equipped in a GaAs film sensor and observed three dimensional magnetic fields at room temperature in air. Medium carbon low alloy steels specimens (JIS, S45C) were used in the experiments. Only the area around the artificial slit had been magnetized and the effect of the magnetization area on the artificial slit was observed.

Magnetic scanometric DNA microarray detection of methyl tertiary butyl ether degrading bacteria for environmental monitoring

A magnetoresistive biosensing platform based on a single magnetic tunnel junction (MTJ) scanning probe and DNA microarrays labeled with magnetic particles has been developed to provide an inexpensive, sensitive and reliable detection of DNA. The biosensing platform was demonstrated on a DNA microarray assay for quantifying bacteria capable of degrading methyl tertiary butyl ether (MTBE), where concentrations as low as 10 pM were detectable. Synthetic probe bacterial DNA was immobilized on a microarray glass slide surface, hybridized with the 48 base pair long biotinylated target DNA and subsequently incubated with streptavidin-coated 2.8 μm diameter magnetic particles. The biosensing platform then makes use of a micron-sized MTJ sensor that was raster scanned across a 3 mm by 5 mm glass slide area to capture the stray magnetic field from the tagged DNA and extract two dimensional magnetic field images of the microarray. The magnetic field output is then averaged over each 100 μm diameter DNA array spot to extract the magnetic spot intensity, analogous to the fluorescence spot intensity used in conventional optical scanners. The magnetic scanning result is compared with results from a commercial laser scanner and particle coverage optical counting to demonstrate the dynamic range and linear sensitivity of the biosensing platform as a potentially inexpensive, sensitive and portable alternative for DNA microarray detection for field applications.

Design of multi-DOF electromagnetic actuators using distributed multipole models and image method

Design and control of many electromagnetic actuators involve solving three dimensional (3D) magnetic fields of permanent magnets and/or electromagnets in the presence of magnetic conducting surfaces. This paper extends the distributed multipole (DMP) method, which offers compact but precise analysis for three dimensional magnetic fields in closed form, to account for the effects of magnetic conducting boundaries using the image method on the torque generated by electromagnetic actuators. We validate the proposed method referred to here as DMP-Image method by comparing the calculated torques against results computed by a finite element method (FEM). While two methods agree to within 5% in maximum torque, the DMP-image method takes less than 1% of the FEM computation time. Finally, we demonstrate the DMP-Image method to design a spherical motor in a class of multi-DOF actuators. While developed in the context of the multi-DOF actuators, the modeling methods presented in this paper are applicable to design of other PM-based actuators.

Light storage in a magnetically dressed optical lattice

Differential Stark shift compensation for ground state $^{87}$Rb atoms trapped in an elliptically polarized optical lattice and "magic" magnetic field, was recently proposed and demonstrated experimentally by N. Lundblad {\it et al.}, arXiv:0912.1528 and analyzed theoretically by A. Derevianko, arXiv:0912.3233. Here we demonstrate for the first time enhanced hyperfine coherence times using the magic field technique. We observe coherent light storage with a 0.32 s lifetime in an atomic Rb gas confined in a one dimensional optical lattice and magnetic field.

The Coma cluster magnetic field from Faraday rotation measures

<i>Aims. <i/>The aim of the present work is to constrain the Coma cluster magnetic field strength, its radial profile and power spectrum by comparing Faraday rotation measure (RM) images with numerical simulations of the magnetic field.<i>Methods. <i/>We have analyzed polarization data for seven radio sources in the Coma cluster field observed with the Very Large Array at 3.6, 6 and 20 cm, and derived Faraday rotation measures with kiloparsec scale resolution. Random three dimensional magnetic field models have been simulated for various values of the central intensity <i>B<i/><sub>0<sub/> and radial power-law slope <i>η<i/>, where <i>η<i/> indicates how the field scales with respect to the gas density profile.<i>Results. <i/>We derive the central magnetic field strength, and radial profile values that best reproduce the RM observations. We find that the magnetic field power spectrum is well represented by a Kolmogorov power spectrum with minimum scale ~2 kpc and maximum scale ~34 kpc. The central magnetic field strength and radial slope are constrained to be in the range (<i>B<i/><sub>0<sub/> = 3.9 <i>μ<i/>G; <i>η<i/> = 0.4) and (<i>B<i/><sub>0<sub/> = 5.4 <i>μ<i/>G; <i>η<i/> = 0.7) within 1<i>σ<i/>. The best agreement between observations and simulations is achieved for <i>B<i/><sub>0<sub/> = 4.7 <i>μ<i/>G; <i>η<i/> = 0.5. Values of <i>B<i/><sub>0<sub/> <i>><i/> 7 <i>μ<i/>G and <i><<i/>3 <i>μ<i/>G as well as <i>η<i/> <i><<i/> 0.2 and <i>η<i/> <i>><i/> 1.0 are incompatible with RM data at 99% confidence level.

Detection of back-side pit on a ferrous plate by magnetic flux leakage method with analyzing magnetic field vector

We have developed a magnetic flux leakage (MFL) system using magnetic resistive (MR) sensors for detecting two dimensional magnetic field components, and an induction coil that generates low magnetic field strengths and extremely low frequencies. The signal at each scanned measurement point ( i) was divided by the signal strength M mes, i and phase α i by a lock-in amplifier. Using the strength M mes, i and phase α i , we calculated the imaginary part of the signal using the common phase β. By optimization of the common phase β to the imaginary part, the analyzed scanning data curve was shown to be effective in estimating the size (depth and diameter) of back-side pits on a ferrous plate. Comparing the two dimensional magnetic field components of leakage, the imaginary part of the y-component parallel to the induced magnetic field was found to be suitable for detecting the back-side pits.

Jeans instability in quantum magnetoplasma with resistive effects

The Jeans instability in dense quantum plasmas is investigated in the presence of two dimensional magnetic fields and resistive effects. The resistive effects are shown to introduce instability whether the perturbation is stable or not in the ideal magnetohydrodynamic model. The analytical expressions of the growth rate of Jeans instability are obtained for both the finite and remarkable resistive effects cases. The results are relevant to dense astrophysical objects, e.g., neutron stars and the interior of white dwarfs, as well as low-temperature laboratory plasmas.

Effects of ferromagnetic components on energetic ion confinement in ITER

By using a fully three dimensional magnetic field orbit-following Monte-Carlo code, the energetic ion confinement was investigated for the current conceptual design of the ferromagnetic components in ITER which will be employed for reducing the toroidal magnetic field (TF) ripple. The ferromagnetic insert is effective in the reference standard scenario with Q = 10 (Scenario No. 2) and steady state scenario with Q = 5 (Scenario No. 4) to improve the energetic ion confinement. Over-compensation appears at half of the full toroidal magnetic field and its effect becomes stronger when the quantity of the ferromagnetic insert is increased in order to more reduce the TF ripple at the full toroidal magnetic field. Though the current design is acceptable, whether to increase the ferromagnetic insert to achieve lower TF ripple amplitude at the full field operation depends on how prospected are possibilities of lower field operations. Planned test blanket modules do not induce large loss (<1%) at the full field in Scenario No. 4. At the half field, however, the loss reaches ∼10% for the alpha particles due to localized large TF ripple.

Electromagnetic fields induced by electric current in an infinite plate with an elliptical hole

Analytical solutions to the electromagnetic field in a thin conductive plate with an elliptical hole are derived by means of complex potentials and conformal mapping techniques. The steady-state current field in a thin conductive plate is two dimensional (2D) and is explored by a standard complex variable technique. The current is disturbed around the elliptical hole, and produces a three dimensional magnetic field. In this case, using the complex variable method to solve the real magnetic field can be challenging. The magnetic boundary conditions take different forms for the soft ferromagnetic and the para- or diamagnetic materials under consideration. A simplified analysis taking account of the magnitude of the magnetic permeability of the magnetic material and air surrounding the material is proposed to reduce the magnetic field in a thin plate to 2D calculations. The magnetic field distributions are derived for each material and the equations of the magnetic components at the tip of elliptical hole are presented.

A new view of quiet-Sun topology from Hinode/SOT

With the recent launch of the Hinode satellite our view of the nature and evolution of quiet-Sun regions has been improved. In light of the new high resolution observations, we revisit the study of the quiet Sun's topological nature. Topology is a tool to explain the complexity of the magnetic field, the occurrence of reconnection processes, and the heating of the corona. This Letter aims to give new insights to these different topics. Using a high-resolution Hinode/SOT observation of the line-of-sight magnetic field on the photosphere, we calculate the three dimensional magnetic field in the region above assuming a potential field. From the 3D field, we determine the existence of null points in the magnetic configuration. From this model of a continuous field, we find that the distribution of null points with height is significantly different from that reported in previous studies. In particular, the null points are mainly located above the bottom boundary layer in the photosphere (54%) and in the chromosphere (44%) with only a few null points in the corona (2%). The density of null points (expressed as the ratio of the number of null points to the number of photospheric magnetic fragments) in the solar atmosphere is estimated to be between 3% and 8% depending on the method used to identify the number of magnetic fragments in the observed photosphere. This study reveals that the heating of the corona by magnetic reconnection at coronal null points is unlikely. Our findings do not rule out the heating of the corona at other topological features. We also report the topological complexity of the chromosphere as strongly suggested by recent observations from Hinode/SOT.

Fabrication of a high temperature superconductor micro-superconducting-quantum-interference-device magnetometer for magnetic hysteresis measurements

A high-temperature-superconductor-type micrometer-sized dc-SQUID (SQUID denotes superconducting quantum interference divice) magnetometer with much higher sensitivity than a commercial system has been developed. Several kinds of YBa2Cu3O7−δ micro-SQUIDs were fabricated with photolithography techniques to have a hole of 4×9μm2 and 2-μm-wide grain boundary Josephson junctions. Combined with a three dimensional magnetic field coil system, the voltage modulation was observed for three different field directions.

High temperature superconductor micro-superconducting-quantum-interference-device magnetometer for magnetization measurement of a microscale magnet

We have developed a high temperature superconductor (HTS) micrometer-sized dc superconducting quantum interference device (SQUID) magnetometer for high field and high temperature operation. It was fabricated from YBa2Cu3O7-delta of 92 nm in thickness with photolithography techniques to have a hole of 4x9 microm2 and 2 microm wide grain boundary Josephson junctions. Combined with a three dimensional magnetic field coil system, the modulation patterns of critical current Ic were observed for three different field directions. They were successfully used to measure the magnetic properties of a molecular ferrimagnetic microcrystal (23x17x13 microm3), [Mn2(H2O)2(CH3COO)][W(CN)8]2H2O. The magnetization curve was obtained in magnetic field up to 0.12 T between 30 and 70 K. This is the first to measure the anisotropy of hysteresis curve in the field above 0.1 T with an accuracy of 10(-12) J T(-1) (10(-9) emu) with a HTS micro-SQUID magnetometer.

Linear magnetic field response spin valve with perpendicular anisotropy ferromagnet layer

In this letter, we present a novel concept for a linear magnetoresistance sensor using a spin valve with the free and reference ferromagnetic layers having out of plane and in plane magnetic anisotropies, respectively. The giant magnetoresistance of such a device is measured with the electrical current perpendicular to the film plane resulting in a linear magnetoresistance of up to 2% with an applied field of 1000Oe. This design is highly advantageous, in terms of sensor cost, space usage, and for the fabrication of a three dimensional magnetic field sensor.

Ferritic insertion for reduction of toroidal magnetic field ripple on JT-60U

Ferritic steel tiles (FSTs) have been installed to improve the energetic ion confinement by reducing a toroidal magnetic field ripple. Aiming at cost-effective installation, orbit-following calculations of energetic ions were carried out for a design of the installation of ferritic steel on the JT-60U by using the fully three dimensional magnetic field orbit-following Monte-Carlo (F3D OFMC) code, which had been developed for ferritic insert experiments on the JFT-2M and can treat the complex magnetic field structure produced by ferritic inserts. The installed FSTs add a non-linear magnetic field on magnetic sensors for plasma control and an equilibrium calculation. The code for real-time control has been modified to take into account the magnetic field by the FSTs. The plasma operation was successfully resumed after usual conditioning processes and real-time plasma control was successfully carried out. The heat load measurement indicates the improved confinement of energetic ions. These results are important for practical application of the ferritic steel, which is a leading candidate of a structural material on a DEMO reactor.

Optimum Design of TFLM With Constraints for Weight Reduction Using Characteristic Function

This paper presents optimum design of transverse flux linear motor (TFLM) to reduce the weight of the machine with the constraints of thrust and detent force. Employing penalty functions, each constraint is included in the characteristic function, and the response value is determined by three dimensional magnetic field analyses. Finally, the contribution and effect of the each design variable on the characteristic function is evaluated by the analysis of means (ANOM), and optimum design set is determined. With this procedure, the weight of initially designed TFLM can be reduced 10% with small variation of thrust and detent force

Magnetic Field Measurements, 3D Field Calculation and Heat Measurements of a Prototype Thick Septum Magnet for 3 GeV Rapid Cycling Synchrotron of J-PARC

Septum magnets used in the injection and extraction section of the 3 GeV RCS (rapid cycling synchrotron) of J-PARC (Japan proton accelerator research complex) require a large aperture for low-loss operations of high intensity beam, protection against high radiation, and high durability making unnecessary frequent maintenance after high activation. Therefore, the septum magnets have been designed to work in DC for mechanical stability. Also it works outside the beam vacuum, thus eliminating any trouble due to the leakage of cooling water in the vacuum system. A prototype extraction septum magnet was constructed. Magnetic field in the gap of the yoke and leakage field outside of the magnetic shield were measured with a three dimensional Hall probe. The experimental results were compared with three dimensional magnetic field calculations made by TOSCA. The measurement of the magnetic field in the gap agrees well with a simple 3D model. On the other hand, leakage field of the measurement is larger than that of the model. Because the thickness of the return yoke is not sufficient, the magnetic flux density approaches saturation. After we made a more detailed model, it was confirmed that the many bolt holes which fasten the return yoke narrow the effective cross sectional area, thus reduce the effective permeability, and make the magnetic reluctance and the leakage field larger. This paper also describes the results of heat measurements of the magnet and efficiency of water cooling