Single Magnetic Element Research Articles

Very high step‐down coupled inductor two‐phase buck converter with single magnetic element and inherent clamp voltage capability

AbstractThis paper proposed a new two‐phase high step‐down DC–DC converter is proposed. This converter is derived from the two‐phase series‐capacitor converter. The proposed converter replaces the series capacitor with a new structure that integrates Valley‐Fill circuit and coupled‐inductors concepts. This replacement can improve the voltage gain of the converter as well as a considerable reduction of diodes voltage stress. The proposed structure implements a dual‐phase buck using a single magnetic element. Also, the proposed structure inherently limits the voltage spikes due to the leakage inductance of coupled inductors without any additional clamp circuit. The proposed converter is analyzed, and design guidelines are provided. A 300–24 V prototype converter is implemented to justify the validity of circuit operation and the theoretical analysis.

Unusual ferrimagnetism in CaFe2O4

Incomplete cancellation of collinear antiparallel spins gives rise to ferrimagnetism. Even if the oppositely polarized spins are owing to the equal number of a single magnetic element having the same valence state, in principle, a ferrimagnetic state can still arise from the crystallographic inequivalence of the host ions. However, experimental identification of such a state as ``ferrimagnetic'' is not straightforward because of the often tiny magnitude expected for $M$ and the requirement for a sophisticated technique to differentiate similar magnetic sites. We report a synchrotron-based resonant x-ray investigation at the Fe ${L}_{2,3}$ edges on an epitaxial film of $\mathrm{Ca}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$, which exhibits two magnetic phases with similar energies. We find that while one phase of $\mathrm{Ca}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$ is antiferromagnetic, the other one is ferrimagnetic with an antiparallel arrangement of an equal number of spins between two distinct crystallographic sites with very similar local coordination environments. Our results further indicate two distinct origins of an overall minute $M$; one is intrinsic, from distinct ${\mathrm{Fe}}^{3+}$ sites, and the other one is extrinsic, arising from defective ${\mathrm{Fe}}^{2+}$ likely forming weakly coupled ferrimagnetic clusters. These two origins are uncorrelated and have very different coercive fields. Hence, this work provides a direct experimental demonstration of ferrimagnetism solely due to crystallographic inequivalence of the ${\mathrm{Fe}}^{3+}$ as the origin of the weak $M$ of $\mathrm{Ca}{\mathrm{Fe}}_{2}{\mathrm{O}}_{4}$.

Miniaturization of worm-type soft robot actuated by magnetic field

Recently, many studies on bio-mimic soft robots have been reported. Among living organisms, the locomotion of soft-bodied creatures, such as snails, worms and nematodes, have been actively studied. These soft creatures locomote by deforming the muscles of the whole body into waveforms and propagating the waves of the deformation. This locomotion of soft creatures could be applicable to develop a worm-type soft robot, which can move in drain pipes and even in a human body. In this study, we developed worm-like robots that could generate wavy motion under a rotating magnetic field using silicone and magnetic rubber, and investigated their movement characteristics. In addition, based on a deformation experiment of a silicone cantilever with a single magnetic element inside made of the same material as a worm-like robot, we investigated the effect of the size of the worm robot for further miniaturization.

High Coercivity and Magnetization in WSe2 by Codoping Co and Nb.

Introducing ferromagnetism in transition metal dichalcogenides has attracted lots of attention due to the possible applications in spintronics devices. Generally, single magnetic element doping is used to introduce magnetism. However, mostly, weak ferromagnetism is observed. In this work, codoping of two kinds of transition metals (Nb and Co) into WSe2 is used to study its magnetic properties. In detail, single crystal WSe2 is codoped with 4 at% Co and various concentrations of Nb by employing the physical ion implantation method. Raman, X-ray diffraction and X-ray photoelectron spectroscopy results reveal the effective substitutional doping of implanted elements (Co and Nb). Magnetic measurements illustrate that both un-doped and 4 at% Co doped WSe2 show weak ferromagnetism whereas magnetization is strongly enhanced when Co and Nb are codoped into WSe2 . The magnetization is comparable with a ferromagnet, which may be attributed to Co, Nb doping and defects. In addition, a large coercivity of ≈1.2 kOe is observed in the 1 at% Nb-4 at% Co codoped WSe2 sample, which may be ascribed to the combined effect of doping-induced stress, defect-dictated pinning and anisotropy of NbSe bond owing to the charge transfer between Nb and Se ions.

Battery Operated Soft Switching Resonant Buck–Boost LED Driver With Single Magnetic Element

A simple buck-boost LED driver suitable for battery operated applications with limited input voltage level is presented in this paper. Soft switching performance is provided for the main switch via a resonant circuit to improve the converter efficiency. The incorporated auxiliary switch also performs under zero voltage switching condition. Both power switches can be driven with a simple gate drive circuit, so, the additional switch does not add any driving complexity. In addition, only one magnetic element is utilized in the proposed LED driver which contributes to circuit simplicity and lower weight and size. Also, all diodes turn off at zero current switching which eliminates the reverse recovery losses and improves efficiency. A laboratory prototype converting 12 V input voltage to 32 V output operating at 26 W output power is implemented and tested to verify the effectiveness of the proposed LED driver.

An AC–DC Isolated MMC-Based Structure Suitable for MV SST Traction Applications

This paper presents the theoretical study and experimental validation of a single-stage bidirectional ac-dc topology for solid-state transformer (SST) applications. This topology is based on the modular multilevel converter (MMC) and employs the concepts of interleaving converters and integrated power stages. A single magnetic element operating at medium frequency is employed to perform galvanic isolation and coupling between the grid-side and load-side converters. The main characteristics of the structure are derived from the aforementioned characteristics, such as passive elements operating with an effective frequency higher than the switching frequency, minimized current ripples at high frequency, as well as reduced volume and weight. Experimental results of the converter are obtained in a small-scale prototype, operating with a switching frequency of 5 kHz, nominal power of 1.5 kW, output voltage of 300 V, and the supply voltage of 165 V at a frequency of 60 Hz. High-power factor of 0.99, low-harmonic distortion of the input current with 3.6%, and efficiency in the 87% were achieved.

Non‐isolated high step‐up three‐port converter with single magnetic element for photovoltaic systems

A new non-isolated high-voltage gain three-port converter for standalone photovoltaic systems is proposed. The magnetic element of this converter is only one coupled inductor. The primary winding of the coupled inductor is shared between battery charger circuit and main converter. Leakage inductance energy of the coupled inductor is either transferred to battery or is regenerated via the passive-clamp circuit. Using switched capacitor and voltage lift techniques, the voltage gain is significantly increased for both low-voltage ports. Single magnetic element, high-voltage gain with reasonable duty cycle, low-voltage stress on the switches, low winding turn ratio of coupled inductor and high efficiency are the merits of this converter. The operation principles and the steady-state analysis are described for the three modes of: single-input single-output, single-input dual-output and dual-input single-output. To verify the theoretical analysis, a laboratory prototype with 28 V input, 48 V battery voltage and 380 V output voltage is implemented and tested.

Multiscale Magnetic Underdense Regions on the Solar Surface: Granular and Mesogranular Scales

The Sun is a non-equilibrium dissipative system subjected to an energy flow which originates in its core. Convective overshooting motions create temperature and velocity structures which show a temporal and spatial evolution. As a result, photospheric structures are generally considered to be the direct manifestation of convective plasma motions. The plasma flows on the photosphere govern the motion of single magnetic elements. These elements are arranged in typical patterns which are observed as a variety of multiscale magnetic patterns. High resolution magnetograms of quiet solar surface revealed the presence of magnetic underdense regions in the solar photosphere, commonly called voids, which may be considered a signature of the underlying convective structure. The analysis of such patterns paves the way for the investigation of all turbulent convective scales from granular to global. In order to address the question of magnetic structures driven by turbulent convection at granular and mesogranular scales we used a "voids" detection method. The computed voids distribution shows an exponential behavior at scales between 2 and 10 Mm and the absence of features at 5-10 Mm mesogranular scales. The absence of preferred scales of organization in the 2-10 Mm range supports the multiscale nature of flows on the solar surface and the absence of a mesogranular convective scale.

Nanotorsional resonator torque magnetometry

Magnetic torque is used to actuate nano-torsional resonators, which are fabricated by focused-ion-beam milling of permalloy coated silicon nitride membranes. Optical interferometry is used to measure the mechanical response of two torsion modes at resonance, which is proportional to the magnetization vector of the nanomagnetic volume. By varying the bias magnetic field, the magnetic behavior can be measured with excellent sensitivity ($\approx 10^8 \mu_B$) for single magnetic elements.

The effect of tilted edges on the shape anisotropy and stray field coupling of uniformly magnetized rectangular elements

The influence of tilted edges on the magnetostatic properties of uniformly magnetized thin rectangular elements is studied. To calculate the magnetostatic energy, the Poisson equation is solved. The shape of the magnetic element is approximated by horizontally assembled thin cuboids and the solutions of Rhodes and Rowlands [Proc. Leeds Phil. Soc. 6, 191 (1954)] are utilized. A second approach is the straightforward integration of the Poisson equation taking into account the trapezoidal shape of the side faces due to the tilted edges. For an adequate number of cuboids, both methods agree very well. It is found that the shape anisotropy of a single magnetic element with tilted edges is reduced compared to that of an ideal cuboid. For a two element system the shape anisotropy competes with the magnetostatic interaction favoring a magnetization orientation parallel to the connecting line of the elements. If the elements are oriented in-line with their short axes, the easy magnetization axis switches at a critical distance between the elements. This distance increases when the elements have tilted edges.

サブミクロン反平行結合膜のスピン反転挙動

Magnetization reversal of patterned magnetic structures consisting of single and antiferromagnetically (AF) coupled magnetic elements was simulated by Landau-Lifshitz-Gilbert equations. It is considered that AF coupled magnetic elements can make the demagnetization field small. Simulation was carried out for changing saturation magnetization, uniaxial anisotropy, magnetic exchange stiffness constant, interlayer exchange coupling, magnetic layer thickness, nonmagnetic layer thickness and element size. As a result, we found that the switching field of AF coupled magnetic elements became smaller than that of single magnetic elements in submicron elements.

Optimization of the magnetic elements of the multipurpose spectrometer (MPS)

The CEBAF Hall A MPS additional capability is planned to consist of two quadrupole magnets and one dipole room-temperature magnet. The physical characteristics of the single magnetic elements have been investigated with two-dimensional and three-dimensional codes. In the case of 2-D studies, a very powerful optimization procedure implemented on the VF/PE2D code has also been used.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

非晶質Ｇｄ遷移金属薄膜の磁気光学効果及び磁性

Magneto-optic Kerr effect of amorphous (a-)GdFe films has been investigated by separating each magneto-optic contribution of Gd and Fe. Amorphous GdCu and YFe alloy films which consist of a single magnetic element have been prepared and their magnetization and polar Kerr rotation in the wavelength range of 400-700 nm have been measured at liq. N2 temperature. From the Kerr spectra of a-GdCu and a-YFe and their magnetization, the constant K(λ) defined by θK=K(λ), M(T) has been estimated. Using the K(λ) values we have separated each contribution of Gd and Fe to the Kerr rotation of a-GdFe. Comparing the Kerr spectrum of a-GdFe with that calculated from θK= KGd(λ) · MGd(T)+KFe(λ) · MFe(T), the Kerr spectrum of a-GdFe is fairly well explained by superposition of the contribution of Gd and Fe. It is concluded that the contribution of each sublattice is quite dependent on the photon energy in the range of 1.5 to 3 eV. Especially, the contribution of Gd becomes large with increasing photon energy and comparable to that of Fe at λ =400 nm.

Magnetic Storms and Solar Eruptions

I HAVE read Sir Oliver Lodge's letter (NATURE, October 7, p. 425) on the above subject with some surprise. The emission theory which he supports, and which he claims to have originated, regards kathode rays from the sun as the electric carriers, and so is presumably the same as has been actively advocated by Prof. Kr. Birkeland for a number of years. He seems, however, to be unaware of the existence of Birkeland's volumes1 on the subject, and of the numerous numerical calculations therein contained. He also makes no reference to the important mathematical work of Prof. Störmer, which cannot, I think, be disregarded by anyone whose theory postulates the introduction of charged particles from without into the earth's magnetic field. The general idea that magnetic storms are due to some action arising in the sun goes back to at least the time of Broun and Balfour Stewart, and different forms of the emission theory have naturally presented themselves to various minds independently, as Röntgen, kathode, and other rays came successively under our ken. It is when we come to details that real troubles arise. Most people, I take it, have little difficulty in believing in a general way that the changes of declination experienced at a single magnetic observatory, say Kew, during a magnetic storm can be accounted for by a stream of electrons in the magnetic meridian, provided it is possible for the direction and intensity of the stream to be altered at frequent intervals. One doubts this just as little as that the motion of the magnet of the declination magnetograph at Kew on September 25 could be reproduced with the aid of a copper wire, a single battery cell, a commutator, and a resistance box. Those who have seen Störmer's calculations and studied Birkeland's volumes will realise, however, that to be regarded as an advance of knowledge at the present day, a theory must afford an explanation, not merely of what is taking place in a single magnetic element at a single station, but of what is taking place in all three elements at a number of stations. Coming, now, to Sir Oliver Lodge's own calculation, it seems based on an inadequate idea of the phenomena of the late storm, derived from a description of one or two of the more striking changes at Kew as recorded in your columns and those of the Times. It is rare for a disturbance to be limited to the declination, i.e. for the disturbing force to be wholly perpendicular to the magnetic meridian. The component in the magnetic meridian is, as a matter of fact, usually the larger. A vertical component is also usually present. A magnetic storm does not usually consist of a disturbing force in a fixed or nearly fixed direction, waxing and waning. Each of the three elements usually exhibits values both above and below the normal, and not infrequently there are many excursions on both sides of the mean. This will, I think, be readily recognised by anyone who consults the reproduction of the Stonyhurst curve of September 25 in your columns and of the Kew curves in the Electrician. After inspecting these curves it will, I think, be recognised that it is quite out of the question to limit the passage of the imaginary solar jet, as Sir Oliver Lodge does, to the fifteen minutes near the end of the storm, when there occurred the prominent declination oscillation to which he has confined his attention. Even whilst this oscillation took place, it was far from representing the total disturbance. Simultaneously with it, but partly overlapping, as is often the case, there was a very large change in progress in the horizontal force. Those looking at the curves will, I think, agree that if there was a jet such as Sir Oliver Lodge supposes, its time of transit took, not fifteen minutes, but at least nine hours. His estimate of the diameter of the cone thus requires multiplication by 36, with a consequent multiplication of the cross-section, if it were circular, by 1296. Large as this may appear, the jet theory requires it to be often exceeded, as the storm of September 25 was an unusually short one. The average duration of the storms in Mr. Maunder's Greenwich list, from 1882 to 1903, was almost exactly thirty hours, so that the cross-section of the average storm-jet would be naturally fully 14,000 times that given by the calculation in your columns. The really crucial thing is that the magnetic disturbances which occur simultaneously at different stations are inter-related. It is in accounting satisfactorily for these inter-relations that Birkeland, who has given years of thought to the subject, encounters his main difficulties.