Use Of Permanent Magnets Research Articles

Using Magnetically Responsive Tea Waste to Remove Lead in Waters under Environmentally Relevant Conditions

We report the use of a simple yet highly effective magnetite-waste tea composite to remove lead(II) (Pb2+) ions from water. Magnetite-waste tea composites were dispersed in four different types of water–deionized (DI), artificial rainwater, artificial groundwater and artificial freshwater–that mimic actual environmental conditions. The water samples had varying initial concentrations (0.16–5.55 ppm) of Pb2+ ions and were mixed with the magnetite-waste tea composite for at least 24 hours to allow adsorption of the Pb2+ ions to reach equilibrium. The magnetite-waste tea composites were stable in all the water samples for at least 3 months and could be easily removed from the aqueous media via the use of permanent magnets. We detected no significant leaching of iron (Fe) ions into the water from the magnetite-waste tea composites. The percentage of Pb adsorbed onto the magnetite-waste tea composite ranged from ∼70% to 100%; the composites were as effective as activated carbon (AC) in removing the Pb2+ ions from water, depending on the initial Pb concentration. Our prepared magnetite-waste tea composites show promise as a green, inexpensive and highly effective sorbent for removal of Pb in water under environmentally realistic conditions.

Electromechanical Energy Scavenging From Current-Carrying Conductors

This paper describes a novel method for scavenging energy for electric power systems sensing applications by the use of permanent magnets that couple to the magnetic field generated by an alternating current flowing through a nearby conductor. The resulting mechanical energy is converted to electrical energy using piezoelectric transduction. This electromechanical AC energy scavenging method is an attractive alternative to coil-based AC energy scavengers in cases where the scavengers cannot encircle the conductor. In such cases, the electromechanical AC energy scavenger has the potential to produce significantly more power than comparable coil-based methods. The components of an electromechanical AC energy scavenger are described in detail, and experimental data from prototypes that are fabricated and tested in our laboratory are shown. The 20 cm3 prototypes generated up to 2.7 mW of power each from 20 A of nearby current. Theoretical power densities of electromechanical AC energy scavengers are compared to the power densities of representative coil-based methods, showing that in some cases the electromechanical AC scavengers can generate an order-of-magnitude more power than coil-based AC scavengers. This paper demonstrates that electromechanical AC energy scavenging is a potential method for powering small size low cost stick-on wireless sensor networks.

ANALYSIS OF RADIAL MAGNETIZED PERMANENT MAGNET BEARING CHARACTERISTICS

The use of permanent magnets as bearings has gained attention of researchers nowadays. The characteristics of forces and moments have to be analysed thoroughly for the proper design of permanent magnet bearings. This paper presents a mathematical model of an axially magnetized permanent magnet bearing (ring magnets) using Coulombian model and a vector approach to estimate the force, moment and stifiness. A MATLAB code is developed for evaluating the parameters for flve degrees of freedom (three translational and two rotational) of the rotor. Furthermore, it is extended to analyse stacked ring magnets with alternate axial polarizations. The proposed model is validated with the available literature. Comparison of force and stifiness results of the presented model with the results of three dimensional (3D) flnite element analysis using ANSYS shows good agreement. Finally, the cross coupled stifiness values in addition to the principal stifiness values are presented for elementary structures and also for stacked structures with three ring permanent magnets.

Dipolar openable Halbach magnet design for High-Gradient Magnetic Filtration

High-Gradient Magnetic Filtration (HGMF) uses heavy electromagnets or c-shaped type permanent magnets in order to generate a magnetic field. When using electromagnets, permanent operation only is possible if an effective cooling system (e.g. water, air) is applied. The operation costs are high due to the electric power consumption. In order to reduce operation costs the use of permanent magnets thus is very advantageous. Most permanent magnet systems that are currently used for HGMF are of the c-shaped type equipped with pole caps and iron yoke which makes them big and heavy. In terms of magnet weight versus magnetic flux density, Halbach type permanent magnets are much more efficient. The present work deals with a dipolar Halbach magnet, called Mandhala (Magnetic Arrangement for Novel Discrete Halbach Layout) which consists of rings from identical magnet blocks that are stacked on top of each other and can be split at optimal angles. We developed a formula which allows to calculate the magnetic flux density along the bore axis for a series of equidistant stacked rings. An optimization program using the genetic algorithm (ga) of MATLAB supports the design and up-scale of the Halbach magnet for HGMF applications as it minimizes the magnet material amount for the user fixed minimum constraints of magnetic flux density and open area for filter introduction. The Halbach magnet that was constructed in this study generates a flux density of 0.37T in the center and offers a region of 160mm within the length of the bore axis in which the magnetic flux density does not fall below 0.29T. This field is sufficiently strong to separate submicron magnetic particles with high efficiency. The built Halbach magnet is more cost-effective, more compact and lighter than c-shaped permanent magnets.

The use of permanent magnets to reduce elasmobranch encounter with a simulated beach net. 2. The great white shark (Carcharodon carcharias)

Beach nets are preventative devices that are utilized to minimize the potential interaction between a beachgoer and a predatory shark. One species, the great white shark (Carcharodon carcharias), the focal species for the present study and a protected species in South African waters, is often killed in beach nets within the KwaZulu-Natal (KZN) region. To address the issue of C. carcharias capture in beach nets and to reduce mortality of this species, two related experiments were carried out: the bait experiment and the magnetic-control barrier experiment. Both experiments were aimed to determine the effect of permanent magnets on C. carcharias. During the bait experiment, a total of twenty C. carcharias interacted with the control and magnetic apparatuses. The results indicate that avoidance and feeding behaviors were significantly associated with treatment type, suggesting that permanent magnets had C. carcharias deterrent capabilities. In addition, it was demonstrated that the likelihood of an avoidance behavior on the magnet-associated baits was not significantly correlated with water visibility or conspecific density. For the second experiment, results from stage I of the magnetic-control barrier experiment indicate that behavior was not associated with treatment zone; however, stage II indicated that behavior was significantly associated with treatment type. Results from the magnetic-control barrier experiment clearly demonstrate that although a visual barrier, such as the procedural control barrier, may be sufficient to deter C. carcharias from an area, the addition of permanent magnets provide additional successful deterrence of C. carcharias. This study demonstrates that C. carcharias are sensitive to strong permanent magnetic fields; therefore a large-scale experiment with a substantially greater sample size is warranted to investigate the potential of a non-invasive magnetic barrier to replace detrimental beach nets in KwaZulu-Natal, South Africa.

Design of a Sustainable Wind Generator System Using Redundant Materials

This paper presents the design of a sustainable wind generator system using redundant materials. The topology makes use of permanent magnets (PMs) from discarded computer hard disk drives. The challenges associated with these magnets are discussed in detail. An axial-flux machine topology is developed, which ensures balanced voltage production and eliminates the large proportion of coil interconnecting leads associated with direct-drive wind generators which operate at low speed and have many poles. The performance of the machine is first predicted using classical machine theory. Detailed 2-D and 3-D numerical analyses of the machine topology are then presented, and a sensitivity analysis is conducted with the help of the numerical analysis, in which the influence of the PM dimensions on the performance of the machine is investigated. Finally, the analytical and numerical results are verified using experimental results.

Performance Comparison Between Surface-Mounted and Interior PM Motor Drives for Electric Vehicle Application

Electric vehicles make use of permanent-magnet (PM) synchronous traction motors for their high torque density and efficiency. A comparison between interior PM and surface-mounted PM (SPM) motors is carried out, in terms of performance at given inverter ratings. The results of the analysis, based on a simplified analytical model and confirmed by finite element (FE) analysis, show that the two motors have similar rated power but that the SPM motor has barely no overload capability, independently of the available inverter current. Moreover, the loss behavior of the two motors is rather different in the various operating ranges with the SPM one better at low speed due to short end connections but penalized at high speed by the need of a significant deexcitation current. The analysis is validated through FE simulation of two actual motor designs.

Direct-Drive Contactless Wind Generator with Concentrated Winding

A clear trend has emerged in the field of wind power industry concerning the creation of low-, medium-, and even high-power direct-drive wind turbines without the use of gearboxes. Such generators are usually multipolar and mostly excited from permanent magnets. In the low-speed performance, multipolarity means a higher specific torque and reliability as well as lower operating costs, which in the case of high-speed generators is hindered by gearboxes. Multipolarity with a high specific torque can be achieved mainly through the use of permanent magnets of high-energy materials (such as NdFeB) and through design solutions for the armature winding. The authors compare two most common types of wind generator's armature windings: the distributed one, which contains a coil embracing several teeth, and the concentrated armature winding - with one coil for one stator tooth. The comparison (along with the experience in developing the wind turbines) shows that the con-centrated winding version has a number of advantages, the main of them being the multipolarity. This means that the generator with a concentrated winding can be more acceptable for the direct-drive wind turbines, is easier to make and simpler to operate. Another very important advantage of concentrated windings shown in this work

ANALYSIS OF AXIALLY MAGNETIZED PERMANENT MAGNET BEARING CHARACTERISTICS

The use of permanent magnets as bearings has gained attention of researchers nowadays. The characteristics of forces and moments have to be analysed thoroughly for the proper design of permanent magnet bearings. This paper presents a mathematical model of an axially magnetized permanent magnet bearing (ring magnets) using Coulombian model and a vector approach to estimate the force, moment and stifiness. A MATLAB code is developed for evaluating the parameters for flve degrees of freedom (three translational and two rotational) of the rotor. Furthermore, it is extended to analyse stacked ring magnets with alternate axial polarizations. The proposed model is validated with the available literature. Comparison of force and stifiness results of the presented model with the results of three dimensional (3D) flnite element analysis using ANSYS shows good agreement. Finally, the cross coupled stifiness values in addition to the principal stifiness values are presented for elementary structures and also for stacked structures with three ring permanent magnets.

フェライト磁石を用いた高性能PMASynRMの構造と特性

SUMMARY Recently, the use of permanent magnet (PM) motors has risen markedly because of improvements in the performance of rare earth PM motors. However, the use of rare earth materials, which is an important aspect of the high-performance PM motor, should be reduced because of the high cost and unpredictability associated with procuring such materials. The performance of motors that use rare earth materials has reached a very high level, one that will not be easy to match without such materials. In this paper, we propose a structure for a high-power-density PM-assisted synchronous reluctance motor involving the use of a ferrite PM. The structure prevents irreversible demagnetization of the PM even in the presence of heavy flux-weakening excitation or an inverter fault. It is shown that the proposed structure achieves high-power and high-efficiency performance. © 2014 Wiley Periodicals, Inc. Electr Eng Jpn, 187(1): 42–50, 2014; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22362

Activités physiques et dépressions chez des aînés arthritiques: Le cercle vicieux ?

In this study, the structure of magnetic field for a Penning ion source has been designed and constructed with the use of permanent magnets. The ion source has been designed and constructed for a 200 keV electrostatic accelerator. With using CST Studio Suite, the magnetic field profile inside the ion source was simulated and an appropriate magnetic system was designed to improve particle confinement. Designed system consists of two ring magnets with 9 mm distance from each other around the anode. The ion source was constructed and the cylindrical magnet and designed magnetic system were tested on the ion source. The results showed that the ignition voltage for ion source with the designed magnetic system is almost 300 V lower than the ion source with the cylindrical magnet. Better particle confinement causes lower voltage discharge to occur.

Cylindrical Hall thrusters with permanent magnets

The use of permanent magnets instead of electromagnet coils for low power Hall thrusters can offer a significant reduction in both the total electric power consumption and the thruster mass. Two permanent magnet versions of the miniaturized cylindrical Hall thruster (CHT) of different overall dimensions were operated in the power range of 50–300 W. The discharge and plasma plume measurements revealed that the CHT thrusters with permanent magnets and electromagnet coils operate rather differently. In particular, the angular ion current density distribution from the permanent magnet thrusters has an unusual halo shape, with a majority of high energy ions flowing at large angles with respect to the thruster centerline. Differences in the magnetic field topology outside the thruster channel and in the vicinity of the channel exit are likely responsible for the differences in the plume characteristics measured for the CHTs with electromagnets and permanent magnets. It is shown that the presence of the reversing-direction or cusp-type magnetic field configuration inside the thruster channel without a strong axial magnetic field outside the thruster channel does not lead to the halo plasma plume from the CHT.

Targeted magnetic delivery and tracking of cells using a magnetic resonance imaging system

The success of cell therapies depends on the ability to deliver the cells to the site of injury. Targeted magnetic cell delivery is an emergent technique for localised cell transplantation therapy. The use of permanent magnets limits such a treatment to organs close to the body surface or an implanted magnetic source. A possible alternative method for magnetic cell delivery is magnetic resonance targeting (MRT), which uses magnetic field gradients inherent to all magnetic resonance imaging system, to steer ferromagnetic particles to their target region. In this study we have assessed the feasibility of such an approach for cell targeting, using a range of flow rates and different super paramagnetic iron oxide particles in a vascular bifurcation phantom. Using MRT we have demonstrated that 75% of labelled cells could be guided within the vascular bifurcation. Furthermore we have demonstrated the ability to image the labelled cells before and after magnetic targeting, which may enable interactive manipulation and assessment of the distribution of cellular therapy. This is the first demonstration of cellular MRT and these initial findings support the potential value of MRT for improved targeting of intravascular cell therapies.

Potentiality of a novel elastomagnetic attenuator for vibration control

A novel elastomagnetic attenuator was developed and tested. The innovation lies in the use of permanent magnets instead of non-magnetic parts in the standard attenuator devices made of alternating elastomeric and rigid metallic elements. In this way, the standard mechanism of passive energy dissipation is reinforced by the action of magnetic forces which can be non-linear and therefore introduce asymmetric strain dependent forces. The performed experimental tests reveal the advantages and the limits of the new attenuator device in contrasting vibrations of a simple structure. The elastomagnetic attenuator shows good vibration control, in terms of amplitude damping and resonance frequency shift towards higher values, for longitudinal oscillations propagating parallel to the main magnetic forces axis and transmitted from the outside through the base of the structure to be protected.

Optical micro-endoscopes for 3D in-vivo imaging

Optical coherence tomography (OCT) is a medical optical imaging technique that can achieve high-resolution 3D images (1 15 m)1 by detecting infrared light scattered by body tissue. It has an imaging depth range of about 3mm in highly-scattered tissue and has already been widely used for external imaging, e.g., for eye diseases and skin cancer diagnosis. It would be useful to apply OCT to internal imaging, since about 85% of all cancers originate from the surface layers of internal organs. As these layers are within its imaging depth range, OCT can detect cancer at an early stage as well as precisely determine tumor margins. However, it is very challenging to apply this technique to internal organs because of stringent size and imaging time constraints. One promising approach is to use microelectromechanical systems (MEMS) scanning micromirrors. Several research groups have demonstrated actuation mechanisms to generate rotational scanning for micromirrors for endoscopic OCT. Among them, electrostatic micromirrors can be very fast and consume low power, but the angular scan range is limited and the required driving voltage is too high ( 100V) to be safe for patients. Electromagnetic micromirrors have also been used for OCT probes, but the assembly process is complicated and the potential electromagnetic interference caused by the use of permanent magnets is another concern. Another problem these mirrors share is that they all have a small fill factor (the ratio of the mirror area to the device area). For a given resolution, the required mirror area is fixed. Thus, a small fill factor leads to a large device, which in turn increases the imaging probe size. Electrothermal mirrors, on the other hand, can achieve a large scan range at low drive voltage, but most of them have large initial tilt angles and significant shift of rotation centers, causing serious optical alignment and coupling problems. Figure 1. Scanning electron micrograph of an electrothermal MEMS mirror. Chip size: 2mm 2mm.

A giant magnetostrictive actuator based on use of permanent magnet

The giant magnetostrictive actuator has some unique performances, such as precision position resolution, several kilonewtons of force output, fast frequency response, etc., so it is suitable for the field of ultraprecision measurement and ultraprecision machining. Due to the effect of temperature, the displacement of traditional giant magnetostrictive actuator based on the use of electromagnetism transforming must present nonlinearity. For avoiding this problem, a kind of giant magnetostrictive actuator based on the use of permanent magnet is present in this paper. The driving magnetic field generated by permanent magnetic field can avoid skin effect and eddy current caused by electromagnetism transforming mode for giant magnetostrictive actuator and the performances of actuator are better than that based on electromagnetism transforming. The structure and principle about this driving mode are described in this paper and the value and uniformity of magnetic field affected by some key parameters are mainly discussed in this paper. At last, through several experiments of displacement and creep, it is verified that the driving mode of actuator based on use of permanent magnet is advanced.

Advances in Novel Plasma Devices Based on the Plasma Lens

We review some new results in the development of novel cylindrical plasma devices based on the electrostatic plasma lens configuration and the concepts of electron magnetic insulation and magnetic field line equipotentialization. The plasma lens configuration of crossed electric and magnetic fields provides an attractive method for establishing a stable plasma discharge at low pressure. Use of the plasma lens configuration in this way has been explored, and a number of easily maintained low-cost plasma devices for ion treatment and deposition of exotic coatings have been developed. These devices make use of permanent magnets and possess considerable flexibility with respect to spatial configuration. They can be operated as a stand-alone tool for ion treatment of substrates, or as part of an integrated processing system together with cylindrical magnetron sputtering, for coating and deposition. Here, we describe the operation and features of some cylindrical plasma devices based on the plasma lens configuration, the results of theoretical investigations of the plasma discharge characteristics, and experimental investigations of the physical mechanisms determining optimal operating conditions for these devices.

Permanent-magnet helicon sources and arrays: A new type of rf plasma

Helicon discharges are known for their ability to produce high densities of partially ionized plasma, their efficiency arising from an unusual mechanism of rf coupling. However, the requirement of a dc magnetic field has prevented their wide acceptance in industry. The use of permanent magnets greatly simplifies helicon sources, and arrays of small sources extend the use of helicons to the processing of large substrates. An eight-tube array was designed and constructed, and its density uniformity measured in a 53×165 cm2 chamber. Three innovations involved (a) the remote field of ring magnets, (b) a low-field density peak, and (c) rf power distribution. High-density plasmas uniform over large areas requires compatibility in all three areas.

Working principle of an electromagnetic wiping system

In galvanizing lines, the gas knife wiping device works well for controlling the zinc coating thickness up to 2 to 3\,m/s strip velocities. But for higher velocities, a strong liquid zinc splash risk forbids the gas pressure increase, which would be necessary to keep the same thickness control efficiency of the knives. That is why a complementary electromagnetic wiping system, whose purpose is to pre-wipe the liquid zinc before the gas knives take over, is presented here. After mentioning different kinds of AC and DC possible electromagnetic solutions, a DC field electromagnetic brake (EMB) system based on the use of permanent magnets is selected for a future experimental implementation. In order to better understand the electromagnetic and fluid mechanics phenomena, an analytical model and then different numerical models are presented here. These models show an interesting wiping effect on the liquid zinc, which seems promising for a future experimental pilot design.

Double dipolar halbach array for rheological measurements on magnetic fluids at variable magnetic flux density B

A new experimental setup for measuring rheological properties of magnetic fluids at variable magnetic flux density B with increased homogeneity is described. The proposed setup is mounted on a commercial strain-controlled ARES rotational rheometer. The magnetic flux is generated via two concentric Halbach cylindrical arrays made from permanent NdFeB magnets. The use of permanent magnets overcomes some of the disadvantages of electromagnets (e.g., excessive heating of the coils, formation of large radial stray fields, cost of electricity, cooling, etc). The performance of the new setup is tested for a magnetorheological fluid in both steady and oscillatory shear regimes.