Permanent Magnet Assembly Research Articles

Moving magnet linear actuator with self‐holding functionality

Electromagnetic design of a moving magnet frictionless linear actuator with self-holding functionality for mechanical gear shifting in a transmission application is presented. The actuator consists of a tubular magnetic circuit with stationary armature and axially moving rotating permanent magnet assembly with radial magnetisation in the air gap. The armature contains a two-piece magnetic core with a space for a winding. The effects of armature slot opening and magnetic circuit materials on the self-holding force and the acting force are studied in the whole moving range. The designed moving magnet linear actuator improves the performance of the vehicle by enabling shift times below 50 ms with no energy consumption between the shifts.

Electron-Spin-Resonance Dipstick.

Electron spin resonance (ESR) is a powerful analytical technique used for the detection, quantification, and characterization of paramagnetic species ranging from stable organic free radicals and defects in crystals to gaseous oxygen. Traditionally, ESR requires the use of complex instrumentation, including a large magnet and a microwave resonator in which the sample is placed. Here, we present an alternative to the existing approach by inverting the typical measurement topology, namely placing the ESR magnet and resonator inside the sample rather than the other way around. This new development relies on a novel self-contained ESR sensor with a diameter of just 2 mm and length of 3.6 mm, which includes both a small permanent magnet assembly and a tiny (∼1 mm in size) resonator for spin excitation and detection at a frequency of ∼2.6 GHz. The spin sensitivity of the sensor has been measured to be ∼1011 spins/√Hz, and its concentration sensitivity is ∼0.1 mM, using reference samples with a measured volume of just ∼10 nL. Our new approach can be applied for monitoring the partial pressure of oxygen in vitro and in vivo through its paramagnetic interaction with another stable radical, as well as for simple online quantitative inspection of free radicals generated in reaction vessels and electrochemical cells via chemical processes.

Direct chill casting of aluminium alloys under electromagnetic interaction by permanent magnet assembly

Direct chill casting is one of the methods used in industry to obtain good microstructure and properties of aluminium alloys. Nevertheless, for some alloys grain structure is not optimal. In this study, we offer the use of electromagnetic interaction to modify melt convection near the solidification interface. Solidification under various electromagnetic interactions has been widely studied, but usually at low solidification velocity and high thermal gradient. This type of interaction may succeed fragmentation of dendrite arms and transport of solidification nuclei thus leading to improved material structure and properties. Realization of experimental small-scale crystallizer and electromagnetic system has been described in this article.

Monte Carlo evaluation of magnetically focused proton beams for radiosurgery

The purpose of this project is to investigate the advantages in dose distribution and delivery of proton beams focused by a triplet of quadrupole magnets in the context of potential radiosurgery treatments. Monte Carlo simulations were performed using various configurations of three quadrupole magnets located immediately upstream of a water phantom. Magnet parameters were selected to match what can be commercially manufactured as assemblies of rare-earth permanent magnetic materials. Focused unmodulated proton beams with a range of ~10 cm in water were target matched with passive collimated beams (the current beam delivery method for proton radiosurgery) and properties of transverse dose, depth dose and volumetric dose distributions were compared. Magnetically focused beams delivered beam spots of low eccentricity to Bragg peak depth with full widths at the 90% reference dose contour from ~2.5 to 5 mm. When focused initial beam diameters were larger than matching unfocused beams (10 of 11 cases) the focused beams showed 16%–83% larger peak-to-entrance dose ratios and 1.3 to 3.4-fold increases in dose delivery efficiency. Peak-to-entrance and efficiency benefits tended to increase with larger magnet gradients and larger initial diameter focused beams. Finally, it was observed that focusing tended to shift dose in the water phantom volume from the 80%–20% dose range to below 20% of reference dose, compared to unfocused beams. We conclude that focusing proton beams immediately upstream from tissue entry using permanent magnet assemblies can produce beams with larger peak-to-entrance dose ratios and increased dose delivery efficiencies. Such beams could potentially be used in the clinic to irradiate small-field radiosurgical targets with fewer beams, lower entrance dose and shorter treatment times.

Understanding the dynamics of superparamagnetic particles under the influence of high field gradient arrays

The aim of this study was to characterize the behaviour of superparamagnetic particles in magnetic drug targeting (MDT) schemes. A 3-dimensional mathematical model was developed, based on the analytical derivation of the trajectory of a magnetized particle suspended inside a fluid channel carrying laminar flow and in the vicinity of an external source of magnetic force. Semi-analytical expressions to quantify the proportion of captured particles, and their relative accumulation (concentration) as a function of distance along the wall of the channel were also derived. These were expressed in terms of a non-dimensional ratio of the relevant physical and physiological parameters corresponding to a given MDT protocol.The ability of the analytical model to assess magnetic targeting schemes was tested against numerical simulations of particle trajectories. The semi-analytical expressions were found to provide good first-order approximations for the performance of MDT systems in which the magnetic force is relatively constant over a large spatial range.The numerical model was then used to test the suitability of a range of different designs of permanent magnet assemblies for MDT. The results indicated that magnetic arrays that emit a strong magnetic force that varies rapidly over a confined spatial range are the most suitable for concentrating magnetic particles in a localized region. By comparison, commonly used magnet geometries such as button magnets and linear Halbach arrays result in distributions of accumulated particles that are less efficient for delivery.The trajectories predicted by the numerical model were verified experimentally by acoustically focusing magnetic microbeads flowing in a glass capillary channel, and optically tracking their path past a high field gradient Halbach array.

Development of a transportable FT-ICR MS associated with a glow discharge ionization source

A transportable FT-ICR/MS associated with a flowing atmospheric pressure afterglow ionization source has been developed for air monitoring applications with the objective of detecting organic compounds with both a good mass resolution and a good sensitivity.The main features of the apparatus and its operation mode are described. The glow discharge source is operated with helium at atmospheric pressure. Excited helium species react with air and the ionic products formed are sent in the mass spectrometer within a gas pulse. They are intercepted using a hexapole trap before being sent to the ICR cell located in a differentially pumped chamber for mass analysis. The permanent magnet assembly generates an axial field, thus enabling ion transfer from an external source. FT-ICR detection with this configuration is characterized both for internal and external ionization. First results obtained for the detection of several polycyclic aromatic hydrocarbons (naphthalene, acenaphthene and acenaphthylene) are presented showing detection limits in the high ppb range, and a detection time of a few seconds.

Electromagnetically actuated biaxial scanning micromirror fabricated with silicon on glass wafer

In this paper, we present an electromagnetically actuated two-axis scanning micromirror with large aperture and tilting angle for laser pointing applications. The two-axis micromirror with the plate size of 3 mm in diameter was realized using gimbaled single crystal silicon with a single-turn electroplated copper coil, and it was assembled with permanent magnets forming radial magnetic field. The micromirror was fabricated on SiOG (Silicon on Glass) wafer using 4 photolithography masks. The permanent magnet assembly composed of a cylindrical and a ring-type magnet was designed to optimize the radial magnetic field, and thus maximize the torque on the coil. Three different magnet assemblies were applied to the fabricated micromirror in order to verify the design. Horizontal resonance frequency of the fabricated micromirror was measured 1.421 kHz and vertical resonant frequency was 396 Hz. The vertical scan angle was 16.87°, 26.32° and 22.61° with the cylindrical magnet diameter of 2.6, 4.0 and 4.8 mm, respectively, at 60 Hz sinusoidal input of 640 mApp. For horizontal scan, maximum scan angle of 24.45° was obtained at 48 mApp input signal in resonance mode. In addition, the temperature distribution on the micromirror surface was measured with the applied current to the coil.

Improvements of a room-temperature magnetic refrigerator combined with Stirling cycle refrigeration effect

A high pressure hybrid refrigerator that combines the active magnetic refrigeration effect with the Stirling cycle refrigeration effect at room temperature is studied here. In the apparatus, a helium-gas-filled alfa-type Stirling refrigerator uses Gd sheets as the regenerator and the regenerator is put in a magnetic field varying from 0 to 1.4 T, which is provided by a Halbach-type rotary permanent magnet assembly. With an operating pressure of 5.5 MPa and a frequency of 2.5 Hz, a no-load temperature of 273.8 K was reached in 9 minutes, which is lower than that of 277.6 K for pure Stirling cycle. For the hybrid operation, cooling powers of 40.3 W and 56.4 W were achieved over temperature spans of 15 K and 12 K, respectively. For the latter case, the cooling power improves by 28.5% if compared with that exploiting only the Stirling cycle refrigeration effect.

Shimming Halbach magnets utilizing genetic algorithms to profit from material imperfections

In recent years, permanent magnet-based NMR spectrometers have resurfaced as low-cost portable alternatives to superconducting instruments. While the development of these devices as well as clever shimming methods have yielded impressive advancements, scaling the size of these magnets to miniature lengths remains a problem to be addressed. Here we present the results of a study of a discrete shimming scheme for NMR Mandhalas constructed from a set of individual magnet blocks. While our calculations predict a modest reduction in field deviation by a factor of 9.3 in the case of the shimmed ideal Mandhala, a factor of 28 is obtained in the case of the shimmed imperfect Mandhala. This indicates that imperfections of magnet blocks can lead to improved field homogeneity. We also present a new algorithm to improve the homogeneity of a permanent magnet assembly. Strategies for future magnet construction can improve the agreement between simulation and practical implementation by using data from real magnets in these assemblies as the input to such an algorithm to optimize the homogeneity of a given design.

Peculiarities of simulation of magnetic field in electromechanical nodes of magnetic-levitation transport system by the method of secondary sources

In recent years increasingly discusses the prospects of application of high-temperature superconductors (HTS) as the winding current-carrying elements of magnetic systems for various purposes. It seems particularly attractive possibility of such systems at liquid nitrogen temperature. The article describes the prototype of module of the magnetic system which is made on the basis of high-temperature superconducting tapes, designed for the installation and testing on a working model of a static levitation. In the working model levitation of the platform carried by the interaction of the magnetic field of the assembly of permanent magnets mounted on the platform with a field similar to assemblies located in the track structure. Compact HTS module replaces the two assemblies of permanent magnets mounted on the platform. Each block of the module represents HTS racetrack coil with current inputs, power structure, positioning system and bracing which is placed in a cryostat, providing at minimum wall thickness of the required mechanical strength and thermal insulation at liquid nitrogen temperature. The prototype of unified superconducting module successfully passed preliminary tests.

DEVELOPMENT AND TESTING PROTOTYPE OF HTS MODULE FOR THE SYSTEM OF MAGNETIC LEVITATION OF VEHICLE

In recent years increasingly discusses the prospects of application of high-temperature superconductors (HTS) as the winding current-carrying elements of magnetic systems for various purposes. It seems particularly attractive possibility of such systems at liquid nitrogen temperature. The article describes the prototype of module of the magnetic system which is made on the basis of high-temperature superconducting tapes, designed for the installation and testing on a working model of a static levitation. In the working model levitation of the platform carried by the interaction of the magnetic field of the assembly of permanent magnets mounted on the platform with a field similar to assemblies located in the track structure. Compact HTS module replaces the two assemblies of permanent magnets mounted on the platform. Each block of the module represents HTS racetrack coil with current inputs, power structure, positioning system and bracing which is placed in a cryostat, providing at minimum wall thickness of the required mechanical strength and thermal insulation at liquid nitrogen temperature. The prototype of unified superconducting module successfully passed preliminary tests.

Innovative Methods for Automated Assembly and Fixation of Permanent Magnets in Electrical Machines

Over the years, the production of electric machines has spread into different designs, creating complex variations in topologies and structure. Based upon a recently completed research project, the handling, assembly and fixation of permanent magnet components for electrical machines containing internal permanent magnets (IPM) is investigated. An assembly and fixation process is presented both of which are economical in terms of use of adhesives and variant flexibility.The developed solution is based on a SCARA-Robot with an attached device that is capable of both separating and assembling the permanent magnet material. The elimination of an off-site magnet separation and a continuous feed of magnets significantly reduces the cycle time for a single rotor. The flexibility of the SCARA concept ensures its application in a broad field of different rotor sizes.Recent solutions for affixing the IPM material are often based on a complete submersion of magnets into resin material. An alternative approach for adhesive application has been developed and integrated into the assembly process that reduces the overall need for adhesive material by over 80%.

Fractional-Slot Concentrated-Winding Axial-Flux Permanent-Magnet Machine With Tooth-Wound Coils

This paper presents the design, finite-element (FE) analyses and experimental validation of a Kaman-type fractional-slot concentrated-winding axial-flux permanent-magnet machine with tooth-wound coils. In this particular topology, the flux travels axially through the permanent magnets, from one stator to the opposite, so that there is no need for any rotor back iron. Thus, the rotor is an assembly of permanent magnets and a suitably designed holder. In order to guarantee adequate mechanical stiffness, stainless steel has been selected as the holder's material. Different designs of this holder are investigated, with the aim of minimizing the induced losses therein. Both no-load and on-load performances are analyzed with 2-D time-stepped FE simulations, with particular attention devoted to rotor losses. A full-scale prototype is built, together with two of the previously investigated holder structures. Experimental tests confirm the validity of the design and of the FE simulations.

Stabilization of magnet assemblies of permanent magnet sodium flowmeters used in fast breeder reactors

Permanent magnet flow meters (PMFMs) are used to measure the sodium flow in sodium cooled Fast Breeder Reactor Circuits. Prototype fast breeder reactor (PFBR) which is under construction at Kalpakkam is a 500MWe, sodium cooled, pool type reactor. Sodium flow measurement in various loops of the reactor is of prime importance from operational and safety point of view. To measure the flow of electrically conducting liquid sodium, in primary and secondary circuit pipe lines of PFBR, permanent magnet flow meters are used. PMFM is a non-invasive device, which works on the principle of generation of motional EMF by magnetic forces exerted on the charges in a moving conductor. Flowmeters of different pipe sizes ranging from 10mm to 200mm pipe diameter are required for PFBR. Long term performance of the flowmeters mainly depends on stability of permanent magnets used in flowmeters to generate constant magnetic field in stainless steel (SS) pipes. This paper describes the effects of time and temperature on permanent magnet assemblies made of ALNICO-V used in PFBR flowmeters. The stabilization methodology for ALNICO-V permanent magnet assemblies is evolved and established. Loss of magnetic field strength with respect to time and temperatures is determined by experiments and found negligible.

Feasibility study of red blood cell debulking by magnetic field-flow fractionation with step-programmed flow

Emerging applications of rare cell separation and analysis, such as separation of mature red blood cells from hematopoietic cell cultures, require efficient methods of red blood cell (RBC) debulking. We have tested the feasibility of magnetic RBC separation as an alternative to centrifugal separation using an approach based on the mechanism of magnetic field-flow fractionation (MgFFF). A specially designed permanent magnet assembly generated a quadrupole field having a maximum field of 1.68T at the magnet pole tips, zero field at the aperture axis, and a nearly constant radial field gradient of 1.75T/mm (with a negligible angular component) inside a cylindrical aperture of 1.9mm (diameter) and 76mm (length). The cell samples included high-spin hemoglobin RBCs obtained by chemical conversion of hemoglobin to methemoglobin (met RBC) or by exposure to anoxic conditions (deoxy RBC), low-spin hemoglobin obtained by exposure of RBC suspension to ambient air (oxy RBC), and mixtures of deoxy RBC and cells from a KG-1a white blood cell (WBC) line. The observation that met RBCs did not elute from the channel at the lower flow rate of 0.05mL/min applied for 15min but quickly eluted at the subsequent higher flow rate of 2.0mL/min was in agreement with FFF theory. The well-defined experimental conditions (precise field and flow characteristics) and a well-established FFF theory verified by studies with model cell systems provided us with a strong basis for making predictions about potential practical applications of the magnetic RBC separation.

Intensity distribution of strong magnetic fields created by opposing linear Halbach assemblies of permanent magnets

The work is devoted to the geometrical configuration of permanent magnets on the basis of opposing geometrically linear assemblies (e.g. Halbach arrays) for the generation of strong magnetic fields, which have been theoretically modeled and experimentally verified. The implementation of these opposing assemblies using NdFeB magnets of a total weight of 3.75kg provided a value of magnetic induction in the middle of an air gap of a width of 20mm that was higher by 56% in comparison with the simplest possible design. When the air gap width was 3mm, the induction reached a value of 2.16T, which represents an increase of more than 100%. Simultaneously, however, unlike in the simplest possible parallel configuration, opposing Halbach assemblies have shown, in the middle of an air gap, a significant decrease of the magnetic induction values when passing from the middle of the assemblies in the direction parallel to the x-axis.

The “Shim-a-ring” magnet: Configurable static magnetic fields using a ring magnet with a concentric ferromagnetic shim

We introduce a permanent magnet assembly that can be configured to obtain uniform, gradient, or tunable field distribution. The design is composed of a single ring shaped permanent magnet and a concentric ferromagnetic shim. Magnetic field is configured by changing the shape of the air gap inside the ring magnet. Circular cross-section produces up to 0.54 T uniform field, whereas rectangular or triangular cross-sections result in gradient magnetic field distributions. Tunable field from a given ring magnet is obtained by changing the thickness of the ferromagnetic shim or the spacing between the shim and the permanent magnet.

Highly Stable and Finely Tuned Magnetic Fields Generated by Permanent Magnet Assemblies

Permanent magnetic materials are the only magnetic source that can be used to generate magnetic fields without power consumption or maintenance. Such stand-alone magnets are very attractive for many scientific and engineering areas, but they suffer from poor temporal field stability, which arises from the strong sensitivity of the magnetic materials and mechanical support to temperature variation. In this work, we describe a highly efficient method useful to cancel the temperature coefficient of permanent magnet assemblies in a passive and accurate way. It is based on the combination of at least two units made of magnetic materials with different temperature coefficients arranged in such a way that the ratio of the fields generated by each unit matches the ratio of their effective temperature coefficients defined by both the magnetic and mechanical contributions. Although typically available magnetic materials have negative temperature coefficients, the cancellation is achieved by aligning the fields generated by each unit in the opposite direction. We demonstrate the performance of this approach by stabilizing the field generated by a dipolar Halbach magnet, recently proposed to achieve high field homogeneity. Both the field drift and the homogeneity are monitored via nuclear magnetic resonance spectroscopy experiments. The results demonstrate the compatibility of the thermal compensation approach with existing strategies useful to fine-tune the spatial dependence of the field generated by permanent magnet arrays.

A comprehensive experimental analysis of gadolinium active magnetic regenerators

The main goal of this study was an experimental comparison of six different active magnetic regenerators (AMRs) with gadolinium as the magnetocaloric material. The analysis was carried out for three different parallel-plate AMRs (with different porosities and different orientations of the plates in the magnetic field) and three different packed-bed AMRs (filled with spheres, powders and cylinders). Since the operation of an AMR is strongly affected by the operating conditions, the experiments were performed at different mass-flow rates and at different operating frequencies. These were required in order to define the optimum corresponding operating conditions for the analyzed AMRs. As comparative criteria the maximum temperature span, the cooling capacity and the experimentally predicted COP were taken into consideration.The experimental analysis was performed on a new prototype of magnetic refrigerator designed as an experimental device. Its operation is based on the linear movement of a permanent-magnet assembly over a static AMR. The magnet assembly provides a measured magnetic field of about 1.15 T.The results reveal that the geometry of the AMR (the form of the magnetocaloric material) has a crucial impact on the performance of the magnetic refrigerator. The best overall cooling characteristics (temperature span, cooling capacity and COP) were obtained for the parallel-plate AMR with the smallest porosity (∼25%) and the orientation of the plates parallel to the magnetic field. This particular AMR generated a temperature span of 20 K, which is also the largest, so-far measured and published temperature span with a parallel-plate AMR for a given magnetic field change generated by permanent magnets. With respect to the comparison of the experimentally predicted COP values, the parallel-plate AMRs show higher efficiencies than the packed-bed AMRs.

Monte Carlo simulation of single-plane magnetically focused narrow proton beams

We present Monte Carlo simulations of magnetically focused proton beams shaped by a single quadrapole magnet. Such beams are narrowly focused in one longitudinal plane but fan out in the perpendicular plane producing elongated elliptical beam spots (a ‘screwdriver’ shape). The focused beams were compared to passively collimated beams (the current standard of delivery for small radiosurgery beams). Beam energies considered were relevant to functional radiosurgery and standard radiosurgery clinical applications. Three monoenergetic beams (100, 125, and 150 MeV) and a modulated beam were simulated. Monoenergetic magnetically focused beams demonstrated 28 to 32% lower entrance doses, 31 to 47% larger central peak to entrance depth dose ratios, 26 to 35% smaller integral dose, 25 to 32% smaller estimated therapeutic ratios, 19 to 37% smaller penumbra volumes, and 38 to 65% smaller vertical profile lateral penumbras at Bragg depth, compared to the collimated beams. Focused modulated beams showed 31% larger central peak to entrance dose ratio, and 62 to 65% smaller vertical lateral penumbras over the plateau of the spread out Bragg peak. These advantages can be attributed to the directional acceleration of protons in the transverse plane due to the magnetic field. Such beams can be produced using commercially available assemblies of permanent rare earth magnets that do not require electric power or cryrogenic cooling. Our simulations suggest that these magnets can be inexpensively incorporated into the beam line to deliver reduced dose to normal tissue, and enhanced dose to elongated elliptical targets with major and minor axes on the order of a few centimeters and millimeters, respectively. Such beams may find application in novel proton functional and standard radiosurgery treatments in and around critical structures.