Permanent Magnet Assembly Research Articles

Tunable and temperature compensated permanent magnet assemblies for green particle accelerators

Particle accelerators are developed worldwide for several societal, industrial, and scientific applications. With the advent of high-strength permanent magnets, the focus is shifting to building particle accelerators using permanent magnets for beam handling. This shift offers the distinct advantage of power efficiency and compactness, over electromagnets. However, such systems face inherent limitations related to temperature sensitivity and lack of tuneability. This paper explores and demonstrates methods for reducing temperature sensitivity and incorporating tuneability in permanent magnet-based systems. Accelerators employing a large number of permanent magnets are more energy efficient as they do not incur running expenditures and are therefore classified as green in this paper. Moreover, we believe that future particle accelerators will be able to leverage these advantages even more. A temperature-compensated magnet using a Nickel–Iron special alloy is designed using the measured temperature-dependent B–H curve of the material. The optimum thickness of the temperature-compensated shunt was determined and cross-verified by constructing a magnet and measuring it in a temperature-controlled environment. Additionally, this paper discusses the design of hybrid magnets integrating permanent magnets and electromagnetic coils highlighting their utility in temperature compensation and tunability. Furthermore, other methods for incorporating tunability and making a permanent magnet system more resilient to temperature changes are also briefly outlined.

Gradient-based optimization of permanent-magnet assemblies for any objective

Gradient-based optimization of permanent-magnet assemblies for any objective

Development of a custom-made 2.8 T permanent-magnet dipole photon source for the ROCK beamline at SOLEIL.

In August 2021, the SOLEIL storage ring was restarted after the summer shutdown with a new bending magnet made entirely of permanent magnets. Producing a magnetic field of 2.8 T, it replaced one of the 32 electromagnetic dipoles (magnetic field of 1.7 T) of the ring to allow the ROCK beamline to exploit more intense photon fluxes in the hard X-ray range, thus improving the time resolution performances of the beamline for experiments carried out above 20 keV. The reduction of the new dipole magnetic gap required to produce the higher field has led to the construction and installation of a new vacuum vessel. The realization of the new dipole with permanent magnets was a technological feat due to the very strong magnetic forces. The permanent-magnet assembly required dedicated tools to be designed and constructed. Thanks to accurate magnetic measurements, a precise modelization of the new dipole was performed to identify its effects on the electron beam dynamics. The first measurements carried out on the ROCK beamline have highlighted the expected increase in photon flux, and the operation performances remain unchanged for the other beamlines. Here, the major developments and results of this innovative project are described in terms of technology, electron beam dynamics and photon beam performance on the ROCK beamline.

How to build the optimal magnet assembly for magnetocaloric cooling: Structural optimization with isogeometric analysis

In the search for more efficient and less environmentally harmful cooling technologies, the field of magnetocalorics is considered a promising alternative. To generate cooling spans, rotating permanent magnet assemblies are used to cyclically magnetize and demagnetize magnetocaloric materials, which change their temperature under the application of a magnetic field. In this work, an axial rotary permanent magnet assembly, aimed for commercialization, is computationally designed using topology and shape optimization. This is efficiently facilitated in an isogeometric analysis framework, where harmonic mortaring is applied to couple the rotating rotor–stator system of the multipatch model. Inner, outer and co-rotating assemblies are compared and optimized designs for different magnet masses are determined. These simulations are used to homogenize the magnetic flux density in the magnetocaloric material. The resulting torque is analyzed for different geometric parameters. Additionally, the influence of anisotropy in the active magnetic regenerators is studied in order to guide the magnetic flux. Different examples are analyzed and classified to find an optimal magnet assembly for magnetocaloric cooling.

DEVELOPING A MOTION MECHANISM FOR A SINGLE MODULE IN A SELF-RECONFIGURABLE MODULAR MICROROBOTICS SYSTEM BY USING EXTERNAL MAGNETIC ACTUATORS

In microrobotics field, self-reconfigurable modular robots (SRMRs) offer several advantages including adaptation to uneven environments, the capability of handling various sets of tasks, and continuous operation in the case of a malfunction of a single module. The current research direction in self-reconfigurable robotic systems is towards reaching million level number of modules working in coherence by means of locomotion, self-reconfiguration, and information flow. This research direction comes with new challenges such as miniaturizing the modules. One should consider looking for alternative ways of locomotion and self-reconfiguration when dealing with SRMRs having million level number of modules. Externally actuating the modules can be a good alternative to micro SRMRs. In this study, we developed a novel motion mechanism for a single module in a micro SRMR system by using external magnetic actuators. An assembly of elastic microtubes and permanent magnets is attached inside a cube-shaped module and periodic motion of the assembly is applied. The motion of a single microtube with permanent magnets inside is generated by using COMSOL Multiphysics software. The results of the simulations are compared with theoretical values to validate the motion mechanism that is introduced in the study.

Rod mangle rotation patterns for adjustable magnetic field generation

The use of adjustable magnetic field sources is becoming an indispensable necessity in numerous applications. In particular, permanent magnet assemblies, such as the rod mangle design, avoid the large power consumption and Joule heating problems present in electromagnets. In this work, we present a systematic 2D study of rod mangle configurations with different number of rods. We observe that the magnetic field homogeneity increases with the number of used rods and, for a sufficiently large number, the behavior of the assembly is similar to that of a perfect Halbach. Generally, the rotation of only one rod changes the direction and decreases the homogeneity and magnitude of the magnetic field. Nevertheless, the impact of such rotation reduces with the increase of the number of rods in the system. We also study how different rotation patterns influence the generated magnetic field and demonstrate how one can: (i) reduce the magnetic field magnitude rotating its direction; (ii) reduce the magnetic field magnitude keeping its direction constant; (iii) invert the magnetic field direction, after being reduced; or (iv) rotate the magnetic field direction keeping its magnitude constant. These results are similar to those obtained by a nested Halbach. In addition to the low cost, the results show that the mangle system is highly versatile, can be easily manipulated and, consequently, has a large application potential. The magnetic model was successfully validated with experimental systems of three and four rods.

Design and implementation of a versatile magnetic field mapper for 3D volumes

Magnetic field mapping is an essential step in research, manufacturing, and maintenance. It helps one find out what’s under the surface of any object and identify areas of high-flux density. Our magnetic field mapper is easy-to-use and has a user-friendly interface. It comprises a triple axis Hall effect-based magnetometer, meaning that it can measure the strength of magnetic fields in 3D. It is made up of three Hall sensors which are mounted on a triple-slot sensor probe which in turn is attached to translation stages allowing motion in three dimensions. The translation in X and Y motion (independent) is from -50 to +50 mm while in Z is from -150 to +150 mm with a nominal resolution of 0.1 mm. The height of the magnetometer is 1000 mm and it’s originally designed for mapping the magnetic field of permanent magnet assemblies for low-field and mobile magnetic resonance scanners. Sometimes, you need to find out how strong the magnetic field in a particular region is or you may want to measure all the three components of the magnetic flux density to find out the homogeneity or isotropy of the field. In high resonant NMR spectroscopy, the magnetic field needs to be highly uniform and homogeneous and to assess such a field, we need a device which can measure the magnetic field, precisely, accurately and reproducibly. The proposed field mapper is useful in all of these situations. It is low cost and easy to manufacture. The maximum measurable magnetic field is ±2 T. Furthermore, all the material required for building this device is easily accessible.

Ferrofluids to improve field homogeneity in permanent magnet assemblies

• Halbach magnet adapted with magnet rings for mechanical shimming. • Novel passive magnetic field shimming method based on ferrofluid suspensions in microvolumes. • Small size light-weight magnet assembly suitable for mobile magnetic resonance applications. A novel principle of passive magnetic field shimming for permanent magnet assemblies is introduced, based on defined amounts of a ferrofluid suspension contained in a microliter volume plastic container that is accurately positioned within the magnet bore. The ferrofluid volume acts as a micromagnet that compensates inhomogeneities in the magnetic field profile. A proof of principle is shown for a permanent magnet assembly, derived from a Halbach design, with two additional movable rings of magnets. These rings result in an average magnetic field strength of 1.06 T inside the bore, 19 % higher than the Halbach alone. Two options for field shimming with ferrofluids are shown: changing the material volume or choosing a ferrofluid with different saturation magnetization value. With the tested simple single-cube ferrofluid implementation the field homogeneity is improved from 86 ppm to 8 ppm over a sampling length of 5.5 mm. Better homogeneity is expected with more sophisticated ferrofluid arrangements. The complete assembly has a size of 5 × 5 × 4.2 cm 3 and a weight of 332 g. The demonstrated concept is particularly attractive for mobile magnetic resonance systems, as it does not require electrical power during operation.

Fabrication and Testing of Modified Magnetorheological Damper Fitted with External Permanent Magnet Assembly

Fabrication and Testing of Modified Magnetorheological Damper Fitted with External Permanent Magnet Assembly

A Miniature Permanent Magnet Assembly with Localized and Uniform Field with an Application to Optical Pumping of Helium

Atomic state preparation can benefit from a compact and uniform magnetic field source. Simulations and experimental measurements have been used to design, build, and test such a source and then apply it to the optical pumping of atomic helium. This source is a 9.5 mm (3/8″) OD × 6.7 mm (1/4″) ID × 9.5 mm (3/8″) long, NdFeB-N42 assembly of 1.6 mm (1/16″) thick customized annular magnets. It has octupole decay with a residual dipole far field from imperfect dipole cancelations. Fast B-field decay localizes the field, minimizing the need for shielding in applications. It has a greater than 50% clear aperture with a uniform and collimated magnetic field consistent with the prediction of several models. The device is applied to a high precision 3,4He laser spectroscopy experiment using σ+ or σ− optical pumping currently resulting in a measured 99.3% preparation efficiency and in accordance with a rate equation model.

An ultra-stable 1.5T permanent magnet assembly for qubit experiments at cryogenic temperatures.

Magnetic fields are a standard tool in the toolbox of every physicist and are required for the characterization of materials, as well as the polarization of spins in nuclear magnetic resonance or electron paramagnetic resonance experiments. Quite often, a static magnetic field of sufficiently large, but fixed, magnitude is suitable for these tasks. Here, we present a permanent magnet assembly that can achieve magnetic field strengths of up to 1.5T over an air gap length of 7mm. The assembly is based on a Halbach array of neodymium magnets, with the inclusion of the soft magnetic material Supermendur to boost the magnetic field strength inside the air gap. We present the design, simulation, and characterization of the permanent magnet assembly, measuring an outstanding magnetic field stability with a drift rate of |D| < 2.8 ppb/h. Our measurements demonstrate that this assembly can be used for spin qubit experiments inside a dilution refrigerator, successfully replacing the more expensive and bulky superconducting solenoids.

Study of a Modified Obstruction Free Pressure Sensor Based Flow Transducer Using Hall Sensors

In the present paper, a modified obstruction free pressure sensor-based flow transducer has been developed using Hall sensors. This technique is a modified version of the earlier inductive method. In this transducer, the fluid pressure in the pipeline is taken as the flow sensing parameter, and various drawbacks of the earlier inductive technique are eliminated. A prototype unit of the transducer is developed and studied in the present work. The transducer consists of two identical C-type Bourdon gauges, each fitted with an identical permanent magnet and Hall sensor assembly to sense the fluid pressure under flow condition and static pressure under no flow condition. The difference between the two Hall sensor outputs is found to vary nonlinearly with flow rate. The mathematical relations describing the working of the prototype unit are derived in the paper. The static characteristic curves of the proposed flow transducer are determined experimentally and reported in the paper. The characteristic curves are found to follow the derived equations to a very good extent with negligible percentage deviation from best-fit nonlinear characteristic.

A preliminary design of the magnetic diverter on-board the eXTP observatory

Charged particles in the space environment can degrade the scientific performances of X-ray detectors in astronomical telescopes. An efficient countermeasure is to place a magnetic diverter at the exit pupil of optics to deflect charged particles away from the sensitive detection area. In this work, we have performed a preliminary design of the magnetic diverter on-board the enhanced X-ray Timing and Polarimetry (eXTP) observatory. It relies on a Monte Carlo method via the GEANT4 toolkit to simulate the mirror responses to charged particles, using the single scattering physics for electrons and the elastic Remizovich physics for protons. It also implements a numerical method to calculate magnetic fields generated by an assembly of permanent magnets and its impact on the trajectories of charged particles. The compact calculation scheme provides efficient access to the background level estimation given the certain radiation environment, which enables the verification of the diverter configuration with the scientific requirements.

Design optimization of a 6.4 mm-diameter electromagnetic 2D scanning micromirror.

We present the design optimization, fabrication, and analysis of an electromagnetic biaxial scanning micromirror with 6.4 mm-diameter. The scanner is composed of a micromirror supported by two concentric gimbal structures with unique single turn coil. A cylindrical permanent magnet assembly is placed under the micromirror to provide a radial magnetic field for actuation. Lumped element model parameters and magnetic circuit have been optimized to maximize the driving torque. Fabricated micromirror has been actuated at 300 Hz and 1,010 Hz and maximum optical scan angle of 25.6° and 35.3° have been obtained for the vertical and horizontal scans, respectively. Crosstalk during the actuation has been analyzed, and improved models have been proposed to reduce the crosstalk.

Magnetic field causes the strong and weak nuclear forces and is the GUT force

The Scalar Theory of Everything (STOE) suggests the four fundamental forces are emergent properties of the magnetic field of permanent magnets. The STOE postulates the fractal (self--similar) principle that suggests small size scales are similar to our everyday size scale. Thus, the assembly of permanent magnets into a sphere is similar to a nucleon. The magnetic force from the sphere varies as the inverse cube of the distance from the center of the sphere (nucleon) which is approximately exponential, it has short range attractive field, it is an assembly of gluons (short photons), it explains the one proton to one electron atomic structure despite the large difference in mass, it suggests a size limit to the nucleon, it reminds of strong and weak forces, and it suggests a structure of the nucleus has protons on an outside shell. The STOE has the feature of the other sense of a ``Theory of Everything'' - that of a ``Grand Unified Theory'' (GUT).

Material Engineering and Design of a Relativistic Engine: How to Avoid Radiation Losses

In a previous paper [1] we have shown that Newton’s third law cannot strictly hold in a distributed system of which the different parts are at a finite distance from each other. This is due to the finite speed of signal propagation which cannot exceed the speed of light at vacuum, causing the total force in the system to not add up to zero. This was demonstrated in a specific example of two current loops with time dependent currents in at least one of the loops [1], or in one-time dependent loop current and a permanent magnet assembly [2, 3]. A relativistic engine was thus suggested. Since the system is affected by a total force for a finite period of time this means that the system acquires mechanical momentum and energy, the question then arises how to accommodate the law of momentum and energy conservation. The subject of momentum conversation was discussed in [4], while a preliminary discussion of the subject of electric energy conservation is given in [5, 6]. Here we discuss some of the radiation losses associated with the engine and their implications on the energy balance.

Design of a System to Compose 50 Hz Alternating and Static Magnetic Field From Induction Coil and Permanent Magnets

We demonstrate a technical solution to achieve an intense 50 Hz alternating magnetic field and a static magnetic field made by a permanent magnet at the same place. A compact coil built using the Bitter coil concept is customized to support alternating current, thus creating an alternating magnetic field. A complementary permanent magnet assembly is built around it to achieve the superposition of both fields along the axis of symmetry. Results from the experimental model are compared to both numerical and analytical models.

Modeling of magnetization and levitation force of HTS tapes in magnetic fields of complex configurations

In many levitation systems superconductors are used in combination with permanent magnets. In this paper we considered three types of magnetic assemblies that are most often used: with magnets oriented in one direction, oppositely oriented magnets and the Halbach array. Based on the H-formalism, we performed modeling of a magnetic field and levitation force in a system consisting of the high temperature superconductor (HTS) tape stack and the assembly of permanent magnets. It was shown that if a spatial distribution of a gradient magnetic field changes in height it is necessary to take into account the magnetic history of the superconductor. The proposed computational model includes a combination of scalar and vector potentials, as well as modeling the real movement of an HTS tape stack in a levitation system. The simulation results were verified by corresponding experiments. The proposed approach is universal for modeling levitation systems of complex configurations.

A low cost, portable NMR probe for high pressure, MR relaxometry.

A low cost, portable, high volume, stainless steel pressure reactor is modified to easily perform magnetic resonance relaxometry at industrially relevant pressures. Unlike existing pressurization strategies common to nuclear magnetic resonance (NMR) spectroscopy, this approach is amenable to realistic samples that feature heterogeneity and have traditionally escaped NMR study at pressure. This pressure reactor/NMR probe combination is easily accommodated by most single-sided and other low magnetic field permanent magnet assemblies. The performance of the probe is demonstrated by accomplishing NMR relaxometry on polydimethylsiloxane at different pressures with two types of unilateral magnets.

New frontiers in magnetic refrigeration with high oscillation energy-efficient electromagnets

This article reports on the novel resistive electromagnetic field source with the magnetic energy recovery, which enables the use of the static magnetocaloric regenerator. Most of the existing prototype magnetocaloric devices that operate near room temperature, use magnetic field sources consisting of permanent magnets. The alternating of the magnetic field that is required for the thermodynamic cycle often comes from the rotation of magnets over the refrigerant, that is, an active magnetocaloric regenerator (AMR). Such systems require moving parts and a motor drive, both of which cause additional costs and reduced energy efficiency. Further restrictions in existing devices result from the speed of the magnetisation/ demagnetisation process, which is, in addition to efficient heat transfer, crucial for the compactness of the device. Another drawback is that the instant change of the magnetic field is not feasible, regardless of the principle of movement. Permanent-magnet assemblies based on neodymium are also constrained by the use of this rare-earth-material. Therefore, a number of global research activities relate to the optimization of permanent-magnet-based magnetic field sources. However, ohmic loss, the active cooling of magnets, and considerable energy consumption are the reasons why another type of magnetic field source, that is, the electromagnet, was generally avoided by the magnetocaloric community. This article presents a novel and unique approach that enables substantially improved energy efficiency and applicable operation of rare-earth-free and static electromagnetic field sources, by implementing for the first time the magnetic energy recovery for magnetic refrigeration and heat pumping. To prove the advantages of such a system, a large number of numerical simulations, as well as an experimental proof, were conducted. A comparative analysis was made for the evaluation of the energy efficiency of the proposed novel system vs an example of the existing rotating-magnet assembly. The results of this study reveal that this new type of electromagnetic field sources provides a number of different and important advantages that can lead to new frontiers in research. However, the energy efficiency is still lower than that of the comparable rotating-magnet assembly.