Cylindrical Magnet Research Articles

A Flexible Surgical Robot with Hemispherical Magnet Array Steering and Embedded Piezoelectric Beacon for Ultrasonic Position Sensing

This article proposes a flexible surgical robot featuring strong magnetic steering achieved by a hemispherical magnet array actuation, and high‐accuracy ultrasonic position sensing achieved by a beacon total focusing method (b‐TFM). The hemispherical magnet array with magnetic focusing is described and its array parameters are optimized through finite element analysis to increase the magnetic field for actuation. The magnetic field strength at 100 mm for the array with the same mass as the cylindrical magnet is about 1.8 times higher than that of the cylindrical magnet. Using the magnet array actuation, the flexible robot exhibits the capability of agile steering to navigate along a predefined trajectory. In addition, a 1 mm × 1 mm lead zirconate titanate (PZT) patch is embedded into the tip of the flexible robot as a beacon for b‐TFM ultrasonic imaging to detect the position of the robot. Therefore, the entire navigation process can be executed under the supervision of the ultrasonic position sensing system, and the maximum error is 0.8 mm when the steering radius is 100 mm.

Intraoperative magnet in removal of intracerebral metallic foreign bodies

Advisability of magnets in neurotrauma is due to pattern of patients admitted to neurosurgical departments of military hospitals with wounds accompanied by intracranial fixation of foreign metallic ferromagnetic bodies. To study dimensions, mass and magnetic properties of fragments extracted from gunshot wounds inflicted by modern weapons; to assess the feasibility of devices and instruments for removing foreign bodies. We analyzed foreign bodies extracted after gunshot wounds. Shape, dimension, weight and magnetic properties were studied. We estimated 532 foreign bodies (497 surgeries) extracted at the Kirov Military Medical Academy and 83 foreign bodies (79 surgeries) extracted at the Burdenko Military Clinical Hospital. Distribution by anatomical regions was established for both groups. We intraoperatively used cylindrical neodymium magnets 3×20 and 5×20 mm to extract magnetic foreign bodies. These magnets were brought to the target using standard surgical tweezers or original devices. The median mass of removed fragments was 0.385 (Q1-Q3=0.12-1.435; min-max≤0.01-30.5) g at the Kirov Military Medical Academy and 0.4 (Q1-Q3≤0.001-1.6; min-max≤0.01-11.4) g at the Burdenko Military Clinical Hospital. Magnetic foreign bodies were found in 501 (94.2%) and 74 (94.8%) cases, respectively. In 8.8% of cases, foreign bodies were not removed due to difficult-to-reach location accompanied by higher risk of adverse outcomes after extraction. Extracted foreign bodies after combat injuries have magnetic properties in 94% of cases. Intraoperative magnet allows for safe extraction of fragments in 91% of cases. Devices with adjustable magnetic field strength seem perspective. Further analysis of indications for removal of wounding projectiles in primary and, especially, repeated surgical treatment of craniocerebral wounds is needed.

Improvement of Measurement Performance in Density Through Magnetic Levitation Using Asymmetrical Cylindrical Magnets

Improvement of Measurement Performance in Density Through Magnetic Levitation Using Asymmetrical Cylindrical Magnets

Permanent magnet systems to study the interaction between magnetic nanoparticles and cells in microslide channels

We optimized designs of permanent magnet systems to study the effect of magnetic nanoparticles on cell cultures in microslide channels. This produced two designs, one of which is based on a large cylindrical magnet that applies a uniform force density of 6MN/m3 on soft magnetic iron-oxide spherical nanoparticles at a field strength of over 300mT. We achieved a force uniformity of better than 14% over the channel area, leading to a concentration variation that was below our measurement resolution. The second design was aimed at maximizing the force by using a Halbach array. We indeed increased the force by more than one order of magnitude at force density values over 400MN/m3, but at the cost of uniformity. However, the latter system can be used to trap magnetic nanoparticles efficiently and to create concentration gradients. We demonstrated both designs by analyzing the effect of magnetic forces on the cell viability of human hepatoma HepG2 cells in the presence of bare Fe2O3 and cross-linked dextran iron-oxide cluster-type particles (MicroMod). Python scripts for magnetic force calculations and particle trajectory modeling as well as source files for 3D prints have been made available so these designs can be easily adapted and optimized for other geometries.

Spinning a Liquid Wheel and Driving Surface Thermomagnetic Convection with Light.

A typical Tesla thermomagnetic engine employs a solid magnetic wheel to convert thermal energy into mechanical energy, while thermomagnetic convection in ferrofluid is still challenging to observe because it is a volume convection that occurs in an enclosed space. Using a water-based ferrofluid, a liquid Tesla thermomagnetic engine is demonstrated and reports the observation of thermomagnetic convection on a free surface. Both types of fluid motions are driven by light and observed by simply placing ferrofluid on a cylindrical magnet. The surface thermomagnetic convection on the free surface is made possible by eliminating the Marangoni effect, while the spinning of the liquid wheel is achieved through the solid-like behavior of the ferrofluid under a strong magnetic field. Increasing the magnetic field reveals a transition from simple thermomagnetic convection to a combination of the central spin of the spiky wheel surrounded by thermomagnetic convection in the outer region of the ferrofluid. The coupling between multiple ferrofluid wheels through a fluid bridge is further demonstrated. These demonstrations not only unveil the unique properties of ferrofluid but also provide a new platform for studying complex fluid dynamics and thermomagnetic convection, opening up exciting opportunities for light-controlled fluid actuation and soft robotics.

The force is strong

Introductory physics courses cover the gravitational and electromagnetic force in some detail, but the strong and weak nuclear forces are often given only a cursory treatment. This paper presents some ideas for teaching students about the strong force using practical hands-on demonstrations and using the strong force potential in teaching certain aspects of calculus. A good analogy to the strong force is to place a strong magnet on a metal whiteboard. The magnet must be very close to the board for the magnet to stick to the metal exemplifying the short range of the strong force. Another analogy that can easily be demonstrated in the classroom is placing two cylindrical magnets with facing like poles in a vertically oriented Perspex tube. Velcro is another analogy since the strong force acts over such a short range it is essentially a contact force. The plot of the strong force versus distance and strong potential versus distance is a practical way of teaching students the reciprocal relationship between differentiation and integration. The Reid potential model of the strong interaction (Reid 1968 Ann. Phys., NY 50 411–448) is a good example of differentiating and integrating exponential functions. A calculation is included that shows that the strong force is approximately 100 times stronger than the electromagnetic force. A link between the strong force and Heisenberg uncertainty principle is also made.

Low-field NMR with multilayer Halbach magnet and NMR selective excitation

This study introduces a low-field NMR spectrometer (LF-NMR) featuring a multilayer Halbach magnet supported by a combined mechanical and electrical shimming system. This setup offers improved field homogeneity and sensitivity compared to spectrometers relying on typical Halbach and dipole magnets. The multilayer Halbach magnet was designed and assembled using three nested cylindrical magnets, with an additional inner Halbach layer that can be rotated for mechanical shimming. The coils and shim-kernel of the electrical shimming system were constructed and coated with layers of zirconia, thermal epoxy, and silver-paste resin to facilitate passive heat dissipation and ensure mechanical and thermal stability. Furthermore, the 7-channel shim coils were divided into two parts connected in parallel, resulting in a reduction of joule heating temperatures from 96.2 to 32.6 °C. Without the shimming system, the Halbach magnet exhibits a field inhomogeneity of approximately 140 ppm over the sample volume. The probehead was designed to incorporate a solenoidal mini coil, integrated into a single planar board. This design choice aimed to enhance sensitivity, minimize B1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${B}_{1}$$\\end{document} inhomogeneity, and reduce impedance discrepancies, transmission loss, and signal reflections. Consequently, the resulting linewidth of water within a 3 mm length and 2.4 mm inner diameter sample volume was 4.5 Hz. To demonstrate the effectiveness of spectral editing in LF-NMR applications at 29.934 MHz, we selectively excited hydroxyl and/or methyl protons in neat acetic acid using optimal control pulses calculated through the Krotov algorithm.

Analytical modeling and experimental verification of a multi-DOF spherical pendulum electromagnetic energy harvester

Low-frequency vibration energy harvesting is a promising technology for providing floating buoys and small marine robots with sustainable energy from ocean waves. A spherical vibration energy harvester with multiple degrees of freedom has the advantages of good multi-directional adaptability and compact structure. However, its magnetic field distribution in three-dimension space is much more complex due to the combined effect of a series of cylindrical permanent magnets mounted on the surface of a gimbaled pendulum. The traditional finite element method is too time-consuming to perform efficient parameter design and optimization. To solve this problem, this work develops an analytical electromagnetic model for the spherical vibration energy harvester based on Biot-Savart Law. This model can be used to predict spatial magnetic flux distribution and electromotive force for given magnet and coil parameters. The accuracy and computational cost of the analytical model is verified by the comparison with the finite element method. Furthermore, the optimization of electromagnetic parameters is implemented to achieve maximum energy conversion efficiency. Finally, an optimized prototype is fabricated and tested in both laboratory and real sea. The resonant frequency and energy conversion efficiency of the prototype reaches 1.0 Hz and 25.45 %, respectively. It is shown that the experimental results are in good accordance with the analytical results.

Magnetic field model of radially magnetized cylindrical permanent magnets in a self-biased magnetic pendulum array

Self-Biased Magnetic Pendulum Array (SBMPA) is an efficient and portable transmitter in ultralow frequency (ULF). The resonance frequency of SBMPA is affected by the magnetic field of the radially magnetized cylindrical permanent magnets. In order to calculate the resonance frequency, the magnetic field model of a single radially magnetized cylindrical permanent magnet is derived based on the concept of magnetic charge. Then, the influence of the demagnetizing field and external magnetic field on the magnetization of permanent magnets is analyzed, and the magnetic field model of SBMPA is established. The results of the magnetic field model are verified through simulation. The average deviation of magnetic field intensity is determined as 0.021%; thus, the magnetic field model and simulation have consistent results. Finally, the influence of the size and distance of permanent magnets on the resonance frequency is analyzed, which could provide theoretical guidance for the dynamic analysis of SBMPA.

Design and study of an eccentric wheel drive-based rotating piezoelectric energy harvester.

A nonlinear rotating piezoelectric energy harvester (N-RPEH) driven by eccentric wheels is proposed to collect rotational energy in the environment. Driven by external rotational motion, an eccentric wheel converts rotational motion into linear motion and realizes electrical energy output through magnetic coupling. To increase the effectiveness of the equipment's energy conversion process, this article aims to transform the rotational motion of an eccentric wheel into a linear motion of a motion board. The effects of the motion board's length L, the cylindrical magnet's height H, and the mass block M at the piezoelectric patch's end on the output performance of N-RPEH are explained by theoretical modeling and simulation. Through theoretical analysis, simulation, and experiment, it is found that when L = 120mm, H = 6mm, and M = 5.0g (medium mass), the output voltage reaches the maximum of 14.16V. Under this parameter, N-RPEH can produce a maximum power of 7.0688 mW when the external resistance value is 2 kΩ. Application experiments show that N-RPEH can light up 60 light-emitting diodes. Therefore, the proposed N-RPEH can effectively collect rotational energy and has a wide range of potential applications in wireless sensor networks.

Modular design of curved beam-based recyclable architected materials

Advances in manufacturing technologies have enabled architected materials with unprecedented properties. These materials are typically irreversibly designed and fabricated with characteristic geometries and specific mechanical properties, thus rendering them suitable for pre-specified requests. However, these materials cannot be recycled or reconstructed into different shapes and functionalities to economically adapt to various environments. Hence, we present a modular design strategy to create a category of recyclable architected materials comprising elastic initially curved beams and rigid cylindrical magnets. Based on numerical analyses and physical prototypes, we introduce an arc-serpentine curved beam (ASCB) and systematically investigate its mechanical properties. Subsequently, we develop two sets of hierarchical modules for the ASCB, thus expanding the constructable shape of architected materials from regular cuboids to complex curved surfaces. Furthermore, we demonstrate that the magnets attached to the centers of specific serpentine patterns of the modules allows the effective in-situ recycling of the designed materials, including sheet materials for non-damage storage, bulk materials for tunable stiffness, and protective package boxes for reshaping into decorative lampshades. We expect our approach to improve the flexibility of architected materials for multifunctional implementation in resource-limited scenarios.

Three-dimensional motion control of an untethered magnetic object using three rotating permanent magnets

Magnetic motion control has been actively studied mainly for the purpose of biomedical applications. However, in many cases, many actuator magnets surround a small magnet to be moved, and they consume large electric power. In some cases, complex calculations are required to estimate the control input of the actuator magnets. This study proposes a simple method to move a small magnet to the desired positions. For this, three cylindrical permanent magnets magnetized in the radial direction were positioned as the sides of a triangle; these actuator magnets were rotated using motors. By monitoring the position of the small magnet and through simple feedback control based on the angles of the three actuator magnets, the untethered small magnet could be moved along arbitrary three-dimensional (3D) paths. The control principle was established by calculating the magnetic force and torque acting on the small magnet for some sets of actuator-magnet angles.

Positioning system design of closed-loop magnetically driven laser steering manipulator for endoscopic microsurgery

This study presents a closed-loop magnetically driven laser steering manipulator positioning system for endoscopic microsurgery. A multimagnetic field strength sensor circuit is embedded in a 16−mm diameter analog laser steering manipulator. The magnetic field distribution of a cylindrical permanent magnet in three-dimensional space is first modeled using an integral model to overcome the large error induced by the magnetic dipole model when the sensor and permanent magnet are close. The integral in the model is then decomposed using the Gauss–Legendre quadrature to improve the computational efficiency of the formulation. Moreover, five commonly used global search optimization methods are compared. Then, the algorithm with the fastest computational rate among these five algorithms, the tree-seed algorithm, is fused with the Levenberg–Marquardt algorithm, which performs well in local search, to obtain a hybrid optimization algorithm. Finally, it is demonstrated through static and dynamic experiments that the system based on the hybrid algorithm can obtain satisfactory computational errors while maintaining a high computational rate.

A high-performance rotational electromagnetic energy harvester based on magnetic plucking: Design, simulation, and experiment

Harvesting rotational energy to supply low-powered electronic devices can optimize the whole power supply system layout. In this paper, we propose a high-performance rotational electromagnetic energy harvester and construct an electro-mechanical dynamic model. The harvester consists of the halbach magnet array (HMA), a radially magnetized cylindrical rotatable magnet, and a copper coil, respectively. The proposed energy harvester is tested in a rotating platform and the correctness of the mathematical model is verified by experimental results. As one of the important components of the harvester, the magnetic field characteristics of the HMA are simulated by the finite element method (FEM) and compared with other magnet arrangements. Additionally, the effect on output when the HMA is rotated individually has also been analyzed. Numerical and experimental results indicate that the rotational energy harvester also has an optimal speed, and the corresponding maximum output power decreases significantly with the increase of the distance between magnets. Numerical results indicate that the maximum power output can be obtained as 516.05 mW at 520 rpm, which is a pretty remarkable result. To verify practical application capability, a rectifier-stable circuit is constructed to light 54 LEDs in experiments.

Dimensional analysis of magnetophoresis

Magnetophoresis is used in various applications requiring selective collection of magnetic particles. This study is aimed at quantitatively describing magnetophoretic systems via dimensional analysis to assess the relative contribution of hydrodynamics, electromagnetism, and particle dynamics. We introduce dimensionless numbers characterizing the transport of magnetic particles in a fluid. Analytical and numerical studies were conducted for magnetophoretic systems where magnetic particles were suspended in a fluid exposed to magnetic fields generated by permanent magnets. The magnetically induced mobility of the magnetic particles was simulated for a range of parameters relevant in biomedical applications, including the particle and fluid properties, flow velocity, and geometries of the particle, flow channel, and magnet. The numerical results obtained in multiphysics modeling of magnetophoretic systems were analyzed based on the proposed dimensionless numbers, resulting in a functional relationship for the particle capture efficiency (CE), defined as the ratio of captured particles to all particles injected in the flow. The performance of magnetophoretic systems predicted with the dimensional analysis was verified in comparison with published experimental data. Using dimensional analysis, 12 input parameters determining the particle CE were reduced to 3 dimensionless numbers characterizing the ratios of magnetophoretic and hydrodynamic forces, cross-sectional areas of the magnet and the flow channel, and length and diameter of the magnet. A set of curves predicting particle CE was obtained using these dimensionless numbers. A close agreement was found between the CEs predicted by the curves and those obtained in both numerical simulations and experiments where cylindrical magnets were placed in a flow through a cylindrical pipe. This study provides a promising framework for analyzing and predicting performance of various magnetophoretic systems for a range of applications.

Development of Empirical Model for Electromagnetic Damping Coefficient Damper

The significance of the electromagnetic damper in vibration systems has attracted considerable interest from researchers, making it a prominent area of research. Various papers have been consulted to explore the vibration concept associated with electromagnetic dampers and their practical applications. A vibration test rig with a simple electromagnetic damper has been designed and tested to investigate the effect of electromagnetic force. An experimental study on the response of the electromagnetic damper was conducted. A logarithmic decrement method was deployed to find the damping coefficient, c, of a one-degree freedom system (mass spring damper system). A test rig and electromagnetic damper element were introduced as a damper in the system. Design factors included the type of geometry, type of material and the current supply to the system. The testing was conducted using the in-house developed vibration test rig. The data obtained from the experiment has been analysed to determine the electromagnetic damping performance. A factorial analysis was performed to identify the significant factors influencing the damping coefficient of the system. Two empirical models obtained through regression analysis of Excel and Minitab. It was found that the influential effects for the response are the type of material (aluminum), slotted geometry and a bigger amount of current (3 A). The application of a cylindrical conductor and magnet as a damper reduced the vibration response of spring mass damper.

Optimization of on-axis magnetic field of uniformly magnetized cones

The magnetic field B induced along the axis of symmetry of axially magnetized cones was studied analytically and experimentally for various cone angles α. An explicit algebraic equation was derived for sharp-pointed and truncated cones. A sharp cone is characterized by singularities of B and ∇B at its apex point. For a truncated cone, the maximum values of these quantities are achieved for αmax∼54.7° and α∇∼39.2°, respectively. Two truncated cones with αuni∼63.4° positioned in a mirrored co-apex configuration produce a uniform axial field in the free-space gap. For smaller angles, the minimum field is located in the center of the airgap, while for larger, it is at the cones’ surfaces with extremum at αmin∼71.6°. These predictions were investigated using a tunable apparatus in which Co–Fe cones are magnetized by cylindrical NdFeB magnets. Strong ∼4 T B-field was achieved. Experimental results are discussed in detail, including incomplete magnetization and other secondary effects.

Exact and Computationally Robust Solutions for Cylindrical Magnets Systems with Programmable Magnetization.

Magnetic systems based on permanent magnets are receiving growing attention, in particular for micro/millirobotics and biomedical applications. Their design landscape is expanded by the possibility to program magnetization, yet enabling analytical results, crucial for containing computational costs, are lacking. The dipole approximation is systematically used (and often strained), because exact and computationally robust solutions are to be unveiled even for common geometries such as cylindrical magnets, which are ubiquitously used in fundamental research and applications. In this study, exact solutions are disclosed for magnetic field and gradient of a cylindrical magnet with generic uniform magnetization, which can be robustly computed everywhere within and outside the magnet, and directly extend to magnets systems of arbitrary complexity. Based on them, exact and computationally robust solutions are unveiled for force and torque between coaxial magnets. The obtained analytical solutions overstep the dipole approximation, thus filling a long-standing gap, and offer strong computational gains versus numerical simulations (up to 106 , for the considered test-cases). Moreover, they bridge to a variety of applications, as illustrated through a compact magnets array that could be used to advance state-of-the-art biomedical tools, by creating, based on programmable magnetization patterns, circumferential and helical force traps for magnetoresponsive diagnostic/therapeuticagents.

Theoretical and experimental study of a novel triple-magnet magnetic dynamic vibration absorber with tunable stiffness

PurposeThe existing Nonlinear Dynamic Vibration Absorbers (NLDVAs) have the disadvantages of complex structure, high cost, high installation space requirements and difficulty in miniaturization. And most of the NLDVAs have not been applied to reality. To address the above issues, a novel Triple-magnet Magnetic Dynamic Vibration Absorber (TMDVA) with tunable stiffness, only composed of triple cylindrical permanent magnets and an acrylic tube, is designed, modeled and tested in this paper.Design/methodology/approach(1) A novel TMDVA is designed. (2) Theoretical and experimental methods. (3) Equivalent dynamics model.FindingsIt is found that adjusting the magnet distance can effectively optimize the vibration reduction effect of the TMDVA under different resonance conditions. When the resonance frequency of the cantilever changes, the magnet distance of the TMDVA with a high vibration reduction effect shows an approximately linear relationship with the resonance frequency of the cantilever which is convenient for the design optimization of the TMDVA.Originality/valueBoth the simulation and experimental results prove that the TMDVA can effectively reduce the vibration of the cantilever even if the resonance frequency of the cantilever changes, which shows the strong robustness of the TMDVA. Given all that, the TMDVA has potential application value in the passive vibration reduction of engineering structures.

Research on the self-levitation of cylindrical magnets with wrapped shells in magnetic fluid: Consideration magnetization direction of magnets

In this paper, the self-levitation of cylindrical magnets wrapped by shells immersed in magnetic fluid (MF) is studied. The calculation formula of the magnetic fluid levitation force (MFLF) received by magnets and shells is derived, and the dependence between MFLF, mass of MF, and levitation height of magnets is studied. Attention is paid to the influence of magnetization direction of magnets and shells on MFLF, and experiments have been designed to study MFLF. Research shows that both the magnetization direction of magnets and shells can affect MFLF, and the use of soft magnetic shells and radial magnetized magnets is beneficial to obtain a smaller axial MFLF. In addition, the magnetization direction of magnets has a significant influence on the distribution and surface instability of MF, which is a key factor affecting MFLF. There are two intervals in which the MFLF changes drastically for the axial magnetized magnets, but only one for the magnets with radial magnetization. The reason is that the surface instability of MF caused by axial magnetized magnets plays a significant role in axial MFLF, while the surface instability caused by radial magnetized magnets has almost no influence on axial MFLF.