Permanent Cylindrical Magnets Research Articles

Определение динамических параметров постоянного магнита при его удержании в импульсном магнитном поле

There are various practical ways to implement magnetic levitation as a method of holding or lifting an object using a magnetic field alone. The following principle of creating the balance of the body is considered in the work. A small cylindrical neodymium magnet is held during electromagnetic interaction with a pulsating current flowing through the coil. For a soaring effect to occur when the magnet approaches the coil, the current through it is switched off by an electronic key that is activated by a digital Hall sensor located on the axis of the coil. Of practical interest is the development of simple recommendations to predict the fact of body retention with a given coil design, current through it, dimensions and properties of a permanent magnet. There are few engineering techniques to determine the position of the body, its stability and the nature of movement in suspension. The aim of the study is a theoretical and experimental study of the dynamic parameters of a permanent magnet when it is held in a pulsed magnetic field and the creation of a simplified computational-experimental technique for determining the characteristics of the body in suspension. Materials and methods . When performing the work, methods of mathematical and computer modeling were used, as well as experimental studies. The created software using the development tools of the Mathcad package was based on well-known methods: numerical integration of a system of differential equations. Results. A simplified computational and experimental technique is proposed for determining magnetic moments for a permanent cylindrical magnet and coil with current, as well as an approximate value of the coordinate of the position of the body in suspension. A mathematical model of the one-dimensional motion of a magnet under the influence of gravity and electromagnetic forces of interaction with a pulsed magnetic field at a known distance at which the current is turned off is developed. Conclusion. It was established experimentally and through computer simulation that the higher the frequency of the pulsations, the more rigid the pulsation amplitude is observed when the body is held and a more stable equilibrium is established. The ripple frequency decreases with increasing mass of the permanent magnet, and there is a critical mass that is no longer held in the electromagnetic field. As the voltage supplied to the coil switch increases, the frequency of the pulsations of the body and the consumed electric power increase, while the duty cycle of the current pulses decreases.

Analytical and physical modeling of the magnetically active part of a linear electric generator with permanent magnets

Linear electric generators are increasingly used in autonomous systems that require a compact source of electricity and when it is necessary to simplify mechanisms of power systems. To study the characteristics of a linear electric generator, an analytical model of its magnetically active part was proposed. The model is based on the assumption of the periodicity of linear translational motion of the armature relative to the stationary cylindrical winding. Based on the representation of the magnetic field of the generator’s armature by cylindrical harmonics of the scalar potential, the magnetic flux generated by the inductor was analyzed. The inductor design contains several pairwise oppositely oriented cylindrical permanent magnets. The use of representations based on cylindrical harmonics for the magnetic flux and EMF induced in a circular circuit has made it possible to substantiate the rational number of cylindrical armature magnets and their geometric parameters. The losses caused by the technological necessity of using annular magnets instead of solid continuous cylindrical ones with the same overall dimensions were estimated. Analysis of losses of the magnetic flux linkage with the current winding resulting from the presence of technologically necessary clearance between the permanent magnets and the winding sections was carried out. An analysis of arrangement and switching of the winding sections was carried out. It has made it possible to justify the choice of rational cross-sectional dimensions. For experimental verification of the analytically obtained results, a physical model of a linear electric generator with an armature containing permanent cylindrical magnets was designed. Its translational periodic movement was provided through an external electric drive. Analysis of the EMF dependences recorded with a digital oscilloscope with a small (5 %) error has confirmed the obtained analytical results and correctness of the theses underlying the model

The electric machine with two-sided stator, axial magnetic flux, permanent magnets and multilayered printing windings

The use of printed windings in electric machines with permanent magnets and axial magnetic flux allows to reduce their axial size and significantly increase the current density in the windings due to the small thickness and correspondingly large width of the conductors of the printed winding and, as a result, their better cooling. The dependences of voltage and power in the generator mode are determined when connecting the windings through the diode bridge to the load. Investigations of the effect of stator teeth on the magnitude of the electromagnetic torque are made. It was found that the presence of teeth on the stator allows you to increase the electromagnetic torque of the electric machine by about 26% compared with the version of the magnetic system without teeth. The effect of the displacement of one stator relative to another on the magnitude of the tooth torque has been studied. A prototype of an electric machine with a double-sided stator, multilayer printed windings and permanent cylindrical magnets was manufactured. The calculated model of the generator adequately describes the physical model. The discrepancy between the calculated and experimental values does not exceed ε = 4%. The characteristics of the studied generators were calculated by the software packages Simcenter MagNet and Simcenter MotorSolve.

Model for Generation of Neutrons in a Compact Diode with Laser-Plasma Anode and Suppression of Electron Conduction Using a Permanent Cylindrical Magnet

A model for acceleration of deuterons and generation of neutrons in a compact laser-plasma diode with electron isolation using magnetic field generated by a hollow cylindrical permanent magnet is presented. Experimental and computer-simulated neutron yields are compared for the diode structure under study. An accelerating neutron tube with a relatively high neutron generation efficiency can be constructed using suppression of electron conduction with the aid of a magnet placed in the vacuum volume.

Design and application of a longitudinal field Aubert permanent magnet composed of identically-shaped blocks for large-scale Magnetic Separation

Magnetic Separation processes such as magnetically enhanced centrifugation (MEC) or magnetic cake filtration, usually require cost-intensive and heavy electromagnets. Permanent cylindrical magnets providing a comparable longitudinal magnetic field may be more advantageous for these applications both in terms of cost and weight. In this publication we propose the use of Aubert magnets. As they may be composed of identically-shaped magnet blocks, the investment costs and running expenses are very low. We analyze the magnetic field in the central bore of an Aubert magnet both by analytic calculations based on a dipole model and by FEM (finite element method) and compare the results to our measured data on such a device. We find very good agreement with an extended dipole model and suggest our analytic method even for the design of large-scale devices. Finally, the pros and cons of both types of magnetic devices are discussed.

Omnidirectional lamb waves by axisymmetrically-configured magnetostrictive patch transducer

This work presents the generation of omnidirectional Lamb waves by a new magnetostrictive patch transducer (MPT) and investigates its generation mechanism. Although MPTs have been widely used for wave transduction in plates and pipes, no investigation reports the generation of omnidirectional Lamb waves in a plate by an MPT. For the generation, we propose an axisymmetrically-configured MPT that installs multiple axisymmetric turns of coil outside of a permanent cylindrical magnet located above the center of a circular magnetostrictive patch. After confirming the omnidirectivity of the proposed MPT experimentally, the mechanism of the Lamb wave generation and its frequency characteristics are investigated. It is also shown that the Lamb wave is most efficiently generated in a test plate when its wavelength is equal to two-thirds of the magnetostrictive patch diameter. If this wavelength¿patch diameter relation holds, the second radial extensional vibration mode of the patch of the proposed MPT is shown to be the mode responsible for generating the Lamb wave in a plate.

Analytical model of batch magnetophoretic separation

Magnetophoresis (the motion of magnetic particles driven by the nonuniform magnetic field), that for a long time has been used for extracting magnetically susceptible objects in diverse industries, now attracts interest to develop more sophisticated microfluidic and batch techniques for separation and manipulation of biological particles, and magnetically assisted absorption and catalysis in organic chemistry, biochemistry, and petrochemistry. A deficiency of magnetic separation science is the lack of simple analytical models imitating real processes of magnetic separation. We have studied the motion of superparamagnetic (generally, soft magnetic) particles in liquid in the three-dimensional field of the diametrically polarized permanent cylindrical magnet; this geometry is basically representative of the batch separation mode. In the limit of the infinite-length magnet, we found the particle magnetophoresis proceeds independently of the magnet polarization direction, following the simple analytical relation incorporating all the relevant physical and geometrical parameters of the particle-magnet system. In experiments with a finite-length magnet we have shown applicability of the developed theory as to analyze the performance of the real batch separation systems in the noncooperative mode, and finally, we have presented an example of such analysis for the case of immunomagnetic cell separation and developed a criterion of the model limitation imposed by the magnetic aggregation of particles.

Detection of nanosecond optoacoustic pulses in steel

The optoacoustic transformation of 5-ns laser pulses was used to excite broadband longitudinal acoustic pulses in a 0.4-mm-thick steel plate. An electromagnetic acoustic transducer that incorporated a flat wire coil with a diameter of 5 mm and an amplifier was proposed as a device for contactless ultrasound detection. A permanent cylindrical magnet and a coil close to the printed-circuit board of an operational amplifier were placed on one side of the sample, thus allowing the detection of the alternating electromagnetic field produced by pressure pulses excited on the opposite side. The frequency spectrum of detected pulses ranged from 5 to 200 MHz.

Dynamic Dipole-Dipole Magnetic Interaction and Damped Nonlinear Oscillations

Static dipole-dipole magnetic interaction is a classic topic discussed in electricity and magnetism text books. Its dynamic version, however, has not been reported in scientific literature. In this article, the author presents a comprehensive analysis of the latter. We consider two identical permanent cylindrical magnets. In a practical setting, we place one of the magnets at the bottom of a vertical glass tube and then drop the second magnet in the tube. For a pair of suitable permanent magnets characterized with their mass and magnetic moment we seek oscillations of the mobile magnet resulting from the unbalanced forces of the anti-parallel magnetic dipole orientation of the pair. To quantify the observed oscillations we form an equation describing the motion of the bouncing magnet. The strength of the magnet-magnet interaction is in proportion to the inverse fourth order separation distance of the magnets. Consequently, the corresponding equation of motion is a highly nonlinear differential equation. We deploy Mathematica and solve the equation numerically resulting in a family of kinematic information. We show our theoretical model with great success matches the measured data.

SU‐FF‐T‐405: The Effect of Magnetic Field On Relative Biological Effectiveness in Yeast Cells

Purpose: To investigate the effect of a magnetic field on the relative biological effectiveness (RBE) in yeast cells irradiated with γ‐rays. Method and Materials: A γ source was used to irradiate Saccharomyces cerevisiae (baker's yeast) with and without a modest magnetic field (0.78 T). A set of NdFeB permanent cylindrical magnets and another set of non‐magnetized pseudo‐magnets were used to obtain data with and without the magnetic field. The cells were located at the center between the pole faces and sandwiched between two layers of non‐nutrient agar to maintain lateral electron equilibrium. The variation of the magnetic field in the cell region was less than 1%. The Monte Carlo code PENELOPE was used to simulate the dose distribution in the presence and absence of the magnetic field to ensure the doses delivered were equal in both cases. Another group of cells without irradiation was used as a control for the two groups being irradiated. The cells were sampled and cultivated after irradiation, and colonies representing surviving cells were counted. Results: In five out of seven experiments the null hypothesis (no effect) could not be rejected with t‐test at p = 0.05. Nonetheless, the results still suggest that the survival rate may drop slightly in the presence of the magnetic field. The survival rate decreased by 3.9% ± 2.7% at about 50% survival rate. At two standard deviation level the effect was less than 10% at B = 0.78 T. Conclusion: The effect of a 0.78 T magnetic field on the RBE of Saccharomyces cerevisiae is smaller than 10%. Although the indication that a strong magnetic field may increase the RBE of the radiation is not conclusive at 0.78 T, further experiments at higher magnetic field (B >2 T) and larger sample size would reduce the uncertainties in the experiments.