Nonmagnetic Plate Research Articles

Synchronized magnet-induced displacement detection in non-magnetic plates via smart materials near-field sensing

Accurate monitoring of small displacements in non-magnetic thin-walled plates is essential for assessing their manufacturing precision and vibrational characteristics. Optical techniques are limited by environmental disturbances and spatial constraints, while contact methods are compromised by mechanical forces and wear. A synchronized magnet-induced displacement detection method (SMDDM) using heteropolar permanent magnets (HPMs) and smart materials for non-magnetic plates is proposed. Supported by a magnetic-mechanical–electrical coupling model and a joint algorithm with dynamic linear extension and analytic hierarchy process (DLE-AHP), the prototype’s parameters are refined through experimental design, neural networks, and multi-objective optimization. Comprehensive tests show that SMDDM achieves an accuracy of 2 μm and a resolution of 1 μm, with smaller measurement errors observed in low-frequency, small-displacement tests. This validates the method’s effectiveness in multi-scale displacement measurement and vibration testing, highlighting its potential for in-situ monitoring in thin-plate applications.

A simple conductivity measurement method using a peak-frequency feature of ferrite-cored eddy current sensor

Eddy current sensing (ECS) is advantageous in metallic measurements, but the existing ECS-based conductivity measurement methods are limited in terms of complexity, accuracy, or measurement range. Based on a peak-frequency feature of sweep-frequency eddy current sensor, a conductivity measurement method for non-magnetic plates is proposed. Deriving from the analytic solution of Dodd-Deeds, it is found that the peak-frequency, which is the peak frequency of the imaginary component of the induction spectrum change, is inversely proportional to the specimen's conductivity; the product of the conductivity and the peak-frequency is solely determined by a geometrical coupled parameter called spatial-frequency, which is independent of the conductivity of the specimen and is specified by the lift-off and the dimensions of sensor coils; the lift-off and the sensor coils dimensions have no impact on the inverse linearity between the conductivity and the peak-frequency, although produce different scales. The findings are also confirmed with finite element method (FEM) simulations and experimental results. Based on the findings, we propose to measure the conductivity using the inverse proportionality between the peak-frequency and the conductivity, and to eliminate the lift-off effect by calibrating the sensor with a known conductivity.In addition, we propose to use ferrite-cored sensor in experimental measurements, to improve the induction intensity in low frequency range in practical. The induction spectra characteristics of eddy current sensors with and without a ferrite core by FEM (finite element method) are compared, and the results show that the ferrite-cored eddy current sensor features the same peak-frequency as the air-cored eddy current sensor, but exhibits a stronger inductive impedance variation.Experiments were carried out on six samples with conductivities from 16.09 MS/m to 57.29 MS/m at different lift-offs. The relative conductivity measurement errors are within 1.26 % and the maximum absolute error is 0.43 MS/m. We analyze the measurement errors in terms of frequency resolution and lift-off, and propose methods for improvement. The conductivity measurement method based on the peak-frequency of ferrite-cored eddy current sensor shows its advantages in terms of simplicity, accuracy, immunity to the lift-off, and wide measuring range in non-magnetic metal plate conductivity measurements, because of the rarely mathematically approximation induced error and the determined inverse ratio between the conductivity and the peak-frequency.

Efficacy of Auricular Point Acupressure with Magnetic Plates on Postpartum Anxiety and Depression in Low Risk Parturient at Thammasat University Hospital: A Randomized Clinical Controlled Trial

Objective: To study the effectiveness of auricular acupressure (AC) with and without magnetic plates in reducing anxiety and depression levels among parturients. Materials and Methods: The present study was a randomized controlled trial conducted at the department of Obstetrics and Gynecology, Thammasat University Hospital, Pathum Thani, Thailand, between March 2022 and February 2023. All participants were term nulliparous pregnant women delivered who during the study period. Participants were randomly allocated into three groups with control for non-AC, study for AC with magnetic plates, and placebo for AC with non-magnetic plates. Three specific auricular points, namely Shenmen (HT7), Heart (CO15), and Subcortex (AT4) were selected. Thai Hospital Anxiety and Depression Scale (Thai HADS) was evaluated at 2, 14, 28, and 42 days postpartum. Results: Two hundred twenty-five cases were recruited and divided evenly into control, study, and placebo groups. The mean age of participants was 28.5 years old. Body mass index (BMI), education level, and demographic characteristics among the three groups were comparable. Prevalence of anxiety and depression was 4.4% (10/225) and 7.5% (17/225). Participants in placebo and study groups had statistically significant relief of anxiety levels within six weeks when compared to the control group. All subjects had lower depression scores within four weeks of delivery. AC with and without magnetic plates reduced postpartum depression compared to the control group. Satisfaction of AC was reported at 84% (126/150). Conclusion: AC with or without magnetic plates at HT7, CO15, and AT4 significantly reduced anxiety and decreased depression with less confidence in postpartum subjects. Keywords: Auricular acupressure; Anxiety; Depression; Postpartum; Magnetic plates

Experimental study on pyramid solar distiller performance with applying magnet field under various operating conditions

ABSTRACT Solar stills are a potential solution to address water scarcity but have low production levels. This study explores using magnets in a pyramidal distiller to increase yield. The effects of magnets at different water heights (1.5, 2, 2.5, and 3 cm) and non-magnetized iron poles were investigated. Various magnetic field intensities (136, 175, and 220 mT) and magnet locations (above and below the basin) were studied. Also, two types of stills, made of sheet metal and acrylic, were compared. Results showed that magnets at 136 mT improved production by 24% (3600 mL/m2/day) compared to the non-magnetized still (2900 mL/m2/day). Non-magnetic plates increased productivity by 12% compared to the still without magnets. The magnetic field alone accounted for a 12% increase. The maximum productivity and energy efficiency were 24% and 39.6% at 1.5 cm water depth, and 11% and 36.6% at 3 cm. Increasing magnetic field intensity from 136 mT to 220 mT raised yield and thermal efficiency to 34% and 41.1% respectively. The acrylic-based still with magnets achieved a 10% increase in distillate (3300 mL/m2/day) compared to the non-magnetized version (3000 mL/m2/day).

Shape and Stability of a Local Heat-Transfer Magnetofluid Coating on a Plate

Purpose. Investigate the shape and stability of a magnetic fluid coating on a flat surface in a non-uniform magnetic field of a permanent magnet.Methods. Magnetic fluids based on transformer oil MMT-44 and MMT-21 with saturation magnetization of 43.8 and 21.2 kA/m, respectively, were used in the experiments. A magnetic-fluid coating was formed on the surface of horizontal and vertical non-magnetic plates in a locally inhomogeneous magnetic field of permanent magnets. The source of the inhomogeneous magnetic field is a system of two rectangular magnets. The size of the magnetic system is 40×12×10 mm. The maximum values of the magnetic field strength and gradient reach 180 kA/m and 8∙104 kA/m2, respectively. The shape and stability of a sessile and suspended magnetic fluid coating were studied for various plate orientations.Results. The shape and stability of the magnetic fluid coating on horizontal and vertical plates are studied. The experimental dependences of the height and length of the coating on the volume of the magnetic fluid are established. It is established that the coating can have a certain maximum volume. When this volume is exceeded, the liquid spreads over the surface of the plate or a part of the liquid volume is separated. The limiting volume of the coating is determined by the magnetic characteristics of the ferrofluid and the magnetic field.Conclusion. The possibility of forming a sessile and suspended local magnetic fluid coating on horizontal and vertical plates is established. The height and length of the magnetic fluid coating on the plate depend on the volume of the magnetic fluid, as well as on the characteristics of the magnetic system and the magnetization of the magnetic fluid. The results obtained can be used in the formation of magnetic fluid coatings of cooled sections of heated surfaces.

Vortex currents and magnetic forces of non-magnetic plate in the process of magneto-pulse treatment on the ideal ferromagnetic platform

Vortex currents and magnetic forces of non-magnetic plate in the process of magneto-pulse treatment on the ideal ferromagnetic platform

СТРУМИ ТА ЕЛЕКТРОМАГНІТНІ ЗУСИЛЛЯ В СИСТЕМАХ МАГНІТНО-ІМПУЛЬСНОЇ ОБРОБКИ З ФЕРОМАГНІТНОЮ ПЛАТФОРМОЮ

The action of high-density pulsed currents (109 A/m2) leads to the appearance of the electro-plastic effect in metal products. It is proposed to use magnetic pulse treatment of nonmagnetic plates by electromagnetic inductors with a U-shaped magnetic circuit for local flow pulsed currents in the nonmagnetic plates. The work aims to establish an influence of a ferromagnetic platform with nonlinear magnetic permeability on pulsed eddy currents and magnetic pressure of nonmagnetic metal plates with different electrical conductivity in modeling magnetic pulse treatment of welded joints to achieve the electro-plastic effect. Numerical simulation of pulsed electromagnetic fields by the finite element method is used. The current calculation in the inductor's winding is performed by solving the equations of the magnetic field and the electric circuit equations for a discrete-time interval. A power source is a capacitor that is charged to a specific voltage. To study the effect of the ferromagnetic platform on eddy currents and forces in a nonmagnetic plate with its different electrical conductivity, the same pulsed current in the inductor's winding is used. The dependence of amplitude values of eddy current density and magnetic pressure on the surfaces of nonmagnetic plates of different electrical conductivity is investigated. The influence of the presence and absence of a ferromagnetic platform and its electrical conductivity and magnetic permeability on the values ​​of eddy currents and magnetic pressure in the nonmagnetic plate have been studied. Ref. 13, fig. 7, table.

Influence of magnetic property of test plates on magneto-rheological behavior

This paper investigated the behaviors of magnetorheological fluids (MRFs) under shear mode with magnetic iron and non-magnetic titanium upper plates, respectively. Based on the Stribeck curve and friction coefficient normalization methods, the lubrication states at the chain end/plate contacts were more at a boundary lubrication state. The restriction of magnetic plate on the particles ends migrations under high magnetic field enhanced the field induced friction to increase the yield stress. Therefore magnetic plate prevented sliding of particles with plate and resulted in a higher yield stress than the easier sliding of particle chains ends on non-magnetic plate. The magnetic property of the upper test plate should be properly considered during the tests of MRFs to derive accurate description of the properties of MRF to be used in the design of various MR actuators.

ВПЛИВ П-ПОДІБНОГО МАГНІТОПРОВОДУ ІМПУЛЬСНОГО ІНДУКТОРА З ДВОМА КОТУШКАМИ НА ВИХРОВІ СТРУМИ ТОНКОСТІННИХ НЕМАГНІТНИХ МЕТАЛІВ У ПРОЦЕСІ МАГНІТОІМПУЛЬСНОЇ ОБРОБКИ

A review of the literature on the use of pulsed electric current to create electro-plastic effect in metal parts is performed. Inductor with a U-shaped magnetic core and pulsed current is investigated for processing thin-walled metal plates with rectilinear welds. With a saturated magnetic core relative magnetic permeability can be low, so using a magnetic core can be impractical. The aim of the work is to establish the influence of a magnetic core of an induction system on voltage, current and magnetic forces when reaching the eddy current density of 109 A/m2 in the weld of a non-magnetic thin-walled metal plate. A two-dimensional model of the induction system with and without the magnetic core is investigated here. Simulation of the distribution of electromagnetic fields with the reduction of the parameters of the two-dimensional model to three-dimensional is performed. A capacitor charged to a certain voltage is a source of pulsed currents in inductor winding. The equation of the electric circuit for determining the current in the inductor’s winding is solved. The influence of the dimensions of the magnetic core on voltage and currents in the inductor’s winding is determined. The influence of the magnetic core on the transients of voltages of capacitor and inductor, the currents in the winding and the weld of the metal non-magnetic plate, the magnetic forces in the weld is studied. The influence of the magnetic core on distribution of magnetic field strength, currents and magnetic forces on the surface of the plate in the area of the weld is studied. Ref. 13, Fig. 4, Table.

An analytical solution to the problem of a cup-cored coil located over a conducting plate with a hole

Pot-core coils are utilised in eddy current non-destructive testing (NDT) to detect defects in conducting materials. In this paper, an analytical solution to the problem of a cup-cored coil placed over a three-layer plate with an inner hole is obtained. Using the truncated region eigenfunction expansion (TREE) method, expressions for the magnetic vector potential of the filamentary coil, and final formulae for the impedance of the cylindrical coil, are derived. These formulae make it possible to model conducting magnetic and non-magnetic plates with an internal hole, a surface hole, a subsurface hole and a through hole. The final expressions in a closed form are implemented in MATLAB. The calculation results are verified using finite element method (FEM) models created with COMSOL Multiphysics, Finite Element Method Magnetics (FEMM) and Ansys Maxwell software packages. Very good agreement for the coil impedance components is obtained within the whole studied frequency range of 1 kHz to 100 kHz.

Transient quasi-3D magneto-thermal analytical solution in PM induction heating device

PurposeThis paper aims to develop a new quasi-three dimensional (3D) analytical model devoted to the study of nonlinear transient magneto-thermal coupled problems in permanent magnet (PM) transverse flux induction heating device (TFIHD).Design/methodology/approachThe presented work is based on analytical development of strongly coupled problem, including electromagnetic and thermal boundary problems. The electromagnetic problem is first solved by using the separation variables method to evaluate the induced currents in the nonmagnetic plate and the resulting power density loss distribution. The plate temperature profile is then obtained thanks to strong involvement of this magnetic model in a new analytical thermal model combining the separation of variables method and the Green’s functions transient regime analysis method. The coupled model is then used in a simulation procedure of the magneto-thermal process allowing taking into account the workpiece electrothermal nonlinear properties. The developed coupled model is validated by computing the performances of the studied PM TFIHD and comparing them to those obtained by finite element simulations.FindingAn efficient transient quasi-3D magneto-thermal analytical model is developed allowing rapid analysis of PM induction heating for core heating of parallelepiped parts. The developed model also allows fast and accurate simulations of nonlinear and transient three dimensional (3D) magneto-thermal phenomena for planar induction heaters.Research limitations implicationsThe developed quasi-3D magneto-thermal analytical model is limited to design induction heating devices of planar structure with PM inductors.Originality/valueA new transient quasi-3D magneto-thermal analytical model accounts for non-linearity and edge effect and helps to fast study and fast design of linear permanent magnet induction heating device.

ORTHODONTIC TREATMENT WITH Nd-Fe-B MAGNETS

The aim. The development of methodology for experimental and theoretical assessment of interaction forces between magnets in an orthodontic apparatus, the test of corrosion resistance of protective oxide and nitride coatings deposited on Nd-Fe-B magnets surface. Materials and methods. The Nd-Fe-B permanent magnets with saturation magnetization Ms≈1100 G and bilayer ZrN / ZrO2 coatings were used. To experimental measure of interaction forces between magnets the device was assembled on the base of analytical balance. The distance between the magnets was varied using non-magnetic plates. The ZrO2 and ZrN coatings have been analyzed for their corrosion properties in 0.9 % NaCl quasi-physiological solution. Results. An original method was proposed for calculating of magnetic interaction forces for materials with high magnetic anisotropy, which has good agreement with experimental measurement of forces. The theoretical model takes into account the size of the magnets and the mutual influence of their opposite faces. An increase of corrosion resistance of magnetic materials can be provided by zirconium oxide or nitride compounds, which contribute to inhibition of electrochemical corrosion of Nd-Fe-B magnets. Conclusions. A method for calculating of interaction forces between permanent magnets, which are used for correction of malocclusion in orthodontic, has been developed. The passivation of the Nd-Fe-B permanent magnets surface can be achieved by applying of bilayer ZrN / ZrO2 coating.

PENINGKATAN SENSITIVITAS SENSOR KOIL DATAR MEMPERGUNAKAN SOFT MAGNETIC VITROVAC

This study reports the design of non-magnetic plate thickness sensors based on Eddy Current principld in the form of flat coils. The principle used in the Eddy Current sensor is a change of mutual coil inductance due to the presence of objects in the magnetic field. The coil is made up of single and double layer coil designed using Corel Draw Software based on printed circuit board (PCB) material with dimensions of 152.4 mm x 101.6 mm, which has a track distance of 0.125 m. Single and double layer coil inductance evaluations are carried out using the EVB LDC 1000 L/V Converter module which converts plate thickness into inductance values. The addition of a 30 mm Vitrovac thin film mounted in the direction of the winding in the 2 mm diameter coil core has been carried out to increase the sensitivity value of the sensor which gives an increase in sensitivity value of S = 0.321 uH / mm or 33.2%. The coil is able to measure plate thickness up to 10mm well.

Permanent magnet linear induction heating device: new topology enhancing performances

PurposeThis work aims to study a new design of linear permanent magnet transverse flux induction heating devices of nonmagnetic parallelepipedic workpiece. In these topologies, the permanent magnet inductor produces a static magnetic field, and the workpiece to be heated is subjected to a linear movement. To study the magnetothermal process, a new analytical coupling method between the magnetic and thermal phenomena is developed. This analytical model described in this study takes into account the variation of the physical properties of the heated workpiece. The analytical results are compared with good agreement to those issued from finite elements simulations, as well as those issued from measurements on an actual prototype.Design/methodology/approachThe research methodology is based on analytical development of coupled problem, including the electromagnetic and thermal boundary problems. A strongly coupled magneto-thermal analytical model is developed; the time dependent magnetic problem is first solved by using the separation of variables method to evaluate the induced currents in the nonmagnetic plate and the resulting power density loss distribution. The plate temperature profile is then obtained, thanks to strong involvement of this magnetic model in a new analytical thermal model based on a synergy of separation of variables method and Green’s function transient regime analysis method.FindingsThe results show that an efficient transient magneto-thermal analytical model was developed allowing fast analysis of permanent magnet induction heater for deep heating of parallelepipedic workpieces. Developed model allows also fast and precise simulations of nonlinear and transient magneto-thermal phenomena for different types of permanent magnet induction heating devices.Practical implicationsThe developed magneto-thermal analytical model can be used for fast designing of permanent magnet linear induction heating devices for moving parallelepipedic nonmagnetic workpiece.Originality/valueA new analytical coupled model, including the electromagnetic and transient thermal boundary problem with additional algebraic equations and taking into account the nonlinearity, has been developed. The developed model accuracy was validated with a permanent magnet linear induction heating device. Developed coupled analytical model allows fast analysis and designing of such permanent magnet linear induction heating devices.

Reducing the Lift-Off Effect on Permeability Measurement for Magnetic Plates From Multifrequency Induction Data

Liftoff variation causes errors in eddy current measurement of nonmagnetic plates as well as magnetic plates. For nonmagnetic plates, previous work has been carried out to address the issue. In this paper, we follow a similar strategy, but try to reduce the lift-off effect on another index, zerocrossing frequency for magnetic plates. This modified index, termed as the compensated zero-crossing frequency, can be obtained from the measured multifrequency inductance spectral data using the algorithm we developed in this paper. Since the zero-crossing frequency can be compensated, the permeability of magnetic plates can finally be predicted by deriving the relation between the permeability and zero-crossing frequency from Dodd and Deeds method. We have derived the method through mathematical manipulation and verified it by both simulation and experimental data. The permeability error caused by liftoff can be reduced within 7.5%.

Casimir free energy and pressure for magnetic metal films

We examine the Casimir free energy and pressure of magnetic metal films, which are free-standing in vacuum, sandwiched between two dielectric plates, and deposited on either nonmagnetic or magnetic metallic plates. All calculations are performed using both the Drude and plasma model approaches to the Lifshitz theory. According to our results, the Casimir free energies and pressures calculated using both theoretical approaches are significantly different in the magnitude and sign even for thin films of several tens of nanometers thickness. Thus, for the Ni film of 47\,nm thickness deposited on a Fe plate the obtained magnitudes of the Casimir free energy differ by the factor of 5866. We show that the Casimir free energy and pressure of a magnetic film calculated using the plasma model approach do not possess the classical limit, but exponentially fast drop to zero with increasing film thickness. If the Drude model approach is used, the classical limit is reached for magnetic films of about 150\,nm thickness, but the Casimir free energy remains nonzero in the limit of ideal metal, contrary to expectations. For the plasma model approach the Casimir free energy of a film vanishes in this case. Numerical computations are performed for the magnetic films made of Ni, nonmagnetic plates made of Cu and Al, and magnetic plates made of Fe using the tabulated optical data for the complex indexes of refraction of all metals. The obtained results can be used for a discrimination between the plasma and Drude model approaches in the Casimir physics and in the investigation of stability of thin films.

Magneto-gravitational convection in a vertical layer of ferrofluid in a uniform oblique magnetic field

The stability of base gravitational convection in a layer of ferrofluid confined between two vertical wide and tall non-magnetic plates, heated from one side, cooled from the other and placed in a uniform oblique external magnetic field is studied. Two distinct mechanisms, thermo-gravitational and thermo-magnetic, are found to be responsible for the appearance of various stationary and wave-like instability modes. The characteristics of all instability modes are investigated as functions of the orientation angles of the applied magnetic field and its magnitude for various values of magnetic parameters when both the thermo-magnetic and gravitational buoyancy mechanisms are active. The original three-dimensional problem is cast in an equivalent two-dimensional form using generalised Squire’s transformations, which significantly reduces a computational cost. Subsequently, full three-dimensional instability patterns are recovered using the inverse Squire’s transformation, and the optimal field and pattern orientations are determined.

Calculation of the Eddy-Current Flow Around a Cylindrical Through-Hole in a Finite-Thickness Plate

A semianalytical solution to the eddy-current induction problem in a conducting, nonmagnetic plate near a cylindrical through-hole is derived by means of the second-order vector potential and the domain truncation technique. The construction of a solution, which simultaneously satisfies the field continuity across the cylindrical surface of the hole and the planar interfaces of the plate, proves to be a very challenging problem, and thus, a special superposition of partial subsolutions is proposed. The presented solution is part of a more general development aiming at the calculation of the probe interaction with material flaws located in the vicinity of the hole by means of the integral equation formalism. These tasks will be the subject of a future paper. The comparison of the semianalytical results against both finite-element simulations as well as experimental data demonstrates excellent agreement.

Thermomagnetic convection in a layer of ferrofluid placed in a uniform oblique external magnetic field

AbstractLinear stability of magnetoconvection of a ferromagnetic fluid contained between two infinite differentially heated non-magnetic plates in the presence of an oblique uniform external magnetic field is studied in zero gravity conditions. The thermomagnetic convection that arises is caused by the spatial variation of magnetisation occurring due to its dependence on the temperature. The critical values of the governing parameters at which the transition between motionless and convective states is observed are determined for various field inclination angles and for fluid magnetic parameters that are consistently chosen from a realistic experimental range. It is shown that, similar to natural paramagnetic fluids, the most prominent convection patterns align with the in-layer component of the applied magnetic field but in contrast to such paramagnetic fluids the instability patterns detected in ferrofluids can be oscillatory. It is also found that, contrary to paramagnetic fluids, the stability characteristics of magnetoconvection in ferrofluids depend on the magnitude of the applied field which becomes an additional parameter of the problem. This is shown to be due to the nonlinearity of the magnetic field distribution within the ferrofluid.

Fundamental performance of Magnetic Compound Fluid (MCF) wheel in ultra-fine surface finishing of optical glass

This study investigates a new semi-fixed-abrasive, ultra-fine finishing method for optical glass using a magneticcompound fluid (MCF) wheel. This MCF wheel generates a thin, uniform MCF slurry layer on the entire circumferentialsurface of a ring-shaped permanent magnet placed between two non-magnetic plates. The MCF slurry is composed ofnano-sized magnetite particles, micron-sized iron particles, several 10 μm-sized α-cellulose fibres and sub-micron-sizedabrasive particles that react to the magnetic field. Following modifications to the design of the MCF, experiments wereconducted to evaluate the performance of the modified wheel in spot-polishing fused silica glass. This paper describes themodifications to the MCF wheel and the experimental setup used to measure its performance. The improvement of themodified wheel over the unmodified wheel in terms of material removal and surfaces roughness is experimentallyconfirmed. The effects of the wheel rotational speed and the clearance between the wheel and the workpiece on materialremoval and the workpiece surface roughness are investigated. The polishing forces are measured, the structure of the MCFslurry is examined and the magnetic field distribution is analysed. A model of material removal in polishing with themodified MCF wheel is developed. The results indicate the following: (1) more material was removed, i.e., greater spotdepths, and better surfaces were obtained in the regions that were near the edges of the magnet; (2) the modified MCF wheelperformed much better than the unmodified wheel in terms of material removal and surface roughness, e.g., 3.1 μm vs. 1.7μm for the maximum spot depth, 0.04 mm3 vs. 0.0088 mm3 for the volume of material removed and Ra = 5.624 nm vs.14.67 nm for the surface roughness; (3) a better work surface and greater material removal were obtained with smallerworking clearances and higher wheel rotational speeds.