Ferromagnetic Body Research Articles

Nondiagonalizable and nondivergent susceptibility tensor in the Hamiltonian mean-field model with asymmetric momentum distributions.

We investigate the response to an external magnetic field in the Hamiltonian mean-field model, which is a paradigmatic toy model of a ferromagnetic body and consists of plane rotators like XY spins. Due to long-range interactions, the external field drives the system to a long-lasting quasistationary state before reaching thermal equilibrium, and the susceptibility tensor obtained in the quasistationary state is predicted by a linear response theory based on the Vlasov equation. For spatially homogeneous stable states, whose momentum distributions are asymmetric with 0 means, the theory reveals that the susceptibility tensor for an asymptotically constant external field is neither symmetric nor diagonalizable, and the predicted states are not stationary accordingly. Moreover, the tensor has no divergence even at the stability threshold. These theoretical findings are confirmed by direct numerical simulations of the Vlasov equation for skew-normal distribution functions.

A local meshless collocation method for solving Landau–Lifschitz–Gilbert equation

This paper is concerned with a meshless simulation of the two dimensional Landau–Lifschitz–Gilbert (LLG) equation which describes the dynamics of the magnetization inside a ferromagnetic body. After elimination of the time variable by a suitable finite difference scheme, a combination of the meshless local RBF and the finite collocation method is used for spatial discretizations of the field variables. Three test problems are numerically investigated and the results reveal the effectiveness of the method.

Investigation of magnetomechanothermodiffusive processes in ferromagnetic body at given diffusing substance concentration on the surface

The input equations describing the electromagnetic field interaction with the substance are suggested. By means of the methods of the similarity and dimensional theory, the system of equations of magnetomechanothermodiffusion and mechanics is reduced to a dimensionless form. Quantitative analysis of dimensionless criteria for the case of hydrogen diffusion in ferrum is carried out for three different meanings of initial temperature. The phenomena, for which dimensionless parameters are much less than a unit are not considered. A reduced coupled system of equations of the model for determination the concentration and temperature is written.

Application of Full-scale Experiments for Structural Study of High-rise Buildings

The paper presents the application of full-scale-model experiments to develop software and design a device for determining the degree of reinforcement bar rusting in concrete elements of high-rise buildings. Operation of the designed device is based on the dependence of the electromagnetic field surrounding a ferromagnetic body on its geometrical parameters and reduction of electromagnetic properties of the ferromagnet by oxidation. To receive primary information about the electromagnetic field an original measuring device is used, which is a matrix of high-precision electromagnetic transducers. In order to determine their position in relation to the control object distance sensors are used. The measurement results are transmitted to a computer model that is adjusted so that the results of modeling the electromagnetic field at the locations of transducers agreed with the results of direct measurements. The required model parameters are the geometric dimensions of the reinforced bar.To raise the measuring device to the height of the building structure it is proposed to install it on a quadrotor.

Application of Block Elements Method to Calculate the Electromechanical Systems Magnetic Field and Force Characteristics

The problem of two-dimensional magnetic field during the calculation in electromechanical systems comprising a ferromagnetic body with nonlinear magnetic characteristics is described. New geometric patterns in the form of block finite and infinite elements of arbitrary shape are proposed to be used in the simulation of magnetic field in a piecewise homogeneous medium electromechanical systems, in which an error can be controlled to perform the linearization of the material characteristics of ferromagnets. Two scalar potentials are used to find the field. Potentials form a complex magnetic potential, which is defined on the boundaries of block elements. Cauchy's integral formula is used for the purpose. The system of algebraic equations for the nodal values of the potentials on the boundaries is solved using the software developed by minimizing the functional errors. The results of the simulation of the magnetic field of the induction motor with a complicated geometry of magnetic systems are shown. The proposed method allows simplifying and improving the accuracy of calculation of the magnetic field in the design of electromechanical systems containing moving ferromagnetic elements.

Undetected intraocular metallic foreign body causing hyphema in a patient undergoing MRI: a rare occurrence demonstrating the limitations of pre-MRI safety screening

The case reported is of a 47-year-old man with an undetected ferromagnetic metallic intraocular foreign body in the right eye who underwent elective MR examinations for chronic neck and low back pain. The patient underwent the MR scans and subsequently developed blurred vision in his right eye caused by a hyphema associated with an anterior chamber metallic foreign body. Case reports of orbital injuries in patients with intraocular metallic foreign bodies undergoing MRI are rare, with only one prior report in the radiology literature. While the incidence of intraocular foreign bodies causing injury in patients undergoing MRI is likely rare even among patients with foreign bodies, this case demonstrates that complications from an IMFB can potentially have a subtle presentation. Our case also illustrates potential limitations of pre-MRI safety questionnaires, particularly pertaining to a patient's understanding of the thoroughness of foreign body removal.

<i>"In Situ"</i> Evaluation of Ferromagnetic Bodies Magnetic Characteristics

The B-H characteristic of an iron body material influences the magnetic field measured in the air. On principle, one can pose the problem of B-H relation determination, by making measurements of the magnetic induction in the neighbourhood of the body. Unfortunately, we have an ill-posed inverse magnetic field problem, for which there is possible that, big variations of the BH characteristic to produce only very small modifications of the magnetic field in the air. It is essential to use a sufficiently sensitive computation procedure in order to produce credible results. This paper proposes a device for the B-H characteristic evaluation, admitting that inside the ferromagnetic bodies the magnetic field distribution is not uniform.

Nonlinear response for external field and perturbation in the Vlasov system.

A nonlinear response theory is provided by use of the transient linearization method in the spatially one-dimensional Vlasov systems. The theory inclusively gives responses to external fields and to perturbations for initial stationary states, and is applicable even to the critical point of a second-order phase transition. We apply the theory to the Hamiltonian mean-field model, a toy model of a ferromagnetic body, and investigate the critical exponent associated with the response to the external field at the critical point in particular. The obtained critical exponent is the nonclassical value 3/2, while the classical value is 3. However, interestingly, one scaling relation holds with another nonclassical critical exponent of susceptibility in the isolated Vlasov systems. Validity of the theory is numerically confirmed by directly simulating temporal evolutions of the Vlasov equation.

Testing thick nickel coatings applied on two-layer (nonferromagnet-ferromagnet) bases by magnetodynamic thickness gauges

The regularities of the formation of informative signals from magnetodynamic transducers that are used for measuring the thickness of thick nickel coatings that are applied on two-layer (nonferromagnet-ferromagnet) bases have been determined. Based on the regularities, the dependence of an additional error of an MTH-1 instrument on the magnetization of a ferromagnetic body and thicknesses of nickel coating and the nonferromagnetic interlayer between the coating and body has been determined relative to combustors of liquid-propellant engines. Techniques and facilities for measurement and automatic compensation of the additional error of the MTH-1 instrument have been developed.

Enhanced spontaneous magnetization in the core of nickel nanoparticles

It is conceptually expected that the decrease of the size of a ferromagnetic body may narrow the energy bands of 3d electrons, so that the spontaneous magnetization Ms will increase from the value for the bulk to that corresponding to the moment of individual magnetic ion. However, most experiments for nickel nanoparticles show Ms to decrease with the decreasing particle size. Such a phenomenon for ferrimagnetic nanoparticles may be explained by a core–shell model with the spontaneous magnetization Ms having the value of the bulk in the core and zero in the shell. In the present work, the size distribution of an assembly of fcc nickel nanoparticles is determined by transmission electron microscopy to well follow a normal probability density function. Using such a function, the measured magnetization curves of the assembly are simulated by the core–shell model. It has been found that although the average Ms is much smaller than that of the bulk, Ms in the core turns out to be much larger than that in the bulk, which seems to support the above-mentioned expectation. The enhanced Ms in the core might result from the effect of core–shell boundary, which narrows the energy bands of 3d electrons of the nickel core. Nevertheless, the magnetic core–shell structure itself is difficult to be completely understood at the moment.

Magnetic fluid with a spherical ferromagnetic body in a uniform magnetic field. Theory and experiment

Magnetic fluid with a spherical ferromagnetic body in a uniform magnetic field. Theory and experiment

Scalar Potential Formulations for Magnetic Fields Produced by Arbitrary Electric Current Distributions in the Presence of Ferromagnetic Bodies

In this paper it is shown how to analyze stationary or quasistationary magnetic fields due to arbitrary distributions of electric current in terms of single-valued scalar potentials. The total scalar potential in a specified region outside the magnetic material bodies, not containing electric currents, is obtained by superposing two single-valued Laplacian scalar potentials. One is produced by the given current distribution in an unbounded space and is determined from the free-space values of the normal component of the magnetic field intensity over the region boundary. The other one is defined in the entire region outside the magnetic bodies and is employed in order to satisfy the boundary conditions. When the magnetic bodies can be considered to be linear and homogeneous or piecewise homogeneous, with no electric current within them, the field inside the bodies can also be expressed in terms of Laplacian scalar potentials. If the material of the bodies can be approximated to be ideal ferromagnetic, then the exterior field problem is a Dirichlet problem and is solved independently of the field inside the bodies. The Neumann boundary condition for the interior field problem is provided from the solution of the exterior problem. Differential equation and integral equation formulations, as well as an illustrative application example, are presented. Since the resultant field is computed in terms of only single-valued scalar potentials, the solution techniques based on the formulations presented in this paper are considerably more efficient than those in usual solution methods.

Variable reluctance harvester for applications in railroad monitoring

We present the design, realization, and testing of a variable reluctance energy harvester for the detection of moving ferromagnetic parts, e.g. the wheels of a train while passing over a train passage detector. Measurements were done to determine the output voltage, the energy output per event and the power output with the frequency of the moving ferromagnetic body. Results are compared with finite element analysis (FEA) to estimate the change in magnetic flux and the output voltages. A maximum energy output of 131 μJ per pulse was measured for a simulated condition of a train wheel passing with a speed of 81.5 km/h, which results in a mean output power of 5.9 mW, with a spacing of 10 mm between wheel and the reluctance circuit. This shows that the variable reluctance principle, a well-known method used for numerous sensor applications, is also a comfortable, energy-autonomous and reliable method to detect passing train wheels or other moving ferromagnetic parts, with a simple setup and fairly high useable output power.

Analysis of potentialities of coil electromagnetic accelerators for the accelerating of ferromagnetic particles

The paper presents an analysis of coil electromagnetic accelerators. Physical limits on the maximum acceleration imparted to a ferromagnetic body are defined. Mathematical modeling of a single-stage coil electromagnetic accelerator has been carried out including three-dimensional simulation of the particle trajectory. The influence of parameters of traction coils, the initial conditions and the particle material on the final speed is analyzed.

Magnet Ingestion

In their article, the authors provide a selective review of the literature based on a PubMed search (1). The selected publications include retrospective studies, reviews, and recommendations. They also discuss the ingestion of magnets in adults, but the majority of such cases occur in children. Ingesting this type of foreign body does, however, entail particular risks. If a magnet is swallowed it should not cause any further problems, depending on its size, shape, and surface consistency. Swallowing several magnets, however, or at least one magnet and a further ferromagnetic body can lead to life-threatening complications (2, 3). A report published by the US Centers for Disease Control and Prevention presents 20 cases in the US between 2003 and 2006; perforation occurred in 90% of cases, and volvulus with subsequent bowel ischemia and sepsis with a fatal outcome in one case (2). The question is whether in such cases, an indication exists for emergency esophagogastroduodenoscopy after conventional radiological diagnostic evaluation, and if queried early surgical intervention, before gastrointestinal complications can develop (3, 4).

Undisclosed and undetected foreign bodies during MRI screening resulting in a potentially serious outcome

The risks associated with performing magnetic resonance imaging (MRI) examinations in patients with ferromagnetic foreign bodies are well known. Accordingly, screening procedures are implemented to identify items that may pose hazards to patients and other individuals before allowing them to enter the MRI system room. This report describes a patient who, despite undergoing proper MRI screening procedures, did not disclose the presence of ferromagnetic foreign bodies, which resulted in a potentially serious outcome.

Free surface of magnetic fluid with a spherical ferromagnetic body in a uniform magnetic field

Free surface of magnetic fluid with a spherical ferromagnetic body in a uniform magnetic field

A study of a magnetic field for a sensor for detection of ferromagnetic bodies in the interior of a steel pipe

A design of a sensor that monitors the presence of ferromagnetic bodies moving inside steel pipes is presented. Calculation of the magnetic field of the sensor is carried out with the help of the ELCUT program, taking into account nonlinearity of magnetic characteristics of pipe material. An estimate is made of the signal level obtained as a result of interaction between a moving ferromagnetic body and the sensor magnetic field.

Magnetization dynamics, gyromagnetic relation, and inertial effects

The gyromagnetic relation—that is, the proportionality between the angular momentum L→ and the magnetization M→—is evidence of the intimate connections between the magnetic properties and the inertial properties of ferromagnetic bodies. However, inertia is absent from the dynamics of a magnetic dipole: The Landau–Lifshitz equation, the Gilbert equation, and the Bloch equation contain only the first derivative of the magnetization with respect to time. In order to investigate this paradoxical situation, the Lagrangian approach, proposed originally by Gilbert, is revisited keeping an arbitrary nonzero inertia tensor. The corresponding physical picture is a generalization to three dimensions of Ampère’s hypothesis of molecular currents. A dynamic equation generalized to the inertial regime is obtained. It is shown how both the usual gyromagnetic relation and the well-known Landau–Lifshitz–Gilbert equation are recovered in the kinetic limit, that is, for time scales longer than the relaxation time of the angular momentum.

Localization of Electromagnetic Force Based on Material Models

Various candidates are known for electromagnetic stress in material media that all coincide in free space with the Maxwell's stress tensor. Although the situation provides various total force computation methods it leaves ambiguous the concept of electromagnetic force density. Instead of considering electromagnetic force per unit of volume we restrict the localization to subvolumes of material bodies. This way classical dipole models for the basic material elements yields uniquely defined local electromagnetic force. The approach is demonstrated by computing the magnetic force on a ferromagnetic body in contact with a permanent magnet.