Magnetic Cloaking Research Articles

Structure, electronic and magneto-elastic properties of rare earth nitrides Ln3NIn (Ln = Nd, Pm, Sm, Eu, Gd, Tb) anti-perovskites

Electronic structure and magneto-elastic characteristics of lanthanide nitrides Ln3NIn (Ln = Nd-Tb) are explored by DFT. The structural reported data are reliable with the experimental outcomes and the observed structural characteristics drop from Nd to Tb due to the small atomic radii of Tb compare to Nd. Electrical resistivity and electronic characteristics demonstrate that all the investigated compounds are metallic. The resistivity at 300 K emphasizes that they are effective conductors. These compounds are ideal for situation where large acting load are expected such as implants that bear a disproportionate amount of weight as endoprostheses for hip, knee and as screw, nails and plates, especially when structural materials need to have sufficient bending fatigue strength for skeletal reconstruction. These compounds are antiferromagnetic and their Neel temperatures are 18, 15, 39, 45, 27, and 33 K, respectively. These compounds might be therefore feasible for magnetic cloaking and storage technologies.

Теоретический анализ задач магнитной маскировки с использованием эллиптических метаматериалов

The conjugation problem and control problems for the 3D model of magnetostatics are considered. These problems are related to the design of three-dimensional magnetic cloaking shells. An elliptical metamaterial is chosen as a cloaking medium that fills a region which is topologically equivalent to a spherical layer. The solvability of boundary and control problems is proved, an optimality system is derived that describes the necessary conditions for an extremum, some properties of optimal solutions are established.

Численная оптимизация в задачах проектирования многослойных магнитных маскировочных оболочек

A multiparameter optimization problem of magnetic cloaking is solved for a two-dimensional model of magnetostatics. This problem arises when designing cylindrical multilayer cloaking devices filled with anisotropic or isotropic magnetic media with tensor, in the general case, magnetic permeabilities. Applying the optimization method for solving inverse problems the considered problem of magnetic cloaking is reduced to a finite-dimensional extremum problem. The results of applying the developed numerical algorithm based on the particle swarm optimization method to solve the extremum problem confirm its high efficiency and make it possible to establish the important property of the obtained optimal solutions.

First principles calculation to investigate the effect of Mn substitution on Cu site in CeCu3-x Mn x V4O12 (x = 0, 1, 2 and 3) system.

Structural, electronic, elastic and magnetic properties of CeCu3-x Mn x V4O12 (x = 0, 1, 2 and 3) system have been carried out through DFT using GGA, GGA+U and HF potential. The investigation of structural optimization reveals that lattice parameters of the understudy system is reliable with the reported results and are increasing with the Mn substitution due to their greater atomic radii as compare to Cu atom. Both the cohesive energy and the enthalpy show that CeCu3V4O12 is the most thermodynamically stable among these compounds. When Mn is replaced by Cu in these compounds, not only it become semi-metals, but the host compound also changes from non-magnetic to anti-ferromagnetic and their electrical resistance provides further credence to their electronic behavior. Mechanical stability, anisotropy, and ductility are all demonstrated through the elastic characteristics of these compounds. Due to anti-ferromagnetic ductile nature of the Mn base compounds, it is expected that the compounds in the system may use for spintronic application and in magnetic cloaking devices.

First-principles calculations to investigate physical properties of three magnetic sub lattice CaCu3Mn4-xIrxO12 (x = 0, 2 and 4) system via symmetry evaluation

Structural, electronic, elastic and magnetic properties of CaCu3Mn4-xIrxO12 (x = 0, 2 and 4) along with the optical properties of CaCu3Mn4O12 perovskites have been carried out in the framework of density functional theory (DFT). The investigation of structural optimization reveals that CaCu3Mn2Ir2O12 is stable in Pn-3 space group and CaCu3Mn4O12 and CaCu3Ir4O12 perovskites are stable in Im-3 space group. The cohesive energy and enthalpy of formation reveal the stability of these compound and shows that CaCu3Mn2Ir2O12 is more stable than the rest compounds. Substitution of Ir by Mn not only transforms these compounds from semiconductor to metallic nature but also transform the host compound from ferrimagnetic to anti-ferromagnetic via spin glass state. The DFT electronic behavior is also supported by the electrical resistivity. Elastic properties demonstrate the mechanical stability, anisotropic and ductile nature of these compounds. The optical properties indicate that CaCu3Mn4O12 is optically active for infrared electromagnetic radiations and could be used in optical devises. The ferrimagnetic ductile nature of CaCu3Mn4O12, spin glass and anti-ferromagnetic nature of CaCu3 Mn2Ir2O12 and CaCu3Ir4O12 makes these perovskites suitable candidates for spintronic and magnetic cloaking applications.

Mechanically Stable Magnetic Metallic Materials for Biomedical Applications.

The structural, electrical, and magneto-elastic properties of lanthanide base nitride (Ln = Dy-Lu) anti-perovskites were investigated using density functional theory (DFT). The reported structural outcomes are consistent with the experiment and decrease from Dy to Lu due to the decrease ofatomic radii of Ln atoms. According to the electronic band profile, the metallic characteristics of these compounds are due to the crossing over of Ln-f states at the Fermi level and are also supported by electrical resistivity. The resistivity of these compounds at room temperature demonstrates that they are good conductors. Their mechanical stability, anisotropic, load-bearing, and malleable nature are demonstrated by their elastic properties. Due to their metallic and load-bearing nature, in addition to their ductility, these materials are suitable as active biomaterials, especially when significant acting loads are anticipated, such as those experienced by such heavily loaded implants as hip and knee endo-prostheses, plates, screws, nails, dental implants, etc. In thesecases, appropriate bending fatigue strength is required in structural materials for skeletal reconstruction. Magnetic properties show that all compounds are G-type anti-ferromagnetic, with the Neel temperatures ranging from 24 to 48 K, except Lu3Nin, which is non-magnetic. Due to their anti-ferromagnetic structure, magnetic probes cannot read data contained in anti-ferromagnetic moments, therefore, data will be unchanged by disrupted magnetic field. As a result, these compounds can be the best candidates for magnetic cloaking devices.

Conformal metamaterial coats for underwater magnetic-acoustic bi-invisibility

Invisible coats inspired by metamaterials have been widely explored for different physical quantities and even with multifunctional response capabilities. In particular, a magnetic cloak has gained special attention for high practicability when compared with its electromagnetic counterparts. In this work, we report a bi-physical metamaterial invisible coating technique that could effectively hide underwater objects from being detected via both magnetic fields and acoustic waves. An ultra-thin coat could work for objects having irregular shapes like squares, greatly broadening potential practical applications. The bilayer magnetic cloaking technique is fully exploited to cast a spatially dependent permeability profile, which could quasi-statically balance out the diamagnetic response of irregular-shaped metals based on field “scattering” cancellation. Integrated with this magnetic cloak, an ultrathin acoustic metasurface made of periodic microbubbles is developed to achieve broadband acoustic absorption for acoustic stealth. This integrated magnetic-acoustic bi-physical conformal coat may lead to important applications not only for military purposes but also for civilian apparatus in shielding the field and wave disturbances, for example, in medical scanning.

New anti-ferromagnetic tri-transition quaternary perovskites for magnetic cloaking and spintronic applications

Magnetism in new tri-transition A-site ordered quaternary perovskites ACu3V4O12 (A = Mn and Cu) are studied using generalized gradient approximation with Hubbard potential (GGA + U) in the domain of density functional theory. The effective Heisenberg model estimates the magnetic exchange coupling constants (J1, J2 and J3) between the spins of Mn and Cu sites. The exchange constants J1 and J3 in MnCu3V4O12 and Cu(1)Cu3(2)V4O12 reveal their long rang interactions through super exchange mechanism. The ground state magnetic order is explained from the optimized energy curves; which reveal the G-type anti-ferromagnetic (AFM) order of MnCu3V4O12 and A-type AFM order of Cu(1)Cu3(2)V4O12. Heisenberg model and magnetic susceptibility are in well agreement in the estimation of Neel temperature 15.1/50 and 15.6/25 K respectively. There is a strong correlation between the magnetism of the A-site atoms (Mn, Cu(1), and Cu(2)), as well as the metallic character of the B-site atoms (V, as well as the tiny contribution of A-site Cu(2) and Mn atoms). Due to AFM metallic nature it is expected that these compounds could be used in spintronic technology and magnetic cloaking devices.

Critical State Theory for the Magnetic Coupling between Soft Ferromagnetic Materials and Type-II Superconductors.

Improving our understanding of the physical coupling between type-II superconductors (SC) and soft ferromagnetic materials (SFM) is the root for progressing to the application of SC-SFM metastructures in scenarios such as magnetic cloaking, magnetic shielding, and power transmission systems. However, in the latter, some intriguing and yet unexplained phenomena occurred, such as a noticeable rise in the SC energy losses, and a local but not isotropic deformation of its magnetic flux density. These phenomena, which are in apparent contradiction with the most fundamental theory of electromagnetism for superconductivity, that is, the critical state theory (CST), have remained unexplained for about 20 years, given the acceptance of the controversial and yet paradigmatic existence of the so-called overcritical current densities. Therefore, aiming to resolve these long-standing problems, we extended the CST by incorporating a semi-analytical model for cylindrical monocore SC-SFM heterostructures, setting the standards for its validation with a variational approach of multipole functionals for the magnetic coupling between Sc and SFM materials. It is accompanied by a comprehensive numerical study for SFM sheaths of arbitrary dimensions and magnetic relative permeabilities , ranging from (NiZn ferrites) to = 350,000 (pure Iron), showing how the AC-losses of the SC-SFM metastructure radically changes as a function of the SC and the SFM radius for . Our numerical technique and simulations also revealed a good qualitative agreement with the magneto optical imaging observations that were questioning the CST validness, proving therefore that the reported phenomena for self-field SC-SFM heterostructures can be understood without including the ansatz of overcritical currents.

Ultrathin Conformal Magnetic Invisible Cloak for Irregular Objects.

Magnetic invisible cloaking has been previously demonstrated but only limited to objects with rotational geometries either in spherical or cylindrical shapes, for which the classic analytical bilayer scheme could be strictly applied to design the hiding coat. In this work, we show that a quasi-static cloaking effect could be achieved for irregular objects, e.g., metals with sharp edges, using a numerical optimization scheme. In the quasi-static limit, it is unambiguously proved that the disturbance of the irregular geometries could be well compensated by the inhomogeneous distribution of the soft ferromagnetic (FM) layer either in permeability values or in shapes under the framework of a bilayer cloak. An FM mesh coat with a constant thickness of 0.5 mm was successfully engineered to meet the specific requirements. Experimentally, good cloaking performance with a field disturbance of less than 0.5% has been achieved for a 2 × 2 × 5 cm3 brass bar in a wide frequency range from ∼10 to 250 kHz. A commercial metal scanner was also applied to verify the practical potential. The general strategy to hide almost arbitrary objects was discussed in the end. In principle, the numerical conformal coat engineered by the composite material proposed here could be broadly extended for objects with various geometries.

Optimization-Based Numerical Analysis of Three-Dimensional Magnetic Cloaking Problems

Inverse problems for a three-dimensional magnetostatic model arising in the design of axisymmetric multilayered shielding and cloaking devices are stated. Assuming that the designed device consists of a finite number of spherical layers, each filled with a homogeneous isotropic medium, an optimization-based numerical algorithm is proposed for solving the problems. As a result, the considered inverse problems are reduced to finite-dimensional optimization ones in which the role of controls is played by the magnetic permeabilities of each elementary layer. The desired controls are found by applying particle swarm optimization. By analyzing numerical results, it is shown that the obtained optimal solutions correspond to cloaking devices having the highest efficiency in the considered class of devices and provide the simplicity of technical implementation.

Numerical Analysis of Two-Dimensional Magnetic Cloaking Problems Based on an Optimization Method

We study inverse problems of magnetostatics that arise when designing two-dimensional multilayered shielding and cloaking devices. It is assumed that the device to be designed has the form of a circular shell consisting of finitely many layers, each filled with a homogeneous isotropic medium. Using an optimization method, the inverse problems under consideration are reduced to finite-dimensional control problems in which the constant permeabilities of the layers play the role of control parameters. A numerical algorithm based on the particle swarm method is proposed for solving the control problems. Some properties of the algorithm proposed and of the resulting optimal solutions are established. Results of computational experiments are discussed.

Magnetic\u2013acoustic biphysical invisible coats for underwater objects

Magnetic fields and acoustic waves are the two fundamental measures to perceive underwater objects, which, however, have never been simultaneously handled before. In this work, we propose and demonstrate a biphysical submillimeter-thick metamaterial coat that can simultaneously make underwater objects invisible to both magnetic fields and acoustic waves. The conformal coat is a subtle integration of an open-cavity acoustic absorber made of a dissipative acoustic metasurface (AMS) and a bilayer magnetic cloak. Experimentally, a magnetic cloaking effect with a field disturbance ratio of <0.5% is obtained over a broad-frequency range (10–250 kHz), and the compound metamaterial coat can strongly attenuate ultrasonic waves with a near-unity absorptivity. The magnetic subcoat can be freely combined with various AMS layers to achieve a wideband acoustic stealth effect for different spectral regimes. This work may open up a new way to build multifunctional devices for various waterborne applications.

Active magnetic cloaking with a dipole

We theoretically propose and experimentally demonstrate an active quasi-static magnetic cloak enabled by a single magnetic dipole. The cloaking effect can be achieved by active cancelation of the background magnetic field using the magnetic dipole. Compared with previous multi-unit designs, the single-unit design drastically reduces the number of control units required. It has potential applications in realizing the homogeneous field in wireless power transfer, magnetic resonance imaging, and other diffusion-based applications.

Optimization method in 2D magnetic cloaking problems

Optimization method in 2D magnetic cloaking problems

Theoretical Analysis of the Magnetic Cloaking Problem Based on an Optimization Method

Control problems are considered for a model of magnetic scattering on a permeable anisotropic obstacle shaped as a spherical layer. Such problems arise in developing technologies for designing magnetic cloaking devices when the corresponding inverse problems are solved by an optimization method. The solvability of the direct and extremal problems for the model in question is proved and the optimality system is derived. Its analysis permits obtaining sufficient conditions on the initial data which ensure the local uniqueness and stability of the optimal solutions.

Static Magnetic Cloak without a Superconductor

Similar to its electromagnetic counterpart, magnetic cloaking also has very important technological applications. However, the traditional method to build a static magnetic cloak requires the use o ...

Three-dimensional magnetic cloak working from d.c. to 250 kHz.

Invisible cloaking is one of the major outcomes of the metamaterial research, but the practical potential, in particular for high frequencies (for example, microwave to visible light), is fatally challenged by the complex material properties they usually demand. On the other hand, it will be advantageous and also technologically instrumental to design cloaking devices for applications at low frequencies where electromagnetic components are favourably uncoupled. In this work, we vastly develop the bilayer approach to create a three-dimensional magnetic cloak able to work in both static and dynamic fields. Under the quasi-static approximation, we demonstrate a perfect magnetic cloaking device with a large frequency band from 0 to 250 kHz. The practical potential of our device is experimentally verified by using a commercial metal detector, which may lead us to having a real cloaking application where the dynamic magnetic field can be manipulated in desired ways.

Magnetic cloaking by a paramagnet/superconductor cylindrical tube in the critical state

Cloaking of static magnetic fields by a finite thickness type-II superconductor tube being in the full critical state and surrounded by a coaxial paramagnet shell is studied. On the basis of exact solutions to the Maxwell equations, it is shown that, in addition to previous studies assuming the Meissner state of the superconductor constituent, perfect cloaking is still realizable at fields higher than the field of full flux penetration into the superconductor and for arbitrary geometrical parameters of both constituents. It is also proven that simultaneously the structure is fully undetectable under the cloaking conditions. Different from the case of the Meissner state, the cloaking properties in the application relevant critical state are realized, however, only at a certain field magnitude.

Superconductor–ferromagnetic metamaterials for magnetic cloaking and concentration

Superconducting–ferromagnetic hybrid systems with effective magnetic properties that allow the cloaking and concentration of static magnetic fields have been recently introduced. These metamaterials consist of different arrangements of superconducting and ferromagnetic pieces whose performance and feasibility depend on the involved materials, their geometrical distribution and the number of pieces constituting the system. In this work we study the performance of these metamaterials for magnetic field cloaking and concentration as a function of the number of pieces and their magnetic properties, concluding that there is an optimum range of parameters within which a good compromise between performance and feasibility of the proposed metamaterials is obtained.