Showing papers on "Magneto published in 2016"

Enhanced magnetic energy harvesting properties of magneto-mechano-electric generator by tailored geometry

Abstract: By tailoring the truncated shape of a cantilever structured magneto-mechano-electric (MME) generator that is composed of a piezoelectric single crystal fiber composite and a magnetostrictive Ni plate, a superior output harvesting power density of over 680% was obtained as compared to a typical rectangular shaped generator. The effect of the MME generator's shape on the strain distribution induced by magnetostriction and vibration characteristics and harvesting properties were simulated by finite element analysis modeling and confirmed experimentally, respectively. The truncated shape was effective for not only utilizing a more uniform in-plane strain distribution in the active piezoelectric area but also magnifying the flexural vibration amplitude, which in turn can make the generator more powerful under tiny magnetic oscillations.

Tunable magneto-granular phononic crystals

Abstract: This paper reports on the study of the dynamics of 1D magneto-granular phononic crystals composed of a chain of spherical steel beads inside a properly designed magnetic field. This field is induced by an array of permanent magnets, located in a holder at a given distance from the chain. The theoretical and experimental results of the band gap structure are displayed, including all six degrees of freedom for the beads, i.e., three translations and three rotations. Experimental evidence of transverse-rotational modes of propagation is presented; moreover, by changing the strength of the magnetic field, the dynamic response of the granular chain is tuned. The combination of non-contact tunability with the potentially strong nonlinear behavior of granular systems ensures the suitability of magneto-granular phononic crystals as nonlinear, tunable mechanical metamaterials for use in controlling elastic wave propagation.

Free vibration analysis of magneto-electro-elastic microbeams subjected to magneto-electric loads

Abstract: Different types of actuating and sensing mechanisms are used in new micro and nanoscale devices. Therefore, a new challenge is modeling electromechanical systems that use these mechanisms. In this paper, free vibration of a magnetoelectroelastic (MEE) microbeam is investigated in order to obtain its natural frequencies and buckling loads. The beam is simply supported at both ends. External electric and magnetic potentials are applied to the beam. By using the Hamilton's principle, the governing equations and boundary conditions are derived based on the Euler–Bernoulli beam theory. The equations are solved, analytically to obtain the natural frequencies of the MEE microbeam. Furthermore, the effects of external electric and magnetic potentials on the buckling of the beam are analyzed and the critical values of the potentials are obtained. Finally, a numerical study is conducted. It is found that the natural frequency can be tuned directly by changing the magnetic and electric potentials. Additionally, a closed form solution for the normalized natural frequency is derived, and buckling loads are calculated in a numerical example.

Perpendicular Exchange Bias and Magneto-Electric Control Using Cr2O3(0001) Thin Film

Abstract: Antiferromagnets themselves do not generate either stray elds or spontaneous magnetization. However, if an antiferromagnet is coupled with a ferromagnet, unique and useful characteristics appear. Exchange bias is one such characteristic that is utilized in spintronic devices like spin-valve lms. To date, exchange bias has been used to induce static effects in devices; however, the exchange bias has not been switchable in these devices. Recently, switchable exchange bias has been developed using Cr2O3, which exhibits a magnetoelectric effect in an antiferromagnetic layer. The promising features of this effect are (1) the strength of the exchange bias is high and its direction is perpendicular to the lm, and (2) the switching is triggered by an electric eld. In this overview, we will summarize our recent results on the unique temperature dependence of high, perpendicular exchange bias and magnetoelectric switching of the induced perpendicular exchange bias. [doi:10.2320/matertrans.ME201506]

The relativistic electro-vortical field—revisiting magneto-genesis and allied problems

Abstract: Following the idea of MagnetoFluid unification [S. M. Mahajan, Phys. Rev. Lett. 90, 035001 (2003)], a very general Electro-Vortical (EV) field is constructed to describe the dynamics of a perfect relativistic fluid. Structurally similar to the electromagnetic field Fμν, the Electro-Vortical field Mνμ unifies the macroscopic forces into a single grand force that is the weighted sum of the electromagnetic and the inertial/thermal forces. The new effective force may be viewed either as a vortico-thermal generalization of the electromagnetic force or as the electromagnetic generalization of the vortico-thermal forces that a fluid element experiences in course of its evolution. Two fundamental consequences follow from this grand unification: (1) emergences of a new helicity that is conserved for arbitrary thermodynamics and (2) the entire dynamics is formally expressible as an MHD (magnetohydrodynamics) like ideal Ohm's law in which the “electric” and “magnetic” components of the EV field replace the standard electric and magnetic fields. In the light of these more and more encompassing conserved helicities, the “scope and significance” of the classical problem of magneto-genesis (need for a seed field to get a dynamo started) is reexamined. It is shown that in models more advanced than MHD, looking for exotic seed-generation mechanisms (like the baroclinic thermodynamics) should not constitute a fundamental pursuit; the totally ideal dynamics is perfectly capable of generating and sustaining magnetic fields entirely within its own devices. For a specified thermodynamics, a variety of exact and semi exact self-consistent analytical solutions for equilibrium magnetic and flow fields are derived for a single species charged fluid. The scale lengths of the fields are determined by two natural scale lengths: the skin depth and the gradient length of the thermodynamic quantities. Generally, the skin depth, being the shorter (even much shorter) than the gradient length, will characterize the kinetic-magnetic reservoir of short scale energy that will drive the dynamo as well as reverse dynamo action—the creation of large scale magnetic and flow fields.

A magnetic shape memory microactuator with intrinsic position sensing

Abstract: This paper presents the design, fabrication and characterization of a linear actuator based on the magnetic shape memory (MSM) effect with intrinsic position sensing using the displacement-dependent change of electrical resistance. Active materials are Ni-Mn-Ga bulk single crystals with dimensions of 2.5 × 20 × 1 mm3 showing 10 M martensite with a dense parallel twin structure at room temperature. This structure gives rise to gradual strain characteristics when applying external stress or a magnetic field. In order to exploit this behavior for positioning applications, the correlation between magneto strain and electrical resistance is investigated as a function of external stress using either a compressive or tensile reset spring. Depending on spring constant, pre-stress as well as the modes of loading and sample fixation, reversible magneto strains up to 3.6% are achieved. The electrical resistance change shows linear correlation with magneto strain within 90% of actuation stroke allowing for position sensing with sensitivities of 2.1 and 2.7 μm/μΩ under compressive and tensile loading, respectively. This performance is simulated using a thermodynamics-based Gibbs free energy model taking into account a linear strain-resistance relationship. Near the end positions at large magnetic field, the magneto resistance effect gives rise to a nonlinear contribution to the magneto strain-resistance characteristics.

Exponential convergence of the stochastic micropolar and magneto-micropolar fluid systems

Abstract: We study the micropolar and magneto-micropolar fluid systems with random forces in two-dimensional case. The additional terms on the equations that govern the time evolution of the velocity and micro-rotational velocity vector fields are more singular than many other equations that have been previously studied, for example Bénard or magnetic Bénard problem. Following the approach of [2] via a coupling method, we prove the existence and uniqueness of their solutions and the invariant measures as well as the exponential convergence of its trajectories to the unique invariant measure.

Tunable magneto-granular phononic crystals

Abstract: This paper reports on the study of the dynamics of 1D magneto-granular phononic crystals composed of a chain of spherical steel beads inside a properly designed magnetic field. This field is induced by an array of permanent magnets, located in a holder at a given distance from the chain. The theoretical and experimental results of the band gap structure are displayed, including all six degrees of freedom for the beads, i.e. three translations and three rotations. Experimental evidence of transverse-rotational modes of propagation is pre- sented; moreover, by changing the strength of the magnetic field, the dynamic response of the granular chain is tuned. The combination of non-contact tunability with the potentially strong nonlinear behavior of gran- ular systems ensures the suitability of magneto-granular phononic crystals as nonlinear, tunable mechanical metamaterials for use in controlling elastic wave propagation.

Method for Forming a Bed of Stabilized Magneto-Caloric Material

Abstract: A method for forming a stabilized bed of magneto-caloric material is provided. The method includes aligning magneto-caloric particles within the casing while a magnetic field is applied to the magneto-caloric particles and then fixing positions of the magneto-caloric particles within the casing. A related stabilized bed of magneto-caloric material is also provided.

Multiaxial magneto-mechanical modelling of electrical machines with hysteresis

Abstract: We present a novel numerical method for modelling of coupled magneto-mechanical behaviour and magnetic hysteresis losses in electrical machine cores under mechanical stress. An energy-based single-valued magneto-mechanical constitutive law is coupled to the Jiles-Atherton model of hysteresis. The material model is implemented in a 2-D finite element method, which solves for both the magnetic vector potential and mechanical displacement in the electrical machine core. The model is applied to analyse stator shrink fitting in a permanent-magnet synchronous machine and centrifugal stress in a high-speed solid-rotor induction machine. The losses in the machines are shown to increase due to the consideration of the mechanical stress.

Eigen value approach to two dimensional problem in generalized magneto micropolar thermoelastic medium with rotation effect

Abstract: Abstract In this study an eigen value approach has been employed to examine the mechanical force applied along with a transverse magnetic field in a two dimensional generalized magneto micropolar thermoelastic infinite space. Results have been obtained by treating rotational velocity to be invariant. Integral transforms have been applied to solve the system of partial differential equations. Components of displacement, normal stress, tangential couple stress, temperature distribution, electric field and magnetic field have been obtained in the transformed domain. Finally numerical inversion technique has been used to invert the result in the physical domain. Graphical analysis has been done to described the study.

Transition Metal Based Magneto Caloric Materials for Energy Efficient Heat Pumps

Abstract: Magnetic refrigeration near room temperature is considered as an environmentally benign alternative for the current compressor-based cooling technology. Two materials that are based on ferromagnetic transition metal compounds are considered as the most promising candidates to be used in real world applications. Here we discuss the main features of these materials.

Magneto-vibro-acoustic analysis of a discoidal switching flux permanent magnet machine dedicated to wind turbine application

Abstract: The aim of this paper is to compare two approaches for modelling the vibro-acoustic behaviour of a three-phase discoidal switching flux permanent-magnet machine (DSFPM) due to electromagnetic origins. The first approach is based on a full transient vibro-acoustic analysis of the DSFPM emitted acoustic noise. The second modelling approach is based on a modal superposition analysis of the DSFPM vibro-acoustic behaviour. This multi-physic study is based on a weak coupling between two 3D Finite-Element (FE) models: an electromagnetic model computing the magnetic pressure and a vibroacoustic model to quantify the vibration/noise performances. Results comparison between the two modelling approaches shows the effectiveness of the modal superposition model in terms of precision and computation time.

Metamaterial magneto inductive lens for magnetic resonance imaging

Abstract: A metamaterial magneto inductive lens is presented for the coil design in magnetic resonance imaging (MRI) applications, which is expected to enhance the magnetic field intensity of surface coils for improvement of the signal to noise ratio (SNR) of the MRI systems. The split-ring based lens is constructed into a pair of parallel two-dimensional arrays, that is, a metamaterial magneto inductive lens, providing minimum loading to the coil. Measurements show that the magnetic field intensity of the coil with metamaterial magneto inductive lens is improved about 2 dB at 295 MHz over a conventional coil at a distance of 10 mm, which is promising for pre-clinical study in a 7T MRI system at 300 MHz band.

Mixed electromagnetic environment monitoring system of power frequency alternating current -direct current

Abstract: The utility model provides a mixed electromagnetic environment monitoring system of power frequency alternating current -direct current, including the mixed electromagnetic field monitoring devices of alternating current -direct current, noise and meteorological data monitoring devices, communication module and information display unit, noise and meteorological data monitoring device and the mixed electromagnetic field monitoring devices's of alternating current -direct current signal input part be connected, the mixed electromagnetic field monitoring devices's of alternating current -direct current signal output part be connected with communication module's input, information display unit be connected with communication module's output, the mixed electromagnetic field monitoring devices of alternating current -direct current include magneto resistive sensor, mix electric field test probe, AD converting circuit and microprocessor, magneto resistive sensor, mixed electric field test probe are connected with AD converting circuit respectively, AD converting circuit and microprocessor are connected the utility model provides an under the power frequency alternating current -direct current condition of mixing electromagnetic environment the problem of monitoring is difficult to to go on.

Investigation of a Bending-Mode Magneto(Elasto)electric Sensor Using a Phase Modulation With a PLL

Abstract: Bending-mode magnetostrictive-piezoelectric sensors clamped at its two extremities show promising results for an enhancement of its magnetic field sensitivity by using a phase modulation (PM) technique. In this operating mode, the sensor is excited by an external carrier at its bending resonant frequency. The results of such a magnetic field sensing by a magneto(elasto)electric bilayer when using a PM technique with a phase locked loop circuitry are presented. The aim of this method is to follow the phase shift at the bending resonant frequency of the sensor, which is proportional to the applied magnetic field for the small-signal regime. We obtained a magnetic sensitivity of ~1.5 kV/T and an equivalent magnetic noise level around 80 nT/$\surd $ Hz at 2 Hz. These performances are presently limited by the noise from our electronics, suggesting that there is room for further improvements.

Magneto-convective and radiation absorption fluid flow past an exponentially accelerated vertical porous plate with variable temperature and concentration

Abstract: A numerical analysis is carried out for an unsteady free convective, radiative, chemically reactive, radiation absorption, viscous, incompressible and electrically conducting fluid past an exponentially accelerated vertical porous plate in the presence of sink. The set of non-dimensional governing equations along with boundary conditions are solved numerically. The effect of various physical parameters on flow quantities are studied with the help of graphs. For the physical interest, the variations in skin friction, Nusselt number and Sherwood number are also studied through tables.

Shear horizontal surface acoustic waves in a magneto-electro-elastic system

Abstract: Abstract Propagation of shear horizontal surface acoustic waves (SHSAWs) within a functionally graded magneto-electro-elastic (FGMEE) half-space was previously presented (Shodja HM, Eskandari S, Eskandari M. J. Eng. Math. 2015, 1–18) In contrast, the current paper considers propagation of SHSAWs in a medium consisting of an FGMEE layer perfectly bonded to a homogeneous MEE substrate. When the FGMEE layer is described by some special inhomogeneity functions – all the MEE properties have the same variation in depth which may or may not be identical to that of the density – we obtain the exact closed-form solution for the MEE fields. Additionally, certain special inhomogeneity functions with monotonically decreasing bulk shear wave velocity in depth are considered, and the associated boundary value problem is solved using power series solution. This problem in the limit as the layer thickness goes to infinity collapses to an FGMEE half-space with decreasing bulk shear wave velocity in depth. It is shown that in such a medium SHSAW does not propagate. Using power series solution we can afford to consider some FGMEE layers of practical importance, where the composition of the MEE obeys a prescribed volume fraction variation. The dispersive behavior of SHSAWs in the presence of such layers is also examined.