Variation Of Magnetic Force Research Articles

Magnetic field effects on characteristics of counterflow diffusion ethylene flame: An experimental study

The present study was aiming to obtain the effects of magnetic gradients with varying direction on counterflow diffusion ethylene flames, including the flame shape, chemical structure and soot concentration distribution. Experiments were performed using flame imaging with a digital camera, two-color pyrometry, and flame speciation with gas chromatography (GC)/mass spectrometer (MS) system. When upward and horizontal outward magnetic gradients were introduced to flames, it was discovered that the mean flame temperature rose and the mean soot concentration dropped in the sooting region, while an opposite trend was observed with the addition of downward magnetic gradient. Meanwhile, results revealed that the presence of the upward or horizontal outward magnetic gradients could accelerate the consumption of ethylene and encourage the conversion of intermediate hydrocarbon species to CO and CO2 in the flame area, while the oxidation of fuel and intermediate hydrocarbon species were inhibited and the formation of the aromatics was promoted with the application of the downward magnetic gradient. Furthermore, it was noted that the changing trend of aromatics was consistent with that of soot. The reason might be understood from the variation of magnetic force imposed on oxygen, which in turn affected the fuel consumption and soot distribution.

Comparison of closed-form solutions to experimental magnetic force between two cylindrical magnets

The force between permanent magnets implemented in many engineering devices remains an intriguing problem in basic physics. The variation of magnetic force with the distance x between a pair of magnets cannot usually be approximated as x-4 because of the dipole nature and geometry of magnets. In this work, the force between two identical cylindrical magnets is accurately described by a closed-form solution. The analytical model assumes that the magnets are uniformly magnetized along their length. The calculation, based on the magnetic field exerted by one magnet on the other along the direction of their orientation, shows a reduction in the magnetic force with the distance x and a dependence on the size parameters of magnets. To verify the equation, the experiment was set up by placing two cylindrical neodymium iron boron type magnets in a vertical tube. The repulsive force between the identical upper and lower magnets of 2.5 cm in diameter and 7.5 cm in length was measured from the weight on the top of the upper magnet. The resulting separation between the magnets was recorded as x. The forces measured at x=0.004-0.037 m differ from the values calculated using the analytic solution by -0.55 % to -13.60 %. The calculation also gives rise to a practical remnant magnetic field of 1.206 T. When x is much large than the equation of force is approximated as a simple form proportional to 1/x-4. The finding can be directly used in magnetic levitation as well as applied in calculating magnetic fields and forces in other systems incorporating permanent magnets.

Closed Loop Control of a Tethered Magnetic Capsule Endoscope.

Magnetic field gradients have repeatedly been shown to be the most feasible mechanism for gastrointestinal capsule endoscope actuation. An inverse quartic magnetic force variation with distance results in large force gradients induced by small movements of a driving magnet; this necessitates robotic actuation of magnets to implement stable control of the device. A typical system consists of a serial robot with a permanent magnet at its end effector that actuates a capsule with an embedded permanent magnet. We present a tethered capsule system where a capsule with an embedded magnet is closed loop controlled in 2 degree-of-freedom in position and 2 degree-of-freedom in orientation. Capitalizing on the magnetic field of the external driving permanent magnet, the capsule is localized in 6-D allowing for both position and orientation feedback to be used in a control scheme. We developed a relationship between the serial robot's joint parameters and the magnetic force and torque that is exerted onto the capsule. Our methodology was validated both in a dynamic simulation environment where a custom plug-in for magnetic interaction was written, as well as on an experimental platform. The tethered capsule was demonstrated to follow desired trajectories in both position and orientation with accuracy that is acceptable for colonoscopy.

TO EVALUATION TEST OF QUALITY OF MAGNETIC FLUIDS FOR MAGNETOFLUID DEVICES

Magnetic fluid is a colloid of magnetic nanoparticles. Using of magnetic fluids in technical devices demands applying of strong non-uniform magnetic fields for a long time. One of the most widespread magnetic fluid devices are magnetic fluid seals of mobile shafts, magnetic fluid supports, bearings, acceleration and angle of inclination gauges, devices for information input in the computer and etc. These devices demand high quality of used fluids. Processes of magnetophoresis and Brownian diffusion in magnetic fluid lead to concentration of magnetic particles in the areas with higher intensity of magnetic field and increase of fluid magnetization in these areas. A local change of particles concentration in the fluid leads to variation of its physical properties. Formation of aggregates from the particles and the further stratification of magnetic fluid, up to its destruction, may be the most serious consequence of redistribution of concentration of magnetic particles. These factors lead to variation of parameters of magnetic fluid devices; cause disturbance of their normal operation and even failure. Therefore, the consistent, high quality magnetic fluids which are not subject to fast stratification in a non-uniform magnetic field are necessary for effective work of the devices. The procedure of evaluation test of quality of magnetic fluids is proposed in this paper. The test is based on studying of influence of processes of magnetophoresis and Brownian diffusion of magnetic particles in magnetic fluid on the forces acting on the volume of fluid in an external non-uniform magnetic field. The procedure is developed on the basis of analysis of magnetic force variation in time under the action of non-uniform field of permanent magnets. Methods of determination of stability of magnetic fluid, known at present, demand rather complicated equipment and laborious and complex investigations. Proposed procedure can be used as an express method for evaluation of magnetic fluid quality for usage in technical devices, and it does not need complicated equipment.

Hysteresis of magnetic force-gap in static and dynamic magnetic levitation with a high-Tcsuperconductor

Hysteresis behavior of magnetic force versus gap between a high- T c superconductor and a magnet, in static and dynamic cases, is studied numerically. Differing from the previous methods, based on macro electromagnetic constitutive relation of superconductors and Maxwell equations, a numerical method with the finite element method (FEM) is established. After numerical code is examined by comparing between numerical and experimental results of the relation of magnetic force-gap, the hysteresis curves of magnetic force-gap including major and minor loops in static case are simulated, and furthermore the dependences of major loop on main parameters including the critical current density and the thickness of superconductor, the residual magnetic field of magnet, and the diameter ratio of superconductor to magnet are studied numerically. In the case of free vibration, by investigating dynamic response of levitated body at different levitation/suspension positions in this magnetic levitation system, we obtain the corresponding results of the variation of magnetic force with gap. All the numerical results of the relation between magnetic force and gap show the strongly nonlinear and highly hysteretic behavior.

Acoustic drive circuit

An acoustic drive circuit for driving a headphone for converting variation of magnetic force, occurring to a voice coil, in sound, and outputting the sound, comprises a power amplifier for amplifying a signal at a frequency within the speech band, and outputting the signal after amplification, at a voltage with a given bias voltage superposed thereon, to one end of the voice coil of the headphone, and a pulse generation circuit for generating a pulse signal at a frequency higher than those in the speech band, having an average voltage equivalent to the bias voltage, and for outputting the pulse signal to the other end of the voice coil. The pulse generation circuit generates rectangular waves at a frequency higher than those in the speech band, having a duty ratio such that the average voltage is equivalent to the bias voltage.

Design of magnetostrictive/piezoelectric laminate composite for coil-less magnetic force control

We propose a magnetic force control device consisting of laminate composites of magnetostrictive material and piezoelectric material. The magnetic force control is based on energy conversion in the composite, such that the variation of magnetization of the magnetostrictive material induced by the piezoelectric material is converted to the variation of magnetic force by magnetic circuits. Because of the capacitive property of the piezoelectric material, the device requires little current in order to maintain control of a constant force. The laminate composite can be fabricated easily and in small sizes. In this paper, we report the magnetic force control properties of a composite of Terfenol-D and piezoelectric material plates (PZTs) and discuss the design of the laminate composite. Our theoretical magnetic force formulation derived by an equivalent magnetic analysis and finite-element analysis of strain distribution in the Terfenol-D, and measurements with various thicknesses of PZT demonstrated that there are appropriate thicknesses to provide large variation of the magnetic force and energy conversion efficiency. Stacking the composites was found effective for increasing the effective area of the Terfenol-D.

Magnetic force control with composite of giant magnetostrictive and piezoelectric materials

We propose a new magnetic force control device, composed of a giant magnetostrictive material (Terfenol-D) and a piezoelectric material (PZT), for coilless magnetic force control. The device uses the inverse magnetostrictive effect, whereby the variation of magnetization of a Terfenol-D rod controlled by PZT is converted to the variation of magnetic force by a magnetic circuit. Because PZT is electrically capacitive, the method has the advantage of low power consumption and low heat generation in static operation. We have fabricated several devices with different geometrical shapes of the rods and magnetic yokes, and we describe their characteristics such as power consumption, heat generation, and response. We discuss a magnetic circuit design strategy that uses the /spl Delta/E effect in magnetostrictive materials to increase the energy conversion efficiency.

Device of magnetostrictive and piezoelectric materials for magnetic force control

A new type of magnetic force control device composed of two functional materials, a giant magnetostrictive material and a piezoelectric material, is proposed for coil-less magnetic force control. The magnetic force control is based on the inverse magnetostrictive effect of Terfenol-D coupled via strain with the piezoelectric actuator and the variation of the voltage applied to the piezoelectric actuator is converted to the variation of magnetic force via a magnetic circuit in the device. Because the piezoelectric actuator is an electrically capacitive load, this magnetic force control method has the advantages of zero power consumption and zero heat generation in steady-state operation. In this paper, the principle of magnetic force controlling is described and the characteristics of the device are investigated with experiments.

Force Evaluation of Magnetic Force Control Element Using Giant Magnetostrictive Material.

This paper addresses characteristics of magnetic force variation and variation ratio depending on a shape of giant magnetostrictive material(GMM)and a magnetic circuit. The force variation is based on the Villari effect that the magnetization of GMM varies with applied stress. This magnetic force control method will be expected to be applicable to magnetic actuators and have advantage such as high response, low heat generation and high-energy efficiency inherent in the characteristics of GMM. In this paper, through experiment using universal test machine was done and some useful results to design the magnetic circuit were obtained. Based on the result, magnetic force variation ratio was theoretically calculated by equivalent magnetic circuit. A agreement with claculated and experiment result confirmed validity of the formulation. The relationships between the strain, stress and magnetic flux were also measured and necessity of total magnetic circuit design has been cleared.

New Magnetic Force Control Method Using Giant Magnetostrictive Material.

A new magnetic force control method using a giant magnetostrictive material(GMM)is proposed. Magnetization of GMM varies with applied stress. In magnetic circuit composed of a permanent magnet and magnetic yokes, the change of magnetization can be transduced into magnetic force variation. The feasibility of this method is examined by a simple experiment. For the purpose of estimating the force variation, the magnetic circuit is analyzed by finite element method on the assumption that the magnetization variation is equivalent to relative permeability change. This magnetic force control method is expected to be applicable to magnetic actuators and has advantages such as high response, low heat generation and high energy conversion efficiency inherent in the characteristics of GMM.

Force-distance relation and properties of repelling Sm-Co5 magnets in orthodontic clinical use: an experimental model.

In recent years, magnets and magnetic forces have been suggested as an alternative to traditional orthodontic devices such as elastics, springs and wires. The purpose of this study was to analyze the reliability and the output of forces for prefabricated orthodontic repelling Sm-Co5 magnets and the force conditions for the magnets after 5 months of maximal loading. The test-machine consisted of a jig where the tested pair of repelling magnets was mounted close to the clinical situation. With a cylindrical strain gauge transducer, a micrometer screw, a bridge-amplifier, and a Mingograph jet recorder, force-distance diagrams were constructed. The force-distance diagrams showed that the force-distance curve was hyperbolic and that the mean force when the magnetic pole faces were almost in contact with each other was 214.9 g, SD 13.42 g. The variation of magnetic force between different Sm-Co5 magnets was 6-9%. The difference in force before and after 5 months of maximal loading of the magnets was not significant. The test results indicate that with proper handling of the forces according to the new force diagrams, the system is reliable for orthodontic use.

Committee to promote observations of daily variation of the horizontal magnetic force between and near the geographic and magnetic equators

The work to be done by this newly‐formed Committee is indicated in Resolution No. 7 adopted at the Oslo Assembly (1948) of the International Association of Terrestrial Magnetism and Electricity. This resolution reads:"The International Association of Terrestrial Magnetism and Electricity endorses resolution No. 14 adopted at the Brussels meeting of the Mixed Commission on the Ionosphere of the International Council of Scientific Unions, namely: 'That, in view of the remarkable geomagnetic control of F2‐layer density and the known abnormal daily variation of the magnetic force in regions where the geomagnetic and geographical equators are widely separated, efforts should be made to achieve operation, for one or two years, of a chain of ionospheric and magnetic stations across these equators near the longitude of Huancayo or in East Africa and, if possible, another chain near a place at which these equators coincide'."

On the variation of magnetic force with the temperature

On the variation of magnetic force with the temperature