Uniform Magnetic Field Distribution Research Articles

Magnetic energy coupling system based on micro-electro-mechanical system coils

In this paper, a high efficiency wireless energy transfer system based on MEMS coils is first developed. The permanent magnetic core used in the transmitting coil can not only enhance the magnetic flux but also applies a strong and uniform magnetic field distribution around the core. Ansoft hfss is then used to analyze the performance of two coupling coils designed to be resonated at the same frequency. The distribution of magnetic field strength and coupling efficiency is modeled and characterized. High-performance bio-compatible MEMS coils were fabricated on a glass wafer by thick glue photolithography and electroplating technique. We measured a peak value of energy transfer at the resonant frequency of 23 MHz, and the coupling efficiency is higher than 10% within the distance of 10–20 cm by sweeping frequencies from 1 MHz to 200 MHz. Experiments also show that the resonant coupling efficiency is not much affected by the relative position of the two coils in a large range.

Optimization and Dynamic Modeling of Galfenol Unimorphs

Design and modeling of a bi-laminate, Galfenol-driven composite beam is presented in which the elasticity of the adhesive layer is considered. The optimal thickness ratio necessary to maximize the tip deflection is found by minimization of the internal energy of the beam. Model simulations show that use of a substrate material with high modulus leads to larger tip deflections. Stainless steel was therefore utilized as substrate in the experiments. In order to reduce eddy currents, a laminated silicon steel frame was employed to magnetize the beam. A dynamic model is proposed by coupling the structural dynamics of the beam and adhesive layer with the magnetostriction generated by the Galfenol layer. The latter is described with a linear piezomagnetic law with uniform magnetic field distribution along the length of the beam. Galerkin discretization combined with Newmark numerical integration are employed to approximate the dynamic response of the beam. The model is shown to describe both the transient and steady-state response of the composite beam tip displacement under harmonic excitation between 10 and 320 Hz. The RMS error between model and data range between 1.44% at 10 Hz and 6.34% at 320 Hz, when the same set of model parameters (optimized at quasistatic frequency) is utilized.

A Broadband UHF Near-Field RFID Antenna

A broadband segmented loop antenna is presented for ultra high frequency (UHF) near-field radio frequency identification (RFID) applications. Using a segmented line, the current distribution along the loop is kept in phase even though the perimeter of the loop is more than two operating wavelengths so that the proposed antenna generates strong and even magnetic field distribution in the near-field zone of the antenna. The antenna prototype, printed onto a piece of FR4 substrate, with an overall size of , achieves a large interrogation zone of with good impedance matching and uniform magnetic field distribution over the entire UHF RFID band of 840-960 MHz.

Stationary levitation and vibration transmission characteristic in a superconducting seismic isolation device with a permanent magnet system and a copper plate

We have devised a magnetic levitation type superconducting seismic isolation device taking advantage of the specific characteristic of HTS bulk that the HTS bulk returns to its original position by restoring force against a horizontal displacement. The superconducting seismic isolation device is composed of HTS bulks and permanent magnets (PM rails). The PMs are fixed on an iron plate to realize the same polarities in the longitudinal direction and the different polarities in the transverse direction. The superconducting seismic isolation device can theoretically remove any horizontal vibrations completely. Therefore, the vibration transmissibility in the longitudinal direction of the PM rail becomes zero in theory. The zero vibration transmissibility and the stationary levitation, however, cannot be achieved in the real device because a uniform magnetic field distribution in the longitudinal direction of PM rail cannot be realized due to the individual difference of the PMs. Therefore, to achieve stationary levitation in the real device we adopted a PM–PM system that the different polarities are faced each other. The stationary levitation could be achieved by the magnetic interaction between the PMs in the PM–PM system, while the vibration transmitted to the seismic isolation object due to the magnetic interaction. We adopted a copper plate between the PMs to reduce the vibration transmissibility. The PM–PM system with the copper plate is very useful for realizing the stationary levitation and reducing the vibration transmissibility.

UHF reader loop antenna for near-field RFID applications

A novel reader loop-type antenna for ultra-high-frequency (UHF) near-field radio frequency identification (RFID) applications is presented. This antenna, printed on a 0.8 mm-thick FR4 substrate with a diameter of 16 cm, is composed of four curved strips and four pairs of coupled stubs, and achieves a wide impedance bandwidth from 840 to 1300 MHz. The proposed structure can make large currents along the loop so that a strong and uniform magnetic field distribution is excited in the region around the antenna. Measurements show that the antenna operating with a commercial reader demonstrates good performance of tag identification with inductive coupling for near-field RFID applications.

UHF near-field RFID reader antenna with capacitive couplers

A segmented loop antenna with capacitive couplers is proposed for ultra-high frequency (UHF) near-field radio frequency identification (RFID) applications, which is capable of generating a strong and uniform magnetic field in a near-field zone even though the perimeter of the loop is comparable to the operating wavelength. As an example, an antenna printed onto an FR4 printed circuit board with an interrogation zone of 154 × 154 mm exhibits good impedance matching and uniform magnetic field distribution over an operating bandwidth of 790-1000 MHz, which is desirable for UHF near-field RFID reader applications.

Segmented loop antenna for UHF near-field RFID applications

A segmented loop antenna is presented for ultra-high frequency (UHF) near-field radio frequency identification (RFID) applications. The proposed segmented configuration makes the current along the loop remain in-phase even though the perimeter of the loop is comparable to the operating wavelength, so that a strong and uniform magnetic field is generated in the region surrounding the antenna. The antenna printed on a FR4 printed circuit board (PCB) with an overall size of 160×180×0.5 mm achieves good impedance matching and uniform magnetic field distribution over an operating bandwidth of 800–1040 MHz, which is desirable for UHF near-field RFID reader applications.

Optimal Design of a Hybrid Winding Structure for Planar Contactless Battery Charging Platform

Planar contactless battery charging platform is an emerging technology that has the potential of unifying the charging protocols of portable consumer electronic products. In this paper, a new hybrid structure which consists of a coil and a spiral winding is proposed for improving the uniform magnetic field distribution over the charging surface. An analysis into an optimal design of the number of turns and the dimension of the spiral winding is presented for a given concentrated coil. The uniform magnetic field distribution of the designed prototype is measured by an electromagnetic compatibility scanner and by an energy-receiving coil. Based on circuit modeling and analysis, the inverter circuit topology and particularly the resonant compensation tank is designed for maximizing power transfer for multiload applications. A design procedure is proposed and verified by the experiments. An efficiency of about 80% has been achieved for the coupled structures when four loads are charged on the platform simultaneously.

A small Maglev car model using YBCO bulk superconductors

Models of two small Maglev cars have been made. The track was paved with NdFeBmagnets. The arrangement of the magnets made it easy to get a uniform magnetic fielddistribution along the length of the track and a magnetic field gradient in the lateraldirection. When the car with YBCO bulk superconductors was field cooled toLN2 temperature at a certain distance above the track, the car could be automatically levitatedover the track and moved along the track without any obvious friction. The model can beused to demonstrate the Meissner effect and a fast transportation system to students andadults.

B203 バルクハウゼン現象の可視化法に関する一考察

Ferromagnetic materials, i.e., iron steel and its composites, are widely used as the frame parts of various artificial products and constructions such as a building, bridge and so on. Because of its mechanical property, iron steel is most popular in use for the frame materials to maintain their mechanical strength. On the other side, nondestructive testing of iron steel is an extremely important way in order to keep their mechanical safeness.One of the deterministic differences between the ferromagnetic and non-magnetic materials is that all of the ferromagnetic materials when applying external magnetic field attracts major magnetic field; and also magnetization process of ferromagnetic materials always accompanies with the Barkhausen effects. Barkhausen effect is a phenomenon, which happens by movement of magnetic domain.Magnetic domain structure evaluation of most magnetic material is performed in the uniform magnetic field distribution. In this paper, we propose a designing strategy of the optimal exciting coil as the first step of a nondestructive testing method employing Barkhausen phenomenon. Further, we propose one of the visualizing methodologies of the Barkhausen phenomenon as the second step.

Kelvin-Helmholtz instability of miscible ferrofluids

We study the stability of an interface between two inviscid magnetic fluids of different densities flowing parallel to each other in an oscillatory manner. The system is pervaded by a uniform oblique magnetic field distribution. The analysis allows for mass and heat transfer across the interface. A general eigenvalue relation is derived and discussed analytically. The classical stability criterion is found to be substantially modified due to the effect of the oblique magnetic field with mass and heat transfer. Some previous studies are reported for appropriate data choices. The longitudinal magnetic field has a strong stabilizing influence on all wavelengths, which can be used to suppress the destabilizing influence of the mass and heat transfer. We conclude with a discussion of the stability of unsteady shear layers on the basis of the results. The parametric excitation of the surface waves is analyzed by means of the multiple-time-scales method. The transition curves are obtained analytically.

The influence of an oscillatory rotation on the stability of miscible cylindrical magnetic fluids

In a previous paper [1], the effect of an unsteady rotation on the electrohydrodynamic stability of a cylindrical interface was investigated. In this work, we extend the analysis to include the effect of the mass and heat transfer on magnetic fluid columns. The system is pervaded by a uniform axial magnetic field distribution. The axisymmetric mode ( m = 0) is only considered. The standard normal modes approach is utilized. The method of multiple time scales is used to achieve the stability of the system. In the zero order problem, a complex transcendental dispersion equation is obtained. Some reported works are recovered upon appropriate data choices. In the first order problem, the solvability condition is derived. The transition curves are obtained. It is found that the mass and heat transfer enhances the stability of the system.

Analysis of Petschek-type reconnection in a Y-type magnetic field distribution

An analytical investigation is performed of Petschek-type reconnection in an incompressible plasma medium with a non-uniform magnetic field distribution, given by B = √ ( 2 z ¯ ) in complex variable notation. The initial two-dimensional (2D) configuration contains a current sheet, modelled as a tangential discontinuity, which runs along the positive x-axis in the complex plane, and which terminates in a Y-type neutral point at one end ( x = 0). In the model, reconnection is initiated through the introduction of a tangential electric field component in a localized part of the current sheet referred to as the diffusion region. Outside the diffusion region, which we approximate as an X-type neutral point, the behaviour of the magnetic field and plasma flow is governed by the equations of ideal magnetohydrodynamics (MHD), which for the purpose of this analysis are transformed into a Lagrangian coordinate system. With the restriction of a small reconnection rate, a perturbation method is applied to solve the MHD equations for the outflow region, containing the reconnected plasma, and the surrounding inflow region. The outflow region is treated as a thin boundary layer, and the usual matching procedure for problems of this type is used. In agreement with the results of previous studies of Petschektype reconnection in non-uniform, asymmetric magnetic field and velocity distributions, the boundary and interior structure of the outflow region is found to consist of a combination of Petschek-type shocks and tangential discontinuities. This is in contrast to the case of an initially uniform magnetic field distribution, analysed originally by Petschek, where the outflow region is entirely bounded by Petschek-type shocks and contains no interior discontinuities. The new features arise because the shocks propagate at the local Alfvén velocity in the medium, whereas plasma entering the outflow region is accelerated to the Alfvén velocity as measured at the reconnection site. As a result of the discrepancy between the plasma outflow speed and the shock propagation speed in the model configuration analysed here, the behaviour of the field and flow is qualitatively and quantitatively different on opposite sides of the X-line. In particular, the outflow region propagating into the direction of increasing field strength (i.e. x increasing) is bounded entirely by Petschek-type shocks, but contains a tangential discontinuity which extends the original current sheet through the leading point (or nose) into the interior of the outflow region. On the other hand, the outflow region propagating into the direction of decreasing field strength ( x decreasing, but remaining positive) is bounded on the front by tangential discontinuities, which emerge out of Petschek-type shocks, and merge into the original current sheet at the nose. When the reconnection rate drops to zero, there is an additional reverse type of behaviour which occurs in the trailing part; tangential discontinuities develop to form the tail end boundary of the outflow region in the former case, and in the latter case a tangential discontinuity develops which penetrates through the tail into the outflow region. We also investigate the consequences of a reconnection site which moves along the current sheet, analyse what happens when there are two successive pulses of reconnection, and briefly discuss the situation when the outflow region propagates beyond the edge of the current sheet.