Change Of Magnetic Flux Research Articles

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.

Magnetic displacement force and torque on dental keepers in the static magnetic field of an MR scanner

To evaluate the effect of the static magnetic field of magnetic resonance (MR) scanners on keepers (ie, ferromagnetic stainless steel plate adhered to the abutment tooth of dental magnetic attachments). Magnetically induced displacement force and torque on keepers were measured using 1.5 Tesla (T) and 3.0 T MR scanners and a method outlined by American Society for Testing and Materials (ASTM). Changes in magnetic flux density before and after exposure to scanner static magnetic field were examined. The maximum magnetically induced displacement forces were calculated to be 10.3 × 10(-2) N at 1.5 T and 13.9 × 10(-2) N at 3.0 T on the cover surface. The maximum torques exerted on the keeper (4 mm in diameter) were 0.83 N × 4 mm at 1.5 T and 0.85 N × 4 mm at 3.0 T. These forces were considerably higher than the gravitational force (7.7 × 10(-4) N) of the keeper but considerably lower than the keeper-root cap proper adhesive force. The keepers' magnetic flux density remained less than that of the Earth. Magnetically induced displacement force and torque on the keeper in the MR scanner do not influence the keeper-root cap proper adhesive force.

Electromagnetic resonant cavity wind energy harvester with optimized reed design and effective magnetic loop

We demonstrate a new electromagnetic resonant cavity wind energy harvester combined with dual-branch reed and turning fork vibrator to harvest wind energy for wireless sensor nodes. Compared with electromagnetic structures in the past, the proposed magnetic circuit has a better linearity and a magnetic loop that more effectively increases the rate of the change of magnetic flux. Moreover, the motion of the free magnet is directed vertically to the direction of the magnetic pole for a zero resistance startup mode and a compact construction. We also designed a tuning fork-like reed structure to reduce system losses. To achieve maximum output power, we defined a virtual resistance to deal with the decrease of the electromotive in the circuit caused by the Lorentz force between the magnet and the induced magnetic field of the coils when the circuit is turned on. The dimensions of the wind inlet were 60mm×60mm. The maximum output power and conversion efficiency can reach 56mW at wind speed of 20.3m/s and 2.3% at wind speed of 4m/s, respectively, with wind speed from 3.2m/s to 21.2m/s. The experiments show that this electromagnetic wind energy harvester has high output power and wide wind speed range.

Surface-scanning coil detectors for magnetoelastic biosensors: A comparison of planar-spiral and solenoid coils

This research introduces a planar spiral coil as a surface-scanning detector for magnetoelastic biosensors, which have been used to detect bacteria directly on food surfaces. The planar coil was compared with the previously investigated solenoid coil, in terms of the magnetic flux change, signal amplitude, and detection distance. Both theoretical calculations and experimental results demonstrated that the planar coil detector yields a dramatically improved signal amplitude and greater detection distance. In addition, simultaneous measurement of multiple biosensors on surfaces was demonstrated. This planar coil is therefore anticipated to facilitate the detection of bacteria on surfaces using magnetoelastic biosensors.

A multi-frequency vibration-based MEMS electromagnetic energy harvesting device

A multi-frequency vibration-based MEMS electromagnetic energy harvesting (EH) device has been presented, fabricated and characterized in this paper. It consists of a permanent magnet and a circular suspension structure on a MEMS EH chip. By emulating the magnetic field of a cylinder magnet, the gap distance between the magnet and EH chip is optimized to be zero for achieving larger magnetic flux change and higher output performance. From the experimental results, the vibration energy can be harvested at three excitation frequencies of 840, 1070 and 1490Hz, which corresponds to the out-of-plane (mode I), torsion (mode II/III) and in-plane (mode IV/V) vibrations of the EH device, respectively. The maximum power densities at these three frequencies are 0.157, 0.014 and 0.117μW/cm3, respectively, for a matched load resistance of 626Ω and an input acceleration of 1.0g. The feasibility study results show promising application potentials for harvesting energy from vibrations of multi-frequency.

Nonlinear magnetic error evaluation of a two-mode watt balance experiment

The watt balance is operated in two asynchronous measurement modes to obtain the voltage–velocity ratio U/v and the force–current ratio mg/I, respectively. The magnetic flux density will change between the two modes when the effect due to the coil current is taken into account, particularly for watt balances using a soft magnetic material in the magnetic circuit. Normally, the linear component of the magnetic flux density change can be easily eliminated by reversing the coil current; however, the quadratic component remains as a systematic error, i.e. a non-linear error. In this paper, we use a theoretical analysis and a differential finite element method to investigate the behaviour of the quadratic dependence in a typical magnetic circuit. Several strategies are discussed to minimize this error in the magnetic system design for the watt balance.

Design of a surface-scanning coil detector for direct bacteria detection on food surfaces using a magnetoelastic biosensor

The real-time, in-situ bacteria detection on food surfaces was achieved by using a magnetoelastic biosensor combined with a surface-scanning coil detector. This paper focuses on the coil design for signal optimization. The coil was used to excite the sensor's vibration and detect its resonant frequency signal. The vibrating sensor creates a magnetic flux change around the coil, which then produces a mutual inductance. In order to enhance the signal amplitude, a theory of the sensor's mutual inductance with the measurement coil is proposed. Both theoretical calculations and experimental data showed that the working length of the coil has a significant effect on the signal amplitude. For a 1 mm-long sensor, a coil with a working length of 1.3 mm showed the best signal amplitude. The real-time detection of Salmonella bacteria on a fresh food surface was demonstrated using this new technology.

Increasing output power of electromagnetic vibration energy harvesters using improved Halbach arrays

This paper extends previously published studies into the performance of Halbach arrays for electromagnetic vibration energy harvesting. A Halbach array is a specific arrangement of permanent magnets that concentrates the magnetic field on one side of the array while cancelling the field to almost zero on the other side. This arrangement can improve electromagnetic coupling in a limited space. Previous research showed that although the Halbach array has higher magnetic field density compared to normal magnet layouts, its magnetic flux change rate is not necessarily high. Thus, output powers of energy harvesters with standard Halbach arrays are not always greater than those with normal magnet layouts. Two improvements to the Halbach arrays that lead to increased output power of electromagnetic vibration energy harvesters are presented in this paper. Test results showed that the proposed improved Halbach arrays can increase the output power of energy harvesters by a factor of seven compared to the standard Halbach array.

Probability-of-existence of vibro-impact regimes in a nonlinear vibration energy harvester

This paper reports on the characterization of high-energy vibro-impacting regimes in a vibration energy harvester with softening Duffing nonlinearity, by mathematical modelling and numerical analysis with experimental validation. The harvester is implemented as a base excited permanent-magnet/ball-bearing arrangement, where oscillations by the ball-bearing induce a change in magnetic flux in a wire coil, which in turn generates a voltage. Symmetric rigid aluminum stops in the harvester structure restrain the amplitude of the ball-bearing motion (within gap Δ) and thus produce vibro-impact behaviour under certain operating conditions—leading to wideband operation. These operating conditions are analysed by means of an event-driven equation switching algorithm, implementing a base-driven Duffing oscillator with conditional hyster–Hertz impact mechanics. In considering the ‘probability-of-existence’ of impact regimes, predictions about the frequency bandwidth of the high-energy impact state are made and compared to the experimental prototype. A trade-off between operating bandwidth and output power is noted. For the non-optimized harvester arrangement examined in this paper, with a gap Δ = 14.7 mm the bandwidth was predicted to be ∼1.3 Hz, and was measured at 0.7 Hz with an output power of 7.4 mW rms. With a gap size Δ = 2.9 mm the bandwidth was predicted to be ∼7.2 Hz, and was measured at 6.1 Hz with an output power of 54 μW rms. The authors believe that the probability-of-existence approach may be useful for characterizing the conditions required for exciting high-energy states of other nonlinear vibration energy harvesting systems.

Design of New Wireless Illuminant Keyboard Based on Three Source Composite Power Supply

With the rapid improvement of people's living standard,computer has become a necessity in daily life, followed by a huge amount of keyboard. The traditional wireless illuminant keyboard brings convenience to the life,however also consumes more energy and causes environmental pollution . Based on this situation, we plan to design a new type of energy-saving illuminant keyboard, on the one hand it can use the travel of keyboard to drive the generator; On the other hand it takes advantage of the magnetic flux changes when pressing to generate electricity. In addition, it can use extrusion of fingers on the keyboard to generate electricity by the plated PVDF film .Ultimately achieving the effect of energy saving and convenient.

Magnetostrictive properties of epoxy resins modified with Terfenol-D particles for detection of internal stress in CFRP. Part 2: evaluation of stress detection

The mechanical performance of carbon fibre reinforced polymers is predominantly limited by internal stress induced by resin shrinkage of the polymer matrix. Terfenol-D particles are investigated as internal sensors to detect the stress situation on a non-destructive way. Part 1 of the article describes the preparation and characterization of the samples used in the investigation of the sensory effect (Kubicka et al. J Mater Sci 47:5752–5759, 2012). Part 2 presents the results of the evaluation of the stress detection. A fundamental discussion is given how these magnetostrictive particles act as stress sensors in epoxy resins using the Villari effect. Analysing this effect in terms of particle content, particle size and particle distribution the most promising parameters are identified. Obviously the higher the particle content (20 wt%) and the smaller the particle size (<20 μm) combined with a strong homogeneous particle distribution the higher the magnetic flux density changes, in case of tensile loads. These corresponding stress situations are quantified by a Hall probe. Interestingly, the magnetic flux density changes (∆B) can be significantly increased by a pre-magnetization step of the samples, allowing a more sensitive detection of the Villari effect.

Rapid Formation and Disappearance of a Filament Barb

We present observations of an activated quiescent filament obtained in Hα from the high-resolution Dutch Open Telescope (DOT) on 20 August 2010. The filament developed a barb in 10 min, which disappeared within the next 35 min. A data set from the DOT spanning 2 h was used to analyse this event. Line-of-sight velocity maps were constructed from the Doppler images, which reveal flows in filament spine during this period. Photospheric magnetograms were used from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO) to determine the changes in magnetic flux in the region surrounding the barb location. The analysis shows flows in the filament spine towards the barb location preceding its formation, and flows in the barb towards the spine during its disappearance. Magnetograms reveal patches of minority polarity flux close to the end of the barb at its greatest elongation. The flows in the spine and barbs are along numerous threads that compose these typical filament structures. The flows are consistent with field-aligned threads and demonstrate that the replacement time of the mass in barbs, and by inference, in the spine is very rapid.

Wave characteristics of single-walled fluid-conveying carbon nanotubes subjected to multi-physical fields

Wave propagation in single-walled carbon nanotubes (SWCNTs) conveying fluids and placed in multi-physical fields (including magnetic and temperature fields) is studied in this paper. The nanotubes are modelled as Timoshenko beams. Based on the nonlocal beam theory, the governing equations of motion are derived using Hamilton's principle, and then solved by Galerkin approach, leading to two second-order ordinary differential equations (ODEs). Numerical simulations are carried out to verify the analytical model proposed in the present study, and determine the influences of the nonlocal parameter, the fluid velocity and flow density, the temperature and magnetic field flux change, and the surrounding elastic medium on the wave behaviour of SWCNTs. The results show that the nonlocal parameter has a considerable influence on dynamic behaviour of the nanotube and the fluid flow inside it. The results also show that the magnetic and temperature fields play an important role on the wave propagation characteristics of SWCNTs.

Manifestation of Constrained Dynamics in a Low-Pressure Spark

Some features of neutron emission from dense plasma focus suggest that the participating deuterons have energy in the range of 105 eV and have a directionality of toroidal motion. Theoretical models of these devices assume that the plasma evolves through a purely irrotational flow and thus fail to predict such solenoidal flow on the scale of the plasma dimensions. Predictions of a relaxation theory are consistent with experimental data [S K H Auluck, Physics of Plasmas,18, 032508 (2011)], but the assumptions upon which it is based are not compatible with known features of these devices. There is thus no satisfactory theoretical construct which provides the necessity for solenoidal flow in these devices. This paper proposes such theoretical construct, namely, the principle of constrained dynamics, and describes an experiment which provides support for this idea. The experiment consisted of low inductance, self-breaking spark discharge in helium at a pressure ~100 hPa between two pointed electrodes separated by 30-50 mm distance kept inside a vacuum chamber mounted on a low inductance high voltage capacitor. The current derivative signal showed reproducible sharp dips at all the extrema of the damped sinusoidal discharge. A planar diamagnetic loop centered with and perpendicular to the discharge axis consistently showed a signal representing rate of change of axial magnetic flux. A qualitative explanation of observed phenomena is obtained using a simple model using the proposed principle.

A novel experimental technique to determine the heat transfer coefficient between the bed and particles in a downer

A novel method for directly measuring the temperature history of mobile hot ferromagnetic particles (steel particles), substituting for reacting particles, in a binary-solid (reacting particles and inert particles) downflow is introduced. The temperature history of the hot steel particles can be obtained by measuring the temperature of the particles at different axial positions using magnetic fields that can separate the steel particles from other bed materials immediately and easily. Employing the magnetic marking method, magnetic sensors were used to detect the change in magnetic flux density in a given magnetic field, and the residence time of the steel particles was also measured. The cross-sectional averaged particle-to-bed heat transfer coefficients were calculated from the experimental results using simple heat balance equations. The measured temperature data have a relatively wide error range; however, the average temperature curves derived from the average particle-to-bed heat transfer coefficients agreed with the temperature plots. Therefore, the experimental method of this study is applicable to the measurement of the particle temperature in a binary-solid downflow. The results showed that there is strong correlation between the particle-to-bed heat transfer coefficients and normalized collision frequency under the laminar gas flow conditions.

Magnetic Flux Changes and Cancellation Associated with X-Class and M-Class Flares

We perform a statistical study of permanent changes in longitudinal fields associated with solar flares by tracking magnetic features. The YAFTA feature tracking algorithm is applied to GONG++ one-minute magnetograms for 77 X-class and M-class flares to analyze the evolution and interaction of the magnetic features and to estimate the amount of canceled magnetic flux. We find that significantly more magnetic flux decreases than increases occurred during the flares, consistent with a model of collapsing loop structure for flares. Correlations between both total (unsigned) and net (signed) flux changes and the GOES peak X-ray flux are dominated by X-class flares at limb locations. The flux changes were accompanied in most cases by significant cancellation, most of which occurred during the flares. We find that the field strength and complexity near the polarity inversion line are approximately equally important in the flux cancellation processes that accompany the flares. We do not find a correlation between the flux cancellation events and the stepwise changes in the magnetic flux in the region.

Change in Surface Magnetic Flux Density in EDM of Permanent Magnets-Influence of Internal Temperature and Shape on Machined Magnets

Traditional machining of a permanent magnet is difficult because of magnetic forces and brittleness of materials. However, electrical discharge machining (EDM), which is a non-contact thermal machining method, has carried out for shape machining of magnetic materials. Magnetic materials have a Curie point. As their magnetic flux density reduces when they are heated to a high temperature. Because EDM is a thermal process, it has the potential to control the magnetic flux density of a machined surface.In this study, to clarify the relationship between magnetic flux density and temperature distributions in depth direction of permanent magnet by EDM, internal temperatures of magnets were investigated using a K type thermocouple during EDM. Neodymium magnets were used as work-pieces. The magnetic flux density of a machined neodymium magnet was measured. In addition, the effects of duty factor (D.F.) and in Diamagnetic Field were also examined. The results showed that the average temperature inside of the magnet is determined by the input energy, depending on the discharge conditions. A decrease of surface magnetic flux density after EDM is affected by the magnitude of the area and the amount of decrease is due to the increase of the internal temperature of the magnet. In a diamagnetic field EDM, the reduction in magnetic flux density is large compared with a regular magnetic field. However, there is no difference in internal temperature each machining. Therefore, it isn’t determined simply by the magnitude of the input energy. It can be said that combination of heat history and machined magnet shape determine the magnetic flux density.

A Miniature Energy Harvesting Device Using Martensite Variant Reorientation

This paper presents a miniature energy harvesting device that makes use of stress-induced cyclic martensite variant reorientation in a Ni-Mn-Ga single crystal of 0.3x2x2 mm³ size. The stress- and magnetic field-induced reorientation is investigated for single crystalline Ni50.2Mn28.4Ga21.4 specimens of 0.3 mm thickness that are cut along the (100) direction and subjected to uniaxial compressive loading. A demonstrator is presented consisting of a FSMA specimen placed in the gap of a magnetic circuit to guide and enhance the field of biasing permanent magnets. The cyclic motion of a piezoelectric bimorph actuator is used to mechanically load the FSMA specimen. The corresponding change of magnetic flux induces an electrical voltage in a pick-up coil (N=2000 turns). The effects of biasing magnetic field, strain amplitude and strain velocity are investigated. An optimum magnetic field of 0.4 T exists, where the output voltage reaches 120 mV at a strain velocity of 0.006 ms-1.

유도전동기의 전압·전류 모델 합성 자속 추정기에 의한 속도제어에 관한 연구

Abstract This study uses the algorithm which estimates the magnetic flux using different models in the low speed driving area and the high speed driving area by the voltage-current model synthesis magnetic flux Estimator and, from this result, estimates the magnetic flux angle to achieve the stable speed control through all the areas from the low speed to the high speed drive.In particular, the current change and the magnetic flux change under variable load were estimated in real time in the low speed area and this made the control characteristic improved in the low speed area. According to this, even under variable load, the more stable simulation and experiment could have been completed using PI current controller and PI flux controller in all the areas. As a result, the outstanding speed control characteristic has been achieved. Key Words : flux estimator, flux angle, PI current controller, PI flux controller, voltage-current model synthesis * Corresponding Author : Lark-Hoon HwangTel: +82-10-5487-5525 email: lhhwang@semyung.ac.kr 접수일 12년 08월 10일 수정일 12년 09월 06일 게재확정일 12년 11월 08일

Finite element analysis of magnetostrictive vibration energy harvester

PurposeThe paper aims to analyze the behavior of the Galfenol rods under bending conditions that are employed in a vibration energy harvester by illustrating the spatial variations in stress and magnetic field.Design/methodology/approachThis paper describes a 3‐D static finite element model of magnetostrictive materials, considering magnetic and elastic boundary value problems that are bidirectionally coupled through stress and field dependent variables. The finite element method is applied to a small vibration‐driven generator of magnetostrictive type employing Iron‐Gallium alloy (Galfenol).FindingsThe 3‐D static finite element modeling presented here highlights the spatial variations in magnetic field and relative permeability due to the corresponding stress distribution in the Galfenol rods subjected to transverse load. The numerical calculations show that about 1.1 T change in magnetic flux density is achieved which demonstrates the effectiveness of the inspected vibration‐driven generator in voltage generation and energy harvesting. The model predictions agree with the experimental results and are coherent with the magnetostriction phenomenon.Originality/valueThis paper fulfils the behavior analysis of Galfenol rods under transverse load that includes both compression and tension. The compressive and tensile stresses contributions to change in magnetic flux densities in the Galfenol rods were calculated by which the effectiveness of the inspected vibration‐driven generator in voltage generation and energy harvesting is demonstrated.