Magnetic Field Modulation Research Articles

Experimental investigation of on-demand ferrofluid droplet generation in microfluidics using a Pulse-Width Modulation magnetic field with proposed correlation

Micro-magnetofluidics offers a promising tool to regulate the drop formation process with versatile applications in engineering and biomedicine. In the present study, on-demand ferrofluid drop generation at a T-junction is investigated utilizing a magnetic pulse. Also, a novel method for ferrofluid droplet formation is introduced using a non-uniform Pulse-Width Modulation (PWM) magnetic field. A novel mechanism of drop generation named “beating regime” was seen for the first time in which the ferrofluid moves back and forth before the breakup. The effect of the magnetic induction, continuous phase flow rate, duty cycle, and applied frequency on the generation frequency and drop diameter was investigated under the PWM magnetic field and compared with those under the DC magnetic field. The results showed that greater values of drop diameter and generation frequency are obtained either when the magnetic induction and/or duty cycle increases or when the applied frequency decreases. The regime maps of ferrofluid droplet formation were presented for different magnetic Bond and Capillary numbers under both PWM and DC magnetic fields and compared with each other. Finally, a correlation was presented to estimate the dimensionless drop diameter on the basis of four nondimensionalized parameters, showing a 7.2 % average relative error.

APPLICATION OF STEM-CP BASED MAGNETIC FIELD AND ELECTROMAGNETIC INDUCTION MODULE TO IMPROVE STUDENTS CREATIVE THINKING SKILLS AT VOCATIONAL HIGH SCHOOL

Materials in physics learning at school are considered difficult to understand, especially in the concept of magnetic field and electromagnetic induction. Contextual issues are required to overcome this problem.STEM-Cp (science, technology, engineering, mathematics-contextual problem) is seen to help students understand the concept of magnetic field and electromagnetic induction through contextual issues. The purpose of this study was to determine the effect of using STEM-Cp based moduleon students creative thinking skill on magnetic field and electromagnetic induction material.The research design used in this study is one-group pretest-posttest design . Data obtained from the results of creative thinking tests conducted in the experimental class before and after learning. The results showed that the students creative thinking skills taught using magnetic field modules and electromagnetic induction based on STEM-Cp before and after learning improved. The effect of the application of the magnetic field module and electromagnetic induction based on STEM-Cp has an average increase of 80,3in the good category. This shows that the creative thinking skills of students learning with magnetic field modules and electromagetic induction are better than before being applied in learning.

Continuous wave electron paramagnetic resonance L-band spectrometer with direct digitalization using time-locked subsampling

This article describes a novel digital L-band EPR spectrometer. The spectrometer uses direct digital detection with time-locked subsampling (TLSS). The device consists of a microwave bridge equipped with a microwave source based on direct digital synthesis (DDS) and a digital receiver.DDS technology combined with an ultra-low noise 1 GHz master clock allowed the development of a digitally controlled microwave source with exceptionally good phase noise characteristics. The obtained level of phase noise is as low as −140 dBc/Hz at 30.5 kHz from the carrier frequency of 1.15 GHz, which is important when registering the EPR dispersion signal.The receiver is equipped with a high-speed A/D converter that enables direct digitalization of the L-band microwave signal. The obtained discrete data are then buffered and averaged in a programmable logic FPGA device. Data packets from FPGA are transferred to a DSP microcontroller that correlates them with the appropriate reference signals. This detection algorithm requires time locking of the generator and the receiver, which is ensured by clocking both devices from the same reference source. This procedure allows the simultaneous detection of the absorption and dispersion signals at the magnetic field modulation frequency and at any of its harmonics.The software to control the spectrometer was designed in the LabView programming environment. The program also allows further data processing. To the best of our knowledge, the described spectrometer is one of the first full implementation of the direct digital detection technique which could replace conventional analog CW spectrometers that utilize magnetic field modulation. For an 11 µm aqueous TEMPOL solution, the new spectrometer obtained a S/N ratio greater than 160 for an EPR spectrum registered in 69 s.

Linear and Weakly Nonlinear Analyses of Magneto-Convection in a Sparsely Packed Porous Medium under Gravity Modulation

This paper deals with the linear stability analysis and weakly non-linear analysis of Magneto-convection in a sparsely packed porous medium with constant vertical Magnetic field and gravity modulation. A linear stability analysis reported here and shows that the gravity modulation has significant effect on the stability limits of the system. The gravity modulation is know to have effect and is treated by a perturbation expansion in powers of the amplitude of modulation. The shift in the critical Rayleigh number is evaluated and depends on the prandtl number and frequency of modulation, using the Venezian method. It is also shown that the onset of convection can be advance or delay by the regulation of various parameters. Weakly nonlinear analysis is performed based on the method of power series, where the disturbance is expressed in terms of power series. A nonlinear Ginzburg-Landau equation to investigate the three different types of gravity modulation on heat transfer is derived as part of this work. Heat transfer have been shown to depend on Nusselt number, further the effect of different types of parameter on heat transport have been studied graphically. Nusselt number graph is also shown for different parameter and explain in detail. The effect of magnetic prandtl number and Chandrasekhar number are stabilize the system. The control of convection is a major issue in systems with fluids as a working media. This is all the more difficult if the fluid system is housed in a porous medium. The paper presents three mechanisms of controlling onset of convection and thereby the heat transfer in such fluid systems. In order the modulation effect is effective in its role, we have considered the system to be a fluid-saturated porous media.

편심 자석 로터의 내·외측 자기장 변조를 이용한 마그네틱 하모닉 기어

In a magnetic harmonic gear, the magnetic field on the high-speed side is modulated by the air-gap movement according to the rotation of the eccentric body. Owing to the modulated magnetic field, the permanent magnet layer outside the high-speed rotor rotates in synchronization with the stator composed of another permanent magnet. Therefore, transferring only the synchronous rotational motion outside the eccentric body to the output side requires a complicated conversion mechanism. In this study, we propose a magnetic harmonic gear that utilizes both the inner and outer magnetic fields of an eccentric permanent magnet layer. The outer magnetic field is utilized for the deceleration function as in the existing harmonic gear, whereas the additional inner magnetic field is utilized to extract the rotational motion. The topology of the system is verified by the harmonic analysis of the air-gap magnetic field and with experimental set-up.

The wide-angle broadband absorption and polarization separation in the one-dimensional magnetized ferrite photonic crystals arranged by the Dodecanacci sequence under the transverse magnetization configuration

Utilizing the transfer matrix method, a multifunctional infrared device possessing the properties of the wide-angle broadband absorption and the polarization separation based on the one-dimensional (1-D) magnetized ferrite photonic crystals (MFPCs) arranged by the Dodecanacci sequence is designed theoretically under the modulation of the external magnetic field. The magneto-optical effect generated in the proposed MFPCs gives birth to the ultra-broadband absorption regions under the transverse electric (TE) mode, one runs at 16.22 THz –30.89 THz and the other covers at 33.52 THz–70.00 THz. The mechanism of the wide-angle (at most 80.89° for TE mode) absorption is analyzed by the interference cancellation condition. Moreover, owing to the different effective permeabilities of the MFPCs under the two polarization modes, the propagation behaviors of the electromagnetic (EM) wave are diverse which present the absorption features under the TE mode and show the transmission properties under the transverse magnetic (TM) mode in the structure. Compared with the periodic and Thue-Morse structures, the complex symmetry of the Dodecanacci sequence makes the absorption features of the MFPCs superior to that of the former. Besides, the influences of the magnetic field intensity and the dielectrics’ thicknesses on the angle-insensitive absorption and polarization separation characteristics are discussed explicitly. This research provides meaningful guidance for the modulation and absorption of the infrared light wave and the design of the multifunctional magnetically tunable optoelectric device.

Arranging Diamagnetic Particles in a Modulated Magnetic Field Originating in Microelectromechanical Systems Compatible with an Integrated Circuit upon Halbach Array Magnet.

In this study, we attempted to expand the applicability of the mechanism for arranging diamagnetic particles in a modulated magnetic field. A Halbach array magnet was prototyped as a portable device for generating a high magnetic field. Despite the magnet being palm-size with dimensions of 50 × 50 × 20 mm, the magnetic field is 1.31 T at 1 mm from the surface. Additionally, an Si substrate on which an Fe thin film is formed and patterned to be compatible with the integrated circuit (IC)—utilizing the microelectromechanical systems process technology—is prototyped as a tool to generate a modulated magnetic field. Regarding the deposition condition of the Fe thin film, holes with diameters of 30 μm are arranged in an array at intervals of 60 μm, and the thickness is approximately 0.5 μm. Finally, a particle magnetic-adsorption experiment was conducted using the prototypes. The diamagnetic particles (diameter: 25 μm) dispersed in the paramagnetic surrounding medium were observed to be arranged in the hole portions. This result indicates that the microparticles are absorbed in their arbitrary positions by the modulated magnetic field. In the end, we succeeded in achieving the portability and implementation on IC for the particle arrangement magnetic mechanism.

Investigation of an Integrated Magnetic-Field-Modulated Brushless Double-Rotor Machine With an Improved PM Rotor

The integrated magnetic-field-modulated brushless double-rotor machine (IMFM-BDRM) can be a promising candidate for the electrical-continuously variable transmission (e-CVT) in hybrid electric vehicles (HEVs) due to its brushless and compact structure. However, the large permanent-magnet (PM) eddy current loss and the conflict between torque density and mechanical strength limit its application. In this article, an IMFM-BDRM with an improved PM rotor is proposed to solve those problems. First, the structure of the proposed machine is introduced, and the magnetic field modulation mechanism is analyzed by the magnetic circuit method. The research shows that the modulated magnetic fields in the proposed IMFM-BDRM are produced mainly because of the variation in the flux paths, which is quite different from that in the traditional IMFM-BDRMs. Second, the electromagnetic performances are analyzed by the finite-element method. The effects of the structure parameters of the two rotors on torque performance are further investigated. Finally, to evaluate the overall performance of the proposed IMFM-BDRM, a traditional IMFM-BDRM with the same stator is designed to compare their performances. The comparison results show that the proposed machine has more advantages of output torque, PM loss, and efficiency than the traditional IMFM-BDRM.

Hysteresis Reduction in Tunneling Magnetoresistive Sensor With AC Modulation Magnetic Field

A simple and practical ac modulation method to reduce the hysteresis in tunneling magnetoresistive (TMR) sensor is demonstrated. It is shown that with a suitable ac modulation magnetic field that is applied along the sensing direction of the TMR sensor, the hysteresis in the sensor can be reduced to a negligible level. Also, depending on the amplitude of the modulation field, the sensitivity and the dynamic range of the TMR sensor can be tuned to meet practical requirements in specific applications. The influence of the modulation on the noise of TMR sensor is also studied.

MNP Enhanced Microwave Imaging by Means of Pseudo-Noise Sensing with Different External Magnetic Field Modulations.

This contribution deals with the detection and imaging of magnetic modulated nanoparticles by means of ultra-wideband sensing. We performed phantom measurements in a practical measurement setup where the magnetic nanoparticles are modulated by a static and a low periodic changing external magnetic field. We investigated the influence of the modulation type of the polarizing magnetic field on both, detectability and imaging of magnetic nanoparticles. We can conclude that both modulations generate a sufficient contrast in order that the nanoparticles were detected at the correct position in a three-dimensional volume. The imaging results, including 32 channels, indicate that the two state (ON/OFF) modulation of the magnetic field under constant environmental conditions shows better results compared to a sinusoidal excitation of the magnetic field.

Analysis of Airgap Field Modulation Principle of Flux Guides

The flux guides are adopted in a number of electric machines, such as the synchronous reluctance machine (SynRM) and the brushless doubly fed reluctance machine (BDFRM). This article further develops a novel and unified theoretical approach for the category of machines with flux guides. Specifically, the magnetomotive force (MMF) modulation operator of variable flux guides is proposed based on the general airgap field modulation theory, to describe the modulation behavior on the source magnetizing MMF distribution in detail. Both machine topologies with flux guides, namely, the SynRM and BDFRM, are addressed in detail from the perspective of airgap field modulation mechanism. It is proven that, three kinds of harmonic components with pole pairs of $p_{f}$ and $(lN_{MB}\pm p_{f})$ correspond to $p_{f}$ pole-pair source magnetizing MMF and their relative amplitudes can be characterized by three magnetic field conversion factors. The magnetic field modulation effects of flux guides and simple salient poles are compared in terms of the torque production ability. In addition, electromagnetic performances such as airgap flux density, torque density, and inductance characteristics are correlated with their initial key topological parameters by certain analytical expressions and compared fairly between the SynRM and BDFRM. The agreement among the theoretical analysis and the two-dimensional (2-D) finite element analysis together with experimental test verifies the effectiveness of the proposed analysis.

Measurement of Magnetic Particles by Hexagonal Pseudo Seven-Channel HTS SQUID Array

We developed a high-Tc superconducting (HTS) three-channel Superconducting Quantum Interference Device (SQUID) array and applied it to the measurement of a flow of magnetic nano-particles (MNPs).Three magnetometers were positioned in-line with a separation of 2.3 mm. The pick-up loop consisted of a 1 mm × 1 mm square loop; the size of a SQUID washer slit was 5 μm × 60 μm. Using this array, we arranged a hexagonal pseudo seven-channel SQUID array. The signal from the water-diluted MNPs, Resovist, in motion was measured by the array in a DC bias magnetic field and an AC modulation magnetic field. The dependence of the SQUID signal on the angle of the MNP flow to the baseline of the array was measured and discussed. The results suggest that the signal peak values are highly dependent on the flow path angle and that most of the flow path can be identified by the shape of the waveforms. This method is a promising candidate for brain activity investigation of small animals.

Investigation of the Power Factor of Magnetic-Field Modulated Brushless Double-Rotor Machine

The magnetic-field modulated brushless double-rotor machine (MFM-BDRM), getting rid of brush and slip ring, is a preferable selection for the power splitting device in hybrid electric vehicles. In practical application, however, the MFM-BDRM is facing the challenge of low power factor owing to its special operating principle—the magnetic field modulation principle. Although some researchers dedicate themselves to improving the power factor of MFM-BDRM, the cause of low power factor in the MFM-BDRM is still not clear. This article will investigate the power factor problem of MFM-BDRM, systematically. First, the inductance feature of MFM-BDRM based on the magnetic field modulation principle is investigated. Second, the fundamental cause of the low power factor of MFM-BDRM is analyzed. Furthermore, three feasible attempts are made and investigated to improve the power factor of MFM-BDRM. Finally, a prototype of MFM-BDRM is manufactured, and parts of the analysis are verified by experiments.

Magnetic Convection in a Nonuniformly Rotating Electroconducting Medium under the Action of External Magnetic Field Modulation

We have analyzed the magnetic convection regime (Rayleigh–Benard problem) in a nonuniformly rotating electroconducting liquid in an external periodic magnetic field. In the linear theory of oscillatory convection, the critical value of Rayleigh number Rac is obtained as a function on the nonuniform rotation profile (Rossby number Ro). It is shown that the Kepler profile of rotation with Rossby number Ro = –3/4 produces a destabilizing effect. Using the method of perturbation theory in small supercriticality parameter of the Rayleigh number, we have derived the Ginzburg–Landau nonlinear complex equation. The numerical solution of this equation has enabled us to determine heat transfer (from the Nusselt number Nu) in the layer of the liquid for different values of amplitudes δ and modulation frequencies ωB. Using the Galerkin method, we have obtained a linear dynamic system of nonautonomous Lorenz-type equations. Numerical analysis of these equations has revealed the possibility of controlling the chaotic behavior of convective flows in a nonuniformly rotating (Ro = –3/4) liquid by varying the modulation parameters of the external magnetic field.

Magnetic field- and light-driven spin molecular logic gates: A first-principles study

We design a novel combinational molecular device consisting of a planar four-coordinate Fe molecule and a 15,16-dinitrile dihydropyrene/cyclophanediene molecule with carbon nanotube bridge and electrode, and investigate its spin-polarized transport properties using density functional theory and non-equilibrium Green's function formalism. The results show the spin-polarized currents are strongly dependent on the magnetic field and light modulations. Perfect spin filtering and large switching effects are realized. The results are explained by spin-resolved transmission spectra, energy levels of molecular projected self-consistent Hamiltonian orbitals, and their spatial distributions. Based on the spin-polarized transport properties, we propose spin molecular AND, OR and NOT gates.

P122 Zinc is likely critical for static magnetic field modulation of NMDA receptor-dependent synaptic plastic in both human and mouse cortex

P122 Zinc is likely critical for static magnetic field modulation of NMDA receptor-dependent synaptic plastic in both human and mouse cortex

Novel Magnetic Field Modulation Concept Using Multiferroic Heterostructure for Magnetoresistive Sensors

The low frequency magnetic field detection ability of magnetoresistive (MR)sensor is seriously affected by 1/f noise. At present, the method to suppress the influence of low frequency noise is mainly to modulate the measured magnetic field by mechanical resonance. In this paper, a novel modulation concept employing a magnetoelectric coupling effect is proposed. A design method of modulation structure based on an equivalent magnetic circuit model (EMCM) and a single domain model of in-plane moment was established. An EMCM was established to examine the relationship between the permeability of flux modulation film (FMF) and modulation efficiency, which was further verified through a finite element simulation model (FESM). Then, the permeability modulated by the voltage of a ferroelectric/ferromagnetic (FE/FM) multiferroic heterostructure was theoretically studied. Combining these studies, the modulation structure and the material were further optimized, and a FeSiBPC/PMN-PT sample was prepared. Experimental results show that the actual magnetic susceptibility modulation ability of FeSiBPC/PMN-PT reached 150 times, and is in good agreement with the theoretical prediction. A theoretical modulation efficiency higher than 73% driven by a voltage of 10 V in FeSiBPC/PMN-PT can be obtained. These studies show a new concept for magnetoelectric coupling application, and establish a new method for magnetic field modulation with a multiferroic heterostructure.

Experimental optimization of atomic magnetometer in nuclear magnetic resonance gyroscope

We present the experimental implementation of dual-axis parametric modulation magnetometer using Rb atoms in the presence of inert gases (129Xe and 131Xe). The presence of 129Xe and 131Xe nuclear spins broaden the resonance linewidth of Rb atoms, which violates the narrow linewidth condition usually considered in previous works. We systematically study the parametric modulation process beyond the narrow linewidth limit, and optimize the controlling parameters including the frequency and amplitude of the modulation magnetic field, and the demodulation phases. Our work demonstrates a comprehensive method to improve the performance of Nuclear Magnetic Resonance Gyroscope.

A Novel Coaxial Magnetic Gear With Unequal Halbach Arrays and Non-Uniform Air Gap

In order to improve the output torque and transmission stability of coaxial magnetic gear (CMG), a novel CMG with unequal Halbach arrays of the inner rotor and non-uniform air gap is proposed in this paper. According to the principle of magnetic field modulation and “one-sided flux” structures, the unequal Halbach arrays could augment the magnetic field in the inner air gap. Moreover, the permanent magnets (PMs) of the eccentric structure could obtain non-uniform air gap, which is helpful to enhance the flux-modulation effect. The proposed CMG topology with 4 inner and 17 outer pole pairs is established. The topology performance is assessed and calculated by finite element analysis (FEA).

The effect of a non-uniform pulse-width modulated magnetic field with different angles on the swinging ferrofluid droplet formation

In this study, ferrofluid droplet formation from a nozzle in the presence of a non-uniform Pulse-Width Modulated (PWM) magnetic field with different angles was studied experimentally. A Drop-on-Demand platform was introduced and three different regimes of droplet formation were observed. The regime map of the droplet formation was presented. A new type of droplet formation evolution was observed in which the droplet is formed while it is swinging around the nozzle, and the satellite droplet is not generated in this regime. The effects of five important parameters including magnetic flux density, applied magnetic frequency, duty cycle, distance between the nozzle and the center of the upper surface of the coil, and the angle of magnetic coil with respect to gravity on droplet diameter, formation frequency, number of pulses for one droplet generation, and droplet formation evolution were investigated. Results demonstrated that by increasing the magnetic flux density and duty cycle, and by decreasing applied magnetic frequency, the droplet diameter decreases, whereas the formation frequency increases. Also, the minimum droplet diameter was observed at the distance of 10mm and the angle of 45°. Finally, a correlation for dimensionless droplet diameter was proposed with an average relative error of 2.8%.