Xiaotao Han

Effects of Current Frequency on Electromagnetic Sheet Metal Forming Process

In the paper, the effects of current frequency on the electromagnetic sheet metal forming process are investigated using an efficient finite element model, which couples analysis of circuit, electromagnetic, and mechanical equations. Based on the initial electrical and structural parameters of the system, the model calculates the pulsed current flowing through the coil, the consequent magnetic force acting on the metal sheet, and finally the generated sheet deformation. The effects of current frequency on the maximum displacement in axial direction of the sheet are analyzed for two sheets by changing the capacitance of capacitor bank, while keeping the stored energy constant. The results show that there exist two optimum frequencies that produce relatively large sheet deformation and the optimum frequencies are related with the thickness of the sheet.

Configurations and control of magnetic fields for manipulating magnetic particles in microfluidic applications: magnet systems and manipulation mechanisms

The use of a magnetic field for manipulating the motion of magnetic particles in microchannels has attracted increasing attention in microfluidic applications. Generation of a flexible and controllable magnetic field plays a crucial role in making better use of the particle manipulation technology. Recent advances in the development of magnet systems and magnetic field control methods have shown that it has great potential for effective and accurate manipulation of particles in microfluidic systems. Starting with the analysis of magnetic forces acting on the particles, this review gives the configurations and evaluations of three main types of magnet system proposed in microfluidic applications. The interaction mechanisms of magnetic particles with magnetic fields are also discussed.

Numerical analysis of magnetic nanoparticle transport in microfluidic systems under the influence of permanent magnets

A finite element technique was employed for analysing the transport behaviour of magnetic nanoparticles (MNPs) under the gradient magnetic field generated by rectangular permanent magnets with different configurations. To predict the exact particle dynamic behaviour, the governing non-linear differential equations, Navier–Stokes and convection–diffusion were coupled with the magnetic field equation. The MNP concentration distribution was calculated and taken as an evaluation parameter to show where MNPs are preferentially captured in a microchannel. Since the dynamic behaviour of MNPs in the flow was dependent on the competition between magnetic and fluidic forces, the effects of the flow velocity and magnetic field strength on the MNP concentration distribution were analysed. Meanwhile, the effects of magnetic design parameters for permanent magnets on the magnetic force and MNP concentration distribution were analysed. Results showed that the MNP concentration in the capture region increased with magnetic field strength and decreased with increasing flow velocity. And the shape and position of the high concentration regions were related to the applied inlet velocity, magnetic field strength, geometry of the magnets and the orientation of the remanent flux density. The simulations performed can be used as a tool for the design and optimization of millimetre-sized rectangular magnets for developing efficient lab-on-a-chip systems.

The Pulsed High Magnetic Field Facility at HUST, Wuhan, China and Associated Magnets

A pulsed high magnetic field laboratory has been funded to be established at the Huazhong University of Science and Technology (HUST), Wuhan, China by the National Development and Reform Committee. The facility is planned to be open for external users in 2011 with the implementation of various experimental techniques in pulsed magnetic fields up to 80 T. Pulse durations are in the range from 15 to 1000 ms with the magnet bore sizes from 12 to 34 mm. The pulsed power supplies are a 12 MJ, 25 kV capacitor bank and a 100 MVA/100 MJ flywheel pulse generator. The design and analysis of the power supplies and the magnets of short and long pulse durations and the multi-stage pulsed magnets with controllable waveforms are presented in this paper.

Analysis and Optimal Design of Magnetic Navigation System Using Helmholtz and Maxwell Coils

The Helmholtz coils combined with the Maxwell coils can be used to generate the magnetic force for navigating a permanent magnet microrobot in the desired direction. To manipulate the microrobot effectively, two points should be noted: 1) High magnetic field uniformity of Helmholtz coils and magnetic field gradient uniformity of Maxwell coils; 2) High magnetic force with less current which reduces coil-heating and power consumption. Considering the two points, we evaluate and optimize the magnetic propulsion system in this paper. Firstly, two perpendicular Maxwell coils are presented to generate gradient magnetic field with theoretical analysis. The results indicate the two pairs of Maxwell coils system has better electrical properties than one pair. Secondly, we optimize the Helmholtz and Maxwell coils for the uniformities with considering coil thickness. The proposed system for the microrobot has higher navigation accuracy and good electrical properties.

Design and Evaluation of Three-Dimensional Electromagnetic Guide System for Magnetic Drug Delivery

A three-dimensional electromagnetic guide system for magnetic drug delivery was designed and theoretically analysed to demonstrate its feasibility. The system is mainly composed of one static Helmholtz coil and two kinetic racetrack coils that can generate compound gradient magnetic fields. In this paper, a Finite Element Model (FEM), relating to magnetic field distribution and the trajectories of the magnetic particles, has been built to investigate the performance of the magnet system. The calculation shows that an improved magnetic field is generated when different magnets work together. And the simplified simulation of particles trajectories suggests the magnetic micro-particles can be delivered and aggregated under the gradient magnetic field generated by the proposed system. The performed simulations reveal significant potential for the application in gene/drug therapy.

Design and Experiments of a High Field Electromagnetic Forming System

The concept of capacity coefficient is introduced to evaluate the processing capacity of electromagnetic forming (EMF). An EMF system design method, including capacity coefficient design, inductance design and strength design, is developed by a finite element method. The geometry and size of the driving coil are optimized by the capacity coefficient design. The inductance design is aimed at obtaining a reasonable pulse width of EMF. Finally, the strength design of the driving coil is presented with respect to the reinforcement. With this design method, a high strength driving coil is designed and wound. The height, inner radius, and outer radius of the driving coil are 25 mm, 5 mm, and 50 mm respectively. The number of turns is 40, resulting in reasonable pulse width of 380 . Experiments with different driving coils and pulse width were carried out. The results show that the processing capability of EMF is improved due to the high strength driving coil.

An active microfluidic mixer utilizing a hybrid gradient magnetic field

A simple active microfluidic mixing system based on magnetic actuation strategy of fluids in the microchannel under a hybrid gradient magnetic field was proposed. The hybrid magnetic field, combined of a static gradient magnetic field and an external AC uniform magnetic field, is specially designed to generate periodic magnetic body forces acting on the mixed fluids. Two-dimensional numerical simulation has been performed to investigate the mixing behavior caused by the interactions of magnetic field, fluid flow and convection-diffusion. Numerical results show that the proposed mixer system achieved up to 97% mixing of the two fluids with a small current flowing in micromagnets.

The Electromagnetic Flanging of a Large-Scale Sheet Workpiece

In this paper, an electromagnetic forming (EMF) system with an energy of 200 kJ (25 kV, 640 μF) was designed and fabricated to flange a large-scale aluminum alloy sheet with bore, whose outer diameter, bore diameter, and sheet thickness are 640 mm, 180 mm, and 5 mm, respectively. The stress distribution of the midplane of the coil was calculated to check the coil structural strength. And a multiphysics coupled finite element model, which involves the coupling of circuit, electromagnetic field, deformation field, and thermal field, was built to assess the forming capacity of the EMF system. Furthermore, the experimental results of electromagnetic flanging in the case of 155 kJ are presented and compared with the numerical results. Both the simulation forming depth 87 mm and experiment forming depth 90 mm show that the EMF system is effective to form the large-scale sheet workpiece.

Short and Long Pulse High Magnetic Field Facility at the Wuhan National High Magnetic Field Center

The pulsed high magnetic field facility funded by the Chinese National Development and Reformation Committee has been developed at the Wuhan National High Magnetic Field Center (WHMFC). Magnets of short pulse, long pulse and the combination of both with bore sizes from 12 to 34 mm have been developed and are operational for electric transport, magnetization, magneto-optics and electron spin resonance at temperatures in the range from 100 mK to 350 K. The power supplies for these magnets consist of a capacitor bank with 12 modules of 1 MJ/25 kV each and 2 modules of 0.8 MJ/25 kV each, a 100 MVA/100 MJ flywheel pulse generator and a 771 V/180 kAh battery bank. A dual-coil magnet driven by the capacitor banks has successfully generated 86.3 T field with a total pulse duration over 350 ms in a 12-mm bore. A dual-coil long pulse magnet wound from soft copper wire energized by the flywheel generator produces 50 T peak field with a 100 ms flat-top and a total 1.1 s pulse duration in a 22 mm bore. A battery bank driven long pulse magnet composed by the series connection of two nested coils generates 32 T peak field with the pulse duration of 1.5 s in a 21-mm bore.