Quanliang Cao

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.

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.

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.

Two-Dimensional Manipulation of Magnetic Nanoparticles in Microfluidic Systems

A magnetic manipulation technique based on a superimposed gradient magnetic field source for controlling magnetic nanoparticles in microfluidic channels was proposed. The designed magnetic field is composed of one gradient magnetic field generated by micro-electromagnetic coils positioned near a microfluidic channel and one external uniform magnetic field generated by large Helmholtz coil pairs. By controlling the configuration of Helmholtz coils, magnetic nanoparticles can be transported in different movement modes. As a proof of concept, the transport behavior of magnetic nanoparticles under different configurations of Helmholtz coils was successfully performed in two-dimensional (2D) geometries.

Design, Implementation, and Testing of a Pulsed Electromagnetic Blank Holder System

In this paper, pulsed attractive electromagnetic force between two coils has been introduced for supplying blank holding force in sheet metal forming process. First, the requirements on the pulsed blank holding force and constraint conditions on the system were specified. Then, a design flow of the coil system fulfilling the requirements was presented. Based on the design, a prototype of a pulsed electromagnetic blank holder was fabricated. Numerical and experimental investigations were carried out to validate the feasibility of the designed system. Results show good agreement between the measured and simulated results of discharge currents and magnetic fields. The system generates a pulsed blank holding force with a magnitude of 930 kN and a rise time of 4.56 ms, which fulfills the specified requirements.

Axially Movable Electromagnetic Forming System for Large-Scale Metallic Sheet

How to generate strong enough electromagnetic forces in the electromagnetic forming process is an important issue for sheet forming. For this purpose, an axially movable electromagnetic forming system was designed, fabricated, and tested. To validate the effectiveness of the system, a series of experiments on the forming of AA1060 with a diameter of 440 mm and a thickness of 3 mm has been carried out. A pulsed magnet with an inner diameter of 100 mm and an outer diameter of 200 mm was used to drive the sheet. A capacitor bank power supply (200 kJ/25 kV/640 μF) has been used to energize the coil. The experimental results have shown that the maximum deformation depth of the workpiece is only about 90 mm when the forming coil was fixed after three discharges. This value can be greatly increased to 130 mm by the use of the proposed forming method in which the distance between the coil and the deformed workpiece was decreased in each discharge process. Meanwhile, the geometric accuracy between the final deformed workpiece and die is less than 3 mm according to the three-dimensional scanning analysis.