Finite element analysis of stiffness characteristics of an electromagnetic device

An electromagnetic device, consisting of a pair of permanent magnets and a non-magnetic coil, has shown its linear advantages for inducing parametric stiffness excitation in the laboratory. The electromagnetic device powered by a DC coil current acts like a mechanical spring with constant stiffness. The effects of design parameters upon the electromagnetic stiffness and its linear operating range (referred as the stiffness characteristics) are important and crucial for the design and usage of the device. Thus, a numerical method, based upon the commercial finite element method (FEM) package ANSYS/Emag, was presented for analyzing the stiffness characteristics of the device with DC coil current. The theory foundation for computing the electromagnetic force using FEM was derived and the program realization in ANSYS was introduced briefly. Two typical examples were chosen to verify the accuracy of the numerical analysis method. Based upon these, the restoring force characteristics of the electromagnetic device with various DC coil currents were obtained utilizing the numerical method. Two important indicators (proportional coefficient between linear stiffness and coil current and linear range of the stiffness) were defined for measuring the stiffness characteristics of the electromagnetic device. Then, the effects of the design parameters (both the electromagnetic and structural parameters) on the two indicators were investigated, respectively. The research results provide useful references for the stiffness design of the electromagnetic device in actual practice.