L. Kvarnsjo

A magnetostrictive electric generator

An electric generator based on the magnetostrictive effect is presented. Longitudinal oscillations of a Terfenol-D rod give rise to a varying flux which induces a current in a coil wound around the rod. A small prototype of such a device is discussed, and both calculations and experiments are performed. The problem of eddy current losses is addressed. >

Nonlinear 2-D transient modeling of Terfenol-D rods

A nonlinear model for simulation of the transient behavior of magnetostrictive Terfenol-D rods has been developed. The model is based on static characterization of the magnetic and mechanical properties of the rods combined with Maxwells equations and classical mechanic laws. Registrations for different rods are stored in a database which is called upon by the model. The model is able to handle longitudinal wave propagation and eddy current influence under transient conditions. Any combination from the set of magnetic field (current), magnetic flux density (voltage), mechanical motion, mechanical stress, and mechanical impedance can be used as the two independent variables in the model. This modeling technique implies that the experimental set-up used for data acquisition of the material properties should be regarded as a part of the modeling process. The experimental set-up used for the characterization of Terfenol-D properties can produce magnetic fields and mechanical stresses independently of each other and of arbitrary shape. A specially designed sample holder provides a homogeneous magnetic field and mechanical stress field inside the rod. >

Dynamic modelling of giant magnetostriction in Terfenol-D rods by the finite element method

As a contribution to the development of methods for the design and the analysis of devices based on giant magnetostrictive materials, a model for the simulation of the dynamic behaviour of the nonlinear magnetoelastic medium is presented. The coupled magnetic, magnetoelastic and mechanical equations that describe the magnetostrictive problem are solved by means of the finite element method. The thin sheets bending principle (surface splines) is used to introduce in the simulation the nonlinear properties of giant magnetostrictive materials, obtained by static characterizations. >

Application of a stress-dependent magnetic Preisach hysteresis model on a simulation model for terefenol-d

A previously reported simulation model for the highly magnetorestrictive material. Terfenol-D has been extended by implementation of the recently developed stress-dependent magnetic Preisach hysteresis model. The model is based on static measurements of material characteristics combined with equations for the dynamic mechanical and magnetic behavior of the material. As a test of the model the authors have simulated the behavior of a Terfenol-D rod for different load conditions. The results show that the model is able to describe the influence of nonlinearities, eddy currents, and hysteresis on the magnetomechanical transduction process of magnetorestrictive materials. >

A set-up for dynamic measurements of magnetical amd mechanical behaviour of magnetostrictive materials

A setup for dynamic studies of giant magnetostrictive rods has been developed. The mechanical load on the magnetostrictive rod can be electronically controlled, which makes it possible to study the magnetomechanical behavior in complex situations. Computer simulations show that the setup can be used as a tool for designing magnetomechanical devices. The setup is described, including the mechanical arrangement, sensors, current feed, and data acquisition, and its preliminary operation and verification are discussed. >

Examination of the interaction between eddy currents and magnetoelasticity in Terfenol‐D

When an electrically conducting magnetic material is magnetized dynamically, eddy currents will be induced inside the material. The eddy currents give rise to a decrease of the flux density obtained at quasistatic conditions at a specific magnetizing field and hence, for a magnetostrictive material such as Terfenol‐D, also a decrease in the magnetostriction. Because of the magnetoelastic interaction in magnetostrictive materials, it is difficult to analytically predict the influence of these eddy currents. By solving the equation for the radial field distribution inside the rod numerically, a model which takes the eddy currents into account can be formulated. This radially resolved model makes it possible to calculate the local eddy current distribution inside the rod, and by choosing the appropriate boundary conditions, the ‘‘effective’’ behavior of the rod can be calculated. Results obtained from a radially resolved model are compared with corresponding results from experiments. Also, a comparison is ma...

Examination of eddy current influence on the behavior of a giant magnetostrictive functional unit

Current simulation models for the magnetoelastic behavior of giant magnetostrictive materials have been successfully used in designing low #x2010;frequency functional units based on magnetostrictiv ...

A method of measuring eddy current impedances in giant magnetorestrictive materials

A method of calculating eddy-current impedances for giant magnetostrictive materials during dynamic magnetization is suggested. The method is based on solving the power-balance equation for each time step of the recorded data. The experimentally obtained impedances can be used for accurately modeling the magnetostrictive process. >