Magnetostrictive materials and applications

The dynamic magnetostrictive properties of materials and their applications will be reviewed. The order of presentation is to first discuss the various dynamic magnetostriction contents (defined by Smith), λ and γ (defined by Butterworth and Smith), and Γ (defined by the present author). Next, the application of the magnetic domain theory to dynamic magnetostriction will be presented. The ΔE-effect, a useful material criterion, will then be examined. Experimental results of the electromechanical coupling factor at an optimum bias are then shown. The second section of the paper will present the magnetostrictive characteristics of Ni, Ni-Fe alloys, Fe-Al alloys, other metals, cobalt rondel, and the ferrites. Much of the emphasis will be placed on the effects of cold reduction, hysteresis phenomena, and the effects of oxide films. Empirical formulas which describe these properties are presented. Large amplitude ferrite vibrators are described. The third part of the study is devoted to a phenomological method of predicting the magnetostrictive characteristics of polycrystalline metals. Experimental data for iron which agrees with the model is presented. The effect of anisotropic grain growth is discussed in terms of the model. The last section is devoted to the mechanical power limitations of magnetostrictive vibrators both from the theoretical and the experimental points of view.