7.1 Introduction

The so-called "smart materials" refers to a class of materials that are highly responsive to an outside influence (either electrical or magnetic, for example) and have the capability to sense and react to changes within themselves. Smart materials have a significant number of uses in commercial as well as military applications. The worldwide sales of smart materials exceed $1 billion annually.

The choice of smart material for an application depends on the nature of the response that is required under operational conditions, i.e. the "process" demand and subsequent plant response. This chapter is designed to give the reader some historical background and insight to the properties and applications of the new generation of magnetoelastic materials, in particular magnetostrictives.

The transduction property of either magnetostrictive or piezoelectric materials is the means by which the energy in magnetic induction or electric polarisation is converted into mechanical movement. Both types of materials form the backbone of active transducer technology. The transductive properties of magnetostrictive materials have significantly improved since the early days since the discovery and understanding of the magnetic and magnetoelastic properties of the rare-earth elements. Alongside the advances in permanent magnet technology, novel bulk magnetostrictive intermetallics containing iron, terbium and dysprosium have become available in commercial quantities. The potential of these improved magnetoelastic properties are now being harnessed in a...