The availability of Terfenol-D in particulate form has given a new impetus to the use of magnetostrictive materials. Their magnetic permeability changes with the applied stress. The change in magnetic permeability may be detected in a number of ways. One method uses the amorphous ribbon as the core of an induction coil while another method monitors high frequency electrical impedance of the material. The change in impedance with applied stress can be very high (<100 per cent) which can result in a very sensitive strain sensor. Conventional metal foil resistance strain gauges and semiconductor strain gauges have gauge factors of 2 and 100 respectively while a magnetic strain sensor can have a gauge factor value of 1500. In addition to monitoring strain, magnetic sensors have successfully been used for cure cycle monitoring when embedded into an epoxy / polyester composite.

A combination of smart materials may be utilized to device sensors and actuators where actuation and sensing actions are performed by two different types of smart materials [Figure 6.2].

Figure 6.2 Hybrid magnetostrictive/ piezoelectric field sensors [Dapino et al, 1999]