Smart Sensor and Actuator Technologies for SHM

Each class of smart material possesses certain unique properties which makes them attractive for specific application. Shape Memory Alloys (SMA) like Nitinol can generate considerable amount of free strain but the operational bandwidth is too low to be used directly for most of the structural dynamic applications. Hence, they are suitable for static shape control and low frequency dynamic applications. The possibilities of high free-strain availability often tempted the scientists to use SMA for controlling the dynamic response. Baz et al [1995] have tried to use it as a spatially distributed stress generator which can make the host beam stiffer and less susceptible to buckling. Materials like optical fiber and magneto-rheological fluids are also clustered in the group of smart materials. Optical fiber is notable for its sensing applications. A comparison of electro-mechanical properties of smart materials is listed in Table 11.1.

Table 11.1 Comparison of electro-mechanical properties of different smart materials         [Crawley, 1994]

Magnetostrictive and piezoelectric materials are particularly useful in dynamic applications. Hence, they are being discussed in some details in view of their usefulness both as actuator and sensor.