Piezoelectric sensors and actuators: smart materials

`Smart´ materials have the ability to perform both sensing and actuating functions. Passively smart materials respond to external change in a useful manner without assistance, while actively smart materials have a feedback loop which allows them to both recognize the change and initiate an appropriate response through an actuator circuit. One of the techniques used to impart intelligence into materials is `Biomimetics´, the imitation of biological functions in engineering materials. Composite ferroelectrics fashioned after the lateral line and swim bladders of fish are used to illustrate this idea. `Very smart´ materials, in addition to sensing and actuating, have the ability to `learn´ by altering their property coefficients in response to the environment. Field-induced changes in the nonlinear properties of relaxor ferroelectrics and soft rubber are utilized to construct tunable transducers. Integration of these different technologies into compact, multifunction packages is the ultimate goal of research in the area of smart materials