Engineering fields have traditionally focused on using uni-functional materials with set mechanical properties to design and build structures and products which fulfill certain design intents. Materials such as wood, concrete, and metals have served vast uses throughout history; allowing the construction of cities and industries. The industrial introduction of metals such as titanium or aluminum alloys and fiber-based composite materials have allowed the production of lightweight structures such as airplane fuselages and numerous inventions. While great strides have been made in the field of materials, modern science and engineering does not tell how to design and manufacture multifunctional materials, which can be designed for multiple design intents such as actuation and sensing in addition to fulfilling load-bearing requirements.
Traditional materials such as wood, concrete and metals are generally highly engineered and optimized to certain design requirements. Systems in Nature however, use complex materials, which are genetically optimized through natural selection to accommodate the changing conditions of a certain operating environment. In many ways current material design concepts are being rethought with an eye towards systems, which integrate active components into traditional materials to create material systems which interact with their environment. One method of accomplishing this goal is the integration of sensors and actuators into laminate materials. This allows the engineering of multi-functional products, which can sense and respond to changes in their environment and thereby increase the functionality of the original design. The field of smart materials seeks to fill the gap between traditional uni-functional and controllable multifunction materials.
The goal of smart materials research is to enable the design of materials that can function beyond the traditional design interests such as strength, stiffness, thermal conductivity, etc. An active or smart material system can generally be thought of consisting of three essential elements, the active material, the passive material, and the control system.
The active material is defined as the actuator or sensor element. As a sensor, the device exists to receive information from the operating environment (such as vibration or mechanical deformation). As an actuator the device enables interaction with the environment via shape or vibration control. The term “passive material” or “host structure” denotes the material that the device is integrated into. Finally, the control system refers to the mechanism or program which collects information from the sensor elements and controls actuation of the material. Modeling of various control systems has been addressed in numerous works, but research into the coupling between device and structure is infrequently addressed. Ideally, the same device should be able to act as a sensor and actuator, thereby lending greater flexibility to fulfilling the specific design requirements of any given application.
