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Multifunctional Materials 311

Matrix
Anode
Electrolyte
Cathode
Metallized contact
Low-o glass fiber
Figure 12.2 ITN Powerfiber with simultaneous battery and structure functionalities.

The integration of sensing into materials has made many advances in recent years. Much of the
research has been conducted under the context of Structural Health Monitoring, or SHM. In line
with the overall theme of this book, researchers seek to make a material sense its environment, feel
internal damage, and signal an alert that repair is needed, essentially mimicking the behavior of
biological organisms. Later in this chapter we provide an approach to integrating sensing into
composite materials. For a comprehensive overview of the field, the reader is directed to a recent
review paper on the subject (Mal, 2004).
This brief introduction to multifunctional materials only scratches the surface of the various
multifunctional concepts developed to date. The remaining sections of this chapter will detail a
further example of a multifunctional material under development at University of California, San
Diego (UCSD), in the first author’s laboratories. The functionalities of this material include
integrated structural, electromagnetic, thermal, healing, and sensing capabilities. While this ma-
terial in no way encompasses all of the possible functionalities that may be integrated into a
material, it offers an example of how such an integration may be achieved while maintaining the
structural integrity of the overall material. Particular attention is given to the interplay and resulting
synergy between the various elements that contribute these functionalities.

12.2 MULTIFUNCTIONAL COMPOSITES

We focus on the issues that relate to integrating multiple functions into fiber-reinforced
polymers to create composites with basic structural attributes that can also perform other functions.
We discuss various methods that have been used to control the mechanical, electromag-
netic (EM), and thermal properties of the material, while introducing self-healing, and environ-
mental-sensing and prognostic capabilities into the material. The polymer matrix of these
composites has the ability to covalently heal microcracks at rates that can be facilitated by
moderate heating through thin conductors which are also used to control the EM properties of
the material. The same conductors can also be used to create sensor-integrated electronic
networks within the composite, capable of sensing, and local and global communications and
decision making.