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Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c012 Final Proof page 337 21.9.2005 11:55pm

Multifunctional Materials 337

Figure 12.32 Composite panel with embedded network consisting of a 10 10 array of individually addressable
thermal sensors. A hand is placed on the panel (left) generating a thermal image (right). The image shown is
generated after about 20 sec, and represents about 38C maximum increase over ambient.

of the embedded sensor composite in a variety of mechanical loading scenarios to determine and
limit any adverse impacts on the strength of the composite. Additionally, detailed electrical design
of the embedded network will need to be undertaken. If higher sensor densities are to be contem-
plated, the network architecture and data handling strategies will also need careful study.
The current work is focused on the implementation of a composite embedded network. As those
problems are solved, it will be necessary to turn to specific structurally significant sensors to finally
realize integrated structural health monitoring of composites. We expect continued progress in
electronic miniaturization and power management. Smaller IC linewidths will drive the overall size
of chip scale packages smaller. Current work in implementing 458 on chip interconnects also promise
to reduce Si real estate demands. Higher levels of integration of MEMS-based sensors with standard IC
processing will result in greater choices of microsensors to integrate into composite structures.

12.3 SUMMARY

The field of multifunctional materials is still in its infancy with regard to various functionalities that
may be integrated into structural materials. With Nature as our guide the possibilities are limitless.
We have presented an overview of a multifunctional composite material being developed at UCSD.
This material incorporates electromagnetic, thermal management, healing and sensing functional-
ities into a structural composite. Integrated copper conductors resonate to provide a tuned dielectric
constant and index of refraction, ranging from negative through positive values. These conductors
may also serve as resistive heating elements to provide thermal management, which may be further
utilized to activate a thermal repair mechanism in a healable polymer matrix. Integrated network
sensors provide in situ sensing and damage detection at scalable and potentially high areal density
with local processing and decision making. Future work will include the fabrication of smaller scale
conductive element designs to achieve EM functionality in the terahertz frequency regime. The
architecture of the braided elements is being tailored to obtain optimal mechanical properties of the
composite structure. We are now studying other sensing technologies, such as piezoelectrics and
MEMS devices, which will interact through a network similar to that which we have demonstrated
with our thermal sensors.