An investigation was performed to develop a flexible sensor network that can be stretched and expanded to cover structures with an order of magnitude larger than its original unexpanded size. The increasing need to cover large areas with a high number of sensors, networks, and electronic devices for structural health monitoring leads to this study. In this paper a flexible polymer with ultra- high stretching capability (linear expansions larger than 1000% the original length) is designed, fabricated and tested for sensor network applications. The stretchability of the polymer is achieved by engineering thousands of micronodes, which house the sensors and electronics, interconnected by extendable and flexible polymer microwires. The extendable microwires are the key element to perform uniform expansions of the network in all directions, to allow precise location of the nodes, to maximize the polymer expansion per unit area and to allow translation only of the nodes. With the proposed microwire design, a linear elongation wider than 1000% was achieved for a 256 nodes network, avoiding failure of the microwires and micronodes during fabrication and extension. It is believed that the proposed flexible, expandable polymer design is a cost-effective approach to integrate networks of thousands of sensors, actuators and electronic devices into large structures.
A study was performed to develop a novel technique to enhance the bond strength between a piezoelectric (PZT)
actuator and a hosting structure. The bond interface has been considered to be a critical linkage between the structure
and the surface-mounted actuators. The loss of interface integrity can have a detrimental effect on the performance of the
PZT actuators. The key feature of the proposed technique is to embed a high-density array of oriented carbon nanotubes
(CNTs film) into the adhesive layer between the structure and the actuators to enhance the interfacial strength. This
presentation focuses primarily on the two fabrication techniques that were developed during the investigation: one is to
grow the CNTs directly on the PZT surface at elevated temperatures and the other is to grow the CNTs film on a
substrate and then transfer it into the bonding layer at significantly lower temperatures. The latter method is a cost-effective
and easy technique which has the potential to be used for structural (as the one proposed here) and for high-performance
electronic applications. Through a microscopic examination of the adhesive, it was found that CNTs were
uniformly dispersed and aligned into the bonding adhesive. Mechanical tests were performed to investigate the shear
strength of the adhesive layer with the embedded CNTs film. Preliminary results show that an increase of the bondline
strength up to nearly 300% could be achieved. However a wide data dispersion was also observed and might be
attributable to the ratio between the length of the CNTs and the actual PZT-structure gap .