Multifunctional sensor nodes in stretchable network for structural health monitoring

A highly expandable and conductive polymer-based substrate for sensor network applications was recently proposed. The concept of the substrate design was to reduce the amount of material that is ultimately integrated in structures, processing time and integration costs. The key of the flexible substrate expandability was to build a high density array of nodes, at the nano/microscale, interconnected by extendible wires. The nodes in the network house the sensors and the electronics while the wires carry the electrical signals. To facilitate the concept development an investigation is performed to add functionalities to the expandable substrate. The main focus is initially devoted to the implementation of sensors such as resistance temperature detectors (RTDs) in the nodes of an expandable substrate and then turns to the investigation of the concept and implementation of a multifunctional expandable sensor network. Conceptually the multifunctional sensor network is an array of functional and expandable cells each controlled by a microcontroller directly built-into the network. The nodes in each cell can host a wide variety of sensors to monitor different parameters (such as temperature, pressure, strain, etc.). In this paper the circuit design, implementation and testing of functional and multifunctional cells is investigated at the node and at the network level. The functional cell includes an array of RTD sensors, while the circuit of the multifunctional cell was designed to include RTDs, strain gages, digital sensors as well as PZTs. These results represent the first step toward the integration of multiple functionalities on an expandable substrate. The capability to build a multifunctional network consisting of numerous nodes on a highly expandable substrate, capable of covering large areas has the potential to be the foundation of the next generation of SHM systems.