Development of Wireless Sensor Nodes for Integration into Fiber Reinforced Composites

Abstract

Rising importance of energy-efficient technology increasingly gives rise to usage of Fibe-Reinforced Polymers (FRP) due to the huge potentials offered for lightweight, durable structures. In order to achieve the desired material properties and subsequent behavior, FRP production has to be carefully monitored and controlled. This thesis presents a collection of novel approaches for monitoring FRP fabrication processes and subsequent structural health monitoring applications, by developing flexible, wireless sensors for integration into FRP. To facilitate industrial application, the overall sensor concept explicitly focuses on simple and cost-efficient producibility, and intentionally targets automated sensor placement in an automated FRP production context. In order to minimize impact on FRP material integrity, and ease vacuum setup and part handling, the sensors need neither wires nor battery for operation, by making use of Radio Frequency Identification (RFID) technology. Two sensor types have been designed, individually targeting the two main applications with a different focus. Both sensors are able to precisely measure local material temperature. This gives insights into FRP fabrication processes, e.g.resin presence and curing temperatures, and later on into FRP operation conditions. Additionally, the first sensor presented is able to measure bi-axial mechanical strain of the finished FRP material by using a temperature-compensated full bridge strain gauge. The second sensor uses a structure of substrate-integrated, interdigital electrodes to give real-time insights into polymer curing behavior by measuring the changing capacitance between the electrode fingers, similar to a common dielectric sensor. To support electrode design for usage with the sensors, a thorough investigation is conducted regarding basic properties of interdigital electrodes, that have been fabricated on flexible polyimide foil via common PCB production technology. This thesis elaborates on development, characterization and limitations of the sensors, and it is shown how they can be used to monitor FRP production and mechanical strain of sensor-integrated specimens.