Electric time-domain reflectometry sensor for online flow sensing in liquid composite molding processing

This paper describes the development of a new sensor type for resin flow detection in liquid composite molding (LCM) processing. The sensor can be applied in any LCM process where lineal and high-resolution flow front detection is required, i.e. during prototyping or as a feedback sensor during flow front control. The operating principle of the embedded sensor is based on electrical time domain reflectometry (E-TDR). The system analyzes changes in the transmission line response during wet-out of the preform. The flat band transmission line, which is interrogated by E-TDR changes its dielectric properties when the resin is on or near the sensor resulting in reflection of the electrical signal. The signal is evaluated in the time-domain by mapping the areas of resin on the sensor. The study illustrates an analytical model to predict the TDR response for different resin systems, validates the accuracy and resolution of the system in a lab-scale set-up and implements the sensor in several different injection scenarios. (C) 2002 Elsevier Science Ltd. All rights reserved.