Development and evaluation of a novel piezoelectric PVDF sensor as a load spectrum counter

Engineering structures, such as aircraft, marine vessels, buildings and offshore platforms, are subjected to a range of uncertain dynamic loadings, due to changes in operational and environmental conditions, etc. Unfortunately, the load spectrum of these structures is usually an unknown with no appropriate device to assess it, leading to over-engineered structures. This project introduces a novel piezoelectric based sensor as a load spectrum counter that can measure the complex loading conditions over the structure's lifetime. The sensor has been designed using piezoelectric poly(vinylidene fluoride) (PVDF) combined with a custom electronic circuit, which counts the number of times the load in a structure surpasses pre-selected amount. Any force applied to the piezoelectric PVDF sensor generates an electrostatic output voltage due to the separation of charges in the atomic structure of the piezoelectric. The output from the piezoelectric PVDF (PE-PVDF) is a pulse wave with an amplitude proportional to the load input and an amplifier connected to the level detector used to enhance the pulse. When the amplitude of the data pulse exceeds a certain level, a signal emitted by the level detector activates the counter and stores the data. To prevent counting of noise an adjustable dead zone is added at each level detector. Therefore, after the load surpasses a specified level and a count is registered, no action occurs (i.e. the output is zero) and the load must drop under the dead zone and then rise again before another count is registered. The concept is validated experimentally both on an aluminium and epoxy/SE70 glass composites yielding load-spectra. The sensor is calibrated for different materials and geometrical conditions need to be investigated. The vision of the project is to make wireless and embedded fatigue counter sensors designed for real industrial applications.