Sensor concepts for Industry 4.0

Abstract: The next industrial revolution has been denoted by Industry 4.0 and is the continuation of the process of knowledge acquisition and further control over the entire production process which has been evolving since the beginning of the industrialization. A paramount driver of Industry 4.0 is the smart sensor. In this master’s thesis, the first stage of a complete smart sensor will be conceptualized. In industrial applications there is a need to determine the stresses that are present in a material when applying external pressure without using invasive methods. The material that will be investigated is Cr-doped Al2O3, i.e. ruby, which is a ceramic with outstanding mechanical properties useful in industrial applications. The doping of Cr3+ ions grants said material with interesting optical properties. Hence, the first stage of a complete smart sensor consists of verifying both quantitatively and qualitatively the fluorescence shift of the so called R fluorescence lines upon externally applying pressure to the Cr-doped Al2O3 material by using optical fluorescence spectroscopy. This physical phenomenon is also called the piezo-spectroscopic effect which is a behaviour that could act as a reliable sensor for monitoring the mechanical response of the material non-invasively. The results were inconclusive as the single crystal ruby acquired internal damage quite early during the piezo-spectroscopic measurements. However, fluorescence spectra was gathered and the R fluorescence lines could reasonably be identified. Ultimately, a fluorescence shift upon externally applied pressure could not be verified quantitatively nor qualitatively. For further work, the experimental setup must improve and conceptualizing a complete sensor for use in the next industrial revolution requires taking into account the effects of temperature and material composition in combination with the piezo-spectroscopic effect.