Fibre-based magneto-optic layer-sensor (FAMOS²)

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Composite-embedded fibre optic strain sensors play an important role for long-term monitoring of safety relevant structures, such as offshore wind turbine power plants or wing or fuselage parts of aircrafts. Until now, no validation procedure for embedded sensors exists that allows the evaluation of the sensors behaviour after installation and during operation of the structure. Therefore, self-diagnostic capability of embedded sensors is required to provide the users information about reliable and long-term stable sensor function. In order to fulfil the requirements, a magnetostrictive layer is to be applied onto the strain-sensitive optical fibre to evaluate the functionality after embedment and during operation of the structure. The sensitive element in the optical fibre is strained by applying a magnetic field. The relation between applied magnetic field and optical response signal of the sensor determines the characteristic calibration curve. Changes in the calibration curve of sensors embedded in materials correspond to changes in the embedment condition (e.g. interface delamination, sliding of the sensor inside the material). This way, the reliable functionality of the sensor can be determined and separated from changes of the material to be evaluated, e.g. material aging.The main goal of this project is the characterisation and performance proof of the self-diagnostic feature of magnetostrictive FBG-elements (Fibre Bragg Grating). Fundamental investigations concerning reproducibility, stability of the calibration curve, precision and long-term stability of the magnetostrictive element should be carried out during this project.If this concept is confirmed to be successful, the evidence of functionality of embedded fibre optic sensors will be possible, and the maintenance periods for the determination of the structures integrity can optimally be planned. This leads to a reduction of maintenance costs and personnel capacity. FBG-elements can then be used as strain sensors in safety-relevant online-monitoring systems, and maintenance of structures is only necessary when the sensor shows a critical signal. This basic research is of principal importance for the use of measurement systems in safety-relevant structures and facilities, when the maintenance costs are very high (e.g. offshore wind turbine power plants, offshore oil platforms), or where the maintenance break must highly efficiently be organized (e.g. maintenance of aircrafts).