Inductive strain sensing using magnetostrictive wires embedded in carbon fibre laminates

The incorporation of sensors and actuators inside composite structures has become a new trend. Such structures are usually called 'smart', due to their capability for sensing and responding to the surrounding environmental stimulus. Among the many different types of sensors used for this purpose, the most popular are those that measure strain. In this paper, we investigated several inductive (noncontact) strain-sensing methods. The basic idea was to incorporate magnetostrictive wires inside composite laminates to act as both structural and sensing elements. The proposed technique does not require the connection of the sensing element (magnetostrictive wire) to the measuring device. Using a single transducer (which is connected to the measuring device), we can acquire strain measurements at any point. This facilitates installation, especially in cases where a large number of sensing elements are involved. In addition, the experimental results showed that the minimum detectable strain value could be around 0.25 mStrain and the resolution up to 0.1 mStrain, which indicates high sensitivity. Using these wires as strain-sensing elements could enable inspections at regular maintenance intervals in order to retrieve the structure's 'strain signature'. The retrieved strain signature could then be compared to previous readings in order to trace potential differences and/or anomalies.