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Embedded Inductively Coupled Sensors for Composite SHM



The desire for long term regular condition information for structures is becoming ever greater and there are several approaches which typically rely on permanently attached sensors. This paper describes an approach, that of embedding a sensor and coupling to it inductively. This is positive in providing reliable repeatable measurements, with a completely passive on structure component. A model of the coupling is developed using linear circuit analysis and reducing the system to a 2 port network. This model is key as it allows a separation of the ultrasonic and electrical parts of the model. In doing this, each can be optimised separately to ensure the best overall performance of the system. This paper will go through the development of this model and show how its output is used to optimise the sensor design, providing insight into the relative importance of different effects. Having shown how the performance may be predicted an experimental validation of this is presented and a discussion of practical implementation issues is carried out. This includes how inspections can be carried out fast enough to be useful, and over what range a practical inspection may be made. Finally the developed sensor package is shown and its performance in isolation and when embedded in a composite material demonstrated. This performance is compared to what would be expected with a conventional wired transducer and predictions as to its sensitivity for SHM applications commented upon.

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