Multifunctional Skin based on Spiral Passive Electromagnetic Sensor for Efficient Structural Health Monitoring of Composite Structures

Abstract

The objective of this research work was to create and validate a low-cost smart-sensor for non-destructive evaluation (NDE) and structural health monitoring (SHM) to be easily embedded or surface mounted on complex aerospace composite skin structures. A Spiral Passive Electromagnetic Sensor (SPES) was designed and fabricated for damage detection. The sensor is a planar two-dimensional inductor circuit of scalable size that resonates at a characteristic frequency when exposed to an electromagnetic field. A change in a material's permittivity or permeability due to the presence of flaws within the structure can be sensed with the SPES by monitoring its resonant response. The devices described herein has already demonstrated, in previous works, the ability to detect flaws within conductive (i.e. carbon fibre) and non-conductive (i.e. fibre glass) structures[1, 2], [3, 4]. Moreover, the SPES can act as de-icing device and detect temperature and humidity variation [5, 6]. A study was conducted to investigate the capability of sensor to give information on the location and on the size of delamination. Multiple sensors were embedded in a smart-layer together with the antenna to create a sensing skin able to monitor composite structures. The sensor use a passive wireless resonant telemetry scheme and/or a wired interrogation method. The use of a passive system eliminates the need for on-board power and exposed interconnects, reduce the instrumentation mass and volume, increasing the life of the device and the reliability due to the continuous operation even in case the damage affect the sensor itself. The sensor presents a great potential to monitor defects in composite structure, acting as SHM sensor. The technique illustrated is able to locate and quantify the presence of damage, giving information on the defect before it causes a failure of the structure.