Additional sensor technologies for low-weight sensorised configurations
The different needs for SHM may be accommodated via matured sensor technologies already available in the market. A short description of the main candidate technologies is given below:



Fibre Bragg Gratings (FBG)
FBG sensors have been used for strain monitoring during cure and subsequent structural health monitoring. New, low radius fibres, comparable to the size of the fibres used in composite structures (~30μm) enable the use of FBG sensors as part of the structure.
Left: An “as received” FBG with fibre optic connector to attach it to the FBG interrogator . Right: Bragg gratings are in essence periodic perturbations of the refractive index along an optical fibre, and they are produced by exposing the core of the optical fibre to an intense spatially-varying pattern of ultraviolet light. A Bragg grating has the property of reflecting light within a narrow band of wavelengths and transmitting all the wavelengths outside that band.

Piezoelectric sensors
The piezoelectric phenomenon is utilized in order to sense and/or actuate according to specific needs. The versatility of piezoelectric sensors in size/geometry makes them ideal for many applications such as structural health monitoring, load measurements, stiffness degradation evaluation, active noise control, impact damage, vibration monitoring and others. The sensor can be embedded in the composite part and used throughout its life cycle.

Magneto-elastic sensors
Magnetic field sensors rely on the measurement of eddy currents induced by an alternating magnetic field. The main advantages of magnetic sensors is that measurements can be performed without the sensor being in contact with the material under test and that in depth measurements are possible. Magneto-elastic sensors have been used for structural health monitoring (crack identification, thermal and mechanical fatigue, corrosion and stress distribution).
 Magnetoelastic strip used as sensing element (metallic strip of thickness 0.1mm
Dielectric sensors
Dielectric sensors measure the changes in the electric field of composite materials. These changes are sensitive to the polymerization reaction, electric conductivity, moisture content and ageing phenomena (glass transition temperature) present in polymeric materials. Dielectric sensors in the form of interdigitated comb electrodes have been used for lab scale in situ monitoring of the curing reaction of composites. New developments in dielectric sensor technology enable the use of robust, durable sensors in industrial applications (RTM, pultrusion). The fabrication of dielectric sensors that can be embedded in the composite structure will make possible the continuous monitoring of the electrical properties of the part during its life cycle. Dielectric sensors mounted in the process tool (mould, pultrusion die) will control the production process leading to improved part quality and cleaner manufacturing process (less scrap, less material loss, faster production cycle). You may find more information on INASCO research activities in dielectric sensors development in directory R&D / Dielectric Sensors .