The Structural Health Monitoring (SHM) is a key technology to detect and prevent critical damages in different kind of structures. Corrosion is one of the main issues affecting metallic structures exposed to wet environments or affected by high levels of moisture, such as in offshore aerogenerators or aircrafts, and, therefore, is a critical parameter to be monitored. In this work, an on-line SHM sensor is presented, based on impedance spectroscopy techniques, which can be used to continuously measure corrosion in the surface of different kind of structures, and which could be implemented in airframe and wind energy generation structures. The impedance of an interdigitated sensor is measured in a frequency range between 16mHz and 200kHz, with resulting impedance values up to 100GOhm. The impedance sensor aims at being a completely wireless and autonomous solution: the sensor integrates wireless data communication and is self-powered by two independent energy harvesting systems. An RF antenna is used to harvest energy from a RF emitter in static and low range applications, while a flexible PV panel is installed to directly harvest energy from the environment, also in moving applications such as wind generator blades. Moreover, the use of thin-film and flexible electronics facilitates the integration of the sensor into any surface with very little aerodynamic impact. All the interdigitated sensor, the associated control electronics and the energy harvesting system can be implemented in polymeric thin flexible substrates, combining printed and hybrid electronics and allowing curved and complex geometries for the sensor device.
The current paper describes the application of lens-free imaging principles for the detection and classification of wear debris in lubricant oils. The potential benefits brought by the lens-free microscopy techniques in terms of resolution, deep of field and active areas have been tailored to develop a micro sensor for the in-line monitoring of wear debris in oils used in lubricated or hydraulic machines as gearboxes, actuators, engines, etc. The current work presents a laboratory test-bench used for evaluating the optical performance of the lens-free approach applied to the wear particle detection in oil samples. Additionally, the current prototype sensor is presented, which integrates a LED light source, CMOS imager, embedded CPU, the measurement cell and the appropriate optical components for setting up the lens-free system. The imaging performance is quantified using micro structured samples, as well as by imaging real used lubricant oils. Probing a large volume with a decent 2D spatial resolution, this lens-free micro sensor can provide a powerful tool at very low cost for inline wear debris monitoring.