Manufacturing smart surfaces with embedded sensors via magnetron sputtering and laser scribing

Magnetron Sputtering (MS) together with patterning via Laser Scribing allows manufacturing of thin film sensors/actuators embedded on the surface of components. These transducers add active monitoring and/or actuation capabilities to the piece, hence they are termed smart surfaces. To embed the sensors/actuators, the target surface is coated by MS with a 2 - 3 mu m insulator layer (usually a metal oxide such as SiO2, Si3N4 or Al2O3), and afterwards with a 0.5 - 2.0 mu m metallic conductor layer. Alternatively, a 15 mu m dielectric lacquer deposited by spray coating is used as the insulator layer. The conductor is then selectively removed by LS without removing the insulator to draw a circuit completely isolated from the piece. The scribing of the circuits is done with a femtosecond laser (lambda = 517 nm) that allows extremely quick (-200 mm/s) and accurate manufacturing of a sensor in a few seconds with -30 mu m space resolution. The type of sensor is determined by the selection of the conductor(s) and insulator(s) materials and the shape of the circuit, and can be manufactured to match the specifications of the application by modifying the MS and LS parameters. In this work two types of embedded sensors were manufactured and tested: Resistive temperature detectors made of Al, Ti, W or Cu, and strain gauges made of NiCr. These embedded sensors can measure with a high degree of precision as they are directly connected with the piece without adhesives or polymer foils, and even without humidity, organics, or oxygen in between. In addition, this technology allows lo locate sensors in components with complex geometries, in places difficult to access with a traditional sensor, and as the sputtered sensors are only a few micrometres-thick they do not affect the dimensional tolerance of the piece.