Directly Deposited Thin-Film Strain Gauges on Curved Metallic Surfaces

This paper shows the possibility of direct deposition of strain gauge sensors on curved metallic surfaces of arbitrary size. A novel, patented sputtering system from the IMPT guarantees the manufacturing directly onto the surface of any component. By this, the need of the undesirable polymer foil and adhesive vanishes, which are both necessary for conventional sensors. Thin-film metal strain gauges thereby enable new measurement positions in harsh environments due to their minimal total thickness of under 5 μm, for example in industrial applications with special needs, as they exist for drilling bottom hole assemblies. This article discusses the optimization of laser cut stainless steel shadow masks for structuring the sensor layer resulting in low resistance differences of 5.3 % for sputtered sensors. The developed constantan strain gauges show a low temperature coefficient of resistance of 74.8 ppm/°C, stability up to at least 210 °C and a k-factor of 1.98. Half-bridge measurements revealed an apparent strain of 156 μm/m at 200 °C and an error of only 6 μm/m when strain is applied.