Measurement Instrument
A microfabricated sensor deposited directly onto a component surface to measure mechanical deformation through changes in electrical resistance offers high spatial resolution and low thermal mass. When used in aerospace applications, a thin film strain gauge eliminates the need for organic adhesives that degrade at high temperatures. This sensor is capable of measuring strain on complex geometries and high speed rotating components.
Because of its low mass, the sensor does not alter the vibration frequency of the component under test.
Sensor Structure
Sputter deposition is used to apply successive layers of dielectric insulation, adhesion promoter, sensing grid and protective topcoat. The active grid is typically patterned using photolithography or metal shadow masks during the deposition process. This multilayer design ensures that the sensor is electrically isolated from the metallic substrate while remaining protected from oxidation.
Signal Generation
Mechanical strain is transmitted from the component through the insulation layer to the metal grid, causing the grid to stretch or compress. This physical deformation alters the length and cross sectional area of the metal pathways, which changes the electrical resistance. This resistance change is measured using a Wheatstone bridge circuit to calculate the strain.
Calibration Check
Calibration and testing are performed to determine the gauge factor and the apparent strain profile of the sensor. The sensor is tested under controlled thermal and mechanical conditions to establish its response curve. This data is used to compensate for temperature effects during live testing, ensuring that the sensor output reflects only the mechanical forces.
