Ultrasensitive all-fiber inline Fabry-Perot strain sensors for aerodynamic measurements in hypersonic flows

This work proposes an ultrasensitive, temperature-insensitive, all-fiber inline Fabry-Perot (FP) strain sensor for aerodynamic coefficients measurements of a hypervelocity ballistic correlation model 2 in a Φ1 hypersonic wind tunnel. The FP sensors fabricated using 157 nm laser micromachining system are structurally simple, small-sized, and high-temperature resistance. 16 FP sensors are installed on a six-force balance, which is mounted inside the model, to sense the aerodynamic forces and moments of the model, and then the model's aerodynamic coefficients are calculated based on aerodynamic theory according to the test data. A new temperature-compensated method is proposed to improve measurement accuracy of aerodynamic coefficients via eliminating temperature-induced measurement errors. Experimental results show, at high temperatures, the FP sensors based on the balance (FP balance) exhibits a high-repeatability precision of the aerodynamic coefficients measurement of less than 1%, and match well with the results of the traditional method using foil-resistive strain sensors. This enhanced-sensitivity FP sensor is currently the most promising alternative to foil-resistive strain sensors for aerodynamic tests among kinds of fiber-optic strain sensors to the best of our knowledge. The FP balance satisfies the requirements of practical application of aerodynamic characteristic tests, and opens up another test system of the field.