A multi-mode extrinsic Fabry-Perot interferometric strain sensor

This paper reports on the fabrication and evaluation of a multi-mode extrinsic Fabry-Perot interferometric (EFPI) sensor which is capable of measuring both tensile and compressive strains. A scanning monochromator was used to measure the absolute cavity length of the EFPI sensor. Sensors of this type were embedded within a 16-ply carbon-fibre-reinforced epoxy composite and tested under quasi-static tensile and compressive loading conditions. Excellent correlation was observed between the EFPI sensor and a surface-mounted extensometer. The sensor system can operate in the strain range from -1 to 1% with an accuracy of better than 30 micro-strain. Preliminary results indicated that the sensor design was relatively insensitive to temperature in the range 38-180 degrees C. An analysis of the relationship between the insensitivity and the sensor geometry is also presented.