Enhanced sensitivity of an in-fibre Bragg grating pressure sensor achieved through fibre diameter reduction

Abstract

Contemporary biomedical pressure sensors are based on miniaturized piezo-resistive, strain-gauge or other solid-state sensing technologies. All of these technologies have key limitations, when packaged into miniaturized sensors, including fragility and long term instability. In-fibre Bragg gratings (FBGs) are an attractive alternative to these electronic technologies because FBGs are biocompatible, robust, immune to electromagnetic interference and mechanically compliant. FBGs can also be used to measure multiple physical parameters and distributions of parameters. We present a FBG-based pressure sensor that has pressure sensitivity 20 times greater than that of a bare fibre FBG, and a major diameter and sensing area of only 200 µm and 0.02 mm2, respectively. Increases in pressure sensitivity are achieved by reducing the diameter of the fibre in the region of the Bragg grating, thereby resulting in reduced cross-sectional area and therefore increased axial strains for a given applied pressure. The presented design is an improvement over other FBG pressure sensors that achieve increased sensitivity through mechanical amplification schemes, usually resulting in major diameters and sensing lengths of many millimetres. Calibration results demonstrate the FBG sensor's ability to measure pressure with ±0.36 kPa repeatability over a 14 kPa range. To our knowledge, this is the only FBG-based pressure sensor of its size to achieve this repeatability.