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.

Review of fiber-optic pressure sensors for biomedical and biomechanical applications

“…and certain chemical quantities. 59,60 Some of the ideas just presented seem to be appellative. However, FOS remains unknown to many engineers, clinicians, and researchers.…”

“…88,93,115 Recently, FBG sensors have also been proposed to assess pressure; namely, in the nucleus pulposus of the intervertebral discs of the spine. 19,20,60,116 However, these apply only to ex vivo experiments. Thus, innovative solutions are mandatory for in vivo and clinical studies, namely to be integrated into specific diagnostic procedures of the spine (e.g., discometry) and surgical procedures (e.g., arthrodesis and arthroplasty).…”

“…A good example of innovation effort was accomplished by Dennison and Wild 60 They developed an FBG sensor with 200 μm OD, a sensitivity of 58.7 pm MPa −1 and a sensing area of only 0.02 mm 2 . Calibration results have demonstrated its ability to measure pressure with AE2.7 mmHg repeatability over a range of 105 mmHg.…”

Multi-curvities femtosecond laser aided microstructures for magnetic field sensing

“…And ( ) z Λ is the grating period, constant for uniform Bragg grating [10]. With temperature remaining constant, the central wavelength shift of the FBG due to axial strain is governed by equation (2),…”

Fiber Bragg grating sensor for two-phase flow in microchannels

“…This method ensures that the FBGs are strain free, isolating the response to a change in refractive index. FBGs are known to have low response to hydrostatic pressure (Dennison 2008): the typical pressure sensitivity of FBGs is 3 pm/MPa allowing resolution of pressures of the order MPa. The maximum hydrodynamic pressures that the sensor would be subjected in the present experiments are of the order of 10 KPa, which would correspond to a shift of approx 0.03 pm compared to the shifts of 400 pm reported here (Fig.…”