We report a distributed fiber-optic pressure sensor based on Bourdon tubes using Rayleigh backscattering metered by optical frequency-domain reflectometry (OFDR). In the proposed sensor, a piece of single-mode fiber (SMF) is attached to the concave surfaces of Bourdon tubes using a thin layer of epoxy. The strain profiles along the concave surface of the Bourdon tube vary with applied pressure, and the strain variations are transferred to the attached SMF through the epoxy layer, resulting in spectral shifts in the local Rayleigh backscattering signals. By monitoring the local spectral shifts of the OFDR system, the pressure applied to the Bourdon tube can be determined. By cascading multiple Bourdon tubes and correspondingly attaching SMF sections (i.e., a series of SMF-modified Bourdon tubes), distributed pressure measurements can be realized. Three Bourdon tubes are employed to demonstrate the proposed spatially distributed sensing scheme. The experimental results showed that linear relationships between spectral shift and pressure were obtained in all three SMF-Bourdon tubes (i.e., at three spatial locations). It is expected that the proposed sensing device, the SMF-Bourdon tube, can be used in applications where distributed/multipoint pressure measurements are needed.
In this paper, we introduce a novel extrinsic Fabry-Perot interferometer (EFPI)-based optical fiber inclinometer for tilt measurements with 0.015 μrad resolution. The reported inclinometer consists of an EFPI sensor, which is formed between endfaces of a suspended rectangular mass block and a fixed optical fiber, packaged inside a rectangular container box with an oscillation dampening device. Importantly, the two reflectors of the EFPI sensor remain parallel while the cavity length of EFPI sensor meters a change in tilt. The sensor design and the measurement principle are discussed. An experiment based on measuring the tilt angle of a simply-supported beam induced by a small load is presented to verify the resolution and accuracy of a prototype inclinometer.