A Noncontact Force Sensor Based on a Fiber Bragg Grating and Its Application for Corrosion Measurement

Abstract

A simple noncontact force sensor based on an optical fiber Bragg grating attached to a small magnet has been proposed and built. The sensor measures the force between the magnet and any ferromagnetic material placed within a few millimeters of the sensor. Maintaining the sensor at a constant standoff distance, material loss due to corrosion increases the distance between the magnet and the corroded surface, which decreases the magnetic force. This will decrease the strain in the optical fiber shifting the reflected Bragg wavelength. The measured shift for the optical fiber used was 1.36 nm per Newton. Models were developed to optimize the magnet geometry for a specific sensor standoff distance and for particular corrosion pit depths. The sensor was able to detect corrosion pits on a fuel storage tank bottom with depths in the sub-millimeter range.

In-fiber Fabry-Perot interferometer for strain and magnetic field sensing

“…The solid line is the magnetic force calculated by a finite element model (FEM) and the circles are the FPI measurements. This force sensor presented a better sensitivity than the one using an FBG (1.3 nm/N) [15]. …”

“…The loose end of the fiber was passed through an acrylic support and glued to it, so that the FPI was located between the acrylic and the magnet. This device can also be adapted to detect corrosion in ferromagnetic structures in the same way as was done by using Fiber Bragg Gratings [15].…”

“…For the first configuration (for magnetic field sensing), the FPI was attached to the surface of a rectangular-shaped magnetostrictive material [14]. For the second configuration (for magnetic force sensing), the fiber was inserted inside a small magnet [15].…”

Preliminary View of a Smart Technique for Materials Testing in the Laboratory using FBG Sensor

“…Two types of this technology are the most commonly adopted; distributed fibre optics (DFO) and Fibre Brag Grating (FBG) sensing techniques. Recently, a conjuncture helical configuration developed by [5] from a single distributed optical fibre for laboratory characterization of materials have shown good correlation when compared with LVDT apart from the advantage of being immune to effect of lightning and electrical short circuiting which the existing devices are vulnerable to Fibre Bragg Grating (FBG) sensing technique is now being used in the laboratory for measuring quantities such as strain, temperature, acceleration and pressure [6]- [9]. The advantages offered by the sensor; extreme sensitivity, light in weight immune to electromagnetic interference (EMI), resistance to hash environment, multiplexing and multifunctionality have rendered the sensor useful in civil and many other engineering disciplines.…”

Multi-Axis Force/Torque Sensor Based on Simply-Supported Beam and Optoelectronics

“…Although there are many methods to measure deformation to calculate external force/torque, for example by attaching polyvinylidene fluoride (PVDF) films [33], strain gauges [20], piezoresistive materials [34], or fibre bragg grating (FBG) [21,35] on the sensor structures, we are proposing light intensity-based measurement using optoelectric technology [36,37,38] and simply-supported beam (Figure 1 and Figure 2) [39]. Our proposed methods have advantages such as immunity to electrical noise, low power consumption, low-level noise, no need for electronic filtering, easy attachment into the sensor body, and low cost [40,41,42,43,44,45].…”