<title>Three-axis strain and temperature fiber optic grating sensor</title>

Abstract

For many applictions it would be highly desirable to be able to measure all three axes of strain and temperature internal to composite materials. Conventional electrical strain gauges are undesirable to embed into composite materials because of their size, conductive nature, susceptibility to electromagnetic interference, incompatibility with the host material and temperature limitations. All of the tests done to date with single element fiber sensors have been limited to the measurement of strain in the in plane dimension. This paper describes an innovative fiber sensor based on dual overlaid fiber gratings on short lengths of birefringent polarization preserving fiber that allows three axes of strain and temperature to be measured at a single point.

Ex vivo measurement of lumbar intervertebral disc pressure using fibre-Bragg gratings

“…FBGs are commonly used to measure physical parameters such as strain (Black et al, 2002; Udd et al, 1996), temperature (Nunes et al, 2004;Yunqi et al, 2000), and pressure (Frank et al, 2003;Xu et al, 1993) and can also be configured to measure profiles of these parameters. The objectives of this study were: (a) to assess the linearity, sensitivity and hysteresis of a FBG sensor in pure hydrostatic compression, (b) to develop methods for implanting FBGs in the intervertebral disc, and (c) to determine the uncertainty in the FBG's measurement of disc pressure in response to compressive load in functional spinal units and to compare its sensitivity to the sensitivity of needle-mounted strain gauge pressure sensors.…”

Fiber grating sensors for structural health monitoring of aerospace structures

“…An axial-strain measuring fiber grating strain sensor can be expanded into a multi-axis strain sensor by using polarization maintaining (PM), or birefringent optical fiber [1][2][3][4]. The residual stress created in the birefringent fiber during manufacturing results in a slight change in the index of refraction along two mutually orthogonal polarization axes.…”

<title>Development of a three-axis strain and temperature fiber optic grating sensor</title>

“…An alternative approach was invented that [4][5] involves writing two overlaid fiber gratings onto birefnngent fiber. In this case the fiber was polarization preserving fiber with a beat length of about two millimeters.…”