A load cell using an optical fiber Bragg grating with inherent mechanical temperature compensation

Abstract

There is increasing demand for monitoring of distributed force loaded at various parts in architectural and civil engineering structures to prevent disasters or maintain performances. For this purpose, an optical fiber Bragg grating (FBG) sensor is one of the most promising candidates due to its simple operational principle and the capability to duplicate by WDM technology. For practical use, the temperature characteristics of the center wavelength of an FBG should be eliminated. Various studies based on optical approaches have been conducted for this purpose. However, the resulting systems are complicated and expensive because special FBGs are needed or the number of FBGs is doubled. This report proposes a load cell, which is a force sensor, using a ready-made FBG that can replace a conventional load cell. This device consists of an ordinary FBG for communication and an octagonal frame that has an athermal mechanism. The idea is based on mechanical behavior of the structure on which the FBG is installed, instead of the optical properties of the FBG. This report describes the design of the temperature compensating structure using the finite element method (FEM), as well as experimental studies of the load and temperature characteristics.