Strain measurements of a multilayer panel via Fiber Bragg Gratings as novel approach for deflection monitoring of tracking particle detectors

摘要

In this work authors propose to calculate the deflection of planar panels from the longitudinal surface strain measurements by means of FBG (Fiber Bragg Grating) sensors arrays properly bonded to (or embedded in) panels. To this aim a simple post processing analysis of FBG strain measurements is proposed and discussed. The relationship between the longitudinal strain and the vertical deflection is derived by classical beam theory. Indeed, a second derivative relationship exists between the displacement orthogonal to the surface and the strain component parallel to it. In order to know the strain components, FBG sensors have to be applied on both surface of the panel. The usefulness of the proposed technique can find important application in deflection monitoring of a novel detector, micromegas (MM), based on a micro mesh gaseous structure will be installed as a tracking detector in the ATLAS experiment at LHC (Large Hadron Collider) at CERN (European Organization for Nuclear Research) by the end of 2018, during a major upgrade of the experiment. Thus, in order to validate the proposed methodology, measurements of the surface strain and then of the deflection of a relatively miniaturized MM panel prototype have been carried out. Furthermore, preliminar experimental results of the indirect deflection measurements on a full size MM panel (with trapezoidal shape) have been carried out showing that deflection measurements with resolution of few tens of microns can be successfully achieved.