Testing of an industrial structure

Patent metadata

Field	Value
Publication number	US-2016377528-A1
Application number	US-201415039788-A
Country	US
Kind code	A1
Filing date	Nov 27, 2014
Priority date	Dec 2, 2013
Publication date	Dec 29, 2016
Grant date	—

Abstract

A method and a device for analyzing a structure by tomography and diffuse acousto-elastic field correlation are provided. An optical fiber comprising a plurality of measurement points of FBG (Fiber Bragg Grating) type, comprising sensors of Bragg grating type, is deployed in or on the structure to be analyzed. The method comprises the emission of light, into the optical fiber, and the measurement by correlation for each pair of FBG sensors. In a development, a prior imaging of the structure is performed by reconstruction of the velocities of propagation. Other developments comprise: the determination of the positions of the FBG sensors, the calibration of the tomography, the rosette configuration of the sensors forming the measurement points, the use of a plurality of optical fibers, of multiplexers, of lasers, of optical circulators, of omnidirectional optical sensors, of active noise sources, such as piezoelectric transducers, incorporated or not in the structure.

First claim

1 . A method for analyzing a structure by diffuse acousto-elastic field correlation, an optical fiber comprising a plurality of measurement points, a measurement point comprising one or more sensors of fiber Bragg grating FBG type, the optical fiber being deployed in or on the structure to be analyzed, the method comprising:
the emission of light into the optical fiber; the interrogation of pairs of FBG sensors measuring, over time, the acousto-elastic waves at the measurement points; the measurement by correlation for at least some of the pairs of FBG sensors, of a diffuse acousto-elastic field being propagated in the structure.

2 . The method as claimed in claim 1 , further comprising a step of reconstruction of the velocities of propagation of the acousto-elastic waves by tomography, the imaging being performed by the reversal of all the times of flight between the FBG sensors, each time of flight for each pair of FBG sensors being deduced from the correlation measurement, the sensors of a pair of sensors being associated with different measurement points.

3 . The method as claimed in claim 2 , wherein the position in space of each measurement point is previously and individually measured.

4 . The method as claimed in claim 2 , wherein the temperature of the structure is measured and a variation of time of flight induced by a change of temperature is compensated.

5 . The method as claimed in claim 2 , comprising a first measurement performed in an initial or reference state of the structure and comprising an imaging of the structure performed by tomography from said first measurement making it possible to identify certain geometrical peculiarities of the structure.

6 . The method as claimed in claim 5 , further comprising a second measurement performed in a subsequent state for the same pairs of measurement points as the first measurement and further comprising a mapping by tomography of the variations of the velocities of propagation in the structure between the initial state and the subsequent state obtained from the differences in times of flight measured between the two states.

7 . The method as claimed in claim 1 , wherein a measurement point comprises an FBG sensor.

8 . The method as claimed in claim 1 , wherein a measurement point comprises three receiving and directional FBG sensors substantially arranged at 120° to one another in a rosette configuration.

9 . The method as claimed in claim 1 , the measurement by correlation comprising a coder correlation of correlations between FBG sensors.

10 . The method as claimed in claim 1 , comprising a plurality of optical fibers as claimed in claim 1 , each FBG sensor being able to be interrogated separately.

11 . A system for analyzing a structure, comprising:
at least one optical fiber comprising a plurality of measurement points, a measurement point comprising one or more sensors of fiber Bragg grating FBG type; a light source coupled to the optical fiber; a photo detector or an optical spectrum analyzer to analyze the reflected light at the end of its path in the optical fiber; signal processing means for performing acousto-elastic field correlation and tomography computations.

12 . The system as claimed in claim 11 , wherein the light source is a laser for which the wavelength is varied or a wide band optical source of determined reflected optical spectrum.

13 . A system comprising a plurality of optical fibers as claimed in claim 11 , the optical fibers being multiplexed by means of at least one optical circulator and/or one spectrum analyzer and/or one multiplexer.

14 . The system as claimed in claim 11 , wherein one or more unidirectional sensors of FBG type are complemented by one or more sensors.

15 . The system as claimed in claim 11 , further comprising one or more active noise sources positioned in or on the structure so as to obtain a diffuse acousto-elastic field.

16 . The system as claimed in claim 1 , at least one active noise source being in a piezoelectric transducer.

Assignees

• Commissariat Energie Atomique

Inventors

• Chapuis Bastien

Classifications

• G01N2201/088

  Using a sensor fibre · CPC title

• G01N21/1702 Primary

  with opto-acoustic detection, e.g. for gases or analysing solids · CPC title

• G01M5/0091

  by using electromagnetic excitation or detection · CPC title

• G01N29/0672

  by acoustic tomography (medical tomography A61B8/13) · CPC title

• G01N29/2418

  using optoacoustic interaction with the material, e.g. laser radiation, photoacoustics (photoacoustic cells G01N21/1702; measuring characteristics of vibrations by using radiation-sensitive means G01H9/00; acousto-optical conversion techniques for short-range imaging G01S15/8965; sound-producing devices using laser bundle G10K15/046) · CPC title