A Temperature Self-Compensated LPFG Sensor for Large Strain Measurements at High Temperature

Abstract

In this paper, a CO2 laser-induced long-period fiber-grating (LPFG) optic sensor was packaged with a hybrid mechanism of elastic attachment and gauge length change for large strain measurements in a high-temperature environment. An emphasis was placed on the use of two cladding modes (LP06 and LP07) of a single LPFG sensor for simultaneous strain and temperature evaluations so that exact temperature was used to compensate strain measurements. Both strain and temperature sensitivities of the LPFG sensor, as well as the strain transfer ratio due to a combined effect of elastic attachment and gauge length change, were analytically derived and validated with tension tests at elevated temperatures. The strain sensitivity of the LPFG sensor switched sign from negative for LP06 or lower modes to positive for LP07 or higher modes, whereas its temperature sensitivity remained positive. The sign switch for the strain sensitivity resulted from two competing changes of grating period and effective refractive index as the gratings are subjected to an axial strain. The LPFG sensor was demonstrated to be operational up to 700 °C for a strain measurement of up to 1.5%.

Department(s)

Civil, Architectural and Environmental Engineering

Second Department

Electrical and Computer Engineering

Keywords and Phrases

High Temperature; Large Strain; Long-Period Fiber Grating (LPFG); Simultaneous Strain And Temperature Measurement; Strain Sensitivity; Strain Transfer Ratio; Temperature Sensitivity; Diffraction Gratings; Refractive Index; Sensors; Strain Gages; Temperature Measurement; Tensile Testing; Strain Measurement

International Standard Serial Number (ISSN)

0018-9456

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2010 Institute of Electrical and Electronics Engineers (IEEE), All rights reserved.

Publication Date

01 Nov 2010

Link to Full Text

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