Simultaneous Measurement of Thermal Gradient and Average Temperature in Concrete Blocks Using Nonuniform Long-Period Optical Fiber Gratings

Abstract

A recent increase in structural integrity requirements has lead to a higher demand for accurate heat flux and temperature readings of building material substrates. In the present work, simultaneous two parameter measurements of the average temperature and the temperature difference in concrete blocks are reported. To this end long period gratings (LPGs) were commissioned in a boron doped photosensitive optical fiber using a pulsed CO₂ laser. The average temperature and the temperature differences were shown to be a linear combination of the spectral shifts of the center wavelength and the changes in the variations in transmitted power <i>I</i>_c minimums. The sensitivity and cross-sensitivity coefficients of the sensitivity matrix are also reported.