Rapid Response All-Fiber Moisture Sensor

Combining the benefits of photothermal conversion in a doped optical fiber with the principle of Fiber Bragg Grating (FBG)-based temperature measurement, a new optical fiber method for the measurement of moisture content has been developed and its performance is reported. This novel all-fiber approach shows the important characteristics of fast response, miniaturization in the design and low power consumption. In this work, a 1480nm pump laser has been used to heat the cobalt-doped fiber used, which has been embedded in the sample under investigation, where the sensor temperature change was obtained by using a FBG written into the cobalt-doped fiber. The fast, in-situ measurement of moisture content developed takes advantage of the linear relationship between the temperature change characteristics experienced during the heating process and the moisture content. To calibrate and characterize the sensor developed, a variable moisture-content test platform was established, and experiments were conducted to investigate the performance of this optical fiber approach. The all-fiber moisture sensor developed in this way has been evaluated by measuring the moisture content of samples of soil and pulverized coal and the data obtained were in good agreement with the results obtained from using the more conventional (and slow) drying method, with a maximum error of just over 1% and a rapid, 2s, optimum measurement time achieved.