An Investigation Of The Hydrogen Sensor By The Use Of LPG Coated With A Thin Pd-Ag Film

Hydrogen is an important clean renewable energy. Since hydrogen is explosive, it should be measured and controlled strictly in industry processing. Among various kinds of hydrogen sensors, the one based on the long period fiber grating has a lot of advantages, such as safe, simple, small, light, immune to the electromagnetic interference, and able to work under the harsh environments. But the research on this kind of hydrogen sensor is still in preliminary stage. In this thesis, a hydrogen sensor based on the long period fiber grating coated with a thin palladium- silver（Pd-Ag） film is investigated. The main contents include:（1） By using the optical couple-mode theory, the working principle of long period fiber grating and the sensor is analyzed. The conclusion is that the refractive index of the Pd-Ag film changes with the absorption of hydrogen, which leads to the change of resonance wavelength of sensor.（2） Improve the writing technology of the long period fiber grating by using CO₂ laser. Three key factors in writing the long period fiber grating: the position of the fiber, the energy of the CO₂ laser, and the scanning times were studied experimentally. By controlling these factors, the long period fiber grating with good quality and consistency is achieved.（3） The sensor is fabricated by coating the long period fiber grating with Pd-Ag film using magnetron sputtering. It is found that the resonance wavelength of long period fiber after coating shifts towards longer wavelength, which agrees with the theory analysis.（4） The specification of the sensor, including the sensitivity, precision, repeatability, response time and recovery time, stability, and temperature characteristic are investigated experimentally. The sensor shows a good response, and the experimental results agree with the theory analysis.