Optical fiber sensor have shown a great potential to become chemical sensors and have appropriate properties as long term stability, immune to electromagnetic radiation and multiplexing capability. In this work we present a way of measure the hydrogen present with just optic fiber as sensing device. The hydrogen enters the fiber following a diffusion behaviour. This hydrogen generates absorption peaks at several frequencies. We study that frequencies and determine witch ones are appropriate to use for a hydrogen sensor. We use the data collected to do a model of the fiber and simulate and validate that model with the experiments. We conclude the analysis with the advantages of that kind of sensor in a nuclear waste repository.
In order to compare their gas sensing properties two kinds of sensors based on silicon cantilevers of similar characteristics have been fabricated: On one side we fabricated gravimetric gas sensors based on silicon cantilevers acting as resonators. The active layers consisted of polymer films deposited on top of the cantilevers. Sensors were maintained oscillating at their natural resonance frequency with electronic circuitry also developed in this work. Basically they consist of mass-spring mechanical resonators in which the mass increment due to gas sorption in the polymer provokes a shift on the resonance frequency. The output signal is a sinusoidal voltage extracted directly from the oscillator, and the amount of gas absorbed is related to the frequency of this output signal. The second type of sensors consisted of capacitors in which one electrode is a silicon cantilever and the other is a fixed metallic electrode fabricated parallel to the silicon cantilever. The silicon cantilever of these devices is covered with the same polymer films as for the resonators. The sensing principle in this case relies on the bending produced by the internal mechanical stress induced by the absorption of the gas in the polymeric layer. In these devices the signal is obtained by measuring the capacitance between the two plates of the capacitor, in this case the out coming signal was the current of the capacitor: an amplitude modulated signal. The gas response of both types of sensors have been characterized and a comparison is presented in this paper.