Hybrid polymer/cobalt chloride humidity sensors based on optical diffraction

Relative humidity (RH) photonic sensors based on hybrid polymer/inorganic materials operating by means of optical diffraction are presented. The sensing film elements are fabricated by casting or spin coating the polymeric/inorganic solution on grating structures and planar glass substrates. The base polymers were synthesized by high vacuum anionic and free radical polymerization techniques and are incorporating cobalt chloride nano- or micro-crystals at various concentrations. The sensors exhibit fast response, reversible behaviour and long-term stability together with a good sensitivity and a relatively large dynamic range. Functional characteristics and, in particular, the operational range can be tuned by sensor material composition.