Viscosity sensor using long-period fiber grating based on transmission amplitude change of resonance wavelength

This work addresses a fiber optical viscosity sensor using long-period fiber grating (LPFG) with a capillary tube mechanism. As soon as the preheated 100 ml fluid reaches an LPFG, the time need was used to determine the discharge time. Thus, a noticeable amplitude change of resonance wavelength in transmission spectrum was observed. The LPFG sensor was first immersed in hot air and then in fluid and the corresponding amplitude-change-based discharge time and transmission spectra were measured at the same test temperature. We simultaneously measured the LPFG-induced discharge time and the transmission spectra both in hot air and AC-20 asphalt (or sunflower oil) at different temperatures. Comparative plot shows that the LPFG-induced discharge time agreed with the asphalt viscosities obtained from the rotational viscometer. The amplitude changes between sensing in air at 60°C and sunflower oil at several temperature increasing and decreasing conditions were also noticeable.