Study On Online Detection Of Biomass Concentration Based On Fiber Bragg Grating

In the biochemical reaction process, there are many factors impact the efficiency of biochemical reactions, such as a variety of bacterial suspensions of microorganisms, microbial activity , biomass concentration, PH value, circulation flow rate, temperature etc. In these factors, the biomass concentration is a significant parameter, carry out it on-line measurement is very important for people to supervision and control the biochemical reaction process. The complexity and uncertainty of these parameters in biochemical reactions process, which increases the difficulty to study the mechanism and optimal control process. The refractive index sensing technology of FBG to measurement biomass concentration has proposed, and the corresponding temperature compensation scheme was proposed to eliminate temperature changed to the influence of the biosensor. The main results are as follows.(1) The online measurement of biomass concentrations based on FBG refractive index sensor was proposed. Etched to a certain extent of the grating, the effective refractive index of the propagation mode will be affected by the change of the surrounding refractive index, the relationship between the Bragg wavelength shift and biomass concentration was studied.(2) Based on the sensing theory of the FBG, designed the online measurement of biomass concentration sensor. The designed theory and fabricated methods were studied, the different diameters of the FBG grating refractive index sensors by etching experiments was fabricated. In the different condition of HF concentrations, the grating cladding etch rate was obtained.(3) Theoretical analysis and experimental study the relationship between the FBG refractive index sensor and the refractive index of chemical solution. The experimental results show that the variation of Bragg wavelength increased as the surrounding refractive index increased, in the low refractive index, the relationship between the Bragg wavelength shift and the surrounding refractive index is linear, on the contrary, showing a nonlinear relationship between them. (4) According to in the low refractive index region, the relation between the Bragg wavelength shift of the FBG refractive index sensor and the surrounding refractive index is a linear; the sensor used to measure of biomass (low refractive index) changes.(5) The sensing principle of the fiber Bragg grating (FBG) biosensor in the low refractive index region was analyzed theoretically, and the corresponding temperature compensation scheme was proposed to eliminate temperature changed to the influence of the biosensor. A single-end etched FBG biosensor was designed and fabricated for the simultaneous measurements of the refractive index and temperature, and the temperature and refractive index sensitivity of the etched region and un-etched region was calibrated, respectively. The experimental results indicated that the Bragg wavelength shift increased as the yeast refractive index increased, showing that the relations between of them was linear. The relative error of the refractive index sensitivity of the sensor was 1.45%. Improved sensors can effectively eliminate the temperature variation to the measurement of biomass concentration.