The Research Of Fluorescence Sensing System Based On Dual Frequency Phase Modulation And Experimental Analysis

In academic or industrial research usually need frequent measurement about p H and oxygen partial pressure. In medicine, p H or oxygen partial pressure plays an important role to evaluate critically ill patient's life characteristics. They commonly used in patients with clinical diagnosis of blood, body fluids and respiratory activity, etc. In the food processing industry, the amount of H+ and O2 is directly related to the quality of drinking water, food freshness and bacterial content of food or drink. For heavy industry, the value of p H is an important indicator in wastewater treatment and environmental monitoring acid rain. In ocean analysis and research, also need to pay close attention to these two parameters.At present, multi-parameter optical fiber sensors still have many problems. In the aspect of production, to turn multiple unrelated sensor into a integrated probe not only makes production more difficult, but also makes the sensing probe bulky. Therefore, the spatial resolution gets worse because each sensor unit in the space is not consistent. In terms of sensing mechanism, each individual sensor need different measurement methods and measurement conditions, thus different design of optical paths or circuits which will result in complicated structure and difficult versatility for every sensor become more necessary.In view of the fact that reliability of measurement in multi-parameter optical fiber sensing technology remains few problems, it is excited to design a new sensing system, which arranges all sensing unit in a probe using different optical modulation to measure two kinds of concentration. Research shows that the symmetric molecules such as oxygen molecules, their structure determines they have only stretching vibration but no vibration produced by change of dipole moment, so that we cannot use optical absorption principle for direct measurement. Fluorescence measurement technology emerges as the times require and become the object of study in many fields because of its high sensitivity and high selectivity.In this paper, firstly, we measure phase information instead of light intensity information which simplifies the design structure. According to the traditional double fluorescence lifetime reference technology, we need to find two different fluorescent substances which have the similar emission wavelength and the similar absorption wavelength. When these two fluorescent substances are excited by the frequency modulated light, they can emit the same frequency but larger wavelength light called fluorescence. Oxygen and hydrogen ion acts as a fluorescence quencher and cause the amplitude and phase of corresponding fluorescence changing. In basis of The fluorescence decay model, we promoted a new calculation method and simulate with Simulink to analyze the design scheme and predict the possible problems.Finally, base on the above analysis, we design a sensor system experimental platform. We measured oxygen concentration in the gas, dissolved oxygen and the value of p H in buffer solution. We use Matlab or 1stotp to fit the relationship between concentration, phase and fluorescence lifetime. The experimental phenomenon is consist of theoretical conjecture. In a word, this paper hopes to promote the multi-parameter measurement technology and the analysis show us a good beginning.