Design And Implementation Of A Solution Concentration Measurement System Based On Dual Acousto-optic Modulation

With the rapid development of modern science and technology and the continuous progress of precision manufacturing,the requirements for precision measurement technology have become higher and higher.The concentration of solution is an important parameter reflecting material information,which is closely related to human production and life,and the concentration of liquid needs to be measured in biosensing,drug detection,chemical production,etc.The accuracy of detection directly affects the subsequent research,so in order to ensure the quality of subsequent products and the accuracy of research,the realization of high-precision measurement of the concentration of solution becomes an urgent problem nowadays.This study combines the measurement requirements for system design from both optical path detection and signal processing.The details of the work are as follows.(1)The improvement and design of the optical path are completed,and the acousto-optic modulation technique is firstly studied,and the parameter characteristics of the acousto-optic modulator involved in this study are analyzed and experimented.Then,for the problem that the diffracted light of each level in the single acousto-optic modulation of the external differential interference system has mutual influence,which leads to the phase interference of the output signal at the same frequency,the external differential interference detection system with double acousto-optic modulation structure is designed.The measurement optical path and reference optical path with symmetric structure are also designed to further improve the anti-interference capability of the system.(2)To complete the processing of the interferometric signal,a dual AD acquisition module controlled by FPGA is designed to acquire the two interferometric signals carrying phase difference information output by the optical path,and the signal is processed and analyzed by digital phase discrimination method.And MATLAB is used to compare and process the data of the real-time acquired beat frequency signal for analysis,and finally the measured signal is obtained according to the relationship between the phase difference information obtained by processing and the measured signal.(3)The testing of the system was completed,and the phase characteristics of the system were experimentally tested to study the experiments,which proved that the system has good linear phase detection capability and provided a theoretical basis for the subsequent measurement of solution concentration based on phase modulation.Different percentage concentrations of solutions were measured,and the experiments showed that the system can achieve high accuracy measurement for low concentration solutions.The system mainly includes two parts: optical circuit detection and signal acquisition and processing.The article elaborates on the research of acousto-optical modulation technology,the principle of detection,the design of optical circuit,the design of intermediate processing circuit and signal acquisition and processing,and tests the function of the system through experiments,so as to complete the design of the concentration measurement system.The experimental results show that the detection system can better complete the detection of solution concentration by processing the information of signal phase difference change,and the maximum relative error is about 8.0% in the range of 0.1% to 0.5%.