Research And Design On A Solution Concentration Measurement System Based On Single-mode Cavity Resonator Perturbation Method

Microwave technology plays an important role in measurement region, based on foundation of Maxwell's electromagnetic theory. With more than one hundred years' development, microwave technology was considered as a fairly mature discipline. As a result, microwave technology have applied in communication system, radar measurement, disease detection, food heating, global positioning satellite and so on. Microwave sensors are insensitive to environmental conditions, satisfying steady signal transmission and online non-contact measurement. As a kind of microwave sensors, single-mode cavity sensor has advantage of high accuracy and sensitivity. Microwave perturbation is based on assumption that a variation of material produces a small change of electromagnetic distribution of sensor, thus resonance frequency shift is attributed to the change of material. Consequently, permittivity of material is calculated from measured resonance frequency shift outside.This paper focuses on saccharide-water solution concentration measurement, based on microwave perturbation. In theory principle and assumption of microwave perturbation is analyzed and characteristic of saccharide-water solution is taken into consideration. As a consequence, the relationship between permittivity and resonance frequency shift at a certain temperature is obtained.This paper presents two designed single-mode cylindrical cavity sensor with work mode of TE011 and TM010, which is designed on electromagnetic software workplace. The study have designed geometrical, material and electrical parameters and optimized key factor coupling device. The detecting precision of two sensors is 10 kHz.The online concentration measurement system is designed on FPGA platform, with combination of software instructions and hardware designs. The system consists of three modules including resonance state detecting module, resonance frequency searching module and frequency measurement module. Software instructions are designed to control measurement process and call different modules, based on C language. By combination of software instructions and hardware designs, FPGA control the process, call three modules and build database. Frequency measurement module is built on FPGA utilizing Verilog language, based on multi-synchronization method. The measurement time period is 1 s and measurement precision is 2×10-8. The least detection limit of saccharide-water solution concentration is 10 mg/L, which is more precise than other methods such as chemical method, near infrared method and interference optical method.