Research On The Method And Device For Measuring Water Content Based On Microwave Cavity Detection

Water resources affect various fields of human life.Currently,the world is short of water resources,which requires us to make rational use of water resources.In the processing and manufacturing industries such as grain,paper,fertilizer,textile,and petroleum,the moisture content of raw materials is the main detection index,which has an important impact on the production and manufacturing process.By detecting the water content of raw materials,scientific and rational use of water resources can be achieved.Therefore,the detection of material moisture content has become a hot topic in scientific research,covering various industries of human life,especially industrial and agricultural production.In this paper,a thorough comparative study has been conducted on the applicable scope and characteristics of commonly used water content detection methods at home and abroad,such as drying method,Karl Fischer method,electrical measurement method,and neutron measurement method.It has been found that drying method is destructive to the sample,Karl Fischer method requires complex instruments,electrical measurement method is subject to many constraints,and neutron measurement method has a high cost,which cannot fully meet the demand for real-time online measurement in industrial and agricultural production.The principle of microwave method is that at microwave frequencies,water molecules will polarize and undergo high-frequency oscillations,during which microwave energy will be lost.Therefore,the moisture content of materials can be indirectly determined by measuring changes in microwave related parameters.The microwave space wave method for measuring the water content of materials requires no damage to the material under test,and has fast measurement speed and high accuracy.The water content detection device manufactured using this technology can meet the requirements of online non-destructive testing of material water content.Reflection,transmission,and scattering are common phenomena during microwave transmission.Scattering can cause errors in measurement and affect measurement accuracy.In this study,a reflective cavity detection structure is designed to solve the scattering problem of microwave space wave method.The specific measurement device structure includes a horn antenna,a slotted waveguide,a microwave signal source,a detection probe,a coaxial line,a microwave power detector,a guide rail unit,a sliding platform,and a control unit.The device drives the detector probe through the motor driven sliding platform of the guide rail unit to move in the slotted waveguide cavity to measure the traveling standing wave signal.The collected raw data signals are analyzed and processed by a control unit based on a GD32 microcontroller to fit the moisture content prediction formula for granular materials.The fitting formula is further analyzed and verified,and after confirming its reliability,the formula is input into the hardware program to complete the calibration of the entire moisture content detection,Thereby realizing the detection of the water content of the material.In this paper,soybean and wheat were selected as experimental materials to conduct experiments,and the obtained microwave cavity detection test data were analyzed and processed.The fitting equations for grain moisture content,standing wave ratio,and extreme position were established.The results showed that the goodness of fit of the soybean prediction model equation was 0.989,the root mean square error was 0.658,and the prediction standard error was 0.637%;The goodness of fit of the wheat prediction model equation is 0.984,the root mean square error is 0.729,and the prediction standard error is 0.703%.The model has high prediction accuracy and good stability,and can achieve rapid and non-destructive testing of the moisture content of soybeans and wheat.This article optimizes and innovates the structure of a microwave water content detection device,using a combination of a slotted waveguide cavity and a movable probe to simplify the device structure,improving its portability,as well as strong anti-interference ability.It can achieve online rapid non-destructive measurement,and has broad application prospects in fields such as agriculture and processing manufacturing.