I. Introduction

1.1 Overview of Microwave Application in Material Measurement

Microwave technology, as an application of high-frequency electromagnetic waves, has played a key role in material science and industry, especially in humidity, density and composition measurement. Non-contact, non-destructive and fast microwave humidity measurement is suitable for all kinds of materials. At the same time, microwave technology can determine the density and composition of materials by analyzing the propagation characteristics, which has a profound impact on the chemical, food, pharmaceutical and other industries.

1.2 Importance of water content measurement

As a key physical attribute of the material, moisture content has a profound impact on processing, storage and transportation. Accurate measurement can ensure product quality, improve efficiency and reduce costs. In the food industry, moisture content is related to the quality and quality of food, while the chemical and medicine field depends on moisture content to ensure product performance and safety. In environmental monitoring and agriculture, water content measurement affects crop yield and water resources management. Therefore, the development of accurate moisture content measurement technology, such as microwave method, is crucial to the progress of various industries, and has broad application prospects.

2. Basic knowledge of microwave

2.1 Definition and characteristics of microwave

 Microwaves, as part of the electromagnetic spectrum, have a frequency range of roughly between 300 MHz and 300GHz at wavelengths between 1 mm and 1 meter. Due to its unique physical characteristics, the electromagnetic wave in this frequency band has been widely used in communication, radar, navigation, remote sensing, industrial heating and material detection.

Microwave characteristics are reflected in the volatility and quantum property, which follow the law of electromagnetic wave propagation, and are suitable for communication and radar signal transmission and target detection. Its quantum properties transfer energy with photons, which affects microwave heating and material detection. Microwave can penetrate non-metallic materials, and is widely used in nondestructive testing and medical imaging. High frequency, short wavelength and good directionality are conducive to the accurate detection of radar and navigation.

2.2 Interactions between microwave and material

The interaction between microwave and material constitutes the application basis of microwave technology in detection and treatment. The interaction produces effects such as absorption, reflection, transmission, and heating. The absorption capacity of the material to the microwave, depending on the dielectric constant, electrical conductivity and frequency, can be used to detect the moisture content and density. Microwave reflection reveals the surface state and internal structure of the material, and transmitted waves provide information about the thickness and density. Microwave heating, with its fast, uniform and energy-saving characteristics, is widely used in food processing and other fields, and can selectively heat specific material components. A deeper understanding of these interaction mechanisms can help to expand the application of microwave technology and improve its efficiency.

3. The working principle of measuring water content by three-microwave method

3.1 Wet measurement principle of transmission attenuation method

Transmission attenuation is a common technique used by microwave to measure water content. It changes the propagation characteristics of microwave when it encounters different media. When the microwave passes through the aqueous material, the water absorbs energy leading to signal attenuation, which is associated to the water content of the material. It can measure the attenuation degree of the signal through the material. The measurement accuracy can be optimized by considering factors including microwave frequency, power and material characteristics. This method has the advantages of fast and simple, suitable for materials with high water content and small thickness, sensitive to moisture changes and high measurement accuracy. However, for materials with thick or low water content, other methods may be adopted.

3.2 Wet measurement principle of resonance cavity method

The resonator method is a common technique for measuring water content by microwave, based on the resonance effect of microwave in the resonator. When the water-bearing material is placed in the cavity, its water content affects the resonant characteristics, resulting in the frequency and amplitude of the microwave signal changes. By monitoring these changes, the water content of the material can be calculated. This method requires the design of resonators with stable frequency and high quality factor to ensure the measurement accuracy and reliability. The advantages are high precision and stability, but the cavity design is complex, the technical requirements are high, and the material position may affect the results, so measures need to be taken to reduce the interference.

4. transmission attenuation method measurement technology

4.1 Construction of wet measurement system for microwave attenuation method

The key to the construction of transmission attenuation wet measurement system is the reliable microwave system, including transmitter, receiver, transmission path, material to be tested and data processing unit. The transmitter generates high frequency microwave, reaches the material through transmission path, the water molecules cause signal attenuation; the receiver switches to electrical attenuation signal, and the data processing unit analyzes the electrical signal to obtain the water content. The system design should consider the accuracy and frequency adaptability of the transmitter and receiver, the transmitter needs high frequency stability, and the receiver needs high sensitivity and wide dynamic range. The transmission path should be designed to reduce attenuation and interference, the air path is suitable for short distance, and the waveguide path is suitable for long distance and complex environment. The algorithm selection of data processing units (e. g., amplitude comparison, phase difference, spectrum analysis) should be optimized according to the application and measurement requirements.

4.2 Experimental design and result analysis

We experimentally verify the effect and accuracy of the transmission attenuation method in measuring the moisture content of materials. The experiments involved multiple moisture content materials, such as soil, wood and paper, as well as different microwave frequency and power combinations. The results show that the microwave signal decay is positively correlated with the water content, and the frequency and power increases. Accordingly, we confirm that the technology has high accuracy and reliability, but the frequency and power selection should be based on the practical application. Future work will focus on system improvements to improve measurement accuracy and stability.

5 microwave resonance cavity method of material moisture measurement

5.1 Resonator cavity perturbation principle and electromagnetic field distribution

The microwave resonator method measures the material moisture based on the disturbance principle of the electromagnetic field in the cavity. In the cavity, the resonant frequency and quality factor are stable; after adding the material, the polarization motion of moisture molecules disturbs the electromagnetic field, causing the frequency offset and quality factor change. In the standing wave mode, the scattering and absorption of materials affect the field distribution, and the change is related to the water content. By monitoring these changes, the moisture content of the material can be measured indirectly.

5.2 Design and simulation of gap array split cylindrical resonator

In order to accurately measure the material water content, it is crucial to design a high-performance microwave resonance cavity, in which the gap array split cylindrical resonance cavity is common because of its simple structure and excellent properties. The design focuses on the configuration of the gap array and the optimization of the cavity size to regulate the electromagnetic field distribution and sensitive detect the water content. Simulation analysis can determine the optimal cavity size and improve the measurement accuracy and range. Electromagnetic field simulation software is used to simulate the electromagnetic field under the influence of materials and optimize the gap array parameters to achieve optimal measurement performance.

5.3 Software simulation of material moisture measurement

After the design and simulation parameters are determined, the software conducts simulation analysis of material moisture measurement, predict the influence of water content on resonance frequency and quality factor, and verify the feasibility of the measurement method. In the simulation, the mathematical model of material and moisture is established, the measurement process is simulated, the changes of frequency and quality factor under different conditions are analyzed, and the measurement accuracy and stability are evaluated. At the same time, the simulation also analyzes the source of measurement error, puts forward the optimization scheme, to provide reference for the actual measurement, and help to establish an accurate and reliable water measurement method.

6 Application and prospect of microwave wet measurement technology

6.1 Practical application cases of microwave wet measurement technology

Microwave wet measurement technology is widely used in industry, agriculture and scientific research, serving for food security, product quality and scientific research exploration. In agriculture, the technology monitors the water content of agricultural products to ensure harvesting, storage and transportation. Industrial field, especially paper making, textile, chemical industry, microwave wet measurement to ensure the stability and safety of production. In scientific research, it reveals the connection between moisture content and material properties, helps the material science and chemical engineering research, and provides a basis for the development of new materials.

6.2 Development trend of microwave wet measurement technology

With the continuous progress of science and technology and the continuous expansion of the application, the microwave wet measurement technology is developing towards the direction of higher precision, faster and more intelligent. First, in terms of the measurement accuracy, the microwave wet measurement technology will continuously improve the measurement accuracy and stability to meet the demand of high-precision measurement in different fields. Secondly, in terms of the measurement speed, the microwave wet measurement technology will further improve the measurement speed, and realize real-time online monitoring and rapid response. In addition, with the continuous development of the Internet of Things, big data and other technologies, microwave wet measurement technology will be combined with these technologies to realize remote monitoring, data sharing and intelligent decision-making and other functions, to provide more convenient and efficient services for all walks of life.

6.3 Future research direction and potential

In the future, the research on microwave wet measurement technology will continue to deepen, focusing on the mechanism of microwave and materials, and improving the theoretical basis. The development of new microwave sensors and devices will enhance measurement accuracy, response speed and adaptability. With the integration of artificial intelligence, technologies will enable intelligent automated data analysis and provide richer information. Developing a composite wet measurement system to cope with a complex environment is another research focus. Microwave wet measurement technology will maintain its important position in various fields and show broad prospects.