Hydrogel-based soil moisture content detection sensor and detection method

Abstract

The invention discloses a hydrogel-based soil moisture content detection sensor, which comprises a cylindrical probe, an electrode A and an electrode B are symmetrically embedded in the cylindrical probe, the electrode A and the electrode B are respectively connected with an insulated wire, the cylindrical probe is filled with a hydrogel matrix, conductive particles are uniformly embedded in the hydrogel matrix, and the conductive particles are respectively connected with the electrode A and the electrode B. And an insulating layer is arranged outside the cylindrical probe. The invention discloses a hydrogel-based soil moisture content detection method. The method comprises the following steps: S1, calibrating a sensor; s2, recording an impedance value; s3, data processing; and S4, displaying a result. Compared with a traditional dielectric constant measurement method, the detection accuracy and applicability are improved. The device is simple in structure and convenient to operate and carry, and detection convenience and flexibility are improved. The soil moisture content information can be obtained in real time, and powerful support is provided for timely adjustment of irrigation strategies, prevention of soil moisture abnormity and the like.

Description

Technical Field

[0001] This invention relates to the field of soil moisture content detection technology, specifically to a hydrogel-based soil moisture content detection sensor and detection method. Background Technology

[0002] In agriculture, environmental science, and engineering, accurate soil moisture content measurement is crucial. It is defined as the ratio of the mass of water in the soil to the mass of the soil in its dry state. In today's world of increasingly scarce water resources, the rational use of water and precision irrigation both rely on accurate understanding of soil moisture content. Currently, existing methods for measuring soil moisture content have several shortcomings: Traditional method: The oven drying method is a classic measurement method. It calculates the moisture content by measuring the difference in mass of the soil before and after drying. Although the measurement results are accurate, the operation is cumbersome and the whole process takes several hours. It cannot meet the needs of real-time monitoring and greatly limits its application in scenarios where timely acquisition of soil moisture content is required.

[0003] Electronic sensors: Modern electronic sensor technologies such as time domain reflectometry (TDR) and frequency domain reflectometry (FDR) can quickly estimate soil moisture content by measuring changes in the dielectric constant, making them suitable for continuous monitoring. However, these methods are sensitive to high-salinity soils, as salinity interferes with the measurement results, leading to decreased accuracy. Furthermore, the measurement results are unstable in soils with different textures, limiting their application range.

[0004] Remote sensing: Remote sensing technology that uses microwave signals carried by satellites or drones to estimate soil moisture over a large area can cover a large area, but its resolution is limited and it cannot accurately obtain soil moisture information in local areas, making it difficult to meet the needs of precision agriculture and small-scale site monitoring. Summary of the Invention

[0005] The purpose of this invention is to provide a soil moisture content detection sensor and detection method based on hydrogel, addressing the aforementioned technical problems.

[0006] The technical solution of the present invention: A hydrogel-based soil moisture content detection sensor includes a cylindrical probe with electrodes A and B symmetrically embedded inside. Electrodes A and B are respectively connected to insulated wires. The cylindrical probe is filled with a hydrogel matrix, and conductive particles are uniformly embedded inside the hydrogel matrix. An insulating layer is disposed on the outside of the cylindrical probe.

[0007] The insulated wire is connected to a measuring device, and the measuring device is connected to a computing device via a data transmission line.

[0008] The measuring device includes an impedance analyzer, and the computing device includes smartphones, tablets, and laptops.

[0009] The hydrogel matrix is ​​a transparent or translucent hydrophilic crosslinked polymer, which includes starch-based and acrylic polymers.

[0010] It also includes an auxiliary reinforcing rod disposed inside the cylindrical probe.

[0011] Electrode A and electrode B are made of corrosion-resistant metallic materials.

[0012] The shapes of electrodes A and B include sheet-like and needle-like.

[0013] The conductive particles include carbon nanotubes and silver nanoparticles.

[0014] A method for detecting soil moisture content based on hydrogels includes the following steps: S1: Sensor Calibration: Prepare a series of standard soil samples with known moisture content, insert the cylindrical probe of the sensor into each standard sample, wait for the cylindrical probe of the sensor to fully absorb the moisture in the soil and reach equilibrium, use a measuring device to measure the sensor impedance value at this time, record the impedance data corresponding to soil samples with different moisture contents, perform fitting analysis on these impedance data, and establish a calibration curve or mathematical model between soil moisture content and sensor impedance value. S2: Record impedance value: Insert the cylindrical probe of the calibrated sensor into the soil to be tested. The measuring device measures the impedance change of the sensor in real time and transmits the measured impedance data to the connected computing device to obtain the impedance value. S3: Data Processing: The computing equipment analyzes and calculates the measured impedance value based on a pre-established calibration curve or mathematical model, thereby indirectly deriving the soil moisture content. S4: Results Display: The calculated soil moisture content is displayed intuitively on the screen of the computing device, thus obtaining the soil moisture content.

[0015] In step S2, the computing device also stores and analyzes the measured impedance values.

[0016] The beneficial effects of this invention are as follows: 1. This application applies hydrogels to the field of soil moisture content detection, utilizing the unique water absorption properties and physicochemical properties of hydrogels that change with moisture content to achieve a sensitive response to soil moisture content. Compared with traditional sensor materials, hydrogels are inexpensive, have good biocompatibility, and are environmentally friendly to the soil environment.

[0017] 2. This application utilizes the principle that the volume expansion of a hydrogel after absorbing water alters the conductive path, leading to impedance changes, to detect soil moisture content. Compared to traditional dielectric constant measurement methods, this detection method, under high-frequency measurement, may reduce interference from soil salinity and texture, thus improving the accuracy and applicability of the detection.

[0018] 3. This application uniformly embeds the hydrogel matrix within the hydrogel, and combines this with symmetrically embedded internal electrodes and externally connected insulated wires to design a sensor with a simple structure and easy operation. The entire device can be designed to be miniaturized, allowing operators to easily carry it to different locations such as fields and construction sites for on-site testing, eliminating the need for complex equipment installation and debugging processes, thus improving the convenience and flexibility of testing.

[0019] 4. In this application, the electrical impedance measurement usually only takes a few seconds, which is much shorter than the hours of the traditional oven drying method. It can obtain soil moisture information in real time, providing strong support for timely adjustment of irrigation strategies and prevention of abnormal soil moisture.

[0020] 5. The hydrogel materials used in this application, such as starch-based or acrylic-based polymers, are inexpensive and widely available, reducing the manufacturing cost of the detection equipment. Simultaneously, the simple structural design reduces the complexity of the manufacturing process, further lowering production costs and making the detection technology easier to promote and apply.

[0021] 6. The technology described in this application works stably in various soil types, reducing the interference of soil salinity and texture on the test results. It can more accurately reflect the true soil moisture content, providing reliable data support for agricultural production, environmental monitoring, and engineering construction. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall appearance and structure of the sensor of the present invention; Figure 2 This is a schematic diagram of the internal structure of the sensor of the present invention; Figure 3 This is a schematic diagram of the distribution of conductive particles in the hydrogel of the present invention; Figure 4 This is a schematic diagram illustrating the application of the sensor in this invention. Figure 5 This is a comparison chart of the moisture content test of the sensor of this invention and the traditional drying method.

[0023] Reference numerals: 1-Cylindrical probe, 2-Electrode A, 3-Electrode B, 4-Hydrogel matrix, 5-Insulating layer, 6-Measuring device, 7-Calculating device, 8-Insulated wire, 9-Auxiliary reinforcing rod. Detailed Implementation

[0024] refer to Figures 1-5 A hydrogel-based soil moisture content detection sensor includes a cylindrical probe 1, with electrodes A2 and B3 symmetrically embedded inside the cylindrical probe 1. Electrodes A2 and B3 are respectively connected to insulated wires 8. The cylindrical probe 1 is filled with a hydrogel matrix 4, and conductive particles are uniformly embedded inside the hydrogel matrix 4. An insulating layer 5 is disposed on the outside of the cylindrical probe 1.

[0025] In this application, to ensure sufficient water absorption and facilitate rapid measurement by insertion into the soil, the cylindrical probe 1 is designed to be 4-6 cm long and approximately 0.8-1.2 cm in diameter.

[0026] Moreover, the hydrogel matrix 4 is soft and elastic, similar to jelly, and can adapt to the natural environment in the soil, reducing damage to the soil structure.

[0027] Electrodes A2 and B3 are symmetrically embedded inside the cylindrical probe 1, ensuring close contact between them and the hydrogel matrix 4, thus guaranteeing good conductivity. In practical applications, both electrodes A2 and B3 have smooth surfaces.

[0028] The insulated wire 8 is connected to the measuring device 6, and the measuring device 6 is connected to the computing device 7 via a data transmission line.

[0029] The measuring device 6 includes an impedance analyzer, and the computing device 7 includes smartphones, tablets, and laptops.

[0030] The hydrogel matrix 4 is a transparent or semi-transparent hydrophilic crosslinked polymer, which includes starch-based and acrylic polymers.

[0031] It also includes an auxiliary reinforcing rod 9 disposed inside the cylindrical probe 1. This arrangement is mainly to enhance the overall strength of the cylindrical probe 1, thereby facilitating the insertion of the cylindrical probe 1 into the soil for measurement.

[0032] Electrodes A2 and B3 are made of corrosion-resistant metal materials. The use of corrosion-resistant metal materials (such as platinum, gold, or stainless steel) for electrodes A2 and B3 primarily extends their service life, thereby extending the lifespan of the sensor.

[0033] The shapes of electrodes A2 and B3 include sheet-like and needle-like shapes.

[0034] Electrodes A2 and B3 can be sheet-like or needle-like to increase the contact area with the hydrogel matrix 4. Electrodes A2 and B3 are each connected to an insulated wire 8. The insulated wire 8 has a certain degree of flexibility and a suitable length, facilitating connection to external measuring equipment 6 such as an impedance analyzer to measure the impedance changes of the hydrogel matrix 4.

[0035] The conductive particles include carbon nanotubes and silver nanoparticles.

[0036] In the actual preparation process, conductive particles, such as carbon nanotubes or silver nanoparticles, are uniformly embedded in the hydrogel matrix 4. The addition of conductive particles gives the hydrogel matrix 4 a measurable electrical impedance, and it can sensitively reflect changes in the conductive path when the hydrogel matrix 4 absorbs water and undergoes volume changes.

[0037] A method for detecting soil moisture content based on hydrogels includes the following steps: S1: Sensor calibration: Prepare a series of standard soil samples with known moisture content, insert the cylindrical probe 1 of the sensor into each standard sample, wait for the cylindrical probe 1 of the sensor to fully absorb the moisture in the soil and reach equilibrium, use the measuring device 6 to measure the sensor impedance value at this time, record the impedance data of soil samples with different moisture contents, perform fitting analysis on these impedance data, and establish a calibration curve or mathematical model between soil moisture content and sensor impedance value. S2: Record impedance value: Insert the cylindrical probe 1 of the calibrated sensor into the soil to be tested. The measuring device 6 measures the impedance change of the sensor in real time and transmits the measured impedance data to the connected computing device 7 to obtain the impedance value. Specifically, the cylindrical probe 1 of the calibrated sensor is inserted into the soil to be tested. The hydrogel matrix 4 inside the sensor rapidly absorbs water from the soil. As water is absorbed, the hydrogel matrix 4 expands in volume, changing the internal conductive path and thus altering the impedance value. The measuring device 6 (impedance analyzer) measures the impedance change of the sensor in real time and transmits the measured impedance data to a connected computing device 7 (such as a smartphone, tablet, or laptop). Simultaneously, the computing device 7 stores and analyzes the measured impedance values ​​for subsequent querying and research.

[0038] S3: Data Processing: The computing device 7 analyzes and calculates the measured impedance value based on a pre-established calibration curve or mathematical model, thereby indirectly deriving the soil moisture content. S4: Results Display: The calculated soil moisture content is displayed intuitively on the screen of the calculation device 7, thus obtaining the soil moisture content.

[0039] The following case study illustrates this point: refer to Figure 5 The soil and rock used in the case came from a dam construction material yard of a hydropower station in Tibet, and the particle size distribution and moisture content were uneven.

[0040] 1. Sample Preparation: Prepare soil samples of different types, including sandy soil, loam, and clay, and adjust their moisture content to different levels: low moisture content (5%–10%), medium moisture content (10%–25%), and high moisture content (25%–35%). Accurately measure the actual moisture content of each sample using the oven drying method, which will serve as the baseline data for subsequent comparisons.

[0041] 2. Sensor Detection: Insert the cylindrical probe 1 based on the hydrogel matrix 4 into each soil sample and wait 5-10 minutes to ensure that the hydrogel matrix 4 has fully absorbed the moisture in the soil and reached a stable state. Use an impedance analyzer to measure the impedance value of the sensor and record the measurement data.

[0042] 3. Result Comparison: The moisture content test results of the cylindrical probe 1 based on hydrogel matrix 4 were compared with the actual moisture content measured by the oven drying method, and the error was calculated. The experimental results show that in different types of soil samples, the error between the measurement results of the cylindrical probe 1 and the measurement results of the oven drying method is within ±3%, which proves the accuracy and reliability of the cylindrical probe 1 in the laboratory environment, as shown in Table 1.

[0043] Table 1

[0044] Moreover, the sensor of this application can work stably in a variety of soil types, reducing the interference of soil salinity and texture on the detection results, as shown in Table 2.

[0045] Table 2

[0046] As can be seen from Table 2, when testing soil samples with different salinity and texture, the measurement error of this sensor is significantly lower than that of traditional time domain reflectance (TDR) and frequency domain reflectance (FDR) sensors, which can more accurately reflect the true moisture content of the soil and provide reliable data support for agricultural production, environmental monitoring and engineering construction.

Claims

1. A soil moisture content detection sensor based on hydrogel, characterized in that... The device includes a cylindrical probe (1), with electrodes A (2) and B (3) symmetrically embedded inside the cylindrical probe (1). Electrodes A (2) and B (3) are respectively connected to insulated wires (8). The cylindrical probe (1) is filled with a hydrogel matrix (4), and conductive particles are uniformly embedded inside the hydrogel matrix (4). An insulating layer (5) is disposed on the outside of the cylindrical probe (1).

2. The hydrogel-based soil moisture content detection sensor according to claim 1, characterized in that: The insulated wire (8) is connected to a measuring device (6), and the measuring device (6) is connected to a computing device (7) via a data transmission line.

3. The hydrogel-based soil moisture content detection sensor according to claim 2, characterized in that: The measuring device (6) includes an impedance analyzer, and the computing device (7) includes a smartphone, tablet computer, and laptop computer.

4. The hydrogel-based soil moisture content detection sensor according to claim 1, characterized in that: The hydrogel matrix (4) is a transparent or semi-transparent hydrophilic crosslinked polymer, which includes starch-based and acrylic polymers.

5. The hydrogel-based soil moisture content detection sensor according to claim 1, characterized in that: It also includes an auxiliary reinforcing rod (9) disposed inside the cylindrical probe (1).

6. The hydrogel-based soil moisture content detection sensor according to claim 1, characterized in that: The electrodes A (2) and B (3) are made of corrosion-resistant metal materials.

7. The hydrogel-based soil moisture content detection sensor according to claim 1, characterized in that: The shapes of electrodes A (2) and B (3) include sheet-like and needle-like.

8. The hydrogel-based soil moisture content detection sensor according to claim 1, characterized in that: The conductive particles include carbon nanotubes and silver nanoparticles.

9. The method for detecting soil moisture content based on hydrogel according to any one of claims 1-8, characterized in that: Includes the following steps: S1: Sensor calibration: Prepare a series of standard soil samples with known moisture content, insert the cylindrical probe (1) of the sensor into each standard sample, wait for the cylindrical probe (1) of the sensor to fully absorb the moisture in the soil and reach equilibrium, use the measuring device (6) to measure the sensor impedance value at this time, record the impedance data of soil samples with different moisture contents, perform fitting analysis on these impedance data, and establish a calibration curve or mathematical model between soil moisture content and sensor impedance value. S2: Record impedance value: Insert the cylindrical probe (1) of the calibrated sensor into the soil to be tested, and the measuring device (6) measures the impedance change of the sensor in real time and transmits the measured impedance data to the connected computing device (7) to obtain the impedance value; S3: Data processing: The computing device (7) analyzes and calculates the measured impedance value according to the pre-established calibration curve or mathematical model, thereby indirectly deriving the soil moisture content; S4: Results display: The calculated soil moisture content is displayed intuitively on the display screen of the calculation device (7) to obtain the soil moisture content.

10. The method for detecting soil moisture content based on hydrogel according to claim 9, characterized in that: In step S2, the computing device (7) also stores and analyzes the measured impedance values.

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