Distributed coaxial waveguide interference rock-soil body moisture sensor

Abstract

The utility model discloses a distributed coaxial waveguide interference rock-soil body moisture sensor which is characterized in that a metal rod is positioned in a metal tube, the metal rod and the metal tube are coaxially arranged, and two ends of the metal rod and the metal tube are aligned; the infiltration sections are arranged on the metal pipe and are axially arranged at certain intervals along the metal pipe, and the infiltration sections consist of through hole arrays which are arranged at equal intervals along the circumference of the wall of the metal pipe; the elastic telescopic cavity is positioned in the metal pipe and is positioned in the same section with the infiltration section; the elastic telescopic cavity is filled with the water absorption expansion medium; and the radio frequency coaxial connector and the terminal load are respectively connected with two ends of the metal tube and are simultaneously contacted with two ends of the metal rod. Electromagnetic waves are injected into the sensor, rock-soil mass moisture permeates into the water absorption expansion medium to drive the distance between the baffles on the two sides of the elastic telescopic cavity to be changed, the baffles on the two sides are medium mutation faces and are two electromagnetic wave reflection points, interference spectrum frequency shift is caused by the distance change of the reflection points, and the moisture content of the rock-soil mass can be measured by monitoring the frequency shift. The system has the advantages of distributed and real-time monitoring.

Description

Technical Field

[0001] The utility model belongs to the technical field of rock and soil monitoring, in particular to a distributed coaxial waveguide interference rock and soil moisture sensor. Background Art

[0002] The spatiotemporal distribution and dynamic changes of soil moisture are key monitoring targets in geotechnical engineering monitoring, and are of great significance for geological disaster early warning and prevention, environmental and ecological protection, and other tasks. However, due to the complexity of the environment in which rock and soil reside and the heterogeneity of the soil itself, large-scale and long-distance rock and soil moisture measurement still presents many challenges. Currently, the main methods for measuring rock and soil moisture include electrical resistance, time domain reflectometry (TDR), and frequency domain reflectometry (FDR). The electrical resistance method determines moisture content by measuring the resistance between two electrodes embedded in the soil. TDR technology calculates the soil's dielectric constant by measuring the time difference between the incidence and reflection of an electromagnetic wave on a wire embedded in the soil, and then uses the dielectric constant to determine moisture content. While these measurement methods can provide a certain degree of moisture information, they are all point-based and cannot provide distributed and real-time measurement of in-situ rock and soil moisture content. Summary of the Invention

[0003] The utility model provides a distributed coaxial waveguide interference rock and soil moisture sensor, which is used to solve the problem of difficulty in achieving distributed and real-time monitoring in existing rock and soil moisture monitoring technology.

[0004] The technical solutions adopted in this utility model are as follows:

[0005] A distributed coaxial waveguide interference rock and soil moisture sensor comprises a coaxial waveguide structure, an elastic expansion cavity and a water absorption and expansion medium; the coaxial waveguide structure comprises a metal rod, a metal tube, an infiltration section, a radio frequency coaxial connector and a terminal load, the metal rod is located inside the metal tube, the two are coaxially arranged and aligned at both ends, the infiltration section is arranged on the metal tube, and the infiltration section is composed of an array of through holes arranged at equal intervals along the circumference of the metal tube wall, the radio frequency coaxial connector and the terminal load are respectively connected to the two ends of the metal tube by threads, and the metal rod is in contact with the central pinholes of the radio frequency coaxial connector and the terminal load; the elastic expansion cavity is located inside the metal tube and is in the same section as the infiltration section; the water absorption and expansion medium fills the interior of the elastic expansion cavity.

[0006] Furthermore, the metal tube has at least one infiltration section, and the infiltration sections are axially arranged at certain intervals along the metal tube.

[0007] Furthermore, the elastic telescopic chamber includes two baffles and a spring. There is a through hole in the center of the baffle. The diameter of the through hole is slightly larger than the outer diameter of the metal rod to facilitate the passage of the metal rod. A groove is provided on the bottom surface of the baffle. The size of the groove matches the outer diameter of the spring. The two ends of the spring are respectively fixed in the grooves of the baffles on both sides.

[0008] Furthermore, the diameter of the elastic telescopic cavity is slightly smaller than the inner diameter of the metal tube, and the length is equal to the infiltration section, and the spring wire in the middle of the elastic telescopic cavity is fixed on a row of through holes in the middle of the infiltration section.

[0009] Furthermore, the water-absorbing and swelling medium is one of water-absorbing resin, bentonite or water-absorbing and swelling rubber.

[0010] Furthermore, the baffle is provided with a water-absorbing expansion medium and an air medium on both sides respectively. The sudden change of the dielectric constant at this location will produce a certain reflection of the electromagnetic wave, thereby forming a reflection point. The two reflection points formed by the baffles on both sides of the elastic telescopic cavity constitute a sensing unit.

[0011] The working principle of this utility model is as follows:

[0012] A distributed coaxial waveguide interferometric rock and soil moisture sensor. When electromagnetic waves are injected into the sensor, the two sides of the baffle are respectively a water-absorbing and swelling medium and an air medium. The sudden change in the dielectric constant at these locations will cause a certain reflection of the electromagnetic waves, thereby forming reflection points. That is, two reflection points are formed at the baffles on both sides of the elastic expansion cavity. The two beams of electromagnetic waves reflected by them meet to form an interference spectrum. When water enters the infiltration section, the water-absorbing and swelling medium in the elastic expansion cavity expands and drives the baffles on both sides to move outward relative to each other. That is, the distance between the reflection points changes, causing the resonance peak of the interference spectrum to produce a frequency shift. By monitoring this frequency shift, the change in moisture content in the rock and soil can be accurately measured.

[0013] The beneficial effects of the utility model are:

[0014] The utility model provides a distributed coaxial waveguide interference rock and soil moisture sensor equipped with multiple continuous sensing units, each of which can monitor changes in the moisture content of the rock and soil, and can detect distributed moisture information at different depths of the rock and soil. In addition, by continuously injecting electromagnetic waves into the sensor and collecting signals in real time, real-time monitoring of changes in the moisture content of the rock and soil can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 Schematic diagram of the structure of a distributed coaxial waveguide interferometric rock and soil moisture sensor of the utility model: (a) is a schematic diagram of the overall structure, (b) is a schematic diagram of the AA section, and (c) is a schematic diagram of the BB section.

[0016] Figure 2 This is a schematic diagram of the three-dimensional structure of a distributed coaxial waveguide interferometric rock and soil moisture sensor of the utility model.

[0017] Figure 3 Schematic diagram of the elastic telescopic cavity structure of a distributed coaxial waveguide interferometric rock and soil moisture sensor of the utility model: (a) is a schematic diagram of the plane structure, and (b) is a schematic diagram of the three-dimensional structure.

[0018] Figure: 1 - metal rod; 2 - metal tube; 3 - infiltration section; 4 - elastic expansion chamber; 5 - baffle; 6 - spring; 7 - water-swelling medium; 8 - RF coaxial connector; 9 - terminal load DETAILED DESCRIPTION

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Figure 1 、 Figure 2 and Figure 3 In the figure, a metal rod 1 is located inside a metal tube 2, coaxially arranged with their ends aligned. An infiltration section 3 is provided on the metal tube 2 and arranged axially at regular intervals along the tube. The infiltration section 3 comprises an array of through-holes arranged at equal intervals along the circumference of the tube 2. An elastic expansion chamber 4 is located inside the metal tube 2 and in the same section as the infiltration section 3. A water-swelling medium 7 completely fills the elastic expansion chamber 4. An RF coaxial connector 8 and a terminal load 9 are respectively threadedly connected to the ends of the metal tube 2, with the metal rod 1 contacting the center pinholes of the RF coaxial connector 8 and the terminal load 9.

[0021] The elastic telescopic chamber 4 includes two baffles 5 and a spring 6. There is a through hole in the center of the baffle 5. The diameter of the through hole is slightly larger than the outer diameter of the metal rod 1, which is convenient for the metal rod 1 to pass through. A groove is provided on the bottom surface of the baffle 5. The size of the groove matches the outer diameter of the spring 6. The two ends of the spring 6 are respectively fixed in the grooves of the baffles 5 on both sides.

[0022] The diameter of the elastic telescopic cavity 4 is slightly smaller than the inner diameter of the metal tube 2 , and its length is equal to the infiltration section 3 . The spring wire in the middle of the elastic telescopic cavity 4 is fixed on a row of through holes in the middle of the infiltration section 3 .

[0023] On both sides of the baffle 5 are the water-absorbing and swelling medium 7 and the air medium. The sudden change in the dielectric constant at this location will cause a certain reflection of the electromagnetic wave, thereby forming a reflection point. When water enters the infiltration section, the water-absorbing and swelling medium 7 in the elastic telescopic cavity 4 expands and drives the baffles 5 on both sides to move outward relative to each other, that is, the distance between the reflection points changes, thereby causing the resonance peak of the interference spectrum to shift in frequency.

[0024] The specific production process of this utility model is:

[0025] First, select a metal rod 1 and metal tube 2 of appropriate size. In this embodiment, the metal rod 1 is a solid copper rod with a diameter of 6 mm, which serves as the inner conductor of the coaxial waveguide structure; the metal tube 2 is a hollow copper tube with an inner diameter of 14 mm and an outer diameter of 16 mm, which serves as the outer conductor of the coaxial waveguide structure. The size selection is based on the fact that the outer diameter of the inner conductor and the inner diameter of the outer conductor in the coaxial waveguide structure must meet the characteristic impedance Z0:

[0026]

[0027] Where ∈r is the relative dielectric constant of the coaxial cable's insulation (the relative dielectric constant of air is generally considered to be 1), a is the outer diameter of the inner conductor, and b is the inner diameter of the outer conductor. According to the above formula, the characteristic impedance of the distributed coaxial waveguide interferometric soil moisture sensor is approximately 50Ω, which is a good match for the electromagnetic wave transmitter.

[0028] Secondly, through holes are drilled on the circumference of the metal tube 2 wall. The array of through holes arranged at equal intervals forms the infiltration section 3, which is arranged axially at certain intervals along the metal tube 2. Two baffles 5 and a spring 6 form an elastic expansion chamber 4, wherein the baffle 5 has a through hole in the center. The diameter of the through hole is slightly larger than the outer diameter of the metal rod 1 to facilitate the passage of the metal rod 1. The bottom surface of the baffle 5 is provided with a groove whose size matches the outer diameter of the spring 6. The two ends of the spring 6 are respectively fixed in the grooves of the baffles 5 on both sides by glue. The diameter of the elastic expansion chamber 4 is slightly smaller than the inner diameter of the metal tube 2, and the length of the elastic expansion chamber 4 is consistent with the length of the infiltration section 3.

[0029] Next, the elastic expansion chamber 4 is completely filled with a water-swelling medium 7, which can be a water-absorbing resin, bentonite, or water-swelling rubber. The elastic expansion chamber 4, now filled with the water-swelling medium 7, is placed inside the metal tube 2, aligning the elastic expansion chamber 4 with the infiltration section 3. The spring wire in the middle of the elastic expansion chamber 4 is secured to a row of through-holes in the middle of the infiltration section 3.

[0030] Finally, the RF coaxial connector 8 and the terminal load 9 are respectively connected to the two ends of the metal tube 2 through threads, and the metal rod 1 is in contact with the central pinholes of the RF coaxial connector 8 and the terminal load 9. The terminal load 9 is a device used to absorb RF energy, improve the matching of the circuit, and avoid signal reflection and signal interference. The RF coaxial connector 8 is connected to the commercial coaxial cable, and is connected to the electromagnetic wave transmitting device through the commercial coaxial cable.

[0031] During on-site monitoring, the distributed coaxial waveguide interference rock and soil moisture sensor is first buried in the rock and soil to be measured. Then, when electromagnetic waves are injected into the sensor, the water-absorbing and swelling medium 7 and the air medium are on both sides of the baffle 5 respectively. The sudden change in the dielectric constant at this point will produce a certain reflection of the electromagnetic wave, thereby forming a reflection point. Two reflection points are formed at the baffles 5 on both sides of the elastic telescopic cavity 4. The two beams of electromagnetic waves reflected by them meet to form an interference spectrum. When the distance between the two reflection points changes, it will cause the interference fringes to shift. The frequency shift of the interference spectrum peak is linearly related to the change in the distance between the two reflection points, that is, the frequency shift of the interference spectrum peak is linearly related to the magnitude of the change in the moisture content of the rock and soil. When moisture enters the infiltration section 3, the water-absorbing and swelling medium 7 in the elastic telescopic cavity 4 expands and drives the baffles 5 on both sides to move outward relative to each other, that is, the distance between the reflection points changes, thereby causing a frequency shift of the coaxial waveguide resonant frequency Δf:

[0032]

[0033] Where N is the resonant frequency number (1, 2, 3, ...); τ is the time delay difference between the two reflected waves; c is the propagation speed of light in vacuum; L is the distance between the reflection points; ∈ r is the relative dielectric constant of the cable insulation.

[0034] Finally, the measured frequency shift change is converted into the moisture change of the corresponding rock and soil mass.

[0035] The above embodiments are only used to further illustrate a distributed coaxial waveguide interferometric rock and soil moisture sensor of the present invention, but the present invention is not limited to the embodiments. Any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the scope of protection of the present invention.

Claims

1. A distributed coaxial waveguide interferometric rock and soil moisture sensor, characterized in that: The invention comprises a coaxial waveguide structure, an elastic telescopic cavity (4) and a water-absorbing expansion medium (7); the coaxial waveguide structure comprises a metal rod (1), a metal tube (2), an infiltration section (3), a radio frequency coaxial connector (8) and a terminal load (9); the metal rod (1) is located inside the metal tube (2), the two are coaxially arranged and the two ends are aligned; the infiltration section (3) is arranged on the metal tube (2), and the infiltration section (3) is composed of an array of through holes arranged at equal intervals along the circumference of the metal tube (2); the radio frequency coaxial connector (8) and the terminal load (9) are respectively connected to the two ends of the metal tube (2) by threads, and the metal rod (1) contacts the central pinholes of the radio frequency coaxial connector (8) and the terminal load (9); the elastic telescopic cavity (4) is located inside the metal tube (2) and is in the same section as the infiltration section (3); the water-absorbing expansion medium (7) fills the elastic telescopic cavity (4).

2. The distributed coaxial waveguide interferometric rock and soil moisture sensor according to claim 1, characterized in that: The metal tube (2) has at least one infiltration section (3), and the infiltration sections (3) are axially arranged at certain intervals along the metal tube (2).

3. The distributed coaxial waveguide interferometric rock and soil moisture sensor according to claim 1, characterized in that: The elastic telescopic cavity (4) comprises two baffles (5) and a spring (6). The baffle (5) has a through hole at its center. The diameter of the through hole is slightly larger than the outer diameter of the metal rod (1) so as to facilitate the passage of the metal rod (1). The bottom surface of the baffle (5) is provided with a groove. The size of the groove matches the outer diameter of the spring (6). The two ends of the spring (6) are respectively fixed in the grooves of the baffles (5) on both sides.

4. The distributed coaxial waveguide interferometric rock and soil moisture sensor according to claim 1, characterized in that: The diameter of the elastic telescopic cavity (4) is slightly smaller than the inner diameter of the metal tube (2), and its length is equal to that of the infiltration section (3). The spring wire in the middle of the elastic telescopic cavity (4) is fixed to a row of through holes in the middle of the infiltration section (3).

5. The distributed coaxial waveguide interferometric rock and soil moisture sensor according to claim 1, characterized in that: The water-absorbing and swelling medium (7) is one of water-absorbing resin, bentonite or water-absorbing and swelling rubber.

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