A crack visualization device for high-power electromagnetic shielding and its use method

Abstract

The present invention belongs to the field of visualization of microwave fracturing of hard rocks, and in particular, is a high-power electromagnetic shielding crack visualization device and a method of using the same. The high-power electromagnetic shielding crack visualization device comprises: a high-power microwave shielding visualization system consisting of a shielding cavity, a composite cutoff circular waveguide, a high-speed camera, and an ultraviolet lamp; and a surface irradiation microwave fracturing rock system consisting of a magnetron, an isolator, a quartz window, an impedance tuner, and a rectangular waveguide. The high-power electromagnetic shielding crack visualization device and the method of using the device shield high-power microwaves with a frequency of 2.45 GHz and a power exceeding 6 kW, and the shielding efficiency of the microwaves is greater than 40 dB. At the same time, a large high-speed camera observation window is provided to avoid microwave damage to the human body and equipment, and to realize the dynamic process visualization monitoring of microwave fracturing rock. The present invention has the advantages of convenience, low cost, high shielding efficiency, and visualization of microwave fracturing rock process.

Description

Technical Field

[0001] The invention relates to the field of hard rock microwave fracturing and electromagnetic shielding, and in particular to a high-power electromagnetic shielding crack visualization device and a use method thereof. Background Art

[0002] Low-frequency electromagnetic waves have higher magnetic field components than high-frequency electromagnetic waves. Therefore, for very low interference frequencies, the magnetic permeability of the shielding material is far more important than the electrical conductivity. For frequencies above 30MHz, the electric field component is usually considered.

[0003] Consider using materials for high-frequency electric field components first, and then materials for high-frequency magnetic field components to further shield the magnetic field. The necessary condition for near-field electromagnetic shielding is to use a metal shield with high conductivity and to perform grounding. Near-field low-frequency magnetic field shielding can use high magnetic permeability materials such as iron, silicon copper sheets, and Permalloy for magnetic shielding, increase the thickness of the shield or use a multi-layer shielding shell to improve its shielding effectiveness.

[0004] High-conductivity metals should be used for near-field high-frequency magnetic field shielding, because at high frequencies, the magnetic permeability of ferromagnetic materials decreases and magnetic losses increase. High-conductivity metals, such as copper and aluminum, should be used for far-field shielding, and grounding should be performed. Taking the electromagnetic leakage of metal plate gaps as an example, the leakage of electromagnetic waves by gaps is analyzed. When there are gaps in the shielding cavity, the impact of magnetic field leakage is usually greater than that of electric field leakage. In most cases, the method of reducing magnetic field leakage is also more suitable for reducing electric field leakage. Therefore, it is necessary to focus on reducing magnetic field leakage.

[0005] When traditional mechanical rock breaking methods are used to excavate rocks with a strength of more than 120 MPa, the wear of excavation equipment such as cutters, drill bits and picks is serious. There are also problems such as low excavation efficiency and high construction costs, which make the efficiency and economy of traditional mechanical rock breaking methods no longer have advantages in hard rock excavation. Researchers around the world have proposed a variety of auxiliary mechanical rock breaking methods, such as hydraulic fracturing, thermal fracturing, laser fracturing and other means. Among them, microwave fracturing is considered to be an efficient auxiliary rock breaking method with extremely high application prospects due to its advantages such as good fracturing effect, simple operation and low impact on the environment.

[0006] Understanding the mechanism of microwave weakening rock strength and cracking rock can provide theoretical support for the selection of microwave fracturing power, parameters and equipment. Studying the effect of microwave irradiation energy on rock heating and understanding the real-time changes of rock crack generation and diffusion under microwave action are crucial to promoting the development of microwave-assisted mechanical rock breaking.

[0007] At present, there are also related methods to study the microwave cracking process. Among them, the observation of the microwave cracking process is mainly experimental observation of microwave irradiation in different time periods. However, this method has the following shortcomings:

[0008] ①. Since the crack generation and diffusion process of microwave irradiation rock fracturing is quite complicated, it is not possible to describe it clearly by only observing the cracks on the rock surface at the initial stage, the middle stage and the final stage. Therefore, the real-time visualization process of microwave irradiation rock fracturing is studied at present.

[0009] ②. In the segmented microwave irradiation test, the microwave system needs to be turned off to photograph the rock surface temperature and cracks during the test, causing the rock surface temperature to drop and the cracks to close. It is difficult to quantitatively analyze the relationship between microwave energy and cracks. Therefore, this method cannot study the generation and expansion of cracks in the process of microwave fracturing of rocks.

[0010] Therefore, there is an urgent need to develop a device that can meet the needs of near-field high-power electromagnetic wave shielding while meeting the needs of visualization research, so as to accurately describe the effects of microwave energy on rock strength weakening and fracturing. Summary of the invention

[0011] The technical problem to be solved by the present invention is to provide a crack visualization device and method for high-power electromagnetic shielding in view of the deficiencies of the above-mentioned prior art. The high-power electromagnetic shielding visualization device and method utilize a composite cutoff waveguide to shield electromagnetic waves. The inner diameter and length of the cutoff circular waveguide are designed so that electromagnetic waves with a frequency of 2.45 GHz and a wavelength of 12.24 cm are shielded in the cutoff circular waveguide. In addition, a porous metal mesh is arranged at the end of the cutoff circular waveguide to further shield the electromagnetic waves. In addition, in order to prevent the cutoff waveguide from overheating when cutting off high-power electromagnetic waves, a water cooling system is arranged to cool the cutoff waveguide. In addition, a high-transparency acrylic plate is arranged in the cutoff circular waveguide to prevent broken rocks from flying out during microwave cracking of rocks.

[0012] In order to achieve the above object, the present invention adopts the following technical solutions:

[0013] A high-power electromagnetic shielding crack visualization device, comprising a high-power microwave shielding visualization system and a surface irradiation microwave cracking rock system;

[0014] The high-power microwave shielding visualization system includes a shielding cavity, a composite cutoff circular waveguide, a high-speed camera and an ultraviolet lamp; the rock is located in the shielding cavity, a circular hole is opened on the shielding cavity, the composite cutoff circular waveguide is installed on the circular hole, the ultraviolet lamp detects flaws on the rock surface through the composite cutoff circular waveguide, and the high-speed camera photographs the crack expansion of the rock under the action of microwaves through the observation port of the composite cutoff circular waveguide;

[0015] The surface irradiation microwave fracturing rock system comprises a magnetron, an isolator, an impedance tuner, a quartz window and a rectangular waveguide. A square hole is opened on a shielding cavity, a rectangular waveguide is arranged between the magnetron and the square hole, and an isolator, an impedance tuner and a quartz window are arranged on the rectangular waveguide in sequence from the magnetron to the shielding cavity.

[0016] As a further preferred scheme, the composite cutoff circular waveguide includes a metal mesh, an acrylic plate, a cutoff circular waveguide, an external cavity, a water inlet, and a water outlet. The cutoff circular waveguide is located in the external cavity, and a metal mesh is provided in the gap at the connection between the cutoff circular waveguide and the shielding cavity. The acrylic plate is located in the middle position of the cutoff circular waveguide, and the water inlet is above the end of one side of the external cavity, and the water outlet is below the end of the other side.

[0017] As a further preferred solution, the shielding cavity is made of aluminum material, the thickness of the shielding cavity is 2 cm, the length, width and height of the shielding cavity are 20×20×20 cm, and the surface of the shielding cavity facing away from the rectangular waveguide is a switchable aluminum metal door for placing rocks.

[0018] As a further preferred solution, the length and width of the rectangular waveguide are 11×5.5 cm, and the diameter of the composite cutoff circular waveguide is 7 cm.

[0019] As a further preferred solution, the metal mesh is made of copper material, with a thickness of 5 mm and a diameter of 5 cm. 271 circular holes with a diameter of 3 mm are opened on the metal mesh, and the shielding effectiveness is 12 dB; the metal mesh transmission coefficient T h The calculation is as follows:

[0020]

[0021] Where n is the number of circular holes, q is the area of ​​each circular hole, and F is the overall area of ​​the metal mesh. The shielding effectiveness S of the metal mesh is calculated as follows:

[0022]

[0023] As a further preferred solution, the cutoff circular waveguide is made of copper material, has a thickness of 2 cm, an inner diameter of 5 cm, a length of 7 cm, and a shielding effectiveness of 31 dB. The shielding effectiveness S of the cutoff circular waveguide is calculated as follows:

[0024]

[0025] f c : cut-off frequency, f: electromagnetic wave frequency, l: cut-off circular waveguide length.

[0026] A method for using a crack visualization device for high-power electromagnetic shielding comprises the following steps:

[0027] (1) Open the metal door of the shielding cavity, pass the rectangular waveguide through the rectangular hole of the shielding cavity, fill the connection between the hole and the rectangular waveguide with a metal mesh, and paste it with aluminum foil to prevent electromagnetic wave leakage;

[0028] (2) The composite cutoff circular waveguide is passed through the circular hole of the shielding cavity, and the connection between the hole and the composite cutoff circular waveguide is filled with a metal mesh and pasted with aluminum foil to prevent electromagnetic wave leakage;

[0029] (3) Place the rock sample in the shielding cavity and select a glass block of appropriate height to pad the bottom of the rock sample to adjust the height of the rock so that the rock is in full contact with the waveguide;

[0030] (4) Adjust the position of the UV lamp and high-speed camera, adjust the angle of the composite cutoff circular waveguide, turn on the UV lamp, and adjust the focus, aperture, contrast, saturation and other parameters of the high-speed camera so that the captured image meets the test requirements;

[0031] (5) Close the rear metal door of the shielding cavity, preheat the microwave system in the container, set the microwave parameters, and match the electromagnetic impedance;

[0032] (6) Turn on the ultraviolet lamp for irradiation and turn on the high-speed camera for filming;

[0033] (7) Start microwave irradiation. When the preset duration is reached or the reflected power increases sharply, the test stops automatically.

[0034] (8) After the test is completed, shut down all equipment and clean the rocks in the shielding chamber and other devices.

[0035] Beneficial Effects

[0036] The electromagnetic shielding device shields high-power electromagnetic waves to realize visualized observation of microwave-induced rock cracking process. In the electromagnetic shielding device, a composite cutoff circular waveguide is used to shield 2.45 GHz microwaves; the circular waveguide in the composite cutoff circular waveguide can shield 97% of electromagnetic waves, and a metal mesh at the end of the circular waveguide can further shield 88% of electromagnetic waves, so that the composite cutoff circular waveguide as a whole can shield 99% of electromagnetic waves. At the same time, an acrylic window is set in the middle of the composite cutoff circular waveguide to prevent gravel from flying out during the test, and a water cooling layer is set in the composite cutoff circular waveguide to prevent the temperature from being too high during the test. A high-speed camera shoots the rock through the observation hole of the composite cutoff circular waveguide, and finally the law of rock crack development is obtained, and the relationship between microwave power, time and crack development is obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the electromagnetic shielding system of the present invention;

[0038] Figure 2 Schematic diagram of composite cutoff circular waveguide;

[0039] Figure 3 Schematic diagram of cavity holes;

[0040] Figure 4 Schematic diagram of cracks on rock surface;

[0041] Among them, 1. magnetron, 2. isolator, 3. impedance tuner, 4. quartz, 5. rectangular waveguide, 6. shielding cavity, 7. high-speed camera, 8. composite cutoff circular waveguide, 9. rock, 10. ultraviolet lamp, 11. metal mesh, 12. acrylic plate, 13. water inlet, 14. external cavity, 15. cutoff circular waveguide, 16. water outlet. DETAILED DESCRIPTION

[0042] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0043] like Figure 1 As shown, a crack visualization device for high-power electromagnetic shielding includes a magnetron 1, an isolator 2, an impedance tuner 3, a quartz window 4, a rectangular waveguide 5, a shielding cavity 6, a composite cutoff circular waveguide 8, a high-speed camera 7 and an ultraviolet lamp 10.

[0044] The magnetron is used to convert electrical energy into electromagnetic waves. The magnetron 1 is connected to the isolator 2, which ensures the unidirectional transmission of electromagnetic waves. The isolator 2 is connected to the impedance tuner 3, which is used to match the impedance between the electromagnetic wave and the rectangular waveguide, so that the radiation power reaches the maximum value. The impedance tuner 3 is connected to the quartz window 4, which is used to isolate the air so that the external air cannot enter the device through the rectangular waveguide 5. The rectangular waveguide 5 penetrates into the shielding cavity 6 through the rectangular holes on the surface of the shielding cavity 6 and directly contacts the rock 9. The size of the rectangular hole is slightly larger than the size of the rectangular waveguide, and its size is 11×5.5cm. The composite cutoff circular waveguide 8 is installed in the circular hole of the shielding cavity 6, and the high-speed camera 7 and the ultraviolet lamp 10 observe the rock surface in real time during the test through the observation port of the composite cutoff circular waveguide 8.

[0045] The shielding cavity 6 is made of aluminum material, and its relative magnetic permeability is 1 and relative electrical conductivity is 0.61. The material thickness of the aluminum shielding cavity is 2 cm, and the length, width and height of the cavity inner diameter are 20×20×20 cm. The aluminum cavity has high electrical conductivity and has a good shielding effect on the near-field high-frequency magnetic field.

[0046] The shielding cavity 6 has two holes on the surface facing the rectangular waveguide 5, which are a rectangular hole with a length and width of 11×5.5 cm and a circular hole with a diameter of 7 cm. Figure 1 ; The circular hole is connected to the composite cutoff circular waveguide; the rectangular hole is connected to the rectangular waveguide.

[0047] The power of the ultraviolet lamp is 10w, and the luminous color is purple. The ultraviolet light emitted by the ultraviolet lamp 10 is irradiated on the surface of the rock 9 through the cutoff circular waveguide for flaw detection on the rock surface. The ultraviolet lamp provides light source for high-speed camera shooting, and shields electromagnetic waves through the composite cutoff waveguide, so that the high-speed camera and the ultraviolet lamp are not affected by the electromagnetic field, thereby damaging the equipment.

[0048] The high-speed camera used is the PhantomVEO710L model, and the shooting speed of the high-speed camera is 100 frames per second. The high-speed camera 7 shoots the crack propagation of the rock under the action of microwaves through the observation port of the cut-off circular waveguide.

[0049] like Figure 2 As shown, the composite cutoff circular waveguide includes a metal mesh 11, an acrylic plate 12, an outer cavity 14, a cutoff circular waveguide 15, a water inlet and a water outlet. The metal mesh 11 and the acrylic plate 12 are connected to the cutoff circular waveguide 15, and the outer side of the circular waveguide 15 has a layer of the outer cavity 14. The cutoff circular waveguide 15 is connected to both sides of the outer cavity 14 by welding, and the water inlet and the water outlet are installed on the outer cavity.

[0050] The acrylic plate 12 is made of highly transparent acrylic material with a refractive index of 1.45. The acrylic plate 12 has a diameter of 5 cm and a thickness of 2 cm. It is installed in the middle of the cutoff circular waveguide along the length direction to prevent gravel generated by microwave cracking of rocks from flying out of the cutoff circular waveguide.

[0051] The metal mesh 11 is made of copper material, with a thickness of 5 mm and a diameter of 5 cm. There are 271 circular holes with a diameter of 3 mm on the metal mesh, and the shielding effectiveness is 12 dB.

[0052] The cut-off circular waveguide 15 is made of copper material, has a thickness of 2 cm, an inner diameter of 5 cm, a length of 7 cm, and a shielding effectiveness of 31 dB.

[0053] The outer cavity 14 is made of copper material, with a thickness of 2 cm, an inner diameter of 7 cm, and a length of 7 cm. A water inlet and a water outlet are installed on the outer cavity for water cooling to reduce the high temperature generated by the cutoff circular waveguide under microwave irradiation; the two ends of the outer cavity and the cutoff circular waveguide are connected by welding, and the thickness of the welding is 2 cm.

[0054] A method for visualizing cracks in high-power electromagnetic shielding, comprising the following steps:

[0055] 1. Open the metal door of the shielding cavity, and place glass blocks and test rocks in the shielding cavity. The blocks are used to adjust the height of the rocks to ensure full contact between the rectangular waveguide and the rock surface.

[0056] 2. Install the composite cutoff circular waveguide into the circular hole, and adjust the angle of the composite cutoff circular waveguide so that the target rock surface can be observed in the circular observation hole of the composite cutoff circular waveguide;

[0057] 3. Fill the gap between the circular hole and the composite cutoff circular waveguide with a metal mesh, and stick aluminum foil on both sides of the shielding cavity inside and outside the gap to fix the composite cutoff circular waveguide while providing electromagnetic shielding;

[0058] 4. Turn on the UV lamp and adjust the angle of the UV lamp so that the light source generated by the UV lamp shines on the rock surface through the circular hole observation hole;

[0059] 5. Turn on the high-speed camera, adjust the position of the high-speed camera, and adjust the focal length, aperture, contrast, saturation and other parameters of the high-speed camera so that the images taken by the camera meet the test requirements;

[0060] 6. Close the rear metal door of the shielding chamber;

[0061] 7. Preheat the microwave equipment and set the power and time of microwave irradiation;

[0062] 8. Turn on the high-speed camera to shoot;

[0063] 9. Turn on the microwave surface irradiation, rotate the impedance tuner, and quickly adjust the impedance in the waveguide;

[0064] 10. The microwave surface is irradiated until the preset duration is reached or the reflected power increases sharply, and the test stops automatically;

[0065] 11. After the experiment is completed, shut down all equipment and clean the rocks in the shielding chamber and other devices.

[0066] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A crack visualization device for electromagnetic shielding, characterized in that: Including microwave shielding visualization system and surface irradiation microwave rock fracturing system; The microwave shielding visualization system comprises a shielding cavity (6), a composite cutoff circular waveguide (8), a high-speed camera (7) and an ultraviolet lamp (10); the rock (9) is located in the shielding cavity (6), a circular hole is opened on the shielding cavity (6), the composite cutoff circular waveguide (8) is installed on the circular hole, the ultraviolet lamp (10) detects flaws on the surface of the rock (9) through the composite cutoff circular waveguide (8), and the high-speed camera (7) photographs crack expansion of the rock (9) under the action of microwaves through the observation port of the composite cutoff circular waveguide (8); The surface irradiation microwave rock fracturing system comprises a magnetron (1), an isolator (2), an impedance tuner (3), a quartz window (4) and a rectangular waveguide (5); a square hole is provided on the shielding cavity (6); a rectangular waveguide (5) is provided between the magnetron (1) and the square hole; and an isolator (2), an impedance tuner (3) and a quartz window (4) are provided on the rectangular waveguide (5) in sequence in a direction from the magnetron (1) to the shielding cavity (6); The composite cutoff circular waveguide (8) comprises a metal mesh (11), an acrylic plate (12), a cutoff circular waveguide (15), an external cavity (14), a water inlet (13), and a water outlet (16); the cutoff circular waveguide (15) is located in the external cavity (14); a metal mesh (11) is provided in a gap at the connection between the cutoff circular waveguide (15) and the shielding cavity (6); the acrylic plate (12) is located in the middle of the cutoff circular waveguide (15); the water inlet (13) is located above one end of the external cavity (14); and the water outlet (16) is located below the other end.

2. The electromagnetic shielding crack visualization device according to claim 1, characterized in that: The shielding cavity (6) is made of aluminum material, the thickness of the shielding cavity (6) is 2 cm, the length, width and height of the inside of the shielding cavity (6) are 20×20×20 cm, and the surface of the shielding cavity (6) facing away from the rectangular waveguide (5) is a switchable aluminum metal door for placing the rock (9).

3. The electromagnetic shielding crack visualization device according to claim 1, characterized in that: The length and width of the rectangular waveguide (5) are 11×5.5 cm, and the diameter of the composite cutoff circular waveguide (8) is 7 cm.

4. The electromagnetic shielding crack visualization device according to claim 1, characterized in that: The metal mesh (11) is made of copper material, has a thickness of 5 mm and a diameter of 5 cm, has 271 circular holes with a diameter of 3 mm, and has a shielding effectiveness of 12 dB; the transmission coefficient T of the metal mesh (11) is h The calculation is as follows: Where n: number of circular holes, q: area of ​​each circular hole, F: overall area of ​​the metal mesh; The shielding effectiveness S of the metal mesh is calculated as follows:

5. The electromagnetic shielding crack visualization device according to claim 1, characterized in that: The cutoff circular waveguide (15) is made of copper material, has a thickness of 2 cm, an inner diameter of 5 cm, a length of 7 cm, and a shielding effectiveness of 31 dB. The shielding effectiveness S of the cutoff circular waveguide is calculated as follows: f c : cut-off frequency, f: electromagnetic wave frequency, l: cut-off circular waveguide length.

6. The method for using the electromagnetic shielding crack visualization device according to claim 2, characterized in that: The following steps are involved: (1) Open the metal door of the shielding cavity, pass the rectangular waveguide through the rectangular hole of the shielding cavity, fill the connection between the hole and the rectangular waveguide with a metal mesh, and paste it with aluminum foil to prevent electromagnetic wave leakage; (2) The composite cutoff circular waveguide is passed through the circular hole of the shielding cavity, and the connection between the hole and the composite cutoff circular waveguide is filled with a metal mesh and pasted with aluminum foil to prevent electromagnetic wave leakage; (3) Place the rock sample in the shielding cavity and select a glass block of appropriate height to pad the bottom of the rock sample to adjust the height of the rock so that the rock is in full contact with the rectangular waveguide; (4) Adjust the position of the UV lamp and high-speed camera, adjust the angle of the composite cutoff circular waveguide, turn on the UV lamp, and adjust the focal length, aperture, contrast, and saturation parameters of the high-speed camera so that the captured image meets the test requirements; (5) Close the rear metal door of the shielding cavity, preheat the microwave system, set the microwave parameters, and match the electromagnetic impedance; (6) Turn on the ultraviolet lamp for irradiation and turn on the high-speed camera for filming; (7) Start microwave irradiation. When the preset duration is reached or the reflected power increases sharply, the test stops automatically. (8) After the test is completed, shut down all equipment and clean the rocks in the shielding chamber device.

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