A single-hole directional radio frequency electromagnetic detection method and system

Abstract

The present invention belongs to the field of geophysical exploration technology. The present invention provides a single-hole directional radio frequency electromagnetic detection method and system, including two coaxially arranged directional drilling antennas, the directional drilling antennas have the same structure, and both include a main board, a radiation structure formed by metal is arranged on the main board, and a radially arranged through slot is arranged at the center of the radiation structure; a feed balun is vertically arranged in the through slot, the metals on both sides are not connected, and the metals on each side are respectively connected to the corresponding radiation structure, the main board is arranged on the side of the filling component, the filling component is hollow in the middle, and the feed balun runs through the middle of the filling component; the supporting component is hollow and is provided with a metal reflector, and the end of the metal reflector and the end of the radiation structure are connected by a lumped element. The present invention can effectively improve the detection angle resolution of directional radio frequency electromagnetic in the hole and realize the fine characterization of the abnormality around the hole.

Description

Technical Field

[0001] The present invention belongs to the technical field of geophysical exploration, and in particular relates to a single-hole directional radio frequency electromagnetic detection method and system. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] With the development of geotechnical and underground engineering technology, the fine detection of sub-meter-level targets has become a key problem in geotechnical and underground engineering. For example, structures such as boulders and karst caves will cause serious wear of the cutterhead during the tunneling of the shield machine, affecting the construction process; water leakage in the foundation pit will cause deformation and damage of the foundation pit, settlement of the surrounding surface, and cracking of buildings. At the same time, since the sizes of these structures are mostly sub-meter-level, conventional detection methods are difficult to detect, and it is urgent to study relevant sub-meter-level target fine detection methods.

[0004] Radio frequency electromagnetic refers to electromagnetic radiation with a frequency of 100kHz to 300GHz, also known as radio waves. Its detection wavelength is short and its detection resolution is high. In particular, the wavelength of radio frequency electromagnetic ranging from hundreds to gigahertz is in the centimeter to meter level, which is comparable to the sub-meter detection target scale. It has the potential to detect sub-meter targets in geotechnical and underground engineering projects in detail. Compared with elastic wave detection methods such as sound waves, radio frequency electromagnetic is more sensitive to water-bearing structures and is more widely used in geotechnical and underground engineering detection. At the same time, single-hole directional radio frequency electromagnetic detection can drill deep into the hole to get close to the target body, avoiding the shortcomings of surface electromagnetic detection being easily interfered by other objects on the ground and insufficient detection depth, and can further finely characterize abnormal structures.

[0005] However, the current electromagnetic detection methods in holes are usually cross-hole detection or single-hole omnidirectional detection schemes, which cannot determine the orientation of the anomaly relative to the borehole; although some technical solutions have disclosed directional antenna solutions, such as Chinese invention patents with publication numbers CN117117472A and CN117060057A, the antenna frequency in the above solutions is low and the resolution is relatively low. Summary of the invention

[0006] In order to solve the above problems, the present invention proposes a single-hole directional radio frequency electromagnetic detection method and system. Based on a directional radio frequency electromagnetic radiation antenna with a spindle-shaped structure, the present invention proposes a single-hole directional radio frequency electromagnetic rotation detection mode. The two antennas rotate for detection at the same time to obtain the reflected electromagnetic signal of the abnormality around the hole and locate it, which can effectively improve the detection angle resolution of the directional radio frequency electromagnetic in the hole and realize the fine characterization of the abnormality around the hole.

[0007] According to some embodiments, the present invention adopts the following technical solutions:

[0008] A single-hole directional radio frequency electromagnetic detection system, comprising two coaxially arranged directional drilling antennas, the directional drilling antennas having the same structure, both comprising a main board, a feeding balun, a metal reflector, a filling component and a supporting component, the main board being provided with a radiation structure formed of metal, the radiation structure being in a shape in which the width at the center position is greater than the width at the end position, and a radially arranged through slot is provided at the center position of the radiation structure;

[0009] A feed balun is vertically arranged in the through slot, and the feed balun includes a PCB board, that is, a printed circuit board (PCB for short), and metal is arranged on both sides of the PCB board, and the metals on the two sides are not connected, and the metals on each side are respectively connected to the corresponding radiation structure;

[0010] The main board is arranged on the side of the filling component, the middle of the filling component is hollow, and the feeding balun runs through the middle of the filling component;

[0011] The support component is hollow and is sleeved on the outside of the main board and the filling component. A metal reflector is provided on the side wall of the support component at the end farther from the main board. The end of the metal reflector and the end of the radiation structure are connected through a lumped element.

[0012] As an optional implementation, the supporting component is cylindrical, and is provided with a notch at an end farther from the main board, the notch is a cutting surface, and the cutting surface is arranged parallel to the main board.

[0013] As a further embodiment, the metal reflective plate is arranged on the cutting surface, and two ends of the metal reflective plate extend out of both sides of the cutting surface, but the extension height does not exceed the horizontal plane where the main board is located.

[0014] As a further embodiment, the extension parts at both ends of the metal reflective plate are arc-shaped, and the arc is consistent with the outer wall of the supporting component.

[0015] As an optional implementation, a gap is provided between the main board and an end of the supporting component closer to the main board.

[0016] As an optional embodiment, the two opposite ends of the filling component respectively have a cutting surface, the cutting surface at one end is used to set the main board, and the cutting surface at the other end is used to be flush with the cutting surface of the supporting component to set a part of the metal reflective plate.

[0017] As a further embodiment, the length of the feed balun is the same as the distance between two cutting surfaces of the filling component.

[0018] As an optional implementation, the metal on one side of the feed balun is in the shape of a long strip, and the long strip is axially arranged at the center of the surface;

[0019] The metal on the other side is in an axisymmetric shape with a gradually decreasing width, and the change in width is in a curved transition, and the width of the smallest portion of the metal on this side is equal to the width of the long strip of metal on the other side.

[0020] As a further feature, the curve varies exponentially.

[0021] As an optional implementation, the radiation structure is an axisymmetric and centrosymmetric shape, with a curve transition from the center to the end, and the curve is determined by an S-shaped function.

[0022] As a further feature, the S-type function is a sigmoid function.

[0023] As an optional embodiment, the filling component and the supporting component are made of polyoxymethylene resin.

[0024] The method based on the above-mentioned single-hole directional radio frequency electromagnetic detection system includes the following steps:

[0025] The two directional drilling antennas are rotated synchronously, one directional drilling antenna is used as a transmitting end to transmit electromagnetic signals to the target anomaly, and the other directional drilling antenna is used as a receiving end to receive the signal fed back by the anomaly;

[0026] Determine a detection threshold of the median method, wherein the detection threshold is the product of the maximum amplitude and the coefficient in the received signal;

[0027] Compare the maximum amplitude of the signal with different rotation directions at the same depth with the detection threshold, and draw a binary quantization result diagram according to the comparison result;

[0028] Calculate the center position of the sequence of target values ​​in the binary quantization result graph, which is the azimuth of the abnormal body.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention provides a single-hole directional radio frequency electromagnetic detection system, including two coaxially arranged directional drilling antennas. The antenna has a small diameter and can move relatively smoothly in a tunnel drilling environment. It has strong applicability and covers an ultra-wide frequency band with the advantage of sub-meter high resolution.

[0031] The observation method and corresponding positioning method of the directional antenna synchronous rotation detection of the present invention utilize the symmetry of the antenna and the data collected by the same antenna at different angles, thereby avoiding the angle error caused by different antenna process errors, and can more accurately identify the orientation of the abnormal body, thereby improving the recognition accuracy and angle resolution.

[0032] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0034] Figure 1 is a front view of a directional drilling antenna structure of an embodiment;

[0035] Figure 2 is a side view of a directional drilling antenna structure according to an embodiment, wherein the support components are not shown;

[0036] Figure 3 is an axial cross-sectional view of a directional drilling antenna structure according to an embodiment;

[0037] Figure 4 is a schematic structural diagram of a mainboard of an embodiment;

[0038] Figure 5 is a schematic diagram of the structure of a feed balun in an embodiment, Figure 5 (a) is the metal structure on one side of the feed balun. Figure 5 (b) shows the metal structure on the other side of the feed balun;

[0039] Figure 6 is a schematic diagram of the directivity coefficient of an antenna at 600 MHz according to an embodiment;

[0040] Figure 7 is a schematic diagram of the voltage standing wave ratio of an antenna at 400-1400 MHz according to an embodiment;

[0041] Figure 8 is a working schematic diagram of a single-hole directional radio frequency electromagnetic detection system according to an embodiment;

[0042] Fig. 9 is a graph showing the maximum amplitude of a signal at the same depth as a function of angle in an embodiment;

[0043] Fig.10 is a binary quantization result diagram of the maximum amplitude of an embodiment.

[0044] Among them, 1. Main board, 2. Lumped components, 3. Filling components, 4. Support components, 5. Metal reflector, 6. Radiation structure, 7. PCB board, 8. Metal parts. DETAILED DESCRIPTION

[0045] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0046] It should be noted that the following detailed descriptions are all illustrative and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0047] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0048] In the absence of conflict, the embodiments in this application and the features in the embodiments may be combined with each other.

[0049] Embodiment 1

[0050] A single-hole directional radio frequency electromagnetic detection system includes two coaxially arranged directional drilling antennas, the directional drilling antennas have the same structure, and both include a main board 1, a feed balun, a metal reflector 5, a filling component 3 and a supporting component 4, such as Figure 2 As shown, the main board 1 is a PCB board, on which a radiation structure 6 formed of metal is arranged. The radiation structure 6 is wide in the center and narrow at both ends.

[0051] In this embodiment, the radiation structure 6 is axially symmetrical and centrally symmetrical, and is also a left-right symmetrical and top-bottom symmetrical structure. It transitions from the center to the end in a curve, and the curve is determined by an S-shaped function.

[0052] In this embodiment, the radiation structure 6 is spindle-shaped.

[0053] In some preferred embodiments, the S-type function is a sigmoid function.

[0054] like Figure 3 and Figure 4 As shown, a radially arranged through slot is provided at the center position of the radiation structure 6, that is, the extension direction of the through slot and the radiation structure 6 are perpendicular to each other, cutting off the radiation structures 6 on both sides; a feeding balun is vertically arranged in the through slot, and the feeding balun includes a PCB board 7, and metal is provided on both sides of the PCB board 7, and the metals on the two sides are not connected, and the metals on each side are respectively connected to the radiation structure 6 on the corresponding side of the through slot, that is, the metals on each side are connected to the radiation structure 6 closer to the side.

[0055] like Figure 5(a) Figure 5 As shown in (b), the PCB board 7 of the feed balun is rectangular, the metal portion 8 on one surface of the PCB board 7 is in the shape of an elongated strip, and the elongated strip is axially penetrated and arranged at the center of the surface, and the metal portion 8 on the other surface is in an axially symmetrical shape with one side narrow and the other side wide, and the narrow side is arranged at the center of the surface, and the width is equal to the width of the elongated strip-shaped metal portion 8 on the other surface.

[0056] In this embodiment, the long strip-shaped metal portion 8 and one side of the narrow metal portion 8 on both sides are just opposite to each other.

[0057] like Figure 4 As shown, the metal on each surface is connected to the radiation structure 6 which is closer to the surface, and the radiation structure 6 is metal.

[0058] In this embodiment, the radiation structure 6 and the corresponding metal part 8 are connected by welding.

[0059] In some preferred embodiments, Figure 5 As shown in (a), the metal portion 8 on one side transitions from a narrow portion to a wide portion in a curve, and the curve changes exponentially.

[0060] like Figure 1 and Figure 2 As shown, the main board 1 is arranged on the side of the filling component 3, the filling component 3 is hollow in the middle, and the feeding balun runs through the middle of the filling component 3;

[0061] The support component 4 is hollow in shape and is sleeved on the outside of the main board 1 and the filling component 3. A metal reflector 5 is provided on the side wall of the support component 4 at the end farther from the main board 1. The end of the metal reflector 5 and the end of the radiation structure 6 are connected through a lumped element 2.

[0062] In this embodiment, if Figure 1 As shown, the support component 4 is in a C-shape, and the support component 4 and the filling component 3 accommodate the main board 1 with the radiation structure 6 therebetween.

[0063] In some embodiments, the supporting component 4 is cylindrical, and is provided with a notch at an end farther from the main board 1 . The notch is a cutting surface, and the cutting surface is provided parallel to the main board 1 .

[0064] Of course, the filling component 3 also has two cutting surfaces, and the two cutting surfaces are arranged opposite to each other. One cutting surface is used to set the main board 1, and the other cutting surface is used to be flush with the cutting surface of the supporting component 4 to set a part of the metal reflector 5.

[0065] like Figure 2As shown, the metal reflector 5 is arranged on the outer edge of the cutting surface of the supporting component 4, and the two ends of the metal reflector 5 extend out of the two sides of the cutting surface, but the extension height does not exceed the horizontal plane where the main board 1 is located, and the extension parts at the two ends of the metal reflector 5 are arc-shaped, and the arc is consistent with the outer wall of the supporting component 4, that is, the metal reflector 5 is in the shape of a bowl as a whole.

[0066] The metal reflector 5 should be connected to the wide edge of the metal on one side of the feed balun and insulated from the metal on the other side.

[0067] like Figure 1 As shown, a gap is provided between the end of the support component 4 closer to the main board 1 and the main board 1, that is, there is a certain distance between the inner wall of the support component 4 and the main board 1 and the radiation structure 6, and it is convenient to make a groove in the middle so that the feeding balun can be placed in it.

[0068] The metal reflector 5 is fixed and its diameter is enlarged by the support member 4. The lower part thereof is cut to be flush with the lower cut part of the filling member 3. The material may be hard foam or the same as the material of the filling member 3.

[0069] In some embodiments, the length of the feed balun is the same as the distance between the two cutting surfaces of the filling component 3 .

[0070] In this embodiment, the filling component 3 is made of polyformaldehyde resin with a relative dielectric constant of 4. The inner diameter of the filling component 3 should be large enough to ensure the structural strength of the filling component 3 after being cut to the width of the mainboard 1. The purpose of the hollowness is to reduce the overall weight of the antenna.

[0071] The two ends of the radiation structure 6 are connected to the corresponding ends of the nearest metal reflector 5 through lumped elements 2. In this embodiment, the four lumped elements 2 are the same, each of which is composed of a resistor and a capacitor connected in series, and the value is 300Ω+10pF.

[0072] Embodiment 2

[0073] The method of the single-hole directional radio frequency electromagnetic detection system provided in Example 1 includes the following steps:

[0074] like Figure 8 As shown, two directional drilling antennas are rotated synchronously, and the reflected electromagnetic signals of anomalies at different angles around the hole are obtained by using the electrical property difference between the anomaly and the surrounding rock;

[0075] Of course, since the directional drilling antenna structure provided in the first embodiment is relatively complex, Figure 8 It is only a schematic diagram, in which the arc-shaped piece represents the metal reflector 5 in the first embodiment, and the black cylinder represents the main board 1 with the radiation structure 6 in the first embodiment.

[0076] When in use, one directional drilling antenna serves as a transmitting end to transmit electromagnetic signals to the target anomaly, and the other directional drilling antenna serves as a receiving end to receive electromagnetic signals fed back by the anomaly.

[0077] In order to solve the problem that the maximum value of the directional pattern is relatively flat, which may make it difficult to distinguish the maximum amplitude point, the median method is used to determine the azimuth of the abnormal body. The specific method is to set a certain detection threshold and select several strong points whose amplitude exceeds the detection threshold. Since the amplitude change near the maximum value is relatively flat, the azimuth corresponding to the center position of these strong points is selected as the azimuth of the abnormal body.

[0078] In this embodiment, select Fig. 9 0.8 times of the maximum amplitude in is used as the threshold. If it exceeds the threshold, it is 1, and if it does not exceed the threshold, it is 0, and the binary quantization result of the detection data is obtained, such as Fig.10 The center position of the sequence of "1" in the binary quantization result is the azimuth of the abnormal body.

[0079] from Fig.10 It can be seen that the center position of the sequence of "1" in the binary quantization result of this embodiment is approximately at an azimuth of 140°, so there should be an abnormal body in this direction. This method is more stable in determining the azimuth of abnormal geological bodies and is more suitable for automated data processing.

[0080] In summary, the intermediate value method for obtaining the azimuth of the anomaly can be summarized as follows:

[0081] To determine the detection threshold of the median method, the maximum amplitude multiplied by a coefficient can be used as the detection threshold;

[0082] The amplitude of the signal at the same depth and in different rotation directions is compared with the detection threshold, and a binary quantization result graph is obtained according to the comparison result;

[0083] The center position of the sequence in the binary quantization result graph is obtained, which is the azimuth of the abnormal body.

[0084] Through simulation experiments, it is found that the diameter of the antenna provided by the present invention is less than 80 mm, and it can move relatively smoothly in a tunnel drilling environment, and has strong applicability.

[0085] Figure 6 This is the H-plane radiation pattern of the antenna at 600MHz in a drilling environment. Red represents the radiation pattern, yellow represents the middle position of the radiation direction, and blue represents the 3dB beam angle. The coordinate axis from the inside to the outside represents the directivity coefficient in dBi. Taking 600MHz as an example, the 3dB beam angle of the antenna radiation pattern is 94.5°, which can more accurately identify the orientation of the anomaly.

[0086] Figure 7 The VSWR of the antenna at 400-1400MHz in a drilling environment is VSWR, which is a voltage standing wave ratio, a parameter that characterizes the antenna return loss, and the minimum is 1. The smaller the VSWR, the smaller the antenna return loss. The bandwidth of the antenna of the present invention with a VSWR less than 2 covers an ultra-wide frequency band of 400-1400MHz, and has the advantage of sub-meter high resolution.

[0087] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art within the spirit and principle of the present invention without creative labor shall be included in the protection scope of the present invention.

Claims

1. A single-hole directional radio frequency electromagnetic detection system, characterized in that: It comprises two coaxially arranged directional drilling antennas, the structures of which are the same, including a main board, a feeding balun, a metal reflector, a filling component and a supporting component, a radiation structure formed of metal is arranged on the main board, the radiation structure is in a shape in which the width at the center position is greater than the width at the end position, and a radially arranged through slot is arranged at the center position of the radiation structure; A feed balun is vertically arranged in the through slot, and the feed balun includes a PCB board, and metal is arranged on both sides of the PCB board, and the metals on the two sides are not connected, and the metals on each side are respectively connected to the corresponding radiation structure; The main board is arranged on the side of the filling component, the middle of the filling component is hollow, and the feeding balun runs through the middle of the filling component; The support component is hollow and sleeved on the outside of the main board and the filling component, and a metal reflector is provided on the side wall of the support component, and the end of the metal reflector and the end of the radiation structure are connected through a lumped element; The supporting component is cylindrical and has a notch on one side, the notch is a cutting surface, and the cutting surface is arranged parallel to the main board; The metal reflective plate is arranged on the cutting surface, and two ends of the metal reflective plate extend out of two sides of the cutting surface, but the extension height does not exceed the horizontal plane where the main board is located; The extended parts at both ends of the metal reflective plate are arc-shaped, and the arc is consistent with the outer wall of the supporting component.

2. A single-hole directional radio frequency electromagnetic detection system as claimed in claim 1, characterized in that: A gap is arranged between the end of the supporting component closer to the main board and the main board.

3. A single-hole directional radio frequency electromagnetic detection system as claimed in claim 1, characterized in that: The two opposite ends of the filling component respectively have a cutting surface, the cutting surface of one end is used to set the main board, and the cutting surface of the other end is flush with the cutting surface of the supporting component.

4. A single-hole directional radio frequency electromagnetic detection system as claimed in claim 3, characterized in that: The length of the feed balun is the same as the distance between the two cutting surfaces of the filling component.

5. A single-hole directional radio frequency electromagnetic detection system as claimed in claim 1 or 3, characterized in that: The metal on one side of the feed balun is in the shape of a long strip, and the long strip is axially arranged at the center of the surface; The metal on the other side is in an axisymmetric shape with a gradually decreasing width, and the change in width is in a curved transition, and the width of the smallest portion of the metal on this side is equal to the width of the long strip of metal on the other side.

6. A single-hole directional radio frequency electromagnetic detection system as claimed in claim 5, characterized in that: The curve follows an exponential trend.

7. A single-hole directional radio frequency electromagnetic detection system as claimed in claim 1, characterized in that: The radiation structure is in an axisymmetric and centrosymmetric shape, with a curve transition from the center to the end, and the curve is determined by an S-shaped function.

8. A single-hole directional radio frequency electromagnetic detection system as claimed in claim 7, characterized in that: The S-type function is a sigmoid function.

9. A single-hole directional radio frequency electromagnetic detection system as claimed in claim 1, characterized in that: The filling component and the supporting component are made of polyoxymethylene resin.

10. A single-hole directional radio frequency electromagnetic detection method, using the single-hole directional radio frequency electromagnetic detection system according to any one of claims 1 to 9, characterized in that: The following steps are involved: The two directional drilling antennas are rotated synchronously, one directional drilling antenna is used as a transmitting end to transmit electromagnetic signals to the target anomaly, and the other directional drilling antenna is used as a receiving end to receive the signal fed back by the anomaly; Determine a detection threshold of the median method, wherein the detection threshold is the product of the maximum amplitude and the coefficient in the received signal; Compare the maximum amplitude of the signal with different rotation directions at the same depth with the detection threshold, and draw a binary quantization result diagram according to the comparison result; Calculate the center position of the sequence of target values ​​in the binary quantization result graph, which is the azimuth of the abnormal body.

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