A device and method for eliminating transient electromagnetic primary fields with adjustable compensating magnetic moment.

Abstract

This invention relates to the field of transient electromagnetic detection technology, and more particularly to a transient electromagnetic primary field elimination device and method with adjustable compensating magnetic moment. According to the invention, the transient electromagnetic primary field elimination device with adjustable compensating magnetic moment includes a device body, which includes a transmitter for feeding a specific current into a circuit and a receiver for measuring the voltage across the circuit as a receiving voltage. It also includes a receiving coil connected to the receiver at both ends and a transmitting coil connected to one pole of the transmitter and used to generate an induced voltage in the receiving coil. Furthermore, it includes a compensation coil, which is a multi-turn coil connected in series with the transmitting coil at the other pole of the transmitter, located between the transmitting and receiving coils. This invention achieves adjustment of the compensating magnetic moment by adjusting the adjustable resistor to change the compensation current, without altering the system's geometry. The adjustment method has strong robustness and can conveniently and reliably eliminate transient electromagnetic primary fields.

Description

Technical Field

[0001] This invention relates to the field of transient electromagnetic detection technology, and in particular to a transient electromagnetic primary field elimination device and method with adjustable compensating magnetic moment. Background Technology

[0002] Transient electromagnetic method (TEM) is a time-domain electromagnetic detection method generally used to detect the electrical distribution of underground media, identify the presence of hidden anomalies, and locate them. Its basic principle is to use a grounded or ungrounded transmitter to generate a stable magnetic field in the detection area, and then quickly shut down the magnetic field source. According to the law of electromagnetic induction, the underground medium will generate a secondary field that varies with time. By observing and recording the induced transient electromagnetic response, the underground electrical distribution is inferred, enabling anomaly identification and location. TEM has advantages such as small volume effect, high efficiency, and high low-resistivity resolution, and is widely used in the field of Earth electromagnetic detection. In practical transient electromagnetic detection work, small-loop transient electromagnetic devices use small-loop transmitters with sizes ranging from sub-meter to ten-meter, offering advantages such as even smaller volume effect, higher efficiency, and stronger environmental adaptability. Therefore, they are widely used in special scenarios such as the detection of water-bearing disaster-causing bodies, underground goaf detection, unexploded ordnance detection, and tunnel early warning.

[0003] The transmitting and receiving coils of a small-loop transient electromagnetic device are typically very close in space, which easily leads to self-inductance and mutual inductance effects. Furthermore, in order to probe deeper underground structures, it is usually necessary to increase the number of turns of the transmitting coil to increase the transmitting magnetic dipole moment, but this also correspondingly enhances self-inductance and mutual inductance effects.

[0004] Currently, a compensation method is commonly used to solve this problem. This involves placing a compensation coil near the receiving coil, whose reverse magnetic moment cancels out the original transmitting coil's, thus eliminating self-inductance and mutual inductance responses, and consequently eliminating primary field aliasing in small-loop transient electromagnetic interference. This compensation method requires zero-adjustment based on the system's operating state to ensure complete or near-complete cancellation of the primary field response in the receiving coil. However, adjusting the physical area of ​​the coil after winding is inconvenient. In practice, the compensation magnetic moment is often fixed, and zero-adjustment is achieved by adjusting the geometric position of the receiving coil. However, the magnetic field near the transmitting coil changes drastically; even small geometric changes can cause significant magnetic field variations, leading to difficulties in zero-adjustment and susceptibility to interference that introduces new distortions. Summary of the Invention

[0005] This invention provides a transient electromagnetic primary field elimination device and method with adjustable compensating magnetic moment, which can overcome some or all defects of the prior art.

[0006] According to the present invention, a transient electromagnetic primary field elimination device with adjustable compensating magnetic moment includes a device body, the device body including a transmitter for feeding a specific current into a circuit and a receiver for measuring the voltage across the circuit as a receiving voltage, and further including a receiving coil connected to the receiver at both ends and a transmitting coil connected to one pole of the transmitter and used to generate an induced voltage in the receiving coil; and further including:

[0007] The compensation coil is a multi-turn coil connected in series with the transmitting coil to the other pole of the transmitter, located between the transmitting coil and the receiving coil; wherein the current direction is opposite to the current in the transmitting coil, so as to generate a second induced voltage in the receiving coil that is opposite to the direction of the first induced voltage generated by the transmitting coil;

[0008] The magnetic flux of the magnetic field emitted by the compensation coil in the receiving coil is calculated using the following formula:

[0009]

[0010] Where n2 is the number of turns of the compensation coil, n r Where μ is the number of turns of the receiving coil, μ0 is the permeability, I2 is the magnitude of the compensation current, L2 is the closed curve enclosed by the compensation coil as the integration path, dl is the differential unit on the integration path; r is the vector from the current element to the field point to be determined, r is the distance from the current element to the field point to be determined, S is the plane enclosed by the receiving coil as the integration plane, ds is the differential unit on the integration plane. The number of turns of the compensation coil is set to be slightly more than the number of turns required for zeroing under ideal conditions, and the device is in an overcompensated state.

[0011] An adjustable resistor is connected in parallel across the compensation coil to adjust the current shunting in the compensation coil and change the magnitude of the current within the compensation coil, thereby adjusting the compensation magnetic moment.

[0012] Preferably, the adjustable resistor is a sliding rheostat.

[0013] Preferably, the transmitter is used to generate a single-frequency sine wave or a transient electromagnetic square wave; the specific current includes a single-frequency sine wave current or a transient electromagnetic square wave current.

[0014] Preferably, the transmitting coil is wrapped around the outside of the receiving coil and is used as a loop for single-frequency sinusoidal current and transient electromagnetic square wave current.

[0015] The magnetic flux of the magnetic field emitted by the transmitting coil in the receiving coil is calculated using the following formula:

[0016]

[0017] Where n1 is the number of turns of the transmitting coil, n rHere, μ0 is the number of turns of the receiving coil, I1 is the permeability, L1 is the magnitude of the transmitting current, L1 is the closed curve enclosed by the transmitting coil as the integration path, dl is the differential unit on the integration path, r is the vector from the current element to the field point to be determined, r is the distance from the current element to the field point to be determined, S is the plane enclosed by the receiving coil as the integration plane, ds is the differential unit on the integration plane, and the number of turns of the compensation coil is set to be slightly more than the number of turns required for zeroing under ideal conditions, and the device is in an overcompensated state.

[0018] Preferably, a current-limiting resistor is also included, connected in series with the compensation coil; this is used to ensure that the compensation coil has a certain resistance value, thereby having the current-limiting capability and preventing excessive current from damaging the device.

[0019] According to a method for eliminating transient electromagnetic primary fields with adjustable compensating magnetic moment according to the present invention, the method is based on the aforementioned device for eliminating transient electromagnetic primary fields with adjustable compensating magnetic moment; specifically, it includes the following steps:

[0020] Step S1: The device body is arranged in a specific manner at the measuring point provided for the target body to be detected;

[0021] Step S2: The transmitter feeds a single-frequency sinusoidal current into the transmitting coil and records the voltage across the receiving coil through the receiver;

[0022] Step S3: Gradually decrease the resistance value of the adjustable resistor and observe the received voltage until the magnitude of the received voltage begins to increase.

[0023] Step S4: Continue to adjust the resistance value of the adjustable resistor until the magnitude of the received voltage is the minimum value that can be obtained by adjustment.

[0024] Step S5: Place the device body flat on the observation surface, feed the transmitter into the transmitting coil with transient electromagnetic square wave current, and complete the transient electromagnetic data acquisition at the measurement point.

[0025] Step S6: Stop the transient electromagnetic data acquisition, and then reset the adjustable resistor to its maximum resistance value to prepare for the acquisition of the next measurement point.

[0026] Step S7: Repeat the above process to complete the acquisition of all measuring points, perform underground medium imaging, analyze the existence of anomalies, and locate the anomalies.

[0027] Preferably, in step S1, the specific method is that the device body is placed vertically on the observation surface, the plane containing the transmitting coil and the receiving coil is perpendicular to the observation surface, and the adjustable resistor is placed at the position of maximum resistance.

[0028] Compared with the prior art, the present invention has the following significant advantages:

[0029] (1) This invention proposes a method to accurately eliminate the transient electromagnetic primary field by adjusting the compensation magnetic moment, which effectively solves the response distortion problem caused by self-inductance and mutual inductance in the transient electromagnetic detection of small loops, and provides effective data for subsequent data processing and interpretation.

[0030] (2) The transient electromagnetic primary field elimination method proposed in this invention changes the compensation current by adjusting the adjustable resistor, thereby adjusting the compensation magnetic moment without changing the geometric structure of the system. The adjustment method has strong robustness and can conveniently and reliably eliminate the transient electromagnetic primary field. Attached Figure Description

[0031] Figure 1 This is a schematic diagram of the transient electromagnetic primary field elimination device in Example 1;

[0032] Figure 2 This is a schematic diagram of the arrangement of measuring points and the structure of the underground buried aluminum pipe in step S1 of the elimination method in Example 1.

[0033] Figure 3 This is a schematic diagram showing the change in the modulus of the received voltage when the adjustable resistor R2 is adjusted in steps S3 and S4 of the elimination method in Example 1.

[0034] Figure 4 The transient electromagnetic data collected in step S5 of the elimination method is shown in the figure. The transient electromagnetic data includes the distorted transient electromagnetic response with primary field (solid line) and the normal transient electromagnetic response after compensation and zeroing (solid line with hollow circles).

[0035] Figure 5 The image shown is of the aluminum tube body in the underground medium imaging after compensation and elimination of the field in step S7 of the elimination method. Detailed Implementation

[0036] Example 1

[0037] This embodiment provides a transient electromagnetic primary field elimination device with adjustable compensating magnetic moment, such as... Figure 1 As shown, it includes:

[0038] A transmitter is used to generate a single-frequency sine wave or a transient electromagnetic square wave, which is fed with a specific current in a conventional circuit.

[0039] A receiver is used to measure, display, and record the voltage across a circuit and to receive the voltage.

[0040] The receiving coil R1 is a 30-turn circular coil with a radius of 0.1 meters. It is connected to the receiver and is used to measure the induced voltage generated by changes in the magnetic field.

[0041] The transmitting coil T1 is an 8-turn circular coil with a radius of 0.6 meters. It is connected to one pole of the transmitter, surrounds the outside of the receiving coil, is coplanar with the receiving coil, and its center coincides with the receiving coil. It is used as a loop for single-frequency sinusoidal current or transient electromagnetic square wave current.

[0042] The compensation coil T2 is a 5-turn circular coil with a radius of 0.3 meters. It is connected in series with the transmitting coil to the other pole of the transmitter, located between the transmitting and receiving coils, and is coplanar with the transmitting and receiving coils. Its center coincides with the transmitting and receiving coils. The current direction is opposite to the current in the transmitting coil. It can be calculated that the number of turns required for zeroing under ideal conditions is 4 turns. The 5-turn coil in this embodiment can make the system in an overcompensated state.

[0043] The current-limiting resistor R1, with a resistance of 2 ohms, is connected in series with the compensation coil to ensure the current-limiting capability of the compensation coil and prevent excessive current.

[0044] The adjustable resistor R2 is a sliding rheostat with a resistance range of 0-10 ohms, connected in parallel across the compensation coil.

[0045] This embodiment also provides a method for eliminating transient electromagnetic primary fields with adjustable compensating magnetic moment based on the aforementioned device for eliminating transient electromagnetic primary fields with adjustable compensating magnetic moment. Specifically, it involves using the aforementioned device to detect and locate underground buried aluminum pipes, the aluminum pipes being 0.3 meters × 0.3 meters × 1 meter in size. Figure 2 As shown, the three aluminum tubes are buried at depths of approximately 2 meters, 3 meters, and 5 meters underground, with a horizontal spacing of approximately 10 meters. The main steps include:

[0046] Step S1: Arrange measuring points on the ground as follows Figure 2 The observation surface is the ground. At the first measuring point, the aforementioned device system is erected vertically on the observation surface, that is, the plane where the transmitting coil and the receiving coil are located is perpendicular to the observation surface, and the adjustable resistor R2 is set to 10 ohms.

[0047] Step S2: The transmitter feeds a single-frequency sinusoidal current into the transmitting coil at a frequency of 80kHz and a current of 5A. The receiver records the voltage across the receiving coil.

[0048] Step S3: Adjust the adjustable resistor R2, gradually decrease the resistance value, and observe the received voltage until the magnitude of the received voltage begins to increase.

[0049] Step S4: Further adjust the adjustable resistor R2 to minimize the magnitude of the received voltage, such as... Figure 3 As shown, the resistance of the adjustable resistor is approximately 6.8 ohms at this time;

[0050] Step S5: Place the device body flat on the observation surface to complete the transient electromagnetic data acquisition at this measurement point, such as... Figure 4 As shown, when the adjustable resistor is adjusted to almost completely eliminate the primary field, a normal secondary field response can be obtained.

[0051] Step S6: Stop transient electromagnetic data acquisition, reset the adjustable resistor R2 to 10 ohms, and prepare for the acquisition of the next measurement point.

[0052] Step S7: Repeat the above process to complete the acquisition of all measuring points and perform subsurface medium imaging. The results are as follows: Figure 5 As shown, it can be seen that after eliminating the primary field using the above-mentioned device, the obtained secondary field response imaging results effectively reflect the existence of the aluminum tube, and the aluminum tube can be accurately located based on the resistivity distribution.

[0053] It is readily understood that those skilled in the art can combine, split, or reorganize the embodiments provided in this application to obtain other embodiments, all of which do not exceed the protection scope of this application.

[0054] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the embodiments shown are only part of the embodiments of the present invention. The actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A method for eliminating transient electromagnetic primary fields with adjustable compensating magnetic moment, based on a device body, the device body comprising a transmitter for feeding a specific current into a circuit and a receiver for measuring the voltage across the circuit as a received voltage, further comprising a receiving coil connected at both ends to the receiver and a transmitting coil connected to one pole of the transmitter and used to generate an induced voltage in the receiving coil; characterized in that: Also includes: The compensation coil is connected in series with the transmitting coil to the other pole of the transmitter, located between the transmitting coil and the receiving coil; The current direction is opposite to that in the transmitting coil, so as to generate a second induced voltage in the receiving coil that is opposite to the direction of the first induced voltage generated by the transmitting coil; the number of turns of the compensation coil is set to be more than the number of turns required for zeroing under ideal conditions, and the device is in an overcompensated state. An adjustable resistor is connected in parallel across the compensation coil to adjust the current shunting in the compensation coil and change the magnitude of the current in the compensation coil, thereby adjusting the compensation magnetic moment. A current-limiting resistor is connected in series with the compensation coil; The transmitting coil is wrapped around the outside of the receiving coil and is used as a loop for single-frequency sinusoidal current and transient electromagnetic square wave current. The elimination method includes: Step S1: The device body is arranged in a specific manner at the measuring point provided for the target body to be detected; Step S2: The transmitter feeds a specific current into the transmitting coil and the receiver records the voltage across the receiving coil. Step S3: Gradually decrease the resistance value of the adjustable resistor and observe the received voltage until the magnitude of the received voltage begins to increase. Step S4: Continue to adjust the resistance value of the adjustable resistor until the magnitude of the received voltage is the minimum value that can be obtained by adjustment. Step S5: Place the device body flat on the observation surface, feed the transmitter into the transmitting coil with transient electromagnetic square wave current, and complete the transient electromagnetic data acquisition at the measurement point. Step S6: Stop transient electromagnetic data acquisition, then reset the adjustable resistor to its maximum resistance value to prepare for the acquisition of the next measurement point. Step S7: Repeat the above process to complete the acquisition of all measuring points, perform underground medium imaging, analyze the existence of anomalies, and locate the anomalies.

2. The transient electromagnetic primary field elimination method with adjustable compensating magnetic moment according to claim 1, characterized in that: The adjustable resistor is a sliding rheostat.

3. The transient electromagnetic primary field elimination method with adjustable compensating magnetic moment according to claim 1, characterized in that: The transmitter is used to generate a single-frequency sine wave or a transient electromagnetic square wave; the specific current includes a single-frequency sine wave current or a transient electromagnetic square wave current.

4. The transient electromagnetic primary field elimination method with adjustable compensating magnetic moment according to claim 1, characterized in that: In step S1, the specific method is that the device body is placed vertically on the observation surface, and the adjustable resistor is set at the maximum resistance value.

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