Novel zero-flux coil and design method thereof

Abstract

The invention discloses a novel zero-flux coil and a design method thereof, relates to the technical field of transient electromagnetic exploration, and solves the problem that primary field interference is difficult to eliminate in the prior art. The novel zero-flux coil and the preparation method thereof, the parameter optimization method and the signal acquisition method have the remarkable technical advantages that firstly, almost complete shielding of a primary field is achieved through special structure configuration of the inner and outer double receiving coils and accurate turn ratio calculation; secondly, determining a d = 0 plane configuration through a parameter optimization method, and enabling a longitudinal stability coefficient to be far higher than that of an existing structure; thirdly, signal oscillation caused by asymmetry of factor coil parameters is effectively eliminated through a double-damping method; and finally, through a specific signal acquisition method, secondary field signals are superposed while the primary field is suppressed, and the detection sensitivity is obviously superior to that in the prior art.

Description

Technical Field

[0001] This invention relates to the field of transient electromagnetic exploration technology, and in particular to a novel zero-flux coil and its design method. Background Technology

[0002] The Transient Electromagnetic Method (TEM) is an important geophysical exploration method widely used in mineral resource exploration, groundwater detection, and engineering geological surveys. In a TEM system, a transmitting coil emits a primary electromagnetic field into the ground, while a receiving coil receives the secondary induced electromagnetic field generated by underground conductors. However, in traditional center-loop or overlapped-loop systems, the receiving coil is typically located inside or overlapped with the transmitting coil. When current flows through the transmitting coil, a high density of magnetic field lines is distributed inside the receiving coil. This magnetic field density is even higher, especially in smaller systems, resulting in a higher primary field flux.

[0003] This strong primary field coupling presents serious technical problems: First, the primary and secondary fields are distributed continuously in time, and the strong primary field signal can mask the early secondary field signal, leading to blind spots in shallow exploration. Second, during the transmit current turn-off period, the rapid change in the primary field generates a strong induced voltage in the receiving coil, which may cause saturation or even damage to the preamplifier of the receiving system. Third, the strong mutual inductance between the transmitting and receiving coils reduces the damping characteristics of the system, limits the bandwidth, and causes distortion of the high-frequency secondary field signal. To address these problems, existing technologies have proposed various weak magnetic coupling coil structures, such as anti-flux structures, differential structures, and compensation ring structures. However, these existing structures still have shortcomings in terms of fabrication processes, parameter design methods, and signal acquisition stability. For example, anti-flux structures require extremely high installation accuracy, but lack systematic parameter optimization methods; differential structures can suppress the primary field, but lack effective methods to eliminate signal oscillations; existing technologies also lack specific fabrication processes for zero-flux coils and signal acquisition methods based on this structure.

[0004] Therefore, there is an urgent need for a novel zero-flux coil structure that is simple in structure, highly stable, and exhibits excellent detection sensitivity, along with corresponding fabrication methods, parameter optimization methods, and signal acquisition methods to overcome the shortcomings of existing technologies. In view of this, a novel zero-flux coil and its design method are required. Summary of the Invention

[0005] In view of the problem that the primary field interference is difficult to eliminate in the prior art, the present invention provides a novel zero-flux coil and its design method, which can make the magnetic fluxes received by the inner receiving coil and the outer receiving coil have equal numerical values and opposite polarities through specific structural design and coil parameter configuration, so as to achieve an approximate zero total magnetic flux, effectively eliminate the primary field interference, and at the same time maintain good detection sensitivity and structural stability. The specific technical solution is as follows: A novel zero-flux coil, comprising: A transmitting coil, having a circular structure with a radius of a ; An inner receiving coil, arranged in the inner region of the transmitting coil, with a radius of b , and b < a. The winding direction of the inner receiving coil is opposite to that of the transmitting coil; An outer receiving coil, having an annular structure, surrounding and arranged outside the transmitting coil. The outer receiving coil includes an inner ring portion and an outer ring portion. The inner radius of the inner ring portion is c and c > a , and the outer radius is f . The winding direction of the inner ring portion is the same as that of the transmitting coil, and the winding direction of the outer ring portion is opposite to that of the transmitting coil; Wherein, the number of turns of the inner receiving coil is , and the number of turns of the outer receiving coil is , and they satisfy: In the formula, is the magnetic flux passing through the single-turn area of the inner receiving coil, and is the magnetic flux passing through the single-turn area of the outer receiving coil.

[0006] Preferably, the inner ring portion and the outer ring portion of the outer receiving coil are of an integrally formed continuous wire structure. The distance between the radius c of the inner ring portion and the radius a of the transmitting coil and the distance between the outer radius f of the outer ring portion and the inner radius c of the inner ring portion are both not less than 50 mm.

[0007] Preferably, the inner receiving coil and the transmitting coil are coaxially arranged and in the same plane. The outer receiving coil and the transmitting coil are coaxially arranged, and the distance d in the vertical direction between the inner receiving coil and the transmitting coil is zero.

[0008] Preferably, the radius b of the inner receiving coil is a0.5 times, the inner radius of the inner ring portion of the outer receiving coil c The radius of the transmitting coil a The outer radius of the outer ring portion is 1.2 to 1.5 times that of the outer ring portion. f The inner radius of the inner ring portion c 1.2 to 1.33 times.

[0009] Preferably, the inner receiving coil and the outer receiving coil are connected in series, and the inner receiving coil and the outer receiving coil are each connected in parallel with a damping resistor. The ratio of the damping resistor Rz1 connected in parallel with the inner receiving coil to the damping resistor Rz2 connected in parallel with the outer receiving coil is equal to the ratio of the inductance L1 of the inner receiving coil to the inductance L2 of the outer receiving coil.

[0010] Preferably, the number of turns of the transmitting coil is The number of turns of the inner receiving coil The number of turns of the external receiving coil The following relationship must be satisfied: And the number of turns ratio : The value range is from 1:30 to 30:1.

[0011] A novel method for preparing a zero-flux coil includes the following steps: S1: Determine the radius of the transmitting coil based on the target detection depth. a and number of turns And calculate the magnetic field distribution generated by the transmitting coil when it is energized; S2: Based on the aforementioned magnetic field distribution, calculate the radius as follows: b The magnetic flux per single turn of the inner receiving coil The magnetic flux of a single turn of the outer ring receiving coil The inner ring radius of the outer receiving coil is... c The outer ring radius is f ; S3: According to the formula Calculate the number of turns of the internal receiving coil Number of turns of the external receiving coil The theoretical ratio; S4: Move the transmitting coil with a radius... a Wind several turns; S5: Position the receiving coil with a radius... b Wind in the opposite direction to the winding of the transmitting coil. The turns form an internal receiving coil; S6: Further enlarge the receiving coil to a radius cThe inner loop of the outer receiving coil is formed by winding one turn in the same direction as the transmitting coil, and then the receiving coil is expanded to a radius of... f And a turn is wound in the opposite direction to the transmitting coil to form the outer loop of the outer receiving coil; S7: Repeat step S6 until the total number of turns of the external receiving coil reaches [the specified value]. Furthermore, the turns ratio of the inner and outer receiving coils reaches the theoretical value; S8: Connect the inner receiving coil and the outer receiving coil in series, and fine-tune the number of turns of the inner and outer receiving coils by the actual received signal to make the total magnetic flux approach zero.

[0012] A method for optimizing the parameters of a zero-flux coil includes the following steps: P1: Establish a conductive loop response model for a zero-flux coil, setting the longitudinal displacement of the receiving coil relative to the transmitting coil as a variable. d Set the horizontal offset as a variable ; P2: With a fixed transmit current turn-off time, measure the peak output voltage of the receiving coil during the turn-off period. up ; P3: Adjust the position of the receiving coil both longitudinally and laterally, and measure the peak output voltage after displacement. u p+ and u p- The decoupling stability coefficient is calculated using the following formula: ; P4: Comparing the differences d The longitudinal stability coefficient α at the value V Choose one that makes α V Maximize d The value is used as the optimal vertical spacing, where when d The longitudinal stability coefficient is maximum when = 0; P5: Comparing the differences The transverse stability coefficient α H To evaluate the lateral stability of the coil; P6: Based on the stability analysis results, the vertical spacing between the inner receiving coil and the transmitting coil is adjusted. d Set it to 0, and set the radial distance between the external receiving coil and the transmitting coil to be no less than 50mm.

[0013] A method for eliminating oscillations in the output signal of a zero-flux coil includes the following steps: T1: Measure the inductance L1, internal resistance R1, and distributed capacitance C1 of the inner receiving coil, and the inductance L2, internal resistance R2, and distributed capacitance C2 of the outer receiving coil. T2: Determine whether the parameters of the inner receiving coil and the outer receiving coil satisfy the symmetry condition L1 / R1=L2 / R2 and C1=C2; T3: When the parameters are asymmetrical, calculate the critical damping resistance value of each sub-coil so that the damping resistance Rz1 connected in parallel with the inner receiving coil and the damping resistance Rz2 connected in parallel with the outer receiving coil satisfy Rz1 / Rz2=L1 / L2. T4: Connect the calculated damping resistors Rz1 and Rz2 in parallel to the two ends of the inner and outer receiving coils, respectively; T5: Connect a damping resistor Rb with a resistance greater than 10kΩ in parallel at the main port to form a double-damped circuit structure, which places the system poles on the negative real axis to eliminate the damped oscillation of the output waveform.

[0014] A method for acquiring transient electromagnetic signals based on a zero-flux coil includes the following steps: M1: Place the zero flux coil as described in any one of claims 1-6 in the detection area, such that the plane containing the inner and outer receiving coils is parallel to the ground; M2: Inject steady-state current into the transmitting coil to generate a primary magnetic field. At this time, due to the zero magnetic flux state, the total induced magnetic flux of the receiving coil tends to zero. M3: Fast cut-off of transmitting current. During the current cut-off period, the zero flux state is used to suppress primary field interference, thereby reducing the peak output voltage of the receiving coil during the cut-off period. M4: After the current is turned off, the secondary field signal generated by the underground conductive anomaly is simultaneously received by the inner and outer receiving coils connected in series. The inner receiving coil receives the secondary field magnetic flux in the internal region of the transmitting coil, and the outer receiving coil receives the secondary field magnetic flux in the external region of the transmitting coil. M5: The electromotive force induced by the inner and outer receiving coils is superimposed and output. Since the polarity of the secondary field magnetic flux passing through the two receiving coils is the same, the amplitude of the superimposed signal is higher than that of the single coil, and the early secondary field signal is undistorted. M6: Amplifies and acquires the output transient electromagnetic signals to achieve high-sensitivity detection of shallow underground anomalies.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: The novel zero-flux coil and its preparation method, parameter optimization method, and signal acquisition method of this invention have significant technical advantages: First, through the special structural configuration of the inner and outer dual receiving coils and the precise calculation of the turns ratio, near-complete shielding of the primary field is achieved; second, the d=0 plane configuration determined by the parameter optimization method results in a longitudinal stability coefficient that is much higher than that of existing structures; third, the dual-damping method effectively eliminates signal oscillations caused by the asymmetry of the coil parameters; and finally, through a specific signal acquisition method, the secondary field signal is superimposed while suppressing the primary field, resulting in a detection sensitivity that is significantly better than that of existing technologies. Attached Figure Description

[0016] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0017] Figure 1 This is a schematic diagram of the overall structure of the novel zero-flux coil of the present invention; Figure 2 This is a schematic diagram of the magnetic field distribution of the transmitting coil and the inner and outer receiving coils of the present invention; Figure 3 This is a schematic diagram of the equivalent circuit model of the zero-flux coil of the present invention; Figure 4 This is a comparison diagram of the stability of the present invention under different spacings; Figure 5 This is a comparison chart of the detection sensitivity of the present invention and existing coil structures; Figure 6 This is a schematic cross-sectional view of the overall structure of the novel zero-flux coil of the present invention.

[0018] Explanation of key figure labels: 1. Transmitting coil; 2. Inner receiving coil; 3. Outer receiving coil; 31. Inner ring; 32. Outer ring. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be understood that, when used in this specification and the appended claims, the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0021] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0022] It should also be further understood that the term "and / or" as used in this specification and the appended claims refers to any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0023] Example 1 like Figure 1 , Figure 6 As shown, the novel zero-flux coil of this invention mainly consists of a transmitting coil 1, an inner receiving coil 2, and an outer receiving coil 3. The transmitting coil 1 has a circular structure and uses a radius of... a The frame is formed by winding multiple turns of wire. For example, the radius of transmitting coil 1... a It can be set to 0.6m, and the number of turns NT is determined according to the emission current requirements.

[0024] The inner receiving coil 2 is located within the inner region of the transmitting coil 1, and its radius is... b smaller than the radius of transmitting coil 1 a Preferred b =0.5 a That is, when a When =0.6m, b =0.3m. The inner receiving coil 2 is wound in the opposite direction to the transmitting coil 1. This reverse configuration ensures that the polarity of the primary electromotive force induced in the inner receiving coil 2 corresponds to the change in the magnetic field generated by the transmitting coil 1. The inner receiving coil 2 and the transmitting coil 1 are arranged coaxially and preferably in the same plane. z To achieve optimal longitudinal stability, the plane (=0 plane) is used.

[0025] The external receiving coil 3 has a ring-shaped structure and is arranged around the outside of the transmitting coil 1. For example... Figure 1 As shown, the outer receiving coil 3 includes an inner ring portion 31 and an outer ring portion 32, forming a continuous ring-shaped receiving structure. The inner radius of the inner ring portion 31 is... c The outer radius is f ,and c >a That is, there is a gap between the inner edge of the inner ring 31 and the outer edge of the transmitting coil 1. Preferably, c =1.2a to 1.5a, for example when a When =0.6m, c A depth of 0.72m to 0.9m is acceptable. f =1.2c to 1.33c, for example when c When =0.65m, f A depth of 0.78m to 0.865m is acceptable.

[0026] The outer receiving coil 3 has a special winding configuration: the inner ring 31 is wound in the same direction as the transmitting coil 1, while the outer ring 32 is wound in the opposite direction to the transmitting coil 1. This configuration causes the outer receiving coil 3 to exhibit specific electromagnetic characteristics, and the polarity of the magnetic flux it receives is opposite to the polarity of the magnetic flux received by the inner receiving coil 2.

[0027] The inner receiving coil 2 and the outer receiving coil 3 are connected in series. The key structural parameter is the turns ratio. Let the number of turns of the inner receiving coil 2 be... The number of turns of the external receiving coil 3 is The two must satisfy a specific proportional relationship: in, This represents the magnetic flux passing through the area of ​​a single turn of the inner receiving coil 2, generated by the magnetic field inside the transmitting coil 1; This represents the magnetic flux passing through the area of ​​a single turn of the outer receiving coil 3, generated by the external magnetic field of the transmitting coil 1. According to electromagnetic field theory, for a radius of... a The transmitting coil has an internal and external magnetic field distribution that follows a specific elliptic integral relationship, and the magnetic flux can be obtained through a first-kind complete elliptic integral. K ( k ) and the second complete elliptic integral E ( k )Calculation determined.

[0028] During actual winding, the selected radius parameter is used. a , b , c , f First, calculate the theoretical magnetic flux ratio. Then determine the turns ratio N_outside:N_inside. For example, when a =0.25m, b =0.125m, c =0.3m, f When =0.4m, the calculation yields =2.2210×10⁻ 7 Wb, =3.079×10⁻ 7 Wb, therefore =1.384:1; when a =0.5m, b =0.5m, c =0.7m, f When the length is 1.0m, the turns ratio is 15:1; when a =1.0m, b =1.0m, c =1.5m, f At a winding length of 2.0m, the turns ratio can reach 30:1. During actual winding, fine-tuning can be performed based on theoretical calculations to optimize the received signal quality.

[0029] To avoid electromagnetic coupling interference between coils and ensure signal stability, appropriate spacing should be maintained between the inner receiving coil 2 and the transmitting coil 1, as well as between the outer receiving coil 3 and the transmitting coil 1. Specifically, the spacing (ca) between the inner ring 31 of the outer receiving coil 3 and the transmitting coil 1, and the spacing (fc) between the outer ring 32 and the inner ring 31, should both be no less than 50 mm. This spacing setting is based on considerations of distributed capacitance and parasitic coupling, and can effectively avoid the problem of non-periodic signals being output in a damped oscillating form due to close-proximity wiring between sub-coils.

[0030] Regarding circuit connections, such as Figure 3 As shown, the inner receiving coil 2 and the outer receiving coil 3 are connected in series to form a receiving coil system. To eliminate output waveform oscillations that may be caused by parameter asymmetry between the two sub-coils (inner receiving coil 2 and outer receiving coil 3), a double-damped structure is preferred. That is, a damping resistor Rz1 is connected in parallel across the two ends of the inner receiving coil 2, and a damping resistor Rz2 is connected in parallel across the two ends of the outer receiving coil 3, satisfying Rz1 / Rz2=L1 / L2, where L1 is the inductance of the inner receiving coil 2 and L2 is the inductance of the outer receiving coil 3. A damping resistor Rb can be connected to the total port, and Rb is usually taken as a large value, such as 100kΩ. This double-damped configuration moves all poles to the negative real axis, making the system overdamped, thereby eliminating oscillations.

[0031] The working principle of this invention is as follows: When a steady-state current is applied to the transmitting coil 1, a high-density magnetic field line is generated inside, and a magnetic field line with opposite polarity is generated outside. The inner receiving coil 2 is located inside the transmitting coil 1 and receives the internal magnetic flux. Because its winding direction is opposite to that of the transmitting coil 1, it generates an induced electromotive force with a specific polarity. The outer receiving coil 3 surrounds the transmitting coil 1. Its inner ring 31 receives the magnetic field of the area near the outside of the transmitting coil 1, and its outer ring 32 receives the magnetic field of the area further away. Overall, it receives the external magnetic flux, and due to its winding configuration, the polarity of its induced electromotive force is opposite to that of the inner receiving coil 2. By precisely configuring the ratio of N_inner to N_outer, the total magnetic flux received by the inner receiving coil 2 is... The total magnetic flux N_outer·|φ_outer| received by the external receiving coil 3 is equal to the value of the external receiving coil 3. When the two are connected in series, the total magnetic flux is zero, thus realizing the zero magnetic flux state.

[0032] When the transmitting current is turned off, due to the zero magnetic flux state, almost no primary field induced voltage is generated in the receiving coil, thus avoiding masking of the early secondary field signal and impact on the amplifier. Simultaneously, due to the series coplanar structure of the inner and outer receiving coils, the overall self-inductance is reduced, and the bandwidth is expanded, which is beneficial for the acquisition of high-frequency early signals. When receiving the secondary field signal, both the inner receiving coil 2 and the outer receiving coil 3 induce the secondary field magnetic flux generated by the underground conductive anomaly. Since the secondary field originates underground, the polarity of the secondary field magnetic flux passing through the two receiving coils is the same. Therefore, the total induced electromotive force after series connection is the sum of the two, rather than canceling each other out, thus ensuring high detection sensitivity for the anomaly.

[0033] Experimental data show that the novel zero-flux coil of this invention exhibits excellent longitudinal stability. When d=0, the longitudinal stability coefficient αV reaches 99.86%, significantly higher than the 27% of the anti-flux structure and the 60.27% of the differential structure. In terms of lateral stability, the lateral stability coefficient αH of the inner receiving coil reaches over 99.56%. Regarding detection sensitivity, the characteristic signal peak value for a shallow conductive cube (side length 4m, burial depth 10m) reaches 11.8μV, significantly higher than the 3.1μV of the anti-flux structure, the 2μV of the compensation ring structure, and the 1.9μV of the differential structure.

[0034] In summary, this invention achieves a zero-flux state through a specific coil structure configuration, including the size, winding direction, turn ratio, and spatial position of the transmitting coil, inner receiving coil, and outer receiving coil. This effectively eliminates primary field interference in transient electromagnetic methods while maintaining high detection sensitivity and excellent structural stability, making it suitable for small-loop devices in shallow transient electromagnetic exploration.

[0035] Example 2 A novel method for preparing a zero-flux coil, characterized by comprising the following steps: S1: Determine the radius 'a' and number of turns of the transmitting coil based on the target detection depth. And calculate the magnetic field distribution generated by the transmitting coil when it is energized; For example, based on the requirement of a target detection depth of 50 meters underground, the radius of the transmitting coil is selected. a =0.5m, number of turns =10 turns. Enameled copper wire with a diameter of 1.5mm is tightly wound 10 turns on a circular frame to form a transmitting coil.

[0036] S2: Based on the aforementioned magnetic field distribution, calculate the radius as follows:b The magnetic flux per single turn of the inner receiving coil The magnetic flux of a single turn of the outer ring receiving coil The inner ring radius of the outer receiving coil is... c The outer ring radius is f ; S3: According to the formula Calculate the number of turns of the internal receiving coil Number of turns of the external receiving coil The theoretical ratio; S4: Move the transmitting coil with a radius... a Wind several turns; S5: Position the receiving coil with a radius... b Wind in the opposite direction to the winding of the transmitting coil. The turns form an internal receiving coil; S6: Further enlarge the receiving coil to a radius c The inner loop of the outer receiving coil is formed by winding one turn in the same direction as the transmitting coil, and then the receiving coil is expanded to a radius of... f And a turn is wound in the opposite direction to the transmitting coil to form the outer loop of the outer receiving coil; S7: Repeat step S6 until the total number of turns of the external receiving coil reaches [the specified value]. Furthermore, the turns ratio of the inner and outer receiving coils reaches the theoretical value; S8: Connect the inner receiving coil and the outer receiving coil in series, and fine-tune the number of turns of the inner and outer receiving coils by the actual received signal to make the total magnetic flux approach zero.

[0037] For example, the implementation process is as follows: First, wind the transmitting coil: on a circular frame with a radius of 0.5m, wind 10 turns clockwise. Then, wind the inner receiving coil: on a circular frame with a radius of 0.25m, wind it counterclockwise (opposite to the transmitting coil). =10 turns. Finally, wind the outer receiving coil: using a continuous winding method, first wind one turn clockwise (same as the transmitting coil) at a radius of 0.6m to form the inner loop, then wind one turn counterclockwise (opposite to the transmitting coil) at a radius of 0.9m to form the outer loop. Repeat this process until the total number of turns of the outer receiving coil reaches [number missing]. The number of turns should reach approximately 4.5 (based on a ratio of 1:2.232, 10 / 2.232≈4.48, rounded down to 4 or 5 turns). Finally, connect the inner receiving coil (10 turns) and the outer receiving coil (4 turns) in series to the test circuit. Inject a 10A current into the transmitting coil and measure the peak output voltage of the receiving coil during the current-off period. If the peak value is not zero, fine-tune the number of turns of the outer receiving coil (increasing or decreasing by half a turn) until the induced voltage during the off period is minimized (approaching zero), at which point the zero flux state is achieved.

[0038] Example 3 A method for optimizing the parameters of a zero-flux coil, characterized by comprising the following steps: P1: Establish a conductive loop response model for a zero-flux coil, defining the longitudinal displacement of the receiving coil relative to the transmitting coil as variable d, and the lateral offset as variable d. ; P2: With a fixed transmit current turn-off time, measure the peak output voltage up of the receiving coil during the turn-off period; P3: Adjust the position of the receiving coil both longitudinally and laterally, and measure the peak output voltage after displacement. u p+ and u p- The decoupling stability coefficient is calculated using the following formula: ; P4: Compare the longitudinal stability coefficient α under different d values. V Choose one that makes α V The maximized value of d is taken as the optimal longitudinal spacing, where the longitudinal stability coefficient is maximized when d=0; P5: Comparing the differences The transverse stability coefficient α H To evaluate the lateral stability of the coil; P6: Based on the stability analysis results, the vertical spacing between the inner receiving coil and the transmitting coil is adjusted. d Set it to 0, and set the radial distance between the external receiving coil and the transmitting coil to be no less than 50mm.

[0039] Example 4 A method for eliminating oscillations in the output signal of a zero-flux coil, characterized by comprising the following steps: T1: Measure the inductance L1, internal resistance R1, and distributed capacitance C1 of the inner receiving coil, and the inductance L2, internal resistance R2, and distributed capacitance C2 of the outer receiving coil. T2: Determine whether the parameters of the inner receiving coil and the outer receiving coil satisfy the symmetry condition L1 / R1=L2 / R2 and C1=C2; T3: When the parameters are asymmetrical, calculate the critical damping resistance value of each sub-coil so that the damping resistance Rz1 connected in parallel with the inner receiving coil and the damping resistance Rz2 connected in parallel with the outer receiving coil satisfy Rz1 / Rz2=L1 / L2. T4: Connect the calculated damping resistors Rz1 and Rz2 in parallel to the two ends of the inner and outer receiving coils, respectively; T5: Connect a damping resistor Rb with a resistance greater than 10kΩ in parallel at the main port to form a double-damped circuit structure, which places the system poles on the negative real axis to eliminate the damped oscillation of the output waveform.

[0040] Example 5 A method for acquiring transient electromagnetic signals based on a zero-flux coil, characterized by comprising the following steps: M1: Place the zero flux coil as described in any one of claims 1-6 in the detection area, such that the plane containing the inner and outer receiving coils is parallel to the ground; For example, the process of setting up the coil is as follows: the prepared zero-flux coil (transmitting coil radius 0.6m, inner receiving coil radius 0.3m, outer receiving coil ring structure) is placed horizontally on the ground of the detection area, ensuring that the planes where the inner and outer receiving coils are located are parallel to the ground, and that the inner receiving coil and the transmitting coil are coaxial and located on the same horizontal plane.

[0041] M2: Inject steady-state current into the transmitting coil to generate a primary magnetic field. At this time, due to the zero magnetic flux state, the total induced magnetic flux of the receiving coil tends to zero. For example, the process of transmitting a single field is as follows: a steady-state current of 10A is injected into the transmitting coil by the transmitter. At this time, due to the magnetic flux cancellation effect of the zero-flux coil, the total magnetic flux passing through the receiving coil is approximately zero, and the induced voltage across the receiving coil is close to zero.

[0042] M3: Fast cut-off of transmit current. During the current cut-off period, the zero flux state is used to suppress primary field interference, so that the peak output voltage of the receiving coil during the cut-off period is reduced to less than 10% of that in the unoptimized state. For example, this step specifically involves: in t The transmitting current is rapidly switched off at time 0, with a turn-off time of 14μs. Due to the zero flux state, the peak output voltage of the receiving coil during the turn-off period is only about -1.5V, while conventional center loop devices without a zero flux structure can achieve peak output voltages of over -50V under the same conditions. This embodiment achieves a first-field rejection ratio of over 97%, effectively avoiding impact on the preamplifier. M4: After the current is turned off, the secondary field signal generated by the underground conductive anomaly is simultaneously received by the inner and outer receiving coils connected in series. The inner receiving coil receives the secondary field magnetic flux in the internal region of the transmitting coil, and the outer receiving coil receives the secondary field magnetic flux in the external region of the transmitting coil. M5: The electromotive force induced by the inner and outer receiving coils is superimposed and output. Since the polarity of the secondary field magnetic flux passing through the two receiving coils is the same, the amplitude of the superimposed signal is higher than that of the single coil, and the early secondary field signal is undistorted. For example, the process of receiving and adding a secondary field signal is as follows: After the current is turned off, the underground conductive anomaly generates a secondary induced electromagnetic field. This secondary field passes through both the inner and outer receiving coils. The inner receiving coil (located inside the transmitting coil) receives the secondary field flux in the internal region, generating an induced electromotive force ε1; the outer receiving coil (located outside the transmitting coil) receives the secondary field flux in the external region, generating an induced electromotive force ε2.

[0043] Since the secondary field originates from underground, the induced electromotive force of the inner and outer receiving coils connected in series has the same polarity (both clockwise or both counterclockwise). Therefore, the total output voltage u(t) = ε1 + ε2, which realizes the superposition and enhancement of the signal.

[0044] M6: Amplifies and acquires the output transient electromagnetic signals to achieve high-sensitivity detection of shallow underground anomalies.

[0045] This step involves feeding the superimposed signal into a preamplifier (1000x gain) for A / D conversion and data acquisition. Because the zero-flux structure extends the bandwidth, the early secondary field signal (0.1-10μs period) is distortion-free, reducing the effective resolution time and enabling highly sensitive detection of shallow (within 10m) underground anomalies. Actual measurements showed a characteristic signal peak of 11.8μV for a conductive cube with sides of 4m and a burial depth of 10m, significantly higher than that of traditional structures.

[0046] In summary, the novel zero-flux coil and its fabrication method, parameter optimization method, and signal acquisition method of this invention have significant technical advantages: First, through the special structural configuration of the inner and outer dual receiving coils and precise turns ratio calculation, near-complete shielding of the primary field is achieved; second, the parameter optimization method determines... d The =0 plane configuration results in a longitudinal stability coefficient that is much higher than that of existing structures. Furthermore, the dual-damping method effectively eliminates signal oscillations caused by the asymmetry of the factor coil parameters. Finally, through a specific signal acquisition method, the secondary field signal is superimposed while suppressing the primary field, resulting in a detection sensitivity that is significantly better than that of existing technologies.

[0047] Those skilled in the art will recognize that the units of the various examples described in connection with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of the invention.

[0048] In the embodiments provided by the present invention, it should be understood that the division of units is only a logical functional division. In actual implementation, there may be other division methods, such as multiple units can be combined into one unit, one unit can be split into multiple units, or some features can be ignored.

[0049] Furthermore, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0050] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, read-only memory (ROM), random access memory (RAM), portable hard drives, magnetic disks, or optical disks.

[0051] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

Claims

1. A novel zero-flux coil, characterized in that, include: The transmitting coil (1) has a circular structure with a radius of [missing information]. a ; The inner receiving coil (2) is arranged in the inner area of the transmitting coil (1) and has a radius of b , and b < a. The winding direction of the inner receiving coil (2) is opposite to that of the transmitting coil (1); An external receiving coil (3) has a ring structure and is arranged around the outside of the transmitting coil (1). The external receiving coil (3) includes an inner ring (31) and an outer ring (32). The inner radius of the inner ring (31) is... c and c > a The outer radius is f The inner ring (31) is wound in the same direction as the transmitting coil (1), and the outer ring (32) is wound in the opposite direction to the transmitting coil (1). The number of turns of the inner receiving coil (2) is: The number of turns of the external receiving coil (3) is And satisfy: In the formula, The magnetic flux passing through a single turn area of ​​the inner receiving coil (2) is The magnetic flux passing through the single-turn area of ​​the outer receiving coil (3) is the magnetic flux.

2. The novel zero-flux coil according to claim 1, characterized in that, The inner ring (31) and the outer ring (32) of the outer receiving coil (3) are integrally formed continuous conductor structures, and the radius of the inner ring (31) is... c The radius of the transmitting coil (1) a The spacing between them and the outer radius of the outer ring (32) f With the inner radius of the inner ring (31) c The spacing between them is not less than 50mm.

3. A novel zero-flux coil according to claim 1, characterized in that, The inner receiving coil (2) is coaxially arranged with the transmitting coil (1) and located in the same plane. The outer receiving coil (3) is coaxially arranged with the transmitting coil (1). The vertical distance between the inner receiving coil (2) and the transmitting coil (1) is... d It is zero.

4. A novel zero-flux coil according to claim 1, characterized in that, The radius of the inner receiving coil (2) b The radius of the transmitting coil (1) a 0.5 times, the inner radius of the inner ring portion (31) of the outer receiving coil (3) c The radius of the transmitting coil (1) a The outer radius of the outer ring portion (32) is 1.2 to 1.5 times that of the outer ring portion (32). f The inner radius of the inner ring (31) c 1.2 to 1.33 times.

5. A novel zero-flux coil according to claim 1, characterized in that, The inner receiving coil (2) and the outer receiving coil (3) are connected in series, and the inner receiving coil (2) and the outer receiving coil (3) are respectively connected in parallel with damping resistors. The ratio of the damping resistor Rz1 connected in parallel with the inner receiving coil (2) to the damping resistor Rz2 connected in parallel with the outer receiving coil (3) is equal to the ratio of the inductance L1 of the inner receiving coil (2) to the inductance L2 of the outer receiving coil (3).

6. A novel zero-flux coil according to claim 1, characterized in that, The number of turns of the transmitting coil (1) is The number of turns of the inner receiving coil (2) The number of turns of the external receiving coil (3) The following relationship must be satisfied: And the number of turns ratio : The value range is from 1:30 to 30:

1.

7. A method for preparing a novel zero-flux coil, characterized in that, Includes the following steps: S1: Determine the radius of the transmitting coil based on the target detection depth. a and number of turns And calculate the magnetic field distribution generated by the transmitting coil when it is energized; S2: Based on the aforementioned magnetic field distribution, calculate the radius as follows: b The magnetic flux per single turn of the inner receiving coil The magnetic flux of a single turn of the outer ring receiving coil The inner ring radius of the outer receiving coil is... c The outer ring radius is f ; S3: According to the formula Calculate the number of turns of the internal receiving coil Number of turns of the external receiving coil The theoretical ratio; S4: Move the transmitting coil with a radius... a Wind several turns; S5: Position the receiving coil with a radius... b Wind in the opposite direction to the winding of the transmitting coil. The turns form an internal receiving coil; S6: Further enlarge the receiving coil to a radius c The inner loop of the outer receiving coil is formed by winding one turn in the same direction as the transmitting coil, and then the receiving coil is expanded to a radius of... f And a turn is wound in the opposite direction to the transmitting coil to form the outer loop of the outer receiving coil; S7: Repeat step S6 until the total number of turns of the external receiving coil reaches [the specified value]. Furthermore, the turns ratio of the inner and outer receiving coils reaches the theoretical value; S8: Connect the inner receiving coil and the outer receiving coil in series, and fine-tune the number of turns of the inner and outer receiving coils by the actual received signal to make the total magnetic flux approach zero.

8. A method for optimizing the parameters of a zero-flux coil, characterized in that, Includes the following steps: P1: Establish a conductive loop response model for a zero-flux coil, setting the longitudinal displacement of the receiving coil relative to the transmitting coil as a variable. d Set the horizontal offset as a variable ; P2: With a fixed transmit current turn-off time, measure the peak output voltage of the receiving coil during the turn-off period. up ; P3: Adjust the position of the receiving coil both longitudinally and laterally, and measure the peak output voltage after displacement. u p+ and u p- The decoupling stability coefficient is calculated using the following formula: ； P4: Comparing the differences d The longitudinal stability coefficient α at the value V Choose one that makes α V Maximize d The value is used as the optimal vertical spacing, where when d The longitudinal stability coefficient is maximum when = 0; P5: Comparing the differences The transverse stability coefficient α H To evaluate the lateral stability of the coil; P6: Based on the stability analysis results, the vertical spacing between the inner receiving coil and the transmitting coil is adjusted. d Set it to 0, and set the radial distance between the external receiving coil and the transmitting coil to be no less than 50mm.

9. A method for eliminating oscillations in the output signal of a zero-flux coil, characterized in that, Includes the following steps: T1: Measure the inductance L1, internal resistance R1, and distributed capacitance C1 of the inner receiving coil, and the inductance L2, internal resistance R2, and distributed capacitance C2 of the outer receiving coil. T2: Determine whether the parameters of the inner receiving coil and the outer receiving coil satisfy the symmetry condition L1 / R1=L2 / R2 and C1=C2; T3: When the parameters are asymmetrical, calculate the critical damping resistance value of each sub-coil so that the damping resistance Rz1 connected in parallel with the inner receiving coil and the damping resistance Rz2 connected in parallel with the outer receiving coil satisfy Rz1 / Rz2=L1 / L2. T4: Connect the calculated damping resistors Rz1 and Rz2 in parallel to the two ends of the inner and outer receiving coils, respectively; T5: Connect a damping resistor Rb with a resistance greater than 10kΩ in parallel at the main port to form a double-damped circuit structure, which places the system poles on the negative real axis to eliminate the damped oscillation of the output waveform.

10. A method for acquiring transient electromagnetic signals based on a zero-flux coil, characterized in that, Includes the following steps: M1: Place the zero flux coil as described in any one of claims 1-6 in the detection area, such that the plane containing the inner and outer receiving coils is parallel to the ground; M2: Inject steady-state current into the transmitting coil to generate a primary magnetic field. At this time, due to the zero magnetic flux state, the total induced magnetic flux of the receiving coil tends to zero. M3: Fast cut-off of transmitting current. During the current cut-off period, the zero flux state is used to suppress primary field interference, thereby reducing the peak output voltage of the receiving coil during the cut-off period. M4: After the current is turned off, the secondary field signal generated by the underground conductive anomaly is simultaneously received by the inner and outer receiving coils connected in series. The inner receiving coil receives the secondary field magnetic flux in the internal region of the transmitting coil, and the outer receiving coil receives the secondary field magnetic flux in the external region of the transmitting coil. M5: The electromotive force induced by the inner and outer receiving coils is superimposed and output. Since the polarity of the secondary field magnetic flux passing through the two receiving coils is the same, the amplitude of the superimposed signal is higher than that of the single coil, and the early secondary field signal is undistorted. M6: Amplifies and acquires the output transient electromagnetic signals to achieve high-sensitivity detection of shallow underground anomalies.

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