Array type electromagnetic induction probe based on differential receiving and detection method thereof
Technical Field
The invention belongs to the field of underground target detection, and particularly relates to an array type electromagnetic induction probe based on differential receiving and a method for detecting an underground metal target.
Background
In order to recover local production and life after war conflict, a large amount of unexploded ammunition left after war needs to be eliminated and cleaned, ordinary live ammunition tests, training and exercises of troops also need to be immediately discovered and cleaned, if the unexploded ammunition cannot be eliminated in time, the unexploded ammunition causes great threat to personnel, vehicles and the like, and accurate finding and positioning of hidden unexploded ammunition is a premise for further eliminating action. In the large-area unexploded bomb searching work, the single portable detecting instrument has the defects of low operation speed and low efficiency, and a manned or unmanned vehicle-mounted system capable of quickly detecting the operation is an effective way for solving the large-area searching. The electromagnetic induction technology is one of the most effective underground unexplosive ammunition detection technologies in the world at present, the application is very wide in portable instruments and vehicle-mounted equipment, and a vehicle-mounted electromagnetic induction detection system usually adopts a multi-coil array type probe and improves the operation efficiency by improving the single detection width of a sensor. The design method of the array type probe is one of key technologies of a vehicle-mounted electromagnetic induction detection system, and has important significance for improving the transmitting efficiency, the receiving signal-to-noise ratio, the detection width, the positioning precision and the anti-interference capability of the system.
Disclosure of Invention
The invention aims to solve the technical problem of providing an array type electromagnetic induction probe based on differential receiving and a detection method thereof.
The invention adopts the following technical scheme:
an array electromagnetic induction probe based on differential receiving is improved in that: the array probe comprises a long waist-shaped transmitting coil positioned at the outermost edge of the array probe, and an array consisting of a plurality of annular receiving coils is uniformly arranged in the transmitting coil, and the transmitting coil and the receiving coil array are positioned in a plane and are symmetrical transversely and longitudinally as a whole.
Furthermore, the transmitting coil is formed by winding a single copper enameled wire, the number of turns is 6-10, the direct current impedance is 1000m omega +/-300 m omega, the inductance is 300 mu H +/-60 mu H, the outer surface of the coil is wrapped by a waterproof material, and an excitation signal is accessed by 1 coaxial cable.
Furthermore, all the receiving coils are completely the same and are formed by processing 8 layers of PCBs, the coils in the PCBs are formed by arranging single copper-clad wires in a forward and reverse direction according to a double-D-shaped balanced differential symmetrical structure, the number of turns is 40-60 turns, the direct current impedance is 13 omega +/-4 omega, the inductance is 1.2mH +/-0.4 mH, and signals are output by a single coaxial cable.
In a detection method using the array type electromagnetic induction probe based on differential receiving, the improvement is that: the receiving coil is of a double-D-shaped balanced differential symmetrical structure, the double-D coil is symmetrical along an X axis, the detection advancing direction is set to be a Y axis direction which is horizontally vertical to the X axis, and when a probe passes through a metal object, because the parameters of the double-D coil of the receiving coil are the same and the winding directions are opposite, secondary fields respectively form receiving signals with opposite polarities in the double-D coil; when a metal object passes through the probe, the amplitude of the signal of the double D coils changes due to the change of the relative position, finally the receiving coil outputs a receiving signal with continuous positive, zero and negative changes, the zero crossing point of the signal change is the central position of the metal object in the X-axis direction of the receiving coil, the target position can be determined by tracking the zero crossing point of the signal change, so that the accurate positioning in the Y-axis direction is realized, and the coordinate of the metal object in the X-axis direction can be obtained by analyzing the signal amplitude phase relation of the adjacent receiving coils.
The invention has the beneficial effects that:
the probe disclosed by the invention generally adopts a structural form that a plurality of receiving coils are horizontally arranged in a single transmitting coil, and the receiving coils adopt a double-D-shaped balanced differential symmetrical structure to realize differential receiving, so that the problems of low positioning precision and weak anti-interference capability of the traditional single-reflection multi-receiving array probe are solved, and the comprehensive performances of instantaneity, detection sensitivity, soil adaptability, positioning accuracy and the like are effectively improved.
The probe disclosed by the invention innovatively adopts the design idea of combining a double-D-shaped balanced differential symmetrical receiving coil technology and a single-transmitting multi-receiving technology, provides an effective array probe design scheme for a vehicle-mounted platform electromagnetic induction detection system, and has wide application prospect in the field of military and civil underground target detection.
The detection method disclosed by the invention adopts the receiving coil with the double-D-shaped balanced differential symmetrical structure, has good inhibition capability on primary field, background soil signals and space electromagnetic interference signals, and solves the problems of soil background adaptation and external electromagnetic interference resistance.
Drawings
FIG. 1 is a schematic plan view of a probe disclosed in embodiment 1 of the present invention;
FIG. 2 is a schematic structural diagram of a transmitting coil disclosed in embodiment 1 of the present invention;
fig. 3 is a schematic structural diagram of a receiving coil disclosed in embodiment 1 of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
Embodiment 1, as shown in fig. 1, this embodiment discloses an array electromagnetic induction probe based on differential reception, which includes a long waist-shaped transmitting coil located at the outermost edge of the array probe, an array formed by a plurality of circular receiving coils is uniformly arranged in the transmitting coil, and the transmitting coil and the receiving coil array are located in a plane and are symmetrical in a transverse direction (X-axis direction in fig. 1) and a longitudinal direction (Y-axis direction in fig. 1) as a whole.
As shown in fig. 2, the transmitting coil is formed by winding a single copper enameled wire, the number of turns is 6-10, the direct current impedance is 1000m Ω ± 300m Ω, the inductance is 300 μ H ± 60 μ H, the outer surface of the coil is wrapped by a waterproof material, and the excitation signal is accessed by 1 coaxial cable.
As shown in fig. 3, each receiving coil has the same physical and electrical parameters and is formed by processing 8 layers of PCBs, the coils inside the PCBs are formed by sequentially arranging single copper-clad wires in the forward and reverse directions according to a double D-shaped balanced differential symmetrical structure, the number of turns is 40 to 60 turns, the direct current impedance is 13 Ω ± 4 Ω, the inductance is 1.2mH ± 0.4mH, and the signal of each receiving coil is output by a single coaxial cable.
The principle of the array type electromagnetic induction probe based on differential receiving disclosed by the embodiment is as follows:
as shown in fig. 2, the transmitting coil is a closed loop formed by a plurality of turns of conducting wires, and mainly exhibits inductance characteristics, and the equivalent series direct current impedance and the equivalent series inductance thereof are important parameters affecting the transmitting performance. After the excitation signal Vin is loaded through the a + and a-ports of the transmitting coil, the current inside the coil increases exponentially from 0, and the time constant τ of the exponential function is L/R, and if L is 300 μ H and the equivalent R of the transmitting loop is 1 Ω, τ is 300 μ s; when Vin is +5V and the emission time is τ, the peak current Ip of the emission coil is (Vin/R) × (1-e-t/τ) 3.16 amperes; in practical application, when the emission time is 100 mus, Ip is about 1.4 amperes. The transmitting coil with low impedance and symmetrical structure can effectively improve the transmitting efficiency, realize instantaneous heavy current excitation, and is more beneficial to exciting to generate the eddy current effect when the field intensity of the primary field is stronger and the change is larger.
When current passes through the transmitting coil, a magnetic field (called a primary field) is formed around the transmitting coil, and the changing transmitting current causes the change of the primary field; if a metal object exists in the primary field, the changed primary field can cause the metal object to generate induction current, and the induction current can excite to generate a corresponding magnetic field (called secondary field), and the secondary field has the characteristics of preventing the change of the primary field and being specific to the shape of the target material.
The magnetic field (receiving field) passing through the inside of the receiving coil is the superposition of the primary field and the secondary field, the receiving field is changed due to the changed exciting current, the changed receiving field causes the receiving coil to generate an induced current, and the induced current is a receiving signal formed by the receiving coil and is output through the B + port and the B-port. The detection system can find the target and identify the type of the target by analyzing the change rule of the received signal, thereby achieving the purpose of detection.
The embodiment also discloses a detection method, wherein the array type electromagnetic induction probe based on differential reception is used, the receiving coil is of a double-D-shaped balanced differential symmetrical structure, as shown in fig. 1, the double-D coils (D + and D-) are symmetrical along an X axis, the detection advancing direction is set to be a Y axis direction which is horizontal and vertical to the X axis, when the probe passes through a metal object, because the parameters of the double-D coils (D + and D-) of the receiving coil are the same and the winding directions are opposite, secondary fields respectively form receiving signals with opposite polarities in the double-D coils (D + and D-); when a metal object passes through the probe, the amplitude of signals of the double D coils (D + and D-) is changed due to the change of the relative position, finally the receiving coil outputs a receiving signal with continuous change of positive, zero and negative directions, the zero crossing point of the signal change is the central position of the metal object in the X-axis direction of the receiving coil, the target position can be determined by tracking the signal change zero crossing point, so that the accurate positioning in the Y-axis direction is realized, and the coordinate of the metal object in the X-axis direction can be obtained by analyzing the signal amplitude phase relation of the adjacent receiving coil.