A half-sine wave electromagnetic transmission system and method for polarization effect

Abstract

The application belongs to a half-sine wave electromagnetic transmitting system and method for polarization effect, which is suitable for electromagnetic geophysical exploration field, especially for excitation and measurement of polarization effect, and the system comprises an RLC series resonant circuit and a power supply, the power supply adopts a bipolar power supply with a large capacity polar capacitor or an inverter bridge output, which is used for generating magnetic source half-sine wave and electric source half-sine wave respectively. By outputting the half-sine wave, the off time of the transmitting current is prolonged, the problem of low detection precision of transient electromagnetic method for polarized medium caused by insufficient prolonging capacity of the existing system is solved, and the signal-to-noise ratio of measuring polarization effect is improved.

Description

Technical Field

[0001] This invention relates to a half-sine wave electromagnetic emission system and method for polarization effects, applicable to the field of electromagnetic geophysical exploration, and particularly suitable for the excitation and measurement of polarization effects. Background Technology

[0002] Polarization is an important electrochemical effect, primarily found in media such as metallic ores and sulfide minerals. When an external electromagnetic field is applied, the positive and negative charges in the medium undergo directional movement; after the electromagnetic field is removed, the charges move in opposite directions and return to their initial state. Compared to inductive fields, polarization fields are more sensitive to metals. Within a certain range, the longer the charge charging and discharging time in a polarized body, the earlier the polarization effect appears and the greater the polarization intensity.

[0003] Time-domain electromagnetic detection methods include two modes: loop source transmission and long-conductor source transmission, namely magnetic source transient electromagnetic method and electric source transient electromagnetic method. The transmitter controls the transmitting coil to output a bipolar pulse current, with current waveforms including square waves, triangular waves, trapezoidal waves, and half-sine waves. During the transmission current transmission and after complete shutdown, the electromagnetic field is converted into an induced electromotive force by the receiving coil and collected by the receiver. Alternatively, magnetic field information can be directly acquired using a superconducting quantum interference device (SQUID). The readout circuit converts the magnetic field into a voltage, which is then recorded by the receiver. Processing and interpreting the acquired data allows for the acquisition of resistivity or polarizability information of the underground medium. Due to its relatively simple operation and low cost, time-domain electromagnetic methods have been widely used in mineral resource exploration, engineering geological surveys, and urban underground space exploration.

[0004] During the rise and turn-off processes of the transmit current in the time-domain electromagnetic method, a changing electromagnetic field is generated, causing the directional movement of positive and negative charges in the underground polarized medium. During this process, a reverse secondary field is received at the surface, resulting in a reversal of the sign in the attenuation curve, i.e., a polarization effect. The timing and intensity of the polarization effect are closely related to the excitation parameters of the transmit current. Numerical simulations based on the Cole-Cole model show that, within a certain range, the longer the turn-off time, the longer the polarization effect charging and discharging time, the earlier the polarization response appears, and the greater the polarization intensity. However, the ability of trapezoidal wave transmit current to extend the turn-off time is limited, resulting in a low signal-to-noise ratio when measuring the polarization effect; in weakly polarized media, the polarization effect may even be unobservable.

[0005] Sine waves can be generated based on RLC series resonance technology. The pulse width is related to the inductance and capacitance. By appropriately setting the inductance, capacitance, resistance and supply voltage, a half-sine wave emission current with large current amplitude and large pulse width can be generated.

[0006] Chinese patent CN112698410B discloses a time-domain electromagnetic detection method for the co-occurrence of induction and polarization in a two-phase conductive medium with an electrical source. By analyzing the characteristics of the induction-polarization co-occurrence effect, a dual controllable target excitation relationship along the trapezoidal wave is constructed. Fast turn-off is used to measure the induction field, and slow turn-off is used to measure the polarization field. This demonstrates the effectiveness of extending the turn-off time of the emission current for observing the polarization effect.

[0007] Chinese patent CN108227011A discloses a controllable falling edge dual trapezoidal wave transmission system and control method. By employing a passive clamping circuit, the turn-off time of the transmission current is changed. The low-voltage clamping circuit extends the turn-off time of the trapezoidal wave transmission current to a certain extent, realizing the slow turn-off of the trapezoidal wave. However, the turn-off time of the trapezoidal wave during slow turn-off is less than 1ms, which still has limited ability to improve the signal-to-noise ratio of polarization effect and cannot effectively observe weakly polarized media. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a half-sine wave transmission system and method for polarization effect. By outputting a half-sine wave, the off-time of the transmission current is extended, which solves the problem of insufficient extension capability of the existing transient electromagnetic method and low detection accuracy of polarized media, thereby improving the signal-to-noise ratio of polarization effect measurement.

[0009] This invention is implemented as follows:

[0010] A half-sine wave electromagnetic transmission system for polarization effect is disclosed. The system includes an RLC series resonant circuit and a power supply. The power supply adopts a bipolar power supply with a large-capacity polarized capacitor or an inverter bridge output, which is used to generate a magnetic source half-sine wave and an electrical source half-sine wave, respectively.

[0011] Furthermore, the power supply structure employing a large-capacity polarized capacitor includes:

[0012] It includes a battery, a first power diode, a second power diode, a first IGBT switch, a second IGBT switch, a third IGBT switch, a fourth IGBT switch, a transmitting coil, a first polarized capacitor, a second polarized capacitor, a non-polarized resonant capacitor, and a resonant inductor; the two terminals of the battery are respectively connected to the first polarized capacitor and the second polarized capacitor, the first polarized capacitor is connected in series with the first power diode and the first IGBT switch, and in parallel across the resonant circuit, the first power diode and the first IGBT switch are used to control the forward conduction of the resonance;

[0013] The second polarized capacitor is connected in series with the second power diode and the second IGBT switch, and then connected in parallel across the resonant circuit.

[0014] The resonant circuit has a third IGBT switch, a resonant capacitor, a resonant inductor, and a fourth IGBT switch connected in series. The resonant capacitor and resonant inductor are used for resonant charging and discharging and to control the pulse width.

[0015] The third and fourth IGBT switches are used to isolate the resonant circuit from the switching circuit. The resonant circuit uses a transmitting coil to emit electromagnetic waves into the ground. When the control signals of the first, third, and fourth IGBT switches are high, positive resonance occurs, emitting a positive half-sine wave current. The second polarized capacitor supplies power to the negative resonant circuit. The second power diode and the fourth IGBT switch are used to control the resonant circuit to conduct negatively. When the control signals of the second, third, and fourth IGBT switches are high, negative resonance occurs, emitting a negative half-sine wave current.

[0016] Furthermore, the power supply adopts a bipolar power supply structure with inverter bridge output as follows:

[0017] The circuit includes a DC power supply, a third power diode, a fifth IGBT switch, a sixth IGBT switch, a seventh IGBT switch, an eighth IGBT switch, a ninth IGBT switch, a tenth IGBT switch, an eleventh IGBT switch, a dummy load, a transmitting coil, a non-polar resonant capacitor, and a resonant inductor. The third power diode, connected in series at the DC power supply output, powers the resonant circuit and the dummy load. The third power diode prevents reverse current from the DC power supply output. The fifth IGBT switch, connected in series with the dummy load, is then connected in parallel with the DC power supply and the third power diode to control conduction when the half-sine wave transmission stops. The sixth, seventh, tenth, and eleventh IGBT switches form a bridge circuit, with the transmitting coil connected in the middle. The transmitting coil is connected in series with the eighth and ninth IGBT switches. A resonant capacitor and a resonant inductor are connected in series between the sixth, eighth, ninth, and eleventh IGBT switches. When the control signals of the sixth, eighth, ninth, and eleventh IGBT switches are high, forward resonance occurs, emitting a positive half-sine wave current. After forward emission, the control signal of the fifth IGBT switch is set to high, and the dummy load is connected to the DC power supply. The seventh and tenth IGBT switches are used to control the negative conduction of the resonant circuit. When the control signals of the seventh, eighth, ninth, and tenth IGBT switches are high, negative resonance occurs, emitting a negative half-sine wave current. After negative emission, the control signal of the fifth IGBT switch is set to high, and the dummy load is connected to the DC power supply.

[0018] A half-sine wave electromagnetic emission method targeting polarization effect is disclosed. This method is based on an RLC series resonant circuit that outputs a fixed pulse width half-sine wave emission current. The RLC series resonant circuit is powered by a bipolar power supply with a large capacity polarized capacitor or an inverter bridge output, which is used to generate a magnetic source half-sine wave and an electrical source half-sine wave, respectively.

[0019] Furthermore, the RLC series resonant circuit employs a structure powered by a large-capacity polarized capacitor, comprising:

[0020] It includes a battery, a first power diode, a second power diode, a first IGBT switch, a second IGBT switch, a third IGBT switch, a fourth IGBT switch, a transmitting coil, a first polarized capacitor, a second polarized capacitor, a non-polarized resonant capacitor, and a resonant inductor; the two terminals of the battery are respectively connected to the first polarized capacitor and the second polarized capacitor, the first polarized capacitor is connected in series with the first power diode and the first IGBT switch, and in parallel across the resonant circuit, the first power diode and the first IGBT switch are used to control the forward conduction of the resonance;

[0021] The second polarized capacitor is connected in series with the second power diode and the second IGBT switch, and then connected in parallel across the resonant circuit.

[0022] The resonant circuit has a third IGBT switch, a resonant capacitor, a resonant inductor, and a fourth IGBT switch connected in series. The resonant capacitor and resonant inductor are used for resonant charging and discharging and to control the pulse width.

[0023] The third and fourth IGBT switches are used to isolate the resonant circuit from the switching circuit. The resonant circuit uses a transmitting coil to emit electromagnetic waves into the ground. When the control signals of the first, third, and fourth IGBT switches are high, positive resonance occurs, emitting a positive half-sine wave current. The second polarized capacitor supplies power to the negative resonant circuit. The second power diode and the fourth IGBT switch are used to control the resonant circuit to conduct negatively. When the control signals of the second, third, and fourth IGBT switches are high, negative resonance occurs, emitting a negative half-sine wave current.

[0024] Furthermore, the RLC series resonant circuit is powered by a bipolar power supply output from an inverter bridge as follows:

[0025] The circuit includes a DC power supply, a third power diode, a fifth IGBT switch, a sixth IGBT switch, a seventh IGBT switch, an eighth IGBT switch, a ninth IGBT switch, a tenth IGBT switch, an eleventh IGBT switch, a dummy load, a transmitting coil, a non-polar resonant capacitor, and a resonant inductor. The third power diode, connected in series at the DC power supply output, powers the resonant circuit and the dummy load. The third power diode prevents reverse current from the DC power supply output. The fifth IGBT switch, connected in series with the dummy load, is then connected in parallel with the DC power supply and the third power diode to control conduction when the half-sine wave transmission stops. The sixth, seventh, tenth, and eleventh IGBT switches form a bridge circuit, with the transmitting coil connected in the middle. The transmitting coil is connected in series with the eighth and ninth IGBT switches. A resonant capacitor and a resonant inductor are connected in series between the sixth, eighth, ninth, and eleventh IGBT switches. When the control signals of the sixth, eighth, ninth, and eleventh IGBT switches are high, forward resonance occurs, emitting a positive half-sine wave current. After forward emission, the control signal of the fifth IGBT switch is set to high, and the dummy load is connected to the DC power supply. The seventh and tenth IGBT switches are used to control the negative conduction of the resonant circuit. When the control signals of the seventh, eighth, ninth, and tenth IGBT switches are high, negative resonance occurs, emitting a negative half-sine wave current. After negative emission, the control signal of the fifth IGBT switch is set to high, and the dummy load is connected to the DC power supply.

[0026] Furthermore, the voltage-current relationship of the resonant circuit is calculated using the following expression:

[0027]

[0028] In equation (1) U C U is the voltage across the resonant capacitor. R U is the voltage across the resonant resistor. L R1 is the voltage across the resonant inductor, R2 is the resistance of the resonant inductor, r is the resistance of the output load, L1 is the inductance of the output load, L2 is the inductance of the resonant inductor, C3 is the capacitance of the resonant capacitor, U1 is the voltage amplitude of the resonant capacitor, i is the current in the circuit, and t is time.

[0029] Solving equation (1), we obtain the expression for the half-sine wave emission current:

[0030]

[0031] In equation (2), ω is the angular frequency of the half-sine wave, I1 is the peak value of the half-sine wave transmitting current, t1 and t3 are the pulse widths of the bipolar half-sine wave, and t2 and t4 are the times when the transmitting current stops transmitting.

[0032] When the output load changes, the pulse width is maintained by changing the resonant inductance value L2. It remains unchanged, and its expression is:

[0033] .

[0034] Compared with the prior art, the beneficial effects of this invention are as follows:

[0035] This invention overcomes the signal-to-noise ratio limitation in the measurement of polarization effects using the time-domain electromagnetic method. Addressing the problem of delayed polarization response due to the short charging and discharging time of the polarizing medium, which makes it difficult to observe, a half-sine wave emission system based on an RLC series resonant circuit is designed. The electric source half-sine wave emission system uses an H-inverter bridge to power the RLC resonant circuit, while the magnetic source half-sine wave emission system uses a polarized capacitor to power the RLC resonant circuit. Two protective switches are installed at the resonant capacitor and resonant inductor terminals to prevent damage to the components. The emission system can output a half-sine wave emission current with a large pulse width, fully charging and discharging the underground polarizing medium during the emission process, extending the charging and discharging time, increasing the polarization response intensity, and allowing for earlier observation of the polarization effect. This significantly improves the signal-to-noise ratio for polarization effect measurements and further enhances the detection capability of the time-domain electromagnetic method for polymetallic minerals. Attached Figure Description

[0036] Figure 1 This is a system overall block diagram provided in the embodiments of the present invention;

[0037] Figure 2 The numerical simulation results of polarization effect of Cole-Cole model under different turn-off times are shown in (a) for Cole-Cole model and (b) for polarization effect numerical simulation results.

[0038] Figure 3 The circuit block diagram (a) and control timing diagram (b) of the magnetic source half-sine wave transmitting system are shown.

[0039] Figure 4 The circuit block diagram (a) and control timing diagram (b) of the electrical source half-sine wave transmitting system are shown.

[0040] Figure 5 It is a waveform diagram of a half-sine wave transmitting current with a pulse width of 5ms;

[0041] Figure 6 This is a comparison chart of polarization response decay curves in a playground experiment based on different emitter current waveforms (small coils) of polarization rings.

[0042] Figure 7 The figures show a comparison of polarization response decay curves based on different emitter current waveforms (large coil) of the polarization ring in field experiments. (a) is a trapezoidal wave, (b) is a triangular wave, and (c) is a half-sine wave. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0044] See Figure 1 As shown, a half-sine wave electromagnetic transmission system based on polarization effect outputs a half-sine wave transmission current with a fixed pulse width based on an RLC series resonant circuit. It has the characteristics of large pulse width, which can increase the charging and discharging time of the polarization medium, effectively measure the polarization effect of underground polaritons, and improve the detection accuracy of transient electromagnetic methods for metal mines.

[0045] The present invention has limited ability to extend the turn-off time of triangular or trapezoidal wave transmitting current using electronic technology. In order to further increase the turn-off time of transmitting current, RLC series resonance technology is adopted, and a magnetic source half-sine wave transmitting system and an electric source half-sine wave transmitting system are designed for measuring polarization effect in small area and large area, respectively.

[0046] See Figure 3 (a) and Figure 3 (b) The magnetic source half-sine wave transmitting system uses a battery for power, which suffers from low voltage. To improve the supply voltage of the RLC series resonant circuit, a large-capacity polarized capacitor is used to power the resonant circuit. Two IGBT switches and two diodes are used to change the direction of the resonant current, achieving bipolar half-sine wave transmission. The capacitors in the resonant circuit are non-polarized high-voltage capacitors, and the inductors are high-current-capacitance inductors. Two IGBT switches are placed across the resonant capacitor and inductor to isolate the resonant circuit from the switching circuit, preventing damage to the IGBT switches. To fix the pulse width of the half-sine wave transmitting current, when the load changes, the resonant capacitor value remains constant, and the inductor value of the resonant circuit needs to be adjusted to ensure a fixed turn-off time for the half-sine wave transmitting current. The transmitter control board outputs three PWM control signals, used to control the resonant forward-conducting IGBT, the resonant negative-conducting IGBT, and the resonant circuit to isolate the IGBT, respectively. The magnetic source half-sine wave transmitting circuit is as follows: Figure 3As shown, the system includes a battery 31, a first power diode 32, a second power diode 35, four IGBT switches (33, 34, 39, 312), namely the first IGBT switch 33, the second IGBT switch 34, the third IGBT switch 39, and the fourth IGBT switch 312, a transmitting coil 36, a first polarized capacitor 37, a second polarized capacitor 38, a non-polarized resonant capacitor 310, and a resonant inductor 311. The battery 31 is connected in series with the first polarized capacitor 37 and the second polarized capacitor 38 to supply power to the first polarized capacitor 37 and the second polarized capacitor 38. The first polarized capacitor 37 supplies power to the forward resonant circuit.

[0047] The first power diode 32 and the first IGBT switch 33 are connected in series, the second power diode 34 and the second IGBT switch 35 are connected in series, and the transmitting coil 36, the third IGBT switch 9 and the fourth IGBT switch 12 are connected between them and two polarized capacitors. The resonant capacitor 310 and the resonant inductor 311 are connected in series between the third IGBT switch 9 and the fourth IGBT switch 12.

[0048] The first power diode 32 and the first IGBT switch 33 are used to control the resonant forward conduction. The resonant capacitor 310 and the resonant inductor 311 are used for resonant charging and discharging and to control the pulse width. The third IGBT switch 39 and the fourth IGBT switch 312 are used to isolate the resonant circuit from the switching circuit. The transmitting coil 36 is used to transmit electromagnetic waves underground. When the control signals of the first IGBT switch, the third IGBT switch, and the fourth IGBT switch are at a high level, forward resonance occurs, and a positive half-sine wave current is transmitted. The second polarized capacitor 38 supplies power to the negative resonant circuit. The second power diode 35 and the second IGBT switch 34 are used to control the resonant negative conduction. When the control signals of the second IGBT switch Q2, the third IGBT switch Q3, and the fourth IGBT switch Q4 are at a high level, negative resonance occurs, and a negative half-sine wave current is transmitted. The transmitting coil of the magnetic source transmitting system is small and easy to operate, and it is used for the detection of underground anomalies in small areas.

[0049] See Figure 4 (a) and Figure 4(b) The electric source half-sine wave transmitting system uses a generator for power supply, converting AC to DC through a DC power supply. To ensure stable generator output power, a dummy load needs to be connected after the transmitting current is turned off. The DC voltage changes the polarity of the supply voltage through an H-bridge circuit, supplying power to the RLC series resonant circuit and outputting a bipolar half-sine wave current. The capacitors in the resonant circuit are non-polar high-voltage capacitors, and the inductors are high-current-capacitance and high-voltage-capacitance inductors. To ensure that the inductance value of the resonant circuit is adjustable, multiple inductors with different inductance values ​​are connected in series to ensure that the pulse width of the output half-sine wave transmitting current is fixed. The transmitter control board outputs four PWM control signals, which are used to control the IGBTs of the positive half-bridge of the H-bridge circuit, the negative half-bridge of the H-bridge circuit, the IGBT of the resonant circuit isolation circuit, and the IGBT of the dummy load switching circuit, respectively. The electric source half-sine wave transmitting circuit is as follows: Figure 4 As shown, the circuit includes a DC power supply 41, a third power diode 42, IGBT switches (43, 45, 46, 48, 411, 412, 413), a dummy load 44, a second transmitting coil 47, a non-polarized second resonant capacitor 49, and a second resonant inductor 410. The DC power supply 41, connected to the third power diode 42, supplies power to the resonant circuit and the dummy load 44. The third power diode 42 is used to prevent the DC power supply output current from reversing.

[0050] The fifth IGBT switch 43 is connected in parallel across the DC power supply 41 and the third power diode 42. It is used to control the dummy load 44 to conduct when the half-sine wave stops transmitting, thus ensuring the stability of the DC power supply.

[0051] The sixth IGBT switch 45 and the eleventh IGBT switch 413 are used to control the forward conduction of the resonant circuit. The second resonant capacitor 49 and the second resonant inductor 410 are connected in series with the eighth IGBT switch 48 and the ninth IGBT switch 411 for resonant charging and discharging and to control the pulse width. The eighth IGBT switch 48 and the ninth IGBT switch 411 are used to isolate the resonant circuit from the switching circuit. The second transmitting coil 47 is used to transmit electromagnetic waves into the ground. When the control signals of the sixth IGBT switch Q1, the eighth IGBT switch Q3, the ninth IGBT switch Q4, and the eleventh IGBT switch Q6 are at a high level, forward resonance occurs, and a positive half-sine wave current is emitted. After the emission is completed, the control signal of the fifth IGBT switch Q7 is set to a high level, and the dummy load 44 is connected to the DC power supply. The seventh IGBT switch 46 and the tenth IGBT switch 412 are used to control the negative conduction of the resonant circuit. When the control signals of the seventh IGBT switch Q2, the eighth IGBT switch Q3, the ninth IGBT switch Q4, and the tenth IGBT switch Q5 are at a high level, negative resonance is performed, and a negative half-sine wave current is emitted. After the negative emission is completed, the control signal of the fifth IGBT switch Q7 is set to a high level, and the dummy load 44 is connected to the DC power supply. The emission line pitch of the electric source emission system is relatively large, and the operation is relatively complex. It is used for the detection of underground anomalies in large areas.

[0052] The voltage-current relationship of a resonant circuit is calculated using the following expression:

[0053]

[0054] In equation (1) U C U is the voltage across the resonant capacitor. R U is the voltage across the resonant resistor. L R1 is the voltage across the resonant inductor, R2 is the resistance of the resonant inductor, r is the resistance of the output load, L1 is the inductance of the output load, L2 is the inductance of the resonant inductor, C3 is the capacitance of the resonant capacitor, U1 is the voltage amplitude of the resonant capacitor, i is the current in the circuit, and t is time.

[0055] Solving equation (1), we obtain the expression for the half-sine wave emission current:

[0056]

[0057] In equation (2), ω is the angular frequency of the half-sine wave, I1 is the peak value of the half-sine wave transmitting current, t1 and t3 are the pulse widths of the bipolar half-sine wave, and t2 and t4 are the times when the transmitting current stops transmitting.

[0058] When the output load changes, the pulse width is maintained by changing the resonant inductance value L2. It remains unchanged, and its expression is:

[0059]

[0060] Based on the above-mentioned transmission system, a half-sine wave electromagnetic transmission method targeting polarization effect is proposed. The method is based on an RLC series resonant circuit that outputs a half-sine wave transmission current with a fixed pulse width. The RLC series resonant circuit is powered by a bipolar power supply with a large-capacity polarized capacitor or an inverter bridge output, which is used to generate a magnetic source half-sine wave and an electrical source half-sine wave, respectively.

[0061] This invention performs feature analysis on the commonly used Cole-Cole polarization effect model. Inductor L1 represents the inductive part of the ground, resistor R1 represents the resistive part of the ground, and resistor R2 and capacitor C1 are used to simulate the polarization of the ground. Polarization models with different time constants and polarizabilities are obtained by combining resistors, capacitors and inductors.

[0062] In order to numerically simulate the polarization effect based on the time-domain electromagnetic method and analyze the relationship between the excitation parameters and the polarization effect, the Cole-Cole complex conductivity model was introduced into Maxwell's equations and the fractional-order equations were solved to analyze the influence of the emission current parameters on the polarization response. The results showed that, within a certain range, extending the turn-off time can observe the polarization effect earlier and the polarization response intensity is greater.

[0063] To compare the detection capabilities of trapezoidal waves, triangular waves, and half-sine waves for polarization effects, a polarization ring was designed based on the Cole-Cole polarization model. A multi-turn coil was used to simulate the inductive part L1 and the resistive part R1 of the ground. A circuit consisting of resistor R2 and capacitor C1 was connected in series with the multi-turn coil to simulate the polarized ground. During the measurement process, the polarization response of the emission current can be obtained by placing the polarization ring directly above the measuring sensor.

[0064] In field experiments, trapezoidal wave, triangular wave and half-sine wave transmission currents were emitted respectively, and electromagnetic response decay curves of polarization rings were obtained using receiving coils and superconducting quantum interference devices (SQUID). The results showed that under the excitation of half-sine wave transmission current, the polarization response appeared earliest and the polarization intensity was the largest. Half-sine wave is more conducive to measuring polarization effects or polymetallic minerals.

[0065] Example

[0066] For example Figure 2 (a) The Cole-Cole polarization effect model is used for feature analysis. Inductor L1 represents the inductive part of the ground, resistor R1 represents the resistive part of the ground, and resistor R2 and capacitor C1 are used to simulate the polarization of the ground. Polarization models with different time constants and polarization rates are obtained by combining resistors, capacitors and inductors.

[0067] To numerically simulate the polarization effect using the time-domain electromagnetic method and analyze the relationship between excitation parameters and the polarization effect, a Cole-Cole complex conductivity model was introduced into Maxwell's equations. Fractional equations were then solved, and the influence of the emission current parameter on the polarization response was analyzed. The results are as follows: Figure 2 As shown in (b), within a certain range, extending the turn-off time allows the polarization effect to be observed earlier, and the polarization response intensity is greater.

[0068] The ability to extend the turn-off time of triangular or trapezoidal wave transmit current using electronic technology is limited. To further increase the turn-off time, RLC series resonant technology is adopted, and a design is made as follows: Figure 3 The magnetic source half-sine wave emission system shown and such Figure 4 The diagram shows a half-sine wave transmitting system with an electric source, and provides timing diagrams of the control signals for the system, used for polarization effect measurements in small and large areas. By adjusting the inductance of the resonant inductor and fixing the half-sine wave pulse width to 5ms, the measured waveform of the half-sine wave transmitting current is shown below. Figure 5 As shown;

[0069] To compare the detection capabilities of trapezoidal waves, triangular waves, and half-sine waves for polarization effects, a polarization ring was designed based on the Cole-Cole polarization model. A multi-turn coil was used to simulate the inductive part L1 and the resistive part R1 of the ground. A circuit consisting of resistor R2 and capacitor C1 was connected in series with the multi-turn coil to simulate the polarized ground. During the measurement process, the polarization response of the emission current can be obtained by placing the polarization ring directly above the measuring sensor.

[0070] In the playground experiment, trapezoidal waves, triangular waves, and half-sine waves were emitted as transmitting currents, and the electromagnetic response attenuation curves of the polarization ring were obtained using a receiving coil, such as... Figure 6 As shown, the results indicate that the polarization response appears earliest and has the largest polarization intensity under half-sine wave emission current excitation. In field experiments, electromagnetic decay curves of the polarization rings for three waveforms were obtained using a superconducting quantum interference device (SQUID), as shown below. Figure 7 As shown, the results indicate that no polarization effect was detected by trapezoidal waves and triangular waves, while a significant polarization effect was detected by half-sine waves; both results demonstrate that half-sine waves are more advantageous for measuring polarization effects or polymetallic minerals.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A half-sine wave electromagnetic transmission system targeting polarization effects, characterized in that, The system includes an RLC series resonant circuit and a power supply. The power supply uses a bipolar power supply with a large capacity polarized capacitor or an inverter bridge output, which is used to generate a magnetic source half-sine wave and an electrical source half-sine wave, respectively. The power supply uses a bipolar power supply structure with inverter bridge output as follows: The circuit includes a DC power supply, a third power diode, a fifth IGBT switch, a sixth IGBT switch, a seventh IGBT switch, an eighth IGBT switch, a ninth IGBT switch, a tenth IGBT switch, an eleventh IGBT switch, a dummy load, a transmitting coil, a non-polar resonant capacitor, and a resonant inductor. The third power diode, connected in series at the DC power supply output, powers the resonant circuit and the dummy load. The third power diode prevents reverse current from the DC power supply output. The fifth IGBT switch, connected in series with the dummy load, is then connected in parallel with the DC power supply and the third power diode to control conduction when the half-sine wave transmission stops. The sixth, seventh, tenth, and eleventh IGBT switches form a bridge circuit, with the transmitting coil connected in the middle. The transmitting coil is connected in series with the eighth and ninth IGBT switches. A resonant capacitor and a resonant inductor are connected in series between the sixth, eighth, ninth, and eleventh IGBT switches. When the control signals of the sixth, eighth, ninth, and eleventh IGBT switches are high, forward resonance occurs, emitting a positive half-sine wave current. After forward emission, the control signal of the fifth IGBT switch is set to high, and the dummy load is connected to the DC power supply. The seventh and tenth IGBT switches are used to control the negative conduction of the resonant circuit. When the control signals of the seventh, eighth, ninth, and tenth IGBT switches are high, negative resonance occurs, emitting a negative half-sine wave current. After negative emission, the control signal of the fifth IGBT switch is set to high, and the dummy load is connected to the DC power supply.

2. The half-sine wave electromagnetic transmission system for polarization effect according to claim 1, characterized in that, The power supply structure, which uses a large-capacity polarized capacitor, includes: It includes a battery, a first power diode, a second power diode, a first IGBT switch, a second IGBT switch, a third IGBT switch, a fourth IGBT switch, a transmitting coil, a first polarized capacitor, a second polarized capacitor, a non-polarized resonant capacitor, and a resonant inductor; the two terminals of the battery are respectively connected to the first polarized capacitor and the second polarized capacitor, the first polarized capacitor is connected in series with the first power diode and the first IGBT switch, and in parallel across the resonant circuit, the first power diode and the first IGBT switch are used to control the forward conduction of the resonance; The second polarized capacitor is connected in series with the second power diode and the second IGBT switch, and then connected in parallel across the resonant circuit. The resonant circuit has a third IGBT switch, a resonant capacitor, a resonant inductor, and a fourth IGBT switch connected in series. The resonant capacitor and resonant inductor are used for resonant charging and discharging and to control the pulse width. The third and fourth IGBT switches are used to isolate the resonant circuit from the switching circuit. The resonant circuit uses a transmitting coil to emit electromagnetic waves into the ground. When the control signals of the first, third, and fourth IGBT switches are high, positive resonance occurs, emitting a positive half-sine wave current. The second polarized capacitor supplies power to the negative resonant circuit. The second power diode and the fourth IGBT switch are used to control the resonant circuit to conduct negatively. When the control signals of the second, third, and fourth IGBT switches are high, negative resonance occurs, emitting a negative half-sine wave current.

3. A half-sine wave electromagnetic emission method targeting polarization effects, characterized in that, This method is based on the output of a fixed pulse width half-sine wave transmitting current from an RLC series resonant circuit. The RLC series resonant circuit is powered by a bipolar power supply with a large capacity polarized capacitor or an inverter bridge output, which is used to generate a magnetic source half-sine wave and an electrical source half-sine wave, respectively. The RLC series resonant circuit is powered by a bipolar power supply output from an inverter bridge. The circuit includes a DC power supply, a third power diode, a fifth IGBT switch, a sixth IGBT switch, a seventh IGBT switch, an eighth IGBT switch, a ninth IGBT switch, a tenth IGBT switch, an eleventh IGBT switch, a dummy load, a transmitting coil, a non-polar resonant capacitor, and a resonant inductor. The third power diode, connected in series at the DC power supply output, powers the resonant circuit and the dummy load. The third power diode prevents reverse current from the DC power supply output. The fifth IGBT switch, connected in series with the dummy load, is then connected in parallel with the DC power supply and the third power diode to control conduction when the half-sine wave transmission stops. The sixth, seventh, tenth, and eleventh IGBT switches form a bridge circuit, with the transmitting coil connected in the middle. The transmitting coil is connected in series with the eighth and ninth IGBT switches. A resonant capacitor and a resonant inductor are connected in series between the sixth, eighth, ninth, and eleventh IGBT switches. When the control signals of the sixth, eighth, ninth, and eleventh IGBT switches are high, forward resonance occurs, emitting a positive half-sine wave current. After forward emission, the control signal of the fifth IGBT switch is set to high, and the dummy load is connected to the DC power supply. The seventh and tenth IGBT switches are used to control the negative conduction of the resonant circuit. When the control signals of the seventh, eighth, ninth, and tenth IGBT switches are high, negative resonance occurs, emitting a negative half-sine wave current. After negative emission, the control signal of the fifth IGBT switch is set to high, and the dummy load is connected to the DC power supply.

4. The half-sine wave electromagnetic emission method for polarization effect according to claim 3, characterized in that, The RLC series resonant circuit, powered by a large-capacity polarized capacitor, includes the following structure: It includes a battery, a first power diode, a second power diode, a first IGBT switch, a second IGBT switch, a third IGBT switch, a fourth IGBT switch, a transmitting coil, a first polarized capacitor, a second polarized capacitor, a non-polarized resonant capacitor, and a resonant inductor; the two terminals of the battery are respectively connected to the first polarized capacitor and the second polarized capacitor, the first polarized capacitor is connected in series with the first power diode and the first IGBT switch, and in parallel across the resonant circuit, the first power diode and the first IGBT switch are used to control the forward conduction of the resonance; The second polarized capacitor is connected in series with the second power diode and the second IGBT switch, and then connected in parallel across the resonant circuit. The resonant circuit has a third IGBT switch, a resonant capacitor, a resonant inductor, and a fourth IGBT switch connected in series. The resonant capacitor and resonant inductor are used for resonant charging and discharging and to control the pulse width. The third and fourth IGBT switches are used to isolate the resonant circuit from the switching circuit. The resonant circuit uses a transmitting coil to emit electromagnetic waves into the ground. When the control signals of the first, third, and fourth IGBT switches are high, positive resonance occurs, emitting a positive half-sine wave current. The second polarized capacitor supplies power to the negative resonant circuit. The second power diode and the fourth IGBT switch are used to control the resonant circuit to conduct negatively. When the control signals of the second, third, and fourth IGBT switches are high, negative resonance occurs, emitting a negative half-sine wave current.

5. The half-sine wave electromagnetic emission method for polarization effect according to claim 4, characterized in that, The voltage-current relationship of a resonant circuit is calculated using the following expression: (1)， In formula (1) The voltage across the resonant capacitor is... The voltage across the resonant resistor is The voltage across the resonant inductor is The resistance of the resonant inductor, The resistance of the output load, For the inductance of the output load, The inductance value of the resonant inductor. This is the capacitance value of the resonant capacitor. The voltage amplitude of the resonant capacitor. The current in the circuit. For time; Solving equation (1), we obtain the expression for the half-sine wave emission current: (2)， In formula (2) The angular frequency of a half-sine wave. The peak value of the half-sine wave emission current. and The pulse width of a bipolar half-sine wave. and The time during which the transmitting current stops transmitting; When the output load changes, the resonant inductance value is adjusted. Ensure pulse width It remains unchanged, and its expression is: 。

Images