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8288 IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 33, NO. 10, OCTOBER 2018

Multifunction Electromagnetic Transmitting Systemfor Mineral Exploration

Meng Wang , Sheng Jin, Ming Deng, Wenbo Wei, and Kai Chen

Abstract—Electrical and electromagnetic methods have longplayed an important role in mineral exploration. For example,in active source prospecting methods, when measuring the val-ues of many electrical parameters, the signal-to-noise ratio can beimproved by increasing the transmitting power. In this paper, wepresent a multifunction borehole ground electromagnetic trans-mitting system that transmits rectangular waves at a frequency of0.01–10 kHz with a frequency error less than 10−8 Hz @ 1 Hz (de-pending on the high-precision temperature compensation crystal)and the initial synchronization error between the transmitter andreceiver is less than ±0.1 µs. During operation, either the maxi-mum transmitting voltage output can reach 950 V or the maximumtransmitting current can exceed 90 A, but both cannot be achievedsimultaneously. We tested the transmitting system at its maximumpower output continuously for over 8 h and the power output wasmore than 48 kW at a current above 60 A. The energy was deliv-ered above ground or underground using existing drill casings toproduce the high-power transmissions. The field experiments showthat the system meets the demands of the controlled-source audio-frequency magnetotelluric and induced polarization methods usedin mineral exploration.

Index Terms—High power, mineral exploration, multifunctionborehole ground electromagnetic transmitter.

I. INTRODUCTION

FOR many years, electrical and electromagnetic (EM) meth-ods have played important roles in mineral explorations

[1], [2]. There has been a trend in the development of thosemethods toward reaching deep earth [3], [4]. For explorationsthat leverage active transmitters, the signal-to-noise ratios canbe improved by enhancing the transmitting power, while theinversion accuracy can be improved by taking advantage of theelectrical parameters. However, this requires the performance ofEM instruments to be enhanced to increase the detection depth,accuracy, and resolutions of measurements [5]–[7].

Much research has been conducted by instrument manufac-turers, research institutes, and academies toward increasing the

Manuscript received July 30, 2017; revised October 15, 2017; acceptedNovember 7, 2017. Date of publication November 17, 2017; date of currentversion July 15, 2018. This work was supported in part by the National HighTechnology Research and Development Program of China (2014AA06A603)and in part by the National Science Foundation of China (41504138). Rec-ommended for publication by Associate Editor T. M. Lebey. (Correspondingauthor: Meng Wang.)

The authors are with the School of Geophysics and Information Technology,China University of Geosciences, Beijing 100083, China (e-mail: [email protected]; [email protected]; [email protected]; [email protected]; [email protected]).

Color versions of one or more of the figures in this paper are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/TPEL.2017.2774817

Fig. 1. Schematic diagram of the multifunction borehole ground EM imagingsystem.

transmitting power of EM instruments. Current equipment sup-ports transmit powers of 30 kW (GGT-30 and T-30 are madeby Zonge and Phoenix, respectively), 50 kW [8], [9], 70 kW[10], [11], to 160 kW (T-200 is made by Phoenix) [12] and200 kW [13]. In particular, the T-200 instrument was designedfor superpower controlled-source audio-frequency magnetotel-luric (CSAMT) and time-frequency EM methods, while the sys-tem designed by Central South University is used for high-powerwide-area EM and pseudorandom signal methods [14]–[16].

We developed a high-power borehole ground EM imagingsystem to detect deep mineral resources [17], [18], as shownin the schematic diagram in Fig. 1. An important componentin this system is the high-power multifunction borehole groundEM transmitter. The receiver arrays are deployed on land orin existing shafts, such as test drill holes in the mineral fieldwhere metal casings have been left in the borehole. In thesecases, the existing metal casings are used as the transmittingelectrodes, and the transmitters and receivers are offset to forma quasi-three-dimensional prospecting configuration.

In the following, we first introduce the design and importantcharacteristics of the developed system.

A. Modular Design

A schematic diagram of the high-power electromagnetictransmitter is shown in Fig. 2. The system is composed of amodular structure that include a high-power generator (shownin the left of Fig. 3), an adjustable direct current (dc) switching

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WANG et al.: MULTIFUNCTION ELECTROMAGNETIC TRANSMITTING SYSTEM FOR MINERAL EXPLORATION 8289

Fig. 2. Schematic diagram of the high-power EM transmitting system.

Fig. 3. High-power generator (left) and dc switching power supply (right).

Fig. 4. Multifunction borehole ground electromagnetic transmitter (left) andthe transmitting current recorder (right).

power supply (shown on the right of Fig. 3), a transmitter (shownin the left of Fig. 4), a transmitting current recorder (shown inthe right of Fig. 4), an external control box (shown on the left ofFig. 5), a portable tablet, which runs the monitoring and control

software, and a set of transmitting antennas and electrodes. Anadvantage of this type of modular structure is that it can be easilytested, repaired, and maintained.

The adjustable dc switching power supply is used to con-vert the fixed triple-phase 50 Hz/380 VAC (alternating current)from the high-power generator into the variable 0–1 kV dc/0–120 A power required by the multifunction borehole ground EMtransmitter. The dc switching power supply contains four powermodules and each module can deliver 500 V/60 A. Multiple-series connections were used to produce the desired output of1 kV dc/120 A. The topology of the four power modules is asfollows. The power modules shown near the top of Fig. 2 aredenoted from left to right as first, second, third, and fourth. Thefirst and second 500 V/60 A power modules are connected inseries to form a 1 kV/60 A power module group, as are the thirdand fourth. The final outputs of these pairs are then connectedin parallel to realize a 1 kV/120 A power module group.

The power modules are connected and controlled throughthe communication bus by the dc switching power supply con-trol unit. The touch keyboard shown in the figure can be used tospecify the voltage and current output, and the output can be dis-played on the LCD screen. Each power module includes a lowfrequency rectifier [19], insulated-gate bipolar transistor (IGBT)H full bridge that operates at 20 kHz [20], [21], pulse width mod-ulation (PWM) control unit [22], high frequency transformer,and rectifier [23], [24]. The control unit monitors the output ofeach module and makes adjustments as required, and facilitatesthe current and voltage sharing of the four power modules.

A schematic diagram of the EM transmitter control system isalso shown in Fig. 2. While there are five power inverter modules(IGBTs) in a traditional transmitter topological diagram, [25],[26], our design only used four IGBTs and did not use a dummy


Fig. 5. External transmitter control box (left) and screenshot of the monitoring and control software on the portable tablet (right).

load. We conducted a time domain induced polarization (TDIP)test, and the power output was about 950 V × 10 A � 10 kW,which was much less than the maximum power output of thegenerator. The transmitter supports the CSAMT method and isable to operate continuously for up to 5 μs without stopping.Thus, a dummy load is not required to protect the generator.The transmitter also incorporates a full H-bridge structure tosupport inversion from dc to ac and includes protection andclamping circuits that employ special high-voltage metallizedpolypropylene film capacitors to absorb and buffer high-voltagespikes and ensure the stable and reliable performance of thetransmitter. The auxiliary acquisition circuit is used to capturethe temperature, output voltage, and output current information.

When the power switching devices in the transmitter are op-erational, significant amounts of noise is generated from thevoltage spikes, which influences the low-voltage control unit[27]. For this reason, the high- and low-voltage circuits wereseparated in the design. The remote-control bus is a shieldedtwelve core cable that includes the signals for the IGBT driversand the auxiliary signals that are used to connect the transmitterto the external control box [28]. The external control box, whichis used to measure the output voltage, internal temperature, rootmean square (RMS) value of the current, and alarm signals fromthe transmitter drive boards, was placed outside the body of thetransmitter to minimize the space EM interference. A portabletablet is included in the system to connect wirelessly to the exter-nal control box for control purposes. The host control softwarewas implemented in the C# programming language with a flex-ible control pattern and a convenient user-friendly interactiveinterface.

The software and hardware in the control unit were designedaround an ARM-based microcontroller (Advanced RISC Ma-chines, STM32F103), and an EPM570 complex programmablelogic device (CPLD) as the main control core. The control unitalso incorporates a Wi-Fi communications module, calibrationcrystal oscillator, global positioning system (GPS) module, andreal-time clock chip for use when generating multifrequencydrive signals. The microcontroller oversees the transmission ofmultifrequency control signals and measures auxiliary infor-mation during EM transmissions. The external control box isused to generate the control signals for the driver circuit ofthe IGBTs, and to change the frequencies, set the transmit-ting times, select among the different transmitting modes, etc.This box is powered by the transmitter, with which it exchanges

TABLE ISAFETY ASSURANCE ANALYSIS OF THE TRANSMITTER

Items Protection contents

Generator Over voltage/over current/over temp/low oil/overload

DC switching power supply Over voltage/over current/short circuit/over temp/overload

Transmitter + external control box Short circuit/over voltage/over current/over temp

auxiliary signals. A high-precision transmitting current recorderis used to acquire the current transmitted by the antennas andelectrodes.

As it is relatively simple to program new codes into theexternal control box, other waveforms, such as 0 Hz (dc), pseu-dorandom sequence waveforms [16], inverse m-sequence mul-tifrequency waveforms, etc., can be loaded and transmitted. Inaddition, different transmitting waveforms can be used to sup-port multiple functions, such as CSAMT (9600–0.9375 Hz),TDIP (1/64th–16 Hz), SIP (100–0.01 Hz), and other multifre-quency methods.

Another advantage of this type of structure is that it facilitatesthe addition of safety assurance and protection functions, aslisted in Table I. For example, if an overvoltage occurs at somepoint in the transmitting system, an alarm signal can be triggeredin the generator, dc switching power supply, or the transmitter.The transmission can then be temporarily halted until the sourceof the alarm has been found.

B. High-Power Output

The power output of the diesel-powered motor generator is80 kVA with a power factor greater than 85% [28]. The dcswitching power supply is designed to provide a very preciseconstant voltage and current output and is capable of producinga 120 kW of power output at an efficiency of more than 90%.When the output of the power supply is connected to a purelyresistive load, the precision of the output is better than ±0.5%of full scale or 1 kV. The adjustment error is therefore ±5 V.

The typical ground resistance of the survey area is about20–200 Ω, and the common voltage output of the transmit-ters is between 50–1200 V (the T200 transmitter can deliver1600 V). Considering the majority of the situations in which thisequipment will be deployed and for safety reasons, although the


Fig. 6. Test results of the transmitter power output shown on the display ofthe dc switching power supply.

transmitting system is able to deliver high currents, the actualtransmitting current is typically less than 60 A.

We tested the transmitter in our laboratory in order to con-firm the total amount of output current. In the first test case,the voltage and current output were set to 750 V and 100 A,respectively. Once the dc switching power supply was enabled,the output voltage and current simultaneously began to rise.When the voltage output reached a predetermined value, thedc switching power supply began operating in constant voltagemode and the actual current output was lower than the selectedvalue. In another test case, when the current output first reacheda predetermined value, the dc switching power supply beganoperating in constant current mode, and the actual voltage out-put was lower than the selected value. The dc switching powersupply screen shown in Fig. 6 illustrates the first situation alongwith the high-power output capability of the transmitter.

We tested the transmitting system at the maximum volt-age, current, and power output, as shown in Fig. 7. The fig-ure shows the operating state of the transmitting system, in-cluding the current, voltage, frequency, temperature, etc. Themaximum voltage and current outputs were 950 V and 90 A.However, as the maximum voltage and current outputs couldnot be achieved simultaneously due to heat dissipation limita-tions, they were obtained separately. The equation for the powerconsumption of the switch circuit is PIGBT = fswitch × (Eon +Eoff ) × Is/Inominal , where fswitch is the switching frequency,Eon and Eoff is the open and closed energy, Is is the work-ing current, and Inominal is the nominal value in the datasheet.When the frequency was 120 Hz and the operating current was80 A, the power consumption was about 2 kW. The continuousmaximum power output was more than 48 kW when the currentwas higher than 80 A.

During our testing, we operated the transmitter at the maxi-mum power output continuously for over 8 h. The test began at00:36 (GMT time, Greenwich Mean Time) and ended at 09:16(GMT time) at a test frequency of 120 Hz, which is representa-tive of the typical test frequencies used in the field. In Fig. 7, thefrequency is plotted using 10 log10 (f) and the voltage is dividedby ten (i.e., voltage/10). The transmitting electrodes were filledwith salt water so that the current would rise versus time, andthe voltage output was decreased in steps.

The output performance of the transmitter was tested versusthe frequency of the IGBT bridge at the rated voltage/currentoutput, and the results are shown in Fig. 8. The test covered41 frequencies from 0.9375–9600 Hz. The left vertical axis isthe current (A) and the right axis is the voltage (V) divided by10. The dc switching power supply was operated in constantvoltage constant mode. The voltage output was about 920 V, thecurrent decreased from 60 to 5 A, which was connected with thelow frequency and high frequency, respectively, and the outputpower of the transmitter was about 54 kW. We noted that thecorner frequency was dependent on the ground load. In this test,the corner frequency was about 1 kHz.

The main task of the electromagnetic transmitting system isto deliver the high-power artificial energy into the ground tostimulate the earth in a mineral exploration. So we require thetransmitter should work at least continuous 8 h during one day,simultaneously at the maximum power output to establish a highsignal-to-noise ratio electromagnetic field. These requirementneeds the equipment should have a perfect reliability, safety, andheat-dissipation design. We adopted the high-power invertingtechnology to support the 1000 V transmitting voltage and 90 Atransmitting current. We used the laminated bus-bar technologyto suppress the adverse effects of bus inductance. We optimizedthe design of forced air cooling to enhance the heat-dissipation.

C. Multifunction and Synchronization of the Transmitter

The transmitter supports several types of waveforms in orderto satisfy the multifunction requirements of the CSAMT, TDIP,frequency-domain induced polarization (FDIP), and other meth-ods. Since in deep prospecting the frequency is inversely relatedto the depth of exploration, the developed system supports fre-quencies from 0.01 Hz to 10 kHz with a frequency error of lessthan 10−8 Hz @ 1Hz. We used the high-precision temperaturecompensation crystal and complex programmed logic designtechnology to support the precise transmitting frequency.

A key feature of our system is the use of accurate synchroniza-tion technology to realize automatic time synchronization and toensure the initial synchronization error between the transmitterand receiver is less than ±0.1 μs. When conducting land-basedexperiments, the timing for the transmitter controller and re-ceivers were synchronized using GPS time and the rising edgeof the pulse-per-second (PPS) signal, which provided an ab-solute phase reference for subsequent processing. This moduleincorporates a signal independent microcontroller, GPS module,temperature compensated high precision crystal, frequency de-tection unit, and digital-to-analog (D/A) unit to calibrate the timedifference between the PPS and the local reference frequency.The frequency detection component in the timing module mea-sures and verifies the crystal output using a real-time proofingalgorithm to ensure the stability and accuracy of the outputclock. Because both the transmitter and receivers used the PPSas their time base, accurate synchronization was achieved.

This method of synchronization was utilized in several trans-mitters (A, B, and C), as shown in Fig. 9 and the synchronizationerror δt1 and δt2 between the transmitters was limited to 10−8 s.

The synchronization error between the rising edge of the PPSand the rising edge of the clock line in the transmitter is shown


Fig. 7. Results of the continuous maximum power output test.

Fig. 8. Output performance versus the frequency of the IGBT Bridge at therated voltage/current output.

Fig. 9. Synchronization between transmitters.

in Fig. 10. Each interval of the abscissa axis is 10 ns in time andthat of the vertical axis is 2 V. The blue line represents the PPScurve and the cyan line represents the clock line that was usedto synchronize the transmitters. The time interval between thetwo lines is about 10 ns, as indicated in the figure.

The clock line is an output from the time clock module de-scribed earlier and is used as the clock signal that instructs thetransmitter when to start and stop transmitting, as the referenceclock that is employed to generate the transmitting frequen-cies, and as the reference clock of the CPLD that generates theIGBT drive signals. The PPS waveform and output current areshown in Fig. 11 to illustrate the synchronization performance.As shown in the figure, there is a fixed 2.5 μs delay between thedigital circuit and switching devices.

D. Full Wave Record of Transmitting Current

To ensure successful mineral exploration, it is essential to ob-tain measurements of different parameters, such as the apparentresistivity and apparent polarizability, in order to characterizethe subsurface structures. To accomplish this, the developedsystem is able to record the full-wave transmitting current.

For this purpose, a special unit was designed to record thefull current waveform using a Hall effect current sensor to pre-cisely capture the real-time transmitting current. The sensor hasa precision, linearity, and range of ±0.5%, 0.5%, and 0–100 A,respectively. The recording unit has a 24-bit analog-to-digitalconverter operating at a sample rate of 24 kHz. When the cur-rent recorder is tracking the waveform, the host control softwarecan be used to monitor and save the real-time waveform, andthereby to determine the status of the transmitter. Fig. 12 showsan image of the data obtained from the data playback softwarein the transmitting current collector. In this image, the frequencyswitches from 7.5–5 Hz. Because of the high-density samplingof the transmitting current, it is possible to identify the currentchanges while the frequency is switching. When using thefrequency tables in the CSAMT, TDIP, or SIP modes, it is


Fig. 10. Synchronization between the PPS and clock line of the transmitter.

Fig. 11. Synchronization between the PPS and output current.

Fig. 12. High-precision and high-density sampling of the transmitting currentwaveform.

important that each falling edge is adjusted to match the fallingedge of the PPS signal so that it is coincident with the integersecond time, and it is preferable that the time when the sys-tem changes to a different frequency to be coincident at theinteger second (00:00:40.000) rather than a fractional second(00:00:40.435). For example, if the start time of the 9600 Hzfrequency is 5:00:00, then the 7680 Hz start time should be

5:01:20, and that of 240 Hz should be 5:10:40, etc. If the exactstart time is not specified, then it is difficult to synchronize thetransmitter and receivers.

E. Transmitting Antenna and Electrodes

The transmitting antenna consists of rubber insulated copperwires with a cross section of 10 mm2 , which is connected to thetransmitter electronics. The electrodes consist of a long piece ofaluminum foil or large sheet of aluminum plate inserted about0.3–0.5 m directly into the soil without an electrical conduit.Water is then added to the ground around the electrodes todecrease the contact resistance and ensure that a current of atleast 60 A is injected into the ground. With the exception of thetraditional transmitting antenna and electrodes, existing steelcasings were used as transmitting electrodes to deliver high-power controlled current.

F. Test of Transmitting System

Several experiments were conducted to validate the featuresof the developed system. One set of tests was conducted fromAugust 1 to August 12, 2016 in Zhangjiakou North in Hebeiprovince, China. The locations where the current and potentialelectrodes were placed are shown in Fig. 13. When the CSAMTmethod was used, the distance between the two transmittingelectrodes was 1.6 km (AB) and the offset between the trans-mitter and receivers was about 8.2 km. There were 20 receivingpoints in the CSAMT test, the distance between the receivingpoints was about 250 m, the distance between the receive elec-trodes was 100 m (MN), and the RMS value of the transmittingcurrent was 22 A. Because the ground resistivity was relativelyhigh in the mineral field, we employed an additional 60 kW dcswitching power supply when testing the system.

When testing the TDIP method, the middle gradient arraywas used. The first pair of TDIP transmitting current electrodeswere located at A and B, and the second was at A’ and B’.

We plan to design a multifunction transmitter which can beused not only in the common CSAMT and IP methods, but also


Fig. 13. Locations of current electrodes and potential electrodes.

Fig. 14. Test results of the rise time of the transmitting voltage and currentwaveform.

in time domain transient method (TDEM). The TDEM methodrequires steep rising and falling edges [29], so we need to payattention to the rising and falling times of the transmitting volt-age and current. During the experiment, we measured the riseand fall times of the transmitted voltage and current waveforms,and the results are shown in Figs. 14 and 15. When the transmit-ting frequency was 0.9375 Hz, the maximum magnitude of the

Fig. 15. Test results of the fall time of the transmitting voltage and currentwaveform.

transmitting voltage was about 900 V, the maximum magnitudeof the transmitting current was 26 A, and the rise and fall timeswere about 650 ns from the bottom to the top or from the top tothe bottom in the voltage waveform. At the same time, the riseand fall times of the current waveform were about 100 μs.

We tested the time-domain response of the IGBT H-bridge,and the result is shown in Fig. 16. The transmitting waveform


Fig. 16. Time-domain response of IGBT H-bridge.

Fig. 17. Time-domain response of the protect circuit.

was a classic TDIP signal that followed the pattern: (2 s)-stop(2 s)-negative (2 s)-stop (2 s). The voltage output was 200 V andthe distance between the two current electrodes was 200 m. Thetime interval of the X-axis in the top of Fig. 16 is 20 μs, whilethat on the bottom is 2 μs. The reverse stop time of one IGBTin the H-bridge is about 8.5 μs, which reflects the performanceof the transmitter and the influence of the load.

As mentioned earlier, the developed system includes overvolt-age and overcurrent alarm functions. The protection mechanismin these cases is a hysteresis comparator, and the time-domainresponse of the associated circuitry is shown in Fig. 17, assum-ing that the higher protection limit (voltage alarm value) is 1 kV.When the output voltage exceeds the set value, the alarm signaloutput will be enabled and automatically pulled to the grounduntil the output voltage recovers to 950 V, which is consideredto be the normal value.

Fig. 18. Land experiment for the transmitting system.

Fig. 19. Normalized EM field and Cagniard apparent resistivity curve.

In order to synchronize the transmitter and receivers, we im-plemented identical frequency tables that included 41 frequen-cies from 9600 Hz to 0.9375 Hz and a duration of 50 min. Thetransmitting and receiving functions were tested by sequentiallylooping through the frequencies. For example, the first loop of9600 Hz started at 00:00:00.000 and the next loop of 9600 Hzstarted at 00:50:00.000. Fig. 18 shows the field test setup.

When testing the transmitting and receiving functions,controlled-source transmitting signals were used to obtain highSNR (signal-to-noise ratio) results of the Cagniard apparent re-sistivity curve [2]. Fig. 19 shows the normalized EM field andCagniard apparent resistivity curve versus frequency, and theseresults are consistent with the regional sedimentary environ-ment. In the frequency-domain, the magnitude of the normal-ized EM field changed smoothly in the near-field area and therange of variation covered the frequency range of 1–104 Hz.All 41 frequencies were used in the processing stage. The testresults validate the overall performance of the transmitter fromthe side.

We next focused on validating the function of the transmit-ter and the acquisition of the induced polarization parameters.


Fig. 20. One segment of apparent chargeability and resistivity from the TDIPtest.

The transmitter was configured to perform a TDIP test using amiddle gradient array. The offset between the transmitting andreceiving electrodes was about 2.5 km (AB) and 20 m (MN),respectively, as shown in Fig. 13. The transmitting current was3 A and the period was 8 s. Fig. 20 shows one segment of the ap-parent chargeability (up) and resistivity (down) versus distance.In general, the apparent resistivity was around 100–200 Ωmwith only minor variations. The apparent chargeability was 2%with no obvious abnormalities. The presence of the high valuein the middle is related to the superficial rocks, and the charac-teristics highlighted by these two parameters are consistent withthe regional sedimentary environment.

Based on our results, it was confirmed that the developedtransmitting system was able to achieve GPS synchronization,time synchronization, and on-time transmission, which is essen-tial when determining the values of the relevant electrical param-eters. At the same time, the stability and validity of the systemwere also confirmed. The transmitter met the requirements of theCSAMT and IP methods. Although the fundamental functionsof the transmitter were realized and the transmitting current andvoltage satisfied the design criteria, in the future, we plan toimprove and optimize the parameters to enable the synchronousoperation of multiple transmitting systems.

II. CONCLUSION

We developed a high-power multifunction borehole groundEM transmitting system for use in metal exploration. The high-lights of the system are as follows.

1) Our transmitting system satisfies the requirements ofhigh-power controlled source electromagnetic methodsfor mineral exploration and provides a maximum currentoutput of up to 90 A, which is higher than that of manyother systems.

2) Our design is modular and separates the transmitter intoseveral units to ensure safe operation and ease of mainte-nance. It also features a wireless remote-control methodthat enables user-friendly interactive control. In addition,

a state-of-the-art unit is used to continuously record thetransmitting current waveform.

3) The synchronization accuracy between the transmitter andreceiver influences the subsequent data processing. Boththe transmitter and receivers regard the GPS PPS as thesame time base, therefore, we design a time clock modulethat contains a signal independent microcontroller, GPSmodule, temperature compensated high precision crys-tal, frequency detection unit, and digital-to-analogy (D/A)unit to calibrate the time difference between the PPS andour own reference frequency. At last, we can provide atime clock module to ensure the initial synchronizationerror between the transmitter and receiver is less than±0.1 μs.

4) The synchronization in the developed system is extremelyprecise, which makes it possible to position two or moretransmitters for use in two or more different directionsand allow them to operate simultaneously. Configurationssuch as this can be used to increase the amount of artificialenergy, increase the controlled-source field magnitude,and improve the SNR of the receivers.

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Meng Wang was born in China, in 1984. He receivedthe M.Sc. and Ph.D. degrees from China Universityof Geosciences, Beijing, China.

Since 2011, he has been with the School of Geo-physics and Information Technology, China Univer-sity of Geosciences, as a Lecturer. He is mainlyengaged in teaching and research of geophysicalinstruments.

Sheng Jin was born in China, in 1970. He receivedthe Ph.D. degree.

After completing the Ph.D., he became a Pro-fessor. He is currently the Director of the School ofGeophysics and Information Technology, China Uni-versity of Geosciences, Beijing, China. He is engagedin the field of geophysical exploration research andteaching. His research interests include electromag-netic exploration and deep geophysical and dynamicresearch.

Ming Deng photograph and biography not available at the time of publication.

Wenbo Wei photograph and biography not available at the time of publication.

Kai Chen photograph and biography not available at the time of publication.