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Review

Progress of Deep Exploration Artificial-Source Electromagnetic Instruments in China: A Review

by
Yangyong Zhang
1,2,3,
Xuan Ye
2,3,
Lei Chen
2,3,
Yue Zhou
4,* and
Daiming Qu
1
1
School of Electronic Information and Communications, Huazhong University of Science and Technology, Wuhan 430074, China
2
Hubei Provincial Key Laboratory for Low-Frequency Electromagnetic Communication Technology, Wuhan 430079, China
3
WMCRI, CSSC, Wuhan 430079, China
4
College of Instrumentation and Electrical Engineering, Jilin University, Changchun 130061, China
*
Author to whom correspondence should be addressed.
Electronics 2025, 14(3), 433; https://doi.org/10.3390/electronics14030433
Submission received: 19 November 2024 / Revised: 13 January 2025 / Accepted: 14 January 2025 / Published: 22 January 2025
Browse Figures
Versions Notes

Abstract

:
As a type of widely used geophysical exploration equipment, artificial-source electromagnetic instruments are effectively used for resource and energy exploration due to their simple operation, deep-detecting depth, and higher resolution in the field, compared to natural-source electromagnetic instruments. However, after years of development, the current work is in a significant period. Due to the exploration requirement gradually shifting from shallow-surface to deep, traditional electromagnetic instruments are facing severe challenges. Over the course of the elaborate study by geophysicists in China, electromagnetic instruments have made innovative breakthroughs during recent years. The application in the deep exploration of artificial-source electromagnetic instruments has been further extended. By taking the time–frequency electromagnetic instrument, the low-temperature transient electromagnetic instrument, the surface electromagnetic prospecting instrument, and the wide-field electromagnetic instrument as examples, the purpose of this paper is to give a systematic introduction to the technical indicators and field applications. Then, an overview of the situation and progress of the instrument is given to help the readers understand the research directions. Finally, we offer the developing trends of the deep exploration artificial-source electromagnetic instrument.

1. Introduction

Accompanying rapid economic development, energy industries such as mineral resources have received increasing attention. Continuous exploitation has led to a sharp decline in resource reserves. The supply and demand conflict of current energy and key mineral resources severely impacts the sustainable development of society and economy. In addition, the complex detection environment has exacerbated this problem [1,2,3]. In order to solve this problem, the exploration of mineral resources has entered a major turning point, which has gradually shifted from shallow-surface exploration (0–500 m) to deep exploration (500–2000 m) and has entered a new stage [4,5]. The traditional exploration technology and instruments have faced severe challenges. Specifically, technical limitations include a lack of precision, resolution, and anti-interference capabilities for deep exploration, resulting in low data accuracy [6]; instrument performance issues arise as traditional instruments struggle under extreme conditions such as high temperature, pressure, and strong magnetic fields [7] and data processing difficulties are compounded by the need to handle large, diverse datasets and complex interpretation calculations, challenging conventional data processing methods [8]. So, it has become urgent to improve the exploration technology level of energy and mineral resources, increase the exploration depth, and expand the exploration scope. Geophysical exploration instruments can be effectively used to detect hidden mineral resources, while as for the widely used geophysical exploration instrument, the electromagnetic instrument has played an important role in detecting geoelectrical structures and metallic ores [9]. Based on the electromagnetic induction method and the difference in physical properties of rocks or ores in the crust, the electromagnetic instruments detect underground target information according to the principle of electromagnetic induction and the distribution of the electromagnetic field [10]. These methods can be used in resource and energy exploration [11], environmental monitoring [12], geological mapping [13], disaster warning [14], and geoelectric structure exploration [15].
Electromagnetic methods have a history of over a hundred years abroad [16,17], whereas China started electromagnetic research relatively late [18]. It was not until the 1950s that China began developing electromagnetic methods, and it made great progress in the 1960s and early 1970s [19]. Up to today, significant advances have been made in the electromagnetic method, and instruments have been further optimized. In terms of deep exploration, better exploration results may be obtained by artificial-source electromagnetic instruments due to the complex electromagnetic noise and the high-level artificial noise generated by power, machine, and communication equipment [20]. Artificial-source electromagnetic instruments include DC resistivity instruments, induced polarization (IP) instruments, controlled-source audio-frequency magnetotelluric (CSAMT) instruments, transient electromagnetic method (TEM) instruments, etc. The DC resistivity instruments have a good ability to resolve the electrical distribution of shallow depth, but it is difficult to achieve high resolution in deep exploration. The data obtained from the deeper depth not only increase the detection cost, but the response signal is also weak and the signal-to-noise ratio is low [21]. Thus, the detection depth is always limited. The IP instruments have the same observation device and similar depth to the DC resistivity instruments. Utilizing the principle of induced polarization, electronic conductors may cause significant IP anomalies, but the inhomogeneity of terrain or non-polarized rock does not cause IP anomalies [22]. Therefore, such an instrument can overcome the multi-solution of other instruments to a certain extent, and it can provide not only resistivity information, but also polarizability information [23]. Concerning the CSAMT instrument, since the transmitter is controllable, it can emit pseudo-random signals with strong anti-interference capabilities [24,25]. The detection depth of the CSAMT instrument is deeper than that of the TEM instrument [26]. Traditional hollow coil TEM instruments introduce severe measurement noise and are not suitable for deep exploration, due to the wide signal bandwidth and low sensitivity [27]. There is a need to improve the instrument’s anti-interference capabilities and signal receiving sensitivity to increase exploration depth.
As shown in Table 1, the developed electromagnetic instruments that can be used for deep exploration are representative of the ‘V series’ frequency-domain electromagnetic instrument, i.e., V5, V6, and V8, produced by Phoenix Geophysical Company of Canada, the ‘GDP series’ DC resistivity electromagnetic instrument, i.e., GDP12, GDP16, and GDP32 of Zonge Company of the United States, the EH4 time-domain electromagnetic imaging system jointly developed by Geometrics Company and EMI Company of the United States, and the ADU frequency-domain geophysical measurement system developed by Germany Metronix. Additionally, the networked time-domain receiving instrument Zonge Electromagnetic Network (ZEN) developed by Zonge Company is also a typical instrument.
Next [28,29], deep exploration artificial-source electromagnetic instruments have made great progress, including in the development of a wireless electromagnetic (WEM) system [30] developed by the Chinese Academy of Sciences as well as the short offset transient electromagnetic (SOTEM) equipment [31], low-temperature superconducting TEM instruments [32], multifunctional CSAMT instruments [33], wide-area electromagnetic instruments based on pseudo-random emission waveforms, and controlled-source time–frequency electromagnetic instruments. Taking some instruments as examples, this paper focuses on the research progress in deep exploration artificial-source electromagnetic instruments in China and provides some references for readers and technicians.

2. Low-Temperature Superconducting Transient Electromagnetic Instrument

The traditional transient electromagnetic instrument (TEM) uses a hollow coil as the receiving coil. The induction signal measured by the coil decays rapidly and is not sensitive to low frequency signals, the bandwidth is narrow, and the sensitivity is low. As a result, the quality of the late-period signal related to the deep depth information is poor, the accuracy of the detection results is low, and it is not suitable for deep detection [34]. In order to improve the quality of the late-period signal received by the TEM instrument to achieve deep exploration, the superconducting quantum interference device (SQUID) had been applied in TEM exploration by the Technology Institute of Physics in Jena, Germany, and the instrument has been developed and applied in engineering [35,36]. Then, the Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, the Forschungszentrum Julich in Germany, and Jilin University collaborated on a series of application studies based on low-temperature SQUID transient electromagnetic technology.
In order to improve the exploration depth of the TEM and realize deep mineral resource exploration, a high-performance, low-temperature SQUID sensor is proposed to replace the hollow coil based on the weakly damped low-temperature SQUID and the monolithic readout technology [37]. The related parameters of the weakly damped SQUID chip are shown in Table 2.
The background noise level of the low-temperature SQUID chip is 7 fT/√Hz@ 1 kHz, the bandwidth is more than 2 MHz, and the swing rate is 1.5 nT·μs−1. The low-temperature SQUID used in the TEM has many advantages such as long effective decay time of the received signal, low noise, high sensitivity, wide bandwidth, and linear response within a wide frequency band.
The technology has been applied in field experiments on Hengsha Island of Shanghai, Siziwang Banner of Inner Mongolia, Ulanhot, and other places, where the instruments have been tested and improved and the practical application has been verified.
A comparison verification between the low-temperature SQUID TEM and the traditional hollow coil TEM was carried out on Hengsha Island in Shanghai. The comparison results show [38] that, the secondary field signal received by the low-temperature SQUID has a longer decay time than that of the hollow coil. By inverting the decay signal, interpretation results from both the hollow coil and the low-temperature SQUID were obtained. In should be noted that the layered distribution of the shallow resistivity was evident and obtained by applying both methods due to the higher SNR in the early-period signals. However, due to the narrow bandwidth of the coil, the resistivity changes within a depth range of 400 m are not significant when using the hollow coil. In contrast, the low-temperature SQUID can clearly reflect these changes. As the detection time increases, the signal is affected by the noise interference, resulting in a lower SNR in the late-period signals. The signals received by the hollow coil would no longer reflect the deep resistivity distribution of the survey area. The interpretation results from 700 m to 1400 m showed that, compared to the hollow coil, the low-temperature SQUID can still clearly observe changes in resistivity, further verifying its capability to detect deep subsurface information.

3. Surface Electromagnetic Prospecting Ground Electromagnetic Instrument

The CSAMT has unique advantages in terms of deep exploration. Therefore, several institutions have carried out research and development primarily focusing on the CSAMT with the increasing demand for depth exploration [39,40,41]. This includes the joint detection instrument of the CSAMT and IP developed by Jilin University [42,43], the large-depth multifunctional electromagnetic detection instrument integrating the AMT, CSAMT, and IP by the Institute of Geophysics and Geochemistry of the Chinese Academy of Geological Sciences [44,45,46], and the surface electromagnetic prospecting (SEP) instrument developed by the Institute of Geology and Geophysics of the Chinese Academy of Sciences [47,48,49]. The performance indicators of these instruments are comparable to the foreign instruments, with some indicators being even better.
The SEP instrument is introduced as an example. As shown in Figure 1, the SEP instrument consists of a transmitter, a receiver, a sensor, and other components. The transmitter employs technologies such as multi-frequency synchronous power supply, high-precision automatic current stabilization, transmitter system autonomous protection, GPS hybrid synchronization, frequency point refinement, and frequency-hopping transmission to achieve single- and multi-frequency synchronous transmission. The receiver uses a distributed data acquisition station based on band-pass negative feedback, which has a wide frequency bandwidth. The acquisition station consists of a multi-channel multi-mode digital receiving unit, embedded main control unit, system timing and synchronization control unit, remote communication unit, etc., with an internal digital filter that has strong capabilities in suppressing powerline interference and crosstalk between channels. The main performance indicators of the transmitter and receiver are shown in Table 3.
The SEP instrument completed comparative testing at five experimental sites, fully verifying the performance of each part of the instrument and the actual fieldwork capability of the overall system. For example, at the Caosiy Molybdenum Mine in Inner Mongolia, a comprehensive comparative CSAMT experiment was conducted with the SEP instrument and the advanced GDP-32 and V8 instruments. The results show [48] that, the resistivity contours inverted from data collected by the SEP instrument are highly similar to results obtained from V8 and slightly different from GDP-32. However, the overall shape is consistent, with the fault zone (1250 m) between low- and high-resistivity areas clearly visible. This indicates that the independently developed SEP ground electromagnetic detection instrument has essentially met or even surpassed the performance of similar foreign products and is capable of undertaking actual field exploration work.

4. Wide-Field Pseudo-Random Electromagnetic Instrument

Although the CSAMT has many advantages such as signal amplitude, detection depth, and resolution, the transition zone is easily entered when using the CSAMT to measure several kilometers away from the field source. Aiming to solve the shortcomings of weak signal and single frequency in one transmission in the CSAMT, the wide-field electromagnetic method (WFEM) was proposed [50,51]. The WFEM can measure in the transition zone and it can detect deeper depths with a smaller transmitter–receiver distance. In addition, the 2n sequence pseudo-random signal-WFEM is formed which combines the WFEM and the 2n sequence pseudo-random signal. It can obtain multiple-frequency geoelectric information in one transmission, not only with deeper detection depth but also high efficiency, greatly expanding the observation range of controlled-source electromagnetic methods.
The wide-field pseudo-random electromagnetic instrument was developed based on WFEM theory [52], including a high-power pseudo-random signal transmitter and wide-field electromagnetic receiver which is suitable for deep exploration. Among them, the multifunctional signal controller plays an important role in the transmitter, which is mainly used to generate pseudo-random control signals. Figure 2 shows the principle of the JSGY-2 WFEM instrument.
The multifunctional signal controller is mainly used for the transmission of 2n sequence pseudo-random signals, with a single-chip microcomputer and complex programmable logic devices as the core, achieving functions such as pseudo-random multi-frequency current transmission and detection. It integrates signal synthesis and measurement, ensuring accurate transmission frequencies with a high-precision clock source and digital signal synthesis technology, allowing for consistency calibration at any time, and features strict isolation between the controller and the strong electrical system. Additionally, it is equipped with power cabinets of varying powers to complete rectification, boosting, voltage regulation, and signal inversion functions. The technical specifications of the JSGY-2 transmission system are listed in Table 4.
The receiver uses digital methods to measure the electric field signal, incorporating various filtering technologies to effectively suppress powerline harmonic noise interference. Pseudo-random signals are a major advantage of the WFEM instrument, transmitting and receiving multiple frequencies simultaneously to enhance measurement efficiency. The technical indicators of the JSGY-2 receiver are listed in Table 5.
The WFEM instrument has been extensively validated through numerous field engineering projects, demonstrating remarkable effectiveness [53,54,55,56]. For example, a survey conducted in the Longshan area of Xiangxi obtained the resistivity distribution of underground carbonaceous shale.
The results show [54] the stratigraphic drilling profile and 2D inversion result of resistivity of the L1 and L2 measuring lines and a sectional drawing for presumptive interpretation. Based on the distribution of the resistivity value, the L1 measuring line can be divided into five electrical layers. The stratified information of the entire resistivity section is clear, with a large gradient of resistivity change. The electrical characteristics of this stratum are significantly different from the upper and lower rock layers. There is no obvious change in the occurrence of the top and bottom plates of the shale. The top plate is buried at a depth of 600 m and the thickness of the shale is about 200 m. The L2 measuring line is similar to the L1 measuring line, but there is a noticeable change in the occurrence of the top and bottom plates of the shale. The top plate of the shale has a deeper burial in the east and is shallower in the west, with the shallowest point at about 200 m and the deepest at about 700 m. The thickness of the shale is approximately 200 m. The geological interpretation results based on the resistivity profile of the WFEM are consistent with the drilling data, indicating that the WFEM is an effective means for obtaining the distribution range and burial depth of shale.

5. Controlled-Source Time–Frequency Electromagnetic Instrument

The above three types of artificial-source electromagnetic instruments are either time-domain or frequency-domain electromagnetic instruments. Time-domain electromagnetic instruments measure the change in geoelectric response over time, while frequency-domain electromagnetic instruments reflect the subsurface structural information at different depths by measuring the geoelectric response at different frequencies. There is a big difference in the working methods. The time-domain electromagnetic instruments use a single-pulse square wave to excite and measure the change in the secondary electromagnetic field over time, whereas the frequency-domain electromagnetic instruments use a series of excitation frequencies to measure the total field spectrum of the electromagnetic field. Additionally, time-domain electromagnetic instruments and frequency-domain electromagnetic instruments are different in their measurement results, ability to resolve target bodies, and application effectiveness [57]. In order to further improve the exploration precision and work efficiency, the time–frequency electromagnetic method (TFEM) was first proposed. Combining the advantages of both methods, the TFEM unifies time-domain exploration and frequency-domain exploration into one system, enabling the acquisition of both time-domain and frequency-domain data in a single collection. Through processing and interpretating, the resistivity and polarization information can be obtained simultaneously [58,59].
Controlled-source TFEM instruments select different frequencies and types of excitation waveforms based on the requirement of different exploration depths. By processing the signals at different frequencies separately, the frequency sounding curves are obtained. By conducting time-domain processing on decay signals with different periods, multiple sets of excitation decay curves are derived. Using high-power excitation can effectively obtain deep fluid polarization information, calculate relevant electrical property parameter anomalies, and delineate favorable boundaries for hydrocarbon reservoirs [60,61].
The instrument structure shares the same basic requirements as the CSAMT or electrical source transient electromagnetic instruments, including both a transmitting system and a receiving system. The transmitting system consists of a generator, transmitter, grounding cable, and signal acquisition station. The receiving system includes a master collector, acquisition stations, electromagnetic probes, and synchronization devices. The transmitting system continuously excites square wave signals from high to low frequency, while the receiving system synchronously collects all signals excited at each frequency through the synchronization device.
The development of the TFEM high-power constant current transmitting system has played a significant role in advancing China’s controlled-source time–frequency electromagnetic instruments. The transmitter mainly consists of a constant current generator, rectifier inverter, and main control unit.
It should be noted [62] that the load output current remains constant, while the generator’s voltage varies with the load changes. This process is achieved through excitation control; when the load increases, the excitation current rises, boosting the generator output voltage and increasing the load current. Conversely, the generator voltage decreases, and the current lowers to maintain a constant load current. The three-phase AC output from the generator, after rectification, is inverted to produce the time–frequency waveforms required for electromagnetic method exploration. Currently, there are two operating modes: time-domain operating mode and frequency-domain operating mode. The main functions of the main control unit include providing various operating frequency waveforms for inversion, acquiring the current and voltage of the main circuit, synchronizing transmission and reception, and setting the generator’s excitation potential. The main parameters of the transmitter are listed in Table 6.
The TFEM networked time–frequency electromagnetic receiver which was developed by the Oriental Geophysical Company of Hebei province, China and the Institute of Electronics of the Chinese Academy of Sciences is the latest time–frequency acquisition system currently available [63]. It could be synchronized with the TFEM high-power constant current transmitter via GPS to jointly complete the time–frequency data acquisition process. This system consists of a main control unit and wireless acquisition stations, featuring functions like secure data storage, long-distance real-time transmission, self-calibration, GPS synchronization, and impedance measurement. The main control unit manipulates the acquisition stations and transmits data wirelessly. The acquisition station includes two 32-bit high-precision data collection channels, a GPS module, a WiFi module, a large-capacity storage module, a built-in lithium-ion battery, etc. With GPS synchronization, the receiver can operate in either blind acquisition mode or networked acquisition mode. The main technical specifications of the receiver are listed in Table 7.
Currently, controlled-source time–frequency electromagnetic technology is applied all over the world, achieving good exploration results. For instance [64], in the oil and gas prediction for the WD14E11 line in the buried hill and internal areas of the Jizhong Depression, a geological model established using seismic drilling and known geological data is presented. And the stratum resistivity values obtained from well logging data are displayed, which are used as the initial resistivity for inversion interpretation to fit the final geoelectric model. Finally, by constraining the resistivity values obtained from fixed-depth, fixed-constraint inversions, the polarization range is defined, and polarization inversion yields the interpreted results. It is evident that the resistivity and polarization information of the reservoir is more accurately separated from the time–frequency data, which is conducive to the precise location and extraction of deep anomalies. This approach more accurately depicts and highlights the anomalies produced by deep buried hills, while the mutual constraints of multiple pieces of information better reflect the lateral physical property changes in the target.

6. Conclusions and Prospects

In the context of resource shortage, improving the level of resource exploration and increasing the depth of resource exploration are key issues in ensuring the sustainable development of society and economy. As effective geophysical exploration instruments, deep exploration artificial-source electromagnetic instruments have played an important role in the deep exploration of important energy and mineral resources. Taking the TFEM high-power instrument, low-temperature SQUID transient electromagnetic instrument, SEP ground electromagnetic instrument, and wide-field pseudo-random electromagnetic instrument as examples, this manuscript summarizes the progress in the research of deep exploration artificial-source electromagnetic instruments and draws the following conclusions:
(1)
The low-temperature SQUID transient electromagnetic instrument uses a low-temperature SQUID to replace the hollow coil, enhancing the exploration depth of the transient electromagnetic method. Field experiments conducted in various locations in China have verified the deep underground detection capabilities of the low-temperature SQUID. However, the metallic components may generate eddy currents when excited by the transmitting field, which can interfere with the SQUID receiving signal. The interference cannot be completely eliminated, thus affecting the detection accuracy.
(2)
The SEP ground electromagnetic instrument includes a high-power transmitter, multi-channel acquisition stations, and a series of magnetic sensors. Comprehensive comparative experiments with the advanced instruments have shown that the performance indicators of the instrument are comparable to these, with some indicators even surpassing the advanced instruments. However, the data processing and geological interpretation of SEP systems require complex inversion algorithms and models. Accurately extracting geological information from raw data remains challenging, especially with complex structures.
(3)
The wide-field pseudo-random electromagnetic instrument has broken through the theoretical constraints and technical flaws of the CSAMT approximate definition of resistivity that hindered deep exploration, solving significant issues such as the limited detection depth, low measurement efficiency, and poor 3D exploration capabilities of traditional artificial-source electromagnetic methods. It has achieved large-area, deep, high-precision, efficient, and multi-parameter detection of geological structures. However, the instrument’s resolution and depth penetration are inferior in shallow measurements, limiting its application in shallow exploration.
(4)
The TFEM high-power instrument integrates the advantages of time-domain and frequency-domain electromagnetic methods, unifying time-domain and frequency-domain sounding within a single system. A single acquisition can obtain both time-domain and frequency-domain data simultaneously, offering outstanding advantages in accurately delineating deep oil and gas anomalies. However, when dealing with high-frequency components, traditional Finite Element Method (FEM) models perform poorly, leading to the insufficient processing of high-frequency components.
Although the above instruments have achieved good exploration results, this is merely the first step in the research of deep mineral resource exploration technology. Further research is still needed for detecting targets at deeper depths, with smaller scales and less electrical property contrast. Combining various electromagnetic detection technologies for deep exploration is crucial for improving interpretation results. Moreover, the portability of high-power transmission systems and the engineering of instruments are also urgently required for practical exploration. Therefore, to further develop deep exploration artificial-source electromagnetic instruments, the following research work is recommended:
(1)
Conduct research on deep electromagnetic detection receiver sensors to further enhance the instrument’s receiving sensitivity and improve the capability to detect the weak electromagnetic signals collected from a deep depth.
(2)
Enhance the anti-interference capabilities of the instruments from a hardware perspective, research cascade analog filtering technology, and increase the stability of the instruments during fieldwork.
(3)
Conduct deep exploration combining various detection technologies, integrating the electromagnetic methods with large-depth seismic methods and array measurement instruments. In order to observe the impact of instrument parameters on measurement results, it is important to arrange the fieldwork plan reasonably and develop electromagnetic detection instruments from large-depth to high-precision exploration.
(4)
Strengthen the exploration of deep marine resources, utilizing the characteristic of extremely low-frequency electromagnetic waves with a lower attenuation rate in seawater to develop extremely low-frequency marine electromagnetic exploration technology.
(5)
Focus on the rational standardization of instrument technical indicators. Instrument manufacturing should be production-oriented, further developing research on the portability of high-power transmission systems and realizing the engineering of instruments.

Author Contributions

Y.Z. (Yangyong Zhang), investigation and writing—original draft preparation; X.Y., resources; L.C., writing—review and editing; Y.Z. (Yue Zhou), supervision; D.Q., project administration. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the open project for the low-frequency electromagnetic communication technology laboratory, grant number DPJJ-2020-03.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Electronics 14 00433 g001
Figure 1. Principle of the SEP ground electromagnetic instrument.
Figure 1. Principle of the SEP ground electromagnetic instrument.
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Figure 2. Principle of the wide-field electromagnetic instrument.
Figure 2. Principle of the wide-field electromagnetic instrument.
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Table 1. Representative electromagnetic instruments that can be used for deep exploration [16].
Table 1. Representative electromagnetic instruments that can be used for deep exploration [16].
Company NameInstrument Series Specific ModelsAttribute
Phoenix Geophysics, Calgary (AB), CanadaV seriesV5, V6, V8Frequency-domain electromagnetic instrument
Zonge, Salt Lake City (UT), USAGDP seriesGDP12, GDP16, GDP32DC resistivity instruments
Geometrics and EMI, Houston (TX), USAEH4 electromagnetic imaging system/Time-domain electromagnetic instrument
Metronix, Berlin, GermanyGeophysical measurement system ADU/Frequency-domain electromagnetic instrument
Zonge, Salt Lake City (UT), USANetworked reception system ZENZEN (Zonge Electromagnetic Network)Time-domain electromagnetic instrument
Table 2. Related parameters of the weakly damped SQUID chip [37].
Table 2. Related parameters of the weakly damped SQUID chip [37].
ParametersMeasured Values
Flux resolution əB/əΦ1.5 nT/Φ0
Chip area5 × 5 mm2
Feedback coil mutual inductanceΦ0/(10.7 μA)
SQUID loop inductance Mf350 pH
SQUID critical current~6.6 μA
Swing voltage~60 μV
Flux voltage transmission coefficient əV/əΦ~380 μV/Φ0
Dynamic resistance Rd~50 Ω
Table 3. The main indicators of the transmitter and receiver in the SEP ground electromagnetic instrument [47].
Table 3. The main indicators of the transmitter and receiver in the SEP ground electromagnetic instrument [47].
TransmitterReceiver
ParametersValue (Unit)ParametersValue (Unit)
Transmitting power100 kWReceiving bandDC~10 kHz
Transmitting frequency16 s~10 kHzDynamic range>120 dB
Synchronization accuracy0.1 μsWorking temperature−20~50 °C
Table 4. The technical indicators of the JSGY-2 transmitter [52].
Table 4. The technical indicators of the JSGY-2 transmitter [52].
Signal ControllerPower Cabinet (30 kW)
ParametersValue (Unit)ParametersValue (Unit)
Frequency range3/256–8192 HzMaximum output voltage1000 V ± 10%
Frequency accuracy>10−3Maximum output current30 A
Frequency stabilityFrequency stability greater than 10−4 within 7 hInsulation requirements≥100 MΩ/1000 V
Weight≤5.5 kgWorking temperature−10~50 °C
Table 5. The technical indicators of the JSGY-2 receiver [52].
Table 5. The technical indicators of the JSGY-2 receiver [52].
ParametersValue (Unit)
Working frequency0 frequency group {3/256, 3/128, 3/64, 3/32, 3/16, 3/8, 3/4 Hz}
1 frequency group {1/64, 1/32, 1/16, 1/8, 1/4, 1/2, 1 Hz}
2 frequency group {3/4, 3/2, 3, 6, 12, 24, 48 Hz}
3 frequency group {1, 2, 4, 8, 16, 32, 64 Hz}
4 frequency group {96, 192, 384, 768, 1536, 3072, 6144 Hz}
5 frequency group {128, 256, 512, 1024, 2048, 4096, 8192 Hz}
Amplitude measurement range10 µV~200 mV
Amplitude measurement errorAmplitude ≤ 100 µV, absolute error ≤ 1 µV
Amplitude > 100 µV, relative error ≤ 1%
Multi-channel consistency error≤1%
Power frequency attenuation≥80 dB
Input impedanceFrequency ≤ 1024 Hz, input impedance ≥ 5 MΩ
Frequency > 1024 Hz, input impedance ≥ 3 MΩ
Input short-circuit noise≤1 uV
Channel isolation≥80 dB
Working temperature−10~50 °C
Table 6. The main parameters of the TFEM transmitter [63].
Table 6. The main parameters of the TFEM transmitter [63].
ParametersValue (Unit)
Transmitter power120 kW
Exciting currentRange0~150 A
Precision5 mA
GeneratorVoltage regulation range0~1000 V
Output power200 kW
Inverter waveformDuty cycle (time-domain)1:1, 1:2, 1:3, 2:1, 3:1
Duty cycle (frequency-domain)1:1
Frequency range2−10~210 Hz
Distance between controller and transmitter30~50 m
Table 7. The main technical specifications of the TFEM receiver [63].
Table 7. The main technical specifications of the TFEM receiver [63].
ParametersValue (Unit)
Frequency range0~1000 Hz
Dynamic range123 dB
Sampling rate4 kb/s (tunable)
Gain×1, ×4, ×16, ×64
Power consumption<6 W
Noise<1 µV
Distortion<0.005%
Data transmissionWired220 m@10 Mb/s
WiFiApparent distance is 30 m and the speed is 54 Mb/s
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Zhang, Y.; Ye, X.; Chen, L.; Zhou, Y.; Qu, D. Progress of Deep Exploration Artificial-Source Electromagnetic Instruments in China: A Review. Electronics 2025, 14, 433. https://doi.org/10.3390/electronics14030433

AMA Style

Zhang Y, Ye X, Chen L, Zhou Y, Qu D. Progress of Deep Exploration Artificial-Source Electromagnetic Instruments in China: A Review. Electronics. 2025; 14(3):433. https://doi.org/10.3390/electronics14030433

Chicago/Turabian Style

Zhang, Yangyong, Xuan Ye, Lei Chen, Yue Zhou, and Daiming Qu. 2025. "Progress of Deep Exploration Artificial-Source Electromagnetic Instruments in China: A Review" Electronics 14, no. 3: 433. https://doi.org/10.3390/electronics14030433

APA Style

Zhang, Y., Ye, X., Chen, L., Zhou, Y., & Qu, D. (2025). Progress of Deep Exploration Artificial-Source Electromagnetic Instruments in China: A Review. Electronics, 14(3), 433. https://doi.org/10.3390/electronics14030433

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