Method and device for detecting low frequency electromagnetic field of moon

Abstract

The present application belongs to the field of deep space exploration and geophysical exploration, and particularly relates to a method and device for detecting lunar low-frequency electromagnetic field, aiming at solving the problem of unstable potential measurement in the lunar surface rare plasma environment. The present application comprises: deploying first, second and third electric field sensor probes in an orthogonal configuration on the lunar surface; applying a controllable bias current to each probe to actively adjust and stabilize the particle exchange process between the probe and the surrounding plasma, so that it works at a stable working point which is not sensitive to environmental disturbance, thereby reliably obtaining the accurate potential at the position of each probe; finally, by calculating the potential difference between the first probe and the second probe, and between the first probe and the third probe, the first and second electric field components which are orthogonal to each other are determined respectively. The present application overcomes the interference of the special lunar surface environment on potential measurement, and realizes stable and reliable detection of the lunar low-frequency electric field.

Description

Technical Field

[0001] This invention belongs to the field of deep space exploration and geophysical exploration, specifically relating to a method and device for detecting low-frequency electromagnetic fields on the moon. Background Technology

[0002] Electromagnetic sounding is an important geophysical method for studying the internal structure of planets. For example, the magnetotelluric sounding (MT), widely used on Earth, simultaneously measures natural alternating electric and magnetic fields on the ground. Utilizing the principle that electromagnetic waves of different frequencies have different skin depths in a medium, it inverts the conductivity structure at different depths underground. The key to the success of this method lies in its ability to simultaneously and accurately acquire electric and magnetic field data.

[0003] Scientists have also attempted to apply similar methods to study the internal structure of the moon. However, the lunar surface environment is vastly different from Earth's, posing significant technical challenges to the measurement of electromagnetic fields, especially electric fields. First, the lunar regolith has extremely high resistivity, making it impossible to achieve the methods commonly used on Earth, such as establishing good electrical contact between electrodes and the soil (i.e., "grounding"), on the moon. Second, the lunar surface lacks the protection of a thick atmosphere and a global magnetic field, directly exposing it to a thin plasma environment composed of solar wind, cosmic rays, and other cosmic forces.

[0004] To measure the electric field, the detector must employ a principle similar to the Langmuir probe, exchanging particles with the surrounding plasma through a metal electrode (i.e., the electric field sensor probe) deployed on the lunar surface to detect the floating potential at the probe's location. However, in the rarefied plasma environment of the lunar surface, the probe's potential is highly susceptible to the photoelectric effect, background plasma density, and minute temperature fluctuations. Both theory and experiments show that the current-voltage (IV) characteristic curve between the probe and the plasma has an extremely small slope in certain operating regions. This means that even a small change in the interference current can cause drastic and irregular jumps in the probe potential, resulting in highly unstable measurement results that cannot accurately reflect the true changes in the background electric field. Therefore, overcoming the influence of the unique lunar environment and achieving stable and reliable measurements of low-frequency electric fields is a critical technical challenge that needs to be addressed in lunar electromagnetic exploration. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, namely the instability of potential measurements in the thin plasma environment of the lunar surface, this invention provides a method and apparatus for detecting low-frequency electromagnetic fields on the moon.

[0006] The first aspect of this invention proposes a method for detecting low-frequency electromagnetic fields on the moon, comprising:

[0007] A sensor probe assembly is deployed on the lunar surface, the sensor probe assembly including a first electric field sensor probe, a second electric field sensor probe and a third electric field sensor probe, wherein the second electric field sensor probe and the third electric field sensor probe are orthogonally arranged relative to the first electric field sensor probe;

[0008] A bias current is applied to the sensor probe assembly to stabilize the particle exchange between the sensor probe assembly and the lunar surface plasma, and the potential of each sensor probe in the sensor probe assembly at its respective position is obtained.

[0009] The first electric field component is determined based on the difference between the potential of the first electric field sensor probe and the potential of the second electric field sensor probe.

[0010] Based on the difference between the potential of the first electric field sensor probe and the potential of the third electric field sensor probe, a second electric field component orthogonal to the first electric field component is determined.

[0011] Furthermore, the deployment steps are as follows: the first electric field sensor probe, the second electric field sensor probe, and the third electric field sensor probe are launched to the target position on the lunar surface at a preset initial ejection velocity and launch elevation angle through the deployment mechanism.

[0012] Furthermore, the step of applying bias current includes: obtaining the current-voltage characteristic curve of the electric field sensor probe by changing the magnitude of the current supplied to the electric field sensor probe and simultaneously measuring its potential value;

[0013] Based on the current-voltage characteristic curve, determine the optimal operating point for the detector to operate in the stable range; and set the bias current to the current value corresponding to the optimal operating point.

[0014] Among them, one or more regions on the current-voltage characteristic curve with a slope greater than a preset threshold are identified;

[0015] Select a point in one or more of the regions as the working point.

[0016] Furthermore, the method also includes simultaneously measuring the magnetic field components on the lunar surface using a magnetic field sensor while deploying and measuring the electric field components.

[0017] In a second aspect, the present invention provides a device for detecting low-frequency electromagnetic fields on the moon, which is used to implement a method for detecting low-frequency electromagnetic fields on the moon, comprising:

[0018] The sensor probe assembly includes a first electric field sensor probe, a second electric field sensor probe, and a third electric field sensor probe;

[0019] The deployment mechanism is configured to deploy the first electric field sensor probe, the second electric field sensor probe, and the third electric field sensor probe on the lunar surface, such that the second electric field sensor probe and the third electric field sensor probe are orthogonally arranged relative to the first electric field sensor probe.

[0020] The signal processing circuit is electrically connected to each electric field sensor probe and is configured to apply a bias current to the sensor probe assembly to obtain its potential, and calculate a first electric field component and a second electric field component that are mutually orthogonal based on the potential.

[0021] Furthermore, the deployment mechanism is a projectile deployment mechanism, which includes: a chute, a spring, and a release mechanism;

[0022] The slide is formed on the housing of the deployment mechanism, the spring is disposed at the bottom of the slide, the electric field sensor probe is placed above the spring and housed in the slide, and the unhooking release mechanism is connected to the spring and is used to trigger the spring to eject the sensor probe assembly when it is to be released.

[0023] Furthermore, the sensor probe assembly is designed in an ellipsoidal shape to ensure that it has a surface that can contact lunar plasma for particle exchange after landing on the lunar surface in any orientation.

[0024] Furthermore, the signal processing circuit includes a current biasing circuit that follows the dynamic potential, the circuit comprising:

[0025] The first operational amplifier receives a control signal for setting a target current at its differential input terminal via an input resistor, and its output terminal is connected in series with the electric field sensor probe via an output resistor.

[0026] The second operational amplifier is configured as a high input impedance current sampling amplifier. Its input terminal is connected to the signal of the electric field sensor probe to detect the actual current flowing through the electric field sensor probe and generate a feedback signal.

[0027] A feedback network is used to combine the current feedback signal with the output signal of the first operational amplifier, and feed the combined signal back to the differential input of the first operational amplifier to form a closed-loop negative feedback loop, thereby ensuring that the current flowing through the electric field sensor probe is accurately determined by the control signal; and

[0028] A high-voltage servo output stage composed of PNP and NPN transistors is used to form an adaptive servo floating supply potential, so that the operating potential of the operational amplifier can adapt to the high potential environment of the lunar surface, and realize the measurement of electric field data with a large dynamic range without saturation.

[0029] The input resistor, output resistor, and resistance parameters in the feedback network are configured such that the floating power supply potentials of the first operational amplifier and the second operational amplifier are linked with the potential of the electric field sensor probe through the high-voltage follower output stage, thereby enabling the operating potentials of the first operational amplifier and the second operational amplifier to follow the potential fluctuation of the electric field sensor probe and decouple them from the common-mode potential of the voltage control signal generated by the DAC.

[0030] Furthermore, the collector of the PNP transistor and the collector of the NPN transistor are connected by a bias and protection branch consisting of multiple resistors and at least two diodes connected in series. The two ends of the branch are coupled to a positive high voltage power supply and a negative high voltage power supply, respectively. This branch is used to provide a stable static operating point bias for the PNP transistor and the NPN transistor, and to provide current limiting protection under abnormal operating conditions.

[0031] Furthermore, the device also includes a three-component magnetic field sensor for synchronously measuring the magnetic field components on the lunar surface, and is integrated with the signal processing circuit to achieve synchronous acquisition of electromagnetic field data.

[0032] The beneficial effects of this invention are:

[0033] This invention proposes a technical solution for measuring low-frequency electric fields on the moon. The solution first applies a series of varying bias currents to an electric field sensor probe and simultaneously records its potential response to obtain the probe's current-voltage characteristics under the current lunar plasma environment. Based on this characteristic curve, its slope is analyzed to identify one or more regions with high slope values, i.e., regions where the potential is insensitive to changes in current. Subsequently, the probe's operating point, i.e., the bias current, is set and maintained within this identified stable region. This adaptive adjustment of the operating point can actively compensate for interference introduced by changes in background plasma parameters or fluctuations in the photoelectric effect during the measurement process, thereby improving the stability of the potential measurement, reducing measurement artifacts introduced by non-geophysical signal sources, and providing a prerequisite for obtaining effective electric field data.

[0034] To implement the above method, this invention includes a specific signal processing circuit. This circuit consists of a high-voltage output stage and a precision feedback control loop decoupled from the output potential. It uses a floating-powered operational amplifier to sample the actual current flowing through the electric field sensor probe. This feedback signal is compared with a low-voltage control signal to drive the high-voltage output stage. This architecture enables the circuit to respond to control commands within a normal voltage range, outputting a programmable, precisely controlled small bias current for a load that may be at a high floating potential. This circuit provides the hardware implementation basis for performing the aforementioned IV characteristic scan and subsequent stable operating point locking.

[0035] Furthermore, this invention also includes a projectile deployment mechanism and sensor probes with a specific geometry. The deployment mechanism uses a projectile method to deploy multiple sensor probes at locations far from the lander. This spatial separation reduces the impact of electromagnetic interference from the lander itself on the measurements, helping to improve the signal-to-noise ratio of the target signal. The sensor probes employ an ellipsoidal shape. This geometry allows them to form an effective charged particle exchange interface with the surrounding plasma environment after landing on the lunar surface in any orientation. This increases the probability of the probes functioning properly after deployment, contributing to improved robustness of the entire exploration mission.

[0036] In summary, this invention, by combining specific measurement procedures, circuit design, and deployment structure, constitutes an electric field detection system suitable for the lunar surface environment. Attached Figure Description

[0037] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0038] Figure 1 This is a flowchart illustrating a method for detecting low-frequency electromagnetic fields on the moon according to the present invention.

[0039] Figure 2 This is a schematic diagram showing the positional distribution relationship between various sensor probes in a lunar low-frequency electromagnetic field detection method of the present invention;

[0040] Figure 3 This is a schematic diagram of the deployment structure in a lunar low-frequency electromagnetic field detection method of the present invention;

[0041] Figure 4 This is a schematic diagram of the state of the sensor probe before ejection in a lunar low-frequency electromagnetic field detection device of the present invention.

[0042] Figure 5 This is a schematic diagram of the sensor probe ejection state in a lunar low-frequency electromagnetic field detection device according to the present invention.

[0043] Figure 6 This is a schematic diagram of the signal processing circuit in a lunar low-frequency electromagnetic field detection device according to the present invention.

[0044] Among them, 10 is the sensor probe assembly; 11 is the first electric field sensor probe; 12 is the second electric field sensor probe; 13 is the third electric field sensor probe; 20 is the deployment mechanism; 21 is the chute; 211 is the inner layer; 212 is the outer layer; 22 is the spring; 23 is the release mechanism; 24 is the signal cable; and 30 is the lander. Detailed Implementation

[0045] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the invention. Furthermore, it should be noted that, for ease of description, only the parts relevant to the invention are shown in the accompanying drawings.

[0046] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0047] like Figure 1 and Figure 2 As shown, the first embodiment of the present invention proposes a method for detecting low-frequency electromagnetic fields on the moon, including:

[0048] A sensor probe assembly 10 is deployed on the lunar surface. The sensor probe assembly 10 includes a first electric field sensor probe 11, a second electric field sensor probe 12, and a third electric field sensor probe 13, wherein the second electric field sensor probe 12 and the third electric field sensor probe 13 are orthogonally arranged relative to the first electric field sensor probe 11.

[0049] A bias current is applied to the sensor probe assembly 10 to stabilize the particle exchange between the sensor probe assembly 10 and the lunar surface plasma, and the potential of each sensor probe in the sensor probe assembly 10 at its respective position is obtained.

[0050] The first electric field component is determined based on the difference between the potential of the first electric field sensor probe 11 and the potential of the second electric field sensor probe 12.

[0051] Based on the difference between the potential of the first electric field sensor probe 11 and the potential of the third electric field sensor probe 13, the second electric field component orthogonal to the first electric field component is determined.

[0052] In this embodiment, the method draws on the principle of magnetotelluric sounding in geophysical exploration, aiming to invert the electrical conductivity structure inside the moon by simultaneously measuring the orthogonal electric field components Ex, Ey, and magnetic field components on the lunar surface. Specifically, the first electric field sensor probe 11, deployed at point A, serves as the reference center. The second electric field sensor probe 12, deployed at point B, and the third electric field sensor probe 13, deployed at point C, are respectively arranged on two measuring lines perpendicular to point A, forming a right-angled triangle with point A as the right-angle vertex. The potential V at points A, B, and C is measured using a signal processing circuit. A V B and V C Subsequently, the electric field components are obtained by calculating the potential difference. The first electric field component, Ex, can be obtained from the potential difference (V) between point A and point B. A -VB ) and the distance L between the two points AB The calculation shows that the second electric field component Ey can be derived from the potential difference (V) between points A and C. A -V C ) and the distance L between the two points AC Calculations show that due to the thin plasma environment on the lunar surface and the extremely high resistivity of the lunar regolith (reaching over 100 MΩ), the particle exchange process between the probe and the environment is highly unstable. Therefore, an active bias current must be applied to each probe to clamp its operating point into a stable state, thereby accurately obtaining the potential at its location. In this way, through differential measurements and orthogonal deployment, a pair of orthogonal horizontal electric field components required for magnetotelluric methods can be obtained, providing the necessary input data for subsequent tensor impedance calculations, thus enabling effective exploration of deep lunar information.

[0053] The deployment steps are as follows: the first electric field sensor probe 11, the second electric field sensor probe 12 and the third electric field sensor probe 13 are launched to the target position on the lunar surface at a preset initial ejection velocity and ejection elevation angle through the deployment mechanism 20.

[0054] In this embodiment, to achieve unmanned deployment and minimize interference from the lander itself to the electromagnetic field measurement, a deployment mechanism 20 is employed. This deployment mechanism 20 is a projectile-type deployment mechanism, mounted on the lander 30, and is used to deploy three electric field sensor probes. The specific deployment scheme is attached. Figure 2 As shown, assume that the first electric field sensor probe 11, as the farthest point, is deployed at point A, while the second electric field sensor probe 12 and the third electric field sensor probe 13, as the near points, are deployed at points B and C, respectively. Taking the lander 30 as the origin, points B and C are deployed approximately 20 meters away from the lander 30, with their deployment directions perpendicular to each other; point A is deployed approximately 28 meters away from the lander 30, with its direction being the angle bisector of the deployment directions of points B and C. Thus, points A, B, and C form an isosceles right triangle with vertex A.

[0055] The step of applying bias current includes: obtaining the current-voltage characteristic curve of the electric field sensor probe by changing the magnitude of the current supplied to the electric field sensor probe and simultaneously measuring its potential value;

[0056] Based on the current-voltage characteristic curve, determine the optimal operating point that allows the detector to operate in the stable range; and set the bias current to the current value corresponding to the optimal operating point.

[0057] Specifically, one or more regions on the current-voltage characteristic curve with a slope greater than a preset threshold are identified; and a point in one or more of these regions is selected as the operating point.

[0058] In this embodiment, to address the issue of unstable probe floating potential in the sparse plasma environment of the lunar surface, an active adaptive biasing method is employed. This method acquires the current-voltage (IV) characteristic curve under the current environment. Specifically, a current that scans and varies within the range of +500nA to -500nA is applied to the probe in a programmable manner controlled by a DAC through a current source in the signal processing circuit, with a scanning accuracy of up to 1nA. At each step of the current scan, the probe's potential value is simultaneously and accurately measured. This yields a series of current and voltage data points, forming the IV characteristic curve.

[0059] Next, the slope of the curve is analyzed. According to the principles of plasma physics, flat regions with a small slope correspond to unstable operating states, while steep regions with a large slope correspond to stable operating states. By setting a slope threshold, one or more steep regions on the curve are automatically identified. A suitable point is selected from these stable regions as the optimal operating point, and the output of the precision current source is fixed at the current value corresponding to this operating point for subsequent long-term potential monitoring. This strategy of scanning first and then locking ensures that the detector always operates in a state least sensitive to environmental disturbances, fundamentally guaranteeing the stability and accuracy of potential measurements.

[0060] The method further includes simultaneously measuring the magnetic field components on the lunar surface using a magnetic field sensor while deploying and measuring the electric field components.

[0061] In this embodiment, based on the principle of the MT method, the impedance tensor Z needs to be calculated using the electric field components Ex and Ey and the magnetic field components Hx and Hy, thereby obtaining the apparent resistivity and phase. Therefore, this method simultaneously measures the two orthogonal electric field components and uses a three-component magnetic field sensor deployed on the lander 30 to synchronously acquire the three orthogonal magnetic field components Hx, Hy, and Hz. All electric and magnetic field data are sampled under the control of the same data acquisition system using a unified clock, ensuring strict temporal synchronization of all components. This synchronous measurement of electromagnetic field components is a prerequisite for subsequent high-quality data processing and inversion, guaranteeing the accuracy and reliability of the calculated parameters such as impedance, apparent resistivity, and phase.

[0062] See Figures 3-6 The second embodiment of the present invention proposes a device for detecting low-frequency electromagnetic fields on the moon, used to implement the aforementioned method for detecting low-frequency electromagnetic fields on the moon, comprising:

[0063] The sensor probe assembly 10 includes a first electric field sensor probe 11, a second electric field sensor probe 12, and a third electric field sensor probe 13.

[0064] The deployment mechanism 20 is configured to deploy the first electric field sensor probe 11, the second electric field sensor probe 12 and the third electric field sensor probe 13 on the lunar surface, such that the second electric field sensor probe 12 and the third electric field sensor probe 13 are orthogonally arranged relative to the first electric field sensor probe 11.

[0065] The signal processing circuit is electrically connected to each electric field sensor probe and is configured to apply a bias current to the sensor probe assembly 10 to obtain its potential, and calculate a first electric field component and a second electric field component that are mutually orthogonal based on the potential.

[0066] In this embodiment, the device is the physical entity that implements the above-described method. It comprises three independent electric field sensor probes, each of which is a metallic body capable of exchanging particles with lunar surface plasma.

[0067] See Figure 3 The deployment mechanism 20 is an independent launcher capable of precisely deploying the probe to predetermined orthogonal measurement points. The signal processing circuit is the core of the entire device. It is connected to each probe via a multi-core shielded cable. The cable is integrated into a sheath, but the electric and magnetic field signals are isolated and shielded from each other. The weak potential signals sensed by the probe are introduced to the electronic unit inside the lander compartment for processing in a remote acquisition manner.

[0068] This circuit not only includes functions for scanning and setting the bias current of the probe, but also a high-precision, high-input-impedance voltage measurement module, and a digital processing unit for calculating the electric field components. Furthermore, the signal processing circuit integrates power management, analog signal boards, and digital signal boards, and employs a backup design to improve mission reliability. The overall design of this device works collaboratively to achieve the entire process from automatic deployment and environmental adaptive adjustment to high-precision data acquisition and processing, forming a complete lunar surface electric field detection system.

[0069] The deployment mechanism 20 is a projectile-type deployment mechanism, which includes: a slide 21, a spring 22 and a release mechanism 23;

[0070] The slide 21 is formed on the housing of the deployment mechanism 20, the spring 22 is disposed at the bottom of the slide 21, the electric field sensor probe is placed above the spring 22 and housed in the slide 21, and the unhooking release mechanism 23 is connected to the spring 22 and is used to trigger the spring 22 to eject the sensor probe assembly 10 when it is ready to be released.

[0071] In this embodiment, as shown in the appendix Figure 3 , Figure 4 and Figure 5As shown, the deployment mechanism 20 is designed as a compact module with an outer envelope size of approximately 200mm × 200mm × 200mm. Before launch, the first electric field sensor probe 11, the second electric field sensor probe 12, and the third electric field sensor probe 13 are respectively placed in three slots 21 opened on the housing of the deployment mechanism 20. The three slots 21 are opened on the housing of the deployment mechanism 20 at preset positions, and the housing of the deployment mechanism 20 is mounted on the lander 30. The ejection force is provided by a highly elastic spring 22, which is compressed and locked before launch. Its elastic coefficient can be designed to be 1.3kgf / mm, and the preset compression space is 100mm. Upon receiving a release command from the lander, the release mechanism 23, such as an electrically controlled locking pin, immediately actuates, instantly releasing the compression of the spring 22. The spring 22 rapidly releases its stored elastic potential energy, propelling the probes out at high speed along the slots 21. The space-grade twisted-pair signal cables 24 connecting to the probe are neatly wound in the cable compartment beforehand and unfold in an orderly manner as the probe flies out. This mechanism has a simple structure, few moving parts, and extremely high reliability in the harsh lunar environment, enabling it to complete long-distance precision deployment missions in a single operation.

[0072] More specifically, the slide 21 is a coaxial double-layer structure, including an inner layer 211 and an outer layer 212;

[0073] The inner layer 211 forms a receiving cavity for accommodating the sensor probe assembly 10, the spring 22, and the release mechanism 23;

[0074] The outer layer 212 is a cable compartment on which the signal cable 24 is wound, and its cross-section is frustum-shaped with the diameter increasing from bottom to top, forming a sloping anti-jamming structure to prevent the signal cable 24 from getting stuck.

[0075] The sensor probe assembly 10 is designed in an ellipsoidal shape to ensure that it has a surface that can contact the lunar plasma for particle exchange after landing on the lunar surface in any orientation.

[0076] In this embodiment, the probe is designed as a smooth ellipsoid, with a size of approximately 40mm × 90mm. Considering that the probe's final landing attitude on the lunar surface after its parabolic motion is random, potentially involving tumbling or lying on its side at any angle, using a flat plate or other shapes with sharp edges and directions could result in the effective sensing surface being separated from the plasma environment or experiencing poor contact after landing, leading to measurement failure. The advantage of an ellipsoidal shape lies in its smooth curvature throughout. Regardless of its orientation on the lunar surface, it always has a sufficiently large curved surface exposed to the plasma sheath above, enabling effective photoelectron emission and absorption of charged particles in the environment, thus establishing a stable potential connection with the surrounding plasma. This design significantly improves deployment fault tolerance and mission robustness, ensuring the probe functions normally regardless of its landing attitude.

[0077] like Figure 6 As shown, in this embodiment, the signal processing circuit includes a current biasing circuit that follows the dynamic potential. The circuit includes:

[0078] The first operational amplifier receives a control signal for setting a target current at its differential input terminal via an input resistor, and its output terminal is connected in series with the electric field sensor probe via an output resistor.

[0079] The second operational amplifier is configured as a high input impedance current sampling amplifier. Its input terminal is connected to the signal of the electric field sensor probe to detect the actual current flowing through the electric field sensor probe and generate a feedback signal.

[0080] A feedback network is used to combine the current feedback signal with the output signal of the first operational amplifier and feed the combined signal back to the differential input terminal of the first operational amplifier to form a closed-loop negative feedback loop, so that the current flowing through the electric field sensor probe is accurately determined by the control signal.

[0081] A high-voltage servo output stage composed of PNP and NPN transistors is used to form an adaptive servo floating supply potential, so that the operating potential of the operational amplifier can adapt to the high potential environment of the lunar surface, and realize the measurement of electric field data with a large dynamic range without saturation.

[0082] The input resistor, output resistor, and resistance parameters in the feedback network are configured such that the floating power supply potentials of the first operational amplifier and the second operational amplifier are linked to the potential of the electric field sensor probe through the high-voltage follower output stage. This allows the operating potentials of the first operational amplifier and the second operational amplifier to follow the potential fluctuation of the electric field sensor probe and decouple them from the common-mode potential of the voltage control signal generated by the DAC.

[0083] In this embodiment, the load generated between the electric field sensor probe and the lunar surface plasma environment is equivalent to R.load By transmitting the lunar surface electric field sensor probe R, which serves as an equivalent load, load A precisely known current is injected to induce particle exchange between the electric field sensor probe and the plasma environment, bringing them into equilibrium. At this point, the potential on the electric field sensor stabilizes, and the voltage Vout established on the probe is accurately measured, thus enabling precise measurement of the lunar surface potential. For this purpose, the signal processing circuit includes a precision current bias circuit that follows the changing potential. This circuit is designed to operate on high-impedance loads up to 100 MΩ and can adapt to the floating high-potential environment of the lunar surface, such as greater than 50 V. Functionally, this current bias circuit is implemented as a precise, high-potential-following voltage-to-current converter.

[0084] The circuit includes: a first operational amplifier Amp1, which serves as the core control unit. Its positive and negative differential input terminals receive differential control signals within the normal ±5V range from the digital-to-analog converter (DAC) through input resistors R3 and R4. These signals are used to set the target current.

[0085] The output of the first operational amplifier Amp1 is connected to the equivalent load R of the electric field sensor probe through a precision resistor R1. load A precise and stable current signal is obtained by connecting the series resistors. The precision resistor R1 is actually a set of precision resistors with opposite temperature coefficients connected in series, used to output a stable bias current signal in environments with large temperature variations on the lunar surface. Both the first operational amplifier Amp1 and the second operational amplifier Amp2 adopt a floating power supply VF+, VF- method. Their floating power supply is determined by the emitters of PNP transistors and NPN transistors, and is not limited by the common-mode potential of the digital-to-analog converter (DAC).

[0086] To address the potential high potential on the lunar surface, by appropriately selecting input resistors R3 and R4, and resistors R2, R5, and R6 in the feedback network, the common-mode output of the first operational amplifier is decoupled from the voltage control signal output by the DAC, allowing it to float within a certain range. A high-voltage servo output stage (also known as a bootstrap power supply), composed of NPN transistor Q1 and PNP transistor Q2, provides a floating operating power supply for the first operational amplifier Amp1 and the second operational amplifier Amp2, enabling them to bootstrap and follow the high potential of the probe. This raises the overall operating potential of the core control circuit, ensuring it does not saturate due to the high common-mode voltage of the probe exceeding its operating range. Ultimately, this circuit achieves precise nanoampere-level current drive for high-impedance, high-potential loads, laying the foundation for accurate measurement of the probe voltage Vout.

[0087] Furthermore, the collector of the PNP transistor and the collector of the NPN transistor are connected by a bias and protection branch consisting of multiple resistors and at least two diodes connected in series. The two ends of the branch are coupled to a positive high voltage power supply and a negative high voltage power supply, respectively. This branch is used to provide a stable static operating point bias for the PNP transistor and the NPN transistor, and to provide current limiting protection under abnormal operating conditions.

[0088] To ensure the stability and safety of the high-voltage servo output stage in this embodiment, a bias and protection branch consisting of multiple resistors and at least two diodes connected in series is used to connect the collectors of NPN transistor Q1 and PNP transistor Q2. The two ends of this branch are coupled to the positive high-voltage power supply Vcc (typically greater than 100V) and the negative high-voltage power supply Vee (typically less than -100V), respectively. In this embodiment, starting from the collector of NPN transistor Q1, an 89kΩ resistor, a 10kΩ resistor, a first diode, a second diode, another 10kΩ resistor, and another 89kΩ resistor are connected in series sequentially, finally connecting to the collector of PNP transistor Q2. The positive high-voltage power supply Vcc and the negative high-voltage power supply Vee are connected to the corresponding nodes of this series chain. This precision voltage divider branch has a dual function: on the one hand, it provides a stable static operating point bias voltage for NPN transistor Q1 and PNP transistor Q2 through reasonable resistor value setting, ensuring their efficient operation in the linear amplification region; on the other hand, when the circuit encounters transient overvoltage or abnormal operating conditions, the resistors and diodes on the branch work together to achieve current limiting and voltage clamping, thereby protecting the critical high-voltage transistors and significantly improving the long-term reliability of the entire measurement device in harsh space environments.

[0089] The device also includes a three-component magnetic field sensor for synchronously measuring the magnetic field components on the lunar surface, and is integrated with the signal processing circuit to achieve synchronous acquisition of electromagnetic field data.

[0090] In this embodiment, in addition to the electric field detection section, the entire device also integrates a highly sensitive three-component magnetic field sensor, specifically a digital fluxgate magnetic field sensor. This magnetic field sensor can measure low-frequency magnetic fields in the DC to 10Hz frequency band, with a range of ±2000nT and a resolution as high as 10pT. To reduce magnetic interference from the lander itself, the magnetic field sensor probe is deployed at a certain distance from the lander body via an extension rod. The fluxgate sensor consists of three sets of mutually perpendicular concentric coils, specifically including an excitation coil, an induction coil, and a feedback coil, enabling simultaneous measurement of the three components of the magnetic field. Its output magnetic field signal, along with the potential signals from the three electric field probes, is sent together to a unified signal processing circuit and data acquisition unit.

[0091] This integrated design ensures that the electric and magnetic field data streams maintain strict time synchronization throughout the acquisition, processing, and storage stages, ultimately outputting a complete, time-aligned multi-component electromagnetic field dataset, providing a high-quality raw dataset for the study of the lunar internal structure.

[0092] The terms “first”, “second”, etc., are used to distinguish similar objects, not to describe or indicate a specific order or sequence.

[0093] The term "comprising" or any other similar term is intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus / device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent in such process, method, article, or apparatus / device.

[0094] The technical solution of the present invention has been described above with reference to the preferred embodiments shown in the accompanying drawings. However, it will be readily understood by those skilled in the art that the scope of protection of the present invention is obviously not limited to these specific embodiments. Without departing from the principles of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the scope of protection of the present invention.

Claims

1. A method for detecting low-frequency electromagnetic fields on the moon, characterized in that, include: A sensor probe assembly is deployed on the lunar surface. The sensor probe assembly includes a first electric field sensor probe, a second electric field sensor probe, and a third electric field sensor probe. The second electric field sensor probe and the third electric field sensor probe are respectively arranged on two measuring lines that are perpendicular to each other with the first electric field sensor probe, such that the positions of the first electric field sensor probe, the second electric field sensor probe, and the third electric field sensor probe form a right-angled triangle with the position of the first electric field sensor probe as the right-angle vertex. A bias current is applied to the sensor probe assembly to stabilize the particle exchange between the sensor probe assembly and the lunar surface plasma, and the potential of each sensor probe in the sensor probe assembly at its respective position is obtained. The first electric field component is determined based on the difference between the potential of the first electric field sensor probe and the potential of the second electric field sensor probe. Based on the difference between the potential of the first electric field sensor probe and the potential of the third electric field sensor probe, a second electric field component orthogonal to the first electric field component is determined.

2. The method according to claim 1, characterized in that, The deployment steps are as follows: the first electric field sensor probe, the second electric field sensor probe, and the third electric field sensor probe are launched to the target position on the lunar surface at a preset initial ejection velocity and launch elevation angle through the deployment mechanism.

3. The method according to claim 1, characterized in that, The step of applying bias current includes: obtaining the current-voltage characteristic curve of the electric field sensor probe by changing the magnitude of the current supplied to the electric field sensor probe and simultaneously measuring its potential value; Based on the current-voltage characteristic curve, determine the optimal operating point for the detector to operate in the stable range; and set the bias current to the current value corresponding to the optimal operating point. Among them, one or more regions on the current-voltage characteristic curve with a slope greater than a preset threshold are identified; Select a point in one or more of the regions as the working point.

4. The method according to claim 1, characterized in that, The method further includes simultaneously measuring the magnetic field components on the lunar surface using a magnetic field sensor while deploying and measuring the electric field components.

5. A device for detecting low-frequency electromagnetic fields on the moon, used to implement the method for detecting low-frequency electromagnetic fields on the moon as described in any one of claims 1-4, characterized in that, include: The sensor probe assembly includes a first electric field sensor probe, a second electric field sensor probe, and a third electric field sensor probe; The deployment mechanism is configured to deploy the first electric field sensor probe, the second electric field sensor probe, and the third electric field sensor probe on the lunar surface, such that the second electric field sensor probe and the third electric field sensor probe are orthogonally arranged relative to the first electric field sensor probe. The signal processing circuit is electrically connected to each electric field sensor probe and is configured to apply a bias current to the sensor probe assembly to obtain its potential, and calculate a first electric field component and a second electric field component that are mutually orthogonal based on the potential.

6. The apparatus according to claim 5, characterized in that, The deployment mechanism is a projectile-type deployment mechanism, which includes: a slide, a spring, and a release mechanism; The slide is formed on the housing of the deployment mechanism, the spring is disposed at the bottom of the slide, the electric field sensor probe is placed above the spring and housed in the slide, and the unhooking release mechanism is connected to the spring and is used to trigger the spring to eject the sensor probe assembly when it is to be released.

7. The apparatus according to claim 5 or 6, characterized in that, The sensor probe assembly is designed in an ellipsoidal shape to ensure that it has a surface that can contact lunar plasma for particle exchange after landing on the lunar surface in any orientation.

8. The apparatus according to claim 5, characterized in that, The signal processing circuit includes a current biasing circuit that follows the dynamic potential, the circuit comprising: The first operational amplifier receives a voltage control signal generated by a DAC to set a target current at its differential input terminal via an input resistor, and its output terminal is connected in series with the electric field sensor probe via an output resistor. The second operational amplifier is configured as a high input impedance current sampling amplifier. Its input terminal is connected to the signal of the electric field sensor probe to detect the actual current flowing through the electric field sensor probe and generate a feedback signal. A feedback network is used to combine the feedback signal with the output signal of the first operational amplifier and feed the combined signal back to the differential input terminal of the first operational amplifier to form a closed-loop negative feedback loop, so that the current flowing through the electric field sensor probe is accurately determined by the control signal. A high-voltage servo output stage composed of PNP and NPN transistors is used to form an adaptive servo floating supply potential, so that the operating potential of the operational amplifier can adapt to the high potential environment of the lunar surface. The input resistor, output resistor, and resistance parameters in the feedback network are configured such that the floating power supply potentials of the first operational amplifier and the second operational amplifier are linked to the potential of the electric field sensor probe through the high-voltage follower output stage. This allows the operating potentials of the first operational amplifier and the second operational amplifier to follow the potential fluctuation of the electric field sensor probe and decouple them from the common-mode potential of the voltage control signal generated by the DAC.

9. The apparatus according to claim 8, characterized in that, The collector of the PNP transistor and the collector of the NPN transistor are connected by a bias and protection branch consisting of multiple resistors and at least two diodes connected in series. The two ends of the branch are coupled to a positive high voltage power supply and a negative high voltage power supply, respectively. This branch is used to provide a stable static operating point bias for the PNP transistor and the NPN transistor, and to provide current limiting protection under abnormal operating conditions.

10. The apparatus according to claim 5, characterized in that, The device also includes a three-component magnetic field sensor for synchronously measuring the magnetic field components on the lunar surface, and is integrated with the signal processing circuit to achieve synchronous acquisition of electromagnetic field data.

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