Electric signal regulation ocean electric field long distance wide band measuring system

Abstract

The application provides a telecommunication signal regulation ocean electric field long-distance wideband measurement system, which uses an electric control electric field modulator to modulate a low-frequency measured electric field to a high-frequency carrier by switching intermittent on-off, adopts completely same electrode structure to measure an electrode and a reference electrode, converts a received modulated electric field into an electric signal through a charge amplifier, differentially amplifies two electrode output signals to suppress an environmental common-mode interference signal, filters various wideband noises and interference signals through a lock-in amplifier narrowband filter, analyzes a measured electric field value through a computer, and drives a control circuit to realize automatic electric control modulation. The application realizes long-distance, wideband underwater electric field measurement, has low drift and high resolution, can not only measure static and slow-changing underwater electric fields, but also measure dynamic and transient electric fields in relatively fast-moving underwater, and can be applied to more extensive fields.

Description

Technical Field

[0001] This invention relates to the field of marine electric field measurement technology, and more specifically, to a long-distance broadband measurement system for marine electric fields controlled by electrical signals. Background Technology

[0002] Oceans cover 70% of the Earth's surface, and many unknowns await human exploration beneath the surface. Due to the unique nature of the ocean as a medium, many physical methods that can be used for measurements in the air cannot be applied there. Current oceanographic measurement systems primarily employ acoustic and low-frequency electric / magnetic detection. Acoustic measurements in seawater are relatively mature, and magnetic measurement research has recently become a hot topic. However, electric field measurements have been studied less extensively and are more challenging. Seawater has good electrical conductivity, meaning high-frequency electric fields cannot be transmitted over long distances. Only very low-frequency, or even static, electric fields can be transmitted over long distances. This is of great significance for marine resource surveys, the study of underwater moving objects, and ocean current movements.

[0003] The most widely used method for measuring ocean electric fields is the spontaneous potential method. This method indirectly calculates the magnitude of the electric field by utilizing the resistive voltage division between two relatively far-distance measuring electrodes placed in seawater and the electric field being measured. The greater the distance to the electric field, the greater the distance between the two measuring electrodes must be. However, various factors, such as the electric field generated by seawater movement between the two measuring electrodes, environmental interference fields, and other electric field couplings, can affect the resolution of the measured electric field. In particular, the static and low-frequency electric fields of the ocean make it difficult to distinguish the interference and drift received by the two measuring probes from the measured electric field, which limits the application of this method in measuring ocean electric fields.

[0004] Patent document CN104155532A (application number: CN201410389299.4) discloses a marine electric field measurement device, including a sealed body and its internal signal acquisition and processing system, multiple pairs of electric field sensors, and a signal amplification system, as well as a signal transmission system connected to the signal acquisition and processing system in the middle of the sealed body. One end of the electric field sensor is sealed and fixedly connected to the outer shell of the sealed body, and the other end is connected to the data acquisition system through the signal amplification system. The cavity of the electric field sensor includes an electrolyte and an electric field measuring electrode immersed in the electrolyte. One end of the cavity is a sealed end, and the other end is an ion-permeable end. One end of the electric field measuring electrode is sealed and connected to a cable. This patent has advantages such as simple structure, minimal impact from marine turbulence, and resistance to marine organism attachment. However, its electric field sensor still adopts the traditional electric field measurement principle, only increasing the number of sensors and improving the packaging and fixing method. Static / low-frequency interference and drift cannot be fundamentally solved.

[0005] For static and very slow-moving electric field measurements, an effective method is to modulate the electric field signal. Existing methods include rotating the probe in the natural potential method to modulate the electric field. However, because the probe rotation agitates the seawater, and the various media and their motions between the two measuring probes and the electric field being measured are closely related, the measurement resolution is low and a long stabilization time is required. Alternatively, the "field grinding" modulation method used in atmospheric electric field measurements can be adopted. However, in conductive seawater, mechanical modulation is difficult to avoid the agitation caused by rotation, and the influence of seawater fluctuations on mechanical modulation cannot be ignored. Furthermore, due to the damping effect of seawater, the modulation frequency is very low (usually less than 1 Hz) regardless of the type of mechanical modulation, resulting in a low measurable electric field frequency. Therefore, a completely new modulation method for controlling the electric field being measured is needed, which can both increase the modulation frequency and reduce the impact of seawater disturbance on the electric field measurement, making broadband electric field measurements of faster underwater motion possible. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the purpose of this invention is to provide a long-distance broadband measurement system for ocean electric fields controlled by electrical signals.

[0007] The long-distance broadband measurement system for ocean electric fields regulated by electrical signals provided by the present invention includes: an electrically controlled electric field modulator, a shielding shell, a reference electrode, a measuring electrode, a first charge amplifier, a second charge amplifier, a differential amplifier, a lock-in amplifier, an A / D converter, a computer, and a control circuit.

[0008] The electrically controlled electric field modulator is installed at the front end of the measuring electrode;

[0009] The shielding shell is connected to ground;

[0010] The reference electrode and the measuring electrode are respectively fixed inside the shielding shell and do not contact the shielding shell;

[0011] The reference electrode is connected to the first charge amplifier;

[0012] The measuring electrode is connected to the second charge amplifier;

[0013] Both the first charge amplifier and the second charge amplifier are connected to the differential amplifier;

[0014] The differential amplifier, lock-in amplifier, A / D converter, computer, and control circuit are connected in sequence.

[0015] The first charge amplifier, the second charge amplifier, the differential amplifier, the lock-in amplifier, the A / D converter, and the computer constitute a sensor signal acquisition / processor;

[0016] By controlling the potential of the electric field structure distributed in the seawater through a switch, the electric field being measured in the seawater is modulated into a modulated electric field by an electronically controlled electric field modulator.

[0017] Preferably, the electric field modulator controls the switches 1 and 2 to be turned on by the control circuit, and applies positive and negative voltages to the plates of electrode 1 and electrode 2 respectively. The positive charges in the seawater are also subjected to the electric field force and move to the lower right of electrode 2, while the negative charges move to the upper right of electrode 1.

[0018] When switches 1 and 2 are off, there is no voltage on electrodes 1 and 2. Both positive and negative charges move horizontally to the right. The electric field being measured passes smoothly through the through-hole of the metal aperture and through the opening of the shielding shell, reaching the electrode being measured. By turning the switches on and off, the electric field being measured is modulated, so that a modulated electric field signal can be obtained on the measuring electrode. The modulation frequency of the electronically controlled electric field modulator is determined by the switching frequency. The highest modulation frequency is determined by the time constant corresponding to the equivalent capacitance of the electrode and the equivalent resistance from seawater to the ground. The lower the time constant, the faster the electrode charges and the higher the highest modulation frequency.

[0019] Electrode 1 and electrode 2 are placed in a shielding structure with the same volume of isolation space;

[0020] The reference electrode, installed on the upper part of the shielded enclosure and almost completely isolated from the space, can only obtain the common-mode interference signal in the seawater; the measuring electrode, installed on the lower part of the shielded enclosure, obtains the modulated electric field signal and interference signal through the shielding opening.

[0021] Preferably, the control circuit outputs a pulse signal to control the frequency of the modulation signal, and simultaneously outputs a reference signal with the same modulation frequency, which, together with the output of the differential amplifier, is sent to the lock-in amplifier for correlation narrowband filtering.

[0022] Preferably, the signals received by the reference electrode and the measuring electrode are converted into voltage signals by a first charge amplifier and a second charge amplifier.

[0023] Preferably, the differential amplifier subtracts the outputs of the first charge amplifier and the second charge amplifier to remove common-mode interference signals; the differential signal is used as input, and the control signal of the control circuit is used as a reference signal to perform correlation narrowband filtering in the lock-in amplifier to filter out various broadband noise signals with different modulation frequencies; then, after A / D conversion, the electric field signal is sent to the computer, and the magnitude of the measured electric field is measured; the computer obtains the modulated electric field signal by controlling the electronically controlled electric field modulator through the control circuit.

[0024] Preferably, the reference electrode and the measuring electrode are planar electrodes of the same material, area, and structure.

[0025] Preferably, the opening of the shielded shell faces the electronically controlled electric field modulator. A measuring electrode is arranged inside the opening of the shielded shell, and a reference electrode is arranged in the closed area of ​​the shielded shell. Seawater flows inside the closed shell, but the measured electric field signal cannot reach the closed shell. The measuring electrode simultaneously receives the modulated electric field and the common-mode interference signal, while the reference electrode can only receive the common-mode interference signal. The differential action between the two suppresses common-mode interference and drift, and the lock-in amplifier suppresses broadband noise and interference signals at the unmodulated frequency.

[0026] Preferably, the differential circuit adopts an instrumentation amplifier circuit, wherein the operational amplifier power supply in the instrumentation amplifier is connected to the positive and negative power supplies respectively, the inverting input of the instrumentation amplifier is connected to the second charge amplifier, and the non-inverting input of the instrumentation amplifier is connected to the first charge amplifier.

[0027] Preferably, the electronically controlled electric field modulator adopts the structure of a controllable electromagnetic lens. The switch controls the conduction of the coil current, controls the focal length of the electromagnetic lens, and controls the magnitude of the electric field being measured in the seawater reaching the electrode being measured, thereby achieving modulation of the electric field being measured.

[0028] Preferably, the electronically controlled electric field modulator adopts a multi-stage structure. When multiple switches are turned on, the multi-stage electric field modulator amplifies the deviation between positive and negative charges, and the charges generated by the seawater electric field are absorbed by each electrode and cannot reach the measuring plate. When the switches are turned off, the electric field smoothly reaches the measuring electrode, realizing electronically controlled electric field modulation.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The system of the present invention uses electric field modulation to realize the measurement of electric fields from static ocean to higher frequency. Electric field modulation transforms a certain bandwidth frequency electric field signal into a fixed high frequency AC modulated electric field, which greatly reduces the influence of electric field drift and low frequency noise, improves the measurement resolution, and greatly widens the measurement bandwidth.

[0031] 2. The system of this invention can not only measure the static electric field of underwater mineral deposits and underwater plants, but also measure the underwater electric field of faster-moving underwater objects such as ships, ocean currents and the movement of aquatic fish, greatly expanding the application range of underwater electric field measurement.

[0032] 3. Because the system of the present invention adopts an electronic control method, it also provides the possibility of array control. If an array-based electronically controlled modulation seawater electric field measurement system is adopted, phased array electric field measurement can be realized, greatly expanding the measurement range and area. Attached Figure Description

[0033] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0034] Figure 1 This is a general block diagram illustrating an electrical signal-controlled broadband measurement system for ocean electric fields involved in this invention.

[0035] Figure 2 This is a schematic diagram of the structure of an electrically controlled electric field modulator provided in an embodiment of the present invention;

[0036] Figure 3 (a) and (b) in the figure are typical charge amplifier schematic diagrams of the measuring electrode and the reference electrode provided in the embodiments of the present invention, respectively;

[0037] Figure 4 A typical instrument amplifier circuit schematic diagram provided for embodiments of the present invention;

[0038] Figure 5 A block diagram of a switch-mixer narrowband filter lock-in amplifier provided for embodiments of the present invention;

[0039] Figure 6 A schematic diagram of an electrically controlled electric field modulator using a controllable electromagnetic lens provided in an embodiment of the present invention;

[0040] Figure 7 This is a schematic diagram of a multi-stage electrically controlled electric field modulator provided in an embodiment of the present invention. Detailed Implementation

[0041] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0042] Example 1

[0043] This invention provides a long-distance broadband measurement system for ocean electric fields controlled by electrical signals. An electrically controlled electric field modulator 103 is installed in front of a measuring electrode 107. The electric field distribution in seawater is controlled by a switch, so that the measured electric field 101 in the seawater is modulated into a modulated electric field 102 by the electrically controlled electric field modulator 103. The measuring electrode 107 and the reference electrode 106 are planar electrodes of the same material, area, and structure. The modulated electric field 102 signal is obtained on the measuring electrode 107, and its modulation frequency is the control frequency of the control circuit 115. The reference electrode 106 can obtain common-mode interference signals from the seawater environment but does not receive signals from the measured electric field 101 or the modulated electric field 102. The measuring electrode 107 and the reference electrode 106... The signal 6 is converted into a voltage signal by the first charge amplifier 108 and the second charge amplifier 109, which respectively convert the received modulated electric field 102 signal and the common-mode interference signal. The differential amplifier 110 subtracts the outputs of the two charge amplifiers to remove the common-mode interference signal. Using the differential signal as input and the control signal of the control circuit 115 as the reference signal 112, correlation narrowband filtering is performed in the lock-in amplifier to filter out various broadband noise signals with different modulation frequencies. Then, the demodulated electric field signal is sent to the computer 114 through the A / D converter 113, and the magnitude of the measured electric field 101 is measured. The computer 114 controls the electronically controlled electric field modulator 103 through the control circuit 115 to obtain the modulated electric field 102 signal. The principle structure of the entire device is as follows. Figure 1 As shown, this measurement method directly measures the electric field in seawater by modulating the electric field 101 under electrical control. This avoids the drift and low resolution problems associated with the traditional natural potential method, which indirectly uses two measuring probes to measure the voltage division in the seawater resistance. Furthermore, the high frequency and stability of the electrical modulation are unmatched by traditional mechanical modulation, significantly improving the system's resolution and frequency measurement range. This system can measure not only static underwater electric fields, such as those observed in underwater mining and underwater plant activity, but also rapidly changing underwater electric fields, such as those generated by underwater ships, ocean currents, and the movement of aquatic fish. The use of electrical control in system construction also makes it possible to develop array-based electrical modulation seawater electric field measurement systems. If phased array electric field measurement is employed, the measurement range and area can be significantly expanded.

[0044] Example 2

[0045] The electrically controlled electric field modulator is activated by a control circuit that turns on switches 1 and 2, applying positive and negative voltages to electrodes 1 and 2 respectively. Figure 2As shown, positive charges in seawater move simultaneously under the influence of an electric field, moving towards the lower right of electrode 2, while negative charges move towards the upper right of electrode 1. Most charges are captured by the grounded metal aperture conductor, and a small portion passes through the through-hole. Due to their rightward oblique movement, they reach the grounded shielding shell but cannot pass through the opening of the shielding shell, thus completely blocking the measured electric field, resulting in no measured electric field signal on the measured electrode. When switches 1 and 2 are turned off, there is no voltage on electrodes 1 and 2, and both positive and negative charges move horizontally to the right. The measured electric field can then pass smoothly through the through-hole of the metal aperture and through the opening of the shielding shell, reaching the measured electrode. By switching the switches on and off, the measured electric field is modulated, allowing a modulated electric field signal to be obtained on the measuring electrode. Here, the switch control signals are simultaneously turned on and off. The modulation frequency of the electronically controlled modulator is determined by the switching frequency, and the highest modulation frequency is determined by the time constant corresponding to the equivalent capacitance of the electrode and the equivalent resistance from seawater to the ground. The lower the time constant, the faster the electrode charges, and the higher the highest modulation frequency. The electronically controlled modulation frequency can be increased by more than five orders of magnitude compared to the mechanical modulation frequency.

[0046] Both the measuring and reference electrodes are made of stable inert silver or carbon fiber electrode materials, and their dimensions, structure, and area are identical. The electrode area is minimized while ensuring high sensitivity, resulting in a low time constant between the electrode and seawater, allowing for high modulation frequencies at higher control frequencies. The electrode material is not easily polarized, exhibits good reversibility, has a low temperature coefficient, and is durable in seawater. The two electrodes are placed... Figure 2 In a shielding structure with the same volume of isolation space, the reference electrode installed on the upper part of the shielding shell, which is almost completely isolated from the space, can only obtain the common-mode interference signal from seawater; the measuring electrode installed on the lower part of the shielding shell can obtain the modulated electric field signal and the interference signal through the shielding opening.

[0047] The measuring and reference electrodes capture charge signals reflecting the effects of the electric field and interference on the plates. These signals must first be converted into voltage signals using a charge amplifier before being processed by subsequent circuitry. A typical charge amplifier is... Figure 3 As shown. The measuring electrode and the reference electrode are equivalent to a current source connected in parallel with a capacitor and a resistor. The equivalent current source of the measuring electrode is simultaneously affected by the measured electric field and common-mode interference, as shown. Figure 3 In (a); the equivalent current source of the reference electrode is only affected by common-mode interference, such as Figure 3 (b) in the middle.

[0048] To improve measurement accuracy, the differential circuit employs a typical instrument amplification circuit, such as... Figure 4As shown, in the instrumentation amplifier, the operational amplifier power supply is connected to both the positive and negative power supplies. The inverting input of the instrumentation amplifier is connected to the output of the second charge amplifier; the non-inverting input of the instrumentation amplifier is connected to the output of the first charge amplifier. The high input impedance of the instrumentation amplifier avoids the influence of the amplifier's input impedance on the charge amplifier. The differential amplifier can subtract the common-mode signal, retain the modulated electric field signal, reduce the influence of interference, and improve the signal-to-noise ratio of the measured electric field signal.

[0049] To reduce the impact of various noise signals in the ocean on measurement resolution, a lock-in amplifier with switching mixer and narrowband filtering is used to further improve the signal-to-weight ratio, such as... Figure 5 As shown, this lock-in amplifier has low power consumption. The control circuit generates a square wave reference signal with the same frequency as the modulation signal while simultaneously generating the modulation signal. The modulation signal, after passing through a charge amplifier and a differential amplifier, is added to the input of the lock-in amplifier to the measured signal terminal. During the positive half-cycle of the measured signal, the reference signal controls switches 1 and 2 to connect to their upper contacts; during the negative half-cycle, the reference signal controls switches 1 and 2 to connect to their lower contacts. At this time, the measured signal is inverted and input to the lower contacts of the two switches. The two switches then perform a mixing function between the measured signal and the reference signal. After passing through two low-pass filters, the DC component is retained, and higher harmonics are filtered out. Because the reference signal and the measured signal are difficult to maintain a strict phase relationship after multi-stage processing by the measurement system, a two-way quadrature signal processing circuit is designed, and the results of the two quadrature signals are calculated by taking the square root of the sum of their squares. In this case, the output is not affected by the phase of the reference signal. In this way, as long as the modulation signal frequency is the same as the reference signal frequency, the amplitude of the measured signal can be accurately measured, and interference from other frequencies is filtered out, achieving very narrow bandpass filtering. The measured value is then sent to the computer via A / D conversion. At this point, the circuit output value is 0.6366 times the amplitude of the measured electric field signal. By dividing this coefficient by 0.6366 using the computer, the magnitude of the measured electric field signal amplitude can be obtained.

[0050] The control circuit generates square wave signals to control the switching of the electronically controlled electric field modulator and generates a reference signal for the lock-in amplifier, such as... Figure 1 As shown, the computer inputs a control signal, which, through the control circuit, generates two square wave signals of the same frequency with a certain driving power. These signals drive the switch of the electrically controlled electric field modulator to turn on and off, and also drive the mixer switch of the lock-in amplifier, thus realizing the measurement of the ocean electric field by electrically controlled electric field modulation.

[0051] Example 3

[0052] The electrically controlled electric field modulator in Example 2 is constructed using a controllable electromagnetic lens structure, such as... Figure 6As shown. When the switch controls the coil current to conduct, it controls the curvature of the equipotential lines, changing the focal length of the electromagnetic lens and controlling the position and magnitude of the electric field being measured in the seawater reaching the electrode being measured; when the switch controls the coil current to turn off, it controls the disappearance of the magnetic field, allowing the charge to propagate in a straight line. This achieves modulation of the measured electric field, improving measurement stability, resolution, and frequency range.

[0053] Example 4

[0054] The electrically controlled electric field modulator in Example 2 adopts a multi-stage structure, such as... Figure 7 As shown, when multiple switches are turned on, the deviation between positive and negative charges is amplified by a multi-stage electric field modulator. The charges generated by the seawater electric field are absorbed by each electrode and cannot reach the measuring plate. When the switches are turned off, the electric field can reach the measuring electrode smoothly, realizing electronically controlled electric field modulation.

[0055] In the description of this application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0056] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A long-distance broadband measurement system for ocean electric fields controlled by electrical signals, characterized in that, include: The components include an electrically controlled electric field modulator (103), a shielded enclosure (104), a reference electrode (106), a measuring electrode (107), a first charge amplifier (108), a second charge amplifier (109), a differential amplifier (110), a lock-in amplifier (111), an A / D converter (113), a computer (114), and a control circuit (115). The electrically controlled electric field modulator (103) is installed at the front end of the measuring electrode (107); The shielding shell (104) is connected to the ground (105); The reference electrode (106) and the measuring electrode (107) are respectively fixed inside the shielding shell (104) and do not contact the shielding shell (104); The reference electrode (106) is connected to the first charge amplifier (108); The measuring electrode (107) is connected to the second charge amplifier (109); The first charge amplifier (108) and the second charge amplifier (109) are both connected to the differential amplifier (110); The differential amplifier (110), lock-in amplifier (111), A / D converter (113), computer (114) and control circuit (115) are connected in sequence; The first charge amplifier (108), the second charge amplifier (109), the differential amplifier (110), the lock-in amplifier (111), the A / D converter (113), and the computer (114) constitute a sensor signal acquisition / processor; By controlling the potential of the electric field structure distributed in the seawater by a switch, the electric field to be measured (101) in the seawater is modulated into a modulated electric field (102) by an electronically controlled electric field modulator (103).

2. The long-distance broadband measurement system for ocean electric fields controlled by electrical signals according to claim 1, characterized in that, The electric field modulator (103) controls the switch 1 and switch 2 to open through the control circuit (115), and applies positive and negative voltages to the plates of electrode 1 and electrode 2 respectively. The positive charge in the seawater moves in the same way as it is subjected to the electric field force, and moves to the lower right of electrode 2, while the negative charge moves to the upper right of electrode 1. When switches 1 and 2 are turned off, there is no voltage on electrodes 1 and 2. Both positive and negative charges move horizontally to the right. The electric field to be measured passes smoothly through the through hole of the metal aperture and through the opening of the shielding shell (104) to reach the measuring electrode. By turning the switches on and off, the electric field to be measured is modulated, so that the measuring electrode can obtain the modulated electric field signal. The modulation frequency of the electronically controlled electric field modulator (103) is determined by the switching frequency. The highest modulation frequency is determined by the time constant corresponding to the equivalent capacitance of the electrode and the equivalent resistance from seawater to the ground. The lower the time constant, the faster the electrode charges and the higher the highest modulation frequency. Electrode 1 and electrode 2 are placed in a shielding structure with the same volume of isolation space; The reference electrode (106), which is installed on the upper part of the shielded shell (104) and almost completely isolated from the space, can only obtain the common mode interference signal in the seawater; the measuring electrode (107), which is installed on the lower part of the shielded shell (104), obtains the modulated electric field signal and the interference signal through the shielding opening.

3. The long-distance broadband measurement system for ocean electric fields controlled by electrical signals according to claim 1, characterized in that, The control circuit (115) outputs a pulse signal to control the frequency of the modulation signal, and at the same time outputs a reference signal (112) with the same modulation frequency, which is sent together with the output of the differential amplifier (110) to the lock-in amplifier (111) for correlation narrowband filtering.

4. The long-distance broadband measurement system for ocean electric fields controlled by electrical signals according to claim 1, characterized in that, The signals received by the reference electrode (106) and the measuring electrode (107) are converted into voltage signals by the first charge amplifier (108) and the second charge amplifier (109), which are the received common-mode interference signal and the modulated electric field (102) signal.

5. The long-distance broadband measurement system for ocean electric fields controlled by electrical signals according to claim 1, characterized in that, The differential amplifier (110) subtracts the outputs of the first charge amplifier (108) and the second charge amplifier (109) to remove common-mode interference signals; the differential signal is used as input, and the control signal of the control circuit (115) is used as the reference signal (112). Correlation narrowband filtering is performed in the lock-in amplifier (111) to filter out various broadband noise signals that are different from the modulation frequency, and demodulation is performed; then the demodulated electric field signal is sent to the computer (114) through the A / D converter (113) and the magnitude of the measured electric field (101) is measured; the computer (114) controls the electronically controlled electric field modulator (103) through the control circuit (115) to obtain the modulated electric field (102) signal.

6. The long-distance broadband measurement system for ocean electric fields controlled by electrical signals according to claim 1, characterized in that, The reference electrode (106) and the measuring electrode (107) are planar electrodes of the same material, area and structure.

7. The long-distance broadband measurement system for ocean electric fields controlled by electrical signals according to claim 1, characterized in that, The opening of the shielded shell (104) faces the electronically controlled electric field modulator (103). A measuring electrode (107) is arranged inside the opening of the shielded shell (104), and a reference electrode (106) is arranged in the closed area of ​​the shielded shell (104). Seawater flows inside the closed shell, but the measured electric field (101) signal cannot reach the closed shell. The measuring electrode (107) simultaneously receives the modulated electric field (102) and the common-mode interference signal. The reference electrode (106) can only receive the common-mode interference signal. The two differentially suppress common-mode interference and drift. The lock-in amplifier (111) suppresses the unmodulated broadband signal.

8. The long-distance broadband measurement system for ocean electric fields controlled by electrical signals according to claim 1, characterized in that, The differential circuit uses an instrumentation amplifier circuit. The operational amplifier power supply in the instrumentation amplifier circuit is connected to the positive and negative power supplies respectively. The inverting input of the instrumentation amplifier circuit is connected to the second charge amplifier (109), and the non-inverting input of the instrumentation amplifier circuit is connected to the first charge amplifier (108).

9. The long-distance broadband measurement system for ocean electric fields controlled by electrical signals according to claim 1, characterized in that, The electric field modulator (103) adopts the structure of a controllable electromagnetic lens. The switch controls the current of the control coil to conduct, controls the focal length of the electromagnetic lens, controls the magnitude of the electric field (101) being measured in the seawater reaching the measuring electrode, and realizes the modulation of the electric field (101) being measured.

10. The long-distance broadband measurement system for ocean electric fields controlled by electrical signals according to claim 1, characterized in that, The electric field modulator (103) adopts a multi-stage structure. When multiple switches are turned on, the positive and negative charges are aggravated by the multi-stage electric field modulator. The charges generated by the seawater electric field are absorbed by each electrode and cannot reach the measuring electrode. When the switch is turned off, the electric field reaches the measuring electrode smoothly, realizing the electric field modulation.

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