A torsion balance noise floor measurement device and method based on heterodyne interference

Abstract

The embodiment of the application discloses a kind of torsion balance background noise measuring device and method based on heterodyne interference, measuring device includes: vacuum system, is formed with the test cavity with vacuum environment;Torsion balance, in the test cavity;Heterodyne laser interferometer system, at least part is located in the test cavity, for providing outgoing laser to the torsion balance, and return forms interference signal;Data acquisition processing system, located outside the test cavity, the interference signal is collected, and according to the interference signal collected, obtains torsion balance background noise.The high integration of the present application is set based on vacuum mode, applies heterodyne interference technology to torsion balance measurement, to improve the measurement accuracy of torsion balance background noise.

Description

Technical Field

[0001] This invention relates to the field of weak force measurement technology, specifically to a torsion balance background noise measurement device and method based on heterodyne interferometry. Background Technology

[0002] For space-based gravitational wave detection, it is necessary to maintain the inertial reference device—the verification mass—in a sufficiently high-precision free-falling motion state, and its combined perturbation acceleration noise level typically needs to be maintained at 10. -15 m / s 2 / Hz 1 / 2 At the order of magnitude. To achieve this, satellites typically carry a complex drag-free control system, with inertial sensors as the core component, using capacitive sensors to precisely measure and control the relative position between the test mass and the satellite. Although gravitational wave detectors ultimately operate in a stable space environment, their complex system structure and noise model necessitate corresponding experimental verification on the ground.

[0003] Torsion balances, as a classic weak force measurement device, are widely used in space technology fields such as space gravitational wave detection and Earth's gravity field measurement, as well as in precision measurement fields such as gravity constant G and high-power laser pressure measurement. Furthermore, with the expansion of measurement fields, increasing demands, and the need for higher measurement accuracy, the device is constantly being developed and improved. Due to its unique structural characteristics, the torsion balance can balance the influence of Earth's gravity in the vertical direction while achieving quasi-free fall motion in the horizontal direction, making it the preferred choice for inertial sensor testing platforms in current space gravitational wave detection devices.

[0004] For torsion balances, the background noise level is the fundamental factor directly determining their accuracy in weak force measurements. The factors influencing this are mainly twofold: thermal noise and readout noise. Thermal noise, limited by the torsion balance's physical structure, cannot be suppressed, making readout noise the key factor affecting the background noise. Different readout systems result in significant differences in the measured noise levels.

[0005] Currently, the testing of the background noise of torsion balances mainly uses commercial autocollimators to read the torsional angle changes of inertial components for testing and evaluation. However, in practical use, the measurement accuracy often cannot be effectively guaranteed. This is because: firstly, commercial autocollimators need to be placed outside the vacuum system, making systematic integration impossible, and their measurement is directly affected by the external environment and the optical window, resulting in measurement errors. Secondly, the measurement accuracy of commercial autocollimators is limited, and the readout accuracy cannot be further improved. Summary of the Invention

[0006] Therefore, embodiments of the present invention provide a torsion balance background noise measurement device and method based on heterodyne interferometry. Based on a highly integrated setup under vacuum, the torsion balance is combined with heterodyne interferometry to improve the accuracy of torsion balance background noise measurement.

[0007] To achieve the above objectives, the embodiments of the present invention provide the following technical solutions:

[0008] In one aspect of the present invention, a torsion balance background noise measurement device based on heterodyne interferometry is provided, comprising:

[0009] A vacuum system that forms a test chamber with a vacuum environment;

[0010] A torsion balance is located in the test chamber;

[0011] A heterodyne laser interferometer system, at least partially located in the test cavity, is used to provide an outgoing laser to the torsion balance and generate an interference signal;

[0012] The data acquisition and processing system, located outside the test chamber, acquires the interference signal and obtains the torsion balance background noise based on the acquired interference signal.

[0013] In a preferred embodiment of the present invention, the torsion balance includes a mounting bracket, an adjustment mechanism disposed on the mounting bracket, a suspension assembly connected to the adjustment mechanism, and an inspection mass located at one end of the suspension assembly away from the adjustment mechanism; wherein...

[0014] The adjustment mechanism can drive the suspension assembly to move in space, and / or drive the suspension assembly to rotate.

[0015] As a preferred embodiment of the present invention, the mounting bracket includes a base plate, at least one support rod vertically disposed on the base plate, and a top plate located at one end of the support rod away from the base plate;

[0016] The suspension assembly includes a first fixed post, a suspension wire, a second fixed post, and a balancing structure sequentially connected from the adjustment mechanism. The balancing structure is used to adjust the balance between the suspension wire and the inspection mass, so that the extension line of the suspension wire along the axial direction passes through the center of gravity of the inspection mass.

[0017] In a preferred embodiment of the present invention, the balancing structure includes at least a connecting frame connected to the second fixed column, a support rod mounted on the connecting frame, and a counterweight disposed on the support rod; wherein...

[0018] The inspection quality is connected to the connecting frame;

[0019] The counterweight is movably mounted on the support rod;

[0020] The axis of the support rod forms an angle with the axis of the suspension wire.

[0021] In a preferred embodiment of the present invention, the axis of the support rod is arranged perpendicular to the axis of the suspension wire.

[0022] In a preferred embodiment of the present invention, the inspection mass is formed into a cubic structure, and the surface of the inspection mass is formed into a light-reflecting surface.

[0023] In a preferred embodiment of the present invention, a reflective film is formed on the surface deposited for quality inspection.

[0024] As a preferred embodiment of the present invention, the heterodyne laser interferometer system includes a laser, an fiber beam splitter, an acousto-optic modulator, an interferometer platform, and a four-quadrant detector; wherein...

[0025] The laser is a frequency-stabilized light source used to emit outgoing laser light;

[0026] The fiber optic beam splitter is connected to the laser via a fiber optic interface and splits the emitted laser beam into multiple beams.

[0027] The acousto-optic modulator receives the multiple laser beams after they have been split, and modulates the frequency difference of the received laser beams according to a preset value to form multiple laser beams with frequency differences.

[0028] The interferometer platform uses laser light, which forms a frequency difference, as the input signal. After optical processing, the laser light forms an interference signal in the four-quadrant detector.

[0029] As a preferred embodiment of the present invention, the data acquisition and processing system includes a phase meter for acquiring interference signals and a data processor for processing the acquired interference signals.

[0030] As a preferred embodiment of the present invention, the vacuum system includes a vacuum tank having the test chamber formed therein, a vibration isolation platform located in the test chamber, and an interface assembly located on the vacuum tank.

[0031] In a preferred embodiment of the present invention, the vacuum level of the vacuum environment is not less than 10. -2 Pa.

[0032] In another aspect of the present invention, a method for measuring the background noise of a torsion balance based on heterodyne interferometry is also provided, employing the aforementioned torsion balance background noise measurement device based on heterodyne interferometry. The method for measuring the background noise of a torsion balance based on heterodyne interferometry includes:

[0033] S100. The torsion balance, heterodyne laser interferometer system and data acquisition and processing system are electrically installed inside or outside the vacuum system.

[0034] S200. Adjust the torsion balance and heterodyne laser interferometer system to establish a position-adaptive optical path between the torsion balance and heterodyne laser interferometer system.

[0035] S300, Adjust the vacuum system to the preset vacuum level, start the heterodyne laser interferometer system, and generate a dynamic interference signal;

[0036] S400: Acquire dynamic interference signals and analyze them to obtain the background noise of the torsion balance.

[0037] As a preferred embodiment of the present invention, in step S400, the analysis process involves analyzing the time-domain signal of the torsion balance angle change based on the collected interference signal, converting it into a noise power spectrum through Fourier transform, thereby obtaining the background noise level of the torsion balance.

[0038] In a preferred embodiment of the present invention, the background noise level of the torsion balance is positively correlated with the change in the interference signal of the heterodyne laser interferometer system caused by the torsion balance. Specifically, this means that the background noise level of the torsion balance is positively correlated with the change in the rotation angle around the suspension wire axis caused by the surrounding environment affecting the inspection quality.

[0039] As a preferred embodiment of the present invention, the relationship between the change in rotation angle of the torsion balance (since the force-bearing body in the torsion balance is the inspection mass, it mainly refers to the inspection mass here) under the action of an external force and the torque of the external force is shown in equation (I):

[0040] in,

[0041] t is a time variable. φ'(t) and φ(t) are the derivatives of the rotation angle of the torsion balance with time, respectively. T(t) is the torque of the external force acting on the torsion balance. I is the moment of inertia of the torsion balance relative to the Z-axis. ξ is the energy dissipation coefficient. Γ is the torsional stiffness of the suspension wire.

[0042] The embodiments of the present invention have the following advantages:

[0043] This invention combines heterodyne interferometry with torsion balance background noise measurement to construct a highly integrated, compact measurement system under vacuum conditions, improving measurement accuracy. Furthermore, based on measurements in a vacuum environment, higher resolution calibration can be achieved, thereby further improving measurement sensitivity. This lays the foundation for the calibration and noise assessment of inertial sensors related to future space gravitational wave detection. Attached Figure Description

[0044] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely exemplary, and those skilled in the art can derive other embodiments based on the provided drawings without creative effort.

[0045] The structures, proportions, sizes, etc. illustrated in this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed herein, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0046] Figure 1 This is a schematic diagram of the structure of the torsion balance background noise measurement device based on heterodyne interferometry provided in an embodiment of the present invention;

[0047] Figure 2 This is a schematic diagram of the structure of a torsion balance provided in an embodiment of the present invention;

[0048] Figure 3 Thermal noise curve of a torsion balance provided in an embodiment of the present invention;

[0049] Figure 4 This is a schematic diagram of the heterodyne laser interferometer system provided in an embodiment of the present invention;

[0050] Figure 5 The sensitivity curve of the interferometer provided in the embodiment of the present invention;

[0051] Figure 6 A flowchart of a method for measuring the background noise of a torsion balance based on heterodyne interferometry, provided in an embodiment of the present invention.

[0052] In the picture:

[0053] 1- Torsion balance; 2- Heterodyne laser interferometer system; 3- Data acquisition and processing system; 4- Vacuum system; 5- Optical platform;

[0054] 11-Base plate; 12-Support rod; 13-Top plate; 14-Adjusting mechanism; 15-Suspension wire; 16-First fixed column; 17-Second fixed column; 18-Balancing structure; 19-Inspection quality;

[0055] 181-Connecting frame; 182-Support rod; 183-Counterweight;

[0056] 21-Laser; 22-Fiber beam splitter; 23-Acousto-optic modulator; 24-Interferometer platform; 25-Four-quadrant detector; 26-Interferometer platform base;

[0057] 31-Phase meter; 32-Data processor;

[0058] 41-Vacuum tank; 42-Vibration isolation platform; 43-Interface assembly. Detailed Implementation

[0059] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0060] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0061] like Figure 1 As shown, the present invention provides a torsion balance background noise measurement device based on heterodyne interferometry, specifically including: a torsion balance 1, a heterodyne laser interferometer system 2, a data acquisition and processing system 3, a vacuum system 4, and an optical platform 5. The torsion balance 1, as the system under test and the measurement unit, is installed together with the heterodyne laser interferometer system 2 on the vibration isolation platform 42 inside the vacuum system 4, and the data acquisition and processing system 3 is placed on the optical platform 5 outside the vacuum system 4.

[0062] Furthermore, the vacuum system 4 can maintain a vacuum level of 10. -3 The high vacuum state of Pa can reduce the influence of environmental factors such as temperature, magnetic field and gas molecule damping to a certain extent, and further reduce the influence of ground noise through the vibration isolation platform 42, which is conducive to improving the measurement accuracy of the background noise of the torsion balance 1.

[0063] like Figure 2 The diagram shown is a structural schematic of a specific torsion scale 1 in this invention, which specifically includes: a base plate 11, a support rod 12, a top plate 13, an adjustment mechanism 14, a suspension wire 15, a first fixed column 16, a second fixed column 17, a balancing structure 18, and a quality inspection unit 19.

[0064] Furthermore, the base plate 11, support rod 12, and top plate 13 constitute the basic structural framework of the torsion balance 1, possessing sufficient rigidity to maintain system stability. The base plate 11 serves as the support seat for the torsion balance 1, located at the bottom. The support rod 12, as a vertical support structure, connects to the base plate 11 at its bottom and to the top plate 13 at its top. The number of support rods 12 can be adjusted according to actual needs; for example, 3-4 rods can be arranged at equal intervals along the circumferential direction. The adjustment mechanism 14 is fixed above the top plate 13 and is configured for four-dimensional adjustment. This facilitates precise alignment with the heterodyne laser interferometer system 2 and unloads residual torsional stress in the suspension wire 15, allowing the torsion balance 1 to reach equilibrium more quickly. The balancing structure 18 corrects the tilt of the inspection mass 19, connected to the connecting frame 181, during installation and use by adjusting the counterweights 183 on both sides of the support rod 182. The upper end of the connecting frame 181 is connected to the second fixed column 17, and the lower end is connected to the inspection quality 19. The support rod 182 is fixed to the connecting frame 181 by threads. The counterweight 183 is installed on the support rod 182. By adjusting the position of the counterweight 183, the slight tilt of the inspection quality 19 itself relative to the vertical direction is adjusted to ensure that the downward extension line of the suspension wire 15 passes through its center of gravity.

[0065] Furthermore, the first fixed post 16 is installed inside the adjusting mechanism 14 and glued to the top of the suspension wire 15; the second fixed post 17 is glued to the bottom of the suspension wire 14 and connected to the top of the balancing structure 18. The connection between the first fixed post 16 and the adjusting mechanism 14, and the connection between the second fixed post 17 and the balancing structure 18, both use nylon screws and washers to maintain electrical insulation between them. The glued connections between the first fixed post 16, the second fixed post 17, and the suspension wire 15 are conductive. The adjusting mechanism 14 has the ability to translate in three dimensions (X, Y, Z) and rotate one dimension around the Z-axis. This allows it to drive the first fixed post 16, and consequently, the inspection mass 19 to move or rotate along the three dimensions (X, Y, Z) (i.e., up and down, left and right, front and back). It should be noted that the inspection mass 19 here is a block structure with a certain mass, which is the inertial force-bearing structure in the torsion balance.

[0066] Meanwhile, to further expand the functionality of the torsion balance 1, an electrostatic control module can be further incorporated therein. Conductive bonding is introduced into the connection between the first fixed post 16 and the second fixed post 17 and the suspension wire 15, thereby introducing an electrical excitation signal to the inspection mass 19. Furthermore, while serving as the inertial element of the entire torsion balance 1, the inspection mass 19 also needs to function as an end-face reflector for the heterodyne laser interferometer system 2 and the data acquisition and processing system 3, i.e., the end-face reflecting surface of the emitted laser. Therefore, the surface of the inspection mass 19 also needs to be formed as an optical mirror, i.e., a light-reflecting surface. This light-reflecting surface can be formed using methods conventionally available to those skilled in the art; for example, a corresponding laser-reflecting film can be deposited on its surface.

[0067] Based on the above structural design, the torsion balance 1 itself has a low thermal noise level, which enables the entire measuring device to obtain the background noise level of the torsion balance 1 with high accuracy, reducing the impact of thermal noise level on the overall noise level of the torsion balance 1, and making it exhibit high sensitivity in weak force measurement.

[0068] like Figure 3 The figure shown is a thermal noise curve of the torsion balance 1 of the present invention. Based on the thermal noise constraint formula for the torsion balance 1 shown below, the structural components of the torsion balance 1 are designed to reduce this value. In a specific embodiment, the inspection mass 19 is made of 6061 aluminum alloy, designed as a cubic structure with a side length of 50mm and a mass of 250g; the suspension wire is made of pure tungsten wire with a diameter of 25 micrometers, a length of 1 meter, and a purity of 99.5%, and undergoes appropriate heat treatment to achieve a quality factor of 2000. Based on the calculation formula shown below, the following can be obtained... Figure 3 The thermal noise curve of the torsion balance 1 in this example is shown.

[0069]

[0070] Among them, T th (ω) represents the torque corresponding to the thermal noise of the torsion balance, K B Γ is Boltzmann constant, T is operating temperature, Γ is suspension stiffness, ω is angular frequency, and Q is suspension quality factor.

[0071] Furthermore, such as Figure 4 The diagram shows a schematic representation of the heterodyne laser interferometer system 2 provided in an embodiment of the present invention. Specifically, it includes: a laser 21, an optical fiber beam splitter 22, an acousto-optic modulator 23, an interferometer platform 24, a four-quadrant detector 25, and an interferometer platform base 26. The core equipment used for measurement is located in a vacuum system 4. For example, at least the acousto-optic modulator 23, the interferometer platform 24, and the four-quadrant detector 25, which are involved in laser modulation and interference processing, are located in the vacuum system 4, so that the entire modulation and interference process of the laser can be performed in a vacuum environment.

[0072] The laser 21 is a frequency-stabilized light source used to emit laser light and is equipped with an FC / APC standard fiber optic interface. The fiber optic beam splitter 22 is connected to the laser 21 via the fiber optic interface, splitting the laser emitted by the laser 21 into two beams with a 1:1 power ratio. The acousto-optic modulator 23 receives the two laser beams input from the fiber optic beam splitter 22 via a standard interface and adjusts the frequency difference between the two beams. The interferometer platform 24 takes the two laser signals with a frequency difference modulated by the acousto-optic modulator 23 as input, guides them through optical elements, and ultimately forms an interference signal at the center of the four-quadrant detector 25. The four-quadrant detector 25 detects the position and intensity changes of the interference light and converts them into electrical signals, outputting them to the data acquisition and processing system 3. The interferometer base 26 supports the interferometer platform 24 under vertical placement conditions and is fixed to the vibration isolation platform 42.

[0073] The data acquisition and processing system 3 includes a phase meter 31 and a data processor 32 (specifically, a data processing computer). The phase meter 31 receives the electrical signals output by the four-quadrant detector 25, acquires the phase information therein, and outputs it to the data processor 32. The data processor 32 performs corresponding calculations on the phase information acquired by the phase meter 31, converting it into time-domain information of angle change, and can also convert it into corresponding angle-change spectrum information through calculations.

[0074] The vacuum system 4 includes a vacuum tank 41, a vibration isolation platform 42, and an interface assembly 43. The vacuum tank 41 provides a vacuum environment with a diameter greater than 2m and a height greater than 2m, achieving a vacuum level of 10⁻³ Pa. The vacuum vibration isolation platform 42 isolates high-frequency ground pulsation noise and provides a mounting surface with a diameter greater than 1.5m. The interface assembly 43 (specifically a vacuum flange) is a standard component, providing at least five sets of SMA interfaces, fiber optic interfaces, and 15-pin connectors. The laser 21 is connected to the vacuum tank 41 via the vacuum flange and is linked to the acousto-optic modulator 23, which is fixed to the vibration isolation platform 42 inside the tank. The phase meter 31 and the data processing computer 32 are both placed on an optical platform 5 outside the vacuum tank 41. Data transmission and power supply for devices inside the tank (including the four-quadrant detector 25) are connected to external equipment via the vacuum flange.

[0075] Based on the above technical solution, the present invention constructs a heterodyne laser interferometer system 2 based on heterodyne interference light readout, which can achieve higher measurement accuracy than the traditional autocollimator. At the same time, its structure is simple, not limited by the structure of the torsion balance 1, can work under vacuum conditions, and is easy to integrate with other devices.

[0076] like Figure 5The figure shown is a noise calibration sensitivity curve of the interferometer platform 24 in this embodiment of the invention. Since the interferometer platform 24 itself also has a certain measurement accuracy, it needs to be calibrated. The interferometer platform 24, as a measuring tool, is physically independent of the platform under test, and therefore can be calibrated separately. In a vacuum environment, the outgoing light is struck by a stable, fixed reflector and returns, interfering with the local optical path. Phase data is collected by the phase meter 31, processed by a data processing computer into angle change information, and finally the background noise data of the interferometer platform 24 is obtained and plotted as shown. Figure 5 The sensitivity curve shown.

[0077] like Figure 6 The diagram shows a flowchart of a measurement method provided in an embodiment of the present invention, which specifically includes:

[0078] S101. Place the torsion balance 1 and the heterodyne laser interferometer system 2 on the vibration isolation platform 42 of the vacuum system 4, and fasten them together with screws.

[0079] S102, laser 21, and data acquisition and processing system 3 are placed on optical platform 5 outside vacuum tank 41. Laser signals, electrical signals, and data signals are introduced into vacuum tank 41 and connected to heterodyne laser interferometer system 2 through interface component 43.

[0080] S103. Simultaneously, let the torsion balance 1 remain stationary in its natural motion state and reach equilibrium under air damping. Adjust the adjustment mechanism 14 and the interferometer platform base 26 so that the laser beam emitted from the interferometer platform 24 hits the center position of the inspection quality 19. At this time, the beat frequency signal of the external oscilloscope reaches its peak value and is symmetrical near the equilibrium position.

[0081] S104. With the device aligned, activate vacuum system 4 to lower the air pressure below 10. -3 Pa collects, records and processes the angle change data of the inspection quality 19 under low environmental noise through the data acquisition and processing system 3, and evaluates the background noise level of the torsion balance based on its power spectral density.

[0082] The process after the vacuum system 4 is turned on is further explained below: The vacuum system 4 provides a vacuum environment. When it starts working, the weak torsional motion generated by the background noise of the torsion balance 1 will cause a slight angle change. This angle change will affect the interference signal between the reflected light from the test quality 19 and the local optical path in the heterodyne laser interferometer system 2. This signal will generate a changing voltage signal in the four-quadrant detector 25. The electrical signal in the four-quadrant detector 25 will be acquired and analyzed by the data acquisition and processing system 3 to obtain the angle change time domain signal. The angle noise power spectral density curve will be obtained through computer software processing, thereby evaluating the background noise of the torsion balance 1.

[0083] Since the background noise is a comprehensive reflection of the torsion balance noise under the current condition, it is usually characterized by torque. Because torque causes a small angular rotation of the inspection mass 19, the magnitude of the noise torque can be determined by reading the change in the rotation angle of the inspection mass 19. The specific conversion process is as follows:

[0084] The equation of motion for the rotational motion about the Z-axis (i.e., the rotational rotation of the inspection mass 19 about the suspension wire 15 as shown in the figure) is as shown in equation (I):

[0085] in,

[0086] t is a time variable. φ'(t) and φ(t) are the derivatives of the rotation angle of the torsion scale with time, respectively; T(t) is the torque of the external force acting on the torsion scale; I is the moment of inertia of the torsion scale relative to the Z-axis; ξ is the energy dissipation coefficient; and Γ is the torsional stiffness of the suspension wire. It should be noted that the motion of the torsion scale in the above formulas is mainly based on the motion of the inspection mass 19 on the torsion scale. That is, φ'(t) and φ(t) are the derivatives of the rotation angle of the inspection mass 19 with time, respectively. T(t) is the torque of the external force acting on the inspection mass 19, and I is the moment of inertia of the inspection mass 19 relative to the Z-axis.

[0087] By transforming Equation (I) into the frequency domain using Fourier transform, the relationship between the torque acting on the torsion balance (mainly the inspection mass 19) and the rotation angle of the torsion balance (mainly the inspection mass 19) is obtained, as shown in Equation (II):

[0088] in,

[0089] ω is the angular frequency of the torsion balance, and i is the imaginary unit. T(ω) and T(ω) are the angle and torque in the frequency domain, respectively.

[0090] Equation (II) is further simplified to Equation (III):

[0091] in,

[0092] Furthermore, it should be noted that an optical path needs to be established between the torsion balance 1 and the heterodyne laser interferometer system 2 so that the emitted laser beam can effectively reach the inspection quality 19.

[0093] Through the above technical solution, the present invention applies heterodyne interferometry to the background noise test of torsion balance, which is stable and highly accurate, and is 1-3 orders of magnitude more accurate than the traditional autocollimator.

[0094] Furthermore, by integrating the torsion balance 1 and the heterodyne laser interferometer system 2 into the vacuum tank 41, they operate under the same vacuum, magnetic field, and thermal conditions, improving the relative stability between the systems and making it easier to obtain high measurement accuracy. Based on this, a modular approach is applied, physically separating each unit so that each can be tested individually before overall assembly, greatly simplifying the design and installation process.

[0095] Furthermore, based on the configuration of the vacuum system 4, this invention provides ample space for the placement of the torsion balance 1, offering favorable conditions for the addition of external noise sources such as temperature control, magnetic control, and gravitational fields. Simultaneously, a drive system can be added to drive the torsion balance's movement, thereby enabling reverse calibration of the interferometer platform 24.

[0096] In summary, the apparatus and method provided by this invention combine heterodyne interferometry with torsion balance background noise measurement to construct a compact measurement system. By placing both within a vacuum system and subjecting them to consistent environmental disturbances, higher resolution calibration can be achieved. This provides further direction for the performance calibration and noise assessment of inertial sensors related to future space gravitational wave detection.

[0097] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A torsion balance background noise measurement device based on heterodyne interferometry, characterized in that, include: Vacuum system (4) forms a test chamber with a vacuum environment; Torsion balance (1) is located in the test chamber; A heterodyne laser interferometer system (2), at least partially located in the test cavity, is used to provide an outgoing laser to the torsion balance (1) and return to form an interference signal; The data acquisition and processing system (3) is located outside the test chamber. It acquires the interference signal and obtains the background noise of the torsion balance (1) based on the acquired interference signal. The heterodyne laser interferometer system (2) includes a laser (21), an optical fiber beam splitter (22), an acousto-optic modulator (23), an interferometer platform (24), and a four-quadrant detector (25); wherein, The laser (21) is a frequency-stabilized light source used to emit outgoing laser light; The fiber beam splitter (22) is connected to the laser (21) through a fiber optic interface and splits the emitted laser beam into multiple beams; The acousto-optic modulator (23) receives the multiple laser beams after beam splitting and modulates the frequency difference of the received laser beams according to a preset value to form multiple laser beams with frequency differences. The interferometer platform (24) uses laser light, which forms a frequency difference, as the input signal. After optical processing, the laser light forms an interference signal in the four-quadrant detector (25).

2. The torsion balance background noise measurement device based on heterodyne interferometry according to claim 1, characterized in that, The torsion scale (1) includes a mounting bracket, an adjustment mechanism (14) disposed on the mounting bracket, a suspension assembly connected to the adjustment mechanism (14), and an inspection mass (19) located at the end of the suspension assembly away from the adjustment mechanism (14); wherein, The adjustment mechanism (14) can drive the suspension assembly to move in space and / or drive the suspension assembly to rotate.

3. The torsion balance background noise measurement device based on heterodyne interferometry according to claim 2, characterized in that, The mounting bracket includes a base plate (11), at least one support rod (12) vertically disposed on the base plate (11), and a top plate (13) located at one end of the support rod (12) away from the base plate (11). The suspension assembly includes a first fixed column (16), a suspension wire (15), a second fixed column (17), and a balance structure (18) connected sequentially from the adjustment mechanism (14). The balance structure (18) is used to adjust the balance between the suspension wire (15) and the inspection mass (19) so that the extension line of the suspension wire (15) along the axial direction passes through the center of gravity of the inspection mass (19).

4. The torsion balance background noise measurement device based on heterodyne interferometry according to claim 3, characterized in that, The balancing structure (18) includes at least a connecting frame (181) connected to the second fixed column (17), a support rod (182) mounted on the connecting frame (181), and a counterweight (183) disposed on the support rod (182); wherein, The inspection quality (19) is connected to the connecting frame (181); The counterweight (183) is movably mounted on the support rod (182); The axis of the support rod (182) forms an angle with the axis of the suspension wire (15).

5. The torsion balance background noise measurement device based on heterodyne interferometry according to claim 4, characterized in that, The axis of the support rod (182) is perpendicular to the axis of the suspension wire (15).

6. A torsion balance background noise measurement device based on heterodyne interferometry according to any one of claims 2-4, characterized in that, The inspection quality (19) is formed into a cubic structure, and the surface of the inspection quality (19) is formed into a light-reflecting surface.

7. The torsion balance background noise measurement device based on heterodyne interferometry according to claim 6, characterized in that, The surface of the inspection quality (19) is deposited with a reflective film.

8. A torsion balance background noise measurement device based on heterodyne interferometry according to any one of claims 1-4, characterized in that, The data acquisition and processing system (3) includes a phase meter (31) for acquiring interference signals and a data processor (32) for processing the acquired interference signals.

9. A torsion balance background noise measurement device based on heterodyne interferometry according to any one of claims 1-4, characterized in that, The vacuum system (4) includes a vacuum tank (41) with the test chamber formed therein, a vibration isolation platform (42) located in the test chamber, and an interface assembly (43) located on the vacuum tank (41).

10. A torsion balance background noise measurement device based on heterodyne interferometry according to claim 9, characterized in that, The vacuum level of the vacuum environment is not less than 10. -2 Pa level.

11. A method for measuring the background noise of a torsion balance based on heterodyne interferometry, characterized in that, The torsion balance background noise measurement device based on heterodyne interferometry according to any one of claims 1-10, wherein the torsion balance background noise measurement method based on heterodyne interferometry includes: S100. The torsion balance, heterodyne laser interferometer system and data acquisition and processing system are electrically installed inside or outside the vacuum system. S200. Adjust the torsion balance and heterodyne laser interferometer system to establish a position-adaptive optical path between the torsion balance and heterodyne laser interferometer system. S300, Adjust the vacuum system to the preset vacuum level, start the heterodyne laser interferometer system, and generate a dynamic interference signal; S400: Acquire dynamic interference signals and analyze them to obtain the background noise of the torsion balance.

12. The method for measuring the background noise of a torsion balance based on heterodyne interferometry according to claim 11, characterized in that, In step S400, the analysis process involves analyzing the time-domain signal of the torsion balance rotation angle change based on the collected interference signal, converting it into the frequency domain power spectral density through Fourier transform, thereby obtaining the background noise level of the torsion balance.

13. The method for measuring the background noise of a torsion balance based on heterodyne interferometry according to claim 12, characterized in that, The background noise level of the torsion balance is positively correlated with the change in the interference signal of the heterodyne laser interferometer system caused by the torsion balance.

14. The method for measuring the background noise of a torsion balance based on heterodyne interferometry according to claim 13, characterized in that, The relationship between the change in rotation angle of the torsion balance under the action of external force and the torque of the external force is shown in equation (I): Equation (I); where, t is a time variable. , , denoted as the derivatives of the rotation angle of the torsion balance with time, respectively; T(t) is the torque of the external force acting on the torsion balance; I is the moment of inertia of the torsion balance relative to the Z-axis; ξ is the energy dissipation coefficient; and Γ is the torsional stiffness of the suspension wire.

Images