Device and method for measuring relative gravitational acceleration

Abstract

The present invention discloses a device and method for measuring relative gravitational acceleration. The device includes a beam stabilization subsystem and a signal detection subsystem. The beam stabilization subsystem is used to emit a stable laser beam into the signal detection subsystem. The signal detection subsystem uses a four-pole structure as a magnetic field source and detects a beam containing displacement information of a suspended ball through a four-quadrant detector. The displacement of the suspended ball is detected using the principle of optical differential detection. When the gravitational acceleration changes, the position of the suspended ball also deviates from the initial equilibrium position. The measurement of the gravitational acceleration change is achieved by detecting the corresponding relationship between the displacement of the suspended ball in the direction of gravity and the gravitational acceleration. The device of the present invention can suspend a larger mass of suspended objects and can achieve higher acceleration measurement accuracy.

Description

Technical Field

[0001] The present invention relates to the field of acceleration measurement, and in particular to a device and method for measuring relative gravity acceleration. Background Art

[0002] As one of the most important basic geophysical information, the Earth's gravity field has extensive application value in the national economy and scientific research. Changes in the Earth's gravity field have important application value in modern defense, military applications, resource exploration, surveying and mapping science, and other fields. A gravimeter is a measuring instrument for determining gravitational acceleration. It is divided into absolute gravimeters and relative gravimeters. An absolute gravimeter is an instrument used to measure the gravitational acceleration value at a certain point. Relative gravity measurement is obtained by measuring the gravitational acceleration difference between a known point and a point to be measured. The basic principle of a relative gravimeter is that an elastic body deforms under the action of gravity. When the elastic force of the elastic body is balanced with gravity, the elastic body is in a certain equilibrium position. When gravity changes, the equilibrium position of the elastic body changes. By observing the change in the two equilibrium positions, the difference in gravitational acceleration between the two points can be determined.

[0003] Patent CN108873090B discloses a gravity measurement device and method based on optical levitation. The patent describes a relative gravitational acceleration measurement method: Before gravity measurement begins, a laser emits light, which, under the control of a feedback control system, levitates a suspended object to a predetermined position, designated as zero. When the gravitational acceleration at the measurement device's location changes, the suspended object deviates from zero, causing a corresponding change in the output of a three-plate capacitor bridge circuit consisting of the suspended object and upper and lower capacitor plates. A capacitance detection circuit processes the bridge output through a lock-in amplifier and an integrator, converting it into a feedback voltage that acts on the suspended object, generating a restoring force directed toward zero and returning the object's displacement to zero. Changes in the feedback voltage during this zeroing process represent changes in local gravity. This feedback voltage is sampled and recorded by a feedback control system to generate a voltage-time series that directly reflects the time-varying gravitational acceleration, thereby achieving relative gravitational acceleration measurement. The device levitates objects using the optical force generated by the laser. However, to achieve high acceleration sensitivity, optical levitation requires vacuuming to reduce the influence of air molecules. In a high vacuum, the reduced number of air molecules reduces collisions between the suspended object and air molecules, causing the suspended object to absorb laser energy in the high vacuum and be unable to dissipate heat, resulting in a decrease in the suspended object's vaporization mass. Furthermore, the larger the mass of the suspended object, the greater the laser intensity required. Therefore, patent CN108873090B can only levitate objects smaller than tens of microns. However, theoretically, the greater the mass of the suspended object, the higher the acceleration sensitivity of the system. Therefore, patent CN108873090B has low acceleration sensitivity. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention proposes a device and method for measuring relative gravitational acceleration. This method utilizes a submillimeter-scale diamagnetic levitation sphere as a highly sensitive sensing unit and employs the principle of optical differential detection to detect the sphere's displacement. As gravitational acceleration changes, the sphere's position deviates from its initial equilibrium position. By detecting the corresponding relationship between the sphere's displacement in the direction of gravity and gravitational acceleration, the change in gravitational acceleration can be measured.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A device for measuring relative gravitational acceleration, comprising a beam stabilization subsystem and a signal detection subsystem;

[0007] The beam stabilization subsystem includes a fiber collimator, an electro-optic modulator, a lens 1, a lens 2, a piezoelectric reflector 1, a piezoelectric reflector 2, a spectroscope 1, a spectroscope 2, a lens 3, a position detector 1, a position detector 2, a spectroscope 3, a photodetector 1, a spectroscope 4, and a photodetector 2; the fiber collimator is used to collimate the laser, and the collimated light beam is transmitted through the electro-optic modulator, and then expanded and collimated by the lens 1 and the lens 2, and then enters the piezoelectric reflector 1, and after being reflected by the piezoelectric reflector 1, it enters the piezoelectric reflector 2, and after being reflected by the piezoelectric reflector 2, it enters the spectroscope 1; the light beam reflected by the spectroscope 1 is incident on the spectroscope 2; the light beam reflected by the spectroscope 2 is incident on the position detector 1, and the light beam transmitted through the electro-optic modulator is then expanded and collimated by the lens 1 and the lens 2, and then enters the piezoelectric reflector 1, and then enters the piezoelectric reflector 2, and then enters the spectroscope 1. The light passing through the second beam splitter is incident on the third lens, and the second position detector is located at the focus of the third lens. After being focused by the third lens, the light is incident on the second position detector. The light beam transmitted through the first beam splitter is incident on the third beam splitter, and the light beam reflected by the third beam splitter enters the first photodetector. The light beam transmitted through the third beam splitter is incident on the fourth beam splitter, and the light beam reflected by the fourth beam splitter is incident on the second photodetector. The light beam transmitted through the fourth beam splitter enters the signal detection subsystem. The first piezoelectric reflector, the second piezoelectric reflector, the first position detector, the third lens, and the second position detector constitute a laser stabilization system to ensure the stability of the light beam pointing. The electro-optical modulator and the first photodetector constitute a feedback loop for suppressing laser RIN noise. The second photodetector is used for monitoring RIN noise.

[0008] The signal detection subsystem includes lens four, a four-pole structure, lens five, a vacuum cavity, a beam splitter five, a beam analyzer, lens six, a four-quadrant detector, an imaging camera, and a three-dimensional translation stage;

[0009] The four-pole structure is located inside the vacuum chamber, and the light beam transmitted through the beam splitter four is focused by lens four onto a suspended ball located in the vacuum chamber; the light beam transmitted through the suspended ball is incident on the beam splitter five after passing through lens five, and the light beam reflected by the beam splitter five is incident on a beam analyzer, and the light beam transmitted through the beam splitter five is focused by lens six and then incident on a four-quadrant detector; the imaging camera is used to collect light scattered by the suspended ball, and cooperates with the three-dimensional displacement stage to achieve precise support and monitoring of the suspended ball; the beam analyzer is used to assist in observing the focusing position of the light beam on the suspended ball.

[0010] Furthermore, the suspended balls are sub-millimeter diamagnetic balls with negative magnetic susceptibility.

[0011] Furthermore, the suspended balls are made of PMMA material or silicon dioxide.

[0012] Furthermore, it also includes a lower base plate, a middle base plate and an upper base plate. Several support columns are connected between the lower base plate and the middle base plate, and between the middle base plate and the upper base plate to ensure the distance and stability between the base plates; there are two connecting shafts on both sides of the entire device for connecting the entire relative gravity acceleration measurement device to an external stable platform;

[0013] The beam stabilization subsystem is located on the middle base plate, and the signal detection subsystem is located on the upper base plate; a small hole is provided on the upper base plate so that the light beam can pass through the small hole from the beam stabilization subsystem to the signal detection subsystem;

[0014] The device further comprises an ion pump which is fixed on the lower base plate and is connected to the vacuum tube via a vacuum tube which passes through the middle base plate and the upper base plate.

[0015] Furthermore, the beam stabilization subsystem further includes a linear polarizer and a half-wave plate sequentially arranged between the fiber collimator and the electro-optical modulator, and a polarization beam splitter, a first reflector, and a second reflector sequentially arranged between the electro-optical modulator and the first lens, wherein the first reflector and the second reflector are used to achieve 180-degree folding of the light beam;

[0016] The beam stabilization subsystem also includes a reflector three located between the lens two and the piezoelectric reflector one, a reflector four, a reflector five, and a reflector six arranged in sequence between the piezoelectric reflector one and the piezoelectric reflector two, a reflector seven arranged between the piezoelectric reflector two and the beam splitter one, a reflector nine arranged between the beam splitter two and the position detector one, a reflector eight and a reflector ten arranged in sequence between the lens three and the position detector two, and a reflector eleven located on the light beam reflected by the beam splitter four, and each reflector is used to achieve deflection of the light beam direction.

[0017] Furthermore, the signal detection subsystem further includes a reflector 12, a reflector 13, and a reflector 14 arranged in sequence. The light beam reflected by the reflector 11 passes through the small hole on the upper base plate and passes through the reflector 12, the reflector 13, and the reflector 14 in sequence before being reflected to the lens 4. The signal detection subsystem further includes a reflector 15 located between the lens 5 and the beam splitter 5, a reflector 16 located between the lens 6 and the four-quadrant detector, and a reflector 17 located between the vacuum chamber and the imaging camera. Each reflector is used to achieve directional deflection of the light beam.

[0018] The reflecting mirror 13, the reflecting mirror 14 and the reflecting mirror 15 are all fixed on a precision electric optical adjustment frame, so that the light beam can be incident on the suspended ball 34 very accurately.

[0019] Furthermore, the components on the middle base plate are arranged around the vacuum tube, and the components on the upper base plate are arranged around the vacuum cavity, thereby making the entire device structure compact.

[0020] Furthermore, the center heights of the various components of the beam stabilization subsystem are all on the same horizontal plane.

[0021] A relative gravitational acceleration measurement method is implemented based on a device for relative gravitational acceleration measurement, and the method comprises the following steps:

[0022] The suspended ball is placed in the magnetic field source formed by the four-pole structure through precise adjustment of the three-dimensional displacement stage, and the suspended ball is stably suspended at a certain equilibrium position in the magnetic field. When the gravitational acceleration changes, the suspended ball deviates from the original equilibrium position, and the laser is focused on the suspended ball. The position change of the suspended ball causes the position where the focused light spot irradiates the ball to change, and the light spot distribution also changes after the light beam passes through the suspended ball. The scattered light from the suspended ball is transmitted through lens five and collimated, and then focused by lens six on the four-quadrant detector. The light power change of the light spot on the four-quadrant detector is measured, and the displacement information of the suspended ball in the direction of gravity is extracted. The change value of the gravitational acceleration is obtained through the relationship between the displacement change of the suspended ball and the acceleration of the suspended ball.

[0023] Furthermore, the force equation of the suspended ball when it is stably suspended in the magnetic field is:

[0024]

[0025] Where ρ is the density of the substance, χ is the volume magnetic susceptibility of the substance, g is the acceleration due to gravity, μ0 is the magnetic permeability of vacuum, B is the magnetic induction intensity, and z is the vertical displacement.

[0026] The beneficial effects of the present invention are as follows:

[0027] 1. Compared with optical levitation, this device can levitate objects with larger mass and achieve higher acceleration measurement accuracy.

[0028] 2. Magnetic levitation uses a magnetic pole structure as a magnetic field source. Antimagnetic levitation has the characteristics of no friction and low stiffness, does not require an energy input source, and is suitable for high-sensitivity acceleration sensing at room temperature.

[0029] 3. The laser stabilization system of the present invention can offset or correct changes caused by vibration, impact vibration, heat dissipation, or other changes to the laser displacement and angle, ensuring the stability of the beam pointing, which is conducive to achieving higher sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. When the following description refers to the drawings, identical numerals in different figures represent identical or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0031] The block diagrams shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically separate entities. That is, these functional entities may be implemented in software, in one or more hardware modules or integrated circuits, or in different networks and / or processor devices and / or microcontroller devices.

[0032] The flowcharts shown in the accompanying drawings are for illustrative purposes only and do not necessarily include all contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps may be decomposed, while others may be combined or partially combined. Therefore, the actual execution order may vary depending on the actual situation.

[0033] Figure 1 FIG. 1 is a schematic diagram of an optical path of a device for measuring relative gravitational acceleration according to one embodiment of the present invention.

[0034] Figure 2 FIG. 1 is a schematic structural diagram of a device for measuring relative gravitational acceleration according to one embodiment of the present invention.

[0035] Figure 3 A top view of a beam stabilization layer for a relative gravity acceleration measurement device according to one embodiment of the present invention.

[0036] Figure 4 This is a top view of an optical signal detection layer of a relative gravity acceleration measurement device according to one embodiment of the present invention.

[0037] In the figure, fiber collimator 1, linear polarizer 2, half-wave plate 3, electro-optic modulator 4, polarization beam splitter 5, reflector 1 6, reflector 2 7, lens 1 8, lens 2 9, reflector 3 10, piezoelectric reflector 1 11, reflector 4 12, reflector 5 13, reflector 6 14, piezoelectric reflector 2 15, reflector 7 16, beam splitter 1 17, beam splitter 2 18, lens 3 19, reflector 8 20, reflector 9 21, position detector 1 22, reflector 10 23, position detector 2 24, beam splitter 3 25, photodetector 1 26, beam splitter Mirror four 27, photodetector two 28, reflector eleven 29, reflector twelve 30, reflector thirteen 31, reflector fourteen 32, lens four 33, suspended sphere 34, vacuum chamber 36, lens five 37, reflector fifteen 38, spectrometer five 39, beam analyzer 40, lens six 41, reflector sixteen 42, four-quadrant detector 43, reflector seventeen 44, imaging camera 45, three-dimensional displacement stage 46, ion pump 47, lower base plate 48, middle base plate 49, upper base plate 50, connecting shaft 51, support column 52, vacuum tube 53, vacuum valve 54. DETAILED DESCRIPTION

[0038] Exemplary embodiments will be described in detail herein, with examples illustrated in the accompanying drawings. In the following description, when referring to the drawings, identical numerals in different figures represent identical or similar elements, unless otherwise indicated. The embodiments described in the following exemplary embodiments are not intended to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the present application, as detailed in the appended claims.

[0039] The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. As used in this application and the appended claims, the singular forms "a," "an," "the," and "the" are intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

[0040] It should be understood that although the terms first, second, third, etc. may be used in this application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from each other. For example, without departing from the scope of this application, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "at the time of" or "when" or "in response to determining".

[0041] It should also be noted that the term "plurality" used in this application refers to two or more. "And / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can mean: A exists alone, A and B exist simultaneously, or B exists alone. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0042] The device for measuring relative gravitational acceleration of the present invention has a cylindrical appearance and structurally comprises a lower base plate 48, a middle base plate 49, and an upper base plate 50. Several support columns 52 support the distance between the lower and middle base plates 48 and 49, as well as between the middle and upper base plates 49 and 50, to ensure stability and spacing between the base plates. Two connecting shafts 51 are located on either side of the device, connecting the entire relative gravitational acceleration measurement device to an external stabilizing platform. An ion pump 47 is secured to the lower base plate 48. This ion pump carries the heaviest weight in the entire measurement device and is placed at the bottom, stabilizing the center of gravity of the entire device. The beam stabilization subsystem is located on the middle base plate 49, while the signal detection subsystem is located on the upper base plate 50. A vacuum tube 53 passes through the middle and upper base plates 49, 50, with one end connected to the ion pump 47 and the other end connected to the vacuum chamber 36 in the signal detection subsystem. This layered optical path layout can greatly reduce the area occupied by the device, which is conducive to the miniaturization and integration of the system.

[0043] The beam stabilization subsystem includes a fiber collimator 1, a linear polarizer 2, a half-wave plate 3, an electro-optical modulator 4, a polarization beam splitter 5, a reflector 1 6, a reflector 2 7, a lens 1 8, a lens 2 9, a reflector 3 10, a piezoelectric reflector 1 11, a reflector 4 12, a reflector 5 13, a reflector 6 14, a piezoelectric reflector 2 15, a reflector 7 16, a beam splitter 1 17, a beam splitter 2 18, a lens 3 19, a reflector 8 20, a reflector 9 21, a position detector 1 22, a reflector 10 23, a position detector 2 24, a beam splitter 3 25, a photodetector 1 26, a beam splitter 4 27, a photodetector 2 28, and a reflector 11 29. Spacers or adapters are used to ensure that the center heights of the various components of the beam stabilization subsystem are on the same horizontal plane, minimizing the system's adjustment structure. Furthermore, the components of the beam stabilization subsystem are arranged around a vacuum tube 53, minimizing the overall size of the device.

[0044] The optical fiber collimator 1 is used to collimate the laser; the collimated light beam is transmitted through the linear polarizer 2, the half-wave plate 3, the electro-optic modulator 4, the polarization beam splitter 5 in sequence, and is reflected and redirected by the reflector 1 6 and the reflector 2 7 to transmit through the beam expansion and collimation unit composed of the lens 1 8 and the lens 2 9, and then reflected by the reflector 3 10 to enter the piezoelectric reflector 1 11. The light beam reflected by the piezoelectric reflector 11 is reflected and redirected by the reflector 4 12, the reflector 5 13, and the reflector 6 14 in sequence. Light is incident on piezoelectric mirror 2 15, reflected by piezoelectric mirror 2 15, then redirected by reflector 7 16 before being incident on beam splitter 1 17. This split light is split into two beams, one of which is reflected and incident on beam splitter 2 18. The reflected beam from beam splitter 2 18 is reflected by reflector 9 21 and incident on position detector 1 22. The light that passes through beam splitter 2 18 is focused by lens 3 19 and reflected by reflector 8 20 and reflector 10 23 to position detector 2 24. The light beam that passes through beam splitter 1 17 is incident on beam splitter 3 25, where the reflected beam enters photodetector 1 26. The transmitted beam enters beam splitter 4 27, the reflected beam enters photodetector 2 28, and the transmitted beam is reflected by reflector 11 29 and enters the signal detection subsystem.

[0045] In terms of functional implementation, this embodiment uses a laser wavelength of 1064 nm. Lenses 8 and 9 form a beam collimation and expansion system, combining different focal lengths to meet the numerical aperture of the detection beam incident on the suspended ball 34. Piezoelectric mirror 1 11, piezoelectric mirror 2 15, position detector 1 22, lens 3 19, and position detector 2 24 form a laser stabilization system that offsets or corrects changes caused by vibration, impact, heat dissipation, or other changes to the laser's displacement and angle, ensuring beam pointing stability. Position detector 1 22 determines laser position stability, while lens 3 19 and position detector 2 24 jointly determine the laser's direction, with position detector 24 located at the focal point of lens 3 19. The electro-optic modulator 4 and photodetector 1 26 in this invention form a feedback loop for laser RIN noise suppression, effectively reducing the device's RIN noise and improving its detection sensitivity. Electro-optic modulator 4 is a Pockels cell modulator. Applying an electric field to the crystal changes the refractive index, generating an electric field-dependent birefringence effect, thereby altering the polarization state of the beam. Electro-optical modulator 4 has a transmission wavelength of 900 to 1250 nm and a clear aperture of 2 mm. Electro-optical modulator 4 and photodetector 1 (26) are both connected to an external lock-in amplifier, forming a feedback loop. Photodetector 1 (26) is an in-loop detector used to suppress feedback. Photodetector 2 (28) directly reads the electrical signal from the external lock-in amplifier to observe laser relative intensity noise (RIN noise). Photodetector 2 (28) is an out-of-loop detector used to monitor RIN noise.

[0046] In this embodiment, the beam splitters all use flat beam splitters, and the transmission and reflection ratio of the beam splitter 17 is 70:30; the transmission and reflection ratio of the beam splitter 2 18 is 50:50; the transmission and reflection ratio of the beam splitter 3 25 is 50:50; and the transmission and reflection ratio of the beam splitter 4 27 is 10:90.

[0047] There are multiple reflectors in the beam stabilization subsystem, the purpose of which is to allow the light beam to be reflected as much as possible, so that the various components can be arranged more compactly on the bottom plate 49, rationally utilizing the space, and thus reducing the volume of the entire device.

[0048] The signal detection subsystem includes a reflector 12 30 , a reflector 13 31 , a reflector 14 32 , a lens 4 33 , a suspended sphere 34 , a four-pole structure 35 , a vacuum chamber 36 , a lens 5 37 , a reflector 15 38 , a spectroscope 5 39 , a beam analyzer 40 , a lens 6 41 , a reflector 16 42 , a four-quadrant detector 43 , a reflector 17 44 , an imaging camera 45 , and a three-dimensional translation stage 46 .

[0049] Similarly, to minimize the size of the device and achieve a compact structure, the various components of the signal detection subsystem are arranged around the vacuum chamber 36. Multiple reflectors are used to deflect the light beam, avoiding the vacuum chamber and distributing it around it, thereby reducing the overall size of the device. A small hole is formed in the upper base plate 50, through which the light beam reflected by the reflector 11 29 passes. This allows the light beam, stabilized by the beam stabilization subsystem, to be introduced into the signal detection subsystem, thereby facilitating the reduction of the overall size of the device. The four-quadrant detector 43 is located within the vacuum chamber 36. During actual measurement, the suspended sphere 34 is released into the vacuum chamber 36 via a three-dimensional translation stage 46, and its position is adjusted so that it is suspended in the center of the four-quadrant detector 43. The light beam reflected by the reflector 11 29 passes through the small hole, is sequentially reflected by the reflectors 12 30, 13 31, and 14 32, and is transmitted through the lens 4 33 and the vacuum chamber 36, where it is focused on the suspended sphere 34. The light beam transmitted through the suspended ball 34 passes through lens five 37 and is reflected by reflector fifteen 38 to spectrometer five 39, wherein the reflected light beam of spectrometer five 39 is incident on the beam analyzer 40, and the transmitted light beam of spectrometer five 39 is transmitted through lens six 41 and focused, and then reflected by reflector sixteen 42 and enters the four-quadrant detector 43.

[0050] The suspended ball is submillimeter-sized and made of PMMA. PMMA has good anti-magnetic properties and a relatively low density, which is beneficial for the suspension of the ball and can be used as a gravity acceleration sensing unit under high vacuum. The scattered signal of the suspended ball 34 is reflected by the reflector 17 44 into the imaging camera 45. The imaging camera 45 and the three-dimensional displacement stage 46 cooperate to achieve precise support and monitoring of the suspended ball 34. The vacuum chamber 36 is fixed to the upper base plate 50 through an adapter. The upper base plate 50 is composed of two separate semicircular base plates, which is conducive to the adjustment of the optical path and the overall installation of the device. The reflector 13 31, the reflector 14 32 and the reflector 15 38 are all fixed on a precision electric optical adjustment frame, so that the light beam can be incident on the suspended ball 34 very accurately. The beam analyzer 40 can check the spot shape after passing through the suspended ball 34, and use the spot shape as the basis for adjusting the position and direction of the light beam incident on the suspended ball 34. Beam splitter 5 39 also uses a flat beam splitter with a transmission and reflection ratio of 10:90.

[0051] The present invention utilizes the diamagnetism of diamagnetic materials to stably suspend them in a magnetic field. Using a rationally designed four-pole structure as a magnetic field source, a suspended ball with a negative magnetic susceptibility is placed in a magnetic field environment. It is subject to the repulsive force of the magnetic field. When the diamagnetic force on the ball is balanced with gravity, the material can achieve stable suspension. When the material is in equilibrium, its force equation is:

[0052]

[0053] Among them, ρ is the density of the material, χ is the volume magnetic susceptibility of the material, g is the acceleration due to gravity, μ0 is the magnetic permeability of vacuum, B is the magnetic induction intensity, and z is the displacement in the vertical direction. It can be seen from the formula that if the acceleration due to gravity changes, the displacement in the vertical direction will also make a corresponding displacement. Based on the above principle, when the acceleration due to gravity changes, the suspended ball will produce a slight displacement change. In the present invention, the suspended ball serves as a sensing unit for measuring the acceleration due to gravity. The laser is focused on the suspended ball and the scattered light of the suspended ball is collected and captured. The change in the displacement of the suspended ball causes the spot distribution of the scattered light on the four-quadrant detector to change, thereby determining the position of the suspended ball. The displacement of the suspended ball is detected using the principle of optical differential detection. When the acceleration due to gravity changes, the position of the suspended ball also deviates from the initial equilibrium position. The measurement of the change in the acceleration of gravity is achieved by detecting the corresponding relationship between the displacement of the suspended ball in the direction of gravity and the acceleration due to gravity.

[0054] Those skilled in the art will understand that the foregoing descriptions are merely preferred embodiments of the invention and are not intended to limit the invention. Although the invention has been described in detail with reference to the foregoing examples, those skilled in the art will still be able to modify the technical solutions described in the foregoing examples or substitute equivalents for some of the technical features therein. Any modifications, equivalent substitutions, etc. made within the spirit and principles of the invention shall be included within the scope of protection of the invention.

Claims

1. A device for measuring relative gravitational acceleration, characterized in that: The device consists of two parts: a beam stabilization subsystem and a signal detection subsystem; The beam stabilization subsystem includes a fiber collimator, an electro-optical modulator, a lens 1, a lens 2, a piezoelectric mirror 1, a piezoelectric mirror 2, a spectroscope 1, a spectroscope 2, a lens 3, a position detector 1, a position detector 2, a spectroscope 3, a photodetector 1, a spectroscope 4, and a photodetector 2; the fiber collimator is used to expand and collimate the laser beam, and the beam after expansion and collimation is transmitted through the electro-optical modulator, and then expanded and collimated by the lens 1 and the lens 2, and then enters the piezoelectric mirror 1, and after being reflected by the piezoelectric mirror 1, enters the piezoelectric mirror 2, and after being reflected by the piezoelectric mirror 2, enters the spectroscope 1; the beam reflected by the spectroscope 1 is incident on the spectroscope 2; the beam reflected by the spectroscope 2 is incident on the position detector 1, and the beam after expansion and collimation is transmitted through the electro-optical modulator, and then enters the piezoelectric mirror 1 and the piezoelectric mirror 2, and then enters the spectroscope 1. The light beam passing through the second beam splitter is incident on the third lens, the second position detector is located at the focus of the third lens, and is focused by the third lens before being incident on the second position detector; the light beam passing through the first beam splitter is incident on the third beam splitter, the light beam reflected by the third beam splitter enters the first photodetector, the light beam passing through the third beam splitter is incident on the fourth beam splitter, the light beam reflected by the fourth beam splitter is incident on the second photodetector, and the light beam passing through the fourth beam splitter enters the signal detection subsystem; the first piezoelectric reflector, the second piezoelectric reflector, the first position detector, the third lens, and the second position detector constitute a laser stabilization system to ensure the stability of the light beam pointing; the electro-optical modulator and the first photodetector constitute a feedback loop for suppressing laser RIN noise; the second photodetector is used for monitoring RIN noise; The signal detection subsystem includes lens four, a four-pole structure, lens five, a vacuum cavity, a beam splitter five, a beam analyzer, lens six, a four-quadrant detector, an imaging camera, and a three-dimensional translation stage; The four-pole structure is located inside the vacuum chamber. The light beam transmitted through the beam splitter four is focused by lens four onto the suspended ball located in the vacuum chamber. The light beam transmitted through the suspended ball is incident on the beam splitter five after passing through lens five. The light beam reflected by the beam splitter five is incident on the beam analyzer. The light beam transmitted through the beam splitter five is focused by lens six and then enters the four-quadrant detector. The imaging camera is used to collect light scattered by the suspended ball and cooperates with the three-dimensional translation stage to achieve precise support and monitoring of the suspended ball. The beam analyzer is used to assist in observing the focusing position of the light beam on the suspended ball. The suspended balls are sub-millimeter diamagnetic balls with negative magnetic susceptibility.

2. The device for measuring relative gravitational acceleration according to claim 1, wherein: The suspended balls are made of PMMA material or silicon dioxide.

3. The device for measuring relative gravitational acceleration according to claim 1, wherein: The device also includes a lower base plate, a middle base plate, and an upper base plate. Several support columns are connected between the lower base plate and the middle base plate, and between the middle base plate and the upper base plate to ensure the distance and stability between the base plates. Two connecting shafts are provided on both sides of the device for connecting the relative gravity acceleration measurement device to an external stable platform. The beam stabilization subsystem is located on the middle base plate, and the signal detection subsystem is located on the upper base plate; a small hole is provided on the upper base plate so that the light beam can pass through the small hole from the beam stabilization subsystem to the signal detection subsystem; The device further comprises an ion pump which is fixed on the lower base plate and is connected to the vacuum tube via a vacuum tube which passes through the middle base plate and the upper base plate.

4. The device for measuring relative gravitational acceleration according to claim 1, wherein: The beam stabilization subsystem further includes a linear polarizer and a half-wave plate sequentially arranged between the fiber collimator and the electro-optical modulator, and a polarization beam splitter, a first reflector, and a second reflector sequentially arranged between the electro-optical modulator and the first lens, wherein the first reflector and the second reflector are used to achieve 180-degree folding of the light beam; The beam stabilization subsystem also includes a reflector three located between the lens two and the piezoelectric reflector one, a reflector four, a reflector five, and a reflector six arranged in sequence between the piezoelectric reflector one and the piezoelectric reflector two, a reflector seven arranged between the piezoelectric reflector two and the beam splitter one, a reflector nine arranged between the beam splitter two and the position detector one, a reflector eight and a reflector ten arranged in sequence between the lens three and the position detector two, and a reflector eleven located on the light beam reflected by the beam splitter four, and each reflector is used to achieve deflection of the light beam direction.

5. The device for measuring relative gravitational acceleration according to claim 4, characterized in that: The signal detection subsystem further includes a reflector 12, a reflector 13, and a reflector 14 arranged in sequence. The light beam reflected by the reflector 11 passes through the small hole on the upper base plate and passes through the reflector 12, the reflector 13, and the reflector 14 in sequence before being reflected to the lens 4. The signal detection subsystem further includes a reflector 15 located between the lens 5 and the beam splitter 5, a reflector 16 located between the lens 6 and the four-quadrant detector, and a reflector 17 located between the vacuum chamber and the imaging camera. Each reflector is used to achieve directional deflection of the light beam. The reflecting mirror 13, the reflecting mirror 14 and the reflecting mirror 15 are all fixed on a precision electric optical adjustment frame, so that the light beam can be incident on the suspended ball very accurately.

6. The device for measuring relative gravitational acceleration according to claim 3, characterized in that: The components on the middle base plate are all arranged around the vacuum tube, and the components on the upper base plate are all arranged around the vacuum cavity, thereby making the entire device structure compact.

7. The device for measuring relative gravitational acceleration according to claim 1, wherein: The center heights of the various components of the beam stabilization subsystem are all on the same horizontal plane.

8. A method for measuring relative gravitational acceleration, characterized in that: The method is implemented based on the device for measuring relative gravitational acceleration according to any one of claims 1 to 7, and comprises the following steps: The suspended ball is placed in the magnetic field source formed by the four-pole structure through precise adjustment of the three-dimensional displacement stage, and the suspended ball is stably suspended at a certain equilibrium position in the magnetic field. When the gravitational acceleration changes, the suspended ball deviates from the original equilibrium position, and the laser is focused on the suspended ball. The position change of the suspended ball causes the position where the focused light spot irradiates the ball to change, and the light spot distribution also changes after the light beam passes through the suspended ball. The scattered light from the suspended ball is transmitted through lens five and collimated, and then focused by lens six on the four-quadrant detector. The light power change of the light spot on the four-quadrant detector is measured, and the displacement information of the suspended ball in the direction of gravity is extracted. The change value of the gravitational acceleration is obtained through the relationship between the displacement change of the suspended ball and the acceleration of the suspended ball.

9. The relative gravitational acceleration measurement method according to claim 8, characterized in that: The force equation of the suspended ball when it is stably suspended in a magnetic field is: ； where ρ is the density of the substance, is the volume magnetic susceptibility of the substance, g is the acceleration due to gravity, μ0 is the magnetic permeability of vacuum, B is the magnetic induction intensity, and z is the vertical displacement.

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