Small-size high-precision gravimeter based on anti-magnetic suspension principle

Abstract

The invention relates to the field of gravity measurement, and aims to provide a small-size high-precision gravimeter based on an anti-magnetic suspension principle. The gravimeter comprises a low-frequency magnetic potential well unit, a suspension mechanical oscillator unit, a displacement detection unit and a cavity enclosing unit, and lens groups of the low-frequency magnetic potential well unit, the suspension mechanical oscillator unit and the displacement detection unit are all located in a cavity of a heat preservation shell on the innermost side. According to the invention, a measurement environment without external influence can be provided for the displacement detection of the suspension oscillator, the adjustment of the frequency in the vertical direction in a magnetic suspension potential well is resisted, the movement of an object to be measured is reflected by the voltage fluctuation brought by the laser intensity change measured by the photoelectric converter, and the high-precision gravity measurement is realized; the vibrator adopts a magnetic suspension mode and does not make mechanical contact with the environment, and long-term irreversible deformation can be avoided; and a temperature control and magnetic shielding device or other auxiliary equipment with a large volume is not needed, so that the gravimeter is small in overall size, convenient to move, low in cost and beneficial to popularization.

Description

Technical Field

[0001] The invention belongs to the field of gravity measurement, and more specifically relates to a small-sized high-precision gravimeter based on the anti-magnetic suspension principle. Background Art

[0002] A gravimeter is an instrument that measures gravitational acceleration and is of great significance in the fields of geophysics and underground resource exploration. Currently, gravimeters can be divided into two categories: absolute gravimeters and relative gravimeters.

[0003] In terms of gravity measurement, absolute gravimeters have higher accuracy; for example, the domestic absolute gravity measurement system based on cold atoms can achieve a detection sensitivity of about 10μGal. However, absolute gravimeters are large in size, complex in structure, and high in equipment cost. They are difficult to use and maintain, which is not conducive to promotion and application. The basic principle of relative gravimeters is that the elastic body deforms under the action of gravity. When the elastic force of the elastic body is balanced with the gravity, the elastic body is in a certain equilibrium position. When the gravity changes, the equilibrium position of the elastic body changes. By observing the change in the equilibrium position twice, the gravity difference between the two points can be determined. The weight of a constant mass m in a gravitational field changes with the change of g. If another force (elastic force, electromagnetic force, etc.) is used to balance the change of this weight or gravity torque, it is possible to measure the gravity difference between the two points by observing the equilibrium state of the object. Depending on the way an object is displaced by changes in gravity, gravimeters can be divided into two categories: translation (or linear displacement) type or rotation (or angular displacement) type. Widely used ones include metal spring gravimeters and quartz spring gravimeters, but gravimeters with this type of structure usually have poor measurement accuracy.

[0004] The researchers proposed a relative gravimeter using a mechanical oscillator. The principle is to measure the position change of the mechanical oscillator caused by the change in gravity. The response of the mechanical oscillator to the external acceleration is:

[0005]

[0006] Where ω0 is the eigenfrequency of the oscillator, ω is the external acceleration frequency to be measured, and γ is the dissipation coefficient of the oscillator.

[0007] When the system needs to measure some stable acceleration similar to gravity, that is, when the external acceleration frequency ω→0: Right now Therefore, in order to improve the acceleration measurement accuracy a, it is necessary to improve the displacement detection accuracy x of the system and reduce the eigenfrequency of the mechanical oscillator.

[0008] In the existing scheme, when constructing a mechanical vibrator gravimeter, the system that meets both requirements is usually a quartz spring or a MEMS micro-electromechanical device. However, such systems are restricted by the characteristics of the materials themselves. During use, due to the irreversible deformation of the materials themselves, the linear drift problem of the system gravity measurement is prominent, usually above 500uGal / day, which seriously affects the accuracy and stability of the measurement and is difficult to meet the requirements of various application scenarios with increasing precision requirements. Suspension systems that do not require mechanical contact with the environment, such as optical suspension and electric suspension, require continuous input of external energy to maintain the suspension state, which not only greatly increases the operating cost of the equipment, but also introduces additional noise, interferes with the measurement signal, and reduces the measurement accuracy. In contrast, magnetic suspension technology plays an important role in low-loss transportation, precision signal sensing, inertial navigation, precision machinery and other fields. Compared with traditional mechanical systems, such as micro-electromechanical systems, magnetic suspension systems have significant advantages such as low loss, long life, and zero energy consumption, and have great potential in the application of gravimeters. However, since the magnetic levitation system is sensitive to factors such as the temperature and magnetic field fluctuations of the external environment, it requires large-scale temperature control and magnetic shielding devices to maintain the stable suspension of the system. As a result, the entire equipment is bulky and costly, greatly limiting its potential for large-scale industrialization.

[0009] In summary, based on the many shortcomings of the existing relative gravimeter technology, the present invention proposes a small-sized, high-precision gravimeter based on the anti-magnetic suspension principle, aiming to effectively solve the above problems and meet the needs of high-precision gravity measurement in practical applications. Summary of the invention

[0010] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a small-sized high-precision gravimeter based on anti-magnetic suspension.

[0011] To solve the technical problem, the solution of the present invention is:

[0012] A small-size high-precision gravimeter based on anti-magnetic suspension is provided, comprising:

[0013] The low-frequency magnetic potential well unit comprises a magnetic confinement potential well formed by a plurality of permanent magnets enclosed in an axially symmetrical manner; the frequency and confinement position of the magnetic confinement potential well can be adjusted by changing the relative positions of the permanent magnets;

[0014] A suspended mechanical oscillator unit comprises an oscillator suspended in a magnetic confinement potential well, and a light shielding component arranged at the top of the oscillator and extending out of the magnetic confinement potential well;

[0015] The displacement detection unit comprises a laser, a lens group and a photoelectric converter, wherein the light blocking component is located on the optical path inside the lens group;

[0016] The cavity enclosure unit includes an outer shell, a magnetic shielding shell and a thermal insulation shell which are nested in sequence and keep a distance from each other, and the cavity of each shell is kept vacuum; the lens group of the low-frequency magnetic potential well unit, the suspension mechanical oscillator unit and the displacement detection unit are all located in the cavity of the innermost thermal insulation shell.

[0017] As a preferred embodiment of the present invention, the multiple permanent magnets are divided into two layers, the upper and lower layers, and the permanent magnets in each layer are respectively arranged in an enclosed manner; the center of the upper magnet is a cavity structure, and the vibrator is suspended in the cavity; the magnetization direction of the lower magnet points to the center, and the magnetic lines of force converge in the central area to generate a vertical magnetic field and a magnetic field gradient, providing anti-magnetic force and constraint for overcoming gravity; the magnetization direction of the upper magnet points from the center to the outside, providing horizontal constraint.

[0018] As a preferred solution of the present invention, the vertical frequency of the magnetic confinement potential well is adjusted by changing the relative distance between the upper and lower layers of permanent magnets; the confinement position of the magnetic confinement potential well is adjusted by changing the relative distance between the permanent magnets in each layer and their enclosed center.

[0019] As a preferred embodiment of the present invention, the vibrator is a monomer structure made of graphite or metal material with anti-magnetic properties; the shape of the vibrator is a columnar structure with a circular or regular polygonal cross section and a relatively contracted bottom.

[0020] As a preferred solution of the present invention, the light blocking component is located on the optical path inside the lens group in the displacement detection unit to serve as a displacement monitoring object, specifically a cross bar or a light blocking plate arranged on the cross bar; the vertical bar fixed on the top of the vibrator is connected to the cross bar, and the latter is located outside the magnetic confinement potential well.

[0021] As a preferred embodiment of the present invention, the emitting end of the laser is connected to the first optical fiber, the receiving end of the photoelectric converter is connected to the second optical fiber, and the lens group is located between the output end of the first optical fiber and the incident end of the second optical fiber; the lens group includes at least two convex lenses, and the light blocking component is located at the focal position of the lens group.

[0022] As a preferred solution of the present invention, the bottom of the outer shell is seated on the machine base, and a plurality of machine foot screws are provided at the bottom of the machine base;

[0023] The magnetic shielding shell is seated on the bottom plate of the outer shell through an insulation pad, and the thermal insulation shell is seated on the bottom plate of the magnetic shielding shell through an insulation pad; or, the magnetic shielding shell is suspended on the top plate of the outer shell through an insulation rope, and the thermal insulation shell is suspended on the top plate of the magnetic shielding shell through an insulation rope; the outer shell, the magnetic shielding shell and the thermal insulation shell are provided with closed side doors in the same direction for installing and adjusting the low-frequency magnetic potential well unit and the suspended mechanical oscillator unit, and the low-frequency magnetic potential well unit is seated on the bottom plate of the thermal insulation shell.

[0024] As a preferred solution of the present invention, there are multiple groups of magnetic shielding shells, which are nested in sequence with a spacing maintained; there are multiple groups of thermal insulation shells, which are nested in sequence with a spacing maintained; and the cavity of each shell is kept vacuum.

[0025] As a preferred embodiment of the present invention, a temperature probe and an electric heater are provided inside the heat-insulating shell, a temperature controller is provided outside the outer shell, and the temperature probe and the electric heater are connected to the temperature controller via a cable; alternatively, the laser and the photoelectric converter are installed on the outside of the outer shell.

[0026] The present invention further provides a method for using the aforementioned high-precision gravimeter, comprising:

[0027] (1) Confirm that all components of the gravimeter are in good condition and the oscillator is located in the magnetic confinement potential well;

[0028] (2) By changing the relative positions of the permanent magnets in the layer, the confinement position of the magnetic confinement potential well is adjusted, so that the vibrator is stably suspended in the upper cavity and the light-blocking component is located on the optical path inside the lens group; by changing the relative positions of the upper and lower layers of permanent magnets, the vertical frequency of the magnetic confinement potential well is adjusted to meet the measurement requirements;

[0029] (3) Close the closed side doors of each shell layer, evacuate the cavity between the shells, and set the temperature of the temperature controller according to the measurement plan;

[0030] (4) Start the laser and use the photoelectric converter to measure the voltage fluctuation caused by the vertical movement of the light-blocking component; obtain the vertical displacement of the vibrator based on the pre-calibrated vertical displacement and voltage relationship curve, and further convert the gravity change.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] 1. The gravimeter proposed in the present invention adopts an anti-magnetic levitation potential well composed of permanent magnets, which can provide horizontal constraints while offsetting the gravitational field of the mass body without any external energy consumption; thereby providing a measurement environment without external influence for the displacement detection of the suspended oscillator, thereby improving the acceleration measurement accuracy.

[0033] 2. The present invention can adjust the vertical frequency in the antagonistic magnetic levitation potential well by adjusting the distance between the upper and lower layers of permanent magnets, thereby meeting the oscillator frequency requirements for gravity measurement.

[0034] 3. The present invention places the suspended oscillator at the focal point of the laser light path, and measures the voltage fluctuation caused by the change of laser intensity through a photoelectric converter to reflect the movement of the object to be measured, thereby achieving high-precision gravity measurement.

[0035] 4. The vibrator adopts magnetic suspension and does not have mechanical contact with the environment, which can avoid long-term irreversible deformation of the material. The actual measurement can suppress the linear drift of gravity measurement to below 100uGal / day.

[0036] 5. The device of the present invention only needs to place the key measurement components inside the heat-insulating magnetic shielding shell, without the need for bulky temperature control and magnetic shielding devices or other auxiliary equipment. Therefore, the overall size of the gravimeter is small, easy to move, low cost and conducive to promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a structural schematic diagram of the gravimeter in the present invention.

[0038] Figure 2 Schematic diagram of the anti-magnetic levitation potential well in the present invention.

[0039] Figure 3 Schematic diagram of the magnetic field generated by two layers of magnets tightly combined.

[0040] Figure 4 Schematic diagram of the magnetic field generated by two layers of alternating magnets.

[0041] Figure 5 Schematic diagram of the suspended oscillator.

[0042] Figure 6 Schematic diagram of the optical path in the displacement detection unit.

[0043] Figure 7 This is the relationship between the voltage and displacement obtained by the photoelectric converter.

[0044] The reference numerals in the figure are: upper magnet 1; lower magnet 2; vibrator 3; displacement detection unit 4; vertical rod 401; laser 402; photoelectric converter 403; temperature control unit 5; temperature probe 501; electric heater 502; temperature controller 503; thermal insulation shell 6; magnetic shielding shell 7; outer shell 8; thermal insulation pad 9; machine foot screw 10. DETAILED DESCRIPTION

[0045] 1. Description of the Invention Principle

[0046] 1. Principle of magnetic levitation:

[0047] A substance with a mass of m and a volume of V (here the volume V is considered to be a small quantity) placed in a static magnetic field B(r) will be induced with a magnetic moment μ(r):

[0048]

[0049] Where χ is the magnetic susceptibility. For diamagnetic materials, χ<0; μ0=4π×10 -7 N / A 2, is the vacuum magnetic permeability, and its corresponding magnetic potential energy E(r) can be expressed as:

[0050]

[0051] According to Earnshaw's theorem, there is no local maximum value of magnetic field strength in a static magnetic field without current, so only diamagnetic materials can be stably bound to the minimum point of the static magnetic field. For ordinary diamagnetic materials, the relative magnetic susceptibility |χ|<<1. In order to make the diamagnetic material stably suspended in the potential field, the total force Need to be zero, that is:

[0052]

[0053] in represents the magnetic field gradient, e z represents an upward unit vector, indicating that the magnetic force on the suspended material in the vertical direction is equal to the gravity, while there is no magnetic force in the horizontal direction. In addition, the stable constraint must satisfy This is true for both xyz directions, and the corresponding frequency of the suspended oscillator is

[0054] Where i = x, y, z, Represents the second-order derivative of energy E in the three directions of xyz.

[0055] 2. Low frequency magnetic potential well unit

[0056] (1) Magnetic confinement potential well design:

[0057] The magnetic confinement potential well (anti-magnetic levitation potential well) is the core innovation of this method. The magnetic confinement potential well must be composed of permanent magnets and does not consume any external energy. On the one hand, the magnetic confinement potential well must be able to offset the gravitational field of the mass body, and on the other hand, it must be able to provide horizontal constraints. The invention proposes to divide the combination of multiple permanent magnets into an upper and lower double-layer structure, with the upper magnet and the lower magnet having opposite polarization directions, thereby forming a stable magnetic potential well in the center. Specifically, Figure 1 As shown. Figure 2-4 As shown in the figure, the arrows in the figure indicate the magnetization direction of the magnet, that is, the magnetization direction of the lower magnet points to the center, and the magnetization direction of the upper magnet is along the center outward. For the permanent magnet structure formed by axial symmetry, the horizontal component of the magnetic field at the center is 0, and there is a limit value point of the magnetic field in the vertical direction, which meets the requirements of the magnetic field structure.

[0058] It should be noted that the specific design is not limited to Figure 2-4The structure shown in the figure shows that a single layer of 8 permanent magnets forms an octagonal structure; of course, according to actual needs, the number of permanent magnets can be changed to different combinations such as 4, 5, 6, 7, etc., and the specific shape can also be adjusted as needed. In addition, the shape and volume of the permanent magnets are accurately quantified using finite element calculations to ensure that the overall anti-magnetic suspension characteristics do not change. The core of this design is that the lower layer of magnets converges the magnetic lines of force in the central area to generate a magnetic field and a magnetic field gradient in the z direction, provide an anti-magnetic force to overcome gravity, and provide constraints in the z direction. The upper layer of magnets forms an enclosed cavity structure in the center, which can provide constraints in the horizontal direction (x, y). In this way, a magnetic confinement potential well is formed in the cavity structure, in which the vibrator can achieve stable suspension in three directions. Based on this magnetic confinement design scheme, the number of permanent magnets, as well as the specific geometric shapes, sizes and other parameters of the permanent magnets and vibrators can be adjusted as needed, and there is no substantial difference in the realization principle of the frequency and constraint position of the magnetic confinement potential well.

[0059] (2) Frequency adjustment:

[0060] The magnetic potential well directly constructed according to the above description, if used directly, has a vertical frequency of Usually above 2π×10Hz ( Represents the second-order derivative of energy E with respect to z), which cannot meet the needs of gravity measurement and requires further adjustment of the permanent magnet structure.

[0061] like Figure 3 As shown, the magnetic fields generated by the upper and lower layers of the combined magnet are written as B1(r) and B2(r) respectively, then the total magnetic field B(r)=B1(r)+B2(r), and the total energy

[0062] At this time, the anti-magnet suspension position z0 satisfies:

[0063]

[0064] The corresponding frequency

[0065] like Figure 4 As shown in the figure, if the upper magnet is moved up by l, the anti-magnet suspension position is moved down to z1, satisfying:

[0066]

[0067] Wherein, g represents the acceleration due to gravity; the subscript z indicates that the above two equations are valid at z=z0 and z=z1 respectively.

[0068] The frequency also decreases to

[0069] Through COMSOL finite element simulation and actual measurement by the applicant's research team, the vertical frequency can be reduced to as low as 2π×1.5Hz, which meets the mechanical oscillator frequency requirements for gravity measurement.

[0070] 3. Suspension mechanics oscillator unit

[0071] According to what has been said before, the force balance condition required for the oscillator suspension is:

[0072]

[0073] The vibrator is preferably made of a material with strong anti-magnetic properties, such as graphite or metal bismuth, so as to utilize anti-magnetic properties to resist gravity and form suspension in a magnetic field. Since the vibrator is not subjected to force in the horizontal direction, the shape is preferably designed to be a cylindrical or regular polygon symmetrical around the vertical axis. According to the COMSOL finite element simulation results, the bottom of the vibrator needs to be appropriately narrowed to avoid the problem of the vibrator's equilibrium position flipping in the suspended state.

[0074] In addition, a rod needs to be used to form a T-shaped or cross-shaped fixed structure at the top of the oscillator, wherein a light-blocking sheet is provided on the cross bar (or the cross bar is directly used as a light-blocking component) for position detection in the optical path; the vertical bar is used to make the light-blocking component extend out of the magnetic confinement potential well.

[0075] 4. Displacement detection unit

[0076] The displacement detection unit includes a laser, a lens group and a photoelectric converter. The light-blocking component is located on the optical path inside the lens group. The laser is connected to the optical fiber for inputting laser light, which is focused on the light-blocking component after passing through the front lens. The light emitted from the light-blocking component is collected by the rear lens and enters the optical fiber, and the laser light is received by the photoelectric converter. The movement of the object to be measured is reflected by measuring the voltage fluctuation of the photoelectric converter.

[0077] Since the voltage of the photoelectric converter is proportional to the received light intensity, it is only necessary to directly measure the relationship curve between the displacement of the light-blocking component and the voltage. By quantitatively moving the relative position of the lens group and the light-blocking component vertically in advance, the voltage V can be measured. z In subsequent practical use, the vertical position of the optical fiber group is adjusted to move the optical path focus to the position on the light-blocking component where the voltage is most sensitive to displacement (such as Figure 7 In this case, the voltage and displacement are approximately linear, so it can be written as:

[0078] ΔV z =ξz·Δz

[0079] Wherein, Δz represents the displacement of the light-blocking component in the vertical direction; ΔV zrepresents the voltage change under this displacement; ξz represents the voltage-displacement conversion coefficient in the vertical direction.

[0080] The light intensity-displacement conversion coefficient can be measured by using voltage value to represent light intensity. According to the actual measurement by the applicant's research team, the conversion coefficient in the horizontal direction is more than one order of magnitude smaller than that in the vertical direction. It can be considered that the total voltage change measured by the photoelectric converter only reflects the displacement in the vertical direction. Therefore, the voltage change can be used to evaluate the displacement under the influence of gravity.

[0081] 5. Cavity enclosure unit

[0082] The system noise in the gravimeter mainly includes temperature noise and tilt noise. In order to further reduce the system noise, the present invention proposes a multi-nested shell design for the device, using the cavity enclosure unit to achieve thermal insulation and magnetic shielding while forming vacuum isolation, and using the temperature control unit to achieve multi-level PID temperature control. The horizontality of the device is controlled by the machine foot screws under the base of the cavity enclosure unit so that the tilt angle during measurement meets the requirements.

[0083] 2. Specific implementation plan

[0084] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0085] 1. Structural description of gravimeter

[0086] like Figure 1 As shown in , the high-precision gravimeter based on the anti-magnetic suspension principle provided by the present invention specifically includes: a low-frequency magnetic potential well unit, a suspension mechanical vibrator unit, a displacement detection unit and a cavity enclosure unit. Among them, the low-frequency magnetic potential well unit includes a magnetic confinement potential well formed by a plurality of permanent magnets enclosed in an axially symmetrical manner; by changing the relative positions of each permanent magnet, the frequency and confinement position of the magnetic confinement potential well can be adjusted. The suspension mechanical vibrator unit includes a vibrator 3 suspended in the magnetic confinement potential well, and a light-shielding component provided at the top of the vibrator 3 and extending out of the magnetic confinement potential well. The displacement detection unit includes a laser 402, a lens group and a photoelectric converter 403, and the light-shielding component is located on the optical path inside the lens group. The cavity enclosure unit includes an outer shell 8, a magnetic shielding shell 7 and a heat-insulating shell 6 which are nested in sequence and keep a distance, and the cavity of each shell is kept vacuum. The low-frequency magnetic potential well unit, the suspension mechanical vibrator unit and the lens group of the displacement detection unit are all located in the cavity of the innermost heat-insulating shell 6.

[0087] The bottom of the outer shell 8 is seated on the machine base, and a plurality of machine foot screws 10 are provided at the bottom of the machine base, which can be used to adjust the horizontality of the machine base and thus control the inclination angle of the equipment. The magnetic shielding shell 7 is seated on the bottom plate of the outer shell 8 through the thermal insulation pad 9, and the thermal insulation shell 6 is seated on the bottom plate of the magnetic shielding shell 7 through the thermal insulation pad 9. Or it can be changed to a hanging mode, the magnetic shielding shell 7 is suspended on the top plate of the outer shell 8 through the thermal insulation rope, and the thermal insulation shell 6 is suspended on the top plate of the magnetic shielding shell 7 through the thermal insulation rope. For the convenience of operation, a closed side door is provided in the same direction of the outer shell 8, the magnetic shielding shell 7 and the thermal insulation shell 6, which is used to install and adjust the low-frequency magnetic potential well unit and the suspended mechanical oscillator unit. The low-frequency magnetic potential well unit is seated on the bottom plate of the innermost thermal insulation shell 6. There can be multiple groups of magnetic shielding shells 7, and they are nested in sequence while maintaining the spacing; there can also be multiple groups of thermal insulation shells 6, and they are nested in sequence while maintaining the spacing. The cavities of each adjacent shell are kept vacuum. The temperature probe 501 and the electric heater 502 are arranged on the inner wall of the innermost heat-insulating shell 6, and the temperature controller 503 is arranged on the outer side of the outer shell 8. The temperature probe 501 and the electric heater 502 are connected to the temperature controller 503 through cables, and together constitute the temperature control unit 5.

[0088] like Figure 2-4 As shown, the low-frequency magnetic potential well unit has multiple permanent magnets and is divided into two layers, the upper and lower layers, and the permanent magnets in each layer are arranged in an enclosure; the center of the upper magnet 1 is a cavity structure, and the vibrator 3 is suspended in the cavity; the magnetization direction of the lower magnet 2 points to the center, and the magnetic lines of force converge in the central area to generate a magnetic field and a magnetic field gradient in the vertical direction, providing antimagnetic force and constraint for overcoming gravity; the magnetization direction of the upper magnet 1 points from the center to the outside, providing horizontal constraints. The vertical frequency of the magnetic confinement potential well is adjusted by changing the relative distance between the upper and lower layers of permanent magnets; the constraint position of the magnetic confinement potential well is adjusted by changing the relative distance between the permanent magnets in each layer and their enclosure center.

[0089] like Figure 5 As shown, the vibrator 3 is a monomer structure made of graphite or metal material with anti-magnetic properties, and its shape is a columnar structure with a circular or regular polygonal cross section and a relatively contracted bottom. The light-shielding component is located on the optical path inside the lens group in the displacement detection unit to serve as a displacement monitoring object, specifically a cross bar or a light-shielding sheet arranged on the cross bar. The vertical rod 401 fixed on the top of the vibrator 3 is connected to the cross bar to form a T-shaped or cross-shaped structure, and the cross bar is located outside the magnetic confinement potential well.

[0090] like Figure 6As shown, the emitting end of the laser 402 is connected to the first optical fiber, the receiving end of the photoelectric converter 403 is connected to the second optical fiber, and the lens group is located between the emitting end of the first optical fiber and the incident end of the second optical fiber; the lens group in the figure includes two convex lenses, and the light blocking component is located at the focal position between the first lens and the second lens. The laser 402 and the photoelectric converter 403 are installed on the outside of the peripheral housing 8.

[0091] 2. Instructions for use of gravimeter

[0092] The high-precision gravimeter based on the anti-magnetic suspension principle of the present invention has a method of use comprising:

[0093] (1) Confirm that all components of the gravimeter are in good condition and the oscillator is located in the magnetic confinement potential well;

[0094] (2) By changing the relative positions of the permanent magnets in the layer, the confinement position of the magnetic confinement potential well is adjusted, so that the vibrator 3 is stably suspended in the upper cavity and the light shield is located on the optical path inside the lens group; by changing the relative positions of the upper and lower layers of permanent magnets, the vertical frequency of the magnetic confinement potential well is adjusted to meet the measurement requirements;

[0095] (3) Close the closed side doors of each shell layer, evacuate the cavity between the shells, and set the temperature of the temperature controller 503 according to the measurement plan;

[0096] (4) Start the laser 402 and use the photoelectric converter 403 to measure the voltage fluctuation caused by the vertical movement of the light shielding plate; according to the previously calibrated vertical displacement and voltage relationship curve, the vertical displacement of the vibrator 3 is obtained, and the gravity change is further converted.

[0097] 3. Specific application examples

[0098] The heat-insulating shell 6 is placed in the magnetic shielding shell 7 through the support of the heat-insulating pad 9, and the magnetic shielding shell 7 is placed in the vacuum chamber shell 8 through the support of the heat-insulating pad 9. The interval area between the heat-insulating shell 6 and the magnetic shielding shell 7, and the interval area between the magnetic shielding shell 7 and the vacuum chamber shell 8 are all vacuum environments. The material of the heat-insulating pad 9 is preferably polyetheretherketone or ceramic, which has low thermal conductivity and further maintains the temperature stability inside the heat-insulating shell 6. The heat-insulating pad 9 is respectively installed at the bottom of the heat-insulating shell 6 and the magnetic shielding shell 7 to improve the stability of the support.

[0099] Another optional installation method is: the heat preservation shell 6 is suspended in the magnetic shielding shell 7 through the heat preservation rope, and the magnetic shielding shell 7 is suspended in the vacuum chamber shell 8 through the heat preservation rope. The installation direction and number of the heat preservation ropes can be changed according to the specific use situation, and the material of the heat preservation rope is aluminum silicate.

[0100] The shapes of the heat-insulating shell 6 , the magnetic shielding shell 7 and the vacuum chamber shell 8 can be cylindrical or rectangular.

[0101] Furthermore, multiple insulation shells 6 can be provided, for example, including three layers of insulation shells 6, which are nested in sequence and keep the spacing and evacuate to improve the insulation effect. Furthermore, an independent temperature control unit 5 can be provided for each independent insulation shell 6. Multiple magnetic shielding shells 7 can be provided, for example, including three layers of magnetic shielding shells 7, which are nested in sequence and keep the spacing and evacuate to improve the shielding effect of the external magnetic field. The nested shell structures are connected by using insulation pads 9 or insulation ropes to maintain the stability between the multiple shells. The vacuum environment formed between the shells can prevent gas heat exchange, and combined with the low thermal conductivity of the insulation pads 9 or insulation ropes, the heat conduction is further reduced. In this way, when the temperature outside the vacuum chamber shell 8 changes, due to its low thermal conductivity, the temperature of the insulation shell 6 can remain stable for a long time, and such a nested structure realizes the first level of passive temperature control. Even when the outside temperature changes by 1K, the temperature change of the insulation shell 6 will be less than 1mK. The above process does not require the participation of the temperature control unit 5.

[0102] Furthermore, the temperature sensor 501 is used to measure the temperature of the inner wall of the heat-insulating shell 6, and transmit the measured temperature data to the PID temperature controller 503 outside the heat-insulating shell 6. The PID temperature controller 503 adjusts the heating power of the heater 502 in real time according to the measured temperature fluctuation, so as to keep the temperature inside the heat-insulating shell 6 stable. Combined with the first-level passive temperature control, the average temperature fluctuation can be less than 0.1mK. The vacuum environment of each shell cavity can be regarded as the second-level passive temperature control. Combined with the temperature control unit 5, the temperature fluctuation of the heat-insulating shell 6 can be within 0.1mK, and finally the temperature fluctuation of the suspension mechanical oscillator unit can reach the level of 10uK.

[0103] When the tilt angle of the entire device is θ, the vibrator 3 will be subjected to the gravity component in the vertical direction. In order to improve the stability of the device during use, the outer shell 8 is fixedly connected to the base. The connection method can be rivet connection, welding or snap connection. A plurality of machine foot screws 10 (for example, three screws that can be precisely adjusted) are installed at the bottom of the base in a threaded connection manner. The machine foot screws 10 are arranged in a triangle under the base, and the purpose of leveling the platform is achieved by screwing and adjusting. According to actual measurements, the tilt angle of the entire device can be controlled within θ<10 -5 , to avoid inclination noise during the measurement process.

[0104] The above describes the specific embodiments of the present invention. It should be understood that the present invention is not limited to the above specific embodiments, and those skilled in the art may make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A small-sized high-precision gravimeter based on the anti-magnetic suspension principle, characterized in that: include: The low-frequency magnetic potential well unit comprises a magnetic confinement potential well formed by a plurality of permanent magnets enclosed in an axially symmetrical manner; the frequency and confinement position of the magnetic confinement potential well can be adjusted by changing the relative positions of the permanent magnets; A suspended mechanical oscillator unit comprises an oscillator suspended in a magnetic confinement potential well, and a light shielding component arranged at the top of the oscillator and extending out of the magnetic confinement potential well; The displacement detection unit comprises a laser, a lens group and a photoelectric converter, wherein the light blocking component is located on the optical path inside the lens group; The cavity enclosure unit includes an outer shell, a magnetic shielding shell and a thermal insulation shell which are nested in sequence and keep a distance from each other, and the cavity of each shell is kept vacuum; the lens group of the low-frequency magnetic potential well unit, the suspension mechanical oscillator unit and the displacement detection unit are all located in the cavity of the innermost thermal insulation shell.

2. The gravimeter according to claim 1, characterized in that: The multiple permanent magnets are divided into two layers, the upper and lower layers, and the permanent magnets in each layer are arranged in an enclosed manner; the center of the upper magnet is a cavity structure, and the vibrator is suspended in the cavity; the magnetization direction of the lower magnet points to the center, and the magnetic lines of force converge in the central area to generate a vertical magnetic field and a magnetic field gradient, providing anti-magnetic force and constraint for overcoming gravity; the magnetization direction of the upper magnet points from the center to the outside, providing horizontal constraint.

3. The gravimeter according to claim 2, characterized in that: The vertical frequency of the magnetic confinement potential well is adjusted by changing the relative distance between the upper and lower layers of permanent magnets; the confinement position of the magnetic confinement potential well is adjusted by changing the relative distance between the permanent magnets in each layer and their enclosed center.

4. The gravimeter according to claim 1, characterized in that: The vibrator is a monomer structure made of graphite or metal material with anti-magnetic properties; the shape of the vibrator is a columnar structure with a circular or regular polygonal cross section and a relatively contracted bottom.

5. The gravimeter according to claim 1, characterized in that: The light blocking component is located on the optical path inside the lens group in the displacement detection unit to serve as a displacement monitoring object, specifically a crossbar or a light blocking sheet arranged on the crossbar; the vertical rod fixed on the top of the vibrator is connected to the crossbar, and the latter is located outside the magnetic confinement potential well.

6. The gravimeter according to claim 1, characterized in that: The emitting end of the laser is connected to the first optical fiber, the receiving end of the photoelectric converter is connected to the second optical fiber, the lens group is located between the output end of the first optical fiber and the incident end of the second optical fiber; the lens group includes at least two convex lenses, and the light blocking component is located at the focal position of the lens group.

7. The gravimeter according to claim 1, characterized in that: The bottom of the outer shell is seated on the machine base, and a plurality of machine foot screws are arranged at the bottom of the machine base; The magnetic shielding shell is seated on the bottom plate of the outer shell through an insulation pad, and the thermal insulation shell is seated on the bottom plate of the magnetic shielding shell through an insulation pad; or, the magnetic shielding shell is suspended on the top plate of the outer shell through an insulation rope, and the thermal insulation shell is suspended on the top plate of the magnetic shielding shell through an insulation rope; the outer shell, the magnetic shielding shell and the thermal insulation shell are provided with closed side doors in the same direction for installing and adjusting the low-frequency magnetic potential well unit and the suspended mechanical oscillator unit, and the low-frequency magnetic potential well unit is seated on the bottom plate of the thermal insulation shell.

8. The gravimeter according to claim 1, characterized in that: The magnetic shielding shells are provided in multiple groups and are nested in sequence with a spacing maintained; the heat preservation shells are provided in multiple groups and are nested in sequence with a spacing maintained; and the cavities of each shell are kept in vacuum.

9. The gravimeter according to any one of claims 1 to 8, characterized in that: A temperature probe and an electric heater are arranged inside the heat-insulating shell, a temperature controller is arranged outside the outer shell, and the temperature probe and the electric heater are connected to the temperature controller via a cable; or, the laser and the photoelectric converter are installed outside the outer shell.

10. The method for using the gravimeter according to any one of claims 1 to 9, characterized in that: include: (1) Confirm that all components of the gravimeter are in good condition and the oscillator is located in the magnetic confinement potential well; (2) By changing the relative positions of the permanent magnets in the layer, the confinement position of the magnetic confinement potential well is adjusted, so that the vibrator is stably suspended in the upper cavity and the light-blocking component is located on the optical path inside the lens group; by changing the relative positions of the upper and lower layers of permanent magnets, the vertical frequency of the magnetic confinement potential well is adjusted to meet the measurement requirements; (3) Close the closed side doors of each shell layer, evacuate the cavity between the shells, and set the temperature of the temperature controller according to the measurement plan; (4) Start the laser and use the photoelectric converter to measure the voltage fluctuation caused by the vertical movement of the light-blocking component; obtain the vertical displacement of the vibrator based on the pre-calibrated vertical displacement and voltage relationship curve, and further convert the gravity change.

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