Device and method for measuring inspection mass surface potential based on milligram-scale torsion balance

Abstract

The invention belongs to the field of precision measurement, and particularly discloses a device and a method for measuring inspection mass surface potential based on a milligram-scale torsion balance. According to the application, the milligram-level torsion balance is adopted to replace a traditional torsion balance, compared with the traditional torsion balance, the milligram-level torsion balance is smaller in rotational inertia and low in torque sensing thermal noise, the torque detection level is superior to 10-18 Nm / Hz0.5, and the detection sensitivity is extremely high; a micron-sized charged microsphere is adopted to replace a source conductor probe to serve as an excitation source, and the spatial resolution can reach the micron dimension. The suspension charged microspheres are small in electric charge quantity and small in size, so that the influence on the potential on the surface of the to-be-detected mass is small and can be ignored, and relatively high spatial resolution is considered; an optical module is adopted to replace a micro-displacement platform, an optical trap gradient force for suspending the charged microspheres is provided, and the positions of the suspended charged microspheres are changed, so that the charged microspheres directly face different areas on the surface of the inspection mass. The suspended microspheres only interact with photons, so that the mechanical contact between the microspheres and other objects is reduced, the friction effect is reduced, and the detection accuracy is improved.

Description

Technical Field

[0001] The present application belongs to the field of precision measurement, and more specifically, to a device and method for measuring the surface potential of a test mass based on a milligram-level torsion balance. Background Art

[0002] In the past two decades, with the need of gravitational experiments, the measurement of conductor surface potential has been paid more and more attention. The current mainstream surface potential measurement methods are mainly divided into electron microscopy technology, Kelvin probe technology, torsion balance technology and optical suspended particle based probe technology.

[0003] The traditional torsion balance solution is to suspend the test mass with a suspension wire and move the source conductor probe through a micro-displacement platform. There is a potential difference between the source conductor probe and the surface of the torsion balance. The torsion balance will deflect under the action of the electrostatic torque. The electrostatic torque exerted on the torsion balance can be measured through capacitive displacement sensor, which can reflect the potential of the sample.

[0004] However, the size of the source conductor probe is in the millimeter range, and its spatial resolution can only reach the sub-millimeter range. Reducing the size of the source conductor probe will reduce the electrostatic force between the probe and the sample, thereby reducing the sensitivity of the potential measurement.

[0005] The probe technology based on optical suspended particles uses laser-suspended solid media as sensitive units, and measures the changes in the motion state of the sensitive units after being acted upon by external forces to obtain the size of the external force field. The size of optically suspended particles is generally in the micron or submicron order. For example, in the paper "Experimental Study on Surface Potential Measurement of Test Mass Based on Suspended Particles", it is only necessary to measure the offset of the equilibrium position of the particles and the stiffness of the light trap in the direction to calculate the electrostatic force on the particles, and then obtain the potential difference between the test mass and the particles. However, this method requires the construction of a complex position detection optical path to measure the position offset of the suspended particles. The theoretical calculation of the stiffness of the light trap in the direction is relatively complex, and there is a certain deviation from the actual situation. The measurement of many parameters in the theoretical calculation is also relatively difficult. Summary of the invention

[0006] In view of the defects of the prior art, the purpose of the present application is to provide a device and method for measuring the surface potential of a proof mass based on a milligram-level torsion balance, aiming to solve the problem that the prior art cannot simultaneously take into account high sensitivity and high spatial resolution of the proof mass surface potential measurement.

[0007] A first aspect of the present application relates to a device for measuring the surface potential of a test mass based on a milligram-level torsion balance, comprising: an optical module, a charged microsphere, a milligram-level torsion balance, a signal monitoring module, and a processing unit; The optical module is used to provide a light trap gradient force for suspending the charged microspheres and to change the position of the suspended charged microspheres so that they face different areas of the inspection mass surface; Suspended charged microspheres are used as excitation sources to electrostatically interact with the charges in the area facing the surface of the test mass; The milligram-level torsion balance is composed of a suspension wire suspending a milligram-level test mass; The test mass is used to cause twisting motion under the action of electrostatic torque when the suspended charged microsphere approaches; The signal monitoring module is used to monitor the torsion angle of the inspection mass and send it to the processing unit; The processing unit is used to calibrate the static electricity of the charged microspheres, calculate the electrostatic torque on the inspection mass in combination with the torsion angle change and transfer function of the inspection mass, and invert the electric potential and overall distribution of each area on the surface of the inspection mass by combining the static electricity of the charged microspheres and the electrostatic torque on the inspection mass.

[0008] Preferably, the device further comprises: a capacitor plate, used to apply a simple harmonic alternating electric field in a horizontal direction to the suspended charged microspheres during the calibration of the electrostatic quantity of the charged microspheres; The optical module is also used to transfer the motion information of the charged microspheres to the optical signal and send the motion power spectrum of the microspheres to the processing unit; The processing unit is also used to calibrate the static electricity amount of the charged microspheres according to the first motion power spectrum in the absence of a simple harmonic alternating electric field and the second motion power spectrum driven by a simple harmonic alternating electric field.

[0009] Preferably, the device further comprises: an electromagnetic shielding cover for shielding the influence of the simple harmonic alternating electric field on the milligram-level torsion balance.

[0010] Preferably, the suspension wire is a quartz wire with a diameter in the micrometer range, and the connection between the quartz wire and the milligram-level inspection mass is laser non-destructive welding.

[0011] Preferably, the electrostatic charge of the charged microsphere is several tens of electrons, and the diameter does not exceed the micrometer level; the distance between the suspended microsphere and the inspection mass is in the micrometer level.

[0012] Preferably, the length of the vacuum light trap generated by the optical module is not less than twice the length of the inspection mass.

[0013] Preferably, the signal monitoring module is an optical lever signal monitoring module.

[0014] The second aspect of the present application relates to a method for measuring the surface potential of a test mass based on a milligram-level torsion balance, comprising: Step 1, calibrating the static electricity of the charged microspheres; Step 2, moving the suspended charged microsphere so that it is close to and facing an area of ​​the test mass until the test mass undergoes a twisting motion; Step 3: Fit the torsion angle change curve during the torsion of the inspection mass to obtain the quality factor, and calculate the electrostatic torque on the inspection mass in combination with the angle-electrostatic torque transfer function; Step 4: Based on the ball-plate electrostatic force theoretical model, the static electricity of the charged microspheres and the electrostatic torque on the test mass are combined to invert the electric potential of the area facing the test mass surface and the suspended charged microspheres.

[0015] Preferably, the method further comprises: Step 5: Change the position of the suspended charged microsphere so that it faces another area of ​​the test mass surface, and repeat steps 3-4 until all areas of the test mass surface are scanned to obtain the test mass surface potential distribution.

[0016] Preferably, the inversion is performed to obtain the potential of a certain area of ​​the surface of the test mass, specifically as follows:

[0017] in, represents the electrostatic torque, represents the torsion angle of the test mass, represents the capacitance between the suspended charged microsphere and the test mass, It represents the static electricity of the suspended charged microspheres. Represents the electric potential of a certain area on the surface of the test mass.

[0018] It can be understood that the beneficial effects of the second aspect mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here.

[0019] In general, the above technical solutions conceived by this application have the following beneficial effects compared with the prior art: (1) This application proposes a device for measuring the surface potential of a test mass based on a milligram-level torsion balance. The milligram-level torsion balance is used to replace the traditional torsion balance. Compared with the traditional torsion balance, the milligram-level torsion balance has a smaller moment of inertia, low thermal noise of torque sensor, and a torque detection level better than 10 -18 Nm / Hz 0.5, with extremely high detection sensitivity; and the milligram-level torsion balance has a high intrinsic frequency, which can supplement the high-frequency detection range not covered by the large-mass torsion balance; using micron-level charged microspheres instead of source conductor probes as excitation sources, the spatial resolution can reach the micron level. Due to the small amount of charge and small size of the suspended charged microspheres, the impact on the potential of the surface of the test mass to be tested is small and can be ignored, taking into account the high spatial resolution; using optical modules instead of micro-displacement platforms to provide light trap gradient forces for the suspension of charged microspheres, and changing the position of the suspended charged microspheres so that they face different areas of the test mass surface. The suspended microspheres only interact with photons, reducing the mechanical contact between the microspheres and other objects, reducing the friction effect, and improving the accuracy of detection.

[0020] (2) This application proposes a device for measuring the surface potential of a test mass based on a milligram-level torsion balance. When calculating the electrostatic torque, what is changed is the equilibrium position of the suspended charged microspheres, and what is measured is the torsional motion information of the test mass. In essence, it still belongs to the torsion balance technology. Compared with the scheme based on optical suspended particles, what is changed is the position of the test mass, and what is measured is the displacement offset of the charged microspheres. Since this application changes the equilibrium position of the suspended charged microspheres, the additional interference factors introduced to the test mass to be measured are reduced, and the electrostatic torque can be calculated more accurately; since this application measures the torsional motion information of the test mass, compared with the scheme based on optical suspended particles, it is necessary to build a complex position detection optical path to measure the position offset of the suspended particles. In the case of achieving the same measurement accuracy, the measurement optical path of this application is simpler and easier to operate. In both measurement schemes, the test mass and the suspended particles to be measured are both in a vacuum container. The space in the container is limited, and the measurement optical path can only be set outside the container. The optical path of this application is simple and can save space. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of a device for measuring the surface potential of a test mass based on a milligram-level torsion balance provided in an embodiment of the present application.

[0022] Figure 2 It is a flow chart of a method for measuring the surface potential of a test mass based on a milligram-level torsion balance provided in an embodiment of the present application.

[0023] Throughout the drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1-milligram-level torsion balance; 2-inspection mass; 3-signal monitoring module; 4-charged microspheres; 5-optical module; 6-capacitor plates; 7-electromagnetic shielding cover. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application 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 application and are not used to limit the present application.

[0025] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0026] like Figure 1 As shown, the present application proposes a device for measuring the surface potential of a test mass based on a milligram-level torsion balance, comprising: an optical module 5, a charged microsphere 4, a milligram-level torsion balance 1, a signal monitoring module 3 and a processing unit (not shown).

[0027] The optical module 5 is used to provide a light trap gradient force for suspending the charged microspheres 4 and to change the positions of the suspended charged microspheres so that they face different areas on the surface of the inspection mass 2 .

[0028] The suspended charged microspheres are used as excitation sources to electrostatically interact with the charges in the area facing the surface of the proof mass.

[0029] The milligram-level torsion balance 1 is composed of a milligram-level test mass suspended by a suspension wire; the test mass is used to generate a torsional motion under the action of an electrostatic torque when a suspended charged microsphere approaches.

[0030] The signal monitoring module 3 is used to monitor the torsion angle of the inspection mass 2 and send it to the processing unit.

[0031] The processing unit is used to calibrate the static electricity of the charged microspheres, calculate the electrostatic torque on the inspection mass in combination with the torsion angle change and transfer function of the inspection mass, and invert the electric potential and overall distribution of each area on the surface of the inspection mass by combining the static electricity of the charged microspheres and the electrostatic torque on the inspection mass.

[0032] Preferably, the suspension wire is a quartz wire with a diameter in the micrometer range, and the connection between the quartz wire and the milligram-level inspection mass is laser non-destructive welding.

[0033] It should be noted that the present application prefers micron-level quartz wire, which has a higher quality factor and lower heat dissipation, and can effectively improve the sensitivity of the milligram-level torsion balance; the present application prefers laser non-destructive welding, which can effectively reduce the connection loss between the suspension wire and the inspection mass.

[0034] In an embodiment shown, the milligram-level torsion balance 1 is composed of a test mass suspended by an ultra-fine quartz wire with a diameter of 3um and a length of 100mm. The test mass 2 has a diameter of 3mm and a thickness of 0.5mm, and is gold-plated on the surface of the test mass to make it a conductor and act as a reflector. The total mass of the milligram-level torsion balance is within 100mg, and the moment of inertia is within 10 -5kg·m 2 The Q value of the torsion mode of the milligram-level torsion balance can reach 10 -5 Theoretically, the torque detection sensitivity at the eigenfrequency can reach 10 -18 Nm / HZ 0.5 , which is at least three orders of magnitude higher than the torque detection sensitivity of a large-mass torsion balance.

[0035] Production of milligram-level torsion balance: 1) Suspension wire: In the torsion pendulum system, the suspension wire material usually selected is quartz. Compared with metal wire, quartz wire has a higher quality factor and lower heat dissipation. This application uses an ultra-fine quartz wire with a diameter of 3um and a length of 100mm.

[0036] 2) Inspection mass: The inspection mass uses quartz with a low thermal expansion coefficient as the substrate, and a layer of gold film is plated on the surface to make it a conductor and act as a reflector. The smaller the thickness of the reflector, the smaller the moment of inertia, so the design inspection mass thickness is 0.5mm, the diameter of the inspection mass is 3mm, and the total mass is within 100mg.

[0037] 3) Welding: Weld the quartz wire and the milligram-level test mass together to make the two into a milligram-level torsion balance. However, the dissipation at the connection between the quartz wire and the test mass will also affect the torque detection sensitivity of the torsion balance. The light beam generated by the carbon dioxide laser can effectively melt the quartz and achieve a good welding effect. The laser power, beam shape and other parameters can be controlled, and no additional airflow is generated. Therefore, this application uses a carbon dioxide laser to weld the quartz wire and the test mass together. The laser provides an amplitude of 0-4.6V, a frequency of 5KHZ, a duty cycle of 1.5%-50%, and a power adjustment range of 10W-150W. The larger the duty cycle, the greater the output power.

[0038] The test mass in the milligram-level torsion balance undergoes torsional motion under the action of the electrostatic torque between it and the suspended microspheres, that is, the present application reflects the magnitude of the electrostatic torque by the torsional motion of the test mass. The signal monitoring module detects the torsional motion of the test mass and can detect the change in torsional angle. The amplitude of the change in torsional angle is then used to fit the Q value of the milligram-level torsion balance, thereby obtaining the magnitude of the electrostatic torque.

[0039] Preferably, the device also includes: a capacitor plate 6, which is used to apply a horizontal harmonic AC electric field to the suspended charged microspheres during the calibration of the electrostatic quantity of the charged microspheres; the optical module is also used to transmit the motion information of the charged microspheres to the optical signal and send the motion power spectrum of the microspheres to the processing unit; the processing unit is also used to calibrate the electrostatic quantity of the charged microspheres based on the first motion power spectrum in the absence of a harmonic AC electric field and the second motion power spectrum driven by the harmonic AC electric field.

[0040] Preferably, the capacitor plate is fixed on a lifting platform, and the position of the capacitor plate relative to the microsphere can be changed by adjusting the lifting platform.

[0041] In the initial state, the milligram-level torsion balance and the suspended microspheres are already in the vacuum chamber. When calibrating the electrostatic quantity of the suspended microspheres, the lifting platform is adjusted to move the electromagnetic shielding cover and cover the milligram-level torsion balance with the electromagnetic shielding cover. When there is no simple harmonic AC electric field, the capacitor plates are below the suspended microspheres; when a simple harmonic AC electric field needs to be applied, the lifting platform is adjusted to move the capacitor plates to both sides of the suspended microspheres, and a simple harmonic AC electric field is applied between the capacitor plates. After the electrostatic quantity calibration of the suspended microspheres is completed, the lifting platform is adjusted to remove the capacitor plates and the electromagnetic shielding cover, and then the optical path is adjusted to move the suspended charged microspheres to the vicinity of the inspection mass.

[0042] Preferably, the device further comprises: an electromagnetic shielding cover 7 for shielding the influence of the simple harmonic AC electric field on the milligram-level torsion balance. The electromagnetic shielding cover 7 is fixed on a lifting platform, and the position of the electromagnetic shielding cover can be changed by adjusting the lifting platform.

[0043] It should be noted that the present application preferably introduces an electromagnetic shielding cover to eliminate the influence of the simple harmonic AC electric field on the milligram-level torsion balance, while also reducing the influence of the milligram-level torsion balance on the calibration results of the electrostatic quantity of the charged microspheres, thereby more accurately calibrating the electrostatic quantity of the charged microspheres.

[0044] Preferably, the electrostatic charge of the charged microsphere is several tens of electrons, and the diameter does not exceed the micrometer level; the distance between the suspended microsphere and the inspection mass is in the micrometer level.

[0045] It should be noted that the interaction force between the suspended microspheres as the excitation source and the test mass to be measured is an electrostatic force, and the static electricity of the microspheres will affect the potential of the surface of the test mass to be measured. The present application preferably has a static electricity of several dozen electrons and a diameter not exceeding the micrometer level. Due to the small amount of charge and the small volume, the effect on the potential of the surface of the test mass to be measured is small and can be ignored, thereby improving the accuracy.

[0046] Preferably, the length of the vacuum light trap generated by the optical module is not less than twice the length of the inspection mass.

[0047] It should be noted that the present application prefers the above-mentioned design to ensure that there is enough space for the suspended microspheres to move, so as to measure the electric potential of each area on the surface of the inspection mass and prevent the electric potential on the surface of the inspection mass from being affected.

[0048] In an illustrated embodiment, the optical module includes a light source for suspending microspheres and its optical path, an acousto-optic modulator AOM (used to adjust the power of the suspended microsphere light beam), and a photodetector and its optical path (used to detect the position change of the microsphere). Specifically, after the light trap capture light emitted by the light source enters the vacuum cavity, it is focused by the focusing lens to form a light trap near the focal position to stably capture the charged microspheres. The light trap structure can be a vertical light trap or a horizontal light trap. In order to reduce the impact of environmental thermal noise on detection, it is necessary to reduce the air pressure in the vacuum cavity. The captured charged microspheres are spherical in shape and made of silicon dioxide.

[0049] Preferably, the signal monitoring module is an optical lever signal monitoring module.

[0050] It should be noted that the present application preferably measures the torsion angle of the test mass based on the principle of optical lever. This method is a non-contact measurement that does not require direct contact with the test mass and will not affect the potential on the surface of the test mass. This method also has high measurement accuracy, reaching sub-microradian levels.

[0051] In an illustrated embodiment, a signal monitoring module is used to monitor the torsional motion of the inspection mass, and it is composed of a laser, a chopper, a position detector PSD, a phase-locked amplifier, a signal acquisition system, and a computer. The position detector is located about 1 m outside the vacuum container window corresponding to the inspection mass, and is used to receive the reflected light from the surface of the inspection mass and convert the reflected light signal into a voltage signal, that is, convert the angle change of the inspection mass into a voltage signal and output it as a voltage signal. The PSD is connected to the phase-locked amplifier in the signal acquisition system, and the phase-locked amplifier extracts and amplifies the voltage signal output by the PSD. The signal acquisition system is connected to the computer, and is used to convert the voltage signal output by the PSD into a digital signal and store it in the computer, that is, to extract the electrical signal converted from the angle change of the movement of the inspection mass.

[0052] The working process of the signal monitoring module: The He-Ne laser with a wavelength of 633nm and a power of about 1mW is used as the light source. The light emitted by it passes through a chopper and becomes a light wave with a certain frequency. Then it passes through a pentagonal prism and a focusing system, is incident on the coating on the surface of the inspection mass and reflected back, and finally focuses on the surface of the position sensor PSD. Through the photoelectric effect, a current proportional to the light intensity is generated at the incident point on the PSD surface, which is converted into two voltages after passing through the conversion circuit. , the two voltages The output is sent to the phase-locked amplifier in the signal acquisition system. The phase-locked amplifier is used to detect the voltage The signal is extracted and amplified, and the amplified signal is converted into a digital signal by the signal acquisition circuit and stored in the computer. When the deflection angle of the inspection mass changes, the reflected light of the optical lever will be deflected accordingly, and then the incident point of the reflected light on the position sensor will also change. In order to reduce the influence of factors such as laser power, the signal of the two voltages is selected. Gives the angular variation of the test mass.

[0053] The entire measuring device is in an environment where a modulated electric field can be applied to calibrate the charge of the microsphere. The charged microsphere and the optical module together constitute an optical suspension auxiliary system. In the suspended micro-assisted system, except for the microsphere located near the test mass to be measured, the remaining optical components are located far away from the test mass to be measured.

[0054] like Figure 2 As shown, the present application discloses a method for measuring the surface potential of a test mass based on a milligram-level torsion balance, comprising: Step 1: calibrate the static electricity of the charged microspheres.

[0055] S11. Adjust the light path to form a double-beam potential well to suspend the charged microspheres.

[0056] Specifically, a single beam of light emitted by a light source is divided into two beams with mutually perpendicular polarization directions through a 1 / 2 wave plate and a beam splitter. The two beams are converged through an acousto-optic modulator, a beam expander and an objective lens, and finally form a counter-radial double-beam potential well in the vacuum cavity to capture the charged microspheres, so that the charged microspheres are stably suspended in the vacuum cavity.

[0057] S12. Obtain a first motion power spectrum of the suspended microspheres in the absence of a simple harmonic alternating electric field, wherein the motion power spectrum includes power intensities of the suspended microspheres at different motion frequencies.

[0058] The movement of the suspended microspheres in the absence of a simple harmonic alternating electric field is recorded for comparison when an alternating electric field is applied.

[0059] S13. Apply a simple harmonic alternating electric field to the suspended microspheres to obtain the second motion power spectrum of the suspended microspheres driven by the alternating electric field force. .

[0060] Specifically, the lifting platform is adjusted to move the capacitor plates to the two sides of the suspended microsphere, and a simple harmonic alternating electric field is applied between the capacitor plates.

[0061] The motion equation of the suspended charged microsphere driven by the alternating electric field force is:

[0062] in, represents the displacement of the suspended charged microsphere, , Respectively The first and second derivatives with respect to time, represents the velocity damping of the microsphere, represents the eigenfrequency of the microsphere, represents the background field force of the microsphere, represents the time of microsphere movement, represents the mass of the charged microsphere, Indicates the static electricity of the charged microsphere, alternating electric field , represents the amplitude of the alternating electric field, Represents the driving frequency of the alternating electric field.

[0063] Convert the above formula into displacement power spectrum density expression:

[0064] in, represents the total power spectral density of the microsphere, represents the angular frequency of the microsphere, represents the Boltzmann constant, Indicates the ambient temperature, represents the sampling time of the photodetector for the optical signal containing the microsphere motion information, represents the Symle function, represents the power spectral density of random thermal noise in the background environment, represents the power spectral density caused by electric field driving.

[0065] S14. Calculate the ratio of the two motion power spectra at the driving frequency of the alternating electric field to calibrate the static electricity of the suspended microspheres.

[0066] remember is the magnitude of the random noise power spectral density at the driving frequency, is the magnitude of the power spectrum density at the driving frequency under the action of the alternating electric field force, the above formula can be converted into:

[0067] Preferably, the electrostatic charge of the suspended microspheres The calculation formula is as follows:

[0068] in, represents the Boltzmann constant, Indicates the ambient temperature, represents the velocity damping of the suspended microsphere, represents the ratio of the two motion power spectra at the driving frequency of the simple harmonic alternating electric field, represents the mass of the suspended charged microspheres, represents the amplitude of the alternating electric field, Indicates the sampling time.

[0069] Step 1 also includes: S15. Build a milligram-level torsion balance unit in the vacuum chamber, and adjust the lifting platform to raise the electromagnetic shielding cover to a suitable height so that it completely covers the milligram-level torsion balance.

[0070] Specifically, the milligram-level torsion balance unit consists of a milligram-level torsion balance and an optical lever signal monitoring module. The parameters such as the upper flange position and the window position of the vacuum container are determined, and the suspension wire length and other parameters are connected. The suspension wire and the test mass are then connected to make a milligram-level torsion balance. The milligram-level torsion balance is suspended by a vacuum guide, and the suspension wire is connected under the vacuum guide, and the test mass is suspended by the suspension wire. The height of the test mass in the vacuum chamber can be changed by rotating the side of the vacuum guide, and the deflection angle of the test mass can be changed by rotating the knob on the top. The height and angle of the test mass are adjusted by the vacuum guide. The optical path of the signal monitoring module is adjusted to monitor the motion signal of the test mass.

[0071] Step 2: Move the position of the suspended charged microsphere so that it is close to and facing an area of ​​the test mass until the test mass undergoes a twisting motion.

[0072] Step 3: Fit the torsion angle change curve during the torsion of the inspection mass to obtain the quality factor, and calculate the electrostatic torque on the inspection mass in combination with the angle-electrostatic torque transfer function.

[0073] Specifically, a laser beam is incident on the inspection mass surface and reflected back, and finally gathered on the surface of the position sensor PSD. Through the photoelectric effect, a current proportional to the light intensity is generated at the incident point, and then flows through the substrate to the electrodes at both ends. After passing through the conversion circuit, it becomes two voltage signals. , In order to reduce the influence of factors such as laser power fluctuation, the division signal of the two voltage signals is selected to give the angle change of the inspection quality. The division signal of the two voltage signals can be written as follows:

[0074] Inspection quality angle change The expression can be written as:

[0075] in, is represented as the distance between the test mass and the detector, Represents the distance between the two detector electrodes. After a period of accumulation, the test quality angle change curve is obtained. express The amount of change.

[0076] The inspection mass angle variation curve is fitted to obtain The electrostatic torque on the test mass is calculated by combining the transfer function with other parameters.

[0077] Taking structural damping into account, the motion equation of the test mass can be written as follows:

[0078] in, represents the angle of motion of the test mass, represents the second derivative of the angle of motion of the test mass, is the moment of inertia of the test mass, represents the torsional elastic coefficient of the suspension wire, represents the imaginary unit, represents the structural damping dissipation factor, , represents the electrostatic torque.

[0079] Performing Fourier transform on the above equation, we get:

[0080] Among them, the torsional elastic coefficient The eigenfrequency and moment of inertia Expressed as The above formula can be written as:

[0081] Preferably, the test mass movement angle With electrostatic torque The relationship is as follows:

[0082]

[0083] in, represents the angle-electrostatic torque transfer function, represents the torsional elastic coefficient of the suspension wire, represents the eigenfrequency of the test mass motion, Represents the quality factor of the milligram-level torsion balance.

[0084] Step 4: Based on the ball-plate electrostatic force theoretical model, the static electricity of the charged microspheres and the electrostatic torque on the test mass are combined to invert the electric potential of the area facing the test mass surface and the suspended charged microspheres.

[0085] Preferably, the inversion is performed to obtain the potential of a certain area of ​​the surface of the test mass, specifically as follows:

[0086] in, represents the electrostatic torque, represents the torsion angle of the test mass, represents the capacitance between the suspended charged microsphere and the test mass, It represents the static electricity of the suspended charged microspheres. Represents the electric potential of a certain area on the surface of the test mass.

[0087] Preferably, the method further comprises: Step 5: Change the position of the suspended charged microsphere so that it faces another area of ​​the test mass surface, and repeat steps 3-4 until all areas of the test mass surface are scanned to obtain the test mass surface potential distribution.

[0088] This application achieves potential measurement in a large dynamic range by moving the position of the microsphere:

[0089] in, represents the surface potential distribution of the test mass, Indicates the inspection quality surface The potential of a certain area of ​​the block is related to the surface potential of The difference in potential of a certain area of ​​the block, Represents the displacement between two small areas.

[0090] It should be understood that expressions such as "including" and "may include" that may be used in the present application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In the present application, terms such as "including" and / or "having" may be interpreted as indicating specific characteristics, numbers, operations, constituent elements, components, or combinations thereof, but may not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.

[0091] The terms "first" and "second" in the specification and claims of this application are used to distinguish different objects rather than to describe a specific order of objects. For example, a first response message and a second response message are used to distinguish different response messages rather than to describe a specific order of response messages.

[0092] In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0093] In the description of the embodiments of the present application, unless otherwise specified, "multiple" means two or more than two. For example, multiple processing units refer to two or more processing units, etc.; multiple elements refer to two or more elements, etc.

[0094] In addition, in the present application, the expression "and / or" includes any and all combinations of the associated listed words. For example, the expression "A and / or B" may include A, may include B, or may include both A and B.

[0095] In the description of the embodiments of the present application, it should be noted that, unless otherwise clearly specified and limited, the term "connection" should be understood in a broad sense. For example, "connection" can be a detachable connection or a non-detachable connection; it can be a direct connection or an indirect connection through an intermediate medium. Among them, "fixed connection" means that the relative position relationship after connection remains unchanged. "Rotational connection" means that the two are connected to each other and can rotate relative to each other after connection. "Sliding connection" means that the two are connected to each other and can slide relative to each other after connection. The directional terms mentioned in the embodiments of the present application, such as "top", "bottom", "inside", "outside", "left", "right", etc., are only reference directions of the accompanying drawings. Therefore, the directional terms used are for better and clearer explanation and understanding of the embodiments of the present application, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the embodiments of the present application.

[0096] In addition, in the embodiments of the present application, the mathematical concepts mentioned are symmetry, equality, parallelism, verticality, etc. These limitations are all for the current state of the art, rather than being absolutely strict definitions in a mathematical sense, and allow a small amount of deviation, approximation to symmetry, approximation to equality, approximation to parallelism, approximation to verticality, etc. are all possible. For example, A and B are parallel, which means that A and B are parallel or approximately parallel, and the angle between A and B can be between 0 and 10 degrees. A and B are perpendicular, which means that A and B are perpendicular or approximately perpendicular, and the angle between A and B can be between 80 and 100 degrees.

[0097] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A device for measuring the surface potential of a test mass based on a milligram-level torsion balance, characterized in that: include: Optical module, charged microsphere, milligram-level torsion balance, signal monitoring module and processing unit; The optical module is used to provide a light trap gradient force for suspending the charged microspheres and to change the position of the suspended charged microspheres so that they face different areas of the inspection mass surface; Suspended charged microspheres are used as excitation sources to electrostatically interact with the charges in the area facing the surface of the test mass; The milligram-level torsion balance is composed of a suspension wire suspending a milligram-level test mass; The test mass is used to cause twisting motion under the action of electrostatic torque when the suspended charged microsphere approaches; The signal monitoring module is used to monitor the torsion angle of the inspection mass and send it to the processing unit; The processing unit is used to calibrate the static electricity of the charged microspheres, and calculate the electrostatic torque on the test mass in combination with the torsion angle change and the transfer function of the test mass; The electrostatic quantity of the charged microspheres and the electrostatic torque on the test mass are combined to invert the electric potential of each area on the test mass surface and its overall distribution.

2. The device according to claim 1, characterized in that The device also includes: a capacitor plate, which is used to apply a simple harmonic alternating electric field in a horizontal direction to the suspended charged microspheres during the calibration of the electrostatic quantity of the charged microspheres; The optical module is also used to transfer the motion information of the charged microspheres to the optical signal and send the motion power spectrum of the microspheres to the processing unit; The processing unit is also used to calibrate the static electricity amount of the charged microspheres according to the first motion power spectrum in the absence of a simple harmonic alternating electric field and the second motion power spectrum driven by a simple harmonic alternating electric field.

3. The device according to claim 2, characterized in that The device also includes an electromagnetic shielding cover for shielding the influence of the simple harmonic alternating current electric field on the milligram-level torsion balance.

4. The device according to claim 1, characterized in that The suspension wire is a quartz wire with a diameter in the micrometer range, and the connection between the quartz wire and the milligram-level inspection mass is laser non-destructive welding.

5. The device according to claim 1, characterized in that The electrostatic charge of the charged microsphere is several tens of electrons, and the diameter does not exceed the micrometer level; the distance between the charged microsphere and the inspection mass is in the micrometer level.

6. The device according to claim 1, characterized in that The length of the vacuum light trap generated by the optical module is not less than twice the length of the inspection mass.

7. The device according to claim 1, characterized in that The signal monitoring module is an optical lever signal monitoring module.

8. A method for measuring the surface potential of a test mass based on a milligram-level torsion balance, characterized in that: include: Step 1, calibrating the static electricity of the charged microspheres; Step 2, moving the suspended charged microsphere so that it is close to and facing an area of ​​the test mass until the test mass undergoes a twisting motion; Step 3, fitting the torsion angle change curve during the torsion of the inspection mass to obtain the quality factor, and combining the angle-electrostatic torque transfer function to calculate the electrostatic torque on the inspection mass; Step 4: Based on the ball-plate electrostatic force theoretical model, the static electricity of the charged microspheres and the electrostatic torque on the test mass are combined to invert the electric potential of the area facing the test mass surface and the suspended charged microspheres.

9. The method according to claim 8, characterized in that The method further includes: Step 5: Change the position of the suspended charged microsphere so that it faces another area of ​​the test mass surface, and repeat steps 3-4 until all areas of the test mass surface are scanned to obtain the test mass surface potential distribution.

10. The method according to claim 8, characterized in that The inversion tests the potential of a certain area on the surface of the mass, as follows: in, represents the electrostatic torque, represents the torsion angle of the test mass, represents the capacitance between the suspended charged microsphere and the test mass, It represents the static electricity of the suspended charged microspheres. Represents the electric potential of a certain area on the surface of the test mass.

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