Method and device for measuring surface charge density and surface potential of dielectric material

Abstract

The invention belongs to but not limited to the technical field of surface analysis, and particularly relates to a dielectric material surface charge density and surface potential measurement method and device, and the method comprises the steps: S1, enabling a to-be-measured dielectric material to be subjected to an electrostatic force F through an external electric field, and transmitting the electrostatic force F to a compound pendulum frame through a sample support; s2, the pendulum frame of the compound pendulum rotates by an angle delta theta under the action of the electrostatic force F; s3, the angle delta theta is equal to the displacement x of a middle pole plate of the bottom capacitance displacement detection system; s4, the differential capacitance delta C of the two capacitors of the capacitance displacement detection system is in direct proportion to the rotation angle delta theta; and S5, after modulation and demodulation of the capacitance sensing circuit, the delta C is converted into a voltage output signal VO.

Description

Technical Field

[0001] The present invention belongs to but is not limited to the field of surface analysis technology, and in particular relates to a method and device for measuring the surface charge density and surface potential of a dielectric material. Background Art

[0002] Surface charge density is an important physical quantity that describes the charge distribution on the surface of a material. It is widely used in materials science, nanotechnology, electronic devices, and biosensors. Accurately measuring surface charge density is crucial to understanding the electrical properties of materials, surface interactions, and the behavior of biomolecules on the surface. For example, in electrochemical reactions, the charge distribution on the electrode surface can significantly affect the reaction rate and selectivity. In biosensors, the binding ability of biomolecules is often closely related to their surface charge density. Therefore, it is particularly important to develop efficient and accurate surface charge density measurement technology. At present, a variety of methods for measuring surface charge density have been developed, including:

[0003] Kelvin probe force microscopy (KPFM) technology is a combination of atomic force microscopy and Kelvin method. The basic principle of Kelvin method ( Figure 2 (as shown) is to measure the surface potential of a sample with a probe of known work function. Before the probe and sample come into contact, their vacuum energy levels are the same, but their Fermi levels are different, so their work functions are also different; when in contact, electrons migrate from the low work function to the high work function, thereby leveling the Fermi level, and the vacuum energy levels of the two change. The difference in vacuum energy levels is the contact potential difference (CPD) V CPD =(Φ tip -Φ sample ) / e. If you want to obtain the specific value of the contact potential difference, you can apply a reverse voltage equal to the contact potential difference between the probe and the sample, which can make the vacuum energy levels of the two levels flush; by measuring the DC voltage applied between the probe and the sample by the circuit, you can get an obvious feature to show the state when the vacuum energy levels of the two are flush, so as to obtain the specific value. The work function of the probe is known, so the work function of the sample can be measured.

[0004] 1. Technological development

[0005] In 1898, the Kelvin probe principle was first proposed by Lord Kelvin, mainly used to measure the contact potential difference between materials. This principle laid the foundation for the later Kelvin probe force microscope. First reported in 1991, researchers combined Kelvin probe technology with atomic force microscopy (AFM) to achieve nanoscale imaging of surface potential, and achieved a lot of results in the fields of surface charge distribution, charge transfer, and work function testing of metal materials. With the continuous development of nanotechnology and materials science, KPFM technology is also constantly improving. Researchers are exploring higher-resolution measurement methods and new application areas. For example, KPFM has shown great potential in quantum computing and the development of new electronic devices. However, it also has some disadvantages that affect its effectiveness and reliability in applications.

[0006] The working principle of the vibrating capacitance electrometer to measure charge density is mainly to use the compensation method, such as Figure 1 The compensation method is to use an electret or an electrode containing an air gap that vibrates at a certain frequency to form a corresponding alternating electric field in the air gap, replacing the dynamic capacitor method to measure the induced alternating current. The specific measurement principle is to add an amplitude modulated reverse phase AC voltage V in the air gap. S , used to compensate the air gap electric field between the electret and the electrode until the air gap electric field E1 is 0 (full compensation is achieved). Then the equivalent surface charge density of the electret with single-sided electrode plating is for:

[0007]

[0008] This method is a contactless measurement. Its basic advantage is that the charge density can be determined without measuring the air gap thickness.

[0009] 2. Practical Application

[0010] The compensation method is a non-contact method, which is commonly used in the market. Figure 2 The EST102 vibrating capacitance electrometer shown.

[0011] Figure 2 The vibrating capacitance electrometer shown is priced at around RMB 22,000.

[0012] In view of the above analysis, the technical problems that need to be solved urgently in the prior art are:

[0013] (1) Surface property dependence: The performance of Kelvin probe microscopy is highly dependent on the surface properties of the sample. Different surface conditions can lead to significant variations in the measurement results, which makes comparisons between different samples difficult. In addition, the cleanliness, roughness, and morphology of the sample will affect the measurement results, which requires that the sample must be carefully prepared and processed before measurement.

[0014] (2) Sensitivity to the environment: Kelvin probe microscopes are very sensitive to environmental conditions such as temperature, humidity, and electromagnetic interference. Slight changes in the environment may affect the measurement results, so it is important to ensure that these variables are controlled when conducting experiments. This high dependence on the environment may limit its applicability in certain practical applications.

[0015] (3) Vibrating capacitance electrometers are not suitable for high-precision experiments and are expensive. Summary of the invention

[0016] In view of the problems existing in the prior art, the present invention provides a method and device for measuring the surface charge density and surface potential of a dielectric material.

[0017] The present invention is achieved by a method for measuring the surface charge density and surface potential of a dielectric material, comprising:

[0018] S1, the external electric field causes the dielectric material to be tested to be subjected to an electrostatic force F, which is transmitted to the compound pendulum frame through the sample holder;

[0019] S2, the compound pendulum frame rotates by an angle Δθ under the action of the electrostatic force F;

[0020] S3, the angle Δθ is equal to the displacement x of the middle plate of the bottom capacitive displacement detection system;

[0021] S4, the differential capacitance ΔC of the two capacitors of the capacitive displacement detection system is proportional to the rotation angle Δθ;

[0022] S5, after modulation and demodulation by the capacitive sensing circuit, ΔC is converted into a voltage output signal V O .

[0023] Furthermore, the equation of motion is:

[0024]

[0025] Where I and θ are the moment of inertia and angular displacement of the pendulum, respectively; K is the stiffness; λ is the damping coefficient; τ is the applied torque; F, L, and ω are the amplitude, arm length, and frequency of the electrostatic force, respectively. The pendulum swings at an angle θ under the action of the electrostatic force F, and the tangential component of gravity Mg sinθ and the electrostatic force F together provide acceleration for the pendulum. If the angle is very small, the tangential component of gravity can be approximately written as Mgθ.

[0026] θ=θ0e -βt cos(ω f t+φ f )+Δθcos(ωt-φ) (2)

[0027] where β = λ / (2I). The first term is the transient solution, where the frequency is ω f , the initial phase is φ f , the initial amplitude is θ0. The second term is the steady-state solution with frequency ω, initial phase φ, and amplitude Δθ, where Δθ can be expressed as:

[0028]

[0029] Where ω0 is the natural frequency of the pendulum, expressed as:

[0030]

[0031] Furthermore, when the electrostatic force frequency ω→0, that is, when the electrostatic force is a constant force, it can be obtained from formula (3):

[0032]

[0033] Therefore, the electrostatic force acting on the compound pendulum is proportional to the angle of rotation of the compound pendulum.

[0034] S is the surface area of ​​the dielectric material to be tested, Q 总 is the total surface charge, then the surface charge density is expressed as:

[0035]

[0036] It is known that the potential difference applied to the electrode plate AB is U, and the distance between the electrode plates AB is D, then the electrostatic force F on the dielectric material can be written as

[0037]

[0038] The surface charge density σ of a dielectric material can be expressed as

[0039]

[0040] s is the thickness of the dielectric material to be measured, ε r The relative dielectric constant of the dielectric material to be measured. Then the relationship between the surface charge density and surface potential of the dielectric material to be measured is:

[0041]

[0042] Furthermore, from equations (5), (8), and (9), it can be seen that the surface charge density, surface potential, and electrostatic force of the dielectric material to be measured are all related to the angle Δθ of the compound pendulum rotation. The measurement principle of the angle Δθ of the compound pendulum rotation is as follows:

[0043] When the swing frame rotates at a very small angle Δθ, Δθ=x, where x is the displacement of the middle capacitor plate of the capacitance detection system placed at the bottom of the swing frame. The variable spacing type-capacitance detection method is used to measure the displacement x of the middle plate.

[0044] When the electrostatic force is 0, the distance between the middle plate and the left outer plate A and the right outer plate B is d. When the electrostatic force is not 0, the middle plate produces a displacement x, the distance between the middle plate and the left outer plate A is dx, the distance between the middle plate and the right outer plate B is d+x, the capacitance C1 formed by the middle plate and the left plate A increases, and the capacitance C2 formed by the middle plate and the right outer plate B decreases, which are:

[0045]

[0046] Where A, d, C0 are the plate area, spacing and capacitance of the capacitor plates when they are facing each other under the test mass balance state, ε air is the dielectric constant of air. Then the difference between the two capacitances can be expressed as:

[0047]

[0048] When x is very small, the higher-order terms are ignored. (12) becomes:

[0049]

[0050] The detected differential capacitance signal ΔC is modulated and demodulated by the capacitance sensing circuit and converted into a voltage output signal V O , V O Linear relationship with ΔC:

[0051] V O =bΔC (14) Equations (5), (13), and (14) can be used to obtain the electrostatic force F and the output voltage V of the capacitance detection circuit O The relationship is:

[0052]

[0053] Where k0 is the proportionality coefficient. Then, from equations (7), (9), and (15), we can obtain the surface charge density σ and surface potential V of the material to be tested: s Relationship with the output voltage of the capacitance detection circuit:

[0054]

[0055]

[0056] Where k1 and k2 are proportional coefficients.

[0057] Another object of the present invention is to provide a device for measuring the surface charge density and surface potential of a dielectric material to realize the method for measuring the surface charge density and surface potential of a dielectric material.

[0058] It includes a pendulum frame, a counterweight, a fixture, a plate A, a calibration bracket, a sample, a plate B, a sample bracket, a reed, a counterweight, an outer plate B, an outer plate A, and a capacitive displacement sensor. In order to ensure the stability of the pendulum frame and meet the installation requirements, the pendulum frame adopts a square frame design, and the middle crossbeam of the frame can be used to install the counterweight and other parts. The reed is fixed by the upper and lower clamps, the upper clamp is fixed on the bracket in the container, and the lower clamp is fixedly connected to the pendulum frame. The vertical posture of the pendulum is adjusted by the counterweight on the pendulum frame, and the counterweight adjusts the stiffness of the pendulum. The calibration bracket is installed on the side of the pendulum frame, and a mass block of known mass can be placed on the calibration bracket to calibrate the stiffness of the pendulum. The material to be tested is installed on the middle sample bracket of the pendulum, and its force is perpendicular to the frame. The plate A and the plate B are connected to the positive and negative poles of the external power supply, placed on both sides of the sample bracket, and the power is turned on to provide an electric field for the sample to be tested. The angular displacement of the pendulum is monitored by a capacitive displacement sensor installed at the bottom of the pendulum.

[0059] Further, building the device framework specifically includes:

[0060] The pendulum frame 1 adopts a U-shaped frame design, and the counterweight 2 is installed in the middle of the frame to adjust the stability of the pendulum frame. The upper and lower clamps 3 on both sides of the frame fix the spring 9, and the center of gravity of the pendulum frame is adjusted by the counterweight 10. The spring 9 is fixed by the upper and lower clamps 3, the upper clamp is fixed on the bracket in the container, and the lower clamp is fixedly connected to the pendulum frame. The calibration bracket 5 is installed on the bottom side of the pendulum frame. The capacitive displacement detection system 11-13 is installed under the pendulum frame to monitor the displacement of the pendulum. The sample is fixed in the middle position of the sample holder 8, and the electrode plates 4 and 7 are distributed on the left and right sides of the sample holder independently of the pendulum frame, and the assembled sample holder is fixed under the frame. Finally, the positive and negative poles of the voltage source are connected to the electrode plates to provide an electric field for the sample to be tested. The constructed compound pendulum device is carefully placed in a stainless steel container to complete the subsequent parameter calibration.

[0061] Furthermore, the calibration step specifically includes:

[0062] For electrostatic force F, surface charge density σ and surface potential V sThe key to accurate measurement is to obtain the proportional coefficient k0. This step is achieved by calibrating the compound pendulum device. After the compound pendulum device is built, the gravity torque method is used to calibrate the stiffness of the compound pendulum system, that is, to measure k0. The basic idea of ​​the gravity torque method is to use an object of known mass to generate a restoring torque on the compound pendulum, and calibrate the system stiffness through this restoring torque. A standard object with a mass of m is placed on the pendulum frame, and its horizontal distance from the suspension point is l. The restoring torque generated by the object on the pendulum can be expressed as mgl. By loading and unloading standard objects on the pendulum, the position of the pendulum will change. According to the local gravitational acceleration g, the mass m of the standard object and its lever arm l, combined with the change in the angle of motion of the compound pendulum Δθ, the relationship can be obtained:

[0063] mgl=KΔθ (18)

[0064] The moment of the electrostatic force F acting on the sample to be tested is L. From equation (5), we can know that

[0065] KΔθ=FL (19)

[0066] (19) shows that the effects of mgl and FL are equivalent. By loading standard objects m with different masses, the output V caused by multiple sets of different mgl is measured. O ,like Figure 7 As shown, mgl and V can be measured O The relationship is mgl = k1V O In fact, FL = k1V O . Thus, we obtain the calibration coefficient k1 by using the known standard mass m through the calibration method. From formula (15), we can know that:

[0067] k0=k1 / L (20)

[0068] Finally, according to equations (16) and (17), the surface charge density σ and surface potential V of the material to be tested can be obtained: s .

[0069] Furthermore, according to the above calibration steps, the calibration coefficient k1 can be obtained. According to equation (17), the electrostatic force F and the output voltage V O The proportional coefficient k0 is between them. Place the dielectric material sample to be tested on the sample holder. Connect the positive and negative electrodes of the voltage source to the electrode plates A4 and B7, close the stainless steel chamber door to prevent interference from air and electromagnetic waves, turn on the voltage source, and use an oscilloscope to observe the output voltage V of the capacitance detection circuit. O Finally, according to equations (16), (17), and (20), the surface charge density σ and surface potential V of the material to be tested can be obtained: s .

[0070] Another object of the present invention is to provide a computer device, which includes a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the method for measuring the surface charge density and surface potential of a dielectric material.

[0071] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to execute the steps of the method for measuring the surface charge density and surface potential of a dielectric material.

[0072] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0073] First, the present invention places the sample to be tested on the sample holder of the compound pendulum, and the sample to be tested is in an external electric field at the same time, and the sample surface charge density / surface potential is measured by measuring the rotation angle of the compound pendulum. The larger the sample surface charge density / surface potential, the greater the electrostatic force on the compound pendulum, and the greater the angle of rotation of the compound pendulum. The angle of rotation of the compound pendulum is converted into a circuit output voltage by a capacitor detection circuit, and the output voltage of the capacitor detection circuit is proportional to the angle of rotation of the compound pendulum, and then proportional to the electrostatic force on the compound pendulum, and then proportional to the sample surface charge density / surface potential. The stiffness of the compound pendulum bracket is mainly provided by gravity and can be adjusted by changing the center of mass. The bracket is directly calibrated using gravity to eliminate the interference of other force coupling. When the stiffness of the pendulum frame system is set to about 1Nm / rad, the electrostatic force measurement range reaches 1000μN, and the measurement accuracy reaches 0.09μN, corresponding to the measurement range of the surface potential of the dielectric material 0-10000V, and the measurement accuracy reaches 0.09V. Therefore, the advantages of the present invention are: (1) having an ultra-wide surface potential measurement range, and (2) having an ultra-high surface potential measurement accuracy within the wide measurement range.

[0074] Second, the technical solution of the present invention solves the technical problem that people have been eager to solve but have never been successful: in terms of surface measurement technology, the current measurement technology is mainly Kelvin probe technology and the use of a vibrating capacitance electrometer. Both have some shortcomings that affect their effectiveness and reliability in application. The present invention places the sample to be tested on the sample holder of the compound pendulum, and the sample to be tested is simultaneously in an external electric field, and the sample surface charge density / surface potential is measured by measuring the rotation angle of the compound pendulum. The larger the sample surface charge density / surface potential, the greater the electrostatic force on the compound pendulum, and the greater the angle of rotation of the compound pendulum. The angle of rotation of the compound pendulum is converted into a circuit output voltage by a capacitor detection circuit, and the output voltage of the capacitor detection circuit is proportional to the angle of rotation of the compound pendulum, and then proportional to the electrostatic force on the compound pendulum, and then proportional to the sample surface charge density / surface potential. The stiffness of the compound pendulum bracket is mainly provided by gravity, which can be adjusted by changing the center of mass. The bracket is directly calibrated using gravity to eliminate the interference of other force coupling. When the stiffness of the swing frame system is set to about 1 Nm / rad, the electrostatic force measurement range reaches 1000 μN, and the measurement accuracy reaches 0.09 μN, corresponding to the measurement range of the surface potential of the dielectric material of 0-10000 V, and the measurement accuracy reaches 0.09 V. Therefore, the advantages of the present invention are: (1) having an ultra-wide surface potential measurement range, and (2) having an ultra-high surface potential measurement accuracy under a wide measurement range.

[0075] Third, the technical solution of the present invention solves the problems of inaccurate, unstable and slow response speed in the measurement of surface charge density and surface potential of dielectric materials in the prior art in industrial applications. The prior art often relies on traditional charge measurement methods, which may be affected by environmental noise and other interferences, resulting in inaccurate measurement results. The present invention, through a complex pendulum frame and a differential capacitance displacement detection system, can measure charge density and surface potential at a higher resolution, avoiding the problem of signal instability caused by weak electrostatic force in traditional methods.

[0076] The significant technical progress of the present invention is that: first, based on the linkage design of the compound pendulum frame and the electrostatic force, it can effectively amplify the subtle charge reaction of the dielectric material to be measured under the electric field, so that the measurement sensitivity is significantly improved. Secondly, the differential capacitance displacement detection system is used to perform high-precision detection of the slight changes in the rotation angle of the compound pendulum, which effectively reduces the interference of environmental factors, thereby obtaining more accurate measurement results. In addition, the modulation and demodulation technology of the capacitance sensing circuit converts the differential capacitance signal into a stable voltage output signal, further improving the response speed and signal stability of the system.

[0077] Therefore, the technical solution of the present invention has strong practicality and advancement in industrial applications, provides an innovative solution for high-precision measurement of surface electrical properties of dielectric materials, and promotes technological progress in materials science, electronic engineering and related fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0078] Figure 1 It is a schematic diagram of the principle of measuring surface charge density using a vibrating capacitance electrometer;

[0079] Figure 2 Schematic diagram of the working principle of the Kelvin probe microscope provided by an embodiment of the present invention;

[0080] Figure 3 It is a schematic diagram of the electrostatic force on the sample to be tested in the electric field provided by the embodiment of the present invention;

[0081] Figure 4 is a schematic diagram of variable spacing capacitance detection provided by an embodiment of the present invention;

[0082] Figure 5 is a schematic diagram of a capacitance sensing circuit provided by an embodiment of the present invention;

[0083] Figure 6 is a logic block diagram provided by an embodiment of the present invention;

[0084] Figure 7 is a schematic diagram of a gravity calibration unit provided in an embodiment of the present invention;

[0085] Figure 8 is a calibration result diagram provided by an embodiment of the present invention;

[0086] Fig. 9 is a structural diagram of a compound pendulum measuring frame provided by an embodiment of the present invention;

[0087] Fig.10 It is a data graph measuring the electrostatic force and applied voltage on the polytetrafluoroethylene film after electret charging;

[0088] In the figure: 1, pendulum frame, 2, counterweight, 3, fixture, 4, plate A, 5, calibration bracket, 6, sample, 7, plate B, 8, sample bracket, 9, reed, 10, counterweight, 11, middle plate, 12, outer plate A, 13, outer plate B. DETAILED DESCRIPTION

[0089] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0090] The device provided by the present invention is used to measure the surface charge density and surface potential of dielectric materials, and its working principle is as follows:

[0091] 1. Electrostatic force: In step S1, an external electric field is applied to the sample 6 to be tested through the electrode plate A4 and the electrode plate B7, generating an electrostatic force F. This force is transmitted to the pendulum frame 1 of the compound pendulum through the sample holder 8, causing the pendulum frame to rotate.

[0092] 2. Rotation of compound pendulum: The electrostatic force F causes the pendulum frame 1 to rotate around the fixed point, resulting in an angle change Δθ. This angle change is proportional to the surface charge density of sample 6. The higher the surface charge density, the greater the electrostatic force, resulting in a greater rotation angle Δθ.

[0093] 3. Displacement detection: The rotation of the swing frame 1 causes the middle plate 11 at the bottom thereof to be displaced relative to the outer plates A 12 and B 13. The capacitive displacement sensor detects the displacement change of the middle plate 11, reflecting the angle change Δθ of the swing frame.

[0094] 4. Signal processing: The capacitive displacement sensor converts the detected displacement change into a differential capacitance signal ΔC. Through the modulation and demodulation of the capacitive sensing circuit, the differential capacitance signal ΔC is converted into a voltage output signal VO. After calibration, the size of VO directly represents the surface charge density and surface potential of the sample 6, realizing the measurement of the electrical properties of the dielectric material.

[0095] The method for measuring the surface charge density and surface potential of a dielectric material provided by the present invention is based on the compound pendulum motion under the action of an electrostatic force and the differential capacitance principle of a capacitive displacement detection system. First, in step S1, an external electric field generates an electrostatic force F on the dielectric material to be measured, and the electrostatic force is transmitted to the compound pendulum frame through a sample holder to generate a force. This force is caused by the reaction of the surface charge of the dielectric material under the external electric field, causing a potential change on its surface.

[0096] In step S2, the electrostatic force F causes the compound pendulum frame to rotate at a certain angle Δθ. This angle Δθ represents the effect of the electrostatic force on the compound pendulum system and is an important parameter for measuring the surface charge density of the dielectric material to be tested. The size of the angle Δθ is proportional to the electrostatic force F, that is, the higher the surface charge density, the greater the electrostatic force generated, resulting in a greater rotation angle.

[0097] Next, in step S3, the angle Δθ is equal to the displacement x of the middle plate in the bottom capacitance displacement detection system. This displacement x corresponds to the rotation angle and reflects the displacement change of the compound pendulum system. The size of the displacement x is also determined by the surface charge density, so it directly reflects the surface potential change of the dielectric material to be tested.

[0098] Finally, in steps S4 and S5, the two capacitors in the capacitive displacement detection system form a differential capacitance, and the differential capacitance ΔC is proportional to the rotation angle Δθ. After modulation and demodulation by the capacitive sensing circuit, the differential capacitance signal ΔC will be converted into a voltage output signal V O . V O The size of can be calibrated to directly represent the surface charge density and surface potential of the dielectric material, thus realizing the measurement of the electrical properties of the dielectric material.

[0099] The compound pendulum test system mainly includes a pendulum frame, a counterweight, a fixture, a plate A, a calibration bracket, a sample, a plate B, a sample bracket, a reed, a counterweight, an outer plate B, an outer plate A, and a capacitive displacement sensor. In order to ensure the stability of the pendulum frame and meet the installation requirements, the pendulum frame adopts a square frame design, and the middle crossbeam of the frame can be used to install the counterweight and other parts. The reed is fixed by the upper and lower clamps, the upper clamp is fixed on the bracket in the container, and the lower clamp is fixedly connected to the pendulum frame. The vertical posture of the pendulum is adjusted by the counterweight on the pendulum frame, and the counterweight adjusts the stiffness of the pendulum. The calibration bracket is installed on the side of the pendulum frame, and a mass block of known mass can be placed on the calibration bracket to calibrate the stiffness of the pendulum. The material to be tested is installed on the middle sample bracket of the pendulum, and its force is perpendicular to the frame. The plates A and B are connected to the positive and negative poles of the external power supply, placed on both sides of the sample bracket, and the power is turned on to provide an electric field for the sample to be tested. The angular displacement of the pendulum is monitored by the capacitive displacement sensor installed at the bottom of the pendulum.

[0100] The measurement principle can be regarded as a compound pendulum. It is a typical second-order system, and the equation of motion is:

[0101]

[0102] Where I and θ are the moment of inertia and angular displacement of the pendulum, respectively; K is the stiffness; λ is the damping coefficient; τ is the applied torque; F, L, and ω are the amplitude, arm, and frequency of the electrostatic force, respectively. The pendulum swings at an angle θ under the action of the electrostatic force F, and the tangential component of gravity Mgsinθ and the electrostatic force F together provide acceleration for the pendulum. If the angle is very small, the tangential component of gravity can be approximately written as Mgθ.

[0103] θ=θ0e -βt cos(ω f t+φ f )+Δθcos(ωt-φ) (2)

[0104] where β = λ / (2I). The first term is the transient solution, where the frequency is ω f , the initial phase is φ f , the initial amplitude is θ0. The second term is the steady-state solution with frequency ω, initial phase φ, and amplitude Δθ, where Δθ can be expressed as:

[0105]

[0106] Where ω0 is the natural frequency of the pendulum, expressed as:

[0107]

[0108] When the electrostatic force frequency ω→0, that is, the electrostatic force is a constant force, we can get from formula (3):

[0109]

[0110] Therefore, the electrostatic force acting on the compound pendulum is proportional to the angle of rotation of the compound pendulum.

[0111] On the other hand, the dielectric material to be tested is subjected to electrostatic forces such as Figure 3 Shown

[0112] S is the surface area of ​​the dielectric material to be tested, Q 总 is the total surface charge, then the surface charge density is expressed as:

[0113]

[0114] It is known that the potential difference applied to the electrode plate AB is U, and the distance between the electrode plates AB is D, then the electrostatic force F on the dielectric material can be written as

[0115]

[0116] The surface charge density σ of a dielectric material can be expressed as

[0117]

[0118] s is the thickness of the dielectric material to be measured, ε r The relative dielectric constant of the dielectric material to be measured. Then the relationship between the surface charge density and surface potential of the dielectric material to be measured is:

[0119]

[0120] Therefore, from equations (5), (8), and (9), it can be seen that the surface charge density, surface potential, and electrostatic force of the dielectric material to be measured are all related to the angle Δθ of the compound pendulum rotation. The measurement principle of the angle Δθ of the compound pendulum rotation is as follows:

[0121] When the swing frame rotates at a very small angle Δθ, Δθ=x, where x is the displacement of the middle capacitor plate of the capacitance detection system placed at the bottom of the swing frame. The variable spacing capacitance detection method is used to measure the displacement of the middle plate x. The principle is as follows: Figure 5 shown.

[0122] When the electrostatic force is 0, the distance between the middle plate and the left outer plate A and the right outer plate B is d. When the electrostatic force is not 0, the middle plate produces a displacement x, the distance between the middle plate and the left outer plate A is dx, the distance between the middle plate and the right outer plate B is d+x, the capacitance C1 formed by the middle plate and the left plate A increases, and the capacitance C2 formed by the middle plate and the right outer plate B decreases, which are:

[0123]

[0124] Where A, d, C0 are the plate area, spacing and capacitance of the capacitor plates when they are facing each other under the test mass balance state, ε air is the dielectric constant of air. Then the difference between the two capacitances can be expressed as:

[0125]

[0126] When x is very small, the higher-order terms are ignored. (12) becomes:

[0127]

[0128] The detected differential capacitance signal ΔC is transmitted through a capacitance sensing circuit (such as Figure 5 After modulation and demodulation, it is converted into a voltage output signal V O , V O Linear relationship with ΔC:

[0129] V O =bΔC (14)

[0130] The main principle logic of the entire patent is Figure 6 As shown:

[0131] According to the logic box Figure 6 , and equations (5), (13), and (14) can be used to obtain the electrostatic force F and the output voltage V of the capacitance detection circuit O The relationship is:

[0132]

[0133] Where k0 is the proportionality coefficient. Then, from equations (7), (9), and (15), we can obtain the surface charge density σ and surface potential V of the material to be tested: s Relationship with the output voltage of the capacitance detection circuit:

[0134]

[0135] Where k1 and k2 are proportional coefficients.

[0136] 1. Build the device framework

[0137] The pendulum frame 1 adopts a U-shaped frame design, and the counterweight 2 is installed in the middle of the frame to adjust the stability of the pendulum frame. The upper and lower clamps 3 on both sides of the frame fix the spring 9, and the center of gravity of the pendulum frame is adjusted by the counterweight 10. The spring 9 is fixed by the upper and lower clamps 3, the upper clamp is fixed on the bracket in the container, and the lower clamp is fixedly connected to the pendulum frame. The calibration bracket 5 is installed on the bottom side of the pendulum frame. The capacitive displacement detection system 11-13 is installed under the pendulum frame to monitor the displacement of the pendulum. The sample is fixed in the middle position of the sample holder 8, and the electrode plates 4 and 7 are distributed on the left and right sides of the sample holder independently of the pendulum frame, and the assembled sample holder is fixed under the frame. Finally, the positive and negative poles of the voltage source are connected to the electrode plates to provide an electric field for the sample to be tested. The constructed compound pendulum device is carefully placed in a stainless steel container to complete the subsequent parameter calibration.

[0138] 2. Calibration steps

[0139] For electrostatic force F, surface charge density σ and surface potential V s The key to accurate measurement is to obtain the proportional coefficient k0. This step is achieved by calibrating the compound pendulum device. After the compound pendulum device is built, the gravity torque method is used to calibrate the stiffness of the compound pendulum system, that is, to measure k0. The basic idea of ​​the gravity torque method is to use an object of known mass to generate a restoring torque on the compound pendulum, and calibrate the system stiffness through the restoring torque. Figure 8 As shown in the figure, a standard object with a mass of m is placed on the pendulum frame, and its horizontal distance from the suspension point is l. The restoring torque generated by the object on the pendulum can be expressed as mgl. By loading and unloading the standard object on the pendulum, the position of the pendulum will change. According to the local gravitational acceleration g, the mass m of the standard object and its lever arm l, combined with the change in the angle of motion of the compound pendulum Δθ, the relationship can be obtained:

[0140] mgl=KΔθ (18)

[0141] On the other hand, the moment of the electrostatic force F acting on the sample to be tested is L. From equation (5), we can know that

[0142] KΔθ=FL (19)

[0143] This shows that mgl and FL have similar effects. By loading standard objects m with different masses, the output V caused by multiple sets of different mgl is measured. O ,like Figure 8 As shown, mgl and V can be calculated O The relationship is mgl = k1V O In fact, FL = k1V O . Thus, the calibration coefficient k1 is obtained by the calibration method using the known standard mass m. From formula (15), we can know that:

[0144] k0=k1 / L (20)

[0145] Finally, according to equations (16) and (17), the surface charge density σ and surface potential V of the material to be tested can be obtained: s .

[0146] 3. Measurement of surface potential

[0147] According to the above calibration steps, the calibration coefficient k1 can be obtained. According to equation (17), the electrostatic force F and the output voltage V O The proportional coefficient k0 is between them. Place the dielectric material sample to be tested on the sample holder. Connect the positive and negative electrodes of the voltage source to the electrode plates A4 and B7, close the stainless steel chamber door to prevent interference from air and electromagnetic waves, turn on the voltage source, and use an oscilloscope to observe the output voltage V of the capacitance detection circuit. O Finally, according to equations (16), (17), and (20), the surface charge density σ and surface potential V of the material to be tested can be obtained: s .

[0148] An application embodiment of the present invention provides a computer device, which includes a memory and a processor. The memory stores a computer program. When the computer program is executed by the processor, the processor executes the steps of a method for measuring surface charge density and surface potential of a dielectric material.

[0149] An application embodiment of the present invention provides a computer-readable storage medium storing a computer program. When the computer program is executed by a processor, the processor executes the steps of a method for measuring surface charge density and surface potential of a dielectric material.

[0150] The present invention can be specifically applied to the following fields:

[0151] 1. Energy storage: - Capacitors and supercapacitors: In energy storage devices, the surface charge characteristics of dielectric materials directly affect their storage capacity and efficiency. By measuring their surface potential and charge distribution, the design of capacitors can be optimized to improve energy density and discharge efficiency.

[0152] 2. Electronic devices: - Performance optimization of semiconductor devices: In the semiconductor field, the distribution of surface charge has a significant impact on the electrical performance of the device. By measuring the surface potential of dielectric materials, we can deeply understand the interface characteristics, thereby improving the performance of devices such as transistors and diodes.

[0153] 3. Sensor technology: - Development of new sensors: Based on the surface charge characteristics of dielectric materials, highly sensitive sensors can be developed. These sensors can be used to detect gases, chemicals, and biomolecules, and are widely used in environmental monitoring, medical diagnosis, and other fields.

[0154] 4. Energy Conversion: - Applications of Triboelectric Materials: In the study of triboelectric materials, methods to visualize and quantify surface charge are very important. By measuring the surface charge of these materials, their properties can be effectively adjusted, promoting applications in energy conversion and energy harvesting. 5. Materials Science: - Material Characterization and Development: In the field of materials science, the measurement of surface charge density can provide important information for the development of new materials. By understanding the behavior of different materials under electric fields, materials with specific electrical properties can be developed, promoting the application of new materials.

[0155] 6. Nanotechnology: - Nanomaterials and devices: In nanotechnology, the measurement method of surface charge is crucial to understand the electrical properties of nanomaterials. This can be used to develop new nanodevices such as nanosensors, nanobatteries, etc., and promote the application of nanotechnology.

[0156] like Fig.10 As shown, it is a data diagram of the electrostatic force and the applied voltage on the polytetrafluoroethylene film after being electret measured using the technology of the present invention.

[0157] In the description of the present invention, unless otherwise specified, "plurality" means two or more than two; the orientations or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", "front end", "rear end", "head", "tail", etc. are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0158] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. It can be understood by a person of ordinary skill in the art that the above-mentioned devices and methods can be implemented using computer executable instructions and / or contained in a processor control code, such as a carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. Such code is provided on the carrier medium. The device and its modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, and can also be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0159] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A method for measuring the surface charge density and surface potential of a dielectric material, characterized in that: include: S1, the external electric field causes the dielectric material to be tested to be subjected to an electrostatic force F, which is transmitted to the compound pendulum frame through the sample holder; S2, the compound pendulum frame rotates by an angle Δθ under the action of the electrostatic force F; S3, the angle Δθ is equal to the displacement x of the middle plate of the bottom capacitive displacement detection system; S4, the differential capacitance ΔC of the two capacitors of the capacitive displacement detection system is proportional to the rotation angle Δθ; S5, after modulation and demodulation by the capacitive sensing circuit, ΔC is converted into a voltage output signal V O .

2. The method for measuring the surface charge density and surface potential of a dielectric material according to claim 1, characterized in that: The equation of motion is: Where I and θ are the moment of inertia and angular displacement of the pendulum, respectively; K is the stiffness; λ is the damping coefficient; τ is the applied torque; F, L and ω are the amplitude, arm and frequency of the electrostatic force, respectively; the pendulum swings at an angle θ under the action of the electrostatic force F, and the tangential component of gravity Mgsinθ and the electrostatic force F jointly provide acceleration for the pendulum; If the angle is small, the tangential component of gravity can be approximately written as Mgθ; θ=θ0e -βt cos(ω f t+φ f )+Δθcos(ωt-φ) (2) where β = λ / (2I); the first term is the transient solution, where the frequency is ω f , the initial phase is φ f , the initial amplitude is θ0; the second term is the steady-state solution with frequency ω, initial phase φ, and amplitude Δθ, where Δθ can be expressed as: Where ω0 is the natural frequency of the pendulum, expressed as:

3. The method for measuring the surface charge density and surface potential of a dielectric material according to claim 2, characterized in that: When the electrostatic force frequency ω→0, that is, the electrostatic force is a constant force, we can get from formula (3): Therefore, the electrostatic force on the compound pendulum is proportional to the angle of rotation of the compound pendulum; S is the surface area of ​​the dielectric material to be tested, Q 总 is the total surface charge, then the surface charge density is expressed as: It is known that the potential difference applied to the electrode plate AB is U, and the distance between the electrode plates AB is D, then the electrostatic force F on the dielectric material can be written as The surface charge density σ of a dielectric material can be expressed as s is the thickness of the dielectric material to be measured, ε r The relative dielectric constant of the dielectric material to be measured; then the relationship between the surface charge density and surface potential of the dielectric material to be measured is:

4. The method for measuring the surface charge density and surface potential of a dielectric material according to claim 3, characterized in that: From equations (5), (8), and (9), it can be seen that the surface charge density, surface potential, and electrostatic force of the dielectric material to be measured are all related to the angle Δθ of the compound pendulum rotation. The measurement principle of the angle Δθ of the compound pendulum rotation is as follows: When the swing frame rotates at a very small angle Δθ, Δθ=x, where x is the displacement of the middle capacitor plate of the capacitor detection system placed at the bottom of the swing frame; the variable spacing type-capacitance detection method is used to measure the displacement of the middle plate x; When the electrostatic force is 0, the distance between the middle plate and the left outer plate A and the right outer plate B is d; when the electrostatic force is not 0, the middle plate produces a displacement x, the distance between the middle plate and the left outer plate A is dx, the distance between the middle plate and the right outer plate B is d+x, the capacitance C1 formed by the middle plate and the left plate A increases, and the capacitance C2 formed by the middle plate and the right outer plate B decreases, which are: Where A, d, C0 are the plate area, spacing and capacitance of the capacitor plates when they are facing each other under the test mass balance state, ε air is the dielectric constant of air; then the difference between the two capacitances can be expressed as: When x is very small, the higher-order terms are ignored; equation (12) becomes: The detected differential capacitance signal ΔC is modulated and demodulated by the capacitance sensing circuit and converted into a voltage output signal V O , V O Linear relationship with ΔC: V O =bΔC (14) Equations (5), (13), and (14) provide the electrostatic force F and the output voltage V of the capacitance detection circuit: O The relationship is: Where k0 is the proportionality coefficient; then from equations (7), (9), and (15), we can get the surface charge density σ and surface potential V of the material to be tested: s Relationship with the output voltage of the capacitance detection circuit: Where k1 and k2 are proportional coefficients.

5. A device for measuring the surface charge density and surface potential of a dielectric material for realizing the method for measuring the surface charge density and surface potential of a dielectric material as claimed in any one of claims 1 to 4, characterized in that: It includes a pendulum frame, a counterweight, a fixture, a plate A, a calibration bracket, a sample, a plate B, a sample bracket, a reed, a counterweight, an outer plate B, an outer plate A, and a capacitive displacement sensor. In order to ensure the stability of the pendulum frame and meet the installation requirements, the pendulum frame adopts a U-shaped frame design, and the middle crossbeam of the frame can be used to install the counterweight and other components. The reed is fixed by upper and lower clamps, the upper clamp is fixed on the bracket in the container, and the lower clamp is fixedly connected to the pendulum frame. The vertical posture of the pendulum is adjusted by the counterweight on the pendulum frame, and the stiffness of the pendulum is adjusted by the counterweight. The calibration bracket is installed on the side of the pendulum frame, and a mass block of known mass can be placed on the calibration bracket to calibrate the stiffness of the pendulum. The material to be tested is installed on the middle sample bracket of the pendulum, and the force on it is perpendicular to the frame. The plate A and the plate B are connected to the positive and negative poles of the external power supply, placed on both sides of the sample bracket, and the power is turned on to provide an electric field for the sample to be tested. The angular displacement of the pendulum is monitored by a capacitive displacement sensor installed at the bottom of the pendulum.

6. The device for measuring the surface charge density and surface potential of a dielectric material according to claim 5, characterized in that: Building the device framework specifically includes: The pendulum frame adopts a U-shaped frame design, and the counterweight is installed in the middle of the frame to adjust the stability of the pendulum frame; the upper and lower clamps on both sides of the frame fix the spring, and the center of gravity of the pendulum frame is adjusted by the counterweight; the spring is fixed by the upper and lower clamps, the upper clamp is fixed on the bracket in the container, and the lower clamp is fixedly connected to the pendulum frame; the calibration bracket is installed on the bottom side of the pendulum frame; the capacitive displacement detection system is installed under the pendulum frame to monitor the displacement of the pendulum; the sample is fixed in the middle position of the sample bracket, the electrode plate is fixed on the left and right sides of the bracket, and the assembled sample bracket is fixed under the frame; finally, the positive and negative poles of the voltage source are connected to the electrode plate to provide an electric field for the sample to be tested; the constructed compound pendulum device is carefully placed in a stainless steel container to complete subsequent parameter calibration.

7. The device for measuring the surface charge density and surface potential of a dielectric material according to claim 5, characterized in that: The calibration steps specifically include: For electrostatic force F, surface charge density σ and surface potential V s The key to accurate measurement is to obtain the proportional coefficient k0; this step is achieved by calibrating the compound pendulum device; after the compound pendulum device is built, the gravity moment method is used to calibrate the stiffness of the compound pendulum system, that is, to measure k0; the basic idea of ​​the gravity moment method is to use an object of known mass to generate a restoring torque on the compound pendulum, and calibrate the system stiffness through the restoring torque; a standard object with a mass of m is placed on the pendulum frame, and its horizontal distance to the suspension point is l, then the restoring torque generated by the object on the pendulum can be expressed as mgl; by loading and unloading the standard object on the pendulum, the position of the pendulum will change; according to the local gravitational acceleration g, the mass m of the standard object and its lever arm l, combined with the change in the angle of motion of the compound pendulum Δθ, the relationship can be obtained: mgl=KΔθ (18) The moment of the electrostatic force F acting on the sample to be tested is L. From equation (5), we can know that KΔθ=FL (19) This shows that mgl and FL have similar effects. By loading standard objects m with different masses, the output V caused by different mgl groups is measured. O , as shown in Figure 7, mgl and V O The relationship is mgl = k1V O ; In fact, FL = k1V O ; From formula (15), we can know that: k0=k1 / L (20) Finally, according to equations (16) and (17), the surface charge density σ and surface potential V of the material to be tested can be obtained: s .

8. The device for measuring the surface charge density and surface potential of a dielectric material according to claim 5, characterized in that: According to the above calibration steps, the calibration coefficient k1 can be obtained; according to formula (17), the electrostatic force F and the output voltage V O The proportional coefficient k0 between them; place the dielectric material sample to be tested on the sample holder; connect the positive and negative electrodes of the voltage source to the electrode plates A4 and B7, close the stainless steel chamber door to prevent interference from air and electromagnetic waves, turn on the voltage source, and use an oscilloscope to observe the output voltage V of the capacitance detection circuit O Finally, according to equations (16), (17), and (20), the surface charge density σ and surface potential V of the material to be tested can be obtained: s .

9. A computer device, comprising a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the method for measuring the surface charge density and surface potential of a dielectric material as claimed in any one of claims 1 to 4.

10. A computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to execute the steps of the method for measuring the surface charge density and surface potential of a dielectric material as claimed in any one of claims 1 to 4.

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