Particle collision contact time measurement method and apparatus

Abstract

A particle collision contact time measurement method and apparatus. The method comprises the following steps: focusing a continuous laser to form a light beam, the beam waist diameter of which is smaller than the diameter of a particle to be measured; emitting said particle to a beam waist position of the laser; quantitatively monitoring a light intensity change; and obtaining a duration in which the laser is occluded by said particle to the greatest extent or obtaining a duration after an output voltage of an oscilloscope is reduced to the minimum. Thus, the measurement of a particle collision contact time is realized. By quantitatively monitoring the light intensity change, the duration in which the laser is occluded by said particle to the greatest extent is obtained, so that the measurement of the particle collision contact time is realized. The method has advantages such as being capable of measuring a particle collision contact time down to the scale of a laser diffraction limit, and not being affected by material limitations of whether a particle is conductive, charged, etc., and the method can record the particle collision contact time with extremely high precision.

Description

Particle collision contact time measurement method and device Technical Field

[0001] The present invention relates to the technical field of particle motion measurement, and in particular to a particle collision contact time measurement method and device. Background Art

[0002] Granular materials, typically composed of discrete particles, are widely present in various fields and possess physical properties at various scales. To better understand the overall properties of macroscopic granular materials, it is necessary to explore the contact mechanics of particles under microscopic conditions. The particle contact process is actually a process of energy transfer, including mechanical energy, thermal energy, electrical energy, and so on. Typically, the particle contact process requires two parameters to jointly describe: the collision restitution coefficient (i.e., the ratio of the particle velocities before and after the collision) and the contact duration. For example, when the Kelvin model is used to represent the constitutive relationship of the contact process, the model schematic is shown in Figure 1.

[0003] The motion equations and boundary conditions corresponding to the model are as follows:

[0004] Where: n (t) represents the deformation that changes with time, k n represents the strength of the elastic term, η n Represents the strength of the viscosity term.

[0005] The experimentally measured e n and t c,n That is, we can get k n and η n ,Right now:

[0006] This fully describes the change of displacement over time during the contact process:

[0007] in:

[0008] Currently, the restitution coefficient can be measured using common velocity measurement methods such as high-speed imaging and laser Doppler velocimetry. However, direct methods for measuring the contact time of single-particle collisions are relatively rare because it is relatively small in three dimensions: time (contact time), space (contact area), and force (contact force). In the article "Comparison of soft-sphere models to measurements of collision properties during normal impacts" published in the journal Powder Technology, the contact time of collisions between centimeter-scale metal spheres was measured for the first time using a closed circuit method. In the article "Contact time of an incident particle hitting a 2D bed of particles" published in Powder Technology, the contact time of collisions between centimeter-scale spheres was measured using high-speed imaging. In the article "Inelastic impact of a sphere on a massive plane: Nonmonotonic velocity-dependence of the restitution coefficient" published in Europhys Lett, the contact time of millimeter-scale particles was measured using a combination of closed circuit and accelerometer methods.

[0009] However, the aforementioned measurement methods can only be used to measure the contact time of larger particles. The accelerometer method also has poor measurement accuracy. The closed-circuit method, which connects the particle to the impact target to form a closed loop, can only be used to measure metallic particles and cannot measure the contact process of charged particles. Furthermore, the introduction of additional contact can affect particle motion. Therefore, it is necessary to develop a new particle collision contact time measurement technology to address the shortcomings of existing particle collision contact time measurement experimental methods. Summary of the Invention

[0010] The purpose of the present invention is to overcome the defects of the above-mentioned prior art, and to realize a particle collision contact time measurement method and device by utilizing the ultra-fast measurement speed of the photodetector and the extremely small size of the laser beam.

[0011] The purpose of the present invention can be achieved by the following technical solutions:

[0012] The present invention provides a method for measuring particle collision contact time, comprising the following steps:

[0013] The continuous laser is focused to form a beam with a waist diameter smaller than the diameter of the particle to be measured. The particle to be measured is launched to the position of the laser beam waist, and the change in light intensity is quantitatively monitored to obtain the duration when the laser is completely blocked by the particle to be measured, thereby achieving the measurement of the particle collision contact time.

[0014] Furthermore, the light beam is close to the impact target surface of the particles to be detected.

[0015] Furthermore, the diameter of the light beam is less than half the diameter of the particle to be measured.

[0016] Furthermore, the diameter of the particles to be tested ranges from 1 μm to 1 cm.

[0017] Furthermore, the particles to be tested are made of a material with a light transmittance less than 1.

[0018] Furthermore, the particles to be tested include silicon dioxide particles, polystyrene particles and stainless steel particles.

[0019] Furthermore, the continuous laser is a Gaussian beam or a flat-top beam.

[0020] Furthermore, the light intensity is quantitatively monitored by a photodetector combined with an oscilloscope, and the sampling time interval of the oscilloscope and the photodetector should be less than half of the contact time.

[0021] Furthermore, the continuous light beam is expanded and then focused to form a light beam with a beam waist diameter smaller than the diameter of the particle to be measured.

[0022] The present invention also provides another method for measuring particle collision contact time, comprising the following steps:

[0023] The continuous laser is focused to form a beam with a waist diameter smaller than the diameter of the particle to be measured. The particle to be measured is launched to the position of the laser beam waist. An oscilloscope combined with a photodetector is used to quantitatively monitor the change in light intensity. The duration after the oscilloscope output voltage drops to the minimum is obtained, thereby achieving the measurement of the particle collision contact time.

[0024] Furthermore, the light beam is close to the impact target surface of the particles to be detected.

[0025] Furthermore, the diameter of the light beam is less than half the diameter of the particle to be measured.

[0026] Furthermore, the particles to be tested are made of a material with a light transmittance less than 1.

[0027] The present invention also provides a measuring device for realizing the particle collision contact time measuring method as described above, comprising a photoelectric detection part and a particle emission part.

[0028] The photoelectric detection part includes a continuous laser, a beam expander, a plano-convex lens, a biconvex lens, a photodetector, an oscilloscope, a light source and a computer. The continuous laser, beam expander, plano-convex lens, biconvex lens and photodetector are arranged in sequence. The illumination range of the light source is aligned between the plano-convex lens and the biconvex lens. The photodetector, oscilloscope and computer are connected in sequence. The target surface is located at the waist position of the light beam between the plano-convex lens and the biconvex lens. The laser generated by the continuous laser passes through the beam expander and the plano-convex lens in sequence and is focused to form a light beam with a waist diameter smaller than the diameter of the particle to be measured. The photodetector receives the light signal converged by the biconvex lens and converts it into an electrical signal. The oscilloscope records the changes in the electrical signal and transmits it to the computer.

[0029] The particle emitting part emits the particles to be measured into the illumination range and places the particles to be measured at the waist of the laser beam.

[0030] Furthermore, the photoelectric detection part also includes a high-speed camera, which is connected to an oscilloscope and a computer respectively. The high-speed camera is aligned with the illumination range and performs image acquisition in a direction perpendicular to the laser propagation.

[0031] Furthermore, the high-speed camera collects images under the triggering of the oscilloscope, and the collected images include images of the entire process of the particles to be measured from emission, approaching the target surface and rebounding from the target surface.

[0032] Furthermore, the continuous laser is a power-stabilized laser with a wavelength of 200-2600 nm.

[0033] Furthermore, the particle emission part includes a laser driven particle emitter, an adsorption type particle emitter, an air gun type particle emitter, a micro fluidized bed powder feeder or a micro vibration powder feeder.

[0034] Furthermore, the light source is an LED light source.

[0035] Furthermore, the time resolution of the photodetector and the oscilloscope is at the sub-nanosecond level.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The present invention converts the contact time into a light intensity signal for measurement. A continuous laser is focused to form a beam with a waist diameter smaller than the diameter of the particle to be measured. The particle to be measured is launched at the laser beam waist position, and the light intensity change is quantitatively monitored to obtain the duration when the laser is maximally blocked by the particle to be measured. This technology can measure the contact time of particle collisions as small as the laser diffraction limit (indicating the minimum spot diameter that the laser can reach after focusing), without being restricted by whether the particle is conductive or charged. It can measure the contact time of material particles with a light transmittance less than 1. At the same time, because the current oscilloscope and photodetector sampling frequency is much higher than the accelerometer and high-speed camera sampling frequency, and the sampling time interval is less than half of the contact time, the contact time of the particle collision can be recorded with extremely high accuracy, providing accurate input parameters for modeling particle-wall collisions. This technology improves the calculation accuracy of time-related physical processes, such as contact heat conduction processes, and provides important guidance for the layout of heat exchange tube bundles in solar collectors, thereby optimizing the design and improving system efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a schematic diagram of the Kelvin model;

[0039] FIG2 is a schematic top view of the device of the present invention;

[0040] FIG3 is a schematic front view of a cross section along line AA in FIG2 ;

[0041] In the figure, 1. Continuous laser; 2. Beam expander; 3. Plano-convex lens; 4. Biconvex lens; 5. Photodetector; 6. Oscilloscope; 7. LED light source; 8. High-speed camera; 9. Contact target surface; 10. Computer; 21. Pulsed laser; 22. Beam expander; 23. Scanning galvanometer; 24. F-Theta scanning lens; 25. Particle emission target; 251. K9 glass layer; 252. Gold film; 253. PDMS film. DETAILED DESCRIPTION

[0042] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0043] Example 1

[0044] This embodiment provides a method for measuring particle collision contact time, comprising the following steps: focusing a continuous laser to form a light beam with a waist diameter smaller than the diameter of the particle to be measured, emitting the particle to be measured to the position of the laser beam waist, quantitatively monitoring the change in light intensity, and obtaining the duration when the laser is maximally blocked by the particle to be measured, thereby achieving the measurement of the particle collision contact time.

[0045] Preferably, the light beam is close to the impact target surface of the particles to be detected.

[0046] Further preferably, the diameter of the light beam is less than half the diameter of the particle to be measured.

[0047] The above method can achieve accurate measurement of the contact time of particle collisions as small as the laser diffraction limit.

[0048] As shown in FIG2 , this embodiment provides a particle contact time measurement device for implementing the above method, including a photoelectric detection part and a particle emission part.

[0049] Among them, the photoelectric detection part includes a continuous laser 1, a beam expander 2, a plano-convex lens 3, a biconvex lens 4, a photodetector 5, an oscilloscope 6, an LED light source 7 and a computer 10. The continuous laser 1, the beam expander 2, the plano-convex lens 3, the biconvex lens 4, and the photodetector 5 are arranged in sequence, the photodetector 5 is connected to the oscilloscope 6, the LED light source 7 is arranged at the contact target surface 9, the oscilloscope 6 and the computer 10 are connected, the beam expander 2 expands the laser generated by the continuous laser 1 into parallel light with a larger diameter, the plano-convex lens focuses the expanded parallel light to less than 1 / 2 of the diameter of the particle to be measured, and then the biconvex lens 4 collects the parallel light that is re-diverged after focusing and inputs it into the photodetector 5, the photodetector 5 converts the optical signal into an electrical signal, and the oscilloscope 6 records the changes in the electrical signal and transmits it to the computer 10.

[0050] In a preferred embodiment, the photoelectric detection part also includes a high-speed camera 8, which is arranged in contact with the target surface 9. The high-speed camera 8 is connected to the oscilloscope 6 and the computer 10 respectively. The high-speed camera 8 records the entire process of the particles from emission, approaching the target surface and rebounding from the target surface at a position perpendicular to the particle incident direction and the laser propagation direction, and transmits it to the computer 10. In this embodiment, the high-speed camera 8 is used for synchronous observation in the vertical direction of light propagation to avoid the simultaneous impact of multiple particles on the measurement results. The high-speed camera can observe the two moments before and after the particle collision when it is very close to the target surface, so it can serve as an auxiliary to avoid the simultaneous impact of multiple particles on subsequent results.

[0051] In the above-mentioned photoelectric detection part, the continuous laser 1 is a helium-neon laser or a similar power-stabilized laser, which can generate continuous laser light of the required wavelength, with a wavelength between 200-2600nm, and can be detected by a high-speed photodetector (detection range 400-1100nm). The photodetector can achieve the required detection speed, with rise and fall times less than 150ps, a bandwidth of 2GHz, and a time resolution of sub-nanosecond level. The oscilloscope can achieve the required detection speed, with rise and fall times less than 500ps, a maximum sampling rate of 8GSa / s, and a time resolution of sub-nanosecond level. Based on the ultra-high sampling frequency of the oscilloscope and photodetector, the particle collision contact time can be recorded with extremely high accuracy.

[0052] The particle launcher can be a laser-driven particle launcher (LIPIT), an adsorption-type particle launcher, an airgun-type particle launcher, a microfluidized bed powder feeder, or a micro-vibration powder feeder. In this embodiment, a laser-driven particle launcher is used, as shown in FIG3 , and includes a pulsed laser 21, a beam expander 22, a scanning galvanometer 23, an F-Theta scanning lens 24, and a particle launch target 25, which are arranged in sequence. The particle launch target 25 is located at the beam waist between the plano-convex lens 3 and the biconvex lens 4 to launch particles at the beam waist.

[0053] Particles to be tested include particles of various sizes ranging from 1μm to 1cm, including conductive metals and non-conductive materials, and both charged and uncharged particles. Materials with a light transmittance of less than 1 should be used, such as silica particles, polystyrene particles, and stainless steel particles.

[0054] When the above-mentioned laser-driven particle launcher is working, the pulse laser 21 generates a pulsed laser, which is expanded by the beam expander 22, and the laser is controlled to focus on the particle launch target 25 above the particle to be launched through the combination of the scanning galvanometer 23 and the F-Theta scanning lens 24. The particle launch target 25 includes a K9 glass substrate 251, a gold film 252 and a PDMS film 253. The K9 glass layer 251 allows the laser beam to pass through without absorbing the laser energy. The laser vaporizes the gold film 252, and the expanding gas causes the PDMS film 253 to expand in a conical shape, pushing the particle to be launched to eject and impact the target 9, wherein the PDMS film 253 can limit the contact between the vaporization products and the particle to be launched and prevent the particle from heating up. During the movement of the particles, continuous laser is generated by continuous laser 1, which outputs parallel light with a larger diameter after passing through beam expander 2. After entering plano-convex lens 3, the laser is focused into a beam (spot) smaller than 0.5 times the diameter of the particle. Then, biconvex lens 4 collects the light that is re-diverged after focusing and enters the detection area of ​​photodetector 5. Photodetector 5 receives the light and converts it into an electrical signal which is input into oscilloscope 6. Oscilloscope analyzes the collected electrical signal. When the falling edge of the signal is detected, the collection signal is output to high-speed camera 8, triggering the action of high-speed camera 8. Oscilloscope 6 and high-speed camera 8 simultaneously save the data near the falling edge and transmit it to computer 10. Computer 10 processes the particle image collected by the high-speed camera and the oscilloscope electrical signal data, and calculates the change in particle incident velocity and the duration of particle contact. When the particle approaches the target surface 9, it will block the light emitted by the continuous laser 1, reducing the light intensity received by the photodetector 6, thereby affecting the output of the photodetector 6 and the size of the electrical signal received by the oscilloscope 6. When the particle contacts the wall, the light is blocked to the greatest extent, and the electrical signal received by the oscilloscope 6 is the minimum value. The time that the electrical signal remains at the minimum value is the contact time during the particle impact process.

[0055] In a specific embodiment, the computer 10 may calculate the duration of the collision contact using the following formula: τ=t2-t1

[0056] Where V is the voltage measured by the oscilloscope, t1 is the moment when the voltage drops to the minimum voltage fluctuation range, t2 is the moment when the voltage rises from 0 to a value greater than the minimum voltage fluctuation range, ΔV is the voltage noise fluctuation measured by the oscilloscope, and the contact time τ is the duration between the two moments.

[0057] In this embodiment, the continuous laser 1 is a helium-neon laser produced by Thorlabs, with a central wavelength of 632.8 nm, an output power of 0.8 mW, and a 1 / e 2The diameter is 0.48mm. Beam expander 2 consists of two achromatic convex lenses with focal lengths of 7.5mm and 150mm, respectively, achieving a 20x beam expansion factor. Plano-convex lens 3 is an achromatic plano-convex lens with a focal length of 50mm. Biconvex lens 4 is an achromatic biconvex lens with a focal length of 50mm. Photodetector 5 is a high-speed free-space bias detector from Sorebo Optoelectronics Technology Co., Ltd., with a spectral range of 400-1100nm, a bandwidth of 2GHz, and rise and fall times of less than 150ps. Oscilloscope 6 is an MSO5354 oscilloscope from Puyuan Jingdian Technology Co., Ltd., with a bandwidth of 350MHz, a maximum sampling rate of 8GSa / s, and a rise time of less than 500ps. LED light source 7 is a Hongzhao S5000 LED fiber cold light source with an average illumination of 572,000 lumens. High-speed camera 8 is a Qianyanlang X213 high-speed camera with a full-frame maximum frame rate of 13,500FPS.

[0058] Example 2

[0059] The present invention also provides another method for measuring particle collision contact time, comprising the following steps:

[0060] The continuous laser is focused to form a beam with a waist diameter smaller than the diameter of the particle to be measured. The particle to be measured is launched to the position of the laser beam waist. An oscilloscope combined with a photodetector is used to quantitatively monitor the change in light intensity. The duration after the oscilloscope output voltage drops to the minimum is obtained, thereby achieving the measurement of the particle collision contact time.

[0061] As shown in FIG2 , a HeNe laser 1 is used to generate continuous laser light, with a central wavelength of λ = 632.8 nm, a stable output power of 0.8 mW, and an exit spot size of 1 / e 2 The diameter is 0.48mm. After the beam is magnified 20 times by the beam expander 2, the diameter reaches D0 = 9.6mm. The expanded beam passes through the plano-convex lens 3, and its focal length f = 50mm. According to the focusing spot formula: The center spot diameter of the laser after focusing The biconvex lens 4 outputs the focused central light spot to the signal receiving area of ​​the photodetector 5, which has a diameter of 250μm and can receive most of the laser energy. Connect the output of the photodetector 5 to the oscilloscope 6, set the oscilloscope 6 to the falling edge trigger, and connect the oscilloscope 6 to the high-speed camera 8, set the high-speed camera 8 to the external trigger mode, and set its acquisition mode to acquisition before triggering. At this time, the spherical particles to be measured, such as silica particles with a diameter of D1 = 50μm, are attached to the particle emission target 25, and the pulsed laser 21 is used to emit the silica particles and collide with the continuous laser focus spot position. Since the incident particle diameter is When the incident particle approaches and hits the target surface 9, the incident particle blocks part of the laser beam. Since the light transmittance of the incident particle is less than 1, the light signal received by the photodetector 5 is smaller than when the incident particle is not blocked. When the light signal received by the photodetector 5 is reduced to the trigger threshold set by the oscilloscope 6, the oscilloscope 6 triggers and records the light signal intensity change data before and after the trigger, corresponding to the moment when the horizontal coordinate is equal to 0 in Figure 4(b), and at the same time sends a signal to trigger the high-speed camera 8 to start acquisition. The acquisition result is shown in Figure 4(a). When the oscilloscope 6 signal decreases to the minimum, it indicates that the incident particle begins to contact the contact target surface 9, and then the incident particle rebounds and leaves the contact surface. After completing a complete recording, check the trigger event recorded by the high-speed camera 8 to determine whether the trigger event is a collision event between a single particle and the contact target surface 9. If so, the time after the oscilloscope is reduced to the minimum is the contact duration of the incident particle colliding with the contact target surface, which corresponds to the contact duration length in Figure 4 (c). The measured contact time τ = 98ns. The contact time calculated here using the classic Hertz model of pure elastic contact on a smooth surface is 114ns. The calculation formula is as follows. The measurement error is 14%, which proves the effectiveness of this method.

[0062] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A method for measuring particle collision contact time, characterized in that: The following steps are involved: The continuous laser is focused to form a beam with a waist diameter smaller than the diameter of the particle to be measured. The particle to be measured is launched to the position of the laser beam waist, and the change in light intensity is quantitatively monitored to obtain the duration when the laser is completely blocked by the particle to be measured, thereby achieving the measurement of the particle collision contact time.

2. The particle collision contact time measurement method according to claim 1, characterized in that: The light beam is close to the impact target surface of the particles to be detected.

3. The particle collision contact time measurement method according to claim 1, characterized in that: The diameter of the light beam is less than half the diameter of the particle to be measured.

4. The particle collision contact time measurement method according to claim 1, characterized in that: The diameter of the particles to be tested ranges from 1 μm to 1 cm.

5. The particle collision contact time measurement method according to claim 1, characterized in that: The particles to be tested are made of a material with a light transmittance less than 1.

6. The particle collision contact time measurement method according to claim 1, characterized in that: The particles to be tested include silicon dioxide particles, polystyrene particles and stainless steel particles.

7. The particle collision contact time measurement method according to claim 1, characterized in that: The continuous laser is a Gaussian beam or a flat-top beam.

8. The particle collision contact time measurement method according to claim 1, characterized in that: The light intensity is quantitatively monitored by a photodetector combined with an oscilloscope, and the sampling time interval of the oscilloscope and the photodetector should be less than half of the contact time.

9. The particle collision contact time measurement method according to claim 1, characterized in that: The continuous light beam is expanded and then focused to form a light beam with a beam waist diameter smaller than the diameter of the particle to be measured.

10. A method for measuring particle collision contact time, characterized in that: The following steps are involved: The continuous laser is focused to form a beam with a waist diameter smaller than the diameter of the particle to be measured. The particle to be measured is launched to the position of the laser beam waist. An oscilloscope combined with a photodetector is used to quantitatively monitor the change in light intensity. The duration after the oscilloscope output voltage drops to the minimum is obtained, thereby realizing the measurement of the particle collision contact time.

11. The particle collision contact time measurement method according to claim 10, characterized in that: The light beam is close to the impact target surface of the particles to be detected.

12. The particle collision contact time measurement method according to claim 10, characterized in that: The diameter of the light beam is less than half the diameter of the particle to be measured.

13. The particle collision contact time measurement method according to claim 10, characterized in that: The particles to be tested are made of a material with a light transmittance less than 1.

14. A measuring device for implementing the particle collision contact time measurement method according to any one of claims 1 to 13, characterized in that: Including photoelectric detection part and particle emission part, The photoelectric detection part includes a continuous laser, a beam expander, a plano-convex lens, a biconvex lens, a photodetector, an oscilloscope, a light source and a computer. The continuous laser, beam expander, plano-convex lens, biconvex lens and photodetector are arranged in sequence. The illumination range of the light source is aligned between the plano-convex lens and the biconvex lens. The photodetector, oscilloscope and computer are connected in sequence. The target surface is located at the waist position of the light beam between the plano-convex lens and the biconvex lens. The laser generated by the continuous laser passes through the beam expander and the plano-convex lens in sequence and is focused to form a light beam with a waist diameter smaller than the diameter of the particle to be measured. The photodetector receives the light signal converged by the biconvex lens and converts it into an electrical signal. The oscilloscope records the changes in the electrical signal and transmits it to the computer. The particle emitting part emits the particles to be measured into the illumination range and places the particles to be measured at the waist of the laser beam.

15. The measuring device according to claim 14, characterized in that The photoelectric detection part also includes a high-speed camera, which is connected to an oscilloscope and a computer respectively. The high-speed camera is aligned with the illumination range and performs image acquisition in a direction perpendicular to the laser propagation.

16. The measuring device according to claim 15, characterized in that The high-speed camera collects images under the triggering of the oscilloscope, and the collected images include images of the entire process of the particles to be measured from emission, approaching the target surface and rebounding from the target surface.

17. The measuring device according to claim 14, characterized in that The continuous laser is a power-stabilized laser with a wavelength of 200-2600 nm.

18. The measuring device according to claim 14, characterized in that The particle emission part includes a laser driven particle emitter, an adsorption type particle emitter, an air gun type particle emitter, a micro fluidized bed powder feeder or a micro vibration powder feeder.

19. The measuring device according to claim 14, characterized in that The light source is an LED light source.

20. The measuring device according to claim 14, characterized in that The time resolution of the photodetector and oscilloscope is at the sub-nanosecond level.

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