WO2025190069A1 - 一种颗粒碰撞接触时间测量方法及装置 - Google Patents

一种颗粒碰撞接触时间测量方法及装置

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Publication number
WO2025190069A1
WO2025190069A1 PCT/CN2025/078932 CN2025078932W WO2025190069A1 WO 2025190069 A1 WO2025190069 A1 WO 2025190069A1 CN 2025078932 W CN2025078932 W CN 2025078932W WO 2025190069 A1 WO2025190069 A1 WO 2025190069A1
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WIPO (PCT)
Prior art keywords
particle
contact time
measured
laser
collision contact
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English (en)
French (fr)
Inventor
王越明
王煜兴
周敏敏
段伦博
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Southeast University
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Southeast University
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N15/00—Investigating characteristics of particles; Investigating permeability, pore-volume or surface-area of porous materials
    • G01N15/02—Investigating particle size or size distribution
    • G01N15/0205—Investigating particle size or size distribution by optical means
    • G01N15/0227—Investigating particle size or size distribution by optical means using imaging; using holography

Definitions

  • 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.
  • 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.
  • 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.
  • the Kelvin model is used to represent the constitutive relationship of the contact process, the model schematic is shown in Figure 1.
  • ⁇ n (t) represents the deformation that changes with time
  • kn represents the strength of the elastic term
  • ⁇ n represents the strength of the viscous term
  • the restitution coefficient can be achieved through common velocity measurement methods such as high-speed imaging and laser Doppler velocimetry.
  • time contact time
  • space contact area
  • action contact force
  • direct methods to measure this parameter are currently rare.
  • the closed circuit method was used to measure the collision contact time between centimeter-scale metal spheres for the first time.
  • the high-speed imaging method was used to measure the collision contact time between centimeter-scale spheres.
  • 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.
  • 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.
  • the present invention provides a method for measuring particle collision contact time, comprising the following steps:
  • 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.
  • the light beam is close to the impact target surface of the particles to be detected.
  • the diameter of the light beam is less than half the diameter of the particle to be measured.
  • the diameter of the particles to be tested ranges from 1 ⁇ m to 1 cm.
  • the particles to be tested are made of a material with a light transmittance less than 1.
  • the particles to be tested include silicon dioxide particles, polystyrene particles and stainless steel particles.
  • the continuous laser is a Gaussian beam or a flat-top beam.
  • 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.
  • 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.
  • the present invention also provides another method for measuring particle collision contact time, comprising the following steps:
  • 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.
  • the light beam is close to the impact target surface of the particles to be detected.
  • the diameter of the light beam is less than half the diameter of the particle to be measured.
  • the particles to be tested are made of a material with a light transmittance less than 1.
  • 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.
  • 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.
  • 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.
  • 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.
  • the continuous laser is a power-stabilized laser with a wavelength of 200-2600 nm.
  • 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.
  • the light source is an LED light source.
  • the time resolution of the photodetector and the oscilloscope is at the sub-nanosecond level.
  • the present invention has the following beneficial effects:
  • 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.
  • 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.
  • Figure 1 is a schematic diagram of the Kelvin model
  • FIG2 is a schematic top view of the device of the present invention.
  • FIG3 is a schematic front view of a cross section along line A-A in FIG2 ;
  • 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.
  • the light beam is close to the impact target surface of the particles to be detected.
  • the diameter of the light beam is less than half the diameter of the particle to be measured.
  • the above method can achieve accurate measurement of the contact time of particle collisions as small as the laser diffraction limit.
  • this embodiment provides a particle contact time measurement device for implementing the above method, including a photoelectric detection part and a particle emission part.
  • 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 oscill
  • 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.
  • 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.
  • 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.
  • 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.
  • LIPIT laser-driven particle launcher
  • 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.
  • Particles to be tested include particles of various sizes ranging from 1 ⁇ m 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.
  • the pulse laser 21 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.
  • continuous laser is generated by continuous laser 1, which outputs parallel light with a larger diameter after passing through beam expander 2.
  • the laser is focused into a beam (spot) smaller than 0.5 times the diameter of the particle.
  • 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.
  • the particle 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.
  • 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.
  • V is the voltage measured by the oscilloscope
  • t1 is the time when the voltage drops to within the minimum voltage fluctuation range
  • t2 is the time when the voltage starts to rise from 0 and exceeds the minimum voltage fluctuation range
  • ⁇ V is the voltage noise fluctuation measured by the oscilloscope
  • the contact time ⁇ is the duration between the two moments.
  • the continuous laser 1 is a helium-neon laser from Thorlabs, with a central wavelength of 632.8 nm, an output power of 0.8 mW, and a 1/ e2 diameter of 0.48 mm.
  • the beam expander 2 is composed of two achromatic convex lenses with focal lengths of 7.5 mm and 150 mm, respectively, to achieve a 20x beam expansion factor.
  • the plano-convex lens 3 is an achromatic plano-convex lens with a focal length of 50 mm.
  • the biconvex lens 4 is an achromatic biconvex lens with a focal length of 50 mm.
  • the photodetector 5 is a high-speed free-space bias detector from Thorlabs, with a spectral range of 400-1100 nm, a bandwidth of 2 GHz, and a rise and fall time of less than 150 ps.
  • the oscilloscope 6 is an MSO5354 oscilloscope from Puyuan Jingdian Technology Co., Ltd., with a bandwidth of 350 MHz, a maximum sampling rate of 8 GSa/s, and a rise time of less than 500 ps.
  • the LED light source 7 is a Hongzhao LED fiber optic cold light source S5000 with an average illumination of 572,000 lumens.
  • the high-speed camera 8 is a Qianyanlang X213 high-speed camera with a full-frame maximum frame rate of 13,500 FPS.
  • the present invention also provides another method for measuring particle collision contact time, comprising the following steps:
  • 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.
  • ⁇ 632.8 nm
  • D 0 9.6 mm
  • 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 250 ⁇ m and can receive most of the laser energy.
  • the output of the photodetector 5 is connected to the oscilloscope 6, which is set to the falling edge trigger.
  • the oscilloscope 6 is connected to the high-speed camera 8, which is set to the external trigger mode and the acquisition mode is set to the pre-trigger acquisition.
  • the light signal received by the photodetector 5 is smaller than when the incident particle is not blocked.
  • 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).
  • 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.
  • the trigger event recorded by the high-speed camera 8 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 ⁇ 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.

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Abstract

一种颗粒碰撞接触时间测量方法及装置，方法包括以下步骤：将连续激光聚焦形成束腰直径小于待测颗粒直径的光束，将待测颗粒发射到激光束腰位置，定量监测光强变化，获得激光被待测颗粒最大程度遮挡的持续时间或者获得示波器输出电压降低到最小后的持续时间，即实现颗粒碰撞接触时间的测量。通过定量监测光强变化，获得激光被待测颗粒最大程度遮挡时的持续时间，从而实现颗粒碰撞接触时间的测量，具有能够测量小至激光衍射极限尺度的颗粒碰撞接触时间，不受颗粒导电、带电与否等材料的限制等优点，同时能够以极高的精度记录颗粒碰撞接触时间。

Description

一种颗粒碰撞接触时间测量方法及装置 技术领域
本发明涉及颗粒运动测量技术领域，尤其是涉及一种颗粒碰撞接触时间测量方法及装置。
背景技术
颗粒材料通常由离散颗粒组成，其广泛存在于各种领域，具有多种尺度的物理性质，为了更好的理解宏观颗粒物质的整体特性，需要探究微观条件下颗粒接触力学特性。颗粒的接触过程实际上是一个能量传递的过程，包括机械能、热能、电能等等，通常颗粒的接触过程需要碰撞恢复系数(即碰撞前后颗粒的速度之比)和接触持续时间两个参数来共同描述，如采用Kelvin模型表示接触过程的本构关系时，其模型示意图如图1所示。
模型所对应的运动方程和边界条件如下：
其中：δn(t)表示随时间变化的变形量，kn表示弹性项强度，ηn表示黏性项强度。
通过实验测得en和tc,n即可以求得kn和ηn，即：
从而完整描述接触过程位移随时间的变化情况：
其中：

目前恢复系数可通过高速成像、激光多普勒测速等常用的测速手段来实现，而对于单颗粒碰撞的接触时间，因其在时间(接触时间)、空间(接触面积)和作用(接触力)大小三个维度上都比较小，目前直接测量该参数的方法较为罕见。在期刊Powder technology上的Comparison of soft-sphere models to measurements of collision properties during normal impacts一文中采用闭合电路方法首次测量了厘米级金属球体间的碰撞接触时间；在Powder technology上的Contact time of an incident particle hitting a 2D bed of particles一文中采用高速成像方法测量了厘米级球体间的碰撞接触时间；在Europhys Lett上的Inelastic impact of a sphere on a massive plane:Nonmonotonic velocity-dependence of the restitution coefficient一文中结合了闭合电路以及加速度计方法测量了毫米级颗粒的接触时间。
但以上几种测量方法均仅可用于测量较大颗粒的接触时间，同时加速度计法测量准确度较差，而闭合电路方法通过将颗粒与撞击靶面连接构成闭合回路，因此只能用于测量金属颗粒，并且不能测量带电颗粒的接触过程，同时由于引入额外的接触，会影响颗粒的运动。因此有必要针对现有颗粒碰撞接触时间测量实验方法的劣势，研发一种新的颗粒碰撞接触时间测量技术。
发明内容
本发明的目的就是为了克服上述现有技术存在的缺陷，借助光电探测器的超快测量速度，利用激光光束的极小尺寸，实现了一种颗粒碰撞接触时间测量方法及装置。
本发明的目的可以通过以下技术方案来实现：
本发明提供一种颗粒碰撞接触时间测量方法，包括以下步骤：
将连续激光聚焦形成束腰直径小于待测颗粒直径的光束，将待测颗粒发射到激光束腰位置，定量监测光强变化，获得激光被待测颗粒完全遮挡时的持续时间，即实现颗粒碰撞接触时间的测量。
进一步地，所述光束贴近待测颗粒的撞击靶表面。
进一步地，所述光束的直径小于待测颗粒直径的一半。
进一步地，所述待测颗粒的直径范围为1μm-1cm。
进一步地，所述待测颗粒为光透射率小于1的材料。
进一步地，所述待测颗粒包括二氧化硅颗粒、聚苯乙烯颗粒和不锈钢颗粒。
进一步地，所述连续激光为高斯光束或平顶光束。
进一步地，所述光强通过光电探测器结合示波器进行定量监测，示波器以及光电探测器采样时间间隔应小于接触时间的一半。
进一步地，所述连续光束经扩束后再聚焦形成束腰直径小于待测颗粒直径的光束。
本发明还提供另一种颗粒碰撞接触时间测量方法，包括以下步骤：
将连续激光聚焦形成束腰直径小于待测颗粒直径的光束，将待测颗粒发射到激光束腰位置，使用示波器结合光电探测器定量监测光强变化，获得示波器输出电压降低到最小后的持续时间，即实现颗粒碰撞接触时间的测量。
进一步地，所述光束贴近待测颗粒的撞击靶表面。
进一步地，所述光束的直径小于待测颗粒直径的一半。
进一步地，所述待测颗粒为光透射率小于1的材料。
本发明还提供一种实现如上所述颗粒碰撞接触时间测量方法的测量装置，包括光电探测部分和颗粒发射部分，
其中，所述光电探测部分包括连续激光器、扩束镜、平凸透镜、双凸透镜、光电探测器、示波器、光源和电脑，所述连续激光器、扩束镜、平凸透镜、双凸透镜、光电探测器依次设置，所述光源的光照范围对准于平凸透镜和双凸透镜之间，所述光电探测器、示波器和电脑依次连接，撞击靶面位于所述平凸透镜和双凸透镜之间的光束束腰位置，所述连续激光器产生的激光依次经扩束镜和平凸透镜后，聚焦形成束腰直径小于待测颗粒直径的光束，所述光电探测器接收经过双凸透镜汇聚的光信号，并转化为电信号，所述示波器记录电信号的变化并传输至电脑；
所述颗粒发射部分将待测颗粒发射于所述光照范围内，并使待测颗粒位于激光束腰位置。
进一步地，所述光电探测部分还包括高速相机，该高速相机分别连接示波器和电脑，所述高速相机对准于所述光照范围，在垂直于激光传播的方向上进行图像采集。
进一步地，所述高速相机在示波器的触发下进行图像采集，采集的图像包括待测颗粒从发射、接近靶面及从靶面反弹的全过程图像。
进一步地，所述连续激光器为功率稳定型激光器，波长大小为200-2600nm。
进一步地，所述颗粒发射部分包括激光驱动颗粒发射器、吸附式颗粒发射器、气枪式颗粒发射器、微型流化床给粉器或微量振动给粉器。
进一步地，所述光源为LED光源。
进一步地，所述光电探测器和示波器的时间分辨率为亚纳秒级别。
与现有技术相比，本发明具有以下有益效果：
本发明将接触时间转换为光强信号进行测量，将连续激光聚焦形成束腰直径小于待测颗粒直径的光束，将待测颗粒发射到激光束腰位置，定量监测光强变化，获得激光被待测颗粒最大程度遮挡时的持续时间，能够实现对于小至激光衍射极限尺度(表示激光经过聚焦后能达到的最小光斑直径)的颗粒碰撞接触时间进行测量，不受颗粒导电与否及带电与否的限制，能够测量光透射率小于1的材料颗粒的碰撞接触时间，同时由于当前示波器以及光电探测器采样频率要远高于加速度计和高速相机采样频率，且采样时间间隔小于接触时间的一半，因此能够以极高的精度记录颗粒碰撞的接触时间，为颗粒与壁面碰撞的建模提供了准确的输入参数。这一技术提升了与时间相关的物理过程的计算精度，如接触导热过程，为太阳能集热器中换热管束的布置提供重要指导，从而优化设计并提高系统效率。
附图说明
图1为Kelvin模型示意图；
图2为本发明装置的俯视示意图；
图3为图2中A-A线截面正视示意图；
图中，1、连续激光器；2、扩束镜；3、平凸透镜；4、双凸透镜；5、光电探测器；6、示波器；7、LED光源；8、高速相机；9、接触靶面；10、电脑；21、脉冲激光器；22、扩束器；23、扫描振镜；24、F-Theta扫描透镜；25、颗粒发射靶；251、K9玻璃层；252、金膜；253、PDMS薄膜。
具体实施方式
下面结合附图和具体实施例对本发明进行详细说明。本实施例以本发明技术方案为前提进行实施，给出了详细的实施方式和具体的操作过程，但本发明的保护范围不限于下述的实施例。
实施例1
本实施例提供一种颗粒碰撞接触时间测量方法，包括以下步骤：将连续激光聚焦形成束腰直径小于待测颗粒直径的光束，将待测颗粒发射到激光束腰位置，定量监测光强变化，获得激光被待测颗粒最大程度遮挡时的持续时间，即实现颗粒碰撞接触时间的测量。
优选地，光束贴近待测颗粒的撞击靶表面。
进一步优选地，光束的直径小于待测颗粒直径的一半。
通过上述方法，能够实现对于小至激光衍射极限尺度的颗粒碰撞接触时间的准确测量。
如图2所示，本实施例提供一种实现上述方法的颗粒接触时间测量装置，包括光电探测部分和颗粒发射部分。
其中，光电探测部分包括连续激光器1、扩束镜2、平凸透镜3、双凸透镜4、光电探测器5、示波器6、LED光源7和电脑10，连续激光器1、扩束镜2、平凸透镜3、双凸透镜4、光电探测器5依次设置，光电探测器5与示波器6连接，LED光源7设置于接触靶面9处，示波器6和电脑10连接，扩束镜2将连续激光器1产生的激光扩束为直径更大的平行光，平凸透镜将3扩束后平行光聚焦至小于待测颗粒直径的1/2，随后双凸透镜4收集聚焦后重新发散的平行光并输入光电探测器5，光电探测器5将光信号转变为电信号，示波器6记录电信号的变化并传输至电脑10。
在优选的实施方式中，光电探测部分还包括高速相机8，高速相机8设置于接触靶面9，高速相机8分别连接示波器6和电脑10，高速相机8在垂直于颗粒入射方向和激光传播方向的位置记录颗粒从发射、接近靶面及从靶面反弹的全过程，并传输至电脑10。本实施例中，从光线传播的垂直方向上利用高速相机8进行同步观测，从而避免多个颗粒同时撞击影响测量结果。高速相机能够观测到颗粒碰撞前后距离靶面非常近的两个瞬间，因此可以作为辅助，避免多个颗粒同时撞击影响后续结果。
上述光电探测部分中，连续激光器1为氦氖激光器或者类似的功率稳定型激光器，能够产生所要求波长的连续激光，波长大小为200-2600nm之间，能够被高速光电探测器探测(探测范围400-1100nm)。光电探测器能够实现所要求的探测速度，上升及下降时间小于150ps，带宽达到2GHz，时间分辨率达到亚纳秒级别。示波器能够实现所要求的探测速度，上升及下降时间小于500ps，最大采样率为8GSa/s，时间分辨率达到亚纳秒级别。基于示波器及光电探测器超高的采样频率，能够以极高的精度记录颗粒碰撞接触时间。
颗粒发射部分可以为激光驱动颗粒发射器(LIPIT)、吸附式颗粒发射器、气枪式颗粒发射器、微型流化床给粉器或微量振动给粉器等颗粒发射装置。本实施例中采用激光驱动颗粒发射器，如图3所示，包括依次设置的脉冲激光器21、扩束器22、扫描振镜23、F-Theta扫描透镜24和颗粒发射靶25，颗粒发射靶25位于平凸透镜3和双凸透镜4之间的光束束腰位置，以将颗粒发射至光束束腰位置。
待测颗粒包括粒径范围为1μm-1cm内各种粒径的颗粒，包括导电的金属材料与不导电材料的颗粒，包括带电的颗粒与不带电的颗粒。待测颗粒应为光透射率小于1的材料，如二氧化硅颗粒、聚苯乙烯颗粒和不锈钢颗粒等。
上述激光驱动颗粒发射器工作时，脉冲激光器21产生脉冲激光，通过扩束器22扩束，通过扫描振镜23和F-Theta扫描透镜24组合控制激光聚焦至待发射颗粒上方的颗粒发射靶25中，颗粒发射靶25包括K9玻璃基板251、金膜252和PDMS薄膜253，K9玻璃层251允许激光束穿过而不吸收激光能量，激光将金膜252气化，膨胀的气体使得PDMS薄膜253发生圆锥体型膨胀，推动待发射颗粒弹射冲击撞击靶9，其中PDMS薄膜253能够限制气化产物与待发射颗粒接触，并避免颗粒升温。在颗粒移动过程中，通过连续激光器1产生连续激光，经过扩束镜2后输出直径较大的平行光，进入平凸透镜3后将激光聚焦为小于0.5倍颗粒直径的光束(光斑)，随后双凸透镜4收集聚焦后重新发散的光线进入光电探测器5的探测区，光电探测器5接收光线并转换为电信号输入示波器6，示波器分析所采集的电信号，当检测到信号下降沿时，输出采集信号进入高速相机8，触发高速相机8动作，示波器6和高速相机8同时保存下降沿附近的数据，传输至电脑10，电脑10处理高速相机采集到的颗粒图像以及示波器电信号数据，计算得到颗粒入射速度变化以及颗粒接触的持续时间。在颗粒靠近撞击靶面9的过程中会遮挡连续激光器1发出的光线，减小光电探测器6接收到的光线强度，进而影响光电探测器6输出及示波器6接收到的电信号大小，当颗粒接触壁面时，光线被最大程度地遮挡，示波器6收到的电信号为最小值，电信号在最小值保持的时间即为颗粒撞击过程中的接触时间。
在某个具体实施方式中，电脑10计算碰撞接触的持续时间的公式可以为：

τ＝t2-t1
其中，V为示波器测量电压，t1为电压下降到最小电压波动范围内的时刻，t2为电压从0开始回升大于最小电压波动范围内的时刻，ΔV为示波器所测电压噪声波动量，接触时间τ为两个时刻之间的时长。
本实施例中，连续激光器1为索雷博光电科技有限公司(Thorlabs)的氦氖激光器，中心波长为632.8nm，输出功率为0.8mW，1/e2直径为0.48mm。扩束镜2由两个消色差凸透镜组成，焦距分别为7.5mm和150mm，实现20x扩束倍数。平凸透镜3为消色差平凸透镜，焦距为50mm。双凸透镜4为消色差双凸透镜，焦距为50mm。光电探测器5为索雷博光电科技有限公司的高速自由空间偏压探测器，光谱范围为400-1100nm，带宽为2GHz，上升下降时间小于150ps。示波器6为普源精电科技有限公司的MSO5354示波器，带宽为350MHz，最大采样率为8GSa/s，上升时间小于500ps。LED光源7为鸿照LED光纤冷光源S5000，平均照度572000流明，高速相机8为千眼狼X213高速摄像机，全画幅最大帧率13500FPS。
实施例2
本发明还提供另一种颗粒碰撞接触时间测量方法，包括以下步骤：
将连续激光聚焦形成束腰直径小于待测颗粒直径的光束，将待测颗粒发射到激光束腰位置，使用示波器结合光电探测器定量监测光强变化，获得示波器输出电压降低到最小后的持续时间，即实现颗粒碰撞接触时间的测量。
参考图2所示，采用氦氖激光器1产生连续激光，其中心波长λ＝632.8nm，稳定输出功率为0.8mW，出口光斑的1/e2直径为0.48mm，该光束经过扩束镜2放大20倍后直径达到D0＝9.6mm，扩束后的光束经过平凸透镜3，其焦距f＝50mm，根据聚焦光斑公式：激光经聚焦后中心光斑直径双凸透镜4将聚焦中心光斑输出到光电探测器5的信号接收区域，该区域直径为250μm，能够接受激光绝大部分能量。将光电探测器5输出连接至示波器6，设置示波器6为下降沿触发，同时将示波器6连接至高速相机8，设置高速相机8为外触发模式，其采集模式设置为触发前采集。此时将待测球形颗粒如直径D1＝50μm的二氧化硅颗粒黏附于颗粒发射靶25上，使用脉冲激光器21将二氧化硅颗粒发射出来并撞击连续激光聚焦光斑位置。由于入射颗粒直径当入射颗粒接近并撞击接触靶面9时，入射颗粒遮挡了部分激光光束，由于入射颗粒的光透射率小于1，因此光电探测器5所接收到的光信号相比入射颗粒未遮挡时减小，当光电探测器5接收到的光信号减小到示波器6所设置的触发阈值时，示波器6触发并记录触发前后的光信号强度变化数据，对应图4(b)中横坐标等于0时刻，同时发出信号触发高速相机8开始采集，采集结果如图4(a)所示。当示波器6信号减小到最小时表明入射颗粒与接触靶面9开始接触，随后入射颗粒发生反弹离开接触表面，完成一次完整的记录后，检查高速相机8所记录的触发事件，确定触发事件是否为一次单个颗粒与接触靶面9的撞击事件，如果是，则示波器减小到最小后所持续的时间即为入射颗粒碰撞接触靶面的接触持续时间，对应于图4(c)中接触持续时间长度，测量得到接触时长τ＝98ns，在此利用经典的光滑表面纯弹性接触赫兹模型计算的接触时间为114ns，计算公式如下，测量误差为14％，证明了本方法的有效性。
以上详细描述了本发明的较佳具体实施例。应当理解，本领域的普通技术人员无需创造性劳动就可以根据本发明的构思作出诸多修改和变化。因此，凡本技术领域中技术人员依本发明的构思在现有技术的基础上通过逻辑分析、推理或者有限的实验可以得到的技术方案，皆应在由权利要求书所确定的保护范围内。

Claims (20)

  1. 一种颗粒碰撞接触时间测量方法，其特征在于，包括以下步骤：
    将连续激光聚焦形成束腰直径小于待测颗粒直径的光束，将待测颗粒发射到激光束腰位置，定量监测光强变化，获得激光被待测颗粒完全遮挡时的持续时间，即实现颗粒碰撞接触时间的测量。
  2. 根据权利要求1所述的颗粒碰撞接触时间测量方法，其特征在于，所述光束贴近待测颗粒的撞击靶表面。
  3. 根据权利要求1所述的颗粒碰撞接触时间测量方法，其特征在于，所述光束的直径小于待测颗粒直径的一半。
  4. 根据权利要求1所述的颗粒碰撞接触时间测量方法，其特征在于，所述待测颗粒的直径范围为1μm-1cm。
  5. 根据权利要求1所述的颗粒碰撞接触时间测量方法，其特征在于，所述待测颗粒为光透射率小于1的材料。
  6. 根据权利要求1所述的颗粒碰撞接触时间测量方法，其特征在于，所述待测颗粒包括二氧化硅颗粒、聚苯乙烯颗粒和不锈钢颗粒。
  7. 根据权利要求1所述的颗粒碰撞接触时间测量方法，其特征在于，所述连续激光为高斯光束或平顶光束。
  8. 根据权利要求1所述的颗粒碰撞接触时间测量方法，其特征在于，所述光强通过光电探测器结合示波器进行定量监测，示波器以及光电探测器采样时间间隔应小于接触时间的一半。
  9. 根据权利要求1所述的颗粒碰撞接触时间测量方法，其特征在于，所述连续光束经扩束后再聚焦形成束腰直径小于待测颗粒直径的光束。
  10. 一种颗粒碰撞接触时间测量方法，其特征在于，包括以下步骤：
    将连续激光聚焦形成束腰直径小于待测颗粒直径的光束，将待测颗粒发射到激光束腰位置，使用示波器结合光电探测器定量监测光强变化，获得示波器输出电压降低到最小后的持续时间，即实现颗粒碰撞接触时间的测量。
  11. 根据权利要求10所述的颗粒碰撞接触时间测量方法，其特征在于，所述光束贴近待测颗粒的撞击靶表面。
  12. 根据权利要求10所述的颗粒碰撞接触时间测量方法，其特征在于，所述光束的直径小于待测颗粒直径的一半。
  13. 根据权利要求10所述的颗粒碰撞接触时间测量方法，其特征在于，所述待测颗粒为光透射率小于1的材料。
  14. 一种实现如权利要求1-13任一所述颗粒碰撞接触时间测量方法的测量装置，其特征在于，包括光电探测部分和颗粒发射部分，
    其中，所述光电探测部分包括连续激光器、扩束镜、平凸透镜、双凸透镜、光电探测器、示波器、光源和电脑，所述连续激光器、扩束镜、平凸透镜、双凸透镜、光电探测器依次设置，所述光源的光照范围对准于平凸透镜和双凸透镜之间，所述光电探测器、示波器和电脑依次连接，撞击靶面位于所述平凸透镜和双凸透镜之间的光束束腰位置，所述连续激光器产生的激光依次经扩束镜和平凸透镜后，聚焦形成束腰直径小于待测颗粒直径的光束，所述光电探测器接收经过双凸透镜汇聚的光信号，并转化为电信号，所述示波器记录电信号的变化并传输至电脑；
    所述颗粒发射部分将待测颗粒发射于所述光照范围内，并使待测颗粒位于激光束腰位置。
  15. 根据权利要求14所述的测量装置，其特征在于，所述光电探测部分还包括高速相机，该高速相机分别连接示波器和电脑，所述高速相机对准于所述光照范围，在垂直于激光传播的方向上进行图像采集。
  16. 根据权利要求15所述的测量装置，其特征在于，所述高速相机在示波器的触发下进行图像采集，采集的图像包括待测颗粒从发射、接近靶面及从靶面反弹的全过程图像。
  17. 根据权利要求14所述的测量装置，其特征在于，所述连续激光器为功率稳定型激光器，波长大小为200-2600nm。
  18. 根据权利要求14所述的测量装置，其特征在于，所述颗粒发射部分包括激光驱动颗粒发射器、吸附式颗粒发射器、气枪式颗粒发射器、微型流化床给粉器或微量振动给粉器。
  19. 根据权利要求14所述的测量装置，其特征在于，所述光源为LED光源。
  20. 根据权利要求14所述的测量装置，其特征在于，所述光电探测器和示波器的时间分辨率为亚纳秒级别。
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