JP2012047648A - Particle size measurement instrument and particle size measurement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a particle size by installing a detector on an optical axis of light irradiated by a light source and detecting back scattered light due to particles included in a particle group, and to unequivocally accurately measure a particle size while reducing the amount of light directly impinging without being scattered by particles, out of light from the light source as much as possible.SOLUTION: Fundamentally, this invention is based on findings that a particle size can be unequivocally measured by measuring a maximum forward scattering intensity while guiding particles included in the particle group to a beam convergence position by means of a radiation pressure generated by a convergent laser beam to reduce, as much as possible, direct transmitted light not scattered by particles. That is, a particle size measurement instrument and a particle size measurement method utilize a radiation pressure of incident light to forcibly move the particles to the convergence position and detect forward scattered light.

Description

  The present invention relates to an apparatus and a method for measuring the particle size of particles in a channel by a forward scattering method. The present invention particularly relates to a particle size measuring apparatus and a particle size measuring method using a radiation pressure generated by condensing a laser beam.

  Conventionally, there is a technique for monitoring the scattering state of compound particles contained in flue gas and particles generated in the natural environment.

  However, the technology for monitoring the particle size is poor in real time. Also, in recent years, there is no technology that can perform real-time measurement with micro- and nano-size environmental chemical monitoring technologies. In particular, small and inexpensive measurement technology is required.

  Further, for example, in Japanese Patent Laid-Open No. 2000-146812 (Patent Document 1), a group of particles dispersed with laser light is irradiated, diffraction / scattered light generated by the laser light irradiation is detected, and detected diffraction is detected. / A particle size measuring device for measuring the particle size distribution of a particle group based on a scattered light intensity signal is disclosed. In such a conventional particle size measuring device, if a light intensity detector is installed on the optical axis of the light source, the intensity of the directly incident light becomes too strong without being scattered by the dispersed particles. ， The particle size cannot be measured accurately. Therefore, the conventional particle size measuring apparatus detects only the component of the scattered light in the specific angle direction.

  However, if only the component in the specific angle direction of the scattered light is detected and calculated by the Mie scattering theory as in the conventional particle size measuring device, the scattering intensity pattern depending on the particle size directly shows the angle dependence. The result is reflected in. FIG. 5 shows a scattering intensity pattern calculated by the Mie scattering theory. As described above, the fact that the angle dependence is directly reflected in the scattering intensity pattern is a cause of inaccurate particle size measurement. In other words, it has been difficult for the conventional particle size measuring device to measure the particle size uniquely and accurately.

JP 2000-146812 A

  Therefore, the present invention has an object to measure the particle diameter by installing a detector on the optical axis of the light emitted from the light source and detecting the forward scattered light generated by the particles contained in the particle group. . Therefore, an object of the present invention is to uniquely and accurately measure the particle size while reducing the amount of light directly incident on the light from the light source without being scattered by the particles.

  The present invention basically uses the radiation pressure generated by the focused laser beam to guide the particles contained in the particle group to the beam focusing position, thereby reducing the direct transmitted light not scattered by the particles as much as possible. Based on the knowledge that the maximum forward scattering intensity can be measured and the particle size can be uniquely measured. That is, the particle size measuring apparatus and the particle size measuring method according to the present invention detect the forward scattered light by forcibly moving the particles to the condensing position using the light radiation pressure by the incident light.

The first aspect of the present invention is a particle size measuring apparatus having a light source 10, a flow path 20, particle guiding means 30, a detector 40, and a calculating means 50.
The light source 10 irradiates the flow path 20 with light.
In the flow channel 20, a particle group that is a target of particle size measurement circulates.
The particle guiding means 30 is a means for guiding particles in the flow path 20 to a light condensing position. As the particle guiding means 30, a lens that is disposed between the light source 10 and the flow path 20 and collects the light irradiated by the light source 10 in the flow path 20 is used. In other words, the lens guides the particles in the flow path 20 to the light condensing position using the light radiation pressure.
Only one detector 40 is arranged on the optical axis of the light emitted from the light source 10. And the intensity | strength of the forward scattered light which arises by presence of the particle | grains contained in the particle group in the flow path 20 is detected.
The calculation means 50 obtains the particle size of the particles based on the intensity of the forward scattered light detected by the detector 40.

  In the present invention, since light is collected in the flow path 20 by the lens 30, particles in the flow path can be guided to the beam condensing position using light radiation pressure (that is, gradient force and scattering force). In this way, the present invention can guide the particles to the beam condensing position, so that the amount of incident light not scattered by the particles can be reduced as much as possible. Therefore, the detector 40 that detects the intensity of the forward scattered light can be disposed on the optical axis of the irradiation light emitted from the light source 10.

  As described above, the present invention can guide the particles in the flow path 20 to the optimum position (that is, the beam condensing position) where the maximum scattering intensity is generated by using the radiation pressure of light. Therefore, unlike the conventional case, there is no need to limit the flow path by a physical structure or to generate an air flow in the flow path so that particles pass through the beam condensing position. Can be.

  In addition, since the detector 40 can be disposed on the optical axis of the light emitted from the light source 10, the present invention provides various effects that could not be achieved in the past. For example, when there is no particle in the flow path 20, the entire light amount of the light emitted from the light source 10 enters the detector 40, so that the dynamic range of the detector 40 can be set in advance. In addition, when particles flow through the flow path 20 and light scattering occurs, the light directly incident on the detector 40 is scattered as scattered light over the entire space, so the forward scattering intensity depends on the amount of scattering. Can be used for particle size measurement.

  The first aspect of the present invention is further arranged between the flow channel 20 and the detector 40, and collects forward scattered light generated by the presence of particles contained in the particle group in the flow channel 20 on the detector 40. A condensing system 60.

  The first aspect of the present invention further includes light diameter changing means that is disposed between the light source 10 and the lens 30 and widens or narrows the light diameter of the light emitted from the light source 10.

  That is, in the first aspect of the present invention, an aperture plate with a variable aperture diameter is installed between the light source 10 and the lens 30. The shape of the opening is circular. In this way, the diameter of the light emitted from the light source 10 is widened or narrowed by changing the aperture diameter. Thereby, the diameter of the condensing point formed in the flow path 20 can be controlled. Therefore, the range of the particle size of the particles that can be measured by the particle size measuring device can be changed.

  The calculating means 50 preferably calculates the mass of the particles together with the particle size of the particles. The mass of the particle is applied to the particle based on the calculated particle size in view of the fact that the velocity of the particle in the beam changes due to the change in the scattering force applied to the particle according to the position in the beam. Scattering power can also be calculated.

  Moreover, it is preferable that the calculation means 50 calculates the mass of a particle together with the particle size of the particle and the mass of the particle. Assuming that the particles are spherical, the volume of the particles can be obtained from the particle size of the particles, and the density of the particles can be obtained based on the volume and mass.

  The second aspect of the present invention relates to a particle size measuring method. In the particle size measurement method, the light from the light source 10 is condensed by the lens 30 to form a condensing point in the flow path 20 through which the particle group flows, and the particles in the flow path 20 are guided to the light condensing position. A step of detecting the intensity of the forward scattered light caused by the presence of particles contained in the particle group in the flow channel 20 by the detector 40 arranged on the optical axis of the light irradiated by the light source 10, and the calculating means 50 Thus, a step of calculating the particle size of the particles based on the intensity of the forward scattered light detected by the detector 40 is included.

  In the second aspect of the present invention, incident light from the light source 10 is detected by the detector 40 before detecting the intensity of diffracted light and forward scattered light caused by the presence of particles contained in the particle group in the flow path 20. A step of detecting the intensity of the transmitted light transmitted through the flow path 20 in which no particle group exists, the intensity of the transmitted light when there is no particle detected by the detector 40 by the calculation means 50, and the front when the particle is present A step of calculating an intensity ratio of the intensity of scattered light.

  In general scattering measurement, the intensity ratio between the light transmission intensity and the scattering intensity is measured, and the particle size is determined by comparing the theoretical formula with the actual measurement value. For example, when the medium is a solution and there is light absorption depending on the solvent, it is necessary to consider the absorption. Therefore, the present invention first detects the intensity of transmitted light that has passed through a solvent in which particles are not present, and obtains the intensity ratio with the intensity of incident light based on the detected intensity of transmitted light. As a result, the intensity of the incident light can be detected together with the scattered light even if the medium is absent. Therefore, the intensity ratio can be measured with only one light source and one detector.

  As described above, the present invention can measure the particle size by installing a detector on the optical axis of the light emitted from the light source and detecting the forward scattered light generated by the particles.

FIG. 1 is a diagram showing a configuration of a particle size measuring apparatus according to the present invention. FIG. 2 is a diagram showing the configuration of the experimental apparatus of the method according to the present invention. FIG. 3 is a graph showing a comparison between the theoretical method values and the experimental values according to the present invention. FIG. 4 is a diagram showing how particles are captured and scattered by the focused laser beam. FIG. 5 is a diagram showing a scattering intensity pattern calculated by the Mie scattering theory.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and includes modifications appropriately made within the scope obvious to those skilled in the art.

  FIG. 1 shows the configuration of a particle size measuring apparatus according to the present invention. As shown in FIG. 1, the light source 10 (laser) irradiates the particle guiding means 30 (lens) with light (laser beam). The lens 30 forms a focal point F in the flow path 20 by the condensed light. The condensing system 60 irradiates the detector 40 with light through the lens 30. The detector 40 detects the intensity of forward scattered light caused by the presence of particles included in the particle group. The calculation means 50 calculates the particle size of the particles based on the detected intensity of forward scattered light.

  At this time, the detector 40 is disposed on the optical axis L irradiated by the light source 10. The lens 30, the flow path 20, and the light collecting system 60 are also arranged on the optical axis L irradiated by the light source 10.

  The light source 10 is a laser light source. For example, a commercially available semiconductor laser may be used. A flow path 20 is installed in the light traveling direction of the light source 10. The channel 20 is a transparent container through which a particle group to be measured passes. The lens 30 is a condensing lens provided between the light source 10 and the flow path 20. In FIG. 1, the lens 30 is represented by a single lens, but may be an optical system in which a plurality of convex lenses and concave lenses are combined. The lens 30 appropriately converges the light from the light source 10 to form a condensing point F in the flow path 20.

  When the condensing point F is formed in the flow channel 20, the particles in the flow channel 20 are guided on the optical axis L by the light radiation pressure and moved to the beam condensing position. The position where the condensing point F is formed is preferably the center of the flow path 20, but if it is within the flow path 20, the particles are guided to the beam condensing position, so Should just be formed. The particles at the beam focusing position scatter the beam light with the maximum scattering intensity. The width of the beam waist is, for example, 1 μm to 100 μm, 5 μm to 80 μm, or 10 μm to 70 μm.

  Further, a light diameter changing means for widening or narrowing the light diameter of the light emitted from the light source 10 may be provided between the light source 10 and the lens 30. The light diameter changing means is an aperture plate with a variable aperture diameter. The shape of the opening of the opening plate is circular. As the light diameter changing means, for example, a metal such as aluminum, copper, or brass is used. The opening diameter of the light diameter changing means has, for example, opening diameters of 1 mm to 50 mm, 1 mm to 10 mm, and 10 mm to 30 mm. In this way, the diameter of the light emitted from the light source 10 is widened or narrowed by changing the aperture diameter. Thereby, the diameter of the condensing point formed in the flow path 20 can be controlled. Therefore, the range of the particle size of the particles that can be measured by the particle size measuring device can be changed.

  The condensing system 60 is a condensing lens provided between the flow path 20 and the detector 40. The condensing system may be a single lens or an optical system that combines a plurality of convex lenses and concave lenses. The condensing system 60 appropriately converges the light scattered by the particles in the flow path 20 and irradiates the detector 40.

  The detector 40 is disposed on the optical axis L of the light emitted from the light source 10. The detector 40 receives direct light from the light source 10 when there is no particle group in the flow path 20, and receives light scattered by the particles when there is a particle group in the flow path 20. . Specifically, the photodetector 40 includes a photoelectric conversion element, and the photoelectric conversion element converts the light collected by the light collection system 60 into an electric signal and transmits it to the calculation means. The photoelectric conversion element can detect a change in forward scattering intensity according to the amount of scattering due to the presence of particles in the flow path 20. Since the forward scattering intensity changes according to the particle size of the particle, the particle size of the particle can be measured from the output signal of the photoelectric conversion element. As this photoelectric conversion element, one photodiode can be used.

  The calculation means 50 is a computer that calculates the particle size of particles contained in the particle group in the flow channel 20 based on the light intensity of the forward scattered light detected by the detector 40. The computer calculates the particle size of the particles using information on the light intensity of the forward scattered light detected by the detector 40 installed on the optical axis L of the light source 10.

Specifically, the calculation means 50 processes the light intensity data based on the generalized Lorentz-Me (GLM) theory. The GLM theory represents a scattered field generated when a monochromatic focused laser beam is incident on one sphere in a uniform medium. According to the GLM theory, when the scattering angle from the incident optical axis is θ in the scattering plane, the scattered light intensity function i ₁ (θ) in the polarization direction perpendicular to the scattering plane and the scattering in the polarization direction parallel to the scattering plane The light intensity function i ₂ (θ) is obtained by the following formulas.

  Thus, the calculation means 50 calculates the particle size of the particles by numerically calculating the particle size dependence of the scattering intensity based on the GLM theory.

  Further, the calculation means 50 may obtain the mass of the particles based on the particle diameter obtained by measuring the scattering intensity. In other words, considering that the speed of the particles in the beam changes due to the change in the scattering force applied to the particles according to the position in the beam, the scattering force applied to the particles is calculated based on the calculated particle size. Can also be calculated. Considering this scattering force and the viscosity of the surrounding medium, the mass of the particles can be obtained by the following equation.

  Further, the calculating means 50 may obtain the particle density based on the particle diameter and mass of the particle calculated by the above calculation. That is, assuming that the particles are spherical, the volume of the particles can be obtained from the particle diameter, and the density of the particles can be obtained based on the volume and mass.

  Further, the calculation means 50 calculates the intensity ratio between the incident light and the forward scattered light based on the intensity of the transmitted light that has passed through the flow path 20 where the particle group detected by the detector 40 does not exist and the intensity of the forward scattered light by the particles. Is calculated.

  Examples of the granular material measuring method according to the present invention will be described below. FIG. 2 shows an experimental system for the particle measurement method. In this experimental system, an Ar ion laser with λ = 514.5 nm was used as the light source 10. The laser light emitted from the light source 10 became parallel light through the lens 30 a and was condensed by the lens 30 b to form a condensing point in the flow path 20. At this time, the diameter of the focused point of the focused beam was 5 μm. A polarizer 80 is interposed between the lens 30a and the lens 30b. Further, in this experimental system, using the light radiation pressure by the focused beam, the particles flowing in the flow channel 20 are forcibly moved to the focal position, and the forward scattered light of the particles is detected. In this experimental system, as shown in FIG. 2, a camera 70 is installed in a direction perpendicular to the beam axis, and the movement of the scatterer to the focal position by incident light and the state of scattering at that position are monitored. did.

  FIG. 3 shows a comparison between the actually measured values of five different particle size samples and the theoretical values of the GLM scattering theory. As shown in FIG. 3, the actual measurement value approximated the theoretical value, and the experimental value obtained a very good agreement with the theoretical value. Further, FIG. 3 shows that in a beam system having a focal diameter of 5 μm, the value is uniquely determined for a particle diameter in the range of 1 μm to 4 μm.

  FIG. 4 shows the movement and scattering of particles by the focused laser beam photographed by the camera 70. As shown in FIG. 4, it can be seen that the particles P are moved in the vicinity of the condensing position W in the laser beam L, and the light is strongly scattered. As described above, by using the particle size measurement method according to the present invention, it is possible to move particles to a very limited region and generate forward scattered light with the maximum intensity.

Claims (8)

A light source (10) that emits light;
A flow path (20) through which a group of particles including particles flows,
Particle guiding means (30) for guiding particles in the flow path (20) to a light collecting position;
A detector (40) disposed on the optical axis of the light irradiated by the light source (10) and detecting the intensity of forward scattered light caused by the presence of particles contained in the particles in the flow path (20);
Based on the intensity of the forward scattered light detected by the detector (40), including calculation means (50) for calculating the particle size of the particles included in the particle group,
The particle guiding means (30) is disposed between the light source (10) and the flow path (20), collects the light irradiated by the light source (10), and collects the light in the flow path (20). A particle size measuring device which is a lens (30) for forming a light spot.
further,
It is arranged between the flow path (20) and the detector (40), condenses forward scattered light caused by the presence of particles contained in the particle group in the flow path (20), and collects the detector (40 The particle size measuring device according to claim 1, further comprising a condensing system (60) that irradiates the light source.
The particle size measuring apparatus according to claim 1, wherein a width of a condensing point formed in the flow path (20) by the lens is 1 µm or more and 100 µm or less.
further,
The particle size measuring device according to claim 1, further comprising: a light diameter changing means for widening or narrowing a light diameter of light emitted from the light source (10) between the light source (10) and the lens (30).
The particle size measuring device according to claim 1, wherein the calculating means (50) further calculates the mass of the particles based on the calculated particle size of the particles.
The calculation means (50) further calculates the mass of the particles based on the calculated particle size and mass of the particles.
The particle size measuring apparatus according to claim 5.
The lens (30) condenses the light from the light source (10) to form a condensing point in the flow path (20) through which the particle group flows, and the particles in the flow path (20) A process of guiding to a condensing position;
The step of detecting the intensity of forward scattered light generated by the presence of particles contained in the particle group in the flow path (20) by the detector (40) arranged on the optical axis of the light irradiated by the light source (10). When,
A particle size measuring method comprising a step of calculating a particle size of particles contained in the particle group based on the intensity of forward scattered light detected by the detector (40) by a calculating means (50).
Before detecting the intensity of diffracted light and forward scattered light caused by the presence of particles contained in the particles in the flow path (20),
Detecting, by the detector (40), the intensity of transmitted light transmitted through the flow path (20) where the incident light from the light source (10) does not exist, and
The calculation means (50) includes a step of calculating an intensity ratio between the intensity of the forward scattered light and the intensity of the transmitted light based on the intensity of the transmitted light detected by the detector (40). The particle diameter measuring method as described.

Images