JP7242062B2 - Moving particle evaluation method and evaluation device - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act [Date of publication of website] March 1, 2019 [Website address] https://jps2019s. gakkai-web. net/ [Date] March 15, 2019 [Meeting Name, Venue] The 74th Annual Meeting of the Physical Society of Japan National University Corporation Kyushu University (744 Motooka, Nishi-ku, Fukuoka City, Fukuoka Prefecture)

The present invention relates to a moving particle evaluation method and evaluation apparatus.

Various methods have been proposed to assess the situation of moving particles. For example, as a method for measuring the moving speed of particles, there is a method using a laser Doppler method described in Patent Document 1. The laser Doppler method is a method of irradiating a moving particle with a laser beam and deriving the moving speed of the particle based on the magnitude of the Doppler shift occurring in the scattered light. In Patent Literature 1, interference fringes formed by laser light are passed through particles, the Doppler frequency is derived from the high frequency component of the scattered light, and the movement speed of the particles is obtained.

U.S. Pat. No. 4,537,507

The laser Doppler method described in Patent Document 1 derives the moving speed of particles based on the Doppler frequency as described above. If the velocity of the particles is low, the Doppler frequency will be low, making it difficult to detect the velocity. There is a need for a method that can evaluate the state of particles even when the particles do not move at a high speed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a moving particle evaluation method and evaluation apparatus capable of evaluating the state of a particle including when the moving speed of the particle is relatively low.

The moving particle evaluation method of the present invention relates to the time change of the intensity of light from the particles as a periodic change in the intensity of the light from the particles caused by the particles traversing the interference fringes of the light. The diffusion rate of the particles is evaluated based on the decrease in height with respect to the delay time in the autocorrelation peak .

According to the moving particle evaluation method of the present invention, the state of a particle is evaluated by capturing periodic changes in the intensity of light emitted from the particle. When the moving speed of the particles is low, the period of the periodic change is only increased, and it is not difficult to capture the periodic change. Therefore, even if the moving speed of the particles is low, it is easy to evaluate the situation of the moving particles. This indicates that the present invention can be applied to a wide range including the case where the particle speed is low, and the application of the present invention is not limited to the case where the particle movement speed is low. Moreover, according to the present invention, periodic changes in light intensity can be appropriately evaluated based on autocorrelation. Therefore, it is possible to appropriately evaluate the state of particles based on such periodic changes. Also, when the particles are diffused, the peak appearing in the autocorrelation is affected by the diffusion and decreases as the delay time in the autocorrelation increases. The degree of this decrease is a magnitude that corresponds to the diffusion rate. Therefore, the diffusion rate can be properly evaluated based on the change in peak height.

Moreover, in the present invention, it is preferable to evaluate that the diffusion rate of the particles increases as the degree of decrease in height with respect to the delay time increases.

Further, the mobile particle evaluation apparatus used in the present invention is an apparatus used in the above evaluation method, comprising an optical system for forming light interference fringes, and a light interference fringe formed by the optical system. deriving means for deriving an autocorrelation for the intensity of light from said particle that occurs when the particle traverses. According to this, at least one of particle movement speed, diffusion speed and non-uniformity can be evaluated based on the autocorrelation derived by the deriving means.

1 is a block diagram showing a schematic configuration of an evaluation device used in a particle state evaluation method according to a first embodiment, which is an embodiment of the present invention; FIG. FIGS. 2(a) to 2(c) show how particles in the sample move. 2 is a graph of a function Is(t) that simulates the intensity of a detection signal acquired by the evaluation device of FIG. 1; Fig. 4 is a graph of the autocorrelation function Is'(?) of Is(t) shown in Fig. 3; 4 is a graph showing the autocorrelation function I'(τ) calculated in one example according to the embodiment described above. FIG. 6 is a graph showing an autocorrelation function I′(τ) calculated in an example performed under conditions different from those in FIG. 5; FIG. 7 is a graph showing the results of deriving the interval Δτ between peaks appearing in the autocorrelation function I′(τ) while changing the interval d between interference fringes in the above example. FIG. 8 is a graph showing the results of deriving Δτ while changing the distance d between interference fringes under speed conditions different from those in FIG. 7 ; FIG. FIG. 11 is a graph showing an autocorrelation function I′(τ) calculated in another example different from the above; FIG. FIG. 10 is a diagram showing the arrangement of particles contained in a sample to be evaluated in the second embodiment, which is another embodiment of the present invention;

[First Embodiment]
A moving particle evaluation method according to the first embodiment, which is one embodiment of the present invention, will be described below. In this evaluation method, the state of particles such as their moving speed is evaluated by utilizing the phenomenon that light is emitted from particles by light emission or scattering when irradiated with laser light. An evaluation apparatus 1 shown in FIG. 1 is used to implement this evaluation method. The evaluation device 1 includes a laser light source 11 , a beam splitter 12 , a plurality of mirrors 13 , lenses 14 to 16 , a spectroscope 17 , a photomultiplier tube 18 , an oscilloscope 19 and an analysis section 20 . A laser beam emitted from a laser light source 11 is split by a beam splitter 12 so as to form two optical paths. These two optical paths are directed to lens 14 by a plurality of mirrors 13 . The lens 14 superimposes the laser beams on the sample S that have passed through the two optical paths. As a result, interference fringes are formed on the sample S, examples of which are shown in FIGS. 2(a) to 2(c). In the interference fringes of FIGS. 2(a) to 2(c), a plurality of streaks of light extending in the vertical direction in the drawing are arranged at intervals d in the horizontal direction in the drawing. The distance d can be obtained by d=λ/(2*sin θ), where 2*θ is the angle between the two optical paths from the lens 14 and λ is the wavelength of the laser light.

The sample S contains particles P to be evaluated. When laser light from the laser light source 11 is irradiated, light is emitted from the particles P by light emission or scattering. Such light is hereinafter referred to as particle emitted light. Each particle P emits particle emission light each time it reaches a line of light. In FIGS. 2(a) to 2(c), the particles P approaching the light streak are indicated by white circles, and the other particles P are indicated by black circles. Particle emission light is emitted from each particle P indicated by a white circle.

As shown in FIG. 1, particle emitted light from particles P contained in sample S is incident on spectroscope 17 through lenses 15 and 16 together with other light. The spectroscope 17 separates the particle emitted light from the incident light and emits the separated light to the photomultiplier tube 18 . The photomultiplier tube 18 generates a current signal corresponding to the photons received from the spectroscope 17 and outputs it to the oscilloscope 19 . The oscilloscope 19 stores in its internal memory waveform data indicating temporal changes in the intensity of the current signal (hereinafter referred to as detection signal) output by the photomultiplier tube 18 . The oscilloscope 19 is connected to the analysis unit 20 via USB (Universal Serial Bus), LAN (Local Area Network), or the like. The waveform data stored in the internal memory of the oscilloscope 19 is transmitted to the analysis section 20 via USB, LAN, or the like.

The analysis unit 20 has a computer that performs various arithmetic processing on the waveform data from the oscilloscope 19 . In a computer, hardware such as a CPU (Central Processing Unit) executes various types of information processing such as arithmetic processing and input/output processing according to software. Based on the waveform data transmitted from the oscilloscope 19, the analysis unit 20 thereby calculates the autocorrelation function of the intensity of the detection signal. Letting I(t) be the function of the intensity of the detected signal with respect to time t, the autocorrelation function I'(τ) is expressed as follows. The analysis unit 20 outputs the autocorrelation function calculated in this way. Based on this output result, the user evaluates the moving speed of the particle P and the like.

[Formula 1]

A method of evaluating the state of the particles P using the evaluation device 1 will be described below. When each particle P moves so as to traverse a line of light included in the interference fringes, as described above, particle emission light is generated from each particle P each time it reaches the line of light. In the examples of FIGS. 2(a) to 2(c), it is assumed that each particle P is moving rightward in the drawing at a constant speed v of the same magnitude. FIG. 2(b) shows a state in which each particle P has moved by half of d from the position in FIG. 2(a). FIG. 2(c) shows a state in which each particle P has moved from the position in FIG. 2(b) by half of d (from the position in FIG. 2(a) by d). As shown in FIGS. 2(a) and 2(c), when all the particles P have the same moving direction and the same moving speed, every time d/v elapses, a certain combination of Particle emission light is generated from a group P of particles P. That is, particle emitted light with the same intensity is generated periodically with a period of d/v. In addition, when particles P exist more sparsely than shown in FIGS. 2(a) to 2(c), particle emitted light of the same intensity is generated periodically at a period of d/v from only one particle P. Sometimes.

In the method for evaluating a moving particle according to the present embodiment, the particle emission light that is periodically generated is captured by the autocorrelation function I′(τ) shown in Equation 1, and the moving speed and the diffusion speed of the particle are calculated as follows. evaluate. Any one of these two items may be evaluated each time the autocorrelation function I′(τ) is calculated, or the two items may be evaluated simultaneously.

First, a method for evaluating the moving speed of the particles P will be described. The graphs of FIGS. 3 and 4 relate to a demonstration of how periodic signals appear in the autocorrelation function. FIG. 3 is a graph of the function Is(t) that simulates the strength of the detection signal, and FIG. 4 is a graph of the autocorrelation function Is'(τ) of Is(t). Is(t) is a function calculated for demonstration purposes by superimposing a signal with constant amplitude peaks appearing repeatedly with period T0 on a signal with random fluctuations. Assuming that the measurement period is finite, Is(t) has a value in the range of t0≦t≦t1 and takes zero in other ranges. Here, t0 corresponds to the start time of the measurement period, and t1 corresponds to the end time of the measurement period. Is'(?) corresponds to I'(?) calculated based on Equation 1 by replacing I(t) with Is(t). As shown in FIG. 4, Is'(τ) shows a peak corresponding to the period T0. The reason why the graph as a whole slopes down is because the measurement period is finite as described above. This is because the range becomes shorter. As a result, the peaks appearing in the graph of FIG. 4 also linearly decrease along the straight line A1 connecting the peaks as τ increases. In addition, the noise intensity due to components other than the component contributing to the peak in the detection signal also linearly decreases along the straight line B as τ increases.

As shown in this demonstration, when the particle emitted light is generated periodically, the autocorrelation function I'(τ) of the intensity I(t) of the detection signal calculated by Equation 1 above shows the particle emitted light with respect to τ. Peaks occur at intervals of the period d/v. Therefore, the interval between peaks in the waveform of the output result of I'(τ) can be derived, and v can be obtained based on the coincidence of this interval with the period d/v. When the particle P traverses the interference fringes in a direction oblique to the direction in which the lines of light are arranged, the obtained v is the magnitude of the component of the velocity of the particle P related to the direction in which the lines of light are arranged. show.

Second, a method for evaluating the diffusion speed of particles P will be described. In the above description, as shown in FIG. 2, it is assumed that all the particles P move in the same direction at the same constant speed v. In other words, a case is assumed in which the positional relationship between the particles P does not change. In this case, particle emitted light of the same intensity is periodically generated from a predetermined group of particles P at a period of d/v. As a result, a linearly decreasing peak appears in the autocorrelation function I'(τ) as shown in FIG. On the other hand, when the particles P tend to move in the same direction as a whole and at the same constant speed v as a whole, but gradually diffuse, the spatial A case is assumed in which the spread increases with the passage of time. In this case, the intensity of the particle emitted light periodically generated with the period d/v gradually decreases due to the influence of diffusion. As a result, the autocorrelation function I'(τ) has peaks at intervals of approximately d/v, but the peaks drop faster than without diffusion. For example, as shown in FIG. 4, with respect to straight line A1 without diffusion, the peak decreases along curve A2 with diffusion. The greater the diffusion, the greater the degree of peak drop. Therefore, the rate of diffusion can be evaluated by evaluating how quickly the peak decreases relative to the rate at which the peak decreases assuming no diffusion. Specifically, it can be evaluated that the rate of diffusion is higher as the rate of peak decrease is greater than the rate of peak decrease when it is assumed that there is no diffusion.

Hereinafter, examples according to the above-described embodiments will be described.

[First embodiment]
In the first example, spherical polystyrene particles with a diameter of 500 nanometers were used as samples. This sample was mixed with pure water so as to have a predetermined concentration, dropped onto a slide glass and spread evenly, and the slide glass was placed in a desiccator for about half a day to dry. After that, the slide glass was placed at the position of the sample in the experimental system having the same configuration as that of FIG. 1, and the slide glass was attached to the cone portion of the speaker to vibrate the speaker. As a result, while moving the particles on the slide glass, the state of the particles was evaluated based on the moving particle evaluation method according to the present embodiment. The equipment used in the experimental system is as follows. As the laser light source 11, SCHERZO (registered trademark) series (50 mW type) manufactured by KLASTTECH (registered trademark) was used. As the spectroscope 17, MC-10N manufactured by Ritsu Applied Optics Co., Ltd. was used. As the photomultiplier tube 18, R928 manufactured by Hamamatsu Photonics (registered trademark) was used.

FIG. 5 shows the autocorrelation function I'(τ) calculated by the above method. Also, FIG. 6 shows the results of calculating the autocorrelation function I'(τ) by performing the evaluation method in the same manner as described above except that the concentration when the sample is mixed with pure water is changed. As shown in FIGS. 5 and 6, the autocorrelation function I'(.tau.) has peaks at positions indicated by arrows. The interval Δτ with respect to τ between these peaks corresponds to the period at which the particle emitted light is generated from each particle.

Derivation of such a peak interval Δτ was performed while changing the interval d of the interference fringes and the velocity v of the particles. Note that the velocity v of the particles was changed by adjusting the frequency of vibration generated in the speaker. Table 1 below and FIGS. 7 and 8 show the results. Numerical values such as 100 and 61 in Table 1 indicate peak intervals Δτ (milliseconds). The points in the graph of FIG. 7 show the results when v=(2.44±0.10)*10^(-5) (m/sec). The solid line, dashed line and dashed line in the graph are the points where d/Δτ is 2.44*10^(-5), 2.54*10^(-5) and 2.34*10^(-5) Each corresponds to a straight line connecting The points in the graph of FIG. 8 show the results when v=(1.21±0.04)*10^(-5) (m/sec). The solid line, dashed line and dashed line in the graph are the points where d/Δτ is 1.21*10^(-5), 1.25*10^(-5) and 1.17*10^(-5) Each corresponds to a straight line connecting As shown in these figures, it can be seen that the particle velocity can be derived using the peak interval Δτ obtained based on the autocorrelation function I′(τ) and the interference fringe interval d.

[Table 1]

[Second embodiment]
An optical cell having a transparent outer wall was filled with pure water (18.6° C.) and placed at the sample position in the same experimental system as in the first example. Then, the same polystyrene particles as in the first embodiment are mixed with water at a concentration different from that in the first embodiment, and 1 to 2 drops of this are added to the pure water in the optical cell to move in the water. The state of particles was evaluated based on the moving particle evaluation method according to the present embodiment. The interference fringes were formed so that the lines of light were aligned not in the direction in which the particles fell, but in the direction orthogonal to the direction in which the particles fell. Therefore, the particle velocities derived in this example relate to the direction perpendicular to the falling direction. Also, the interval d between the interference fringes was set to 2.01*10^(-6) (m). FIG. 9 shows the autocorrelation function I'(τ) thus calculated. A peak appeared at the position indicated by the arrow in the graph of FIG. The spacing between peaks was approximately 2000 ms. On the other hand, based on the diffusion coefficient in water D = 8.52 * 10 ^ (-13) (m ^ 2 / sec) obtained based on the particle size of polystyrene and the water temperature, the particle velocity V is 1.31 * 10 ^(-6). Based on this velocity V and the above d, the interval between peaks appearing in the autocorrelation function is d/V=1540 milliseconds. Thus, it is shown that the theoretical values and the experimental values generally correspond.

According to the present embodiment described above, the state of a particle is evaluated by capturing periodic changes in the intensity of light emitted from the particle based on the autocorrelation function. Regardless of whether the moving speed of the particles is high or low, periodic changes in the intensity of light from the particles can be captured appropriately based on the autocorrelation function. Therefore, it is easy to evaluate the situation of the moving particles regardless of the moving speed of the particles.

[Second embodiment]
A second embodiment, which is another embodiment of the present invention, will be described. In the second embodiment, the evaluation device 1 is used as in the first embodiment. In the method for evaluating moving particles according to the present embodiment, by capturing the periodically emitted light emitted from particles by the autocorrelation function I′(τ) shown in Equation 1 above, non-uniformity in the arrangement of particles can be evaluated as follows. Evaluate on the street.

As shown in FIG. 10, the sample S to be evaluated in this embodiment is a particle group composed of particles T that are generally uniformly arranged. Some particles T deviate from the uniform arrangement, forming non-uniform regions A1 to A3. Such a particle group includes, for example, particles of ink toner on the surface of printed matter on which characters, images, etc. are formed. In this case, the area where the particles T are uniformly arranged corresponds to the area where characters, images, etc. are appropriately formed on the printed matter. On the other hand, the non-uniform areas A1 to A3 correspond to areas where printing is disturbed. The evaluation method according to the present embodiment evaluates how much non-uniform regions such as regions A1 to A3 exist in a uniform region based on the autocorrelation function derived according to Equation 1 as follows. .

In this embodiment, as in the first embodiment, interference fringes are formed on the sample S as shown in FIGS. 2(a) to 2(c). Along with this, the entire sample S is forcibly moved in a constant direction at a constant speed v. When the sample S is formed on the printed matter as described above, the entire sample S may be moved by moving the printed matter using, for example, a transport mechanism provided in a printing apparatus. Particle emission light generated when the particles T contained in the sample S pass through the interference fringes is captured by the spectroscope 17, the photomultiplier tube 18 and the oscilloscope 19, and the autocorrelation function I'(τ) is derived based on Equation 1 above.

When the entire sample S is moved in a constant direction at a constant speed v, the particles T Particle emission light is generated at a period corresponding to the interval D between the particles, and particle emission light is generated at a period d/v. On the other hand, in the regions A1 to A3 where the particles T are arranged non-uniformly, the particle emission light is not generated with the period corresponding to the interval D, but the particle emission light is generated with the period d/v. At this time, the peak generated in the autocorrelation function I'(τ) corresponding to the generation of the particle emitted light with the period d/v becomes higher as the number of particles T included in the non-uniform region increases. Therefore, the non-uniformity of the particles T in the sample S can be evaluated based on the height of the peak corresponding to the period d/v appearing in I'(τ).

Specifically, the non-uniformity evaluation value is obtained by dividing the net height of the peak corresponding to the period d/v appearing in I′(τ) by the noise intensity at τ where the peak appears. For example, in the graph of FIG. 4, the net height of peak P1 is a obtained by subtracting b, which is the height of noise intensity (position of straight line B), from the height of peak P1 (position of straight line A1). In this case, (nonuniformity evaluation value)=a/b. The larger the non-uniformity evaluation value, the more particles T are non-uniformly arranged in the sample S, that is, the sample S is evaluated to have high non-uniformity. The reason why the net height of the peak is used to calculate the non-uniformity evaluation value is that this net height is a factor that directly reflects the non-uniformity. Also, the reason why the net height is divided by the noise intensity is to eliminate the influence of the autocorrelation function I'(τ) falling downward due to the finite measurement time.

<Modification>
Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope described in the Means for Solving the Problems. It is possible.

For example, in the above-described embodiment, the autocorrelation function regarding the intensity of the detection signal is calculated in order to capture the periodicity of the intensity of light generated from the particles P, but other methods may be used. For example, various frequency analysis methods such as FFT (Fast Fourier transform) may be used. Specifically, the period of the intensity of the detection signal may be derived based on the frequency of the intensity of the detection signal detected by frequency analysis.

S Sample 1 Evaluation device 11 Laser light source 20 Analysis part

Claims (3)

At the peak appearing in the autocorrelation of the time change of the light intensity from the particle as a periodic change in the intensity of the light from the particle due to the particle crossing the interference fringes of the light, the delay time is A method for evaluating a moving particle, wherein the diffusion speed of the particle is evaluated based on a decrease in height relative to the moving particle. 2. The moving particle evaluation method according to claim 1, wherein the evaluation is such that the diffusion speed of the particles increases as the degree of height reduction with respect to the delay time increases. A device used in the evaluation method according to claim 1 or 2 ,
an optical system that forms interference fringes of light;
a deriving means for deriving an autocorrelation relating to the intensity of the light from the particle generated when the particle traverses the interference fringes of light formed by the optical system. .

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