CN104697906A - Particle granularity measuring device and method based on near-field scattering - Google Patents

Abstract

The invention discloses a particle granularity measuring device and a particle granularity measuring method based on near-field scattering, wherein the particle granularity measuring device based on near-field scattering comprises a laser device, a spatial filter, a collimating lens, a lens group, a CCD camera, and a computer. The laser device is used for emitting a coherent light beam; the spatial filter filters the coherent light beam emitted by the laser device and obtains a Gauss light beam; the collimating lens converts the Gauss light beam into a straight light beam; the lens unit is used for setting a focal length, and images scattered spots at a Z position from a measurement zone; the CCD camera is used for collecting a near-field scattered spot image that is imaged by the lens unit; and the computer processes the near-field scattered spot image collected by the CCD camera in order to obtain a particle granularity distribution. Comparing the prior art, the particle granularity measuring device and the particle granularity measuring method based on near-field scattering make the system equipment simple in the condition of not adding a complex device for removing the central light strength; the particle granularity measuring device and the particle granularity measuring method based on near-field scattering are able to achieve the measurements of the granularity and the distribution of the measured particles without any angle resolved detections, thereby expanding the range of the scattering angle and achieving the granularity measurement of nanometer particles.

Description

A kind of grain graininess measurement mechanism based on near-field scattering and method

Technical field

The invention belongs to grain graininess field of measuring technique, be specifically related to a kind of grain graininess measurement mechanism based on near-field scattering and method.

Background technology

Along with the progress of social civilization, the fast development of science and technology, particle issues more and more receives publicity in the fields such as industry, agricultural, medical science, scientific research and environment.Grain graininess and distribution are one of main contents of current particle sizing.In the numerous methods measuring grain graininess, light scattering method is strong with its applicability, granulometry wide ranges, measuring repeatability are good, fast in real time, robotization and intelligence degree is high, disturbing factor is few, thus on-line measurement etc. obtains pay abundant attention, be current most widely used general and the most promising particle sizing technology.

Common light scattering measurements mainly contains dynamic light scattering method and little angle static light scattering method.Dynamic light scattering method is that the physical parameter required for this method is few, but high to experimental provision technical property requirements, and expensive by setting up associating thus obtaining candidate particles Particle size and distribution of scattered light intensity and time in different directions.Little angle static light scattering method be by measure far field scattered light intensity thus be finally inversed by grain graininess and distribution, but there are some restrictions in this method, wherein maximum shortcoming is that the removal of central light strength needs light path is strictly aimed at, and the existence of ambient stray light needs to carry out blank measure, make device more complicated, measuring accuracy reduces, and stability is not high.

Summary of the invention

Technical matters: be subject to the shortcomings such as stray light, device is complicated, stability is low when the present invention is directed to small angle scattering commercial measurement grain graininess, propose a kind of be different from traditional small angle scattering grain graininess measuring technique near-field scattering method and measurement device grain graininess and distribution.

Technical scheme: a kind of grain graininess measurement mechanism based on near-field scattering, it is characterized in that: comprise laser instrument, spatial filter, collimation lens, lens combination, CCD camera and computing machine, described laser instrument is used for sending coherent light beam; Described spatial filter carries out filtering to the relevant light velocity that described laser instrument sends and obtains Gaussian beam; Described collimation lens is used for converting described Gaussian beam to collimated optical beam; The speckle at Z place, range observation region, for setting focal length, is carried out imaging by described lens combination; Described CCD camera is for gathering the near field speckle image of described lens combination imaging; Described computing machine carries out process to the near field speckle image that described CCD camera gathers and obtains particle size distribution.

Described computing machine to the concrete grammar that near field speckle image processes is: gather obtain every frame near field speckle image be converted to gray-scale value matrix, and to the N frame collected independently image make normalized, obtain nondimensional near field speckle intensity; Fast Fourier change is carried out to the near field speckle intensity after normalization, obtains the power spectrum of near field speckle intensity; The scattered light intensity comprising grain graininess information is obtained by the power of near field speckle intensity; Particle size distribution is finally inversed by again according to Mie scattering theory.

Described laser instrument is the He-Ne laser instrument of continuous luminous.

A method for grain graininess measured by grain graininess measurement mechanism based on near-field scattering, it is characterized in that, comprises the steps:

The coherent light beam that step one, laser instrument send irradiates the solution to be measured containing particle, and CCD camera collection Z place, range observation region interferes by transmitted light and scattered light the speckle image I (x, y) formed;

$I(x,y)=I_0+2\mathrm{Re}\left[E_0{E}_s^{*}(x,y)\right]---\left(1\right)$

In formula, I ₀transmitted intensity, E ₀transmission field, E _sbe scattered optical field, Re represents and gets real part computing, and No. * is get conjugate operation, x, y representative be the arrangement sequence number of pixel in digital picture, choosing of Z must meet characteristic number D*=2ZNA<D, NA is the numerical aperture of lens, and D is the beam sizes of coherent source;

Step 2, the N frame speckle image I that CCD camera is gathered ₁(x, y), I ₂(x, y) ... I _n(x, y) makes normalized:

First to a series of speckle image I gathered ₁(x, y), I ₂(x, y) ... I _n(x, y) does on average, obtains average intensity:

${\stackrel{\&OverBar;}{I}}_{(x,y)}=\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{I}_i(x,y)---\left(2\right)$

Then, normalization obtains the normalized value i (x, y) of speckle intensity,

$i(x,y)=\frac{I_1(x,y)-\stackrel{\&OverBar;}{I}(x,y)}{\stackrel{\&OverBar;}{I}(x,y)}---\left(3\right)$

It is that the region of m × n is carried out Fast Fourier Transform (FFT) and obtained power spectral value S (q that step 3, the normalized intensity value obtained step 2 choose picture size _x, q _y):

$S(q_x,q_y)={\left|\mathrm{FFT}\left(i(x,y)\right)\right|}^2={\left|\frac{1}{m}\frac{1}{n}\underset{x=0}{\overset{m-1}{\mathrm{\&Sigma;}}}\underset{y=0}{\overset{n-1}{\mathrm{\&Sigma;}}}i(x,y)e^{-i(q_x\frac{x}{m}+q_y\frac{y}{n})}\right|}^2---\left(4\right)$

In formula, FFT represents Fast Fourier Transform (FFT) operator, the Fourier vector relevant with spatial frequency, $q_x=2\mathrm{\&pi;}{f}_x=2\frac{x}{\mathrm{m\&Delta;x}},q_y=2{\mathrm{\&pi;f}}_y=2\mathrm{\&pi;}\frac{y}{\mathrm{n\&Delta;y}},$ Δ x is CCD pixels across size, and Δ y is longitudinal Pixel Dimensions;

Step 4, to the power spectrum of the speckle intensity that step 3 obtains by on average obtain average power spectra S (q), wherein S (q) for internal diameter is q external diameter be q+ Δ q annulus in the mean value of each value; Scattered light intensity I is calculated according to average power spectra S (q) _s(Q):

I _s(Q)＝S(q)＝<S(q _x,q _y)> _q(5)

In formula, < ... > represents computing of averaging, represent that wave vector is transmitted in scattering, be defined as scattering wave vector with incident wave vector difference, wave vector is transmitted in scattering modulus $Q=\sqrt{2}k{[1-\sqrt{1-{(q/k)}^2}]}^2=\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}\sin (\mathrm{\&theta;}/2),$ θ is scattering angle, and λ is laser wavelength;

Wave vector is transmitted in scattering the scope specific formula for calculation of modulus Q is as follows:

$[Q_{\min },Q_{\max }]=[\frac{2\mathrm{\&pi;}}{L},\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}\sin ({\mathrm{\&theta;}}_{\max }/2)]---\left(6\right)$

Wherein, m represents the enlargement ratio of lens, θ _max=arcsin (NA);

Step 5, the heat radiation light intensity obtained according to step 4, utilize and adopt inversion algorithm to obtain the domain size distribution of detected solution to formula (7) integral equation:

I _s(Q)＝∫I _Mie(Q,R)[M(R)] ^-1W(R)dR (7)

In formula, I _miethe particle of (Q, R) to be radius be R is Mie scattered light intensity when scattering is transmitted ripple to lose size be Q, and M (R) is quality (M (R)=(4/3) ρ π R of particle ³, ρ is particle density), W (R) namely needs the domain size distribution be finally inversed by.

The present invention is based on near-field scattering optical principle, a kind of grain graininess measuring method based on near-field scattering and device are proposed, its basic ideas are: laser instrument sends coherent light beam, via spatial filter, the parasitic light that filtering major part is produced by laser instrument, again by the collimation lens of lens combination, laser is collimated, collimated light beam irradiates solution generation scattering to be measured, then the focal length of lens after measured zone is regulated, make speckle image formed by the superposing of the transmitted light at Z place, range observation region and scattered light, through lens combination, by CCD camera record, the near field speckle image of last CCD camera collection obtains candidate particles size-grade distribution via described computer disposal, complete one-shot measurement.

Beneficial effect: traditional small angle scattering technology obtains scattered light intensity in the far field of measurand scattering, and adopts optical devices to realize the mapping one to one of sensing station and scattering angle.But near-field scattering technology obtains scattered light intensity at the near field place of measurand scattering, detects without any need for angular resolution.What adopt the scattered light intensity that finally obtains of near-field scattering and traditional small angle scattering has consistance, but near field light scatterometry device is simply compact, precision is high, the impact of easy elimination parasitic light, is the good alternative method of one of small angle scattering technology.

When near-field scattering grain graininess measuring technique is without the need to removing the complex appts of central light strength, makes system equipment simple, the measurement of measurand granularity can be realized; Expansion range of scatter angles, makes it to measure nano particles, and overcomes the impact of the parasitic light in optical system on scattered light intensity, improve measuring accuracy; Stray light component in the speckle of near field can be removed in image processing algorithm, therefore low to the requirement of environment for use.

Accompanying drawing explanation

Fig. 1 is the structural representation of the grain graininess measurement mechanism based on near-field scattering of the present invention;

Fig. 2 is that the power spectrum of speckle image solves qualitative modeling schematic diagram.

Wherein, laser instrument 1, spatial filter 2, collimation lens 3, lens combination 4, CCD camera 5, computing machine 6.

Embodiment

Below in conjunction with the drawings and specific embodiments, illustrate the present invention further.Should understand these embodiments to be only not used in for illustration of the present invention and to limit the scope of the invention, after having read the present invention, the amendment of those skilled in the art to the various equivalent form of value of the present invention has all fallen within the application's claims limited range.

Principle of work of the present invention: laser instrument sends coherent light beam, via spatial filter, the parasitic light that filtering major part is produced by laser instrument, again by collimation lens, laser is collimated, collimated light beam irradiates solution to be measured, scattering is there is because of the existence of particle, then the focal length of lens after measured zone is regulated, make speckle image formed by the superposing of the transmitted light at Z place, range observation region and scattered light, by CCD camera record, the near field speckle image of last described CCD camera collection obtains particle size distribution via described computer disposal

As shown in Figure 1, the grain graininess measurement mechanism based on near-field scattering of the present invention mainly comprises laser instrument 1, spatial filter 2, collimation lens 3, lens combination 4, CCD camera 5, computing machine 6.Light source can adopt continuous wave laser line source 1 (as He-Ne laser instrument 1, wavelength is 632.8nm, beam sizes D ~ 10mm).Lens combination 2 be ordinary optical camera lens (as lens multiplication factor 40x, NA ~ 0.65, design parameter can experimentally demand select).CCD camera 5 is connected with computing machine 6 by signal cable.Under the control of the image data processing software in computing machine 6, the total tunes such as image acquisition, storage and process can be completed.

Composition graphs 1, below in conjunction with long 2mm, solution particles granulometry to be measured in the square tube of wall thickness 1mm, with He-Ne laser instrument (λ ~ 632.8nm, D ~ 10mm) for light source, the lens (NA ~ 0.5) of enlargement factor M=20, CCD camera (UI-2230SE, 1024 × 768pixel, pixel size Δ l ~ 4.65 μm of 12, framerate ~ 80fps), the course of work of the present invention and image processing flow are illustrated:

(D*=2ZNA=2 × 1.5mm × 0.5=1.5mm<D=10mm meets near-field scattering condition to step one, CCD camera sample plane distance square tube Z=1.5mm.) adjustment CCD camera position, make lens focus in sample plane.Coherent light beam that laser instrument sends irradiates the solution to be measured containing particle, and due to the scattering process of light, what CCD camera gathered Z place, range observation region interferes by transmitted light and scattered light the speckle image formed, and is transferred on computing machine and carries out Storage and Processing.Setting CCD camera takes an image every Δ t=1s, shooting N=60 frame, total Measuring Time T=N × Δ t=60s.

Step 2, the N frame speckle image I that CCD camera is gathered ₁(x, y), I ₂(x, y) ... I _n(x, y) makes normalized.First to a series of speckle image I gathered ₁(x, y), I ₂(x, y) ... I _n(x, y) does on average, obtains average intensity.

${\stackrel{\&OverBar;}{I}}_{(x,y)}=\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{I}_i(x,y)---\left(1\right)$

Then normalization obtains the normalized value i (x, y) of speckle intensity.

$i(x,y)=\frac{I_1(x,y)-\stackrel{\&OverBar;}{I}(x,y)}{\stackrel{\&OverBar;}{I}(x,y)}---\left(2\right)$

In formula, x, y representative is the arrangement sequence number of pixel in digital picture.

It is that the region of m × n is carried out Fast Fourier Transform (FFT) and obtained power spectral value S (q that step 3, the normalized intensity value obtained step 2 choose picture size _x, q _y).

$S(q_x,q_y)={\left|\mathrm{FFT}\left(i(x,y)\right)\right|}^2={\left|\frac{1}{m}\frac{1}{n}\underset{x=0}{\overset{m-1}{\mathrm{\&Sigma;}}}\underset{y=0}{\overset{n-1}{\mathrm{\&Sigma;}}}i(x,y)e^{-i(q_x\frac{x}{m}+q_y\frac{y}{n})}\right|}^2---\left(3\right)$

In formula, FFT represents Fast Fourier Transform (FFT) operator, the Fourier vector relevant with spatial frequency, $q_x=2\mathrm{\&pi;}{f}_x=2\frac{x}{\mathrm{m\&Delta;x}},q_y=2{\mathrm{\&pi;f}}_y=2\mathrm{\&pi;}\frac{y}{\mathrm{n\&Delta;y}}.$ Δ x is CCD pixels across size, and Δ y is longitudinal Pixel Dimensions.Concrete result of calculation is as follows:

$q_x=2\mathrm{\&pi;}{f}_x=2\mathrm{\&pi;}\frac{x}{\mathrm{m\&Delta;x}}=1.76\&times;{10}^{-3}x{\mathrm{\&mu;m}}^{-1},q_y=2\mathrm{\&pi;}{f}_y=2\mathrm{\&pi;}\frac{y}{\mathrm{n\&Delta;y}}=1.76\&times;{10}^{-3}\mathrm{y\&mu;}{m}^{-1}.$

Step 4, to the power spectrum of the speckle intensity that step 3 obtains by on average obtain average power spectra S (q).Concrete operations as shown in Figure 2, to choose internal diameter be q external diameter be q+ Δ q annulus in the mean value of each value represent S (q) corresponding to q.The power spectrum of two dimension near field speckle intensity distributions contains the information of scattered light intensity, and average energy spectrum S (q) and scattered light intensity I _s(Q) there is relation of equivalence.Namely

I _s(Q)＝S(q)＝<S(q _x,q _y)> _q(4)

In formula, < ... > represents computing of averaging. represent that wave vector is transmitted in scattering, be defined as scattering wave vector with incident wave vector difference, wave vector is transmitted in scattering modulus $Q=\sqrt{2}k{[1-\sqrt{1-{(q/k)}^2}]}^2=\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}\sin (\mathrm{\&theta;}/2),$ θ is scattering angle, and λ is laser wavelength.

Wave vector is transmitted in scattering the concrete result of calculation of scope of modulus Q is as follows:

$[Q_{\min },Q_{\max }]=[\frac{2\mathrm{\&pi;}}{L},\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}\sin ({\mathrm{\&theta;}}_{\max }/2)]=[3.52\&times;{10}^{-2}{\mathrm{\&mu;m}}^{-1},{5.14\mathrm{\&mu;m}}^{-1}]---\left(5\right)$

Wherein, θ _max=arcsin (NA)=arcsin0.5=30 °.

The scattered light intensity of step 5, experiment measuring contains the size information of particle, adopts inversion algorithm just can obtain the domain size distribution of detected solution to formula (7) integral equation.

I _s(Q)＝∫I _Mie(Q,R)[M(R)] ^-1W(R)dR (6)

In formula, I _miethe particle of (Q, R) to be radius be R is Mie scattered light intensity when scattering is transmitted ripple to lose size be Q, and M (R) is quality (M (R)=(4/3) ρ π R of particle ³, ρ is particle density), W (R) namely needs the domain size distribution be finally inversed by.

Claims (6)

1. the grain graininess image collecting device based on near-field scattering, it is characterized in that: comprise laser instrument, spatial filter, collimation lens, lens combination and CCD camera, described spatial filter is positioned on the output light path of described laser instrument, described collimation lens is positioned on the output light path of described spatial filter, set gradually described lens combination and CCD camera in the rear end of described collimation lens, the picture plane of described lens combination is on the target surface of described CCD camera.

2. a kind of grain graininess image collecting device based on near-field scattering according to claim 1, is characterized in that: described laser instrument is the He-Ne laser instrument of continuous luminous.

3. based on a grain graininess measurement mechanism for near-field scattering, it is characterized in that: comprise laser instrument, spatial filter, collimation lens, lens combination, CCD camera and computing machine, described laser instrument is used for sending coherent light beam; Described spatial filter carries out filtering to the relevant light velocity that described laser instrument sends and obtains Gaussian beam; Described collimation lens is used for converting described Gaussian beam to collimated optical beam; The speckle at Z place, range observation region, for setting focal length, is carried out imaging by described lens combination; Described CCD camera is for gathering the near field speckle image of described lens combination imaging; Described computing machine carries out process to the near field speckle image that described CCD camera gathers and obtains particle size distribution.

4. a kind of grain graininess measurement mechanism based on near-field scattering according to claim 3, it is characterized in that: described computing machine to the concrete grammar that near field speckle image processes is: be converted to gray-scale value matrix gathering the every frame near field speckle image obtained, and to the N frame collected independently image make normalized, obtain nondimensional near field speckle intensity; Fast Fourier change is carried out to the near field speckle intensity after normalization, obtains the power spectrum of near field speckle intensity; The scattered light intensity comprising grain graininess information is obtained by the power of near field speckle intensity; Particle size distribution is finally inversed by again according to Mie scattering theory.

5. a kind of grain graininess measurement mechanism based on near-field scattering according to claim 3 or 4, is characterized in that: described laser instrument is the He-Ne laser instrument of continuous luminous.

6. adopt a kind of grain graininess measurement mechanism based on near-field scattering according to claim 3 to measure a method for grain graininess, it is characterized in that, comprise the steps:

The coherent light beam that step one, laser instrument send irradiates the solution to be measured containing particle, and CCD camera collection Z place, range observation region interferes by transmitted light and scattered light the speckle image I (x, y) formed;

$I(x,y)=I_0+2\mathrm{Re}\left[E_0{E}_s^{*}(x,y)\right]---\left(1\right)$ In formula, I ₀transmitted intensity, E ₀transmission field, E _sbe scattered optical field, Re represents and gets real part computing, and No. * is get conjugate operation, x, y representative be the arrangement sequence number of pixel in digital picture, choosing of Z must meet characteristic number D*=2ZNA<D, NA is the numerical aperture of lens, and D is the beam sizes of coherent source;

Step 2, the N frame speckle image I that CCD camera is gathered ₁(x, y), I ₂(x, y) ... I _n(x, y) makes normalized:

First to a series of speckle image I gathered ₁(x, y), I ₂(x, y) ... I _n(x, y) does on average, obtains average intensity:

$\stackrel{\&OverBar;}{I}(x,y)=\frac{1}{N}\underset{i=1}{\overset{N}{\mathrm{\&Sigma;}}}{I}_i(x,y)---\left(2\right)$

Then, normalization obtains the normalized value i (x, y) of speckle intensity,

$i(x,y)=\frac{I_1(x,y)-\stackrel{\&OverBar;}{I}(x,y)}{\stackrel{\&OverBar;}{I}(x,y)}---\left(3\right)$

It is that the region of m × n is carried out Fast Fourier Transform (FFT) and obtained power spectral value S (q that step 3, the normalized intensity value obtained step 2 choose picture size _x, q _y):

$S(q_x,q_y)={\left|\mathrm{FFYT}\left(i(x,y)\right)\right|}^2={\left|\frac{1}{m}\frac{1}{m}\underset{x=0}{\overset{m-1}{\mathrm{\&Sigma;}}}\underset{y=0}{\overset{n-1}{\mathrm{\&Sigma;}}}i(x,y)e^{-i(q_x\frac{x}{m}+q_y\frac{y}{n})}\right|}^2---\left(4\right)$ In formula, FFT represents Fast Fourier Transform (FFT) operator, the Fourier vector relevant with spatial frequency, $q_x=2\mathrm{\&pi;}{f}_x=2\mathrm{\&pi;}\frac{x}{\mathrm{m\&Delta;x}},q_y=2\mathrm{\&pi;}{f}_y=2\mathrm{\&pi;}\frac{y}{\mathrm{n\&Delta;y}},$ Δ x is CCD pixels across size, and Δ y is longitudinal Pixel Dimensions;

Step 4, to the power spectrum of the speckle intensity that step 3 obtains by on average obtain average power spectra S (q), wherein S (q) for internal diameter is q external diameter be q+ Δ q annulus in the mean value of each value; Scattered light intensity I is calculated according to average power spectra S (q) _s(Q):

I _s(Q)=S (q)=<S (q _x, q _y) > _q(5) in formula, < ...) represent computing of averaging, represent that wave vector is transmitted in scattering, be defined as scattering wave vector with incident wave vector difference, penetrate transmission wave vector modulus $Q=\sqrt{2}k{[1-\sqrt{1-{(q/k)}^2}]}^2=\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}\sin (\mathrm{\&theta;}/2),$ θ is scattering angle, and λ is laser wavelength;

Wave vector is transmitted in scattering the scope specific formula for calculation of modulus Q is as follows:

$[Q_{\min },Q_{\max }]=[\frac{2\mathrm{\&pi;}}{L},\frac{4\mathrm{\&pi;}}{\mathrm{\&lambda;}}\sin ({\mathrm{\&theta;}}_{\max }/2)]---\left(6\right)$ Wherein, m represents the enlargement ratio of lens, θ _max=arcsin (NA);

Step 5, the heat radiation light intensity obtained according to step 4, utilize and adopt inversion algorithm to obtain the domain size distribution of detected solution to formula (7) integral equation:

$I_s\left(Q\right)=I_{\mathrm{Mie}}(Q,R){\left[M\left(R\right)\right]}^{-1}W\left(R\right)\mathrm{dR}---\left(7\right)$ In formula, I _miethe particle of (Q, R) to be radius be R is Mie scattered light intensity when scattering is transmitted ripple to lose size be Q, and M (R) is quality (M (R)=(4/3) ρ π R of particle ³, ρ is particle density), W (R) namely needs the domain size distribution be finally inversed by.