CN105300856A - Method for measuring particle concentration and sizes on basis of ultraphonic impedance spectrum - Google Patents

Abstract

The invention relates to a method for measuring particle concentration and sizes on the basis of an ultraphonic impedance spectrum. The method comprises that steps that 1, a theoretical impedance real component spectrum is obtained through an ECAH model and theory; 2, a theoretical curve of particle size-resonant frequency and a theoretical curve of a concentration-resonant amplitude are obtained; 3, an acoustic impedance spectrum is obtained from experiments according to an ultrasonic transducer and calculation, a real time component is taken from the acoustic impedance spectrum, and an experimental impedance real component spectrum is obtained; treatment is conducted on signals obtained from the experiments through a formula in the third step, resonant frequency for measuring the object impedance real component spectrum can be obtained, the resonant frequency fR is extracted, and the concentration and the particle size of a measured object can be obtained from the curves of the particle size-resonant frequency and the concentration-resonant amplitude determined in the second step. According to the method for measuring the particle concentration and sizes on the basis of the ultraphonic impedance spectrum, a system is simple in structure and low in cost, online measurement can be achieved, and the method can be used for the laboratory science research; compared with utilizing the ultrasonic attenuation and phase velocity, the method is more suitable for measurement of particles in a high concentration two-phase mixture.

Description

The measuring method to granule density and size is composed based on ultrasonic impedances

Technical field

The present invention relates to a kind of ultrasonic measurement method, particularly a kind of based on the method for the grain diameter in ultrasonic impedances spectrum principle measurement two-phase mixture with its concentration.

Background technology

Multiple fields such as the energy, chemical industry, food, medicine are covered due to particle, and the character of particle all has impact to these field products and process control, as the infringement to equipment in the utilization factor of the result of use of medicine, effective period of food quality, the energy and manufacturing process.Visible particle plays vital effect in industrial aspect, is also paid close attention to widely the detection of particle and studies.In some researchs nearest, dynamic light scattering method, PIV, image method, all useful in measurement particle on.But they all also exist various shortcoming, one of them common drawback is exactly the detection not being easy for particle under high concentration.And ultrasonic when measuring the sample of high concentration, do not need dilution.The virgin state maintaining sample of maximum possible, avoids the original appearance changing sample because of dilution, as dilution causes reunion to be separated or contaminated samples, thus makes the result of measurement more close to actual conditions.

Ultrasonic method had had many application in particle size and measurement of concetration, mainly make use of ultrasonic phase velocity spectrum and decay spectra.Utilize receive MUT by the ultrasound wave after measured zone, the signal spectral analysis through obtaining obtains phase velocity spectrum and decay spectra, can obtain the relevant nature of particle according to corresponding theory from the phase velocity spectrum obtained and decay spectra.But when surveyed material to ULTRASONIC ABSORPTION excessively strong or be not easy the other end install receiving transducer time, transmitted acoustic pulse or echo method are no longer appropriate to the measurement of grain diameter and concentration.If utilize from the reflective sound wave between buffer stopper and measurement sample, its signal is not subject to the impact of concentration of medium and attenuation characteristic, can avoid the problems referred to above.The object of the invention is exactly the relation by setting up ultrasonic reflection signal and impedance spectrum and particle two-phase medium, and obtains impedance spectrum with experiment, determines corresponding grain diameter and concentration by formant frequency in impedance spectrum and amplitude.

Summary of the invention

The present invention be directed to existing particle sizing technology and there is degradation problem under high concentration transmissivity, propose one and utilize ultrasonic impedances compose, realize non-intrusion type and survey high concentration online or the method for decay stronger condition middle particle concentration and particle diameter.

Technical scheme of the present invention is: a kind of method measuring grain diameter and concentration based on ultrasonic impedances spectrum principle, comprises following several step:

1), theoretical impedance real part spectrum is obtained with ECAH model and theory calculate

Utilize reflectance spectrum to carry out the characteristic of characterizing particles, set up the relation between acoustic impedance and particle two-phase medium according to ultrasonic particle sizing ECAH model; For particle two-phase system, by using quality, momentum and law of conservation of energy, ess-strain and acoustics and thermodynamic equations to obtain wave of compression, shearing wave, the wave equation of heat wave in the spherical solid particles and continuous phase medium of flexible, isotropy, heat conduction, the mathematic(al) representation of its complex wave number κ is:

κ＝ω/c(ω)+iα(ω)

Wherein ω is angular frequency.From above formula, the real part of complex wave number κ is relevant with phase velocity c (ω), and its imaginary part is relevant to attenuation coefficient α (ω); It is as follows that the acoustics of ECAH model to particle two-phase medium describes final expression formula:

${\left(\frac{\mathrm{\κ}}{{\mathrm{\κ}}_c}\right)}^2=1+\frac{3\mathrm{\φ}}{{{\mathrm{i\κ}}_c}^3{R}^3}\underset{n=0}{\overset{\mathrm{\∞}}{\Σ}}(2n+1)A_n$

Wherein κ _cfor known incident wave of compression wave number, φ is the volumetric concentration of particle in medium, and R is particle radius, A _nfor scattering coefficient, calculated by ECAH model;

The definition of impedance is:

$Z=\mathrm{\ρ}c\left(\mathrm{\ω}\right)\left(1-i\frac{\mathrm{\α}\left(\mathrm{\ω}\right)\mathrm{\λ}}{2\mathrm{\π}}\right)$

Wherein ρ is particle two-phase medium average density, and λ ultrasonicly propagates wavelength in two-phase medium, combines the final expression formula that can obtain impedance Z to be by above-mentioned three formulas:

$Z=\mathrm{\ρ}\mathrm{\ω}\left(1-i\frac{\mathrm{\α}\left(\mathrm{\ω}\right)\mathrm{\λ}}{2\mathrm{\π}}\right)/\mathrm{Re}\left({\mathrm{\κ}}_c\sqrt{1+\frac{3\mathrm{\φ}}{{{\mathrm{i\κ}}_c}^3{R}^3}\underset{n=0}{\overset{\mathrm{\∞}}{\Σ}}\left(2n+1\right)A_n}\right)$

Write corresponding calculation procedure according to this formula, number of times of suing for peace in calculating gets 20 times, and Re represents and asks for real part computing, obtains theoretical impedance real part spectrum;

2), the theoretical curve of " particle diameter-resonant frequency " and the theoretical curve of " concentration-resonant amplitude " is obtained:

According to 1) step obtain impedance real part spectrum in, extract different-grain diameter and corresponding resonant frequency thereof, obtain the theoretical curve of " particle diameter-resonant frequency ", and extract different concentration and corresponding amplitude thereof, obtain the theoretical curve of " concentration-resonant amplitude ";

3), by ultrasonic transducer and the acoustic impedance spectrum calculating experiment gained, real part is got to it and then obtains experiment impedance real part spectrum:

First make the front end face of ultrasonic transducer parallel with the interface of medium with buffer stopper, under exciting circuit effect, ultrasound wave launch and accept transducer T/R sends a branch of impulse ultrasound intensity of wave is I ₀, through buffer stopper A, reflect in the interface of buffer stopper A and sample area B, it is I that transmitted wave is obtained reflected ultrasonic intensity by ultrasound emission transducer T/R reception again after buffer stopper A ₁, and the collection of collected card is preserved in a computer; When placing the known demarcation medium of acoustic properties in sample cell, then reflection R _cknown, record one group of reflected signal I _1c, to the reflection wave obtained, under obtaining multiple frequency by Fast Fourier Transform (FFT), signal intensity is composed, the reflection wave I that each frequency is corresponding ₁(f), I _1c(f) and I ₀f the relation of () is:

$I_1\left(f\right)=I_0\left(f\right)R_s{e}^{-2{\mathrm{\α}}_c{l}_1}$

$I_{1c}\left(f\right)=I_0\left(f\right)R_c{e}^{-2{\mathrm{\α}}_c{l}_1}$

Wherein R _sthe reflection coefficient between buffer stopper and sample media, α _cthe attenuation coefficient of buffer stopper, l ₁for the thickness of buffer stopper;

Can be obtained by above two formulas

$R_s=\frac{I_1\left(f\right)}{I_{1c}\left(f\right)}$

After calculating reflection coefficient above, corresponding different frequency uses formula Z respectively _s=Z _c(1+R _s)/(1-R _s) calculate, wherein Z _sand Z _cbe respectively the acoustic impedance of medium and the acoustic impedance of buffer stopper, just can obtain impedance spectrum Z (f), unit is Pa*s/m, f is ultrasonic frequency, can obtain the acoustic impedance spectrum of testing gained, gets real part then obtain experiment impedance real part spectrum to it;

4) signal, by experiment obtained, through 3) formula manipulation described in step, just can obtain the resonant frequency of measuring object impedance real part spectrum, extract resonant frequency f _r, then from 2) " particle diameter-resonant frequency ", " concentration-resonant amplitude " two curves of determining step can look into concentration and the grain diameter that value obtains measuring object.

Beneficial effect of the present invention is: the present invention directly utilizes the reflective sound wave of buffer stopper to obtain impedance spectrum information analysis granule density and particle diameter, the acoustic impedance spectrum of measured zone particle two-phase medium is analyzed according to reflection wave, again because the ultrasound wave of characteristic frequency and the particle effect of certain particle size can produce resonance effect, embody in reflection wave impedance spectrum as specific resonance peak.On the one hand, the relation curve of grain diameter and resonant frequency and the relation curve of granule density and resonant amplitude can be obtained according to theoretical prediction; On the other hand, obtain the impedance spectrum curve of candidate particles two-phase medium by experiment, and resonance peak respective frequencies and amplitude are contrasted with theoretical curve, the size of acquisition particle and concentration.Because the method is without the need to measuring transmission signal, when transmitted wave cannot receive or weak output signal still can use, be conducive in Practical Project On-line sampling system application.

The method measuring grain diameter and concentration based on ultrasonic impedances principle of the present invention, simple in measurement system structure, cheap, method can realize on-line measurement, can be used for laboratory science research, be specially adapted to the application of industry spot, compared to the particle sizing method of other principle as electro-induction method, image method, light scattering method etc., the conditional request of ultrasonic method to measured zone is lower, form is opened without the need to extra, can be implemented in line non-intrusion type Non-Destructive Testing and, utilize from the reflective sound wave between buffer stopper and measurement sample, its signal is not subject to the impact of concentration of medium and attenuation characteristic, so relatively with utilize ultrasonic attenuation, phase velocity, the more practical measurement with particle in excessive concentrations two-phase mixture of the method.

Accompanying drawing explanation

Fig. 1 is measuring principle figure of the present invention;

Fig. 2 is for when concentration is 10%, and theoretical modeling acoustic impedance real part is with the situation of change of grain diameter size;

Fig. 3 is for when particle diameter is 22.2m, and theoretical modeling acoustic impedance real part is with the situation of change of potpourri middle particle concentration size;

Fig. 4 is resonant frequency and particle size theory curve;

Fig. 5 is concentration and resonant amplitude theory curve;

Fig. 6 is the actual impedance real part curve map recorded.

Embodiment

Illustrate below in conjunction with accompanying drawing and embodiments of the invention be described in further detail.

A kind of based on ultrasonic impedances spectrum grain diameter and concentration measuring method, specifically comprise the steps:

1), utilizing reflectance spectrum to carry out the characteristic of characterizing particles, need according to ultrasonic particle sizing classical model---the relation between acoustic impedance and particle two-phase medium set up by ECAH model (Epstein – Carhart – Allegra – Hawley).This model fairly comprehensive consideration stickiness loss, thermal loss, scattering loss and absorbed inside.For particle two-phase system, obtain wave of compression, shearing wave, the wave equation of heat wave in the spherical solid particles and continuous phase medium of flexible, isotropy, heat conduction by using quality, momentum and law of conservation of energy, ess-strain and acoustics and thermodynamic equations.The mathematic(al) representation of its complex wave number κ is:

κ＝ω/c(ω)+iα(ω)

Wherein ω is angular frequency.From above formula, the real part of complex wave number κ is relevant with phase velocity c (ω), and its imaginary part is relevant to attenuation coefficient α (ω).It is as follows that the acoustics of ECAH model to particle two-phase medium describes final expression formula:

${\left(\frac{\mathrm{\κ}}{{\mathrm{\κ}}_c}\right)}^2=1+\frac{3\mathrm{\φ}}{{{\mathrm{i\κ}}_c}^3{R}^3}\underset{n=0}{\overset{\mathrm{\∞}}{\Σ}}(2n+1)A_n$

Wherein κ _cfor wave of compression wave number, φ is the volumetric concentration of particle in medium, and R is particle radius, A _nfor scattering coefficient, calculated by ECAH model.

The definition of impedance is:

$Z=\mathrm{\ρ}c\left(\mathrm{\ω}\right)\left(1-i\frac{\mathrm{\α}\left(\mathrm{\ω}\right)\mathrm{\λ}}{2\mathrm{\π}}\right)$

Wherein ρ is Media density, and λ is ultrasonic propagation wavelength in media as well, combines the final expression formula that can obtain impedance Z to be by above-mentioned three formulas:

$Z=\mathrm{\ρ}\mathrm{\ω}\left(1-i\frac{\mathrm{\α}\left(\mathrm{\ω}\right)\mathrm{\λ}}{2\mathrm{\π}}\right)/\mathrm{Re}\left({\mathrm{\κ}}_c\sqrt{1+\frac{3\mathrm{\φ}}{{{\mathrm{i\κ}}_c}^3{R}^3}\underset{n=0}{\overset{\mathrm{\∞}}{\Σ}}\left(2n+1\right)A_n}\right)$

Write corresponding calculation procedure according to this formula, number of times of suing for peace in calculating gets 20 times, and Re represents and asks for real part computing, can obtain theoretical impedance real part spectrum.

2), according to 1) obtain, in the real part spectrum of impedance, can showing that the change of impedance real part with granules of polystyrene particle diameter is as Fig. 2, and with the change of concentration as Fig. 3.Frequency corresponding to impedance real part peak-to-peak value is particle resonant frequency, and it presents decline trend with the increase of polystyrene particle diameter.And resonant amplitude presents increasing trend with the increase of concentration.So, extract different-grain diameter and corresponding resonant frequency thereof and can obtain the theoretical curve of " particle diameter-resonant frequency " as Fig. 4, extract different concentration and corresponding amplitude can obtain the curve of " concentration-resonant amplitude " equally as Fig. 5.

3), as shown in Figure 1, the front end face of ultrasonic transducer 1 is parallel with the interface of Polystyrene suspension with buffer stopper A, and under exciting circuit effect, ultrasound wave launch and accept transducer T/R sends a branch of impulse ultrasound intensity of wave is I ₀, through buffer stopper A, reflect in the interface of buffer stopper A and sample area B, it is I that transmitted wave is obtained reflected ultrasonic intensity by ultrasound emission transducer T/R reception again after buffer stopper A ₁, and the collection of collected card is preserved in a computer.When not holding any sample in sample cell, one group of reflected signal I can be recorded _{1 (air)}.To the reflection wave obtained, under obtaining multiple frequency by Fast Fourier Transform (FFT) (FFT), signal intensity is composed, the reflection wave I that each frequency is corresponding ₁(f) and I ₀f the relation of () is

$I_1\left(f\right)=I_0\left(f\right)R_s{e}^{-2{\mathrm{\α}}_c{l}_1}$

Because the impedance of air is very little, so can by R _c=1, now I _{1 (air)}(f) and I ₀f the pass of () is then

$I_{1\left(air\right)}\left(f\right)=I_0\left(f\right)e^{-2{\mathrm{\α}}_c{l}_1}$

Wherein R _sthe reflection coefficient between buffer stopper and sample, α _cthe attenuation coefficient of buffer stopper, l ₁for the thickness of buffer stopper.

Can be obtained by above two formulas

$R_s=\frac{I_1\left(f\right)}{I_{1\left(air\right)}\left(f\right)}$

Utilize the ratio of two signals also can avoid measuring A accurately ₀value.Decrease the inaccurate row of measurement.It should be noted that R herein _sfor plural number.

The signal obtained in device is as shown in Figure 1 after above process computation obtains reflection coefficient.Corresponding different frequency uses formula Z respectively _s=Z _c(1+R _s)/(1-R _s) calculate, wherein Z _sand Z _cbe respectively the acoustic impedance of medium and the acoustic impedance of buffer stopper.Just can obtain impedance spectrum Z (f), unit is Pa*s/m, f is ultrasonic frequency, so just can obtain the acoustic impedance spectrum of testing gained, gets real part then obtain experiment impedance real part spectrum to it.

4), by the signal of experiment acquisition, through 3) described in formula process, just the acoustic impedance real part spectrum of Polystyrene suspension can be obtained as Fig. 6, extract resonant frequency f, with the amplitude of correspondence, then according to 2) in " particle diameter-resonant frequency ", " concentration-resonant amplitude " two curves of determining just can obtain concentration and the grain diameter of measuring object granules of polystyrene.

Claims (1)

1. measure a method for grain diameter and concentration based on ultrasonic impedances spectrum principle, comprise following several step:

1), theoretical impedance real part spectrum is obtained with ECAH model and theory calculate

Utilize reflectance spectrum to carry out the characteristic of characterizing particles, set up the relation between acoustic impedance and particle two-phase medium according to ultrasonic particle sizing ECAH model; For particle two-phase system, by using quality, momentum and law of conservation of energy, ess-strain and acoustics and thermodynamic equations to obtain wave of compression, shearing wave, the wave equation of heat wave in the spherical solid particles and continuous phase medium of flexible, isotropy, heat conduction, the mathematic(al) representation of its complex wave number κ is:

κ＝ω/c(ω)+iα(ω)

Wherein ω is angular frequency.From above formula, the real part of complex wave number κ is relevant with phase velocity c (ω), and its imaginary part is relevant to attenuation coefficient α (ω); It is as follows that the acoustics of ECAH model to particle two-phase medium describes final expression formula:

${\left(\frac{\mathrm{\κ}}{{\mathrm{\κ}}_c}\right)}^2=1+\frac{3\mathrm{\φ}}{{{\mathrm{i\κ}}_c}^3{R}^3}\underset{n=0}{\overset{\mathrm{\∞}}{\Σ}}(2n+1)A_n$

Wherein κ _cfor known incident wave of compression wave number, φ is the volumetric concentration of particle in medium, and R is particle radius, A _nfor scattering coefficient, calculated by ECAH model;

The definition of impedance is:

$Z=\mathrm{\ρ}c\left(\mathrm{\ω}\right)(1-i\frac{\mathrm{\α}\left(\mathrm{\ω}\right)\mathrm{\λ}}{2\mathrm{\π}})$

Wherein ρ is particle two-phase medium average density, and λ ultrasonicly propagates wavelength in two-phase medium, combines the final expression formula that can obtain impedance Z to be by above-mentioned three formulas:

$Z=\mathrm{\ρ}c\left(\mathrm{\ω}\right)(1-i\frac{\mathrm{\α}\left(\mathrm{\ω}\right)\mathrm{\λ}}{2\mathrm{\π}})/\mathrm{Re}\left({\mathrm{\κ}}_c\sqrt{1+\frac{3\mathrm{\φ}}{{{\mathrm{i\κ}}_c}^3{R}^3}\underset{n=0}{\overset{\mathrm{\∞}}{\Σ}}(2n+1)A_n}\right)$

Write corresponding calculation procedure according to this formula, number of times of suing for peace in calculating gets 20 times, and Re represents and asks for real part computing, obtains theoretical impedance real part spectrum;

2), the theoretical curve of " particle diameter-resonant frequency " and the theoretical curve of " concentration-resonant amplitude " is obtained:

According to 1) step obtain impedance real part spectrum in, extract different-grain diameter and corresponding resonant frequency thereof, obtain the theoretical curve of " particle diameter-resonant frequency ", and extract different concentration and corresponding amplitude thereof, obtain the theoretical curve of " concentration-resonant amplitude ";

3), by ultrasonic transducer and the acoustic impedance spectrum calculating experiment gained, real part is got to it and then obtains experiment impedance real part spectrum:

First make the front end face of ultrasonic transducer parallel with the interface of medium with buffer stopper, under exciting circuit effect, ultrasound wave launch and accept transducer T/R sends a branch of impulse ultrasound intensity of wave is I ₀, through buffer stopper A, reflect in the interface of buffer stopper A and sample area B, it is I that transmitted wave is obtained reflected ultrasonic intensity by ultrasound emission transducer T/R reception again after buffer stopper A ₁, and the collection of collected card is preserved in a computer; When placing the known demarcation medium of acoustic properties in sample cell, then reflection R _cknown, record one group of reflected signal I _1c, to the reflection wave obtained, under obtaining multiple frequency by Fast Fourier Transform (FFT), signal intensity is composed, the reflection wave I that each frequency is corresponding ₁(f), I _1c(f) and I ₀f the relation of () is:

$I_1\left(f\right)=I_0\left(f\right)R_s{e}^{-2{\mathrm{\α}}_c{l}_1}$

$I_{1c}\left(f\right)=I_0\left(f\right)R_c{e}^{-2{\mathrm{\α}}_c{l}_1}$

Wherein R _sthe reflection coefficient between buffer stopper and sample media, α _cthe attenuation coefficient of buffer stopper, l ₁for the thickness of buffer stopper;

Can be obtained by above two formulas

$R_s=\frac{I_1\left(f\right)}{I_{1c}\left(f\right)}$

After calculating reflection coefficient above, corresponding different frequency uses formula Z respectively _s=Z _c(1+R _s)/(1-R _s) calculate, wherein Z _sand Z _cbe respectively the acoustic impedance of medium and the acoustic impedance of buffer stopper, just can obtain impedance spectrum Z (f), unit is Pa*s/m, f is ultrasonic frequency, can obtain the acoustic impedance spectrum of testing gained, gets real part then obtain experiment impedance real part spectrum to it;

4) signal, by experiment obtained, through 3) formula manipulation described in step, just can obtain the resonant frequency of measuring object impedance real part spectrum, extract resonant frequency f _r, then from 2) " particle diameter-resonant frequency ", " concentration-resonant amplitude " two curves of determining step can look into concentration and the grain diameter that value obtains measuring object.