CN101813598B

CN101813598B - Viscosity coefficient measurement method based on photoacoustic effect

Info

Publication number: CN101813598B
Application number: CN2010101391199A
Authority: CN
Inventors: 娄存广; 邢达
Original assignee: South China Normal University
Current assignee: South China Normal University
Priority date: 2010-03-30
Filing date: 2010-03-30
Publication date: 2011-07-20
Anticipated expiration: 2030-03-30
Also published as: CN101813598A

Abstract

The invention discloses a method for measuring viscosity coefficient based on photoacoustic effect. The method includes: placing a liquid sample with a known viscosity coefficient in a container, focusing a pulsed laser and irradiating the liquid sample to excite a photoacoustic signal; collecting the photoacoustic signal of the liquid sample, and extracting the main frequency of the photoacoustic signal ; Obtain the photoacoustic pressure function P(t) by using ultrasonic transducer detection; according to the frequency domain expression equation of the photoacoustic signal, the constant α is obtained; the liquid to be measured is placed in a container, and the pulsed laser is focused and irradiated on the liquid to be measured Above, the photoacoustic signal is excited; the photoacoustic signal of the liquid to be tested is received by the ultrasonic detector, and the data is collected after being amplified by the signal amplifier; the recorded photoacoustic signal is processed by Matlab, and the recorded photoacoustic signal is Fourier transformed. The main frequency of the photoacoustic signal is extracted; according to ξ _n = l _vn ρ _n c _sn , the viscosity coefficient ξ _n of the liquid to be measured is obtained. The method has the advantages of high speed, high precision, non-destructive, strong on-line measurement ability and strong practicability.

Description

A Measuring Method of Viscosity Coefficient Based on Photoacoustic Effect

技术领域technical field

本发明属于物理测量技术领域，特别涉及一种基于光声效应的粘滞系数测量方法。The invention belongs to the technical field of physical measurement, in particular to a method for measuring viscosity coefficient based on photoacoustic effect.

背景技术Background technique

粘滞系数是一个表示流体性质的重要物理量，液体的粘滞系数又称内摩擦系数，在工程技术和生产技术以及医学等方面，测定液体的粘滞系数具有重大的意义。例如研究水、石油等流体在长距离输送时的能量损耗，造船工业中研究减小运动物体在液体中阻力，医学上通过测定血液的粘滞力可以得到有价值的诊断等，这些均与测定液体的粘滞系数有关。Viscosity coefficient is an important physical quantity that expresses the properties of fluid. The viscosity coefficient of liquid is also called internal friction coefficient. In engineering technology, production technology and medicine, it is of great significance to measure the viscosity coefficient of liquid. For example, to study the energy loss of water, oil and other fluids during long-distance transportation, to reduce the resistance of moving objects in liquids in the shipbuilding industry, to obtain valuable diagnosis by measuring the viscosity of blood in medicine, etc., all of which are related to the measurement The viscosity coefficient of the liquid is related.

斯托克斯法是测定液体粘滞系数的基本方法。传统测量方法存在以下三个问题：1、使用秒表人工计时，精度低。2、难以判断小球是否沿着玻璃管中心线下落，而恰恰是实验误差的一个来源。3、落球测量时间重复性差。The Stokes method is the basic method for determining the viscosity coefficient of liquid. The following three problems exist in the traditional measurement method: 1. Using a stopwatch for manual timing, the accuracy is low. 2. It is difficult to judge whether the ball falls along the centerline of the glass tube, which is just a source of experimental error. 3. The repeatability of falling ball measurement time is poor.

光声效应以及光声层析成像技术的研究在近几年受到越来越多的关注。当用脉冲光源或调制光源辐照某物体时，物体内瞬间温度的起伏会引起其体积的伸缩，因而向外辐射声波。这种现象称为光致声场效应(简称光声效应)。光声效应实际上是一种能量转换过程，激光与受辐照物体相互作用的机理非常复杂，产生的效应不仅与激光参数有关，又很大程度上取决于物体本身光学、热学及力学等特性参数的影响。粘滞系数正是热力学中的一个重要参数，直接影响由热能(吸收的激光能量)向机械能(热膨胀)的转换。本发明针对粘滞性对光声信号产生的影响，提出了一种利用光声效应无损测量液体粘滞系数的快速有效方法。The research on photoacoustic effect and photoacoustic tomography has received more and more attention in recent years. When an object is irradiated with a pulsed light source or a modulated light source, the instantaneous temperature fluctuation inside the object will cause its volume to expand and contract, thus radiating sound waves outward. This phenomenon is called photoacoustic field effect (referred to as photoacoustic effect). The photoacoustic effect is actually an energy conversion process. The mechanism of the interaction between the laser and the irradiated object is very complicated. The effect is not only related to the laser parameters, but also largely depends on the optical, thermal and mechanical properties of the object itself. influence of parameters. The viscosity coefficient is just an important parameter in thermodynamics, which directly affects the conversion from thermal energy (absorbed laser energy) to mechanical energy (thermal expansion). Aiming at the influence of the viscosity on the photoacoustic signal, the invention proposes a fast and effective method for non-destructively measuring the viscosity coefficient of the liquid by using the photoacoustic effect.

发明内容Contents of the invention

为了克服现有传统的粘滞系数测量仪的不足，本发明的目的在于提供一种利用光声效应测量液体粘滞系数的方法；该方法快速、高精度、有很强实用性。In order to overcome the deficiencies of existing traditional viscosity coefficient measuring instruments, the object of the present invention is to provide a method for measuring liquid viscosity coefficient by using photoacoustic effect; the method is fast, high-precision and has strong practicability.

为实现上述目的，本发明采用如下技术方案：一种基于光声效应的粘滞系数测量方法，包括以下操作步骤：In order to achieve the above object, the present invention adopts the following technical scheme: a method for measuring viscosity coefficient based on photoacoustic effect, comprising the following steps:

(1)将已知粘滞系数ξ₁的液体样品放置于容器中，将脉冲激光聚焦后辐照在液体样品上，激发光声信号；(1) A liquid sample with a known viscosity coefficient _ξ1 is placed in a container, and the pulsed laser is focused and irradiated on the liquid sample to excite a photoacoustic signal;

(2)利用采集系统记录液体样品的光声信号，提取光声信号的主频或带宽ω₁；采用超声换能器探测得到光声压函数P(t)；根据下述光声信号频域表达方程式中光声信号主频

与粘滞系数的关系，得到待定常数α的数值；(2) Use the acquisition system to record the photoacoustic signal of the liquid sample, extract the main frequency or bandwidth _ω1 of the photoacoustic signal; use the ultrasonic transducer to detect the photoacoustic pressure function P(t); according to the following photoacoustic signal frequency domain The main frequency of the photoacoustic signal in the expression equation

The relationship with the viscosity coefficient, the value of the undetermined constant α is obtained;

$P P ((t t)) = = \frac{Γ Γ {I I}_{00}}{a a {c c}_{s the s 11} \sqrt{44 - - {a a}^{22} {l l}_{v v 11}^{22}}} {e e}^{- - {a a}^{22} {c c}_{s the s 11} {l l}_{v v 11} t t} sin sin ((22 a a {c c}_{s the s 11} \sqrt{11 - - {a a}^{22} {(({l l}_{v v 11} / / 22))}^{22}} t t)) * * [[A A ((x x)) \frac{&PartialD; &PartialD;}{&PartialD; &PartialD; t t} f f ((t t)) - - {c c}_{s the s 11} {l l}_{v v 11} f f ((t t)) \frac{{&PartialD; &PartialD;}^{22}}{&PartialD; &PartialD; {x x}^{22}} A A ((x x))]]$

其中，Γ为格留乃森参数，I₀为正比于光能量密度的因子，A(x)为样品位置x处能量沉积，f(t)为激光脉冲波形，c_s1为液体样品中超声传播速度(下标1表示样品编号)，

为脉冲激光函数表达式，τ为激光脉冲宽度，l_v1＝ξ₁/ρ₁c_s1为液体样品的粘滞长度，ρ₁为液体样品的密度；Among them, Γ is the Grunesen parameter, I ₀ is a factor proportional to the optical energy density, A(x) is the energy deposition at the sample position x, f(t) is the laser pulse waveform, c _s1 is the ultrasonic propagation in the liquid sample speed (the subscript 1 indicates the sample number),

is the pulse laser function expression, τ is the laser pulse width, l _v1 = ξ ₁ /ρ ₁ c _s1 is the viscous length of the liquid sample, and ρ ₁ is the density of the liquid sample;

(4)将待测液体置于容器中，将与步骤(1)所述脉冲激光相同频率的脉冲激光聚焦后辐照在待测液体上，激发光声信号；(4) placing the liquid to be measured in a container, focusing the pulsed laser with the same frequency as the pulsed laser described in step (1) and then irradiating it on the liquid to be measured to excite a photoacoustic signal;

(5)利用超声探测器接收待测液体的光声信号，将光声信号经信号放大器放大后进行数据采集记录；(5) Utilize the ultrasonic detector to receive the photoacoustic signal of the liquid to be tested, amplify the photoacoustic signal through the signal amplifier, and carry out data collection and recording;

(6)用Matlab处理记录的光声信号，对记录的光声信号进行傅里叶变换，提取光声信号的主频ω_n(下标n表示样品编号)，根据k₁＝ω₁/c_s1，k_n＝ω_n/c_sn和lv_n ²＝lv₁ ²+(k₁ ²-k_n ²)/a⁴，得到待测液体的粘滞长度l_vn(下标n表示样品编号)，所述c_sn为待测液体中超声传播速度；然后根据ξ_n＝l_vnρ_nc_sn，得到待测液体的实际粘滞系数ξ_n，所述ρ₁为待测液体的密度。(6) Process the recorded photoacoustic signal with Matlab, perform Fourier transform on the recorded photoacoustic signal, and extract the main frequency ω _n of the photoacoustic signal (the subscript n represents the sample number), according to k ₁ =ω ₁ /c _s1 , k _n ＝ω _n /c _sn and lv _n ² ＝lv ₁ ² +(k ₁ ² -k _n ² )/a ⁴ , get the viscous length l _vn of the liquid to be tested (the subscript n indicates the sample number) , the c _sn is the ultrasonic propagation velocity in the liquid to be tested; then according to ξ _n =l _vn ρ _n c _sn , the actual viscosity coefficient ξ _n of the liquid to be tested is obtained, and the ρ ₁ is the density of the liquid to be tested.

步骤(1)所述τ为1ns～1us。The τ in step (1) is 1 ns-1 us.

步骤(1)和(4)所述脉冲激光是由脉冲激光发生器或连续调制的连续激光器发出。The pulsed laser in steps (1) and (4) is emitted by a pulsed laser generator or a continuously modulated continuous laser.

步骤(1)和(4)所述聚焦是将脉冲激光通过透镜进行聚焦，研究粘滞性对光声信号产生的影响。The focusing in steps (1) and (4) is to focus the pulsed laser light through a lens to study the influence of viscosity on photoacoustic signals.

本发明的原理是：Principle of the present invention is:

声振动作为一个宏观的物理现象，必然要满足三个基本的物理定律，即牛顿第二定律、质量守恒定律以及描述压强、温度与体积等状态参数关系的物态方程。运用这些基本定律，可以分别导出推导出三个物理量之间关系的三个方程的运动方程、连续性方程和物态方程。利用上述理想介质声场特性的三个基本方程，可以完整地描述处于静止无源的状态下声场特性。当脉冲激光照射在介质上，由于介质的吸收效应导致光能量的沉积、温度的增加和超声信号的产生。在这状态下，介质中的声场变为了有源场，介质中的吸收体都可以看成超声波发生源。此时，用于描述压强、温度与体积等状态参数关系的物态方程会有适当的修正。As a macroscopic physical phenomenon, acoustic vibration must satisfy three basic physical laws, namely Newton's second law, the law of conservation of mass, and the equation of state describing the relationship between state parameters such as pressure, temperature, and volume. Using these basic laws, the equation of motion, continuity equation and equation of state of the three equations that deduce the relationship between the three physical quantities can be derived respectively. Using the above three basic equations of the sound field characteristics of the ideal medium, the sound field characteristics in a static passive state can be completely described. When the pulsed laser is irradiated on the medium, the absorption effect of the medium leads to the deposition of light energy, the increase of temperature and the generation of ultrasonic signals. In this state, the sound field in the medium becomes an active field, and the absorber in the medium can be regarded as the source of ultrasonic waves. At this time, the equation of state used to describe the relationship between state parameters such as pressure, temperature, and volume will be appropriately corrected.

粘滞性对运动方程的影响用Navier-Stokes方程描述：The effect of viscosity on the equation of motion is described by the Navier-Stokes equation:

$ρ ρ \frac{&PartialD; &PartialD; &upsi; &upsi;}{&PartialD; &PartialD; t t} + + ρ ρ ((ν ν \cdot &Center Dot; &dtri; &dtri;)) ν ν = = - - &dtri; &dtri; p p + + {η η &dtri; &dtri;}^{22} ν ν + + ((ξ ξ + + \frac{11}{33} η η)) &dtri; &dtri; ((&dtri; &dtri; \cdot &Center Dot; ν ν)) - - - - - - ((11))$

其中ξ为容积粘滞，η为剪切粘滞。where ξ is the bulk viscosity and η is the shear viscosity.

忽略热传导方程中的热扩散并带与连续性方程结合，得到Ignoring thermal diffusion in the heat conduction equation and combining it with the continuity equation, we get

$\frac{&PartialD; &PartialD; ρ ρ}{&PartialD; &PartialD; t t} + + &dtri; &dtri; \cdot &Center Dot; ((ρν ρν)) = = \frac{β β}{{C C}_{p p}} H h ((r r,, t t)) - - - - - - ((22))$

将声压及密度用平衡值加上小的声扰动来表示，即p＝p₀+δp，ρ＝ρ₀+δρ。The sound pressure and density are represented by the balance value plus a small sound disturbance, that is, p=p ₀ +δp, ρ=ρ ₀ +δρ.

线性化方程(1)(2)并由关系式δp＝C_s ²δρ得到：Equations (1)(2) are linearized and obtained from the relationship δp=C _s ² δρ:

${&dtri; &dtri;}^{22} P P - - \frac{11}{{Cs Cs}^{22}} \frac{{&PartialD; &PartialD;}^{22}}{{&PartialD; &PartialD; t t}^{22}} P P = = - - \frac{β β}{{C C}_{p p}} \frac{&PartialD; &PartialD;}{&PartialD; &PartialD; t t} H h - - \frac{ξ ξ + + \frac{44}{33} η η}{{ρ ρ}_{00} {Cs Cs}^{22}} ((\frac{&PartialD; &PartialD;}{&PartialD; &PartialD; t t} {&dtri; &dtri;}^{22} P P - - \frac{β β {Cs Cs}^{22}}{{C C}_{p p}} {&dtri; &dtri;}^{22} H h)) - - - - - - ((33))$

令

(格留乃森参数)，H＝I₀A(r)f(t)(I₀为正比于光能量密度的因子；A(r)为样品位置r处能量沉积；f(t)为激光脉冲波形，通常为高斯函数，即

上式可化为：make

(Grunesen parameter), H=I ₀ A(r)f(t) (I ₀ is a factor proportional to the light energy density; A(r) is the energy deposition at the sample position r; f(t) is the laser The pulse shape, usually a Gaussian function, that is

The above formula can be transformed into:

$\frac{11}{{Cs Cs}^{22}} \frac{{&PartialD; &PartialD;}^{22}}{{&PartialD; &PartialD; t t}^{22}} P P = = {&dtri; &dtri;}^{22} P P + + \frac{ξ ξ + + \frac{44}{33} η η}{{ρ ρ}_{00} {Cs Cs}^{22}} \frac{&PartialD; &PartialD;}{&PartialD; &PartialD; t t} {&dtri; &dtri;}^{22} P P - - \frac{ξ ξ + + \frac{44}{33} η η}{{ρ ρ}_{00} {Cs Cs}^{22}} ((Γ Γ {I I}_{00} f f {&dtri; &dtri;}^{22} A A)) + + \frac{{ΓI Γ I}_{00}}{{C C}_{s the s}^{22}} A A \frac{&PartialD; &PartialD;}{&PartialD; &PartialD; t t} f f - - - - - - ((44))$

如果仅考虑均匀黏弹介质中沿x轴方向传播的平面波解，则上式化为If only the plane wave solution propagating along the x-axis direction in the homogeneous viscoelastic medium is considered, the above formula can be transformed into

$\frac{11}{{Cs Cs}^{22}} \frac{{&PartialD; &PartialD;}^{22}}{{&PartialD; &PartialD; t t}^{22}} P P ((x x,, t t)) = = \frac{{&PartialD; &PartialD;}^{22}}{{&PartialD; &PartialD; x x}^{22}} P P ((x x,, t t)) + + \frac{ξ ξ + + \frac{44}{33} η η}{{ρ ρ}_{00} {Cs Cs}^{22}} \frac{{&PartialD; &PartialD;}^{33}}{&PartialD; &PartialD; t t {&PartialD; &PartialD; x x}^{22}} P P ((x x,, t t)) + + [[\frac{Γ Γ {I I}_{00}}{{C C}_{s the s}^{22}} A A ((x x)) \frac{&PartialD; &PartialD;}{&PartialD; &PartialD; t t} f f ((t t)) - - \frac{ξ ξ + + \frac{44}{33} η η}{{ρ ρ}_{00} {Cs Cs}^{22}} ((Γ Γ {I I}_{00} f f ((t t)) \frac{{&PartialD; &PartialD;}^{22}}{{&PartialD; &PartialD; x x}^{22}} A A ((x x))))]] - - - - - - ((55))$

将源项设为S，即令

则上式化为：Set the source term as S, that is,

Then the above formula becomes:

$\frac{11}{{Cs Cs}^{22}} \frac{{&PartialD; &PartialD;}^{22}}{{&PartialD; &PartialD; t t}^{22}} P P ((x x,, t t)) = = \frac{{&PartialD; &PartialD;}^{22}}{{&PartialD; &PartialD; x x}^{22}} P P ((x x,, t t)) + + \frac{ξ ξ + + \frac{44}{33} η η}{{ρ ρ}_{00} {Cs Cs}^{22}} \frac{{&PartialD; &PartialD;}^{33}}{&PartialD; &PartialD; t t {&PartialD; &PartialD; x x}^{22}} P P ((x x,, t t)) + + S S - - - - - - ((66))$

先考虑x＝0处一脉冲激发源作用下方程的解，令S＝δ(x，t)，上式可化为First consider the solution of the equation under the action of a pulse excitation source at x=0, let S=δ(x, t), the above formula can be transformed into

$\frac{11}{{Cs Cs}^{22}} \frac{{&PartialD; &PartialD;}^{22}}{{&PartialD; &PartialD; t t}^{22}} P P ((x x,, t t)) = = \frac{{&PartialD; &PartialD;}^{22}}{{&PartialD; &PartialD; x x}^{22}} P P ((x x,, t t)) + + \frac{ξ ξ + + \frac{44}{33} η η}{{ρ ρ}_{00} {Cs Cs}^{22}} \frac{{&PartialD; &PartialD;}^{33}}{&PartialD; &PartialD; t t {&PartialD; &PartialD; x x}^{22}} P P ((x x,, t t)) + + δ δ ((x x,, t t)) - - - - - - ((77))$

设P(x，t)＝e^iaxP(t)，带入(7)中，得到Let P(x, t)=e ^iax P(t), bring it into (7), and get

$\frac{11}{{Cs Cs}^{22}} \frac{{&PartialD; &PartialD;}^{22}}{{&PartialD; &PartialD; t t}^{22}} P P ((x x,, t t)) + + {a a}^{22} P P ((x x,, t t)) + + {a a}^{22} \frac{ξ ξ + + \frac{44}{33} η η}{{ρ ρ}_{00} {Cs Cs}^{22}} \frac{&PartialD; &PartialD;}{&PartialD; &PartialD; t t} P P ((x x,, t t)) = = δ δ ((t t)) - - - - - - ((88))$

对方程两边取傅里叶反变换，得到其频域的两个根，并用留数定理计算得到方程的解为：Take the inverse Fourier transform of both sides of the equation to get the two roots in the frequency domain, and use the residue theorem to calculate the solution of the equation as:

$P P ((x x,, t t)) = = \frac{Γ Γ {I I}_{00}}{a a {c c}_{s the s} \sqrt{44 - - {a a}^{22} {l l}_{v v}^{22}}} {e e}^{iax iax} {e e}^{- - {a a}^{22} {c c}_{s the s} {l l}_{v v 11} t t} sin sin ((ωt ωt - - ax ax)) * * [[A A ((x x)) \frac{&PartialD; &PartialD;}{&PartialD; &PartialD; t t} f f ((t t)) - - {c c}_{s the s} {l l}_{v v} f f ((t t)) \frac{{&PartialD; &PartialD;}^{22}}{&PartialD; &PartialD; {x x}^{22}} A A ((x x))]] - - - - - - ((99))$

其中为光声信号频率。

为粘滞长度，α为常数。当只考虑沿一个方向传播的平面波时，光声压可以进一步简化为：in is the photoacoustic signal frequency.

is the viscous length, and α is a constant. When only plane waves propagating in one direction are considered, the photoacoustic pressure can be further simplified as:

$P P ((t t)) = = \frac{Γ Γ {I I}_{00}}{a a {c c}_{s the s} \sqrt{44 - - {a a}^{22} {l l}_{v v}^{22}}} {e e}^{- - {a a}^{22} {c c}_{s the s} {l l}_{v v 11} t t} sin sin ((22 a a {c c}_{s the s} \sqrt{11 - - {a a}^{22} {(({l l}_{v v} / / 22))}^{22}} t t)) * * [[A A ((x x)) \frac{&PartialD; &PartialD;}{&PartialD; &PartialD; t t} f f ((t t)) - - {c c}_{s the s} {l l}_{v v} f f ((t t)) \frac{{&PartialD; &PartialD;}^{22}}{&PartialD; &PartialD; {x x}^{22}} A A ((x x))]] - - - - - - ((1010))$

上式说明了粘滞系数对光声效应转化效率的影响，粘滞性不仅影响光声信号的幅值，还影响其频率及带宽。通过下述方程可以反演计算出被测样品的粘滞系数。The above formula shows the influence of the viscosity coefficient on the conversion efficiency of the photoacoustic effect. The viscosity not only affects the amplitude of the photoacoustic signal, but also affects its frequency and bandwidth. The viscosity coefficient of the measured sample can be calculated inversely by the following equation.

$\frac{(({k k}_{n no}^{22} - - {k k}_{11}^{22}))}{{lv lv}_{11}^{22} - - {lv lv}_{n no}^{22}} = = {a a}^{44},, {lv lv}_{n no}^{22} = = {lv lv}_{11}^{22} + + (({k k}_{11}^{22} - - {k k}_{n no}^{22})) / / {a a}^{44},, {ξ ξ}_{n no} = = {lv lv}_{n no} {ρc ρc}_{s the s} - - - - - - ((1111))$

其中波数

where the wave number

本发明基于光声产生原理，利用粘滞系数对光声信号产生的影响，通过光声频移反演计算得到液体实际的粘滞系数值。Based on the photoacoustic generation principle, the present invention utilizes the influence of the viscosity coefficient on the photoacoustic signal to obtain the actual viscosity coefficient value of the liquid through photoacoustic frequency shift inversion calculation.

本发明相对于现有技术具有如下的优点及有益效果：本发明方法与传统的粘度计法相比，具有快速，在线测量的能力的特点；本发明与基于声在粘滞介质传输过程中高频衰减的方法相比，不需要在粘滞介质中传输较长路径来提取粘滞系数，而只需很小的样本量就能实现快速精确测量；本发明方法操作简便，快速，精度高，有着很强的实用性。Compared with the prior art, the present invention has the following advantages and beneficial effects: compared with the traditional viscometer method, the method of the present invention has the characteristics of fast and on-line measurement capability; Compared with the method of the present invention, it does not need to transmit a long path in the viscous medium to extract the viscosity coefficient, but only needs a small sample size to realize fast and accurate measurement; Strong practicality.

附图说明Description of drawings

图1是本发明系统的结构示意图，其中1-1为光声激发源发生器，1-2为光传输媒质(光纤或反光影)，1-3为光声信号探测器，1-4为信号放大器，1-5为计算机，1-6为函数发生器，1-7为数据采集系统，1-8为被测物质。Fig. 1 is the structural representation of the system of the present invention, wherein 1-1 is photoacoustic excitation source generator, 1-2 is optical transmission medium (optical fiber or reflective shadow), 1-3 is photoacoustic signal detector, 1-4 is Signal amplifiers, 1-5 are computers, 1-6 are function generators, 1-7 are data acquisition systems, and 1-8 are measured substances.

图2为不同粘滞系数甘油水溶液光声信号时域及频域图，其中(a)为所示，光声信号幅值随着粘滞系数增加有较明显的减小，其光声化转化效率有较大幅度的减小；(b)为所示，光声信号主频随着粘滞系数增加而向下偏移，带宽减小。Figure 2 is the time-domain and frequency-domain diagrams of the photoacoustic signals of glycerin aqueous solutions with different viscosity coefficients, where (a) shows that the amplitude of the photoacoustic signal decreases significantly with the increase of the viscosity coefficient, and its photoacoustic conversion The efficiency is greatly reduced; (b) shows that the main frequency of the photoacoustic signal shifts downward with the increase of the viscosity coefficient, and the bandwidth decreases.

图3为利用本发明方法测量不同粘度甘油水溶液的粘度结果图，图中直线表示甘油水溶液实际粘滞系数值。Fig. 3 is the result figure of measuring the viscosity of glycerol aqueous solution with different viscosities by using the method of the present invention, and the straight line in the figure represents the actual viscosity coefficient value of glycerin aqueous solution.

具体实施方式Detailed ways

下面结合实施例及附图对本发明作进一步详细的描述，但本发明的实施方式不限于此。The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto.

实施例1、测量不同粘滞系数的甘油水溶液的时域光声信号：Embodiment 1. Measuring the time-domain photoacoustic signal of glycerol aqueous solutions with different viscosity coefficients:

(1)将不同粘滞系数ξ_n的液体样品分别放置于容器中，将脉冲激光聚焦后辐照在液体样品上，激发光声信号；(1) Liquid samples with different viscosity coefficients ξ _n are placed in containers respectively, and the pulsed laser is focused and irradiated on the liquid samples to excite photoacoustic signals;

(2)利用采集系统记录液体样品的光声信号P(t)。用Origin绘制热声信号图2(a)，并通过已知的参数计算出热声转化效率。(2) Using the acquisition system to record the photoacoustic signal P(t) of the liquid sample. Use Origin to plot the thermoacoustic signal Figure 2(a), and calculate the thermoacoustic conversion efficiency through known parameters.

通过该图可以看出，随着粘滞系数的增加，液体热声信号幅值有所减小，并与方程(10)的变化规律相符。由于粘滞性引起的热耗散影响，热声信号转化效率有明显的降低。It can be seen from the figure that with the increase of the viscosity coefficient, the amplitude of the liquid thermoacoustic signal decreases, which is consistent with the change law of equation (10). Due to the effect of heat dissipation caused by viscosity, the conversion efficiency of thermoacoustic signal is significantly reduced.

实施例2、测量不同粘滞系数的甘油水溶液的频域光声信号：Embodiment 2, measuring the frequency-domain photoacoustic signal of glycerol aqueous solution with different viscosity coefficients:

(2)利用采集系统记录液体样品的光声信号P(t)。利用采集系统记录液体样品的光声信号用Matlab对记录的光声信号进行傅里叶变换，得到不同粘滞系数液体热声信号频谱图2(b)。(2) Using the acquisition system to record the photoacoustic signal P(t) of the liquid sample. Use the acquisition system to record the photoacoustic signal of the liquid sample. Use Matlab to perform Fourier transform on the recorded photoacoustic signal, and obtain the spectrum of the liquid thermoacoustic signal with different viscosity coefficients in Figure 2(b).

通过该图可以看出，随着粘滞系数的增加，液体热声信号主频及带宽均有所减小，并与方程(10)的变化规律相符。It can be seen from the figure that with the increase of the viscosity coefficient, the main frequency and bandwidth of the liquid thermoacoustic signal decrease, which is consistent with the change law of equation (10).

实施例3、通过热声信号频移计算得到不同粘滞系数甘油水溶液的粘滞系数：Embodiment 3, obtain the viscosity coefficient of glycerol aqueous solution with different viscosity coefficients by thermoacoustic signal frequency shift calculation:

(1)将已知粘滞系数ξ₁的甘油水溶液放置于容器中，将脉冲激光(连续调制的激光)聚焦后辐照在甘油水溶液上，激发光声信号；(1) Place an aqueous glycerol solution with a known viscosity coefficient _ξ1 in a container, focus a pulsed laser (continuously modulated laser) and irradiate it on the aqueous glycerol solution to excite a photoacoustic signal;

(2)利用采集系统记录液体样品的光声信号P(t)，并用Matlab对记录的光声信号进行傅里叶变换；(2) Use the acquisition system to record the photoacoustic signal P(t) of the liquid sample, and use Matlab to perform Fourier transform on the recorded photoacoustic signal;

(3)提取光声信号的主频或带宽ω₁，根据k₁＝ω₁/c_s1得到波长k₁；利用超声换能器探测得到光声压函数P(t)，根据下述光声信号频域表达方程式中光声信号主频

与粘滞系数的关系，得到待定常数α的数值；(3) Extract the main frequency or bandwidth ω ₁ of the photoacoustic signal, and obtain the wavelength k ₁ according to k ₁ = ω ₁ /c _s1 ; use the ultrasonic transducer to detect the photoacoustic pressure function P(t), according to the following photoacoustic Main frequency of photoacoustic signal in signal frequency domain expression equation

其中，Γ为格留乃森参数，I₀为正比于光能量密度的因子，A(x)为样品位置r处能量沉积，

为高斯脉冲激光函数表达式，c_s1为液体样品中超声传播速度(下标1表示样品编号)，τ为激光脉冲宽度，l_v1＝ξ₁/ρ₁c_s1为液体样品的粘滞长度，ρ₁为液体样品的密度；Among them, Γ is the Grunesen parameter, I ₀ is a factor proportional to the light energy density, A(x) is the energy deposition at the sample position r,

is the Gaussian pulse laser function expression, c _s1 is the ultrasonic propagation velocity in the liquid sample (subscript 1 indicates the sample number), τ is the laser pulse width, l _v1 = ξ ₁ /ρ ₁ c _s1 is the viscous length of the liquid sample, _ρ1 is the density of liquid sample;

(4)将不同浓度的待测粘滞系数的甘油水溶液置于容器中，将与步骤(1)所述脉冲激光相同频率的脉冲激光聚焦后辐照在待测粘滞系数的甘油水溶液上，激发光声信号；(4) placing the aqueous glycerol solution of the viscosity coefficient to be measured in different concentrations in the container, focusing the pulsed laser with the same frequency as the pulse laser described in step (1) and irradiating it on the aqueous glycerol solution of the viscosity coefficient to be measured, Excite photoacoustic signal;

(5)利用超声探测器接收待测粘滞系数的甘油水溶液的光声信号，将光声信号经信号放大器放大后进行数据采集记录；(5) Utilize the ultrasonic detector to receive the photoacoustic signal of the glycerol aqueous solution of the viscosity coefficient to be measured, and carry out data acquisition and recording after the photoacoustic signal is amplified by the signal amplifier;

(6)用Matlab处理记录的光声信号，对记录的光声信号进行傅里叶变换，提取光声信号的主频或带宽ω_n，根据k_n＝ω_n/c_sn和lv_n ²＝lv₁ ²+(k₁ ²-k_n ²)/a⁴，得到待测液体的粘滞长度l_vn，所述c_sn为待测液体中超声传播速度；然后根据ξ_n＝l_vnρ_nc_sn，得到待测粘滞系数的甘油水溶液的实际粘滞系数ξ_n(结果如图2所示，图3横坐标为已知粘滞系数ξ₁，纵坐标为测量所得实际粘滞系数ξ_n)，所述ρ₁为待测粘滞系数的甘油水溶液的密度。(6) Process the recorded photoacoustic signal with Matlab, carry out Fourier transform to the recorded photoacoustic signal, extract the main frequency or bandwidth ω _n of the photoacoustic signal, according to k _n =ω _n /c _sn and lv _n ² = lv ₁ ² +(k ₁ ² -k _n ² )/a ⁴ , to obtain the viscous length l _vn of the liquid to be measured, and the c _sn is the ultrasonic propagation velocity in the liquid to be measured; then according to ξ _n =l _vn ρ _n c _sn , obtain the actual viscosity coefficient ξ _n of the aqueous glycerol solution of the viscosity coefficient to be measured (results are shown in Figure 2, the abscissa of Figure 3 is the known viscosity coefficient ξ ₁ , and the ordinate is the measured actual viscosity coefficient ξ _n ), said ρ ₁ is the density of the aqueous glycerol solution of the viscosity coefficient to be measured.

上述实施例为本发明较佳的实施方式，但本发明的实施方式并不受实施例的限制，其他的任何未背离本发明的精神实质与原理下所作的改变、修饰、替代、组合、简化，均应为等效的置换方式，都包含在本发明的保护范围之内。The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the embodiment, and any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principles of the present invention , all should be equivalent replacement methods, and are all included in the protection scope of the present invention.

Claims

1. coefficient of viscosity measuring method based on optoacoustic effect is characterized in that comprising following operation steps:

(1) with known coefficient of viscosity ξ ₁Fluid sample be positioned in the container, with irradiation behind the pulse laser focusing on fluid sample, the exciting light acoustical signal;

(2) utilize the photoacoustic signal of acquisition system recording liquid sample, handle the photoacoustic signal of record, the photoacoustic signal of record is carried out Fourier transform, extract the dominant frequency ω of photoacoustic signal with Matlab ₁Adopt ultrasonic transducer to survey and obtain optoacoustic pressure function P (t); According to photoacoustic signal dominant frequency in the following photoacoustic signal frequency domain presentation equation

With the relation of the coefficient of viscosity, obtain the numerical value of undetermined constant α;

P (t) = \frac{{ΓI}_{0}}{{ac}_{s 1} \sqrt{4 - a^{2} {l_{v 1}}^{2}}} e^{- a^{2} c_{s 1} l_{v 1} t} \sin (2 {ac}_{s 1} \sqrt{1 - a^{2} {(l_{v 1} / 2)}^{2}} t) * [A (x) \frac{&PartialD;}{&PartialD; t} f (t) - c_{s 1} l_{v 1} f (t) \frac{{&PartialD;}^{2}}{{&PartialD; x}^{2}} A (x)]

Wherein, Γ is a gruneisen parameter, I ₀For being proportional to the factor of optical energy density, A (x) is sample position x place energy deposition,

Be Gauss pulse laser function expression, c _S1Be ultrasonic propagation velocity in the fluid sample, τ is a laser pulse width, l _V1=ξ ₁/ ρ ₁c _S1Be the viscous length of fluid sample, ρ ₁Density for fluid sample;

(3) testing liquid is placed container, behind the described pulse laser focusing that will be identical with step (1) irradiation on testing liquid, the exciting light acoustical signal;

(4) utilize ultrasonic detector to receive the photoacoustic signal of testing liquid, photoacoustic signal is amplified laggard line data acquisition and recording through signal amplifier;

(5) handle the photoacoustic signal that writes down with Matlab, the photoacoustic signal that writes down is carried out Fourier transform, extract the dominant frequency ω of photoacoustic signal _n, according to k ₁=ω ₁/ c _S1, k _n=ω _n/ c _SnAnd lv _n ²=lv ₁ ²+ (k ₁ ²-k _n ²)/a ⁴, obtain the viscous length l of testing liquid _Vn, described c _SnBe ultrasonic propagation velocity in the testing liquid; Then according to ξ _n=l _Vnρ _nc _Sn, obtain the actual coefficient of viscosity ξ of testing liquid _n, described ρ _nDensity for testing liquid.

2. a kind of coefficient of viscosity measuring method based on optoacoustic effect according to claim 1 is characterized in that: the described laser pulse width τ of step (1) is 1ns～1 μ s.

3. a kind of coefficient of viscosity measuring method according to claim 1 based on optoacoustic effect, it is characterized in that: step (1) and (3) described pulse laser are to be sent by laser generator, and described laser generator is the continuous wave laser of pulsed laser or continuous modulation.