Background technology
Utilize nanosecond science and technology to traditional industry, particularly heavy industry is transformed, brought new opportunity to conventional industries, have very big expanding space.The performance of the granularity of material and structures shape material, the physical dimension of nano material and shape characterization are significant to the research nano material.Grain size is determining of granularity, and the significance of ubiquity is arranged in scientific research and actual production.Therefore, early oneself becomes people's common recognition as the important means that guarantees product quality and develop new product the test of grain graininess and size-grade distribution.Although existing several different methods can be measured granularity and the shape of particle, present measuring technology can't satisfy the needs of nano material fast development, so be very urgent and important to the nano material Study of test method.Because the singularity of nano material and nanometer technology, nanometer materials for detecting needs the instrument and equipment of the dollar of hundreds of thousands easily of specialty, is enough to allow general certifying agency be hung back.Therefore developing quick, economic nano material detection technique is the inevitable requirement of current nano materials research and nanometer industry development.
In order to carry out the measurement of grain diameter, people have been developed multiple grain diameter measurement technology, sieve method, optical microscope number scale, sedimentation, electro-induction method, laser diffraction and scattering method, electrophoresis, computer picture imaging method are arranged, the measurement lower limit of these methods has had reduction significantly, but, they all approach or have reached the limit of these instrument work, are far from its best or rational measurement range, are difficult to guarantee reliable measuring accuracy.Every kind of technology has the optimal adaptation situation of oneself, on the whole, for the measurement of grain diameter, when particle diameter greater than

The time, present most measuring techniques can draw result more accurately, and when grain diameter measurement was generalized to the nm level, measurement result was also unsatisfactory at present.In numerous nano particle measuring methods, light scattering method is wide owing to having applicability, grain diameter measurement haves a wide reach, measure accurately, precision height, fast, the good reproducibility of speed, the tested particle that need know and the physical parameter amount of dispersion medium are few, and the robotization of instrument and intelligent degree are high and be suitable for advantage such as on-line measurement and obtain developing rapidly and use comparatively widely.The utility model namely adopts dynamic light scattering method wherein that nano particles is measured, and obtains accurate grain diameter size.
In order to realize quick and precisely measuring the particle diameter of nano particle, need digital correlator that the signal from photo-detector is handled in real time, therefore the photon correlation measuring technique has very high requirement to operational precision and the dynamic range of digital correlator, inversion algorithm to particle diameter also has very high requirement simultaneously, any slight error or complementary operation instability appear among the related function real-time operation result that digital correlator provides, the gross error that all very easily causes the data inversion result, and now a lot of businessmans utilize chip such as single-chip microcomputer to carry out the development of software correlator, and chips such as single-chip microcomputer are the serial operations, this must cause accuracy and the real-time variation of related operation, and this is to restrict chips such as utilizing single-chip microcomputer to carry out soft relevant principal element.In addition, inversion algorithm is to adopt traditional semi-invariant algorithm mostly now, but traditional semi-invariant algorithm logarithm operation amplifies near the small noise of related function zero point, when change correlation time, its result of calculation changes obviously, when particularly getting bigger correlation time, result of calculation departs from actual value, and accuracy reduces greatly.
Summary of the invention
The utility model is in order to remedy the deficiencies in the prior art, provide a kind of fast, accurately, cheaply based on the nano particle size measuring system of Virtex-5 Series FPGA.
The utility model is achieved by the following technical solution:
Nano particle size measuring system based on the Virtex-5 Series FPGA of the present utility model is characterized in that: comprise the light source, input path, scattering light path, photodetector, digital correlator and the signal processing system that set gradually;
It is the green laser of 532nm that light source adopts wavelength;
Input path is made up of polaroid and incident lens, and the incident lens are used for obtaining as far as possible little scattering volume;
Two micropores of scattered light route and an optical filter are formed, and optical filter is used for the filtering parasitic light to improve signal to noise ratio (S/N ratio);
Photodetector is mainly realized by end window photomultiplier, and weak one is converted into electric signal, through after amplification, examination and the shaping, becomes the train of impulses of Transistor-Transistor Logic level form;
Digital correlator is realized by the FPGA digital correlator of Virtex-5 series, photon pulse is carried out high speed acquisition, and finish the computing of light intensity autocorrelation function;
Signal processing system mainly is computing machine, cooperates Visual C++ software to form;
Photodetector, digital correlator, computing machine connect successively.
The laser that laser instrument sends shines in the sample cell that fills sample solution after focusing on through polaroid, incident lens, the scattered light of particle scattering enters photodetector through micropore and optical filter, the photo-signal of photodetector output becomes the train of impulses of Transistor-Transistor Logic level form after amplification, examination and shaping, send in the digital correlator and gather, and in digital correlator, calculate its light intensity autocorrelation function, by serial ports correlation function value is sent into computing machine then, and then calculate the size of nano particle diameter in the solution.
The utility model compare with domestic existing nano particle size measuring technique have the real-time height, advantage such as precision height, good reproducibility, specific as follows:
(1) grain diameter measurement method of the present utility model adopts dynamic light scattering method, it is wide that dynamic light scattering method has applicability, grain diameter measurement haves a wide reach, measure accurately, precision height, fast, the good reproducibility of speed, the tested particle that need know and the physical parameter amount of dispersion medium are few, therefore can guarantee real-time, repeatability and the accuracy of grain diameter measurement.
(2) input path in the utility model is made up of polaroid and condenser lens, and scattered light route optical filter and two micropores are formed, and the effect of incident lens is to obtain as far as possible little scattering volume, and optical filter is used for the filtering parasitic light to improve signal to noise ratio (S/N ratio).
(3) photodetector in the utility model adopts the more additional peripheral circuits of end window photomultiplier to realize, end window photomultiplier has characteristics such as quick response, antijamming capability are strong, low noise, high detection efficiency, light signal can be converted into can detected electric signal, peripheral circuit can further be converted into this electric signal the train of impulses of stable Transistor-Transistor Logic level form, for the accuracy that guarantees pulse collection and related operation lays the foundation.
(4) the utility model adopts the Virtex-5 Series FPGA to realize the high-speed figure correlator.Because the method for operation of FPGA walks abreast, and the Virtex-5 Series FPGA adopts the senior silicon chip group compound module of second generation ASMBL() row formula framework, the range of choice that ratio FPGA series before this provides is big, compare with the Virtex-4 device, one to two speed step of average lifting, this can guarantee that related operation can real-time carrying out, satisfied nano particle size measure for
NsThe demand in level sampling time has guaranteed the degree of accuracy of related operation simultaneously, and this is that the chip of serial operation such as single-chip microcomputer is not available.
(5) computing machine mainly is to cooperate Visual C++ software to finish the realization of particle diameter inversion algorithm in this measuring system, and by the image of interface display correlation curve and the size of particle diameter, the particle diameter inversion algorithm adopts the Levenberg-Marquardt algorithm, can realize that nano particle diameter measures fast and accurately.The Levenberg-Marquardt algorithm is the effective ways that solve known nonlinear relation Estimation of Parameters problem, it introduces damping factor on Gauss-Newton method basis, absorbed the advantage of Gauss-Newton method optimizing at one stroke, relax to some extent choosing on the scope of initial value again, have global convergence, can realize that nano particle diameter measures fast and accurately.
Embodiment
Accompanying drawing 1 is a kind of concrete enforcement of the present utility model.
Nano particle size measuring system based on the Virtex-5 Series FPGA of the present utility model comprises the light source, input path, scattering light path, photodetector, digital correlator and the signal processing system that set gradually;
It is the green laser of 532nm that light source adopts wavelength;
Input path is made up of polaroid and incident lens, and the incident lens are used for obtaining as far as possible little scattering volume;
Two micropores of scattered light route and an optical filter are formed, and optical filter is used for the filtering parasitic light to improve signal to noise ratio (S/N ratio);
Photodetector is mainly realized by end window photomultiplier, and weak one is converted into electric signal, through after amplification, examination and the shaping, becomes the train of impulses of Transistor-Transistor Logic level form;
Digital correlator is by the FPGA(field programmable gate array of Virtex-5 series) the digital correlator realization, photon pulse is carried out high speed acquisition, and finish the computing of light intensity autocorrelation function;
Signal processing system mainly is computing machine, cooperates Visual C++ software to form;
Photodetector, digital correlator, computing machine connect successively.
The high-speed figure correlator mainly contains the control module that resets, clock control module, photon counting module, related operation module, fifo module and serial communication modular and forms, the control module that resets can send corresponding instruction to FPGA by computing machine, it is resetted, can remove the design of hardware reset circuit from, and more more convenient than hardware reset, stable; Clock control module mainly is made up of phaselocked loop and some frequency division modules, be used for providing the clock signal of each module, but also can send corresponding instruction to FPGA by computing machine, make it carry out frequency division automatically, the sample frequency that obtains wanting, to determine best sample frequency, guarantee the accuracy of particle diameter inverting; The photon counting module adopts double counters, can realize photon pulse is carried out seamless counting, has guaranteed the accuracy of related operation; The related operation module is made up of many groups linear dependence computing module, the sampling time is constant in the group, the sampling time doubles between group, and every group of related operation module is made up of IODELAY module, shift register module, multiplication module, accumulator module, preposition adder Module and supervision channel module; Fifo module mainly is used between related operation module and the serial communication modular and plays buffer action; Serial communication modular is used for realizing communicating by letter between FPGA and the computing machine.
The laser that laser instrument sends shines in the sample cell that fills sample solution after focusing on through polaroid, incident lens, the scattered light of particle scattering enters the photomultiplier of photodetector through micropore and optical filter, the photo-signal of the output of photomultiplier is after amplification, examination and shaping, become the train of impulses of Transistor-Transistor Logic level form, how many sizes of light intensity is represented with the umber of pulse in the unit interval.Train of impulses is sent in the double counters of FPGA digital correlator and is gathered, and digital correlator is done real-time related operation to the particle scattered light signal and handled, and realizes the real-time operation of light intensity autocorrelation function in other words.When computing machine sends the instruction that transmits data to FPGA, FPGA just is transferred to computing machine to the result of related operation through serial ports, computing machine cooperates Visual C++ software that related data is changed storage accordingly, carry out normalized earlier, utilize the Levenberg-Marquardt algorithm to carry out curve fitting then, obtain half-linear width

, substitution formula (1) is obtained nano particle diameter
dSo both accelerate speed, also guaranteed repeatability and accuracy.
Particle diameter
dIt is the important parameter of describing nano particle.Particle diameter is the diameter of nano particle, when certain physical characteristics of tested particle or the homogenous spheres of physical behavio(u)r and a certain diameter (or combination) are the most close, just the equivalent grain size of the diameter of this spheroid (or combination) as tested particle.Generally particle diameter is divided into the single particle size that represents the individual particle size and the mean grain size that represents the population of being formed by particles with different sizes.The method for solving of particle diameter d is seen formula (1).
Wherein
Be the translation coefficient of diffusion of particle in solution,
Be Scattering of Vector,
Be incident light wavelength in a vacuum,
For incident light and at the formed angle of the scattered light of detector direction,
Be the thermodynamic temperature of solution,
Be the refractive index of solution,
Be the coefficient of viscosity of solution,
Be Boltzmann constant, these parameters are constant.
Be the half-linear width of scattered light spectrum, this parameter can obtain by correlation curve is carried out match.
Fig. 2 has provided nano particle size measuring system flow process, and Fig. 3 has provided particle diameter and found the solution flow process.Concrete steps are as follows.
(1) light source employing wavelength is the green laser of 532nm, and the grain diameter measurement method adopts dynamic light scattering method;
(2) laser that sends of laser instrument is in input path shines the sample cell that fills sample solution, input path is made up of polaroid and condenser lens, the scattered light of particle scattering enters photodetector through optical fiber, scattered light route optical filter and two micropores are formed, the effect of incident lens is to obtain as far as possible little scattering volume, optical filter is used for the filtering parasitic light improving signal to noise ratio (S/N ratio), incident light be taken as 90 degree at the formed angle of the scattered light of detector direction;
(3) photodetector mainly adopts the more additional peripheral circuits of end window photomultiplier to realize, spectral response range is 300nm~650nm, peak wavelength is 420nm, the photodetection useful area is φ 24mm, have characteristics such as quick response, antijamming capability are strong, low noise, high detection efficiency, light signal can be converted into can detected electric signal, peripheral circuit comprises amplifying circuit, discriminator circuit and shaping circuit, this electric signal further can be converted into the train of impulses of stable Transistor-Transistor Logic level form.
(4) Virtex-5 Series FPGA links to each other with computing machine with photodetector, finishes the realization of high-speed figure correlator, is used for photon pulse is gathered, and carries out the computing of light intensity autocorrelation function.This high-speed figure correlator can reach 128 passages, and dynamic range can reach
, being limited to 25ns under the sampling time, the particle size range that this nano particle size measuring system can accurately be measured is 1
-5
When the computing machine instruction that transmission transmits data to FPGA, FPGA just is transferred to the result of related operation in the computing machine through serial ports, obtains current light intensity auto-correlation function value:
Wherein
The expression sampling time,
Expression the
Photon pulse that inferior sampling obtains counting, in other words the
Arrive the photon pulse quantity of digital correlator in the individual sampling time,
Expression the
The photon pulse number that inferior sampling obtains.
Be total sampling number, the experimental period length overall
By formula (2) as can be seen, for obtaining complete related function curve, the correlator pulse signals is carried out periodic sampling, and with signal lag, corresponding different delayed time time point multiplies each other current sampled signal and time delayed signal, and the result is added up.The signal lag of corresponding certain delay time, phase multiply accumulating and the realization of buffer memory output in correlator are referred to as a passage.The inside schematic diagram of high-speed figure correlator as shown in Figure 4, the top layer schematic diagram of high-speed figure correlator as shown in Figure 5, the schematic diagram of related operation module is as shown in Figure 6.
(5) computing machine links to each other with the Virtex-5 Series FPGA, mainly finishes the realization of particle diameter inversion algorithm, and the Levenberg-Marquardt algorithm that namely adopts in the utility model is by image and the particle diameter of interface display correlation curve
dSize, and can deposit in the database, so that later on statistics is inquired about, relatively reached to measurement result.Below the principle of inversion algorithm is simply introduced.
In actual applications, distribute is the distribution of particle swarm more, for this class distributed granule group, light field autocorrelation function
Can not be expressed as a decaying exponential function simply, and should be expressed as a class index attenuation function and or integration, as shown in Equation (3)
Wherein,
Be normalized
Distribution function, namely
,
Formal expansion with Taylor series obtains:
Bringing formula (3) into following formula obtains:
Further be reduced to
(6)
Because light intensity autocorrelation function
, formula (6) substitution is got:
(7)
Intercept polynomial two stepwises:
(8)
Formula (8) put in order:
Can carry out curve fitting with the Levenberg-Marquardt algorithm, thereby calculate live width
, with live width
Value substitution formula (1) in, obtain particle diameter
dSize, the inversion algorithm flow process is as shown in Figure 7.