The Research On Multi-channel Dynamic Light Scattering Autocorrelation System Based On FPGA

The application of nanoparticles in chemical industry,biomedicine,aerospace and other industries is of great significance.The special properties of nanoparticles depend on its scale effect.Dynamic light scattering technology can effectively characterize the particle size of nanoparticles.Autocorrelator plays an important role in dynamic light scattering technology.Its performance determines the accuracy of dynamic light scattering experimental results.In order to improve the test efficiency and accuracy of multi angle dynamic light scattering experiment,a multi-channel autocorrelation system based on FPGA is developed for signal acquisition and analysis of dynamic light scattering device in this paper.The main research contents of this paper are as follows:(1)Based on the dynamic light scattering theory,carry out research on the linear,exponential and multi-tau correlator structures,analyze the dynamic range and resolution of photon correlator under the three correlator structures.Under the structure of multi-tau correlator,develop a multi-channel dynamic light scattering autocorrelation system.(2)Develop a multi-channel dynamic light scattering autocorrelator based on FPGA.The sampling time of autocorrelator down to 100ns.The dynamic range of autocorrelator up to 10~4.The autocorrelator realizes accurate collection and data processing of four parallel high frequency signals.The autocorrelator uses FPGA to sample photon pulse signals from four scattering angles at the same time,which realizes 50MHz high-frequency pulse sampling and autocorrelation calculation.Because of the counting error of single counter,design a double counter module to ensure high-frequency lossless counting.In order to alleviate the shortage of hardware resources introduced by multi-channel parallel design,a method combining on-chip ring register with off-chip DDR3 chips is proposed to realize dynamic data storage.The PLL frequency division capability of FPGA is limited.Design the clock control module to meet the complex clock required by the design of multi-tau correlator.(3)Study the particle size inversion algorithm,and program the visualization software for inversion of nano-particle size.Study the normalization method of light intensity autocorrelation function and the calculation method of average particle size.Program the visualization software for particle size inversion,which implementing related algorithms,controlling the experimental process,receiving experimental data,and displaying experimental results(4)Connect the autocorrelator to a multi-angle dynamic light scattering device,and verify the dynamic light scattering of polystyrene particles at 50nm,100nm and200nm.The results show that the smaller the minimum correlation time,the higher the resolution of the autocorrelation function,when the minimum correlation time is0.1μs,the autocorrelation function doesn’t decay to the baseline part.As the scattering angle increases,the duration of the smoothing period before the decay of the intensity autocorrelation function decreases and the time to decay to the baseline decreases.The experimental results of multi-angle dynamic light scattering reduce the relative error of particle size measurement to 3%by further extrapolation calculation.