Research On Rainbow Technique Based On Empirical Modal Decomposition Method

Empirical Mode Decomposition(EMD)method was proposed at the end of the 20th century,which is good at analyzing non-stationary and non-linear signals.The feature of this method is that it can adaptively decompose complex multi-component signals into a finite number of Intrinsic Mode Functions(IMF)and a residual component without any prior knowledge according to the characteristics of the signal itself.After more than 20 years of development,this method has its own advantages in the field of non-stationary signal decomposition.The measurement method of particles based on rainbow measurement technology(We call this Rainbow Measurement Technique in the following paragraphs)is a non-contact optical measurement method for the refractive index and diameter of small transparent or translucent particles,which can measure the particles' diameter and refractive index simultaneously.The measurement principle is based on the rainbow phenomenon in the nature,so it is called Rainbow Measurement Technology.The formation of the rainbow originates from the light shining on the droplets,some of which rays are directly reflected by the outer surface of the droplets,and some of which rays are transmitted from the outer surface and reflected by the inner surface.These rays have experienced the mutual superposition and interference of different light paths inside and outside the droplets of different times.The interference fringes formed near the rainbow angle of geometric optics are the rainbow,so the rainbow distribution has influence on the diameter and refractive index of the particles,and it's very sensitive.Rainbow Measurement Technology is widely used in the field of small particles' parameter measurement due to its advantages of non-contact,large amount of information,fast response speed and high precision.At the same time,the EMD method and the theory of Rainbow Measurement Technology are deeply studied in this paper.A Rainbow-EMD method is proposed,which can realize the high-precision on-line measurement of particles'parameters.In the rainbow signal,there is a large amount of information.This paper studied the sensitivity of different component structures in the rainbow signal to different parameters of particles.Through the different sensitivity of different components to different parameters,the empirical mode decomposition method is used to extract the complete component structures from the rainbow signal,and these components are used to realize the high-precision inversion calculation of various parameters of particles.EMD has its own irreplaceable advantages in the decomposition of rainbow signal,but there are still some problems to be solved.In this paper,every step of EMD process is analyzed,and an Improved EMD method for rainbow signal is proposed,which solves the problems such as envelope fitting,end-point divergence and mode aliasing in the decomposition process of rainbow signal.The effectiveness of Rainbow-EMD method is verified by experiments.Furthermore,based on the rainbow-empirical mode decomposition method,three kinds of measurement systems are designed for different application fields.The measurement systems cleverly use the plane mirror and slide,and use the relative rotation angle of the plane mirror to calibrate the rainbow scattering angle.This method solves the problem that the scattering angle cannot be accurately measured in the Rainbow Measurement Technology.At last,the running software based on Windows system and GUI visual graphic interface based on MATLAB software are programmed,and the online measurement of particles' parameters based on Rainbow-EMD method is realized.Through experiments,the method,rainbow signal acquisition device and software system proposed in this paper are verified.The experimental results show that the research results of this paper have good reliability and high precision.The application value in engineering is very high.