Research On Metal Particle Detection In Oil Based On The Magnetic Field Theory Of Micro Inductive Coil

As the blood of mechanical equipment,lubrication oil can be used to cool,clean,alleviate the wear of machine component and so on.The lubrication oil is polluted when the mechanical equipment is working,thus,the normal operation of machinery and equipment is affected.Among all of the contaminants in the oil,solid particle is the main cause of mechanical wear,and the metal particle is most harmful to mechanical equipment.Though distinguishing the ferrous and non-ferrous metal particles,counting the number and measuring the size of the particles by oil detection,the source of particle and degree of wear can be evaluated.Through the oil detection method,equipment maintenance costs can be saved;equipment reliability can be improved;failure probability can be reduced;and service life of equipment can be extended.Inductance detection is one of the commonly used metal particle detection methods,combined with the microfluidic chip technology,which can distinguish ferromagnetic and non-ferromagnetic metal particles,measure the size of metal particles and count the particles.According to the National Natural Science Foundation of China,based on the electromagnetic theory,the influence of the ferromagnetic and non-ferromagnetic metal particles in microfluidic channel on the original electromagnetic field distribution of the inductive coil is analyzed.The electromagnetic models about the ferromagnetic and non-ferromagnetic metal particles are established,combined with the finite element method and experimental verification,several contents are researched as following:(1)Magnetization theory and Maxwell equations are used to establish theoretical models of detecting ferromagnetic metallic particles and non-ferromagnetic metallic particles with inductive coil,respectively;the inductance change is obtained by the theoretical calculation using mathematical calculation software Mathematica.And the theoretical analyses are verified by simulation and experimental researches.(2)The function of inductance change of coil is related to the electrical conductivity of metal particle material is obtained based on the magnetic vector.According to the result of experimental measurement,the inductance change of coil is obtained when the non-ferromagnetic metal particle passes through the coil.Then,the electrical conductivity of the metal particle is obtained based on the function and experimental result.Thus,the kinds of non-ferromagnetic metal particles can be differentiated.(3)The equivalent circuit method is introduced to analyze the working principle and the electromagnetism characteristic of inductive microfluidic chip in detecting metal particle,which is representing the coupling between the inductive coil and the metal particle.The part of the power supply(AC excitation)is equivalent to the internal circuit,the inductor and the metal particles are equivalent to the external circuit.The equivalent circuit method is introduced to improve the detection sensitivity of ferromagnetic and non-ferromagnetic metal particles.(4)The mathematical model of coil inductance change affected by the relative velocity of metal particles is established,and the model is verified by experiment.The mathematical model of coil inductance change affected by the shape of metal particles is established,and the model is verified by the experiment.The influence of the radial distribution of metal particle on the output of inductance change is studied based on the relationship between the magnetic induction inside the coil and the internal radial of coil;Based on the research result,the structure of chip is improved by the design of two micro coils focusing.