| As an important part of microfluidic control system,micropumps are mainly used to regulate and drive microfluidic and are widely used in biomedical,aerospace and electronic chips.Aiming at the requirement of microfluidic control by on-line measurement of matrix ion concentration in agricultural culture,and the fact that most micropumps are either driven by high voltage,complex manufacturing process and low cost at present,a study of active valve micropumps based on rotating magnets was carried out to analyze their microfluidic control performance and influencing factors in order to improve the output performance and reduce manufacturing cost.The main findings of the study are as follows:(1)Analysis of micropump structure design and working principle: Firstly,by analyzing the application field,driving mode and structural characteristics of micropump,an active valve micropump based on rotating magnets is proposed and designed,and its microfluidic working principle is analyzed.Then the magnetic forces between the three-dimensional magnetic field and the array of magnets in circular magnetic space are analyzed by using equivalent magnetic load model.Based on the theory of thin plate deformation and hydrodynamics,a diaphragm deformation model and a micropump flow model are constructed.(2)Analysis of magnetic drive and output performance and influencing factors of micropumps: The multi-physical field coupling software COMSOL Multiphysics modeled the transient fluid-solid coupling of micropump driven diaphragm and conveying fluids.When the difference in magnetization angle between the circular magnetic arrays is 0～180°,the output flow is parabolic and reaches a maximum of 90°.The magnetic force between the magnets can effectively increase the output flow per unit time of the micropump,but it does not affect the frequency range of the micropump.With the decrease of micropump diaphragm thickness and the increase of pump cavity diameter,the deformation of driving diaphragm will increase and damping will decrease when the micropump works,which will lead to the gradual increase of output flow per unit of micropump and the decrease of optimal working frequency.(3)Micropump Preparation and Performance Experimental Study: The micropump body was first prepared by laser etching PMMA,the PDMS driven diaphragm was prepared by die-casting,and the micropump structures were bonded by hot pressing,die injection and thermal adhesion.The micropump sample size was 48 mm × 20 mm × 15 mm,with a pump cavity diameter of 8mm and driving diaphragm thickness of 500 um.Then a test platform was set up to test the output performance of the micropump.The optimum operating frequency of the active valve micropump was 40 Hz,the maximum output flow per unit of time of the micropump was 10.55 m L/min,and the maximum output backpressure was 1026 Pa.The performance of micropumps is influenced by the properties of the medium in which the fluid is transported,and the performance of micropumps decreases when the fluid is transported with higher density or viscosity.Finally,the micropump cutoff performance test was carried out and the maximum pressure at the entrance was457 Pa when the micropump was not working.When the inlet pressure is greater than 457 Pa,there is water leakage at the outlet of the micropump,and with the increase of the inlet pressure,the leakage flow at the outlet increases almost linearly.The active valve micropump based on rotating magnet drive has the advantages of low driving voltage,high output efficiency and simple manufacturing method.It is suitable for microfluidic control in agricultural engineering such as on-line detection of ion concentration of cultivated substrate. |
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