A Lumped Element Model On The Valveless Piezoelectric Micropump With Wall-attached Jet Element

Valveless piezoelectric micropump with wall-attached jet element is a novel micro power unit,which plays an important actuated role in the microfluidics and MEMS.An accurate computational model that can simulate the function and predict the performance under specific conditions is beneficial to the design and optimization of the micropump.In this paper,a lumped element model on the valveless piezoelectric micropump with wall-attached jet element is present:A typical valveless piezoelectric micropump with wall-attached jet element is divided into two main parts,the piezoelectric actuator part and the wall-attached jet element part.The dynamic modeling and numerical simulation fitting are utilized on each part respectively,and the connection between two part is built through the volume flow rate.Based on the working principles of the micropump,an impedance analogy is used to construct a equivalent electric circuit.In this equivalent electric circuit,voltage and current represent pressure difference and volume flow rate,and resistance,capacitance and inductance indicate energy loss,potential energy variation and kinetic energy variation.An ideal transformer is employed to describe a energy conversion from electrical domain to fluidic domain.The frequency response function is obtained via circuit theory,which indicate the relationship between flow rate at the outlet and working frequency.Based on the small deflection theory of elastic thin plate,the Kirchhoff basic hypothesis is used on the double layer composite structure piezoelectric vibrator to derive the vibration displacement equation.The effective piezoelectric constant and transformer coefficient are obtained through solving the equation.Each equivalent lumped parameter of the vibration membrane is derived by analogy on momentum equation.Numerical simulations on different diffuser angles(15°,30°,45°,60°,75°)and throat widths(100μm,150μm,200μm,250μm,300μm)are carried out under different Reynolds numbers(Re=400,600,800).Results show that: the volume flowrate increases with the increase of Re;when the diffuser angle and throat width increase,the flow rate increases firstly and then decreases;there is an optimal diffuser angle and optimal throat width during the changes.The equivalent total impedance of the wall-attached jet element is obtained via fitting the simulation results.Two sample micropumps are fabricated on a silicon substrate which the diffuser angles are 30° and 45° respectively.The external characteristics experiments are carried out and the results show that: the volume flow rate increases with the increase of voltage amplitude within the acceptable strength range of vibrator;the working frequency is the key factor affects the micropump performance;the volume flow rate increases firstly and then decreases with the frequency increases,and there is an optimal working frequency that is 75Hz;the volume flow rate of 45° sample micropump is 40% higher than 30° sample micropump at the optimal frequency.Both material parameters and LEM parameters are substituted into the equivalent electric circuit,the the calculation is performed by MATLAB Simulink.Then the estimated volume flow rate at each working frequency is obtained.The trend between two curves of model calculation and experiment measurement follows a good consistency to verify the LEM model reliability.