Sensitivity to pumping back-pressure in a bulk acoustic wave piezoelectric positive displacement micropump

Dynamic structural and fluid flow analysis of a bulk acoustic wave piezoelectric positive displacement micropumps is carried out for the transport of water. The micropumps consist of trapezoidal prism inlet/outlet elements; the pump chamber, a thin structural layer and a piezoelectric transducer element, as the actuator. Flow contraction and expansion, through the trapezoidal prism inlet and outlet respectively, generates net fluid flow. Governing equations for the flow fields and the structural-piezoelectric bi-layer membrane motions are considered. For the compressible flow formulation, an isothermal equation of state for the working fluid is employed. Two-way dynamic coupling of forces and displacements between the solid and the liquid domains in the systems are considered where actuator deflection and motion causes fluid flow and vice-versa. In order to consider a realistic initial condition and to eliminate immediate water hammer effects the back-pressure is gradually applied on the micropump. The effects of the pumping back-pressure on the solid displacement, fluid velocity and pressure fields are investigated for pressure values 0.0 kPa to 40.0 kPa where the pressure boundary conditions include the effect of pumping resistance seen by the pump. At high back-pressures shear and normal forces imposed on the solid membranes increases. The deflection of the pump membrane attenuates yielding to reduced flow rates produced by the micropump at higher values of the back-pressure and higher order modes of the deflections are attenuated as well. The findings imply that generated flow by the pump strongly depends on the back-pressure seen by the pump. Comparison of the pumping characteristics of the micropumps operated at different back-pressures can be utilized to design MEMS based micropumps in drug delivery and biomedical applications especially if the micropump has to operate against the blood pressure of the patient.