Study of fluid damping effects on resonant frequency of an electromagnetically actuated valveless micropump

Abstract

As fluid flow effects on the actuation and dynamic response of a vibrating membrane are crucial to micropump design in drug delivery, this paper presents both a mathematical and finite-element analysis (FEA) validation of a solution to fluid damping of a valveless micropump model. To further understand the behavior of the micropump, effects of geometrical dimensions and properties of fluid on the resonant frequency are analyzed to optimize the design of the proposed micropump. The analytical and numerical solutions show that the resonant frequency decreases with the slenderness ratio of the diffuser and increases with the opening angle, high aspect ratio, and thickness ratio between the membrane and the fluid chamber depth. A specific valveless micropump model with a 6-mm diameter and 65-μm thickness polydimethylsiloxane (PDMS) composite elastic membrane was studied and analyzed when subjected to different fluids conditions. The resonant frequency of a clamped circular membrane is found to be 138.11 Hz, neglecting the fluid. For a gas fluid load, the frequency is attenuated by slightly shifting to 104.76 Hz and it is significantly reduced to 5.53 Hz when the liquid fluid is loaded. Resonant frequency remarkably shifts the flow rate of the pump; hence, frequency-dependent characteristics of both single-chamber and dual-chamber configuration micropumps were investigated. It was observed that, although the fluid capacity is doubled for the latter, the maximum flow rate was found to be around 27.73 μl/min under 0.4-A input current with an excitation frequency of 3 Hz. This is less than twice the flow rate of a single chamber of 19.61 μl/min tested under the same current but with an excitation frequency of 4.36 Hz. The proposed double-chamber model analytical solution combined with the optimization of the nozzle/diffuser design and assuming the effects of damping proved to be an effective tool in predicting micropump performance and flow rate delivery.