The fixed-geometry valve micropump is a seemingly simple device in which the interaction between mechanical, electrical, and fluidic components produces a maximum output near resonance. This type of pump offers advantages such as scalability, durability, and ease of fabrication in a variety of materials. Our past work focused on the development of a linear dynamic model for pump design based on maximizing resonance, while little has been done to improve valve shape. Here we present a method for optimizing valve shape using two-dimensional computational fluid dynamics in conjunction with an optimization procedure. A Tesla-type valve was optimized using a set of six independent, non-dimensional geometric design variables. The result was a 25% higher ratio of reverse to forward flow resistance (diodicity) averaged over the Reynolds number range 0 Ͻ Reഛ 2000 compared to calculated values for an empirically designed, commonly used Tesla-type valve shape. The optimized shape was realized with no increase in forward flow resistance. A linear dynamic model, modified to include a number of effects that limit pump performance such as cavitation, was used to design pumps based on the new valve. Prototype plastic pumps were fabricated and tested. Steady-flow tests verified the predicted improvement in diodicity. More importantly, the modest increase in diodicity resulted in measured block-load pressure and no-load flow three times higher compared to an identical pump with non-optimized valves. The large performance increase observed demonstrated the importance of valve shape optimization in the overall design process for fixed-valve micropumps.

Piezoelectric bimorph actuation has been successfully used in numerous types of microdevices, most notably micropumps. However, even for the simple case of circular geometry, analytical treatments are severely limited. This study utilized the finite-element method to optimize the deflection of a circular bimorph consisting of a single piezoelectric actuator, bonding material and elastic plate of finite dimensions. Optimum actuator dimensions were determined for given plate dimensions, actuator-to-plate stiffness ratio and bonding layer thickness. Dimensional analysis was used to present the results for fixed-and pinned-edge conditions in a generalized form for use as a design tool. For an optimally-thick actuator, the optimum actuator-to-plate radius ratio ranged from 0.81 to 1.0, and was independent of the Young's modulus ratio. For thin plates, a bonding layer minimally affected the optimum dimensions. The optimized actuator dimensions based on a model of an actual device were within 13% of the fixed-edge condition.

The pulsed ultrasonic Doppler velocimeter has been used extensively in transcutaneous measurement of the velocity of blood in the human body. It would be useful to evaluate turbulent flow with this device in both medical and non-medical applications. However, the complex behaviour and limitations of the pulsed Doppler velocimeter when applied to random flow have not yet been fully investigated.In this study a three-dimensional stochastic model of the pulsed ultrasonic Doppler velocimeter for the case of a highly focused and damped transducer and isotropic turbulence is presented. The analysis predicts the correlation and spectral functions of the Doppler signal and the detected velocity signal. The analysis addresses specifically the considerations and limitations of measuring turbulent intensities and one-dimensional velocity spectra.Results show that the turbulent intensity can be deduced from the broadening of the spectrum of the Doppler signal and a mathematical description of the effective sample-volume directivity.In the measurement of one-dimensional velocity spectra at least two major complicacations are identified and quantified. First, the presence of a time-varying, broad-band random process (the Doppler ambiguity process) obscures the spectrum of the random velocity. This phenomenon is similar to that occurring in laser anemometry, but the ratio of the level of the ambiguity spectrum to the largest detected velocity spectral component can be typically two to three orders of magnitude greater for ultrasonic technique owing to the much greater wavelength.Secondly, the spatial averaging of the velocity field in the sample volume causes attenuation in the measured velocity spectrum. For the ultrasonic velocimeter, this effect is very significant.The influence of the Doppler ambiguity process can be reduced by the use of two sample volumes on the same acoustic beam. The signals from the two sample volumes are cross-correlated, removing the Doppler ambiguity process, while retaining the random velocity. The effects of this technique on the detected velocity spectrum are quantified explicitly in the analysis for the case of a three-dimensional Gaussianshaped sample-volume directivity.

Micropumps that utilize fixed-valves, i.e., valves having no moving parts, are relatively easy to fabricate and inherently reliable due to their simplicity. Since fixed-valves do not close, pumps based on them need to operate in a well-designed resonant mode in order to attain flow rates and pressures comparable with other designs. However, no methodology currently exists to efficiently investigate all the design parameters including valve size to achieve optimal resonant response. A methodology that addresses this problem is 1) the determination of optimal parameters including valve size with a low-order linear model capable of nonempirical prediction of resonant behavior, and 2) the independent determination of the best valve shape for maximal valve action over a target Reynolds number range. This study addresses the first of these two steps. The hypothesis of this study is that the resonant behavior of a fixed-valve micropump can be accurately predicted from first principles, i.e., with knowledge only of geometric parameters and physical constants. We utilized a new low-order model that treats the valves as straight rectangular channels, for which the unsteady solution to the Navier-Stokes equations is exact and with which the problem was linearized. Agreement with experiment using pump-like devices with valves replaced by straight channels was found to be excellent, thereby demonstrating the efficacy of the model for describing all aspects of the pump except actual valves. Agreement with experiment using pumps with Tesla-type valves was within 20 percent. With such accuracy and without the need for empirical data, the model makes possible reliable, efficient investigation and optimization of over 30 geometric and material parameters.