Electrostatic micropump

Fig. 6.118. Electrostatic micropump Vibration diaphragm with piezo- Pump chamber...

Bourouina T, Bosseboeuf A, Grandchamp JP (1997) Design and simulation of an electrostatic micropump for drug-delivery applications. J Micromechan Microengin 7 186-188... 

An additional advantage of the integrated circuit technology is the ability to integrate the various components, such as the transducer, reactor, valve, pump etc., within the electronic system, forming refined flow-analysis systems on silicon wafers. Several approaches, such as electrostatic, electromagnetic, piezoelectric, thermopneumatic and thermoelectric can be employed for force transduction in the microvalves, these are also applicable to micropumps. Based on these approaches, two versions of micropumps have been developed. These are connected in parallel the first pump (dual pump) is activated with periodic two-phase voltage, while the second pump (the buffer pump) is driven by two piezoelectric actuators. Microsensors of two kinds are described below a thermopile based- and a thermistor based microbiosensor. 

A review of micro-electromechanical systems (MEMS)-based delivery systems provides more detailed information of present and future possibilities (52). This covers both micropumps [electrostatic, piezoelectric, thermopneumatic, shape memory alloy bimetallic, and ionic conductive polymer films (ICPF)] and nonmechanical micropumps [magnetohydrodynamic (MHD), electrohydrodynamic (EHD), electroosmotic (EO), chemical, osmotic-type, capillary-type, and bubble-type systems]. The biocompatibility of materials for MEMS fabrication is also covered. The range of technologies available is very large and bodes well for the future. 

Fig. 2 Schematic illustration of the principal types of membrane actuations in micropump, (a) Thin-film piezoelectric actuation, (b) stack piezoelectric actuator, (c) parallel plate electrodes for electrostatic actuation, (d) thermopneumatic actuation using thermal expansion of a secondary working fluid...

Leaks, back pressure, and actuator dynamics all influence the performance of peristaltic pumps. Leaks and back pressure effects will alter the distribution of fluid as actuators open and close. The dynamics of the actuators determines the maximum actuatitm rate, which in turn limits the maximum flow rate. These effects can be incorporated into lumped-parameter models for analysis and simulation. We do not pursue this further in this entry, but refer the reader to the literamre. One general approach is presented in Ref. [7]. Also relevant for further smdy are Refs. [6, 8], and [13], which present dynamic models for pneumatic and electrostatic pumps, respectively. All of these works are applied to liquid pumps. For gas pumps, or robustness to bubbles, compressibility becomes a factor. Some considerations of micropumps for compressible fluids may be found in Ref. [1]. Finite-element analysis of individual chambers can also be used to obtain detailed predictions of pump dynamic performance. 

A second topic paralleling microvalves is the development of micro dosing elements and micropumps. The developments are concentrated primarily on the miniaturized diaphragm pump. These micropumps normally consist of a displacement diaphragm driven periodically using piezoelectric, thermal or electrostatic principles, and two passive check valves that direct the flow of liquid from the inlet to the outlet. 

The electrostatic actuation for membranes in micropumps provides several advantages fast response time, compatibility with micromachining techniques, ability to operate at high frequencies and good reliability however, electro-... 

Mechanical pumping Micromechanical pumps are usually based on the movement of a membrane, which results in periodic delivery of a fluid. The actuation schemes utilized for moving the membrane of a pump include piezoelectric, electrostatic, thermopneumatic, pneumatic, and electromagnetic devices, and shape memory alloys and electro wetting. The resulting fluid motion is pulsed, not continuous. The rotary displacement micropump is an example of a mechanical pump not based on membrane movement. External syringe... 

For an electrostatically activated micromembrane pump fabricated by bulk micro-machining transient measurements of the pump chamber pressure and the inlet and outlet pressures were made. From these values also the time dependent flow rate can be deduced. A complex dynamic behaviour can be observed, with a low frequency oscillation of the maximum pressure. Measurements can be compared and predicted with the results of an simulation tool PUSI for micropumps connected to a peripheral fluid system. 

In the past decade a technology known as micromachining has developed out of IC technology ll. It uses the same techniques, but instead of fabricating electronic circuits on a chip, three dimensional physical structures on a micrometer scale can be made. Intriguing devices such as 100 micrometer electrostatic motors, tweezers, bridges and oscillating beams, 10 nm filters, micropumps and valves have all l n made in silicon and other IC compatible materitds. 

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