A review of the state of the art in micropumping technologies for driving fluid through micro-channels is presented with a particular emphasis on small-scale cooling applications. An extensive variety of micropumping techniques developed over the past fifteen years in the literature is reviewed. The physical principles, engineering limitations, and advantages of approximately twenty different kinds of micropumps are reviewed. The available micropump-ing techniques are compared quantitatively, primarily in terms of the maximum achievable flow rate per unit cross-sectional area of the microchannel and the maximum achievable back pressure. A concise table is developed to facilitate the convenient comparison of the micro-pumps based on different criteria including their miniaturization potential, size ͑in-plane and out-of-plane͒, actuation voltage and power required per unit flow rate, ease and cost of fabrication , minimum and maximum frequency of operation, and suitability for electronics cooling. Some important performance characteristics of the micropumps, which are likely to be decisive for specific applications, are also discussed. The current state of the art in micropump design and fabrication is also comprehensively reviewed. There are 171 references cited in this review article.

/pdf/microscale-pumping-technologies-for-microchannel-cooling-56ha3rerze.pdf

Microscale pumping technologies for microchannel cooling systems

This paper presents a micro check valve that features a bulk-micromachined valve seat (with an orifice) and a new twist-up tethered Parylene-membrane. The twist-up tethers allow large membrane displacement, and thereby reduce membrane-induced flow resistance to a negligible level. Testing results confirm the excellent performance of our valves. For example, the valves have low cracking pressures (less than 0.5 kPa for nitrogen), high reverse pressure (seater than 600 kPa) and low reverse leakage (undetectable with a 0.2 ml/min flow meter resolution). Fluid flow models and analysis of the performance characteristics of the micro valves are presented.

A Parylene micro check valve

A Parylene Micro Check Valve

This paper presents the world's first surface-micromachined parylene dual-valved microfluidic system for on-chip unpowered microflow regulation. Incorporating a normally closed and a normally open passive check valve in a back-to-back configuration inside a microchannel, the dual-valved system has successfully regulated the pressure/flow rate of air and liquid without power consumption or electronic/magnetic/thermal transduction. By exclusively using parylene C (poly-para-xylylene C) as the structural material, the fabricated valves have higher flexibility to shunt flows in comparison to other conventional thin-film valves. A state-of-the-art multilayer polymer surface-micromachining technology is applied here to fabricate parylene microvalves of various designs. The parylene-based devices are completely biocompatible/implantable and provide an economical paradigm for fluidic control in integrated lab-on-a-chip systems. Design, fabrication, and characterization of the parylene dual valves are discussed in this paper. Testing results have successfully demonstrated that the microflow regulation of the on-chip dual-valved system can achieve a bandpass profile in which the pressure control range is 0-50 mmHg with corresponding flow rates up to 2 mL/min for air flow and 1 muL/min flow rate for water flow. This regulation range is suitable for controlling biological conditions in human health care, with potential applications including drug delivery and regulation of elevated intraocular pressure (IOP) in glaucoma patients

/pdf/surface-micromachined-parylene-dual-valves-for-on-chip-344srhufp6.pdf

Surface-Micromachined Parylene Dual Valves for On-Chip Unpowered Microflow Regulation

Micro-Tensile Test Technique Development and Application to Mechanical Property Determination

For identifying constitutive properties of materials used in microstructures, a micro tensile testing-machine is developed. The concept of a load frame, consisting of two parallel positioned springs is used in designing the micro tensile testing-machine. The load frame is installed in a conventional tensile testing machine. The two parallel springs ensure axial loading of the specimen, even if the pull rods of the testing machine should not be absolutely axial. First experimental results indicate that this testing-system can be used successfully for determining constitutive properties of microspecimens.

Tensile testing device for microstructured specimens

The combination of a stiff titanium membrane and a flexible polyimide membrane was used to form a check valve for a micropump. This work is concerned with calculating the performance of such a microvalve and modifying its design so that instead of acting as an inlet valve, it functions as an outlet valve. It will be demonstrated here by application of the finite element method how design solutions can be found to this problem. Both the deflection behavior of the microvalve membrane exposed to the pressure and the stresses generated at the clamping points of the membrane structures have been calculated.

http://iopscience.iop.org/article/10.1088/0960-1317/5/3/004/pdf

Development of passive microvalves by the finite element method

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Tensile testing device for microstructured specimens

Development of passive microvalves by the finite element method