Microvalves

Numbering up microchannels to large-scale capacity reactors is driven by a rigorous understanding of pressure drop in every parallel circuit Passive flow distribution permits sufficient flow to each channel. No serious evaluation of microvalves or actuators has been undertaken for high-capacity systems with thousands to tens... 

Ayhan, A.E. 2002. Design of a piezoelectrically actuated microvalve for flow control in fuel cells. M.S. Thesis, University of Pittsburgh, School of Engineering, Pittsburgh, PA. 

A number of devices have been made based on this microvalve system. One of the first devices built was a cell sorter on a chip. By manipulating nanoliters of fluid, different strains of fluorescently activated E. coli were introduced, sorted according to their fluorescent properties, recovered from the chip, and cultured. 

Heukel, S. Silicon Microvalve Fabricated on Bimetallic Diaphragms, Sensors, 4 (December 1991). 

Initially, the main goal of miniaturization was to enhance the analytical performance of devices rather than to reduce their size. However, it was found that such tools had the advantage of reducing the consumption of sample and reagents, for example, the smaller consumption of carrier and mobile phases in separation systems (the first analytical system to be miniaturized was the gas chromatograph). Research in this area focused on the development of components such as micropumps, microvalves, and chemical sensors. 

Several techniques for miniaturization of simple chemical and medical analysis systems are described. Miniaturization of total analysis systems realizes a small sample volume, a fast response and reduction of reagents. These features are useful in chemical and medical analysis. During the last decade many micro flow control devices, as well as the micro chemical sensors fabricated by three dimensional microfabrication technologies based on photofabrication, termed micromachining, have been developed. Miniaturized total analysis systems (pTAS) have been studied and some prototypes developed. In microfabricated systems, microfluidics , which represent the behavior of fluids in small sized channels, are considered and are very important in the design of micro elements used in pTAS. In this chapter microfluidics applied flow devices, micro flow control devices of active and passive microvalves, mechanical and non-mechanical micropumps and micro flow sensors fabricated by micromachining are reviewed. 

Keywords Microfluidics, micro total analysis system (pTAS), microvalve, micropump, micro flow sensor. 

Microvalves are classified into two categories active microvalves (with an actuator) and passive microvalves (without an actuator). Micropumps are also... 

In this chapter, first the simple pTAS concepts for chemical and medical analysis using mechanical micro components are presented. Micro components of pTAS considering the microfluidics are described next. The micro flow control devices of microvalves, micropumps and micro flow sensors are then reviewed. 

Disposable pTAS will be ideal for medical use [14]. However, the high fabrication cost of sophisticated pTAS including micropumps and microvalves is a real problem. One of the basic components of medical pTAS taking this into account is illustrated in Fig. 2. A detector cell consists of micro sensors and a 3-way microvalve is placed at the sample inlet. Flow is controlled by a suction pump and an injection pump connected to the detector cell. The calibration solution flow is also controlled by an individual pump and a 3-way valve. In this system, only sample flow reaches the detector cell. The upper parts of the system are free from contamination and corrosion so that they can be reused many times, while the detector cell has to be disposed of. To realize this system, a 3-way microvalve which can handle whole blood is indispensable. A separable channel type microvalve whose channel part is disposable while actuator part is reusable is useful for the 3-way microvalve of the detector cell [15]. Mechanically fixed stack structures including disposable parts are useful in many medical pTAS. 

Almost all kinds of actuators described above have been applied to fabricate gas flow control microvalves [1, 25]. However, for liquid flow control only a few microvalves have been developed. 

Fig. 9. Structure of the 3-way microvalve using the piezoelectric stack actuator [26]...

Fig. 11. Structure of the microvalve using SMA coil and bias spring actuator [12]...

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