A microvalve is microscale

valve A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or slurries) by opening, closing, or partially obstructing various passageways. Valves are technically fittings ...

, i.e. a

microfluidic Microfluidics refers to the behavior, precise control, and manipulation of fluids that are geometrically constrained to a small scale (typically sub-millimeter) at which surface forces dominate volumetric forces. It is a multidisciplinary field tha ...

two-port component that regulates the flow between two fluidic ports. Microvalves are basic components in microfluidic devices, such as Labs-on-a-chip, where they are used to control the fluidic transport. During the period 1995-2005, a lot of

Microelectromechanical systems Microelectromechanical systems (MEMS), also written as micro-electro-mechanical systems (or microelectronic and microelectromechanical systems) and the related micromechatronics and microsystems constitute the technology of microscopic devices, ...

-based microvalves were developed. Microvalves found today can be roughly categorized as ''active'' microvalves and ''passive'' microvalves. Based on the medium they control, microvalves can be divided into gas microvalves and liquid microvalves. Based on their initial mode, microvalves can be divided into normally open, normally closed and bistable microvalves.

Types of microvalves

Active microvalves

Active mechanical microvalves consist of mechanically movable membrane or boss structure, coupled to an actuation method, that can close of an orifice, thus blocking the flow path between the inlet and outlet ports. The actuator can either be an integrated magnetic, electrostatic, piezoelectric or thermal

microactuator A microactuator is a microscopic servomechanism that supplies and transmits a measured amount of energy for the operation of another mechanism or system. As a general actuator, following standards have to be met: * Large travel * High precision * Fa ...

, a "smart" phase change, e.g.

Shape-memory alloy In metallurgy, a shape-memory alloy (SMA) is an alloy that can be deformed when cold but returns to its pre-deformed ("remembered") shape when heated. It may also be called memory metal, memory alloy, smart metal, smart alloy, or muscle wire. P ...

, or

rheological Rheology (; ) is the study of the flow of matter, primarily in a fluid (liquid or gas) state, but also as "soft solids" or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an applie ...

material, or an externally applied actuation mechanism, such as an external magnetic field or pneumatic source.

Passive microvalves

Passive microvalves are valves for which the operational state, i.e. open or close, is determined by the fluid they control. Most common passive microvalves are flap valves, membrane microvalves and ball microvalves.

Microvalve applications

Gas Microvalves

Controlling a gas flow with MEMS microvalves has the following general benefits: the integration of the actuation mechanism with the other microvalve components allows component miniaturization; and the small scale of the component results in a rapid response time and a low-power consumption. However, despite the potential for cost-efficient batch fabrication offered by microelectromechanical systems (MEMS) technologies, gas microvalves have so far failed to reach the critical cost-per-performance ratio needed for a wide adoption of this technology.

Check valves

Most check valves, are incorporated in inlets and outlets of reciprocal displacement

micropump Micropumps are devices that can control and manipulate small fluid volumes. Although any kind of small pump is often referred to as micropump, a more accurate definition restricts this term to pumps with functional dimensions in the micrometer ran ...

s, where they provide the liquid rectification needed for the valve to have a net pump flow in one direction.

References

{{reflist Valves Microfluidics