The Physics and Technology of Microvalves: Progress and Prospects

Microvalves have been in use for roughly thirty years. The earliest efforts focused on electrostatically- and electromagnetically-actuated microvalves for control of gas flow. Subsequently, most R&D efforts addressed the development of a variety of actuator means, using movable geometry microvalves (that is, where a solid membrane is moved toward, and away from, a valve seat) to control the flow of both liquids and gases. More recently, the advent of microfluidics (that is, the control and distribution of biologically-significant liquids) has driven the development of fixed geometry microvalves (or, more properly, fluidic gates), wherein surface or fluid phenomena (such as surface tension, electrowetting, or electro-osmosis), or fluid phase change (from solid to liquid) is used to control the flow.

This talk will look broadly at selected portions of the landscape of microvalve research and development. Particular emphasis will be given to the progress made by Redwood Microsystems in the development of simple, single-valve products, as well as complex, multi-valve/multi-channel, integrated compressible gas flow distribution and control systems. Examples of advances made will be drawn from some of the achievements made at Redwood, including: fundamental modeling of flow through an orifice, and through a microvalve; lumped-element, multiphysics modeling of thermopneumatic microvalves; design of silicon membranes with complex geometries; fundamental reliability of silicon membranes and microvalves; novel sensor structures based on thin silicon membranes; high-performance mass flow control systems with self-diagnosis and auto-calibration; and micro-pneumatic logic.

The talk will conclude with a speculative view toward present and future applications of microvalves, and prospects for further advancement of microvalve physics and technology.