This Tiny Valve Keeps The Pressure On
Redwood MicroSystems Inc. in Menlo Park, Calif., makes a valve the size of your thumbnail. Small but mighty, it can close against a pressure of 3,000 pounds per square inch--a feat equal to lifting 10,000 times its own mass. Combined with tiny semiconductor sensors and other electronic circuitry, the microvalve can release minute quantities of chemical reagents with precision. That may allow scientists to reduce the necessary sample size for DNA sequencing and the amount of reagent required. Such gas microvalves are now undergoing trials in hospitals, helping to maintain pressure in the stomach cavity as a surgeon operates through a tube or to regulate the flow of anesthesia during the operation.
The key to precision is a flexible silicon membrane. This is essentially a tiny pit etched in silicon and sealed between two Pyrex wafers. When heated, fluid in the pit expands, causing the membrane to flex. That precisely controls the flow of gas through a network of channels and holes in the wafer. Redwood has a three-year, $7 million cooperative research and development agreement with Lawrence Livermore National Laboratory to make valves for portable environmental monitors and other instruments.