A MICROVALVE SYSTEM FABRICATED BY THERMOPLASTIC MOLDING

A process for the fabrication of microvalve systems by thermoplastic molding and membrane techniques has been developed. The valve system consists of three individual valves formed by two parts molded from polymethylmethacrylate PMMA and a polyimide membrane. The mold inserts were manufactured by milling of a brass substrate using a 300 mu m diameter head. The three-dimensional microstructure of the inserts consists of four different levels for valve seats, orifices, alignment pins and cavities. The overall diameter and height of the whole valve system is 7 mm and 1.9 mm, respectively. The valves are designed to be normally open. To close the valves, the pressure in an actuator chamber above the membrane is raised by a heater coil and the membrane is pressed onto the valve seat. First measurements at a difference pressure of 1000 hPa showed a rate of water flow through a single valve of 171 mu ls(-1). An actuator pressure of 180 hPa was reached by heating air with a resistive heater and continuous electrical power of 158 mW. A valve supplied with nitrogen at 130 hPa was closed by an electrical power of 116 mW.