Figure 1. The Previous Version of the Valve, like the present version, was opened by applying a voltage that caused the piezoelectric actuator to contract slightly.
Efforts are underway to implement an improved design of the device described in "Normally Closed, Piezoelectrically Actuated Microvalve" (NPO-20782), NASA Tech Briefs, Vol. 25, No. 1 (January 2001), page 39. To recapitulate: This valve is being developed as a prototype of valves in microfluidic systems and other microelectromechanical systems (MEMS). The version of the valve reported in the cited previous article (see Figure 1) included a base (which contained a seat, an inlet, and an outlet), a diaphragm, and an actuator. With the exception of the actuator, the parts were micromachined from silicon. The actuator consisted of a stack of piezoelectric disks in a rigid housing. To make the diaphragm apply a large sealing force on the inlet and outlet, the piezoelectric stack was compressed into a slightly contracted condition during assembly of the valve. Application of a voltage across the stack caused the stack to contract into an even more compressed condition, lifting the diaphragm away from the seat, thereby creating a narrow channel between the inlet and outlet.

The improvements are being pursued because of the following deficiencies of the previous version of the valve:

  • The valve-seat design was marginal in that dirt particles easily became stuck between the diaphragm and the tops of sealing rings, contributing to leakage.
  • By virtue of the placement of the inlet orifice under the actuator, the inlet flow and pressure opposed the sealing force, thereby reducing the ability to seal against high pressure with low leakage.
  • The piezoelectric actuator stack could not be machined as precisely as could the silicon parts. As a consequence, if the valve cap (the item designated the actuator housing in Figure 1) was flexible and the piezoelectric stack was thicker than the actuator housing, then the valve could not be actively opened. If the piezoelectric stack was thinner than the actuator housing, then the valve would always be open.

Figure 2. The Present Version of the Valve features a pressure-aided-sealing design and other improvements intended to overcome the deficiencies of the previous version.
Figure 2 depicts some aspects of the improved version of the valve. The inlet is repositioned from the previous version, such that now the inlet flow and pressure contribute to sealing and thus to the desired normally-closed mode of operation. The piezoelectric actuator stack and the cap have been redesigned to conform to this pressure-aided-sealing design. The valve seat has been redesigned to replace the former blunt-cross- section sealing rings with knife-edge sealing rings that would be less susceptible to trapping of particles between the rings and the diaphragm. The micromachined parts of the improved design are assembled by roomtemperature indium hermetic bonding.

This work was done by Eui-Hyeok Yang and David Bame of Caltech for NASA's Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp  under the Mechanics category. NPO-30158

Topics:
Assembling Emissions Exhaust emissions Manufacturing processes Mechanical Components Mechanics Microelectromechanical devices Particulate matter (PM) Parts Pressure Seals and gaskets Seats and seating Sensors and actuators Soils Valves
This Brief includes a Technical Support Package (TSP).
Document cover
Improved Piezoelectrically Actuated Microvalve

(reference NPO-30158) is currently available for download from the TSP library.

Don't have an account?

Magazine cover
NASA Tech Briefs Magazine

This article first appeared in the January, 2002 issue of NASA Tech Briefs Magazine (Vol. 26 No. 1).

Read more articles from the archives here.

Overview

The document discusses the development of an improved piezoelectrically actuated microvalve, aimed at enhancing microfluidic systems and micro-electromechanical systems (MEMS). This project, conducted by NASA's Jet Propulsion Laboratory (JPL), builds upon a previous design described in a NASA Tech Brief from January 2001. The original valve design included a base with a seat, inlet, outlet, diaphragm, and a piezoelectric actuator. However, it faced issues such as leakage due to dirt particles getting stuck between the diaphragm and sealing rings, and a design that reduced the sealing ability against high pressure.

The new design addresses these deficiencies by incorporating a novel valve seat and a custom-designed piezoelectric actuator. The improvements focus on enhancing the sealing capability and reducing leakage rates, which are critical for applications in space environments where reliability is paramount. The new valve is designed to open under high pressure (3000 psia) and is capable of producing a sealing force greater than what is required, thanks to the actuator's strength (50 MPa).

Key innovations include a normally closed sealing feature, low-temperature indium hermetic bonding, and a detailed seat filter design that is currently under development. These enhancements are particularly important for microfluidic MEMS systems, which are being explored for applications such as micro propulsion and miniature chemistry labs in space. The document emphasizes that typical commercial-off-the-shelf (COTS) MEMS valves do not adequately address the specific needs of space applications, often relying on thermal or magnetic actuation methods that are not suitable for the required sealing performance.

The motivation behind this development stems from the need for reliable valves that can provide precise fluid control in microfluidic systems. The new valve design aims to overcome the limitations of previous models and existing commercial options, ensuring that it meets the rigorous demands of space exploration and other advanced applications.

Overall, this document outlines a significant advancement in valve technology, highlighting the ongoing efforts to improve the functionality and reliability of microvalves for critical applications in challenging environments.