A proposed normally-closed microvalve would contain a piezoelectric bending actuator instead of a piezoelectric linear actuator like that of the microvalve described in the preceding article. Whereas the stroke of the linear actuator of the preceding article would be limited to ≈6 μm, the stroke of the proposed bending actuator would lie in the approximate range of 10 to 15 μm — large enough to enable the microvalve to handle a variety of liquids containing suspended particles having sizes up to 10 μm. Such particulate-laden liquids occur in a variety of microfluidic systems, one example being a system that sorts cells or large biomolecules for analysis.

Bimorph and Unimorph Versions of a microvalve actuated by a piezoelectric bender have been proposed. The bimorph version could operate at higher pressure; the unimorph version would be more compact.
In comparison with the linear actuator of the preceding article, the bending actuator would be smaller and less massive. The combination of increased stroke, smaller mass, and smaller volume would be obtained at the cost of decreased actuation force: The proposed actuator would generate a force in the approximate range of 1 to 4 N, the exact amount depending on operating conditions and details of design. This level of actuation force would be too low to enable the valve to handle a fluid at the high pressure level mentioned in the preceding article.

The proposal encompasses two alternative designs — one featuring a miniature piezoelectric bimorph actuator and one featuring a thick-film unimorph piezoelectric actuator (see figure). In either version, the valve would consume a power of only 0.01 W when actuated at a frequency of 100 Hz. Also, in either version, it would be necessary to attach a soft elastomeric sealing ring to the valve seat so that any particles that settle on the seat would be pushed deep into the elastomeric material to prevent or reduce leakage.

The overall dimensions of the bimorph version would be 7 by 7 by 1 mm. The actuator in this version would generate a force of 1 N and a stroke of 10 μm at an applied potential of 150 V. The actuation force would be sufficient to enable the valve to handle a fluid pressurized up to about 50 psi (≈0.35 MPa).

The overall dimensions of the unimorph version would be 2 by 2 by 0.5 mm. In this version, an electric field across the piezoelectric film on a diaphragm would cause the film to pull on, and thereby bend, the diaphragm. At an applied potential of 20 V, the actuator in this version would generate a stroke of 10 μm and a force of 0.01 N. This force level would be too low to enable handling of fluids at pressures comparable to those of the bimorph version. This version would be useful primarily in microfluidic and nanofluidic applications that involve extremely low differential pressures and in which there are requirements for extreme miniaturization of valves. Examples of such applications include liquid chromatography and sequencing of deoxyribonucleic acid.

This work was done by Eui-Hyeok Yang of Caltech for NASA’s Jet Propulsion Laboratory.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to

Intellectual Assets Office JPL Mail Stop 202-233 4800 Oak Grove Drive Pasadena, CA 91109 (818) 354-2240 E-mail: This email address is being protected from spambots. You need JavaScript enabled to view it.

Refer to NPO-30563, volume and number of this NASA Tech Briefs issue, and the page number.

Topics:
Elastomers Emissions Exhaust emissions Mechanical Components Mechanics Motion Control Particulate matter (PM) Parts Polymers Pressure Seals and gaskets Seats and seating Sensors and actuators Valves
This Brief includes a Technical Support Package (TSP).
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Larger-Stroke Piezoelectrically Actuated Microvalve

(reference NPO-30563) is currently available for download from the TSP library.

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Motion Control Tech Briefs Magazine

This article first appeared in the December, 2003 issue of Motion Control Tech Briefs Magazine (Vol. 27 No. 12).

Read more articles from the archives here.

Overview

The document outlines a technical support package from NASA's Jet Propulsion Laboratory (JPL) detailing the development of a novel microvalve actuated by a miniaturized piezoelectric bender actuator. This innovation addresses the limitations of existing micro-electromechanical systems (MEMS) valves, which often fail to meet the necessary requirements for pressure range, response time, and leak rates in microfluidic applications.

The primary motivation for this development stems from the need for microvalves that can handle liquids containing particulates, particularly those with sizes ranging from 5 to 10 microns. Such applications are prevalent in fields like DNA sequencing and cell sorting. Current commercial MEMS valves are typically too bulky, consume excessive power, and do not operate effectively under the required pressure conditions (approximately 50 psi).

The proposed solution is a miniaturized valve design that utilizes a bimorph piezoelectric bender actuator. This actuator is capable of achieving a high stroke of approximately 15 microns while consuming only 0.01 watts of power at a frequency of 100 Hz. The total volume of the valve is remarkably small, measuring just 0.05 cm³, making it suitable for compact liquid systems. The design aims to provide a fast response time (under 50 ms) and moderate to high pressure handling capabilities, addressing the critical needs of modern microfluidic systems.

The document also highlights the novelty of using a bending mode actuator, which occupies less space and weight compared to traditional piezoelectric stack actuators. However, it notes that this design generates a smaller block force, which may not be sufficient for certain high-pressure applications, such as micro-propulsion systems. Despite this limitation, the actuator is deemed effective for most microfluidic systems requiring high stroke capabilities.

In summary, this technical report presents a significant advancement in microvalve technology, showcasing a solution that combines miniaturization, efficiency, and functionality. The development is expected to enhance the performance of microfluidic systems, paving the way for more effective handling of liquids with particulates in various scientific and industrial applications.