MEMS Microvalves Research Articles

Design and characterization of a silicon MEMS microvalve for proportional flow control based on electrostatic bending actuators

AbstractWe designed a MEMS microvalve based on the nanoscopic electrostatic drive (NED) technology (Nat Commun 6:10078, 2015). NED actuators, electrostatically controlled bending beams, are implemented in a clamped-clamped configuration. A normally open plunger valve was designed and characterized. The device is manufactured from silicon. Gas flow rates of up to 37 SCCM can be proportionally controlled between 10% and 100%. A 10% leakage is always present at low backpressures (< 10 kPa) and increases to roughly 20% at 75 kPa backpressure. The structure has been tested up to backpressures of 300 kPa without damage to the structures, but the leakage increases to over 95%. Our unprecedented microvalve concept shows that it is possible to manufacture all-silicon MEMS microvalves with proportional control of the flow rate. The presented work is a proof of concept to test the capabilities of the NED technology for the use in microvalves. There are plans to decrease the leakage in future designs by introducing an additional sealing layer as well as manufacturing a shutter instead of a plunger design.

Design and simulation of MEMS microvalves for silicon photonic biosensor chip

For the early and easy diagnosis of diseases, we have proposed a silicon photonic biosensor chip with two kinds of MEMS microvalves for a multiple-item detection system. The driving voltage of the vertical type with the circular-plate capacitor structure and that of the lateral type with the comb-shaped electrode are investigated. From mechanical calculations, the driving voltage of the vertical type is estimated to be 30 V and that of the lateral type to be 15 V. The propagation loss at the intersecting waveguides of arrayed ring-resonator biosensors is also estimated. In the case of optimized intersecting waveguides, more than 67% transmittance of TE-mode light is simulated for the series connection of 20 intersecting waveguides. It is confirmed that it is possible to fabricate an 8 × 12 arrayed biosensor chip in an area of 1 × 1.5 mm2 taking the device size of the microvalves into consideration. We have, for the first time, designed a whole system, including sensors and a fluid channel with MEMS microvalves.

A piezoelectric micro control valve with integrated capacitive sensing for ambulant blood pressure waveform monitoring

We have designed and characterized a MEMS microvalve with built-in capacitive displacement sensing and fitted it with a miniature piezoelectric actuator to achieve active valve control. The integrated displacement sensor enables high bandwidth proportional control of the gas flow through the valve. This is an essential requirement for non-invasive blood pressure waveform monitoring based on following the arterial pressure with a counter pressure. Using the capacitive sensor, we demonstrate negligible hysteresis in the valve control characteristics. Fabrication of the valve requires only two mask steps for deep reactive ion etching (DRIE) and one release etch.

Magnetostatic Microvalve for High Momentum Rate Pulsed Jet Generation

A fully integrated magnetic driven MEMS Micro-valve providing pulsed jets was developed and characterized for active aerodynamic control. The device is composed of a microvalve, a magnetostatic actuator and a packaging allowing accurate positioning on the models or prototypes. The microvalve is a resonator actuated by a specific coupling between an inductive driving coil and a NdFeB permanent magnet. The generated force was optimized to provide 250mN at 0.5A. High momentum rate, fully modulated pulsed jets have been obtained in the frequency range [0 – 500Hz] with velocities up to 150m/s. The actuation method allowed a good control over the pulsed jets characteristics that reached the required values for real scale automotive and aeronautic flow control experiments.

Effects of cell-to-cell fuel mal-distribution on fuel cell performance and a means to reduce mal-distribution using MEMS micro-valves

Achieving uniform flow among the cells of a fuel cell stack plays a significant role in being able to operate at maximum capability and efficiency. This paper presents experimental data showing the importance of cell-to-cell fuel flow balancing on fuel cell performance, and a fuel cell energy management (FCEM) technique that has demonstrated the ability to improve stack performance. In a specially instrumented four-cell polymer electrolyte fuel cell that allows external control of the air, fuel, and water-cooling flows to each cell, fuel to a single cell was reduced. V– I curves collected under these unbalanced conditions are compared to curves collected when the fuel flow to each cell was balanced. Reducing the fuel flow to a single cell by 11% decreased the V– I curve cutoff load by 10%—demonstrating the degree of negative effect that unbalanced fuel flows can have on stack performance. Typical fuel cell stacks have no dynamic means to keep flows in the stack balanced between the cells, but through the use of custom-built, piezoelectric micro-valves, a simple flow control strategy, and this custom four-cell laboratory stack, the positive effects of FCEM flow balancing at three different fuel flow rates was demonstrated.

A MEMS microvalve with PDMS diaphragm and two-chamber configuration of thermo-pneumatic actuator for integrated blood test system on silicon

In this paper, a thermo-pneumatic in-channel microvalve applicable to integrated blood test system is presented. Thermo-pneumatic actuator separated in drive chamber part and thermal expansion chamber part (two-chamber configuration) is newly proposed for the purpose to reduce direct heat transfer from microheater to flow channel. Polydimethylsiloxane (PDMS) is employed as the diaphragm material for a long stroke actuation in microvalve operation and high sealing performance of liquid. It is also used as adhesive layer between glass and silicon in the structure. The microvalve with the proposed structure was fabricated. Both static and dynamic flow control characteristics were evaluated with a liquid sample (DI water) and a gas sample (N 2), respectively. A high ON/OFF ratio of liquid sample was obtained thanks to the soft PDMS diaphragm. Liquid sealing performance in the closed state was high enough for our application (<1 μL/min at 300 hPa). As a disadvantage of PDMS diaphragm, sticking problem which causes hysteresis and instability of sample flow-rate was observed. Also, the microvalve requires some improvements in its dynamic response. Some problems in actual use are remained in the present device. However, causes and countermeasures are discussed in this paper, and its high liquid sealing performance and heat shielding effect of the two-chamber configuration are very attractive for various applications including the blood test system that we have been developing.

Fabrication of a high frequency piezoelectric microvalve

The fabrication of an active MEMS microvalve driven by integrated bulk single crystal piezoelectric actuators is reported. The valve has a nine-layer structure composed of glass, silicon, and silicon on insulator (SOI) layers assembled by wafer-level fusion bonding and anodic bonding, as well as die-level anodic bonding and eutectic bonding. Valve head strokes as large as 20 μm were realized through hydraulic amplification of the small stroke of the piezoelectric actuator. A flow rate of 0.21 ml/s was obtained at 1 kHz. The fabrication, bonding and assembly process, as well as some test results are described.

MEMS microvalves to optimise reactant flows

MEMS microvalves to optimise reactant flows