MEMS Valve Research Articles

Development of an electrostatically-driven fast pneumatic MEMS valve with lower driving voltage

Development of an electrostatically-driven fast pneumatic MEMS valve with lower driving voltage

Emulation of semi-active flow control for evaporator superheat regulation

This paper considers superheat control of a vapor compression cooling cycle. Earlier research presented a hybrid expansion valve (HEV) that combines fast-acting mechanical pressure control with a slower electronic controller to regulate superheat, providing significant improvements in superheat control over standard valves. This paper shows that these improvements can be recreated with a simpler implementation of purely electronic control and a single expansion valve actuator. Simulations explore the actuator requirements, and experiments using a commercially available thermally-actuated MEMS valve show that the control architecture is suitable for both single and multiple evaporator systems, provided the actuator is fast enough.

Single-use MEMS sealing valve with integrated actuation for ultra low-leak vacuum applications

The design, modeling, fabrication and successful demonstration of a bulk-micromachined MEMS valve that enables high gas flow rates of hundreds of sccm in its initial open state and ultra low-leak, permanent sealing against gas flow once closed are demonstrated. When the valve is open, a high aspect ratio ring of solder surrounds its flow orifice without blocking the flow path. When the valve is thermally actuated by an integrated resistive heater, the solder melts and reflows, creating an irreversible seal over the flow orifice. The flow orifice is formed in a silicon ‘island’ that is supported on a thermally-insulating membrane to limit heat conduction to the surrounding silicon and to minimize the input power that is needed to close the valve. The valve’s measured open flow rate is up to approximately 400 sccm. The flow orifice is observed to seal when about 0.3 W of power are input to the resistive heater. To within the measurement uncertainty, the measured leak rate during valve testing is comparable to the measured leak rate when flow is measured through a solid plate, indicating that the valve’s leakage is less than the test system’s parasitic leakage and outgassing. The minimum, average, and maximum values of difference between the valve leak rate and the system’s parasitic leak rate are 0 sccm, 0.65 × 10–4 sccm, and 1.65 × 10–4 sccm respectively when a 1 atmosphere pressure difference is applied across the valve. The average value corresponds to an open-to-closed flow rate ratio of greater than 6 × 106. This compact sealing valve may be combined with low and high vacuum micropumps to enable MEMS vacuum systems with both initial rough evacuation and long-term high vacuum maintenance capabilities.

Development of a ‘bi-layer lift-off’ method for high flow rate and high frequency Nitinol MEMS valve fabrication

This paper presents modeling, fabrication and testing results for a high flow rate and high frequency nickel titanium alloy (Nitinol) MEMS valve. ANSYS® is used to evaluate several Nitinol MEMS valve structural designs with the conclusion that a pentagonal flap with five legs produces higher frequencies and higher strengths without the inherent rotation problem present in four-leg designs. The Nitinol penta-leg design was fabricated using a novel bi-layer lift-off method. A polymethylglutarimide (PMGI) polymer layer is initially used as an underlayer while a chromium layer is used as a top layer to produce a non-rotational ortho-planar Nitinol MEMS valve array without the problems inherent in conventional Nitinol wet etching. The array consists of 65 microvalves with a single valve having dimensions of 1 mm circumference, 50 µm leg width and 8.2 µm Nitinol thickness. Each microvalve covers an orifice of 220 µm diameter and 500 µm in length and is capable of producing 150 µm vertical deflection. The Nitinol MEMS valve array was tested for flow rates in a hydraulic system as a function of applied pressure with a maximum water flow rate of 16.44 cc s−1.