Microvalves

Monostable Shape Memory Alloy Microvalves

Shape Memory Alloy (SMA) microvalves comprise a polymer housing with an integrated fluid chamber, membrane, and SMA microactuator. The microactuator is deflected by a plunger, e.g., a microball. At zero current, the microvalve is in open state. In this case, the fluid is able to flow through the valve, if a supply pressure is present. By electrical heating, the microactuator changes to its planar shape memory state and thereby closes the microvalve.

Monostable microvalves close and open in power-off condition and by electrical heating, respectively. In order to enable a compact design at preferably high fluidic power, a micro-machined SMA foil is used for actuation. Monostable microvalves are designed in a modular way to reduce the number of components. This enables economic fabrication of normally-open (NO) and normally-closed (NC) microvalves as well as fast adjustment to required pressure and flow range.

For dosing applications and pressure-independent flow control, the system is extended by a flow sensor and closed-loop control.

Size: lateral Height (NO) Height (NC)   10 x 10 mm2 7 mm 11 mm   Heating power < 500 mW   Response time < 100 ms   Lifetime > 106 cycles   Ø valve seat 500 μm NC Flowgas (200 kPa) 880 sccm Flowliq (200 kPa) 8 ml/min NO Flowgas (200 kPa) 2000 sccm Flowliq (200 kPa) 12.5 ml/min

Fluidic control system

The fluidic control system consists of up to nine SMA microvalves, electrical circuit, and fluidic backplane. The microvalves are attached to the fluidic backplane by a reversible magnetic plug-in interface. The system enables guiding and regulation of gases and liquid flows.

Bistable Shape Memory Alloy Microvalves

Bistable Shape Memory Alloy (SMA) microvalves only consume energy during switching and, thus, are suitable for fluidic systems operating at low average power consumption and low duty cycles.

Bidirectional actuation is realized by two counteracting and selectively heated SMA microbridge actuators. In power-off condition the stable positions are held by magnetostatic latching forces..

Performance Characteristics Power consumption only during switching Magnetic structures for latching High work densities Modular layered design Very small dimensions Control of liquids and gases 2/2- and 3/2-way behavior Low energy consumption Separated fluidic and actuation Polymer housing Batch fabricated low cost-effective components

Size: 11 x 6 x 4 mm3   Heating power < 500 mW   Switching energy 0.1 J   Response time < 100 ms   Lifetime > 106 cycles   Ø valve seat 400 μm 2/2 Flowgas (300 kPa) 215 sccm Flowliq (100 kPa) 11.3 ml/min 3/2 Flowgas (200 kPa) 1250 sccm Flowliq (100 kPa) 11.3 ml/min

Further information:

• T. Grund, C. Megnin, J. Barth and M. Kohl, Batch fabrication of shape memory actuated polymer microvalves by transfer bonding techniques, The Journal of Microelectronics and Electronic Packaging 6, (2009) 219-227.
• J. Barth, B. Krevet and M. Kohl, A bistable shape memory microswitch with high energy density, Smart Mater. Struc. 19, (2010) 094004.
• J. Barth, C. Megnin, M. Kohl, A Bistable Shape Memory Alloy Microvalve With Magnetostatic Latches, Journal of Microelectromechanical Systems 21, (2012) 76-84
• M. Brammer, C. Megnin, A. Voigt, M. Kohl, and T. Mappes, Modular Optoelectronic Microfluidic Backplane for Fluid Analysis Systems, Journal of Microelectromechanical Systems 22, (2013) 462-470
• C. Megnin, and M. Kohl, Shape Memory Alloy Microvalves for a Fluidic Control System, Journal of Micromechanics and Microengineering 24, (2014) 025001