Christof Megnin

A Bistable Shape Memory Alloy Microvalve With Magnetostatic Latches

This paper presents the layout, fabrication, and characterization of a first-of-its-kind bistable shape memory microvalve. The main functional components are two counteracting shape memory alloy microbridges for switching and magnetic layers to maintain two stable switching states in power-off condition. The high demands on alignment accuracy are met by a novel fabrication process, where all components are assembled to a self-aligning valve stack. This allows full electrical, mechanical, and fluidic performance tests as well as fine adjustment of layer thicknesses prior to final bonding. The overall dimensions of first demonstrators are 11 mm × 6 mm × 3 mm. Bistable operation is shown for differential pressures up to 300 kPa for gas (N2) at high flow rates of 2200 seem.

Shape memory alloy microvalves for a fluidic control system

This paper presents the design, fabrication, and performance of shape memory alloy (SMA) microvalves with a novel plug-in interface that enable arbitrary combinations and interchange of individual valve components in order to realize customized fluidic control systems. Actuation of the valves relies on a micromachined SMA foil, which is prestrained in order to adjust for a given flow, and pressure requirement. A demonstrator system is presented consisting of up to nine microvalves, flow channels and control electronics arranged in different functional layers that are stacked onto each other. The microvalves are designed for flow rates of 12.5 ml min−1 (water) in open state at a pressure difference of 200 kPa. Flow regulation is tested in closed-loop control mode using a flow sensor with a short time constant. The accuracy of flow control is in the order of 1.5%. The response times are below 24 ms.

Batch Fabrication of Shape Memory Actuated Polymer Microvalves by Transfer Bonding Techniques

Polymer based microvalves offer outstanding properties for biomedical and life science applications. They can be produced cost efficiently by batch fabrication methods. Further, by adapting the polymer material, custom-tailored properties of the valve are possible. For mechanically active microvalves, actuation with smart materials like shape memory alloys is highly attractive due to their high work output per volume and favorable scaling behavior. For the integration of such smart materials, fabrication process incompatibilities between the actuator material and the polymer target system need to be avoided. This can be achieved by novel transfer bonding technologies being optimized for batch fabrication. These technologies are demonstrated for polymer microvalves actuated by a shape memory alloy but they can also be applied to other functional materials and structures.

A bistable shape memory microvalve

This paper presents the layout, fabrication and performance characteristics of a first-of-its-kind bistable shape memory microvalve that uses two counteracting shape memory alloy (SMA) microbridges for switching and magnetic layers to maintain the switching states in power-off condition. The high demands on alignment accuracy are met by a novel fabrication process, where all components are assembled to a self-aligning valve stack. This allows full electrical, mechanical and fluidic performance tests as well as fine-adjustment of layer thicknesses prior to final bonding. The overall dimensions of first demonstrators are 11×6×3 mm3. Bistable operation is shown for a differential pressure up to 100 kPa at high flow rates of 800 sccm (N2) and 3.5 ml/min (H2O).

A modular microfluidic backplane for control and interconnection of optofluidic devices

A modular microfluidic backplane with integrated microvalves enabling the flexible interconnection, supply, and control of optofluidic devices has been fabricated from polymers in two designs, providing two- or three-dimensional device assemblies.

Modular Optoelectronic Microfluidic Backplane for Fluid Analysis Systems

We report on the development of backplane modules with integrated microvalves and optical switches enabling custom-made system design of analysis systems. The backplane modules are reversibly interconnected by magnetostatic connectors and provide optical and fluidic coupling to four neighboring backplane modules and one optical sensor module, which is mounted on top. This concept allows for selectively guiding fluids and light to the sensor modules to be operated. We integrated shape memory alloy (SMA) microvalves in different designs and two kinds of optical switches, i.e., one linearly actuated assembly of optical elements and one based on an electrostatically deflectable mirror. We manufactured the modules in polymers and carried out optical and fluidic characterization. The functionality of the backplane is demonstrated by interconnecting two optical sensor modules with integrated spectrometer and photodiode color sensor, respectively. Herewith, we carried out fluorescence transmission experiments.

Optofluidic backplane as a platform for modular system design

Most Lab-on-a-Chip systems require a platform with external supply and control units to be operated. In this manuscript, we report on the development of a modular optoelectronic microfluidic backplane, enabling the flexible interconnection, supply, and control of microfluidic and optofluidic devices. The developed system was fabricated in polymers and consists of backplane modules that may be individually connected with each other. Each module holds one dedicated port on top for a device to be operated. In particular, we introduce an optical backplane module based on a novel optomechanical light switch to guide light to the device of choice within the system. This modular approach allows assembling an arbitrary number of different devices in three dimensions. In conclusion, the backplane provides a configurable platform for multiple optofluidic applications.

A bistable shape memory microvalve for three-way control

This paper reports on the design, fabrication and performance of a novel bistable three-way shape memory microvalve for diverting and mixing applications. A symmetric arrangement of two counteracting shape memory alloy (SMA) microbridges is used for switching. Magnetic microstructures provide magneto-static contact forces in power-off condition allowing for stable open and closed states. A detailed design study on the geometry of magnetic microstructures and of spacer layers is performed to meet the requirements of large pressure range and identical flow performance in the outlet ports. The overall dimensions of first demonstrators are 11×6×4 mm3. Bistable operation is shown for a differential pressure up to 300 kPa at flow rates of 2200 sccm (N2).

SMA Foils for MEMS: From Material Properties to the Engineering of Microdevices

In the early nineties, microelectromechanical systems (MEMS) technology has been still in its infancy. As silicon (Si) is not a transducer material, it was clear at the very beginning that mechanically active materials had to be introduced to MEMS in order to enable functional microdevices with actuation capability beyond electrostatics. At that time, shape memory alloys (SMAs) have been available in bulk form, mainly as SMA wires and SMA plates. On the macro scale, these materials show highest work densities compared to other actuation principles in the order of 107xa0J/m3, which stimulated research on the integration of SMA to MEMS. Subsequently, two approaches for producing planar materials have been initiated (1) magnetron sputtering of SMA thin films and (2) the integration of rolled SMA foils, which both turned out to be very successful creating a paradigm change in microactuation technology. The following review covers important milestones of the research and development of SMA foil-based microactuators including materials characterization, design engineering, technology, and demonstrator development as well as first commercial products.

Film and Foil-Based Shape Memory Alloy Microactuators for Fluid Handling

In this contribution, the potential of film and foil-based shape memory alloy (SMA) microactuators for fluid handling applications is explored. SMAs provide a high work density and allow for compact and robust actuator designs based on the one-way shape memory effect. Compared to more commonly used wires, actuators fabricated from thin film or foil material allow for more complex designs having several degrees of freedom and enable shorter switching times in the range of 10 ms. In order to commercialize such actuators, the “memetis GmbH” was founded as a high-tech spin-off of the Karlsruhe Institute of Technology (KIT) in Germany. Memetis is focused on miniature fluid handling products and combines rapid prototyping and rapid manufacturing techniques such as 3D printing, laser cutting and CNC milling of polymer housings for customer-specific device development. A normally open microvalve is presented here as an example, which is actuated by a novel fatigue-free TiNiCu film actuator.