Batch fabrication of polymer microsystems with shape memory microactuators
This paper introduces the technologies of ultrasonic welding and heat-activated bonding for batch integration of micromachined polymer layers and shape memory alloy (SMA) foils or films. A series of ultrasonic welding tests is performed to achieve matter-free bonds on the wafer level with vertical accuracy of 1 mum. Heat-activated bonding is tested for various pressure and temperature conditions using micromachined foils of 60 mum thickness. The technologies are combined in a new process flow for batch fabrication of mechanically active polymer microsystems. The process flow is validated by the fabrication and characterization of SMA-actuated polymer microvalves.
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.
Ignition and burning rates of segregated waste combustion in packed beds.
Recent developments in national recycling and re-use programmes for municipal waste have led to segregation of an increasing proportion of waste to enhance material recovery. Several of the segregated streams contain materials that can not viably be re-used or recycled but can be used for energy recovery. In this study, the combustion of cardboard and waste wood was investigated in a small-scale packed bed reactor in order to provide fundamental data for the design/operation of moving bed furnaces. Key parameters of combustion including the ignition and burning rates were evaluated for various air flowrates and compared to the modelling results. Two successive stages of combustion were identified for both samples: the propagation of ignition front into the bed and combustion of the fuel above the ignition front. The burning rate of cardboard reached a peak of about 300 kg/m(2)h at the air flowrate of 936 kg/m(2)h and decreased at higher air flowrates. For waste wood, both the ignition and burning rates increased in the tested range of the air flowrate up to 702 kg/m(2)h, of which the values were very close to those for the cardboard. The model prediction was in good agreement with the test results for waste wood. However, the burning rate for cardboard was under-predicted due to strongly irregular shapes of the fuel.