A self-regulating hydrogen generator for micro fuel cells

The ever-increasing power demands and miniaturization of portable electronics, micro-sensors and actuators, and emerging technologies such as cognitive arthropods have created a significant interest in development of micro fuel cells. One of the major challenges in development of hydrogen micro fuel cells is the fabrication and integration of auxiliary systems for generating, regulating, and delivering hydrogen gas to the membrane electrode assembly (MEA). In this paper, we report the development of a hydrogen gas generator with a micro-scale control system that does not consume any power. The hydrogen generator consists of a hydride reactor and a water reservoir, with a regulating valve separating them. The regulating valve consists of a port from the water reservoir and a movable membrane with via holes that permit water to flow from the reservoir to the hydride reactor. Water flows towards the hydride reactor, but stops within the membrane via holes due to capillary forces. Water vapor then diffuses from the via holes into the hydride reactor resulting in generation of hydrogen gas. When the rate of hydrogen consumed by the MEA is lower than the generation rate, gas pressure builds up inside the hydride reactor, deflecting the membrane, closing the water regulator valve, until the pressure drops, whereby the valve reopens. We have integrated the self-regulating micro hydrogen generator to a MEA and successfully conducted fuel cell tests under varying load conditions.     

A liquid-triggered liquid microvalve for on-chip flow control

This work introduces a novel surface tension and geometry based liquid-triggered liquid microvalve for on-chip liquid flow control. The simultaneous presence of two liquid plugs at the uncomplicated valve junction triggers the further movement of the liquids and overcomes the stop valve function of the device, thereby providing a precise means of timing liquid movement on-chip. The generic structure was shown to successfully function and forms the basis for several novel and useful functions, including fluidic AND gates, contactless on-chip liquid sample control, timing of independent processes on the same microchip, bubble-free joining of liquids, all of which pose great challenges in the area of microfluidics. The device may be applied to chemical analysis, drug discovery, medical diagnostics and biochemistry.     

微型泵和微型阀的进展

微型泵、阀及微量流体控制系统由于其广泛的应用前景，成为微型机械研究中一活跃的分支。本文着重介绍微型泵、阀的研究现状，论述微型泵、阀的结构设计，致动原理及其实现性能等。     

Photoresponsive polymer gel microvalves controlled by local light irradiation

This paper presents independent control of multiple microvalves, which are opened by local light irradiation. The application of photoresponsive polymer gel, which was developed by our research group, to photoresponsive microvalve was systematically examined. Photoresponsive polymer gels, which were composed of poly(N-isopropylacrylamide) functionalized with spirobenzopyran chromophore (pSPNIPAAm), were fabricated by in situ photo-polymerization at the desired positions in microchannels. Blue light irradiation to the pSPNIPAAm gels induced shrinkage of the gels and caused the microvalves composed of the gels to open. Local light irradiation to the discrete microvalves enabled independent control of three photoresponsive polymer gel microvalves, which had been fabricated on a single microchip. Each microvalve was opened by 18–30 s light irradiation.     

A vapor based microfluidic flow regulator

We introduce a flow regulating technology that uses trapped air bubbles in a hydrophobic microfluidic channel. We present basic designs for flow regulators and flow valves using trapped air. Experiments have successfully demonstrated the capability of this technique for delivering constant and varying flow rate, and for on-off valving. This approach to valving provides a simple, yet effective way to monolithically integrate flow and valve control on polymer Lab-on-Chip devices.     

A high-stroke, high-pressure electrostatic actuator for valve applications

This paper presents a novel large-stroke electrostatic valve actuator for high-pressure applications. The combination of pressure balancing and flexible electrode structures ensures large flow gaps at a low actuation voltage. A simulation tool was built to evaluate the design parameters. Design specific, as well as general optimisations are performed. The model shows a 5.6 times (theoretical) performance improvement compared to earlier designs. A micromachined test structure was fabricated and evaluated. Measurement results are presented and discussed.     

Polymer micro valve with a hydraulic piezo-drive fabricated by the AMANDA process

A normally-closed piezo-driven micro valve for gases and liquids has been developed. Due to the small deflection of piezo-actuated bending disks made of PZT a hydraulic transmission was constructed, which increases the displacement of the piezo disk up to the 25-fold. The switching times of the valve are shorter than 1.8 ms.

Silicone gel serves as a transition medium in the hydraulic. It simplifies the manufacturing process and allows a flexible adaptation to different pressure requirements up to a differential pressure of 150 kPa switched with 300 V. Additionally, this silicone gel supports the sealing of the valve so it achieves an open-to-close ratio of 1:150,000 or higher.

The overall dimensions of the valve are 13 mm×13 mm×3 mm, the dead volume is 0.33 μl, and the inner diameter of the valve seat is 200 μm. A transformer as small as the micro valve is able to produce driving voltages of up to 300 V with a response time of 2 ms. Therefore, the valve could be integrated into hand-held systems which are battery powered with 5–15 V.