T.T. Veenstra

Characterization method for a new diffusion mixer applicable in micro flow injection analysis systems

A new mixer is designed for mixing a phenolic solution into water. The mixer design is such that it can be easily adjusted for the controlled mixing of a specific compound within a certain time. This paper describes the working principle of the mixer as well as a suitable characterization method for the mixer. Measurement results are presented which show the correct working of the mixer. A quantitative measure is introduced to express the extent of mixing performed by the mixer. The characterization method allows the measurement of the flow rate, pressure drop and extent of mixing.

Use of Selective Anodic Bonding to Create Micropump Chambers with Virtually No Dead Volume

Membrane micropump chambers of 11 mm diam with virtually zero dead volume were realized using selective anodic bonding. The selective bonding was achieved with less than 1 nm thick metallic antibonding layers on the glass wafer. Experiments were carried out to come to a better understanding of the selective anodic bonding process. It was concluded that a conductive antibonding layer on the glass wafer prevents the formation of a bond, because in that case the electrostatic attraction between the Pyrex and silicon wafers will vanish upon contact. Chromium and Platinum were found to be suitable antibonding layers. Furthermore, it was found that during the anodic bonding process, the transport of oxygen ions from Pyrex toward the silicon-Pyrex interface results in the formation of SiO2, which forms the actual bond between both substrates. At positions of an intermediate antibonding layer the oxygen ions form oxygen gas. The Pyrex or silicon substrate may deform locally due to the buildup of oxygen gas pressure. This can be prevented by adding a gas outlet to the design. ©2001 The Electrochemical Society. All rights reserved.

A light detection cell to be used in a micro analysis system for ammonia

This paper describes the design, realization and characterization of a micromachined light detection cell. This light detection cell is designed to meet the specifications needed for a micro total analysis system in which ammonia is converted to indophenol blue. The concentration of indophenol blue is measured in a light detection cell. The light detection cell was created using KOH/IPA etching of silicon. The KOH/IPA etchant was a 31 wt.% potassium hydroxide (KOH) solution with 250 ml isopropyl alcohol (IPA) per 1000 ml H(2)O added to it. The temperature of the solution was 50 degrees C. Etching with KOH/IPA results in 45 degrees sidewalls ({110} planes) which can be used for the in- and outcoupling of the light. The internal volume of the realized light detection cell is smaller than 1 mul, enabling measurements on samples in the order of only 1 mul. Measurements were performed on indophenol blue samples in the range of 0.02 to 50 muM. In this range the measurements showed good reproducibility.

Pressure drop of laminar gas flows in a microchannel containing various pillar matrices

The pressure drop of gas flows in a microchannel filled with a dense pillar matrix was investigated with specific attention to a pillar shape. Pillars of height 250 µm and aspect ratio of about 10 were etched in silicon using an optimized Bosch deep reactive ion etching process. The pressure drop head-loss coefficient due to compression and expansion of gas at the inlet and outlet of the pillar matrix was estimated to be about 1.4 for an opening ratio of 10. A comparison of friction factor correlations for circular pillar cross-sections agreed rather well with the correlations proposed for the macroscale. Experimentally determined friction factor correlations for several pillar cross-sections for Reynolds numbers in the range of 50–500 are presented. Among the various pillar cross-sections considered, sine-shaped pillars have the lowest friction factor. These pillar structures with low pressure drop but a rather large wetted area can be used quite effectively as regenerative materials enabling the development of microcryocoolers.

The design of an in-plane compliance structure for microfluidical systems

Two compliance structures for the use in liquid-based microfluidic systems have been realized with the aid of silicon micromachining. The basic principle is that these structures contain air bubbles that dampen the flow and pressure variations that may arise from a micropump. The compliance structures were specifically designed to work with the no moving parts valve (NMPV) pump [Proc. ASME Fluids Eng. Division, 1995, in press]. The structures were modeled and simulated. From the results of these simulations and the model, design rules for the compliance are formulated. Measurements on the compliance structures could only be performed for the steady state. These measurements were in very good agreement with the model. Working with two sets of pumps showed that pumps without the compliance structure needed an external compliance in order to get them to work, whereas the pumps with the on-chip compliance pumped right away.

Development of a 4K Sorption Cooler for ESA's Darwin Mission: System-Level Design Considerations

ESA’s Darwin mission is a future space interferometer that consists of six free-flying telescopes. To guarantee a proper mechanical stability of this system, hardly any vibration of the optical system with integrated cryocoolers can be tolerated. This paper presents the system design of a 4.5 K, 10 mW vibration-free sorption cooler chain, of which the helium stage is currently in development under an ESA-TRP contract. A sorption cooler is a favorite option because it has no moving parts and it is, therefore, essentially vibration-free. A two-stage helium/hydrogen cooler is proposed which needs 5 Watts of input power and which applies two passive radiators at 50 K and 80 K. The paper includes the following aspects: system modelling, radiator configurations, activated carbons, different multi-stage cooler options, and integration aspects of the compressor cells with the radiators.

MiRTH-e: Micro reactor technology for hydrogen and electricity

Research groups of six companies, institutes and universities have joint forces in a European Community funded project, to develop a miniaturized, low-power fuel processor for the conversion of methanol into clean hydrogen for use in a proton exchange membrane (PEM) fuel cell. The integrated unit will provide a portable power source and is an alternative for battery packs or hydrogen storage in metal hydrides. In the realization of this small-scale fuel processor, microreactor technology will play a key role. Based upon a so-called pinch analysis, a conceptual design of the fuel processor is made, consisting of three combined microreactors/heat exchangers.

Monolithic Versus Modular Integration of a Micro-FIA System for Ammonium Determination

Two differently constructed µ-FIA ammonium detection systems have been realized and tested. A monolithic system (Full-Lab-On-A-Chip) shows reproducible measurements for 10 and 20 mM ammonium samples. A modular version of this system could measure ammonium concentrations down to 1.67 mM.

A mixer based on diffusion mixing designed for the MAFIAS-project

The MAFIAS project (Micro Ammonia Flow Injection Analysis System) aims at the development of a monolithic micromachined flow injection analysis system for the detection of ammonia. From the applied chemistry, design restrictions for the micromechanical ammonia detection system are deduced. These restrictions involve the temperature control of the system at 37° C. Also the time available for the mixing of the compounds used in Berthelot’s method is restricted to less than 20 seconds. This last restriction calls for a mixer since the compounds itself would take at least three times as long to mix. A new type of mixer based upon diffusion is proposed. Theory for deriving the exact geometry for the mixer is deduced. With this mixer, the mixing time can be reduced to 2 seconds.

Chip-to-world interfaces for high-throughput lab-on-a-chip devices

Chip-to-world interfaces are of prime importance for the implementation of lab-on-a-chip devices in high-throughput environments. In this contribution, a matrix of interfacing methods for bi-directional small liquid exchange between chip based microchannels and robotics is presented. The central underlying principle is the use of a hydrophobic coated micromachined port in the channel wall giving direct access to the liquid inside.