Zeno Rummler

Polymer micro piezo valve with a small dead volume

A polymer valve with a small dead volume in the range of 6 nl and a response time faster than 1 ms is presented. The valve structure is simple and therefore easy to fabricate by injection molding or hot embossing. A layer of silicone rubber applied by a stamping technique not only promotes the sealing of the valve but also defines the gluing area during assembly. The fabrication is based on the AMANDA-process, which allows low-cost batch production of polymer micro devices.

The design of metal strain gauges on diaphragms

Metal strain gauges need to be designed differently from strain gauges made from silicon. In this paper equations are derived that allow us to calculate the resistance change of metal strain gauges as a function of the position on a thick diaphragm, a thin membrane and a disc simply supported at the rim. The results of finite element calculations presented reveal that large deviations from these equations occur for strain gauges on thin membranes made of soft materials.

Low-Cost Flow Transducer Fabricated with the Amanda-Process

A flow transducer for liquids and gases from polymer manufactured by the AMANDA-process has been developed. Outer dimensions of the transducer are just 5.5 × 4.5 × 1.2 mm3 (Fig.1). The transducer is based on the thermal anemometric principle and is operated in pulse-mode. A heater from gold or platinum enclosed in a 2.4 µm thick polyimide membrane is mounted in the center of a channel. Transducers with channels with different cross-sections have been tested to obtain a variety of flow ranges. The production costs of a transducer without electric and fluidic connectors can be less than 4 € (Euro) because the housings of the transducers are fabricated by hot embossing of polysulfone and most of the fabrication steps are performed in batches.

Dosing system for the nanolitre range, fabricated with the AMANDA process

We present a dosing system, which consists of four microvalves (presented by Rogge et al in the Proceedings of Eurosensors XVI, Prague, 2002, pp 109–110) for controlling and a movable membrane for flow measurement that divides a cavity into two chambers. The flow rate is determined from the straining of the membrane caused by the entering fluid. The displaced volume is detected by strain gauges integrated in the membrane. The overall dimensions of the membrane and the entire system are 2 mm and 10 × 50 × 6 mm3, respectively. A simple control was coded for dosing a certain amount of volume. This simple system has already achieved an accuracy of about 10%. The dosing system is manufactured with the AMANDA process, which allows for low-cost production of microcomponents from polymers.

Entwicklung und Optimierung eines Mikroentgasers für die HPLC unter dem Aspekt der industriellen Herstellbarkeit

Development and Optimization of a Micro Degasser for the HPLC considering the industrial feasability ln liquid chromatography, degassers are used to reduce the amount of gas dissolved in the solvents used. The solvents are typically stored in contact with the surrounding air so that they usually are in a gas saturated state. These dissolved gases adversely affect the chromatographic measurements. lf a solvent mixture is used, for example alcohol/water, the gas solubility of the mixture may be reduced in comparison with that of the single substance. This Ieads to the formation of gas bubblas which have detrimental effects on the stability of the fluid flow and the composition of the solvents. Oxygen dissolved in a solvent adversely affects detection sensitivity. ln UV detection, the high solubility of oxygen in eluents is noticeable, and large fluctuations of oxygen concentration can Iead to pronounced detection noise at wavelength below 260 nm. The high absorbance even can be used to measure the oxygen content. ln fluorescence the presence of oxygen causes the quenching effect which may Iead to a suppression of the fluorescence detection. For this reason, fluorescence measurements can only be made when using degassed solvents. To avoid gasbubblas and to improve analyses results given by the detectors, it is imperative to degas the liquids being used. The development of the degasser is based on the on-line vacuum degassing technique. A membrane permeable for gases and less permeable for liquids is used for degassing. The liquid is Iead through a cavity, which is covered by that membrane. On the other side of the membrane, another cavity is evacuated by a vacuum pump. The dissolved gases permeate through the membrane in the evacuated cavity driven by the pressure difference and are removed by the vacuum pump. The membrane is made out of PTFE (Polytetrafluorethylene) only having a thickness of about 5 !Jm. The manufacturing process is the AMANDA-Process, developed at the Institut für Mikrostrukturtechnik of the Forschungszentrum Karlsruhe. A new process is developed to join chemically inert that thin membrane and a housing, also made out of PTFE, to create the fluid cavity. The process costs are very low, the process is fast and a connection without destroying the thin membrane is achieved at a very high output rate. A FEP-Foil is used as a welding foil between the membrane and the housing. By pressing a thermode on the membrane and heating the assembly to the melting point of the FEP, a connection is established within 1 0 to 15 s. The evacuated cavity contains a supporting structure, which prevents the thin PTFE-membrane from being damaged by the Ioad of the high pressure difference of about 1 bar. Experiments have been made to evaluate the maximum stretched circular area of the membrane without any support structure to achieve a lifespan of about 5 years. The maximum radius of such an area is about 16 IJm. The geometrical dimensions of the micro degasser, described in this report are smaller than usual online vacuum degassers. The degassers inner volume is 60 times smaller so the chromatograph can be put into operation in a shorter period of time. The performance of the first prototype (66 mAU) already is about one third of the usual used degassers performance (200 mAU). All materials used are chemically inert.

Mass separation using thin PTFE membranes

Devices for mass separation have been engineered and were fabricated using the AMANDA process. The key component is a 5 micrometers thin, semi-permeable PTFE membrane with a circular diameter of 42 mm. The membrane is encapsulated in a PTFE and PEEK housing. In experiments, this novel device separated a gas flow of approximately 1 (mu) l/min from a methanol feed stream of 1 ml/min at a pressure difference of 900 hPa. The separation process was simulated in FE- calculations exploiting analogies between diffusion theory and heat transfer. Mechanical stability and creeping of the PTFE membrane were investigated as well. All parts in contact with the fluids to be separated are made of chemically inert polymers. As a consequence, a welding process had to be developed for bonding the PTFE membrane to the PTFE housing. This was accomplished with an intermediate FEP layer. Extension of this bonding technique to other AMANDA products will facilitate fabrication of chemically inert micropumps, valves, and sensors.