Lena Klintberg

Sodium hypochlorite as a developer for heavy ion tracks in polyimide

The developing and etching of heavy ion tracks in polyimide with sodium hypochlorite have been studied to gain control over the parameters that affect the etch result. The shape of the resulting pores is a function of both alkalinity and hypochlorite content of the solution. Sodium hypochlorite decomposes during etching, and the rate constant has been determined as a function of the alkalinity at 62 °C. Polished cross-sections have been examined to determine the pore shape, and this method has shown to be a straightforward way to characterise the pores. Decreasing the alkalinity gives more cylindrical pores, but increases the decomposition rate of the hypochlorite solution and decreases the etch rate.

Viton-based fluoroelastomer microfluidics

Viton is an elastomer with low permeability and high chemical resistance. This paper presents the main characteristics and technical issues involved in fabricating Viton-based microfluidics by micromoulding, bonding and metallization. A PDMS (polydimethylsiloxane) mould is used to imprint the Viton compound in a curing step that is followed by a post-curing without the mould. Viton was fusion bonded, with high quality, to itself and to stainless steel when clamped together during a post-curing step. Having low permeability to hydrocarbon liquids, Viton is a well-suited elastomer for making paraffin membrane microactuators, as demonstrated here. These kinds of microactuators may find their applications in fluid handling with hydraulic oils, in vacuum systems or in reactors and analytical systems, where Viton comes in direct contact with fluids that would permeate or degrade other elastomers.

High-Pressure Peristaltic Membrane Micropump With Temperature Control

A high-pressure peristaltic membrane micropump, which is capable of pumping against a back pressure of 150 bar, has been evaluated. The main focus was to maintain the flow characteristics also at high back pressures. The pump was manufactured by fusion bonding of parylene-coated stainless-steel stencils. A large-volume expansion connected to the solid-to-liquid phase transition in paraffin was used to move 10-μm-thick stainless-steel membranes. The pump was evaluated by using two different driving schemes, a four-phase cycle and a six-phase cycle. With the six-phase cycle, a constant flow rate of 0.4 μL min-1 was achieved over an interval ranging from atmospheric pressure to 130 bar. At lower back pressures, the more energy efficient four-phase cycle achieved slightly higher flow rates than the six-phase cycle. However, it required higher driving voltage at high back pressures. Since the pump is thermally activated, a temperature sensor was integrated to control the melting and solidification of paraffin, implying capability of increasing the performance of the pump. With a thickness of only 1 mm as well as a simple and robust design, the micropump is well suited for integration in analytical systems. The high pressures managed are in the region needed for, e.g., high-performance liquid chromatography systems.

A thermal microactuator made by partial impregnation of polyimide with paraffin

We have fabricated and tested thermal, paraffin-impregnated polyimide actuators, utilizing the large volume increase associated with the solid-to-liquid phase transition of paraffin. In the bimorph-like device, the top layer was made porous by ion track technology. Stochastically distributed pores of various lengths (95, 70, 45 and 20 µm) and various lateral coverages (5–45%) were filled with paraffin by liquid substitution or from vacuum, and sealed with epoxy. Actuators, 125 µm thick, 35 mm long and 7 mm wide, have been characterized with respect to tip deflection and load-carrying capacity with one end rigidly clamped. Loaded with 0.6 g or about ten times their own weight at their free end, about 50% of the maximum stroke (17 mm) was still attained.

Manufacturing and characterization of a ceramic microcombustor with integrated oxygen storage and release element

A microscale ceramic high-temperature combustor with a built-in temperature sensor and source of oxygen has been designed, manufactured and characterized. The successful in situ electroplating and ...

High-pressure stainless steel active membrane microvalves

In this work, high-pressure membrane microvalves have been designed, manufactured andevaluated. The valves were able to withstand back-pressures of 200 bar with a response timeof less than 0.6 s. T ...

Desktop microfabrication : initial experiments with a piezoceramic

A method for building microstructures from a suspension of micrometre-sized piezoelectric particles by depositing droplets on top of droplets and promoting drying is devised. A micromachined dispensing unit similar to a drop-on-demand inkjet-printer head is used. The relation of the vertical building rate to the ejection frequency and the substrate temperature is established, and a mechanism explaining the tubular structures built is proposed.

Thermomechanical properties and performance of ceramic resonators for wireless pressure reading at high temperatures

This paper reports on the design, fabrication, and thermomechanical study of ceramic LC resonators for wireless pressure reading, verified at room temperature, at 500 °C and at 1000 °C for pressures up to 2.5 bar. Five different devices were fabricated from high-temperature co-fired ceramics (HTCC) and characterized. Alumina green tape sheets were screen printed with platinum paste, micromachined, laminated, and fired. The resulting samples were 21 mm × 19 mm with different thicknesses. An embedded communicator part was integrated with either a passive backing part or with a pressure-sensing element, including an 80 µm thick and 6 mm diameter diaphragm. The study includes measuring thermally and mechanically induced resonance frequency shifts, and thermally induced deformations. For the pressure sensor device, contributions from changes in the relative permittivity and from expanding air trapped in the cavity were extracted. The devices exhibited thermomechanical robustness during heating, regardless of the thickness of the backing. The pressure sensitivity decreased with increasing temperature from 15050 ppm bar−1 at room temperature to 2400 ppm bar−1 at 1000 °C, due to the decreasing pressure difference between the external pressure and the air pressure inside the cavity.

A high-temperature calorimetric flow sensor employing ion conduction in zirconia

This paper presents the use of the temperature-dependent ion conductivity of 8 mol % yttria-stabilized zirconia (YSZ8) in a miniature high-temperature calorimetric flow sensor. The sensor consists of 4 layers of high-temperature co-fired ceramic (HTCC) YSZ8 tape with a 400 μm wide, 100 μm deep, and 12 500 μm long internal flow channel. Across the center of the channel, four platinum conductors, each 80 μm wide with a spacing of 160 μm, were printed. The two center conductors were used as heaters, and the outer, up- and downstream conductors were used to probe the resistance through the zirconia substrate around the heaters. The thermal profile surrounding the two heaters could be made symmetrical by powering them independently, and hence, the temperature sensing elements could be balanced at zero flow. With nitrogen flowing through the channel, forced convection shifted the thermal profile downstream, and the resistance of the temperature sensing elements diverged. The sensor was characterized at nitrogen...

Fracture strength of glass chips for high-pressure microfluidics

High-pressure microfluidics exposes new areas in chemistry. In this paper, the reliability of transparent borosilicate glass chips is investigated. Two designs of circular cavities are used for fra ...