Current projects

Optogalvanic Detection of Isotope Ratios (OGIR)
Planar Hall Effect Sensor for Space (PHES)
Silicon-Based High-Temperature Microfluidics
Ceramic High-Temperature Microfluidics
Rotationally Symmetric Micronozzles
Electric Sail Propulsion Technology (ESAIL)
Salinity Sensor for Miniature Submersibles
Velocity Sensor for Submersible Navigation and Two-dimensional Flow Measurements
Microflow meter
Schlieren photography
Reflect Arrays

(a selection)


Optogalvanic Detection of Isotope Ratios (OGIR)
Recently, a new technique for measuring isotopic ratios based on the optogalvanic effect has been demonstrated. It shows a sensitivity similar to the best mass spectrometers, and much better prospects for miniaturization, since it does not require vacuum. The aim of this project, is to study and develop a miniaturized optogalvanic sensor system for a lander or rover, to measure the 13C/12C ratio in the atmosphere, regolith and/or bedrock of Mars.

The optogalvanic effect describes the electrical response of a plasma to an optical perturbation. Applied to measurements on isotopic ratios of carbon, the plasma is created by oxidizing a carbonic sample in a plasma cell and the perturbation is introduced by an isotope-specific laser which excites the molecules causing a change in the plasma impedance. The impedance depends on the number of excited molecules and thus on the amount of carbon of the particular isotope.

Project team: Anders Persson, Martin Berglund and Greger Thornell.


Intense microplasma in the gap of a
so called split ring resonator.

Optogalvanic effect signal (mV) vs
sample mass (ng).

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Planar Hall Effect Sensor for Space (PHES)
Here, a new kind of magnetic field sensor principle is studied and developed in order to complement the SDTM sensors. The ultimate objective is to design, manufacture and evaluate a first version of a PHES, aiming for the requirement of measuring magnetic fields of 0.1 nT at 1 Hz in space. An iteration of the design will be necessary both to fulfil this requirement, and to refine the theoretical model developed in th eproject. The secondary objective is to provide scientific knowledge and technology for non-space applications, such as vehicle navigation, gradiometry, and medical analysis.

Project team: Hugo Nguyen, Anders Persson and Greger Thornell.


Set of newly diced chips for measurement of low-frequency magnetic field.

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Silicon-Based High-Temperature Microfluidics
In fact, this is not a single project, but a number of studies and device developments based on a method to create thick thermal oxides from silicon. This enables mecanically robust oxide structures and thermal barriers monolithically integrated with silicon, which is the baseline material of microsystems technology. As thermal oxidation of silicon is limited to a thickness of a few micrometers, a trick is employed, where deep trenches are etched into structural elements, e.g., beams and chamber walls, before they are oxidized. By this, it is not the diffusion-limited oxide thickness that sets the limit, but instead the attainable etch depth. In the individual projects, the thick oxide walls are used, for instance, for microrocketry and microcells for high-temperature reactions.

Project team: Kristoffer Palmer, Hugo Nguyen and Greger Thornell.


Three gas channels intersecting microreactor embedded in insulating silicon dioxide and lined with silicon to enable uniform heating.

Thermography of similar, but sealed and resistively heated, cell. (The magnification is about 5X less.)

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Ceramic High-Temperature Microfluidics
Like with the silicon/silicon dioxide technology, this is a project, or rather group of projects, addressing the need for thermally more robust materials than silicon in certain applications. Here, however, tapes consisting of ceramic particles and a polymeric binder are embossed and punched with microtools, before they are laminated and metallized into geometrically complex devices which are completed after sintering.

Project team: Ville Lekholm, Fredric Ericson, Anders Persson and Greger Thornell.


Heating of ceramic flow sensor to 1000C with the help of probes.

Semitransparent ceramic device with two microrocket nozzles with integrated flow sensors and heaters.

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Rotationally Symmetric Micronozzles
Most of ÅSTC's silicon-based microfluidics has been realized through deep reactive ion etching (DRIE), which provides cross-sections of more or less rectangular shape. In some situations, like, e.g., when employed for thruster nozzles, the corresponding non-symmetrical flow, may pose problems. At the same time, it may be advantageous to do all structuring in a single equipment, instead of using combinations of DRIE with, e.g., isotropic wet etching or laser ablation. Therefore, this projects investigates, first, how the so called area loading effect, i.e., the slowing down of etching with decreasing size of mask openings, can be used to create vertically rounded features in a single etch step, and, second, how the symmetry of the channels affects the symmetry of the exhaust from them.

Project team: Ernesto Vargas Catalan, Kristoffer Palmer, Ville Lekholm and Greger Thornell.


Design model of nozzle.

Cross section of nozzle throat etched in silicon.

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Electric Sail Propulsion Technology (ESAIL)
Unlike solar sails which use light pressure (photons) from sun with a gigantic membrane to propel a spacecraft, the electric sail, ESAIL, employs an electrically charged structure reminding of a wire wheel repelling itself by the solar wind's protons. Although the 10-20 km long 50-100 spokes of the craft are only a few tens micrometers thick, they interact with the wind with an affective width of hundreds of meters. By this, the spacecraft should be given a thrust of around 1 N, which is enough to enable missions for instance to the heliopause boundary at 200 AU in 15-20 years.


ÅSTC's main role in this first prototyping collaboration, is to design, manufacture and test the so called remote unit, which is an autonomous pico-spacecraft tethered at the end of each spoke.

Partners:
Finnish Meteorological Institute, FMI, Finland
University of Helsinki, UH, Finland
University of Jyväskylä, UJ, Finland
German Aerospace Center, DLR, Germany
Ångström Space Technology Centre, ÅSTC, Sweden
Nanospace AB, Sweden
Tartu Observatory, Tartu, Estonia
University of Pisa, Pisa, Italy
Alta S.p.A., Alta, Italy


PI: Pekka Janhunen, Finnish Meteorological Institute, FMI, Finland

Funding: EU through FP7

Local project team: Johan Sundqvist, Sven Wagner and Greger Thornell.


Conceptual drawing of solar wind interaction with ESAIL craft. (Courtesy of Pekka Janhunen.)

3-D CAD of remote unit showing (thin blue) tether to main craft (cf. spoke in left picture) and tape-like tethers to neighboring units.
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Salinity Sensor for Miniature Submersibles
Salinity is a very important water parameter. Usually, it is determined from simultaneous measurements of conductivity (C), temperature (T) and pressure/depth (D) with a CTD instrument which is both very accurate and big, hoisted overboard with a crane or hanging under a buoy. Aimed for here, is an instrument smaller than a matchbox. So far, the sensor elements have been miniaturized to less than the size of a finger nail. Unique for this device, besides from its size, is that the conductivity measurements are made at MHz frequencies.

Project team: Jonas Jonsson, Katarina Smedfors, Leif Nyholm and Greger Thornell.


Impedance vs. frequency of water samples ranging from brine (#1) to fresh (#8).

Complete CTD sensor element chip on thumb nail.

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Velocity Sensor for Submersible Navigation and Two-dimensional Flow Measurements
Based on finitie element analysis and experience from one-dimensional gas flow sensors, this work aims to develop a sensor for two-dimensional measurements of liquid flow over, e.g., the hull of the miniature DADU explorer, and to understand how biofouling could affect its performance. With the help of data from such a sensor, one could either assist the inertial measurment unit in the submersible's navigation, or, if the craft is held stationary, perform flow measurements on water currents. The sensor works by heating the water very locally and measuring how the temperature profile of the liquid is skewed by the flow. The current prototype consumes less than 15 mW and is able to measure at speeds ranging from 0 to 40 mm/s with a direction error less than 8%.

Project team: Kristoffer Palmer, Jonas Jonsson, Johan Sundqvist, Hugo Nguyen and Greger Thornell.


Four thin film temperature gauges around a central
heater on a glass substrate through which the
texture of a paper tissue is seen.

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Microflow meter
As a more or less generic component of all fluid-based micropropulsion systems, a thermally and chemically robust flow sensor is proposed and studied here. The calorimetric principle with two temperature sensors (one upstreams, and one downstreams, from a heater) is well known and has been employed earlier at ÅSTC.

In this project, these elements are shielded from the flow and made of tougher materials to facilitate measurements on agressive fluids at high temperatures. With this concept, there are materials and processing challenges relating especially to the stresses of the oxide/nitride membrane between the fluid and the sensor elements, and the patterning of the elements on this thin and transparent substrate. As for the performance, the relationship of, e.g., response time and sensitivity to element configuration and membrane design, is investigated. In addition, larger sets of elements and a time-of-flight mode are studied.

Project team: Kristoffer Palmer, Hugo Nguyen and Greger Thornell.


Wire bonded silicon device under evaluation. (PCB is used as a fluidic and electrical interface.)

Example of signals from indivdual temperature sensor elements, as well as the difference between them, vs gas flow.

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Schlieren Photography
To gain further understanding of the consequences of miniturizarion and the design compromises involved, on gas and liquid flows, schlieren imaging techniques, which produce a focused image of chages in refractive index in transparent media, are developed and evaluated. With this method, different types of microfluidic devices are studied under varying conditions. For instance, schlieren imaging was used to observe the acoustic interference obtained with the miniature sonar, and is also of help in characterization of microrockets.

Project members: Ville Lekholm, Kristoffer Palmer, Greger Thornell


Flow of xenon gas through a hypodermic needle. The gas is partially deflected by a larger needle.

Mach discs clearly visible in 0.1 mm wide exhaust from microrocket nozzle just beneath the curved fixture edge to the left.

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Reflect Arrays
A reflect array can be used to shape an electromagnetic wave similarly as the common parabolic antenna. The reflect array antenna is flat and consists of a multitude of resonant elements mimicking the phase response of a parabolic antenna. Reflect arrays have been used frequently in the radio- and microwave-frequency domain, and recently an interest to use this technology at infrared and even visible wavelengths has emerged. In the project at ÅSTC, several demonstrator devices will be built and tested.

Project team: Kristoffer Palmer and Greger Thornell.


Four array elements under finitie element analysis.

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