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Development of Microcomponents for Attitude and Communication Systems on Small Vehicles in Space and Extreme Environments
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In this thesis, components intended for vehicles in space and other extreme environments have been realized using microsystems technology to facilitate miniaturized, yet high-performing systems beneficial for small spacecraft and other vehicles with limited size and power.

Cold gas thrusters commonly used on spacecraft basically accelerate a gaseous propellant stored under high pressure. When miniaturized, their performance is reduced because of viscous forces. Here, with a special masking and etching scheme, making silicon micronozzles close to rotationally symmetric, this shortcoming was mitigated as indicated by schlieren imaging of the rocket exhaust and a comparison with conventionally manufactured micronozzles with rectangular cross-sections. Schlieren imaging was also used to detect leakage, quantify thrust vector deviation, and measure shock cell periods in the exhaust. Correlation was made to operational conditions.

Similarly operating zirconia thrusters with integrated heaters and flow sensors were developed to allow for higher operating temperature. Successful testing at 1000°C, suggests that the propellant efficiency could be increased by 7.5%, and also makes them candidates for chemical propulsion.

A silicon thruster operating in rarefied gas regimes was also developed. Being suspended in a silicon dioxide frame reducing heat losses, a total efficiency of 17% was reached.

Relating to the integrated micropropulsion systems, two types of flow sensors were developed. Through finite element modeling, the insertion of sensor fingers in the fluid was shown to be an interesting concept for high-pressure applications.

Utilizing the same principle, a velocity sensor for a miniaturized submersible was developed. With a power consumption below 15 mW, it was able to measure directions with an accuracy of ±8º, and speed with an error less than 22%.

To enable high-speed optical communication between spacecraft, a Free Space Optics communication system, and particularly its dual-axis beam-steering actuator, was developed. Through thermal actuation, optical angles larger than 40º were obtained. A lumped thermal model was used to study design changes, vacuum operation and feedback control.

Understanding and mastering heat transfer in microsystems have been vital in many of the studies conducted. Throughout, advanced micromachining and modeling have been used as a step towards high-performance systems for space and other extreme environments.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. , 43 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1003
National Category
Other Engineering and Technologies
Research subject
Administrative Law
Identifiers
URN: urn:nbn:se:uu:diva-186862ISBN: 978-91-554-8555-9 (print)OAI: oai:DiVA.org:uu-186862DiVA: diva2:573758
Public defence
2013-01-11, Polhelmsalen, Lägerhyddsvägen 1, Uppsala, 10:00 (English)
Supervisors
Available from: 2012-12-21 Created: 2012-11-29 Last updated: 2013-02-11Bibliographically approved
List of papers
1. Schlieren Imaging of Microthruster Exhausts for Qualitative and Quantitative Analysis
Open this publication in new window or tab >>Schlieren Imaging of Microthruster Exhausts for Qualitative and Quantitative Analysis
2012 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 23, no 8, 085403- p.Article in journal (Refereed) Published
Abstract [en]

Abstract. Schlieren imaging is a method used to visualize differences in refractiveindex within a medium. It is a powerful and straightforward tool for sensitiveand high-resolution visualization of, e.g., gas flows. Here, heated cold gasmicrothrusters were studied with this technique. The thrusters are manufacturedusing microelectromechanical systems technology, and measure 22×22×0.85 mm. Thenozzles are approximately 20 µm wide at the throat, and 350 µm wide at the exit.Through these studies, verification of the functionality of the thrusters, and directvisualization and of the thruster exhausts was possible. At atmospheric pressure,slipping of the exhaust was observed, due to severe overexpansion of the nozzle. Invacuum (3 kPa), the exhaust was imaged while feed pressure was varied from 100 to450 kPa. The nozzle was overexpanded, and the flow was seen to be supersonic. Theshock cell period was linearly dependent on feed pressure, ranging from 320 to 610 µm.With activated heaters, the shock cell separation increased. The effect of the heaterswas more prominent at low feed pressure, and an increase in specific impulse of 20%was calculated. It was also shown that schlieren imaging can be used to detect leaks,making it a valuable, safe, and noninvasive aid in quality control of the thrusters.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2012
Keyword
Schlieren imaging, microthrusters, MEMS, shock cells
National Category
Other Engineering and Technologies not elsewhere specified
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-186252 (URN)10.1088/0957-0233/23/8/085403 (DOI)000306366600039 ()
Funder
VINNOVA
Available from: 2012-11-29 Created: 2012-11-28 Last updated: 2017-12-07Bibliographically approved
2. Investigation of exhausts from fabricated silicon micronozzles with rectangular and close to rotationally symmetric cross sections
Open this publication in new window or tab >>Investigation of exhausts from fabricated silicon micronozzles with rectangular and close to rotationally symmetric cross sections
2013 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 23, no 10, 105001- p.Article in journal (Refereed) Published
Abstract [en]

Close to rotationally symmetric in-plane silicon micronozzles with throat and exit diameters of 45 and 260 µm, respectively, have been fabricated using semi-isotropic SF6 etching through an array mask utilizing microloading and reactive ion etching lag. Comparison with nozzles fabricated using deep reactive ion etching (DRIE) and having a rectangular cross-section but a similar hydraulic diameter in the throat, showed that the Reynolds numbers were almost equal even though the DRIE-etched nozzle had an almost five times larger cross-sectional area, hence implying less viscous losses and higher efficiency with the nearly symmetrical nozzles. The nozzle shapes have been studied using x-ray computed tomography. Comparison of the nozzles' exhaust jets using schlieren imaging, showed that the rectangular nozzles' jets deviate from the nozzle axis direction. It is believed that it is caused by the inclined side walls resulting from the DRIE etching. The results from intentionally misaligning the wafers, each containing half a nozzle, 50 µm parallel with or perpendicular to the nozzle axis, showed that the exhaust deviated and widened, respectively. The findings show that the nozzle symmetry affects both the shape and the pointing direction of the exhaust and that schlieren imaging is a powerful tool for determining nozzle thrust vector deviations.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-186774 (URN)10.1088/0960-1317/23/10/105001 (DOI)000324672700002 ()
Available from: 2012-11-29 Created: 2012-11-29 Last updated: 2017-12-07Bibliographically approved
3. High-temperature zirconia microthruster with integrated flow sensor
Open this publication in new window or tab >>High-temperature zirconia microthruster with integrated flow sensor
Show others...
2013 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 23, no 5, 055004- p.Article in journal (Refereed) Published
Abstract [en]

This paper describes the design, fabrication and characterization of a ceramic, heated cold-gas microthruster device made with silicon tools and high temperature co-fired ceramic processing. The device contains two opposing thrusters, each with an integrated calorimetric propellant flow sensor and a heater in the stagnation chamber of the nozzle. The exhaust from a thruster was photographed using schlieren imaging to study its behavior and search for leaks. The heater elements were tested under a cyclic thermal load and to the maximum power before failure. The nozzle heater was shown to improve the efficiency of the thruster by 6.9%, from a specific impulse of 66 to 71 s, as calculated from a decrease of the flow rate through the nozzle of 13%, from 44.9 to 39.2 sccm. The sensitivity of the integrated flow sensor was measured to 0.15 m Omega sccm(-1) in the region of 0-15 sccm and to 0.04 m Omega sccm(-1) above 20 sccm, with a zero-flow sensitivity of 0.27 m Omega sccm(-1). The choice of yttria-stabilized zirconia as a material for the devices makes them robust and capable of surviving temperatures locally exceeding 1000 degrees C.

Keyword
Keywords: Zirconia, YSZ, HTCC, schlieren imaging, flow sensor, microthruster
National Category
Other Engineering and Technologies not elsewhere specified
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-186257 (URN)10.1088/0960-1317/23/5/055004 (DOI)000317739100004 ()
Funder
Vinnova
Available from: 2012-11-28 Created: 2012-11-28 Last updated: 2017-12-07Bibliographically approved
4. Fabrication and evaluation of a free molecule micro-resistojet with thick silicon dioxide insulation and suspension
Open this publication in new window or tab >>Fabrication and evaluation of a free molecule micro-resistojet with thick silicon dioxide insulation and suspension
2013 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 23, no 6, 065006- p.Article in journal (Refereed) Published
Abstract [en]

A silicon free molecule micro-resistojet (FMMR) with a thermally insulating suspension frame composed of silicon dioxide has been designed, fabricated and tested. The concept was developed to increase the efficiency of FMMRs, especially in silicon-based integrated systems. Fabrication of the thick insulating frame was performed through oxidation of high-aspect ratio silicon trenches. The thermal properties of the 1 cm(2) thruster were evaluated using an IR camera, and it was found that when the volume inside the frame is heated more than 200 degrees C using integrated nickel heaters, the temperature increase in the volume outside the frame is less than 50 degrees C. During operation in vacuum, the thrust range was calculated to be about 13-1070 mu N and the maximum specific impulse 54 s. At maximum thrust, and a power consumption of 1.6 W, the total efficiency of the thruster was 17%. Designs of more efficient and versatile systems are discussed.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-186775 (URN)10.1088/0960-1317/23/6/065006 (DOI)000319451300006 ()
Available from: 2012-11-29 Created: 2012-11-29 Last updated: 2017-12-07Bibliographically approved
5. A highly integratable silicon thermal gas flow sensor
Open this publication in new window or tab >>A highly integratable silicon thermal gas flow sensor
2012 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 22, no 6, 065015- p.Article in journal (Refereed) Published
Abstract [en]

Thermal flow sensors have been designed, fabricated, and characterized. All bulk material in these devices is silicon so that they are integratable in silicon-based microsystems. To mitigate heat losses and to allow for use of corrosive gases, the heating and sensing thin film titanium/platinum elements, injecting and extracting heat, respectively, from the flow, are placed outside the channel on top of a membrane consisting of alternating layers of stress-balancing silicon dioxide and silicon nitride. For the fabrication, an unconventional bond surface protection method using sputter-deposited aluminum instead of thermal silicon dioxide is used in the process steps prior to silicon fusion bonding. A method for performing lift-off on top of the transparent membrane was also developed. The sensors, measuring 9.5 x 9.5 mm(2), are characterized in calorimetric and time-of-flight modes with nitrogen flow rates between 0 sccm and 300 sccm. The maximum calorimetric sensor flow signal and sensitivity are 0.95 mV and 29 mu V sccm(-1), respectively, with power consumption less than 40 mW. The time-of-flight mode is found to have a wider detectable flow range compared with calorimetric mode, and the time of flight measured indicates a response time of the sensor in the millisecond range. The design and operation of a sensor with high sensitivity and large flow range are discussed. A key element of this discussion is the configuration of the array of heaters and gauges along the channel to obtain different sensitivities and extend the operational range. This means that the sensor can be tailored to different flow ranges.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-176814 (URN)10.1088/0960-1317/22/6/065015 (DOI)000304609600015 ()
Available from: 2012-06-27 Created: 2012-06-26 Last updated: 2017-12-07Bibliographically approved
6. Finite Element Analysis of the Effect on Employing Thermal Through Vias and Heat Fingers to Increase Heat Transfer to Fluid in Calorimetric Flow Sensors
Open this publication in new window or tab >>Finite Element Analysis of the Effect on Employing Thermal Through Vias and Heat Fingers to Increase Heat Transfer to Fluid in Calorimetric Flow Sensors
2013 (English)In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 201, 49-57 p.Article in journal (Refereed) Published
Abstract [en]

Measurement results of a robust silicon calorimetric flow sensor with a 25 μm thick silicon dioxide membrane with thermal silicon vias have been compared with results obtained from three-dimensional Finite Element Analysis (FEA). Based on the fabricated device, the sensor has been further developed to include heat-exchanging fingers extending down into the integrated flow channel for increased heat transfer. Using FEA, different designs of the fingers have been compared with respect to signal strength, sensitivity, power consumption and pressure loss in the channel at flow rates from 0 to about 650 sccm. Using heat fingers, the sensor signal was improved by a factor of five. The sensor signal, i.e. the temperature difference between downstream and upstream elements, was more than 60 °C when the central heater was heated 300 °C above room temperature, which was comparable to a thin-membrane device modeled. The maximum sensitivity using the finger design was about 1.4 °C sccm−1, and the maximum power consumption was almost 700 mW, which is considerably higher than for thin-membrane sensors. A figure of merit used for evaluation, was the ratio of signal strength to power consumption. The results show that the device design is a promising concept that is suitable in systems requiring robust monolithically integratable flow sensors.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-186776 (URN)10.1016/j.sna.2013.05.018 (DOI)000325836400006 ()
Available from: 2012-11-29 Created: 2012-11-29 Last updated: 2017-12-07Bibliographically approved
7. Two-Dimensional Thermal Velocity Sensor for Submersible navigation and Minute Flow Measurements
Open this publication in new window or tab >>Two-Dimensional Thermal Velocity Sensor for Submersible navigation and Minute Flow Measurements
2013 (English)In: IEEE Sensors Journal, ISSN 1530-437X, E-ISSN 1558-1748, Vol. 13, no 1, 359-370 p.Article in journal (Refereed) Published
Abstract [en]

A 2-D thermal velocity microsensor for use as a navigational aid and for flow measurements on a miniaturized submersible is developed in this paper. The sensor with nickel heater and temperature sensors on a Pyrex substrate, designed for mounting on the outside of the submersible hull, is fabricated and tested in an application-like environment and proven to be able to measure water speed from zero to 40 mm/s with a power consumption less than 15 mW and determine the flow direction with an error less than ±8°. Finite Element Analysis is used to investigate design and operation parameters and possible biofouling effects on the sensor signal. The effect on shape and orientation of the sensor's mounting surface is also studied.

National Category
Other Materials Engineering
Research subject
Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-171767 (URN)10.1109/JSEN.2012.2216866 (DOI)000313685400028 ()
Available from: 2012-03-27 Created: 2012-03-27 Last updated: 2017-12-07Bibliographically approved
8. A micromachined dual-axis beam steering actuator for use in a miniaturized optical space communication system
Open this publication in new window or tab >>A micromachined dual-axis beam steering actuator for use in a miniaturized optical space communication system
Show others...
2010 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 20, no 10, 105007- p.Article in journal (Refereed) Published
Abstract [en]

The design, fabrication and evaluation of an electrothermally actuated micromachined beam steering device for use in a free-space optical communication system intended for use on micro-and nanospacecraft in kilometer-sized formations are presented. SU-8 confined in v-grooves is heated to create bending movement in two orthogonal directions for two-axial steering with large static bending angles and low actuation voltages. Standard MEMS processing is used to fabricate the devices with square mirror side lengths of 1, 3.5 and 5 mm. In addition, a method to prevent thermal damage to SU-8 during deep reactive ion etching has been successfully developed. Characterization shows optical scan ranges larger than 40 degrees in both directions with the maximum driving voltage of 16 V corresponding to a total power consumption of 1.14 W. Infrared imaging is used to investigate thermal cross-talk between actuators for the two scanning directions. It is found that a silicon backbone on the joint backside is crucial for device performance. Differences from expected performance are believed to arise from the SU-8 curing process and excessive heating during fabrication. A finite element method simulation is used to find the eigenfrequencies of the structures, and these are in good agreement with the measured frequency response.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-134362 (URN)10.1088/0960-1317/20/10/105007 (DOI)000282270300020 ()
Available from: 2010-11-25 Created: 2010-11-24 Last updated: 2017-12-12
9. Dynamic characterization and modelling of a dual-axis beam steering device for performance understanding, optimization, and control design
Open this publication in new window or tab >>Dynamic characterization and modelling of a dual-axis beam steering device for performance understanding, optimization, and control design
Show others...
2013 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 23, no 4, 045020- p.Article in journal (Refereed) Published
Abstract [en]

This paper presents a lumped thermal model of a dual-axis laser micromirror device for beam steering in a free-space optical (FSO) communication system, designed for fractionated spacecraft. An FSO communication system provides several advantages, such as larger bandwidth, smaller size and weight of the communication payload and less power consumption. A dual-axis mirror device is designed and realized using microelectromechanical systems technology. The fabrication is based on a double-sided, bulk micromachining process, where the mirror actuates thermally by joints consisting of v-grooves filled with the SU-8 polymer. The size of the device, consisting of a mirror, which is deflectable versus its frame in one direction, and through deflection of the frame in the other, is 15.4 × 10.4 × 0.3 mm3. In order to further characterize and understand the micromirror device, a Simulink state-space model of the actuator is set up using thermal and mechanical properties from a realized actuator. A deviation of less than 2% between the modelled and measured devices was obtained in an actuating temperature range of 20–200 °C. The model of the physical device was examined by evaluating its performance in vacuum, and by changing physical parameters, such as thickness and material composition. By this, design parameters were evaluated for performance gain and usability. For example, the crosstalk between the two actuators deflecting the mirror along its two axes in atmospheric pressure is projected to go down from 97% to 6% when changing the frame material from silicon to silicon dioxide. A feedback control system was also designed around the model in order to examine the possibility to make a robust control system for the physical device. In conclusion, the model of the actuator presented in this paper can be used for further understanding and development of the actuator system.

National Category
Communication Systems
Research subject
Engineering Science with specialization in Microsystems Technology; Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-185627 (URN)10.1088/0960-1317/23/4/045020 (DOI)000316299900021 ()
Available from: 2012-11-27 Created: 2012-11-27 Last updated: 2017-12-07Bibliographically approved

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