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| 2. |
- Knaust, Stefan, et al.
(författare)
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Characterization of dielectric properties of polycrystalline aluminum nitride for high temperature wireless sensor nodes
- 2013
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Ingår i: Journal of Physics. - London : Institute of Physics (IOP).
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Konferensbidrag (refereegranskat)abstract
- An aluminium nitride (AlN) passive resonance circuit intended for thermallymatched high temperature wireless sensor nodes (WSN) was manufactured using thick-lmtechnology. Characterization was done for temperatures up to 900C in both a hot-chuck forfrequencies below 5 MHz, and using wireless readings of resonating circuits at 15 MHz, 59 MHz,and 116 MHz. The substrate for the circuits was sintered polycrystalline AlN. Using a simpliedmodel for the resonators where the main contribution of the frequency-shift was considered tocome from a shift of the dielectric constant for these frequencies, the temperature dependency ofthe dielectric constant for AlN was found to decrease with increasing frequency up to 15 MHz.With an observed frequency shift of 0.04% at 15 MHz, and up to 0.56% at 59 MHz over atemperature range of 900C, AlN looks as a promising material for integration of resonancecircuits directly on the substrate.
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| 3. |
- Knaust, Stefan, 1985-, et al.
(författare)
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Influence of flow rate, temperature and pressure on multiphase flows of supercritical carbon dioxide and water using multivariate partial least square regression
- 2015
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Ingår i: Journal of Micromechanics and Microengineering. - : Institute of Physics Publishing (IOPP). - 0960-1317 .- 1361-6439. ; 25:10
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Tidskriftsartikel (refereegranskat)abstract
- Supercritical carbon dioxide (scCO(2)) is often used to replace harmful solvents and can dissolve a wide range of organic compounds. With a favorable critical point at 31 degrees C and 7.4 MPa, reaching above the critical point for scCO(2) is fairly accessible. Because of the compressible nature of scCO(2) and the large changes of viscosity and density with temperature and pressure, there is a need to determine the behavior of scCO(2) in microfluidic systems. Here, the influence of how parameters such as flow rate, temperature, pressure, and flow ratio affects the length of parallel flow of water and scCO(2) and the length of the created CO2 segments are investigated and modeled using multivariate data analysis for a 10 mm long double-y channel. The parallel length and segment size were observed in the laminar regime around and above the critical point of CO2. The flow ratio between the two fluids together with the flow rate influenced both the parallel length and the segment sizes, and a higher pressure resulted in shorter parallel lengths. Regarding the segment length of CO2, longer segments were a result of a higher Weber number for H2O together with a higher temperature in the channel.
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| 4. |
- Knaust, Stefan, 1985-, et al.
(författare)
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Influence of surface modifications and channel structure for microflows of supercritical carbon dioxide and water
- 2016
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Ingår i: Journal of Supercritical Fluids. - : Elsevier BV. - 0896-8446 .- 1872-8162. ; 107, s. 649-656
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Tidskriftsartikel (refereegranskat)abstract
- Miniaturization offers a possibility to increase the performance and decrease the time scales of systems. Existing microsystems using supercritical CO2 mainly utilizes multiphase segmented flows. To allow for a broader toolbox for future systems, also parallel flows are useful which eases the separation of the different phases. Here, the effect of different surface coatings are studied for multiphase flows of scCO2 and H2O in flat microchannels, with and without a 4 μm high ridge guide, which allows for pinning of the fluid interface inside the 190 μm wide and 35 μm high channel. Three different surfaces with different wettings towards scCO2 and H2O are studied, where a surface terminated with a hydrocarbon-based silane was observed to be neutral in the H2O/scCO2 system, a surface terminated with a fluorocarbon-based silane was hydrophobic, and an uncoated glass surface was hydrophilic.Using two flow rates of 5:5 μl/min (CO2:H2O) and 6.5:3.5 μl/min (CO2:H2O), a parallel flow between scCO2 and H2O was observed for uncoated and flat channels where the H2O flow pushed the CO2 to the side, before the flows eventually breaks up into segments. With a ridge guide in the middle of the channel, the interface was pinned at half the channel width, although still breaking up into segments. The neutral hydrocarbon-based surface coating with approximately 90° contact angles resulted in evenly created segments without a ridge guide. Including a guide in the middle of the channel, a parallel flow was observed throughout the channel, although occasionally small CO2 segments entered the H2O outlet. Using the fluorocarbon-based silane resulted in an unstable segmented system with pressure fluctuations.Using surface modifications, an increased control can be achieved for either segmentation or parallel flow where a neutral surface is favored for a stable flow behavior. Together with a ridge guide, the fluid interface was pinned at the center.
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| 5. |
- Knaust, Stefan, 1985-, et al.
(författare)
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Mannitol for High Temperature Phase Change Actuators
- 2014
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- To enable valves for hot water microsystems, the possibility of using the volume expansion of the phase transition from solid to liquid in mannitol for strong high temperature actuators was studied. From room temperature to 160°C, a linear expansion of 4% was measured, and the expansion at the phase transition from solid to liquid at 160°C to 180°C was measured to be 7%. Stainless steel structures with a stainless steel diaphragm was filled and repeatedly heated up to 180◦C while measuring the deflection of the diaphragm using a laser sensor. The height differences was measured to be 25 μm at 180°C.In combination with a fluidic system, the mannitol actuator should capable as a valve for hot water microsystems.
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| 6. |
- Knaust, Stefan
(författare)
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Microsystems for Harsh Environments
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- When operating microsystems in harsh environments, many conventionally used techniques are limiting. Further, depending on if the demands arise from the environment or the conditions inside the system, different approaches have to be used. This thesis deals with the challenges encountered when microsystems are used at high pressures and high temperatures.For microsystems operating at harsh conditions, many parameters will vary extensively with both temperature and pressure, and to maintain control, these variations needs to be well understood. Covered within this thesis is the to-date strongest membrane micropump, demonstrated to pump against back-pressures up to 13 MPa, and a gas-tight high pressure valve that manages pressures beyond 20 MPa.With the ability to manipulate fluids at high pressures in microsystems at elevated temperatures, opportunities are created to use green solvents like supercritical fluids like CO2. To allow for a reliable and predictable operation in systems using more than one fluid, the behavior of the multiphase flow needs to be controlled. Therefore, the effect of varying temperature and pressure, as well as flow conditions were investigated for multiphase flows of CO2 and H2O around and above the critical point of CO2. Also, the influence of channel surface and geometry was investigated.Although supercritical CO2 only requires moderate temperatures, other supercritical fluids or reactions require much higher temperatures. The study how increasing temperature affects a system, a high-temperature testbed inside an electron microscope was created.One of the challenges for high-temperature systems is the interface towards room temperature components. To circumvent the need of wires, high temperature wireless systems were studied together with a wireless pressure sensing system operating at temperatures up to 1,000 °C for pressures up to 0.3 MPa.To further extend the capabilities of microsystems and combine high temperatures and high pressures, it is necessary to consider that the requirements differs fundamentally. Therefore, combining high pressures and high temperatures in microsystems results in great challenges, which requires trade-offs and compromises. Here, steel and HTCC based microsystems may prove interesting alternatives for future high performance microsystems.
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| 7. |
- Ogden, Sam, 1979-, et al.
(författare)
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On-chip pump system for high-pressure microfluidic applications
- 2013
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Konferensbidrag (refereegranskat)abstract
- This paper presents a micropump system with four integrated paraffin actuated pumps: Two mobile phase pumps and two sample injector pumps. The mobile phase pumps are evaluated by their ability to deliver a stable, low-ripple flow to be used in chip-based high performance liquid chromatography. It is shown that the two mobile phase pumps can be driven in combined operation with an induced offset to significantly lower flow fluctuations.
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| 8. |
- Sturesson, Peter, et al.
(författare)
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Thermomechanical behaviour and pressure sensing of ceramic wireless devices for high-temperature environments
- 2014
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Konferensbidrag (refereegranskat)abstract
- This paper reports on the design, fabrication and thermomechanical characterization of wirelessceramic devices, one with an integrated pressure sensor element. The project aims at developingmicrosystems for sensing in harsh environments where conventional electronic devices are restrained.Here, the devices are LC resonating circuits made from High-Temperature Co-fired Ceramic (HTCC)aluminium oxide green tapes. For the fabrication, the tapes were screen-printed with platinum paste,micromachined, stacked, laminated and fired. The additional sensor element was made from the samematerial and with the same processes, and contains a cavity sealed with a capacitive membrane.Thermomechanical characterization was made by investigating the bimorphic behaviour due to CTEmismatch as well as the resonance frequency of the devices as a function of mechanical displacement.Also, the resonance frequency as a function of pressure was demonstrated for the device with anintegrated pressure sensor node. The wireless readings were performed with a tuneable resonating loopantenna. The devices showed a relatively low quality factor value. The bimorphic behaviour is lowwith only small variations for temperatures up to 400°C. As for the mechanical displacement, theresonance frequency was only affected for thin devices at forced deformations that were larger thanthose observed as a function of temperature. For the device with an integrated pressure sensor, a clearpressure-induced frequency shift of 6785 ppm was observed at 1.5 bar. This indicates that the devicesare robust for high temperatures and also applicable for pressure readings. Future work will furtherexpand on high-temperature characterization of the devices.
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| 9. |
- Sturesson, Peter, et al.
(författare)
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Thermomechanical properties and performance of ceramic resonators for wireless pressure reading at high temperatures
- 2015
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Ingår i: Journal of Micromechanics and Microengineering. - Bristol : Institute of Physics Publishing (IOPP). - 0960-1317 .- 1361-6439. ; 25:9
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Sturesson, Peter, et al.
(författare)
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Thermomechanical rigidity of a wireless pressure senosr node for high-temperature applications
- 2014
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Ingår i: 25th Micromechanics and Microsystems Europe workshop (MME 2014), 2014, P39 (4 pp).
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Konferensbidrag (refereegranskat)abstract
- Aimed for here, are microsensorequippednodes for environments too harsh for conventionalMEMS devices, especially with respect totemperature. Therefore, a prototype pressure sensorhas been made from micromachined, laminated andfired High-Temperature Co-fired Ceramic (HTCC)aluminium oxide green tapes. The Sensor is readwirelessly using LC resonating circuits made ofplatinum screen-printed on the tapes. In the specificwork package reported on here, the focus is on thethermomechanical characterization of the stackforming the device, since the bimorphic behavior dueto CTE mismatch of its constituents was believed toaffect the sensor performance. This part was conductedboth by optical profilometry of samples,ranging from 410 to 890 μm in thickness, heated to400°C, and by monitoring the frequency shift whenthe samples were subjected to three-point bending atroom temperature. With only negligible deformationsobserved for temperatures up to 400°C, a highthermomechanical rigidity was demonstrated.Furthermore, only when deformations larger thanthe thermomechanically induced ones were imposedon the thinnest samples, a shift in resonance frequencywas observed, indicating that the LC circuitrywill not be affected by the thermomechanicaldeformation of the sensor node. The sensor element,being a capacitor formed by a membrane sealing acavity and deflecting with changes in the ambientpressure, integrated in one of the samples, exhibiteda clear pressure-induced frequency shift of6785 ppm at 1.5 bar and room temperature. Inconclusion, the sensor node concept has been verifiedto have high thermal robustness.
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