| 1. |
- Hedsten, Karin, 1964, et al.
(författare)
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MEMS-based VCSEL beam steering using replicated polymer diffractive lens
- 2008
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Ingår i: Sensors and Actuators, A: Physical. - : Elsevier BV. - 0924-4247 .- 1873-3069. ; 142:1, s. 336-345
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Tidskriftsartikel (refereegranskat)abstract
- Abstract. This paper describes a fully integrated micro-optical system, in which dynamic angular control of the beam from a VCSEL (vertical cavity surface emitting laser) is realized by laterally moving a collimat¬ing diffractive lens in the light path. The lens is mounted on a translatable silicon stage, which consists of a frame with an opening for the light to traverse the lens and electro-statically driven comb actuators, by which the lateral movement is achieved. Devices implementing both 1D and 2D scanning have been fabricated and evaluated. Integration of the lens onto the translatable silicon stage is done using a newly developed fabrication process based on hot embossing of an amorphous fluorocarbon polymer. This fabrication process relies on a reversed-order protocol, where the structuring of the optical element precedes the silicon microstructuring. Assembly and packaging of the VCSEL-MOEMS system, using LTCC (low temperature cofired ceramic) technique, is also demonstrated. Optical evaluation of the system and beam steering function shows significant beam deflection for a relatively low driving voltage (~70 V).
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| 2. |
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| 3. |
- Melin, Jonas, et al.
(författare)
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Microreplication in a Silicon Processing Compatible Material
- 2005
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Ingår i: IEEE/LEOS Optical MEMS 2005: International Conference on Optical MEMS and Their Applications, Oulu, Finland, 1-4 August 2005. - 9780780392786 ; , s. 89-90
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Konferensbidrag (refereegranskat)abstract
- We present a novel fabrication process for the integration of polymer micro-optical elements on silicon. The process relies on a reverse order protocol based on embossing in an amorphous fluorocarbon polymer, Cytop™.
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| 4. |
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| 5. |
- Bengtsson, Peter, 1974-
(författare)
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Development towards an efficient and sustainable biofuel drying
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The usage of biofuel as well as wood fuel has increased in Sweden and all of Europe during recent decades, and there are several reasons to believe that this increase will continue. An important reason for this increase is that the environmental and climate problems caused by fossil fuels are becoming even more evident. By replacing fossil fuel with biofuel, the problem of emissions from, among others carbon dioxide and sulphur compounds can be alleviated. However, substitution requires in many cases high quality processed biofuel. An early stage in the processing of biofuel is drying. Previous work treats the possibility of drying wood fuel in an efficient and environmentally sustainable manner.This thesis studies the bed drying technique, conducted both experimentally and through modeling of the drying process. The experimental work is based on continuous temperature measurements in the fuel bed and provides characteristics of the drying zone that develops in the bed during drying. The character of the drying zone is affected by both the qualities of the fuel and the operating parameters, and is decisive regarding the possibility of making the drying more efficient, i.e. optimize the usage of energy and produce a fuel with low and homogeneous moisture content.A mathematical simulation model has been developed to increase the understanding of bed drying. The model is based on fundamental physical principles and is made up of five differential equations that describe vapor flow, air flow, the fuel’s moisture content, and the bed’s pressure and temperature. The modeling work complements the experimental work and a simulation of the temperature distribution, pressure and the drying zone’s dispersion is in agreement with the experimental result.The drying of wood can signify an environmental and human health risk, since volatile organic compounds (VOC) are emitted during drying. The thesis studies these emissions with regards to type and quantity. The measurements show that the majority of the emitted compounds from Norway spruce and Scots pine are volatile monoterpenes, but also that other compounds are emitted, especially higher terpenes. Further, major differences between how the compounds are emitted and the quantities of the emitted compounds from heartwood and sapwood are shown. There are also large differences between types of wood, i.e. spruce and pine. It can be stated that both emission rate and total amount of emitted compounds increase with an increase in temperature.To reduce VOC emissions, the drying temperature should be maintained low. To develop an efficient bed drying process for wood biofuels, additional parameters must be analyzed further and weighed against each other. Based on the experimental method and the simulation model presented here, the drying can be optimized towards a more efficient use of thermal energy and a low and even moisture content in the dried biofuel.
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| 6. |
- Bengtsson, Peter, 1974-, et al.
(författare)
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Evaluation of hydrocarbon emissions from heart- and sapwood of Scots pine using a laboratory-scale wood drier
- 2004
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Ingår i: Holzforschung. - : Walter de Gruyter. - 1437-434X .- 0018-3830. ; 58:6, s. 660-665
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Tidskriftsartikel (refereegranskat)abstract
- The subject of study is the emission of Volatile Organic Compounds (VOC) during the drying of wood. Heartwood and sapwood from Scots pine were dried at different temperatures (50, 70 and 90°C) in a laboratory kiln. The sampling method, Solid Phase Microextraction was used to collect the different volatile organic compounds during the drying. The gas chromatograph and mass spectrometer was used to identify and quantify the organic matter. The total hydrocarbons were measured with a flame ionization detector. Primarily, different monoterpenes were released during the drying process. 3-carene and α-pinene were most common and were also analytically quantified. The diterpene, pimaral, was found in an estimated large amount in the later stage of the drying process but was not exactly quantified. Large differences in both release behaviour and total amount of released hydrocarbon between heart- and sapwood were obtained. Emissions of VOC from heartwood were of a magnitude approximately three times higher than that from sapwood.
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| 7. |
- Bengtsson, Peter, 1974-
(författare)
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Experimental Analysis of Low-Temperature Bed Drying of Wooden Biomass Particles
- 2008
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Ingår i: Drying Technology. - : Taylor & Francis. - 0737-3937 .- 1532-2300. ; 26:5, s. 602-610
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Tidskriftsartikel (refereegranskat)abstract
- This report investigates the low-temperature bed drying of biomass particles for use in a gasification process. Experimental drying equipment capable of drying up to 0.25 m 3 of biomass batchwise was constructed. The experimental result indicates that the drying equipment and applied method are appropriate to evaluate different drying parameters and their influence on the drying course. Drying parameters such as air temperature, air velocity, bed height, and type of wood are studied regarding the drying rate, final moisture content in the material, and bed pressure drop. The constant-rate and falling-rate drying period are studied to obtain an energy efficient drying process. Measurements show that the drying zone (where the actual drying occurs) progresses irregularly through the bed.
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| 8. |
- Bengtsson, Peter, 1974-, et al.
(författare)
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Modeling the drying of porous material
- 2009
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The following report presents a mathematical model regarding the drying of porousmaterial. The considered drying technique is fixed-bed drying, where the material is fixed in abed and exposed to a drying gas stream. The drying material is wooden biomass particles. Thedeveloped simulation model is, however, fundamental in nature and thus applicable to varioustypes of porous material.The model is based on coupled equations for air, water vapor, moisture content in theparticles, enthalpy, and pressure. The equations are solved by using the finite-differencemethod. The model predicts the drying course for different drying conditions, and quantitiessuch as temperature, moisture content, drying time and pressure drop along the bed may beobtained (functions of bed height and time). The iterative calculation for moisture content,temperature and water vapor flow requires 17 lines in Mathcad. The computer time for atypical case is only a few minutes. The Mathcad simulation code is appended.Simulation of a reference drying case is presented and the result is discussed in detail. Thedrying process was divided into two phases: an initial phase involving heating of the bedmaterial and a drying phase. The initial phase is rather short, typically only a few minutes.The drying of two common types of biomass material, sawdust and wood chips, issimulated and compared to real drying experiments. Properties such as temperaturedistribution, drying rate and character of the drying zone are well predicted by the model.In its present form, the model gives valuable information of the drying process and agreeswell with experimental data, though some main parameters are possible to optimize further.The model is a useful tool to analyze and evaluate drying processes
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| 9. |
- Bengtsson, Peter, 1974-
(författare)
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The release of Hydrocarbons from softwood drying : Measurement and modeling
- 2004
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Ingår i: MADERAS. - : SciELO Agencia Nacional de Investigacion y Desarrollo (ANID). - 0717-3644 .- 0718-221X. ; 6:2, s. 109-122
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Tidskriftsartikel (refereegranskat)abstract
- The release of volatile organic compounds (VOC) during the drying of Norway spruce and Scots pine was experimentally studied. Heartwood and sapwood were separately dried at 60 ºC. The Flame Ion Detector (FID) was used to measure the total amount of hydrocarbons (THC) released during the drying process. A large difference of the emissions course between heartwood and sapwood were found. For heartwood, a release maximum of hydrocarbons followed by a typical negative exponential course was found. When drying sapwood, the released amount of hydrocarbons was evidently more fluctuating before reducing to zero. A model describing the release of hydrocarbons during the drying with only diffusion as transport mechanism was applied. The aim was to obtain a suitable explanation of the characteristic release behavior from sapwood and develop a model describing the process.
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| 10. |
- Berg, Jonas, 1973, et al.
(författare)
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Electrical Properties of Si-SiO2-Si Nanogaps
- 2005
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Ingår i: Nanotechnology. - : IOP Publishing. - 1361-6528 .- 0957-4484. ; 16:10, s. 2197-2202
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Tidskriftsartikel (refereegranskat)abstract
- The chances of attaching organic molecules to silicon surfaces can be considerably enhanced if a robust nanogap structure with silicon electrodes can be used to connect the molecules. We describe the electrical properties of such an electrode structure, with a separation of the silicon surfaces in the 37 nm range. These silicon nanogaps are manufactured by partly removing the silicon dioxide insulator from a siliconoxidesilicon material stack, by using a selective oxide etchant. After the activation of the gap (the etching), current instabilities appear, which are comparable to the properties of thin oxides after soft breakdown. Applying a constant voltage can reduce these current instabilities. We also address the issue of surface leakage currents for these nanogap structures.
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