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de Graaf, G. (author), Vriesendorp, Maurits Frans (author), Amin Hassan, H.M. (author), French, P.J. (author)In this research fluorescent optochemical pH probes for the detection of ischaemia have been investigated. Myocardial ischaemia is the most prominent risk during heart surgery. During open heart surgery the heart is temporarily arrested and, since there no blood flowing, oxygen supply and removal of waste products is stopped and heart cells...journal article 2022
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Cai, Z. (author), van Veldhoven, Robert (author), Suy, Hilco (author), de Graaf, G. (author), Makinwa, K.A.A. (author), Pertijs, M.A.P. (author)<br/>book chapter 2019
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Cai, Z. (author), van Veldhoven, Robert (author), Suy, Hilco (author), de Graaf, G. (author), Makinwa, K.A.A. (author), Pertijs, M.A.P. (author)The measurement of carbon-dioxide (CO2) concentration is very important in home and building automation, e.g. to control ventilation in energy-efficient buildings. This application requires compact, low-cost sensors that can measure CO<sub>2</sub> concentration with a resolution of <200 ppm over a 2500ppm range. Conventional optical (NDIR...conference paper 2018
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Cai, Z. (author), van Veldhoven, Robert (author), Suy, Hilco (author), de Graaf, G. (author), Makinwa, K.A.A. (author), Pertijs, M.A.P. (author)This paper presents a readout circuit for a carbon dioxide (CO&#2082;) sensor that measures the CO&#x2082;-dependent thermal time constant of a hot-wire transducer. The readout circuit periodically heats up the transducer and uses a phase-domain &#x0394; &#x03A3; modulator to digitize the phase shift of the resulting...journal article 2018
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Middelburg, L.M. (author), de Graaf, G. (author), Bossche, A. (author), Bastemeijer, J. (author), Ghaderi, M. (author), Wolffenbuttel, F.S. (author), Visser, J. (author), Soltis, R. (author), Wolffenbuttel, R.F. (author)Measuring the ethanol/water ratio in biofuel of high ethanol content, such as E85, is important when used in a flex-fuel engine. A capacitive probe is generally used for measuring the ethanol/gasoline ratio. However, the water content in E85 biofuel cannot be disregarded or considered constant and full composition measurement of biofuel is...journal article 2017
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Middelburg, L.M. (author), Ghaderi, M. (author), Bossche, A. (author), Bastemeijer, J. (author), de Graaf, G. (author), Wolffenbuttel, R.F. (author), Soltis, Rick (author), Visser, Jaco (author)A capacitive probe is generally used in a flex-fuel engine for measuring the ethanol content in biofuel. However, the water content in biofuel of high ethanol content cannot be disregarded or considered constant and the full composition measurement of ethanol, gasoline and water in biofuel is required. Electrical impedance spectroscopy with a...conference paper 2017
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Middelburg, L.M. (author), de Graaf, G. (author), Ghaderi, M. (author), Bossche, A. (author), Bastemeijer, J. (author), Visser, J.H. (author), Soltis, R.E. (author), Wolffenbuttel, R.F. (author)The optical absorption of water-containing bio-fuel is investigated as a parameter to determine the gasoline content of this fuel. Optical measurements reveal that gasoline shows an interesting and useful spectrum with typical absorption behavior in the UV range between 230 and 300 nm. This result indicates that significant information can be...journal article 2016
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Ayerden, N.P. (author), de Graaf, G. (author), Wolffenbuttel, R.F. (author)A miniaturized methane (CH4) sensor based on nondispersiveinfrared absorption is realized in MEMS technology. A high level offunctional integration is achieved by using the resonance cavity of a linearvariable optical filter (LVOF) also as a gas absorption cell. For effectivedetection of methane at λ = 3.39 µm, an absorption path length of at...journal article 2016
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Karimi Shahmarvandi, Ehsan (author), Ghaderi, M. (author), Ayerden, N.P. (author), de Graaf, G. (author), Wolffenbuttel, R.F. (author)The design of a metamaterial-based absorber for use in a mid-IR microspectrometer-based gas sensor is reported.The microspectrometer consists of a linear variable optical filter (LVOF) that is aligned with an array of thermopiledetectors, which is fabricated on a SiN membrane and covered with the absorber. Special emphasis was put on theCMOS...journal article 2016
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Ayerden, N.P. (author), Ghaderi, M. (author), De Graaf, G. (author), Wolffenbuttel, R.F. (author)The design, fabrication and characterization of a highly integrated optical gas sensor is presented. The gas cell takes up most of the space in a microspectrometer and is the only component that has so far not been miniaturized. Using the tapered resonator cavity of a linear variable optical filter as a gas cell enables ultimate miniaturization,...conference paper 2015
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Ghaderi, M. (author), Ayerden, N.P. (author), De Graaf, G. (author), Wolffenbuttel, R.F. (author)The design and CMOS-compatible fabrication of airgap-based optical filters in a surface micromachining process with sacrificial release using thevapour phase is presented. An airgap-dielectric layer combination offers a higher refractive index contrast, as compared to the conventional all-dielectriclayer based filters, which results in a higher...conference paper 2015
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de Graaf, G. (author), Abarca Prouza, A.N. (author), Wolffenbuttel, R.F. (author)Conventional thermal conductivity detectors (TCDs) demonstrate a flow dependence. The approach presented here to reduce the flow dependence is based on the on-line flow compensation using two thin-film sensors on membranes in parallel on the same chip that are differentially operated. These are laterally identically, but with a different depth...conference paper 2015
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Ghaderi, M. (author), Ayerden, N.P. (author), De Graaf, G. (author), Wolffenbuttel, R.F. (author)In CMOS-compatible optical filter designs, SiO2 is often used as the low-index material, limiting the optical contrast (nHi/nLo) to about 2. Using the air as low-index material improves the optical contrast by about 50%, thus increasing the reflectivity and bandwidth at a given design complexity. The design and fabrication of a 4-layered air...journal article 2014
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Silva, M.F. (author), Rodrigues, J.A. (author), Oliveira, M.J. (author), Fernandes, A.R. (author), Pereira, S. (author), Costa, C.G. (author), Ghaderi, M. (author), Ayerden, P. (author), Goncalves, L.M. (author), De Graaf, G. (author), Wolffenbuttel, R.F. (author), Correia, J.H. (author)This paper presents the design, fabrication and characterization of two Fabry Perot type optical filters (415 nm and 540 nm) for enabling Narrow Band Imaging (NBI) in medical devices (MD). The two-colour illumination should satisfy a highly specific optical design, which is composed of a thin-film optical filter stack of titanium dioxide (TiO2)...journal article 2014
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Ayerden, N.P. (author), Ghaderi, M. (author), De Graaf, G. (author), Wolffenbuttel, R.F. (author)A set-up for optical gas composition measurement based on absorption spectroscopy is composed of a white light source, a gas cell and a spectrometer. The Fabry-Perot optical filter is suitable for miniaturization of this system, as it is composed of only two reflectors with a transparent layer in-between. Varying the width of this optical...journal article 2014
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Emadi, A. (author), Wu, H. (author), De Graaf, G. (author), Wolffenbuttel, R.F. (author)This paper presents the design, fabrication and characterization of Infra-Red (IR) Linear Variable Optical Filter (LVOF)-based micro-spectrometers. Two LVOF microspectrometer designs have been realized: one for operating in the 1400 nm to 2500 nm wavelength range and another between 3000 nm and 5000 nm. The IR LVOFs have been fabricated in an IC...journal article 2013
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Emadi, A. (author), Wu, H. (author), De Graaf, G. (author), Enoksson, P. (author), Higino Correia, J. (author), Wolffenbuttel, R. (author)An IC-compatible linear variable optical filter (LVOF) for application in the UV spectral range between 310 and 400 nm has been fabricated using resist reflow and an optimized dry-etching. The LVOF is mounted on the top of a commercially available CMOS camera to result in a UV microspectrometer. A special calibration technique has been employed...journal article 2012
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Emadi, A. (author), Wu, H. (author), De Graaf, G. (author), Wolffenbuttel, R.F. (author)In this paper the concept of a microspectrometer based on a Linear Variable Optical Filter (LVOF) for operation in the visible spectrum is presented and used in two different designs: the first is for the narrow spectral band between 610 nm and 680 nm, whereas the other is for the wider spectral band between 570 nm and 740 nm. Design...journal article 2011
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Wu, H. (author), Vollebregt, S. (author), Emadi, A. (author), De Graaf, G. (author), Ishihara, R. (author), Wolffenbuttel, R.F. (author)A thermopile based detector array has advantages when used for an infrared (IR) micro-spectrometer, as compared to an array of photon detector, such as flat spectral response and uncooled operation. A thermal detector requires a good absorber to achieve a high absorption coefficient in the spectral range of interest. Several solutions are...journal article 2011
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Wu, H. (author), Emadi, A. (author), De Graaf, G. (author), Leijtens, J. (author), Wolffenbuttel, R.F. (author)A sun sensor is usually included in a satellite for optically measuring the position relative to the sun. The accuracy of a conventional sun sensor is affected by reflected sunlight at the nearby earth atmosphere: the albedo radiation. The part of the spectrum at near IR (1.5 ?m) is not included in the albedo radiation, due to the high water...journal article 2011